Preparation of low-dust stabilisers

Details Preparation of low-dust stabilisers Preparation of low-dust stabilisers

2001-03-23

2004-05-25

Sanders, Kriellion A. (Department: 1714)

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

Synthetic resins

Processes of preparing a desired or intentional composition...

C252S400230, C252S400240, C252S401000, C252S407000, C523S223000, C524S094000, C524S100000, C524S102000, C548S257000

Reexamination Certificate

active

06740694

ABSTRACT:

The present invention relates to a process for the preparation of low-dust stabilisers by extruding a subcooled melt, to the use of the products of this process for stabilising organic polymers, to novel amorphous modifications, e.g. of 2,2′-methylenebis(4-[1,1,3,3-tetramethylbutyl]-6-benzotriazol-2-yl-phenol), to a novel crystalline modification of 2-(2-hydroxy-3,5-di-tert-butylphenyl)-5-chlorobenzotriazole, to a process for its preparation and processing as well as to compositions stabilised therewith.
The development of stabiliser which are low-dust and therefore generally easier to handle has been pursued for some time; specific stabilisers have, inter alia, been mounted on inorganic substrates (e.g. U.S. Pat. No. 5,238,605).
GB-A-2267499 describes the preparation of a mixture of tetraalkylpiperidine type stabilisers of high and low molecular weight by mixing in a melted state.
U.S. Pat. No. 5,597,857 describes a process for the preparation of low-dust stabilisers by extruding a calcium stearate melt; JP-A-59-104348 and EP-A-565184 also propose extruding a melt. DE-A-19541242 proposes pastillising a mixture consisting of crystalline and melted plastic additives.
The use of a regular melt during extrusion is only possible to a limited degree owing to its low viscosity.
Amorphous modifications of individual stabilisers and their use for stabilising organic polymers have already been described, inter alia, in EP-A-278579, U.S. Pat. No. 4,683,326, EP-A-255743, U.S. Pat. No. 5,373,040, U.S. Pat. No. 5,489,636, JP-A-59-104348, U.S. Pat. No. 5,574,166. They are usually prepared by rapidly cooling (chilling) the melt to prevent crystallisation. EP-A-278579 describes the preparation of a partially crystalline stabiliser mixture consisting of amorphous tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxymethyl]methane and a crystalline organic phosphite by subcooling the melt.
EP-A-514784 describes the extrusion of tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxymethyl]methane and the mixtures thereof with inorganic salts of fatty acid salts at temperatures in the melting range.
Surprisingly, it has now been found that the metastable state which is passed during the preparation of low molecular weight amorphous stabilisers, the subcooled melt, is excellently suitable for use as granulation liquid or binder during the extrusion. It is remarkable that the formation of crystalline modifications of the low molecular weight stabilisers is unexpectedly highly inhibited, making it possible to process the plastic extrusion compositions to granules by conventional methods.
Accordingly, this invention relates to a process for the preparation of a low-dust stabiliser, which comprises extruding a subcooled melt of a stabiliser having a molecular weight of 200 to 1500 g/mol, or the plastic composition of the mixture consisting of the subcooled melt of the stabiliser and of a crystalline stabiliser and/or other customary additives. The plastic composition therefore consists of the subcooled melt as homogeneous continuous phase and, where appropriate, of further components dispersed therein (disperse phase(s)).
The processing to marketable, low-dust, flowable and storage-stable forms with good meterability, e.g. for pelletisation, pastillation, melt granulation and compounding, is thus made substantially easier or possible at all. The moulding of the product can, for example, also be carried out before or during the cooling process by dividing the subcooled melt or the mixture, for example by dripping in the liquid state or by dividing in the plastic state with subsequent cooling. The process of this invention therefore also encompasses a process for granulating a stabiliser, which comprises extruding and dividing a subcooled melt of the stabiliser or the plastic compound consisting of the mixture of the subcooled melt of the stabiliser and of crystalline stabiliser and/or other customary additives. Solidification after extrusion gives a low-dust stabiliser, e.g. as granules.
This invention also relates to the granules obtainable by the novel process as well as to the use of a subcooled melt for extruding a stabiliser or stabiliser mixture, in particular for pelletisation, melt granulation or compounding.
The subcooled melt is single-phase and accordingly has only one single glass transition temperature; it can, however, consist of one or several chemical compounds and it preferably consists of 1 to 3 main components. Main components are to be understood as being those compounds, the proportion of which in the subcooled melt is 10% by weight or more, preferably 30% by weight or more. Also important is a subcooled melt which consists mainly, i.e. usually to 60% by weight or more, preferably to 70% by weight or more, of 1 chemical compound (weight always being based on the total weight of the homogeneous subcooled melt).
The amount of tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxymethyl]methane in the subcooled melt is preferably less than 80% by weight, more preferably from 0-60% by weight. A particularly important process of this invention is that, wherein tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxymethyl]methane is not a main component of the subcooled melt.
The molecular weight of the chemical compounds forming the subcooled melt (main components) is usually 300-1200 g/mol, preferably 300-1000 g/mol, particularly preferably 500-1000 g/mol. These chemical compounds are normally one or several organic compounds, for example hydrocarbons containing 6 to 100 carbon atoms and, where appropriate, 1 to 30 hetero atoms, such as O, N, S, P, halogen. The melting point (m.p.) of the chemical compound, which forms a main component, preferably any component present to more than 5% by weight, is usually 130° C. or higher, preferably 140° C. or higher, more preferably 170° C. or higher, and the glass transition temperature (T
G
) is in the range from 10-120° C., preferably from 20-100° C. The ratio of glass transition temperature (T
G
) to melting point (m.p.), each measured in Kelvin (K), is preferably in the range from 0.6 to 0.9; more preferably in the range from 0.65 to 0.85.
The compounds which form the subcooled melt are usually light stabilisers or antioxidants, for example those cited in the list given hereinbelow under the items 1, 2 and 4, provided they meet the stated criteria regarding molecular weight, melting point and glass transition temperature. They preferably belong to the class consisting of UV absorbers, sterically hindered amines (HALS), phenolic antioxidants, phosphites, phosphonites, lactones. In the novel process it is generally possible to use those compounds which, by themselves or as mixtures, are obtainable also in single-phase amorphous form by chilling the melt.
The following compounds are preferably used in the novel process:
1) 2,2′-methylenebis(4-[1,1,3,3-tetramethylbutyl]-6-benzotriazol-2-yl-phenol) (CAS reg. No. 103597-45-1) of formula
2) bis(2-methyl-4-hydroxy-5-tert-butylphenyl)sulfide (CAS reg. No. 000096-69-5),
3)
(CAS reg. No. 069851-61-2),
4) N,N′-bis(3-[3′,5′-di-tert-butyl-4′-hydroxyphenyl]propionyl)hexamethylenediamine (CAS reg. No. 023128-74-7),
5) 1,3,5-trimethyl-2,4,6-tris(3′,5′-di-tert-butyl-4′-hydroxybenzyl)benzene (CAS reg. No. 001709-70-2),
6) 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-1,3,5-triazine-2,4,6(1H,3H,5H)trione (CAS reg. No. 027676-62-6),
7)
(CAS reg. No. 032687-78-8),
8) 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)1,3,5-triazine-2,4,6-(1H,3H,5H)trione (CAS reg. No. 040601-76-1),
9) di(1,2,2,6,6-pentamethylpiperidin-4-yl)-2-(3,5-di-tert-butyl-4-hydroxybenzyl)-2-n-butylmalonate (CAS reg. No. 063843-89-0),
10) 2-(2′-hydroxy-3′,5′-bis(1,1-dimethylbenzyl)phenyl)benzotriazole (CAS reg. No. 070321-86-7) of formula
11) 2-(2′-hydroxy-3′,5′-di-tert-butylphenyl)benzotriazole (CAS reg. No.003846-71-7);
12) isomeric mixtures (CAS reg. No. 181314

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