Initiating system for solid polyester granule manufacture

Details Initiating system for solid polyester granule manufacture Initiating system for solid polyester granule manufacture

2001-08-23

2003-03-18

Davis, Brian (Department: 1621)

Compositions

Fire retarding

Material physically quantified

C252S610000, C252S611000, C525S007100, C528S272000, C560S098000

Reexamination Certificate

active

06533967

ABSTRACT:

This invention relates to the preparation of solid polyester granules of the type used as matting agents in paints. In particular the invention relates to a new redox initiating system for use in the suspension polymerisation process used to manufacture these solid polyester granules. This new initiating system provides advantages in terms of a reduction in odour in the resulting bead slurry due to more effective conversion of monomer into polymer, and production of less volatile and less toxic initiator residues than those produced using current initiating systems.
Solid polyester granules or beads are used as matting agents in paints, especially flat paints, to provide increased mar and burnish resistance. When included in flat paints they provide outstanding resistance to wet and dry abrasion. The granules are generally added to paint formulations in the form of a dispersion in an aqueous continuous phase. In some cases the polymer beads contain a pigment, such as titanium dioxide, and in other cases they are unpigmented. In view of the process used to manufacture these beads, the dispersion contains a significant amount of free or unreacted styrene.
Generally, the largest of these thermoset granules are approximately the thickness of a paint film in diameter. They protrude through the surface of the film and act as stationary ball bearings. Clothing, cleaning cloths and other objects that would normally mar the film only come into contact with the beads, and hence the paint film is very burnish resistant. This is in marked contrast to conventional flat paint films, where abrasion produces a large and unsightly localised increase in gloss.
In white and light tint paints, titanium dioxide containing solid beads are used in conjunction with external titanium dioxide to obtain the required opacity and tint strength. In dark or coloured tint bases, unpigmented beads are generally used. For these paints, opacity and tint strength are obtained from external pigmentation.
There are a number of problems with the current processes used to manufacture solid polyester granules. Solid polyester granules, such as solid SPINDRIFT® beads (Orica Australia Pty Ltd), are produced by emulsification in water and colloid stabilisers of an unsaturated polyester in styrene solution in which low levels of benzoyl peroxide and azobis(isobutyronitrile) have been incorporated. Emulsification is achieved through medium shear stirring and is carried out until the correct bead size has been obtained (typically 30-40 &mgr;m topsize). When that has been achieved, a low level of N,N-diethylaniline is added to the batch to complete the redox couple (with benzoyl peroxide) to initiate the suspension polymerisation. The azobis(isobutyronitrile) thermal initiator assists in the latter part of the exotherm to increase conversion. The batch may or may not be stirred during this stage, but stirring has traditionally been maintained to prevent any risk of settlement of the newly formed beads.
Solid beads have been made by this process for many years. However, in more recent times, significant safety, health and environment and raw material procurement issues became apparent, namely:
(a) Use of N,N-diethylaniline which is toxic and odorous. N,N-diethylaniline (DEA, CAS no. 91-66-7) is a liquid which can be absorbed through the skin resulting in surface irritation as well as causing methaemoglobinaemia with resulting anoxia and central nervous system depression. More significantly, these latter effects may arise if vapours are inhaled in significant amount (LC
50
rat=1920 mg/m
3
/4 h). These hazards are significant in the case of DEA as it is a liquid. It is classified as a harmful/dangerous substance (class 6.1) under the Australian Code for the Transport of Dangerous Goods by Road and Rail.
(b) Use of azobis(isobutyronitrile) (AIBN) which cannot be transported at temperatures above 25° C. by law, cakes on storage and produces a toxic by-product (tetramethylsuccinonitrile CAS No. 3333-52-6) which persists in the beads.
(c) Higher than acceptable levels of free styrene by today's standards (1500 ppm or 0.15 wt-% for clear solid beads and 3000 ppm or 0.30 wt-% for pigmented solid beads) due to poor conversion.
A number of alternative less odorous/toxic initiating systems have been evaluated in the production of solid beads, however none have proved successful. Alternatives, while curing the polyester phase, have not been successful in maintaining stability during polymerisation, or of improving conversion levels, and spiking regimes partway through or just after the exotherm have also been investigated but without success.
It has now been found that the use of an initiating system comprising hydroxyl-containing aromatic amines and a diacyl peroxide can significantly reduce the odour and, on the available data, toxicity of the resultant bead slurry. Conversion of monomer into polymer is also improved. The use of this initiator system can also obviate the need for AIBN, although in some circumstances the presence of some AIBN may be advantageous.
Accordingly the invention provides the use of a diacyl peroxide in combination with an aromatic amine of formula (I):
where R
1
is C
1
-C
20
alkyl having at least one hydroxy substituent or —(CHR′CHR′—O)
n
H where n is 1 to 10 and each R′ is independently selected from H and C
1
-C
3
alkyl;
R
2
is C
1
-C
20
alkyl optionally substituted with one or more hydroxy groups, or —(CHR′CHR′—O)
n
H where n=1 to 10 and each R′ is independently selected from H and C
1
-C
3
alkyl; and
Ar is an optionally substituted aryl group;
as a redox initiating system in a process for the manufacture of polyester granules by suspension polymerisation.
Preferably R
1
and R
2
are each linear C
1
-C
6
alkyl groups having terminal hydroxy substituents. More preferably one or both of R
1
and R
2
are hydroxyethyl groups.
Preferably Ar is an optionally substituted phenyl group.
Preferably when R
1
or R
2
is —(CHR′CHR′O)
n
H at least one R′ on each —(CHR′CHR′O)— unit is hydrogen. More preferably both R′ on each unit is hydrogen.
The optional substituents on the aryl group are preferably selected from electron donating groups. Examples of suitable electron donating groups include phenyl C
1
-C
6
alkyl, or C
1
-C
6
alkoxy. Preferably the phenyl group is substituted in the meta or para positions.
The presence of electron withdrawing groups interferes with the reactivity of the amine and accordingly they are not preferred.
Particularly preferred aromatic amines include N-ethyl-N-hydroxyethyl aniline, N,N-bis hydroxyethyl aniline, N-ethyl-N-hydroxyethyl-p-toluidine and N,N-bis hydroxyethyl-p-toluidine.
The diacyl peroxide may be selected from compounds of the formula II:
where R′ and R″ may be the same or different and may be optionally substituted alkyl, optionally substituted aryl, or optionally substituted alkoxy. Preferably the diacyl peroxide is (di)benzoyl peroxide.
The term “alkyl”, used herein denotes straight chain, branched or cyclic alkyl, preferably C
1-20
alkyl or cycloalkyl. Examples of straight chain and branched alkyl include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, amyl, isoamyl, sec-amyl, 1,2-dimethylpropyl, 1,1-dimethylpropyl, hexyl, 4-methylpentyl, 1-methylpentyl, 2-methylpentyl, 3-methylpentyl, 1,1-dimethylbutyl, 2,2-dimethylbutyl, 3,3-dimethylbutyl, 1,2-dimethylbutyl, 1,3-dimethylbutyl, 1,2,2-trimethylpropyl, 1,1,2-trimethylpropyl, heptyl, 5-methylhexyl, 1-methylhexyl, 2,2-dimethylpentyl, 3,3-dimethylpentyl, 4,4-dimethylpentyl, 1,2-dimethylpentyl, 1,3-dimethylpentyl, 1,4-dimethyl-pentyl, 1,2,3,-trimethylbutyl, 1,1,2-trimethylbutyl, 1,1,3-trimethylbutyl, octyl, 6-methylheptyl, 1-methylheptyl, 1,1,3,3-tetramethylbutyl, nonyl, 1-, 2-, 3-, 4-, 5-, 6- or 7-methyl-octyl, 1-, 2-, 3-, 4- or 5-ethylheptyl, 1-, 2-, or 3-propylhexyl, decyl, 1-, 2-, 3-, 4-, 5-, 6-, 7- and 8-methylnonyl, 1-, 2-, 3-, 4-, 5-, 6-ethyloctyl, 1-, 2-, 3- or 4-propylheptyl, u

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