A liquid concentrate comprises between about 4 and about 25 wt % of 4,5-dichloro-2-(n-octyl-4-isothiazolin-3-one), between about 25 and about 88 wt % of a plasticizer in which said isothiazolinone compound is soluble and between about 8 and about 50 wt % of benzyl alcohol which stabilizes the concentrate against crystallization and/or freezing at sub-freezing conditions.

The present invention is directed to liquid concentrates of 
4,5-dichloro-2-(n-octyl-4-isothiazolin-3-one) which are stable to 
crystallization or freezing at sub-freezing temperatures. 
BACKGROUND OF THE INVENTION 
It is well known to add biocides to thermoplastic resin compositions to 
protect articles formed from such compositions against microbial 
degradation. For processing reasons, it is known to provide biocides as 
concentrates, such as liquid concentrates as taught, for example, in U.S. 
Pat. No. 4,758,609, or solid concentrates as taught, for example, in U.S. 
Pat. No. 4,086,297, the teachings of each of which are incorporated herein 
by reference. Although a number of biocides have been suggested for use in 
thermoplastic resins, including isothiazolinones, the standard 
anti-microbial agent in the industry has been and remains 
10,10'-oxybisphenoxarsine (OBPA). While OBPA has proven to be a very 
effective biocide for use in the plastics industry, OBPA may not be 
optimal for all compounds and processes. 
Isothiazolinone compounds are an important family of chemicals with 
considerable biocidal effectiveness in paint, textiles and metal working 
fluids. For outdoor weathering applications 
4,5-dichloro-2-(n-octyl-4-isothiazolin-3-one) (referred to herein as 
"DCOIT")shows promise to be a particularly effective biocide in plastics 
applications. At room temperature DCOIT is in solid form and therefore 
difficult to handle. DCOIT is more easily handled if dissolved in a liquid 
carrier, particularly a plasticizer which serves its normal plasticizing 
function in the end-use plastic composition. 
However, even though stable at room temperature (eg 20.degree.-25.degree. 
C.) plasticizer solutions of DCOIT to freeze when the temperature of the 
solution becomes cold, as might be encountered during shipping and storage 
in winter climates. This is highly undesirable as a plastics manufacturer 
who might receiver frozen concentrate would not only have to thaw the 
concentrate but take steps to ensure that the DCOIT is fully re-dissolved 
and that the concentrate is homogeneous. 
U.S. Pat. No. 5,498,344, the teachings of which are incorporated herein by 
reference, discusses this freeze problem and suggests the addition of 
monoalkylphenols, particularly nonylphenol, to solve the freezing problem. 
Unfortunately, nonylphenol, the most commercially available of such 
monoalkylphenols, is becoming increasingly disfavored from an 
environmental standpoint. Furthermore, nonylphenol is an irritant. 
Accordingly, it is desired to have more environmentally friendly and safer 
concentrates of DCOIT which do not freeze under typical low-temperature 
shipping and storage conditions. 
SUMMARY OF THE INVENTION 
In accordance with the invention, a liquid concentrate comprises between 
about 4 and about 25 wt of an isothiazolinone compound, between about 25 
and about 88 wt % of a plasticizer(s) in which said isothiazolinone 
compound is soluble, and between about 8 and about 50 wt % of benzyl 
alcohol. The benzyl alcohol stabilizes the concentrate against 
crystallization and/or freezing at sub-freezing conditions. 
Preferably, a concentrate contains at least about 10 wt % DCOIT and at 
least about 15 wt % benzyl alcohol and, under certain circumstances, 
preferably at least about 15 wt % DCOIT and at least about 40 wt % benzyl 
alcohol. 
DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS 
Generally any plasticizer in which DCOIT is soluble is suitable for forming 
a concentrate in accordance with the present invention. Examples of such 
plasticizers include, but are not limited to tricresyl phosphate, 
dipropylene glycol dibenzoate, diphenylcresyl phosphate, dipropylene 
glycol dibenzoate, diphenylcresyl phosphate, epoxidized soya, epoxidized 
tallate, dioctyl azelate, di(2-ethyl hexyl)phthalate, alkyl aryl 
phosphates, diisobutyl phthalate, diisodecyl phthalate (DIDP), 
hydrogenated methyl rosin ester, n-octyl n-decyl phthalate, mixed n-alkyl 
phthalates, butyl benzyl phthalate, di-n-octyl phthalate, di-n-decyl 
phthalate, 3,4-epoxycyclohexyl methyl 3,4-epoxycyclohexane carboxylate, 
trioctyl trimellitate and low molecular weight polymeric plasticizers such 
as Paraplex.RTM. G-30 plasticizer sold by Rohm & Haas Co. and the like. Of 
these plasticizers, di(2-ethyl hexyl) phthalate, diisodecyl phthalate, 
butyl benzyl phthalate and epoxidized soya are preferred. 
The freezing/crystallization problem with DCOIT occurs because DCOIT is 
solid at room temperature, having a melting point of above 40.degree. C. 
This compound, exhibits improved stability (weatherability) relative to 
other isothiazolinone compounds heretofore used as biocides, such as 
liquid 2-(n-octyl-4-isothiazolin-3-one), in outdoor conditions. Thus, the 
desire to provide concentrates of this compound.