Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1989-11-22
1992-11-24
Hoke, Veronica P.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
252406, 524176, 524177, 524178, 524180, 524289, 524304, 524305, 524330, 524331, 524333, 524392, 524434, 524435, C08K 557, C08K 556, C08K 537
Patent
active
051662418
DESCRIPTION:
BRIEF SUMMARY
This invention concerns a stabilization process for vinyl chloride homopolymer and/or copolymer-based blends during processing as well as the stabilisation systems for this purpose.
The process invented employs stabilizing compositions aimed at protecting vinyl chloride homopolymers and copolymers (PVC) from the undesirable effects of heat when they pass through processing machines such as calenders, extruders, mixers, injection-moulding machines and gellation tunnels.
This process allows the initially desired colour to be obtained and colour stability and thermal stability to be maintained for sufficiently long periods.
It is common knowledge that PVC require the addition of chemical compounds in order to make them suitable for processing with heat. These compounds are commonly called thermal stabilizers, and they have four roles to play:
a) to ensure the desired colour or absence of colour;
b) to maintain the initial colour of the melt, without embarrassing change, for a sufficiently long period;
c) to prevent the thermal degradation of the melt for a sufficiently long period and
d) in the case of finished products which must be transparet, not to alter the intrinsic transparency of the polymer.
During processing, the temperature of the melt in the case of PVC is between 160.degree. C. and 230.degree. C. according to different factors: the nature of the PVC (flexible or rigid), the K value of the PVC and finally the shearing rate the melt is subjected to in the machine. In general the temperature of flexible PVC is between 160.degree. C. and 190.degree. C. and that of rigid PVC between 200.degree. C. and 230.degree. C.
The length of colour stability and thermal stability for a given blend is inversely proportional to the temperature of the melt. For every 10.degree. C. rise in temperature, the length is reduced approximately by half. This means, for example, that a thermal stabilization system which is adequate for the processing of a flexible PVC at 180.degree. C., can be totally unsuitable for the processing of rigid PVC at 220.degree. C.
These technological particularities and considerations of stabilization cost explain why such a great range of thermal stabilizers is offered by producers in order to satisfy the large and varied market of PVC processing.
The use of organic compounds containing --SH functions as PVC stabilizers in combination with other known thermal stabilizers has been proposed.
For example, they are used:
in association with Ba, Sr, Ca, Cd, Zn, Pb, Sn, Mg, Co, Al, Ni, Ti salts of phenols, aromatic carboxylic acids, fatty acids and epoxydized fatty acids (U.S. Pat. No. 3,144,422);
in association with dialkylated tin carboxylates (U.S. Pat. No. 3,063,963);
in association with organo-tin oxides or organo-antimony oxides (DE-C-1 217609).
U.S. Pat. No. 3,715,333 mentions the association of organo-tin trichloride with a thio-organo-tin of general formula R.sub.2 Sn(SR').sub.2.
However, thio-organo-tin type stabilizers occupy a privileged position, especially those which correspond to the following formula:
At present, this type of stabilizer is the only one able to fulfil in the simplest conditions the four-fold role mentioned above, in the case of rigid PVC processing at temperatures between 200.degree. C. and 230.degree. C. These stabilizers are almost exclusively used for the processing of PVC into sheets and transparent rigid films, hollow bodies--except mineral-water bottles for organo-leptic reasons--and rigid tubes in the USA and Japan and partly in Europe, as a substitute for stabilizers containing lead.
The main disadvantages of these stabilizers are the complexity of their manufacture, the high tin content (14% to 20%), and the high cost.
The object of the present invention is to give compositions of thermal stabilizers which are capable of the same performances as thio-organo-tin type stabilizers in the processing of rigid PVC but which offer important advantages: simplicity of manufacture, reduction of the metal content to about 1% and a considerable reduction in the cost of
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Hoke Veronica P.
Kasper Horst M.
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