Page 4 - Combined_4_OCR
P. 4
plugging; their main disadvantages are ache, depressed feeling, and insomnia. The current Maximum Allowable
less efficient mixing and excessive over TDI is also a powerful irritant to the Concentration (MAC)4 is also a ceiling
spray. eyes and skin. If digested, it will cause concentration not to be exceeded. This
irritation io the gastrointestinal tract. value is based on the capacity of TDI
Short exposures to concentrations of to produce sensitization of the respira
HEALTH HAZARDS
TDI at or near the Maximum Allowable tory tract. It may be low enough to
The most toxic chemicals used are the Concentration of 0.02 parts per mil prevent sensitization, but it is not low
isocyanates. In general, all isocyanates lion4 have caused progressive disabling enough to prevent attacks after sensiti
exhibit the unusual characteristic of a illness characterized by breathlessness, zation has occurred. Apparently, such
low oral toxicity with a high chronic chest discomfort, and reduced pulmon sensitization can follow a few exposures
inhalation toxicity. All isocyanates have ary function. Exposure to higher con of short duration to relatively high con
the potential for producing asthma-like centrations has caused, within minutes, centrations of vapors, or a larger num
symptoms. tracheal and laryngeal irritation and ber of exposures to concentrations above
The most important of the isocyanates severe coughing spasms, leading to em the MAC but below levels of detection
is toluene diisocyanate, generally re barrassed respiration and cyanosis. by odor or irritation. Tests indicate
ferred to as TDI. Reports in European Permanent respiratory disability can re that the least detectable odor of TDI is
literature and industrial experience in sult from repeated attacks after inhala approximately 0.4 ppm. Irritation of
the United States have proven that TDI tion eposure to TDI. At least four the nose and throat occurs at about 0.5
vapors have a severe irritating effect on deaths have been associated with TDI ppm, and appreciable odor is recog
the mucuous membranes, especially the exposure by inhalation. Two of three nized at 0.8 ppm.
respiratory tract. Coughing and asthma other persons have died as a result of Two other diisocyanates of major
like reactions may occur. Other symp chronic cardiopulmonary disease as usage in the foaming process are di
toms that may be experienced are head sociated with TDI inhalation.5 phenylmethane diisocyanate (MDI) and
Figure 3. One-Shot Process (New)
Polyol
(Polyether -100 parts)
Isocyanate_____________
(TDI - 40 to 60 parts)
See first process Foam product
stater
(3.5 to 5.5 parts)
Catalyst _______
(Diazodlcycloocfane er
triethylaminediomine plus
stannous oefefe)
Figure 4. Pre-polymer Process
A portion of the polyol is pre-reacted with an isocyanate to form a
liquid pre-polymer. This component is mixed with a second pre-mixed
blend of additional polyol, catalyst, and blowing agent.
(7 to 9.5%
Pre-polymer excess NCO)
Isocyanate polyether (40 / 100}
See first process Foam product
JfaiSX_____ ___ _
(2 to 3 parts to amt. pre- polymer)
Catalyst
(N-methyl morpholine, Methyl amine,etc»)
i . i
