Low resilience urethane foam

Details Low resilience urethane foam Low resilience urethane foam

1999-01-29

2001-03-20

Cooney, Jr., John M. (Department: 1711)

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

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S155000, C521S170000

Reexamination Certificate

active

06204300

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to low resilience urethane foam having excellent low resilience useful as an impact energy absorbing material, a sound insulating material and a vibration damping material. The material is capable of ensuring a uniform pressure distribution to reduce fatigue and pressure gangrene, when used as a cushioning material for chairs and mattresses.
2. Description of the Prior Art
Low resilience urethane foam useful as the impact energy absorbing material, the sound insulating material, the vibration damping material and the cushioning material for chairs and mattresses is known. With the known type of low resilience urethane foam, components of the urethane foam, namely, type of polyisocyanate, functionality and hydroxyl value of polyol, are selected and formulated such that glass transition can be caused at temperature for the urethane foam to be used, i.e., at room temperature, so that low resilience can be imparted to the urethane foam by the glass transition phenomenon.
This known type urethane foam, formulated such that the glass transition can be caused at room temperature, shows excellent low resilience by the glass transition phenomenon at room temperature, but it has a disadvantage that at a temperature less than that of occurence of the glass transition, e.g., at low temperatures of 0° C. or less, the urethane foam becomes glassy and its hardness increases rather drastically from that at room temperature.
SUMMARY OF THE INVENTION
It is, therefore, the object of the present invention to provide low resilience urethane foam having excellent low resilience at room temperature and being low in increase of hardness even at low temperature.
The present invention provides low resilience urethane foam produced by reaction of urethane foam compositions comprising polyol (a), polyisocyanate (b), catalyst (c) and blowing agent (d), characterized in that the low resilience urethane foam has at least one glass transition point in each of a temperature range of −70° C. to −20° C. and a temperature range of 0° C. to 60° C.; and that where the glass transition point is expressed as a tan &dgr; peak obtained when measurement on dynamic viscoelasticity of the low resilience urethane foam is performed at a frequency of 10 herz, the tan &dgr; peak(s) at the temperature range of −70° C. to −20° C. is/are 0.15 or more and the tan &dgr; peak(s) at the temperature range of 0° C. to 60° C. is/are 0.3 or more.
It is preferable that the polyol (a) is at least one polyol selected from the group consisting of polyoxyalkylene polyol, vinyl polymer-containing polyoxyalkylene polyol, polyester polyol, and polyoxyalkylene polyester block copolymer polyol.
Further, it is preferable that the polyol (a) comprises polyol (a-1) of 1.5 to 4.5 in average functionality and 20-70 mgKOH/g in hydroxyl value and polyol (a-2) of 1.5 to 4.5 in average functionality and 140-300 mgKOH/g in hydroxyl value and also contains therein the polyol (a-1) ranging from 32 weight percent to 80 weight percent and the polyol (a-2) ranging from 20 weight percent to 68 weight percent.
It is then preferable that the polyol (a-1) comprises polyoxyalkylene polyol and polyoxyalkylene polyester block copolymer polyol and also contains therein the polyoxyalkylene polyol and the polyoxyalkylene polyester block copolymer polyol, with the range from 30 weight percent to 70 weight percent, respectively. It is also preferable that the polyol (a-2) is polyoxyalkylene polyol in which oxyethylene units of not less than 20 weight percent, particularly preferable not less than 60 weight percent, are contained in the oxyalkylene unit.
The polyisocyanate (b) is preferably toluene diisocyanate, and the blowing agent (d) is preferably water.
Also, it is preferable that a storage modulus (E′), which is obtained together with the tan &dgr; peak when the measurement on the dynamic viscoelasticity of the low resilience urethane foam is performed at a frequency of 10 herz, is not more than 5 MPa at temperature of not less than 0° C., further preferably not more than 5 MPa at temperature of not less than −20° C.
The low resilience urethane foam of the present invention has an excellent low resilience of the impact resilience (ball rebound) modulus of not more than 20% at 25° C. and yet minimizes the tendency to increase the hardness even at low temperatures. Therefore, even in a low temperature range, the urethane foam can be effectively used as the impact energy absorbing material, the sound insulating material, the vibration damping material and the cushioning material for chairs and mattresses.


REFERENCES:
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M. Omoto et al., PU China '95 Conference Papers, pp. 325-328 (Nov. 8-10, 1995).
[Interim Publication] M. Kageoka et al., PU China '98 Conference Papers, Paper 35, pp. 1-6 (Apr. 1-3, 1998).
[Interim Publication] M. Kageoka et al., Polyurethanes Expo '98 Conference Proceedings, pp. 115-120 (Sep. 17-20, 1998).

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