Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Reexamination Certificate
1998-11-23
2002-01-01
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, C521S914000
Reexamination Certificate
active
06335379
ABSTRACT:
The present invention is concerned with flexible polyurethane foams and a process to prepare such flexible polyurethane foams.
Flexible polyurethane foams are widely known. Such foams show a relatively high resilience (ball rebound), a relatively low modulus, a relatively high sag factor and a relatively low hysteresis loss.
Such foams further show a major glass-rubber transition below ambient temperature, generally in the temperature range of −100° C. to −10° C. The commonly applied relatively high molecular weight polyether and polyester polyols in such foams are responsible for the sub-ambient glass transition temperature (Tg
s
). These polyether and polyester polyols are often referred to as soft segments. Above Tg
s
the foam displays its typical flexible properties until softening and/or melting of the isocyanate-derived urethane/urea clusters (“hard domains”) takes place. This softening and/or melting temperature (Tg
h
and/or Tm
h
) often coincides with the onset of thermal degradation of polymer segments. The Tg
h
and/or Tm
h
for flexible polyurethane foams is generally higher than 100° C., often even exceeding 200° C. At the Tgs a sharp decrease of the modulus of the flexible foam is observed. Between Tg
s
and Tg
h
/Tm
h
the modulus remains fairly constant with increasing temperature and at Tg
h
/Tm
h
again a substantial decrease of the modulus takes place. A way of expressing the presence of Tg
s
is to determine the ratio of the Young's storage modulus E′ at −100° C. and +25° C. as per Dynamic Mechanical Thermal Analysis (DMTA measured according to ISO/DIS 6721-5). For conventional flexible polyurethane foams the
E
′
-
100
°
C
.
E
′
+
25
°
C
.
ratio is at least 25.
Another feature of Tg
s
by DMTA (ISO/DIS 6721-5) is that for conventional flexible polyurethane foams the maximum value of the ratio of
Young
’
s
loss
modulus
E
″
Young
’
s
storage
modulus
E
′
(
tan
δ
max
.
)
over the −100° C./+25° C. temperature range varies from 0.20-0.80 in general. The Young's loss modulus E″ is measured by DMTA (ISO/DIS 6721-5) as well.
In the context of the present application a polyurethane foam is regarded as flexible when the ball rebound (measured according to ISO 8307 with the proviso that no preflex conditioning is applied, that only one rebound value per sample is measured and that test pieces are conditioned at 23° C. ±2° C., (50±5% relative humidity) is at least 40%, preferably at least 50% and most preferably 55-85% in at least one of the three dimensional directions. If in the present application ISO 8307 is mentioned it refers to the test as described above including the provisos. Preferably such flexible foams have a Young's storage modulus at 25° C. of at most 500 kPa, more preferably at most 350 kPa and most preferably between 10 and 200 kPa (Young's storage modulus measured by DMTA according to ISO/DIS 6721-5). Further, such flexible foams preferably have a sag factor (CLD 65/25) of at least 2.0, more preferably at least 3.5 and most preferably 4.5-10 (measured according to ISO 3386/1). Still further such flexible foams preferably have a CLD hysteresis loss (ISO 3386/1) of below 55%, more preferably below 50% and most preferably below 45%.
In the context of the present patent application polyurethane foams are considered as rigid if the ball rebound is below 40%, as measured according to ISO 8307, at a free rise core density of the foam of 3-27 kg/m
3
.
Preferably the ratio E′
−100° C.
/E′
+25° C.
of such a rigid foam is 1.3-15.
Conventional flexible foams are made by reacting a polyisocyanate and a relatively high molecular weight isocyanate reactive polymer, often a polyester or polyether polyol, in the presence of a blowing agent and optionally further using limited amounts of relatively low molecular weight chain extenders and cross-linkers and optionally using additives like catalysts, surfactants, fire retardants, stabilisers and antioxidants. The relatively high molecular weight isocyanate reactive polymer in general represents the highest weight fraction of the foam. Such flexible foams may be prepared according to the one-shot, the quasi- or semi-prepolymer or the prepolymer process. Such flexible foams may be moulded foams or slabstock foams and may be used as cushioning material in furniture and automotive seating and in mattresses, as carpet backing, as hydrophilic foam in diapers and as packaging foam. Further they may be used for acoustic applications, e.g. sound insulation. Examples of prior art for these conventional flexible foams are EP--10850, EP--22617, EP-111121, EP-296449, EP-309217, EP-309218, EP-392788 and EP-442631.
Conventional rigid foams are made in a similar way with the proviso that often the polyisocyanates have a higher isocyanate functionality, the amount of high molecular weight polyols used is lower and the amount and functionality of the cross-linkers is higher.
WO92/12197 discloses an energy-absorbing, open-celled, water-blown, rigid polyurethane foam obtained by reacting a polyurethane foam formulation, comprising water which acts as a blowing agent and a cell-opener, in a mould wherein the cured foam has a moulded density of about 32 to 72 kg/m
3
and a crush strength which remains constant from 10 to 70% deflection at loads of less than 70 psi. The foams have minimal spring back or hysteresis.
GB2096616 discloses a directionally flexibilized, rigid, closed-cell plastic foam. The rigid foams are flexibilized in order to use them for e.g. pipe-insulation. Cells should remain closed.
U.S. Pat. No. 4,299,883 discloses a sound-absorbent material made by compressing a foam having closed cells to such an extent that the foam recovers to 50-66% of its original thickness. By the compression the cells are ruptured and the foam becomes flexible and resilient; it may replace felt. The disclosure mainly refers to polycarbodiimide foams.
EP561216 discloses the preparation of foam boards having improved heat insulation properties, wherein the foam has anisotropic cells having a length ratio of the long and the small axis of 1.2-1.6 and a density of 15-45 kg/m
3
and wherein the cells have been crushed in the direction of the plate thickness. The disclosure actually refers to polystyrene boards. Since the disclosure refers to foams having improved heat-insulation properties, the foams actually have closed cells.
EP641635 discloses a process for preparing foam boards, having a dynamic stiffness of at most 10 MN/m
3
, by crushing a board of 17-30 kg/m
3
density at least twice to 60-90% of its original thickness. Preferably closed-celled polystyrene is used. In the examples it is shown that a polystyrene foam which has been crushed showed a better heat insulation than an uncrushed one.
U.S. Pat. No. 4,454,248 discloses a process for preparing a rigid polyurethane foam wherein a partially cured rigid foam is softened, then crushed and re-expanded and fully cured.
Surprisingly a completely new class of flexible polyurethane foams was found such foams having no major glass-rubber transition between −100° C. and +25° C. In more quantitative terms these foams show a ratio E′
−100° C.
/E′
+25° C.
of 1.3 to 15.0, preferably of 1.5 to 10 and most preferably of 1.5 to 7.5. The tan &dgr;
max
over the −100° C. to +25° C. temperature range is below 0.2.
The free rise core density of such foams may range from 4-30 kg/m
3
and preferably ranges from 4-20 kg/m
3
(measured according to ISO/DIS845). Preferably the foams according to the present invention have a major glass transition above 50° C. and most preferably above 80° C.
The flexible polyurethane foams according to the present invention are prepared by reacting a polyisocyanate and a polyfunctional isocyanate-
Cunningham Anthony
Eling Berend
Leenslag Jan Willem
Cooney Jr. John M.
Imperial Chemical Industries PLS
Pillsbury & Winthrop LLP
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