Multidensity foam article and method of preparation

A multidensity polyurethane foam article suitable for use as a seat cushion includes a supportive layer of firm foam and a comfortable layer of softer foam. The multidensity article has a sag factor of about 3.0 to about 4.5, and the two foam layers are bonded together without employing adhesives. The multidensity foam article is prepared by placing a first formulation capable of yielding a firm foam into a mold and permitting said formulation to start creaming, rising and foaming; introducing a second liquid formulation capable of forming a soft foam into the mold after the first formulation has completed 10 to 80% of its potential rise so that the second formulation passes through the rising first formulation and the first formulation floats upon the second formulation; and then permitting the two formulations to cream, foam, rise and cure into a single multidensity article having a firm supportive foam layer and a soft foam layer, which layers are bonded and knitted together at their common boundary during the curing process.

The present invention relates to a multidensity foam article especially 
useful as a cushion for vehicle seats and to a method of preparing such 
articles. 
BACKGROUND OF THE INVENTION 
In the past, various methods have been used to make foam cushions which 
provide both safe, suppportive means as well as a soft, comfortable seat 
for the rider of a vehicle such as a snowmobile or a mobile piece of heavy 
industrial equipment. The methods of preparing such cushions for the most 
part have involved the bonding together of different types of foams and/or 
foams of different hardnesses to form laminated cushions having the 
desired properties. Such methods have been effective in that they do 
provide cushions having the desired comfort and safety for use in such 
vehicle seats; however, the methods are not only time consuming, but they 
are also expensive. 
The present invention provides a method for producing a novel, multidensity 
foam article which is suitable as a seat cushion and which has a firm, 
supportive inner layer as well as a soft, comfortable outer layer. 
Moreover, the multidensity foam article is produced by a method which is 
economical and practical as will be evident from the following 
description. 
SUMMARY OF THE INVENTION 
The present invention relates to a multidensity polyurethane foam article 
which has a sag factor of about 3.0 to about 4.5 which makes it suitable 
for use as a cushion for vehicle seats. The multidensity foam article 
includes a firm, supportive inner or lower layer of high density, high 
modulus foam, and a soft, comfortable outer or top layer of lower density, 
lower modulus foam. The two layers are bonded or knitted together without 
the use of adhesives. 
The present invention also relates to a novel method of preparing the 
multidensity foam article which comprises partially filling a mold with a 
first formulation which yields a firm or semi-flexible foam having a high 
modulus; allowing this formulation to cream, foam and start to rise and 
then adding to the mold a second formulation which yields a soft foam 
having a low modulus. The second formulation which is a liquid and of 
higher specific gravity passes through the foaming first formulation and 
the foaming first formulation floats upon the second formulation. Both 
formulations are then allowed to cream, foam and rise to fill the closed 
mold. When sufficiently cured, the article is removed from the mold. It is 
inverted 180.degree. for use as a cushion with the soft, comfortable foam 
on top and the firm, supportive foam on the bottom. 
In the method, the second foam formulation cannot be added immediately 
after the addition of the first. It is necessary that a slight time delay 
exist which permits the first formulation which yields the firm or high 
modulus foam to start to cream and reduce its specific gravity. The length 
of time delay which is required depends on the reaction rates of the two 
foams being utilized primarily the reaction rate of the first foam 
formulation. The length of time delay between pouring the two foam 
formulations must be such that the mass of the first or firm foam 
formulation which is rising or creaming will float on top of the newly 
poured second or soft foam formulation. If the mass of the firm foam 
formulation has increased too far in the foaming reaction, the viscosity 
of the mass will be such that the soft foam formulation being added will 
not be able to penetrate the firm foam formulation, hence, the firm foam 
formulation will not float on the surface of the rising soft foam and will 
not subsequently occupy the bottom of the mold cavity. If the foaming 
reaction of the first firm foam formulation mass has not advanced 
sufficiently far, the soft foam will co-mingle with the firm foam 
formulation and the resulting article will not exhibit the desired 
stratified layers of foams of different densities or have the desired 
cushioning properties. In the preferred practice of the method, a time 
delay of 10 to 30 seconds is acceptable as the first formulation will have 
resin between about 10% to about 80% of its potential rise in that period 
and the second formulation will still pass through the first without 
detrimental effects. 
The method of the present invention provides substantial advantages over 
the previously known practices in that it permits the pour molding of a 
multidensity, foam article which is a simple, inexpensive, time saving 
method of mass producing articles suitable for use as seat cushions. 
The primary objects of the present invention are to disclose a multidensity 
foam article suitable for use as a cushion for a vehicle and a simple, 
inexpensive, time saving method of preparing such a cushion. 
These and other objects will be apparent to those skilled in the art from 
the description which follows.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
In FIG. 1 of the drawings is seen a multidensity, polyurethane foam article 
10 suitable for use as a seat cushion. The multidensity foam article 10 is 
comprised of a firm, foam inner or lower layer 11 and a soft foam upper or 
top layer 12. The two layers 11 and 12 are bonded or knitted together at 
their common boundary 13. 
The function of the firm foam layer 11 in a cushion is to either provide 
the cushion with high support qualities or to provide an energy absorbing 
or energy insulating layer within the cushion. The function of the soft 
foam layer 12 is to provide a comfortable load distributor which gives the 
overall cushion a soft and luxurious feel. The two layers are bonded 
together along their common boundary 13 during the curing process 
eliminating the need for the use of adhesives. 
The method of preparing the multidensity foam article 10 will now be 
described in connection with FIGS. 2 to 7 of the drawings. 
The multidensity foam article 10 is prepared in a mold 14 such as shown in 
FIG. 2 or in molds of other suitable configurations. The mold 14 includes 
a lid 15 and a container 16. Toggle clamps 17, 18 and 19 are provided for 
securing the lid 15 to the container 16. The mold 14 is preferably placed 
on a conveyor line (not shown) and liquid formulations for the foams 
poured into the mold. The formulations are then allowed to rise and cure 
in the closed mold to form the foamed article 10. 
In the preferred practice of the method of the present invention, a first 
firm foam liquid formulation 20 is poured into the mold 14 (FIG. 2). After 
the first foam formulation 20 has started to cream and rise and has 
completed about 10% to about 80% of its potential rise (FIG. 4), a second 
soft foam formulation 21 which is a liquid is poured into the mold 14 
(FIG. 5). The liquid formulation 21 can be poured directly upon the rising 
formulation 20. 
The rising foam formulation 20 has a specific gravity which is less than 
the liquid second formulation 21. Therefore, the formulation 21 passes 
through the rising formulation 20 and the formulation 20 floats upon the 
upper surface of the liquid second formulation 21 (FIG. 6). The mold 14 is 
then closed with the lid 15 and the contents permitted to rise and cure. 
The time required for curing ranges from between about 6 to about 10 
minutes and varies with the ingredients of the formulations and the amount 
and type of catalyst utilized. The resulting foam article 10 is then 
removed from the mold and, if desired, crushed through squeeze rollers to 
crush closed cells and allowed to further cure. When used as a cushion, 
the article 10 is inverted 180.degree. so that the soft foam layer 12 is 
at the top and firm layer 11 is at the bottom as seen in FIG. 1. 
The firm layer 11 is preferably of a high density polyurethane foam and it 
has an I.L.D. (indentation load deflection) or hardness of about 70 to 140 
or higher. The soft foam layer 12 preferably has an I.L.D. of about 15 to 
about 50. The multidensity foam article has a sag factor or I.L.D. (65/25) 
index of between about 3.0 to about 4.5 when intended for use as a seat 
cushion for snowmobiles or industrial equipment. 
The following examples will further illustrate the advantages of the 
present invention, and provide a more complete understanding of the 
preferred process. 
EXAMPLE 1 
Multidensity Foam Article 
Into a 4".times.15".times.15" mold, there was placed 160 grams of 
formulation No. 1. 
______________________________________ 
Formulation No. 1 Grams 
______________________________________ 
Polyether triol, 4800 M.W. 34.0 hydroxyl number. 
63.20 
(NIAX Polyol 11-34) 
Acrylonitrile Polymer Polyol Hydroxyl number 28, 
35.00 
(NIAX Polyol 31-28) 
Diethanolamine 1.80 
Water 2.30 
Tertiary amine catalyst 1.90 
Non-hydrolyzable silicone surfactant 
0.20 
(Silicone C5303) 
Fluorocarbon blowing agent 8.00 
Quasi Prepolymer 32% free NCO 
56.60 
(NIAX isocyanate SF 50) 
______________________________________ 
Formulation No. 1 is allowed to cream and rise for 45 seconds in which time 
it has risen to 65% of its total potential. Then, 640 grams of formulation 
No. 2 is dispensed into the mold by pouring it on top of the still rising 
Formulation No. 1. 
______________________________________ 
Formulation No. 2 Grams 
______________________________________ 
Polyether triol, 4800 M.W. hydroxyl number 34.0 
60.00 
(NIAX Polyol 11-34) 
Acrylonitrile Polymer Polyol hydroxyl 
number 28.0 35.00 
(NIAX Polyol 31-28) 
Ethoxylated triethanolamine hydroxyl number 635 
5.00 
(Thanol SF 265) 
Water 2.50 
Tertiary amine catalyst 1.35 
Organo-tin catalyst 0.03 
Non-hydrolyzable silicone surfactant 
0.60 
(Silicone L5307) 
Modified poly isocyanate 40% free NCO 
34.7 
(Mondur MT 40) 
______________________________________ 
Formulation No. 2 which is added as a liquid has a higher specific gravity 
than the creaming, rising Formulation No. 1 and passes through it. 
Formulation No. 1 thus floats on the surface of Formulation No. 2. The lid 
of the mold is then closed and clamped, and the contents allowed to foam, 
rise and cure for 10 minutes. The article is then removed from the mold, 
and crushed through squeeze rollers to fracture closed cells and allowed 
to cure at room temperature for 7 days. 
The resultant multidensity foam article exhibited the following load 
bearing properties: 
______________________________________ 
Load Indentation Deflection 
______________________________________ 
25% Deflection 26.0 lbs. 
65% Deflection 115.0 lbs. 
Sag Factor 4.42 lbs. 
______________________________________ 
The ingredients of Formulations 1 and 2 having the brand name Niax and the 
silicone surfactant, are available from Union Carbide. The ethoxylated 
triethanol amine (Thanol SF 265) is available from the Jefferson Chemical 
Company and the modified polyisocyanate (Mondur) is available from Mobay 
Chemical. The products of other manufacturers having equivalent properties 
and serving the same functions can be substituted. 
EXAMPLE 2 
For comparative purposes, two foam articles were made using the procedure 
set forth in Example 1 except that only one formulation was used to make 
each article. The articles produced were characterized as follows: 
______________________________________ 
Article from Formulation No. 1 
______________________________________ 
800 gram sample 4" .times. 15" .times. 15" 
Load Indentation Deflection 
25% Deflection 
76.0 lbs. 
65% Deflection 
219.0 lbs. 
Sag Factor 
2.88 lbs. 
______________________________________ 
Article from Formulation No. 2 
______________________________________ 
800 gram sample 4" .times. 15" .times. 15" 
Load Indentation Deflection 
25% Deflection 
24.0 lbs. 
65% Deflection 
66.0 lbs. 
Sag Factor 
2.75 lbs. 
______________________________________ 
The foam articles produced from the individual formulation were not 
satisfactory for use as seat cushions since they had a sag factor of less 
than 3.0. 
EXAMPLE 3 
This example was conducted to demonstrate that it is desirable to allow the 
first foam formulation to advance in rise to about 10% to about 80% of its 
total potential rise before adding the second formulation. A foam article 
was made by a process in which 160 grams of Formulation No. 1 was 
dispensed into a 4".times.15".times.15" mold, and then 640 grams of 
Formulation No. 2 was poured into the mold immediately without allowing 
Formulation No. 1 to rise. The resultant foam article exhibited the 
following load bearing characterisitics: 
______________________________________ 
Load Indentation Deflection 
______________________________________ 
25% Deflection 
41.0 lbs. 
65% Deflection 
118.0 lbs. 
Sag Factor 
2.88 lbs. 
______________________________________ 
The article was unacceptable for use as a seat cushion because of the low 
sag factor figure. 
EXAMPLE 4 
This example was conducted to demonstrate that the second foam formulation 
should be added before the first foam formulation has risen too 
completely. A sample was prepared by dispensing 160 grams of Formulation 
No. 1 into the mold and waiting for 135 seconds before adding the 640 
grams of Formulation No. 2. After 135 seconds, the Formulation No. 1 had 
risen to approximately 90 to 100% of its total potential rise. The mold 
was closed and formulations allowed to rise and cure as in Example 1. The 
resultant foam article was undersized and had very poor appearance because 
the formulation of the first foam had been too far advanced when the 
second foam was added. As a result, the second foam formulation did not 
penetrate without disrupting the cell structure of the first foam, thereby 
"killing" some of the first foam. 
The articles prepared in the Examples were judged by the appearance of the 
article and its appropriateness for use as a cushion, the appearance of a 
cross section of the article and the sag factor. 
The article in Example 1, was acceptable for use as a cushion as the top 
and sides of the article were covered with the soft foam layer and the 
bottom of the cushion contained the layer of firm, supportive foam. The 
article had a good, soft, luxurious feel which is desirable in a cushion. 
A cross section of the article indicated that there was a clear 
stratification of the two foam layers and that a strong knitting line 
joined the layers. 
The articles prepared in the other Examples were unacceptable for use as 
cushions. They either had inadequate sag factors, or contained 
unacceptable voids or uneven stratification of the foams. 
The methods of determining the load indentation deflection values was that 
described in ASTM D 1564-63T. The sag factor or I.L.D. (65/25) index is 
the ratio of a 65% compression value divided by the 25% value. This ratio 
indicates to some extent a more or less linear relationship between 
ratings taken to form a resilience curve. A sag factor of 3 to 4.5 pounds 
is considered acceptable for a seat cushion for a snowmobile or piece of 
industrial equipment. 
Although for purposes of illustration, specific formulations have been 
described for Formulations No. 1 and No. 2, it will be readily understood 
by those skilled in the art that any polyurethane foam formulations which 
yield foams having the desired properties when used in the method of the 
invention can be employed. The selection of ingredients will depend upon 
the function the foam layer is desired to perform. When the function of 
the firm foam layer is to provide high support, a high I.L.D. foam is 
preferred. However, if the primary function of the firm foam layer is to 
provide an energy absorbing layer, the formulation should be designed to 
yield a semi-flexible foam with a high degree of cross linking. The soft 
foam layer is preferably a high resiliency low I.L.D. foam. However, any 
soft foam formulation which results in a soft foam layer which functions 
as a comfortable load distributor and gives the overall cushion a soft and 
luxurious feel can be employed. 
Polyurethane foams are formed by the reaction of a polyol and a 
polyisocyanate in the presence of a blowing agent, a catalyst and 
surfactant. The blowing agent produces gas for foaming, the catalyst 
speeds the reaction and the surfactant stabilizes the rising foam and 
controls cell size. By varying the type and amount of these ingredients, 
urethane foams can be made by those skilled in the art to meet the 
requirements of the firm, supportive layer and soft, comfortable layer. 
It is, therefore, to be understood that the scope of the present invention 
is not to be limited by the specific formulations which have been included 
for purposes of illustration. 
It will also be apparent to those skilled in the art that the novel pour 
molding method of preparing the novel multidensity foam articles of the 
present invention provides a substantial cost and time saving advantage 
over the previously employed laminating methods.