Method for manufacturing multihardness foamed articles

A method for manufacturing a multihardness foamed article, including the steps of, placing a mold for foaming such that its bottom surface is inclined with respect to the horizontal plane, pouring a first liquid formulation which will form a portion having a certain hardness designed to constitute the surface area of the foamed article at or adjacent to a higher point of the inclined bottom surface, and allowing the formulation to flow and spread over the entire bottom surface as a continuous thin layer while sticking at its undersurface to the bottom surface, immediately after pouring of the first formulation, pouring a second liquid formulation which will form another portion of another hardness designed to constitute a portion other than the surface area of the foamed article at or adjacent to the higher point, and allowing the second formulation to flow and spread over the flowing and spreading first formulation as a second continuous thin layer which will not commingle with the first layer, and allowing these two layers to foam and cure respectively in a contiguous but independent state to form the multihardness foamed article which has a clear and distinct common boundary defined between portions of different hardness and is combined unitarily along the common boundary. A third liquid formulation which will form a portion of yet another hardness designed to constitute yet another portion of the foamed article may be poured at or adjacent to the higher point or onto side recesses of the mold, and allowing the third formulation to flow and spread over the flowing and spreading second formulation as a third continuous thin layer which will not commingle with the second layer.

TECHNICAL FIELD 
The present invention relates to a method for manufacturing a multihardness 
foamed article. 
BACKGROUND ART 
In the past, laminated foam cushions composed of two or more foams of 
different hardness have been known and utilized as, for example, in 
vehicle seats. 
Among many methods for preparing such multilayer or multihardness foam 
cushions, the first one involves foaming different foams of different 
hardness in separate molds, cutting respective foams into required shapes 
and dimensions, piling up various cut foams and bonding the same together 
to form a unitary foam cushion. This method is extremely time and labor 
consuming in that it requires separate molding and foaming steps, cutting 
steps and bonding steps; and, moreover, the products of this method cannot 
be expected to have high quality and be comfortable. 
The second method in the prior art involves preparing a first foam of first 
hardness, placing the same in a mold, pouring the second stock of second 
hardness onto the first foam and causing the stock to foam thereat to 
thereby produce a multihardness unitary foam article. The second method is 
also disadvantageous in that it is time consuming and it cannot define, as 
intended, a clear and distinct interface or boundary between different 
layers of different hardness. 
The third method is described in U.S. Pat. No. 3,257,149 issued June 21, 
1966 which utilizes partitions in the mold to prevent two or more foaming 
formulations from admixing with each other. This method has widely been 
employed in the industry and deemed conventional. 
Well advanced as compared to the prior methods as mentioned above, the 
fourth one is a method described in Japanese Laid-Open Publication No. 
96195/80 "Multidensity Foam Article and Method of Preparation" 
(Application No. 123753/79). Briefly, this method is shown in FIG. 10 
attached hereto and comprises partially filling a mold a having a lid b 
with a first formulation c which will yield a firm foam having a high 
modulus, allowing this formulation to foam to some extent, then pouring 
onto the foaming first formulation c a second formulation d which will 
yield a soft foam having a low modulus. The second formulation d which is 
a liquid and of higher density passes through the foaming first 
formulation c of lower density to the bottom surface of the mold a. Thus, 
the foaming first formulation c floats upon the second formulation d. The 
lid b is closed and both formulations c and d are allowed to foam, rise to 
fill the entire mold, and cure to thereby produce a composite foam article 
as shown in FIG. 11 which has a firm foam C and a soft foam D joined 
together. For use as a seat cushion, the article shown in FIG. 11 will be 
inverted 180.degree. with the soft foam D on top and firm foam C on the 
bottom. The inverted cushion will have an upper surface U and a bottom or 
rear surface R. This type of cushion is purported to have comfortableness 
and supportiveness owing to its structure comprising the soft, comfortable 
foam on the top and the firm, supportive foam on the bottom. However, some 
defects and disadvantage are found in this cushion made according to the 
fourth method. 
(1) While a major portion of the first foaming formulation yielding a firm 
portion floats upon the liquid second formulation, a thin membrane of the 
first foaming formulation remains stuck to the bottom surface of the mold. 
Upon completion of foaming and curing, this sticking membrane produces a 
thin firm layer C' on the upper surface U as shown in FIG. 11. This firm 
layer C' is an undesirable product and spoils comfortableness, supporting 
and fitting feelings intended to be produced by the soft layer D. 
Uncomfortable vehicle seats do not assure good safety and may lead to 
traffic accidents. 
(2) The second liquid formulation d poured after the first formulation 
starts to foam penetrates the foaming formulation and sinks toward the 
bottom. A trace of the second formulation remaining in the first 
formulation may produce flaws D' on the rear surface R as shown in FIG. 
11. This degrades appearance of the foamed article. 
(3) Also, the second formulation poured afterwards may break yielding cells 
in the first formulation which leads to degradation of the firm portion C' 
of the finished article. 
(4) The two portions C and D are not sufficiently strongly bonded together 
along their boundary because time interval between the first and second 
pouring is large and the consistencies of the first and second 
formulations become different from each other. 
(5) Waiting intervals are necessary between the first and second pouring, 
e.g. 30 seconds or more, and this amounts to large time losses in the 
overall production lines and may require a large number of automated 
systems. 
DISCLOSURE OF THE INVENTION 
Accordingly, it is an object of the invention to provide a method for 
manufacturing a multihardness foamed article which has a clear and 
distinct boundary or interface defined between portions of different 
hardness, and can enjoy as high comfortableness as intended, good 
supportive and fitting feelings, as well as good appearance and high 
quality. The method of this invention can achieve shorter production time 
than the prior art methods and requires less expensive production 
facilities than the prior one. 
In brief, the method of the present invention comprises holding a mold for 
foaming with its bottom surface inclined with respect to the horizontal 
plane, and pouring a plurality of liquid formulations yielding, 
respectively, different hardness portions of foamed article successively 
without substantial time intervals on the same or substantially the same 
higher point of the inclined bottom surface of the mold. The different 
formulations poured successively are allowed to flow and spread over the 
entire bottom surface as distinct layers which will not commingle with 
each other. The different distinct layers are allowed to foam and cure 
simultaneously to yield a unitary foamed article having clear and distinct 
boundaries between portions of different hardness. 
"Successively without substantial time intervals" herein means that the 
formulation poured first is not given time for substantial foaming before 
pouring a succeeding formulation. Practically, only 0-7 seconds are 
permitted between successive pourings in the present invention. This time 
interval is called "creaming time". 
In the past, it was commonly believed that two or more liquid formulations, 
if poured successively one over the other, would commingle with each other 
and would not define in any way an interface therebetween. Applicants 
challenged this commonly believed thought, and after extensive studying 
and efforts, have found that, if pourings of different formulations are 
conducted successively without substantial time intervals, they do not 
commingle with each other and do define clear and distinct interfaces 
between distinct and independent layers which, respectively foam and cure 
leaving clear and distinct boundaries as intended to yield a unitary 
foamed article. 
In the present invention, it is desirable that the bottom surface of the 
mold on which foamings take place is slightly tilted with respect to the 
horizontal plane. Although it is noted that formulations poured even on a 
horizontal bottom would spread and extend around the point on which they 
are poured as distinct layers, but in this case, they do not spread 
uniformly in all directions. On the other hand, when the bottom surface is 
greatly tilted, e.g., more than 40 degrees, formulations poured thereon 
flow down too fast to form layers of uniform thickness and accumulate on 
the lower area of the inclined bottom surface. Accordingly, it is 
necessary that the bottom surface is inclined from about 4 degrees to less 
than 40 degrees with respect to the horizontal plane. Preferably, the 
bottom surface is inclined 4-20 degrees and most preferably 5-12 degrees. 
It is noted that a liquid formulation poured on the inclined surface goes 
slightly upwards from the point on which it is poured while foaming and 
rising so that it can be said that the liquid formulation spreads over the 
entire bottom surface in all directions.

PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION 
Referring now to the drawings, the invention will be described in more 
detail. 
An embodiment of the invention is shown in FIGS. 1 through 5 in which FIG. 
1 is a partly cut away sectional view showing the pouring steps of liquid 
formulations onto an inclined bottom surface; FIG. 2 is a plan view of the 
mold indicating a pouring point P and directions in which liquid 
formulations spread and extend; FIG. 3 is a sectional view of the closed 
mold in which two different hardness formulations have risen completely to 
fill the mold; FIG. 4 is a sectional view taken substantially along the 
line IV--IV in FIG. 2 showing a unitary foamed article taken out from the 
mold and inverted 180.degree., and FIG. 5 is a sectional view of the same 
article taken substantially along the line V--V in FIG. 2. 
Now, the method of the present invention is illustrated in the following 
specific examples in conjunction with the drawings. 
EXAMPLE I 
An aluminum mold 1 having dimensions of 300.times.300.times.50 mm is 
provided as shown in FIGS. 1 and 2. The bottom surface 2 of the mold 1 is 
inclined at an angle .theta. ranging from 5 to 10 degrees with respect to 
the horizontal plane. The mold 1, especially its bottom 2, is preheated to 
a temperature of about 55.degree. C. by using an electrical heater (not 
shown) and 90 g of a first liquid formulation A as below mentioned is 
poured onto a higher point P on the inclined bottom surface 2 by using a 
low pressure foaming machine, such as Type 600-2 machine sold by Shin 
Admiral Co., Ltd., Japan. 
Operating conditions were: delivery rate at 13 kg/min., flow rate 1.8 
m/sec., liquid temperature 22.degree. C., liquid viscosity 500 cps. 
Immediately after pouring the first formulation A, 180 g of a second liquid 
formulation B is poured over the same point P by using a low pressure 
foaming machine, such as Type MEG-MINI machine of Maruka Kakoki Co., Ltd., 
Operating conditions were: delivery rate 9 kg/min., flow rate 0.45 m/sec., 
liquid temperature 25.degree. C., and liquid viscosity 800 cps. 
The first formulation A is the below-mentioned composition. 
______________________________________ 
FIRST FORMULATION A (SOFT) 
______________________________________ 
Ingredients Parts by weight 
______________________________________ 
EXENOL 910.sup.(1) 
30 
EXENOL 832.sup.(2) 
70 
diethanol amine .5 
water 2.5 
TEDA.sup.(3) .2 
L5309.sup.(4) 1.0 
Ashahi Fron.sup.(5) 
5 
M.sup.(6) 37.2 
______________________________________ 
Notes: 
.sup.(1) acrylonitrile copolymer polyether polyol (OH 
(OH value 28) manufactured by Asahi Glass 
Co., Ltd. 
.sup.(2) polyether polyol (OH value 33) by Asahi Glass 
Co., Ltd. 
.sup.(3) triethylene diamine by Toyo Soda Co., Ltd. 
.sup.(4) silicon foam controlling agent by Nippon 
Unika Co., Ltd. 
.sup.(5) fluorocarbon foaming agent by Asahi Glass 
Co., Ltd. 
.sup.(6) isocyanate by MD Kasei Co. Ltd. 
Typical Properties of Foamed Article 
______________________________________ 
bulk density 53 b/cm.sup.3 
indentation load 16 kg/314 cm.sup.2 
surface hardness 32.degree. 
(Type F Rubber Tester) 
______________________________________ 
______________________________________ 
SECOND FORMULATION B (FIRM) 
______________________________________ 
Ingredients Parts by weight 
______________________________________ 
EXENOL 910.sup.(1) 
30 
EXENOL 832.sup.(2) 
70 
diethanol amine 2 
water 2.1 
TEDA.sup.(3) .2 
L 5309.sup.(4) .5 
TDI 80.sup.(7) 9.1 
HSQ 730.sup.(8) 36.2 
______________________________________ 
Notes: 
.sup.(1)-(4) are same as in A 
.sup.(7) tolylene diisocyanate by Sumitomo Bayer Co., 
Ltd. 
.sup.(8) tolylene diisocyanate prepolymer by Mitsui 
Toatsu Chemical Co., Ltd. (free isocyanate 
29.6%) 
Typical Properties of Foamed Article 
______________________________________ 
bulk density .067 g/cm.sup.3 
Indentation load 46 kg/314 c.sup.2 
surface hardness 80.degree. 
(Type F Rubber Tester) 
______________________________________ 
In FIGS. 1 and 2, the first liquid formulation A spreads over the entire 
bottom surface 2, i.e., in the directions X and Y as well as in the upward 
direction from the point P. The undersurface a of the flowing and 
spreading first formulation A sticks to the bottom surface 2 while 
extending itself as a continuous layer. 
On this liquid later A, the second liquid formulation B is poured at the 
same higher point P by the same inlet tube 3 as previously used for the 
first formulation A. The second formulation B has substantially the same 
density as that of the first formulation A. The second liquid formulation 
B spreads over the first formulation A which is now in the form of a thin 
layer continually extending in all directions. The second formulation B 
spreads in substantially the same manner and directions as those of the 
first formulation A. 
While spreading and extending, both formulations start to foam slightly. As 
the time interval between the first and second pourings is very short, 
e.g., from 0 to 3 seconds, the two formulations A and B remain at 
substantially the same density level, and because of the surface tensions 
exhibited by the respective formulations, a clear and distinct interface 
is defined between the two layers of formulations. Surprisingly, the two 
formulations will not be admixing with each other and spread respectively 
as separate and contiguous layers the full extent of the mold. 
In FIG. 3, the lid 4 is closed against the mold 1 and fastened by an 
appropriate clamp means (not shown). In these conditions, the formulations 
A and B are allowed to foam, rise and cure for a period of about 5 minutes 
to yield an intended multihardness foamed article which is composed of a 
soft portion A resulting from the first formulation and a firm portion B 
from the second formulation. These two portions A and B having different 
hardness respectively are strongly bonded together at a common boundary or 
interface f which is defined clearly and distinctly as intended. 
In order to visually confirm this interface f, an appropriate blue tint may 
be added to the liquid second formulation B in contrast to yellowish color 
of the first formulation A upon foaming and curing. 
After being taken out from the mold 1, the multihardness foamed article may 
be subjected to an ordinary crushing operation to make closed cells open 
and to a further curing operation. 
The multihardness foamed article thus obtained is shown in cross sectional 
views in FIGS. 4 and 5. When viewed in longitudinal cross section in FIG. 
4 (along the line IV--IV in FIG. 2), both layers of soft (A) and firm (B) 
portions have uniform thickness. In FIG. 5 taken along the widthwise 
direction of the foamed article, the soft portion A poured first is 
thickened at both sides and thinned in the central portion. Surface 
hardness measured by Type F Rubber Tester at the surface a of the portion 
A is 35.degree. and 78.degree. at the rear surface b. 
Example I as described above can be varied such that the First Formulation 
yields a firm portion on the top and the Second Formulation yields a soft 
portion on the bottom of a foamed article. 
EXAMPLE II 
A second embodiment of the invention is illustrated in FIGS. 6-9. The mold 
11 having the inner configuration as shown in FIG. 6 is heated to 
50.degree.-55.degree. C. by means of a hot air circulator (not shown). The 
mold 11 is held with its major bottom surface 12 tilted to an angle 
.theta. ranging from 7.degree.-12.degree.. 
A type MEG-HK 650 high pressure foaming machine with four-component-MQ 
heads sold by Maruka Kakoki Co., Ltd. was employed. This machine was 
adapted such that a single inlet 13 can be connected to either side A or 
side B of the machine and different formulations can be continuously 
poured through the single inlet 13 by controlling values without any 
intermission. 
A Third Formulation as mentioned below is employed as a first liquid 
formulation A and assigned to side A of the machine, and a Fourth 
Formulation as mentioned below is assigned to side B of the machine as a 
second liquid formulation B. 
______________________________________ 
THIRD FORMULATION (SOFT) 
______________________________________ 
Ingredients Parts by weight 
______________________________________ 
EP 30-33.sup.(9) 60 
POP 31-28.sup.(10) 
40 
water 3.6 
diethanol amine 1.5 
TEDA.sup.(3) .13 
NIAX A-1.sup.(11) 
.1 
SRX 274C.sup.(12) 
1.0 
SUMIJULE VT 80.sup.(13) 
48.5 
______________________________________ 
Notes: 
.sup.(3) is the same as in EXAMPLE I 
.sup.(9) Polyether Polyol (OH value 33) by Mitsui 
Toatsu Chemical Co., Ltd. 
.sup.(10) acrylonitrile polymeric polyether polyol (OH 
value 28) by Mitsui Toatsu Chemical Co., Ltd. 
.sup.(11) amine catalyst by UCC 
.sup.(12) silicon foam controlling agent by Toray 
Silicones 
.sup.(13) isocyanate by Sumitomo Bayer Urethane 
Typical Properties of Foamed Article 
______________________________________ 
bulk density .044 g/cm.sup.3 
indentation load 20 kg/314 cm.sup.2 
surface hardness 48.degree. 
(Type F Rubber Tester) 
______________________________________ 
______________________________________ 
FOURTH FORMULATION (FIRM) 
______________________________________ 
Ingredients Parts by weight 
______________________________________ 
EP 30-33.sup.(9) 
35 
POP 31-28.sup.(10) 
65 
water 3.5 
diethanol amine 2 
TEDA.sup.(3) .13 
niax A-1.sup.(11) 
.1 
L5309.sup.(4) 1 
blue tinting agent 
.1 
SUMIJULE 49.2 
______________________________________ 
Notes: 
.sup.(3)(4)(9)(10)(11)(13) are the same as in previous 
notes. 
Typical Properties of Foamed Article 
______________________________________ 
bulk density .045 g/cm.sup.3 
indentation load 30 kg/314 cm.sup.2 
surface hardness 75.degree. 
(Type F Rubber Tester) 
______________________________________ 
Referring now to FIG. 6, the inlet 13 is positioned over the point slightly 
inside a rib 17 formed on the apex of the inclined bottom surface 12. 280 
g of a first liquid formulation A (Third Formulation) is poured from the 
inlet 13 through side A of the machine mentioned above with 180 kg/min. 
delivery rate, 1.1 m/sec. flow rate, 28.degree. C. liquid temperature, and 
500 cps liquid viscosity. Immediately, 280 g of the second formulation B 
(Fourth Formulation) is discharged through side B of the same machine with 
18 kg/min delivery rate, 1.1 m/sec flow rate, 30.degree. C. liquid 
temperature and 800 cps liquid viscosity. As shown in FIG. 7 which shows a 
foamed seat cushion in plan view by numerals in circles, the first pouring 
and the second pouring (1 and 2 in a circle) are made at the identical 
point on the bottom surface. 
About 3 seconds later, 120 g of the first formulation A (Third Formulation) 
again through side A of the machine is poured by the inlet 13 moved about 
7 mm upward from the first and second pouring point. This is shown in FIG. 
7 by encircled numeral 3. Following this, 190 g and 220 g each of the 
second formulation B (Fourth Formulation) are discharged through side B 
of the machine onto both side parts of the mold as shown by encircled 
numerals 4 and 5 in FIG. 7. 
It is imporatnt in the present invention that the different formulations 
such as A, B and A constituting at least a central sitting portion 22 
(FIG. 7) of the seat cushion be poured into the mold successively without 
substantial time intervals, and that they spread, as distinct layers not 
commingling with each other, over the entire bottom surface in the same 
directions and to the same extent. In this connection, reaction rates, 
consistencies and other properties of the respective formulations as well 
as the points at which the respective formulations are poured must 
carefully be chosen and determined. 
Upon completion of all requisite pourings, an upper half 14 of the mold is 
closed and fastened against the lower half 11 by means of a clamp (not 
shown). Different layers of different formulations are allowed to foam, 
rise and cure in the closed mold for about 5 minutes to form a unitary 
multihardness foamed article. After taken out from the mold, the article 
is subjected to a crushing operation to make the closed cells open. 
The article thus obtained, i.e., a seat cushion for a vehicle, is shown in 
FIGS. 7, 8 and 9. The central sitting portion 22 of the seat has the same 
configuration as that of the mold bottom surface 12 and side portions 23 
and 24 have configurations formed by recessed side portions (not shown) of 
the mold. A rear protrusion 28 is formed by a rear recessed portion 18 of 
the mold. Slot 27 surrounding the central portion 22 is formed by the rib 
17 formed around the mold bottom surface 12. 
As seen from FIGS. 8 and 9, the central sitting portion 22 has a 
3-layer-structure of soft portion A, firm portion B and soft portion A' 
defining therebetween clear and distinct interfaces and strongly bonded 
together therealong. The soft portion A' has the same composition as that 
of A, but the former is the one poured thirdly as described above. The 
seat cushion is provided on its undersurface with recesses 25 and 26 
corresponding to the protrusions 15 and 16 on the upper mold half 14. 
Surface hardnesses measured by Type F Rubber Tester are 48.degree. on the 
surface of the portion A, 49.degree. on the opposite rear surface of the 
portion A' and 68.degree. at the interface between A and B (25 mm from the 
surface of A). 
Using substantially the same procedure as in EXAMPLE II, a foamed article 
having firm (B)--soft (A)--firm (B) structure can be easily obtained. 
EXAMPLE III 
In this example, a polyurethane foam stock system H 255/H 210 manufactured 
by Sumitomo Bayer Urethane Co., Ltd. was employed. This system is 
commercially available as the so called "ALL MDI Cold Cure Urethane Foam 
Stock", its H 255 being mixture of polyester polyol with foaming catalyst 
and so on H, 210 being isocyanate comprising mainly diphenylmethane 
diisocyanate. By varying the ratio of H 255 and H 210 in this system, 
hardness of the foamed article to be obtained can be freely and easily 
changed. 
Table I shows typical ratios of the two components H 255 and H 210 and 
corresponding properties, though unlimited changes in ratio and properties 
are practically available. 
TABLE I 
______________________________________ 
Component Ratio 1 Ratio 2 Ratio 3 
______________________________________ 
H 255 100 100 100 
H 210 46 51 56 
Properties of Foam 
density (g/cm.sup.3) 
.053 .053 .053 
indentation load 
19 27 34 
(kg/314 cm.sup.2) 
surface hardness 
37 58 78 
(Type F Rubber Tester) 
______________________________________ 
The same mold 11 as in EXAMPLE II was used, adjusted to the mold 
temperature of 53.degree.-58.degree. C. and held with its bottom surface 
12 inclined 5.degree.-12.degree.. Type MEG-HK 430 Foaming Machine with MQ 
head sold by Maruka Kakoki Co., Ltd. was utilized. This machine is adapted 
to freely vary the output of H 210 isocyanate while pouring or during 
intervals between pourings. Thus, it is possible to shift continuously 
from Ratio 1 to Ratio 2 or from Ratio 3 to Ratio 1 or the like. Moreover, 
this machine can provide smooth flow of stocks without splashing. 
In operation, 24 g of Ratio 1 stock was poured on the higher point of the 
inclined bottom surface with conditions of delivery rate at 18 kg/m, 
liquid velocity at 1.1 m/sec, liquid temperature at 28.degree. C. and 
liquid viscosity at 700 cps and, then without any intervals, 240 g of 
Ratio 1 and 120 g of Ratio 3 stock were poured over the same point. Next, 
160 g and 240 g each of Ratio 3 stocks were respectively poured onto side 
recesses of the mold. Stocks forming separate and distinct layers are 
allowed to foam and cure in the closed mold in the same manner as in 
EXAMPLE II and subjected to crushing operation. 
The foamed article thus obtained had surface hardness of 38.degree. at the 
upper surface, 55.degree. at 20 mm depth from the upper surface, 
respectively. Surface hardness at the rear surface was 75.degree.. 
Pouring of Ratio 3, Ratio 2 and Ratio 1 stocks in this order as well as in 
another order can also be made in EXAMPLE III. 
In the present invention, high quality foamed articles defining clear and 
distinct boundaries as intended and strongly bonded together therealong 
can easily and economically be obtained by pouring concurrently without 
substantial time intervals a plurality of liquid formulations having 
selected hardness or modulus with no fear of any operational troubles 
caused by differences in foaming and curing rates, density and so on of 
the different formulations. 
The multihardness foamed article according to the present invention can be 
widely utilized as vehicle seat cushions as well as home furniture and 
office furniture such as beds, sofas, arm chairs, mats, and so on in 
various combinations of soft and firm or hard portions in unitary foamed 
articles. 
Contrary to commonly believed concepts, the present invention makes it 
possible to pour two or more liquid formulations of different hardness and 
modulus successively without substantial time intervals, with the 
successful result of yielding a unitary foamed article having a clear and 
distinct interface defined between portions of different hardness which 
are bonded together along the common interface strongly by chemical 
reactions occurring during the course of curing. The concurrent pouring of 
different formulations can prevent any sink marks, flaws or other defects 
from being made in any portions of the foamed article so as to achieve 
high comfortableness, supportive and fitting feelings as intended. 
The present invention can eliminate any time losses in the overall 
production lines and can attain shorter production time and can use 
smaller production facilities.