Production of polyurethane foams

There is provided a method of producing an open-cell polyurethane foam comprising heating a mixture of an aqueous emulsion of a polyurethane-forming composition and a fluorocarbon compound of 1 to 3 carbon atoms having a boiling point of 5.degree. to 100.degree. C. The above emulsion may further contain an ionic surfactant.

FIELD OF THE INVENTION 
This invention relates to a method of producing an open-cell polyurethane 
foam using a new aqueous emulsion formulation. 
DESCRIPTION OF THE PRIOR ART 
Open-cell polyurethane foams are generally used as synthetic leather and 
carpet backings, for instance. For the production of open-cell 
polyurethane foams, the following methods, among others, are generally 
employed. In one of the methods, a polyol component and a diisocyanate 
(generally, tolylene diisocyanate) component are cast into a mold and 
allowed to expand to shape in situ under pressure and heat in the presence 
of an inert solvent. Another known method comprises admixing a polyol 
component and a diisocyanate component and causing the mixture to react 
and undergo chemical foaming in the presence of a small amount of water. 
The maximum foaming rate that can be achieved in an open-cell foam is 
invariably about 10 times the initial volume but because a highly reactive 
toxic diisocyanate component is used, neither of the methods is easily 
available to anybody and anywhere. Moreover, the product foam is liable to 
crack and the internal cellular structure is invariably not as fine as 
would be desired. 
On the other hand, as one of the recent technologies for the production of 
synthetic leather, there is known a method in which an aqueous emulsion 
containing a polyurethane-forming composition is mechanically foamed and 
deposited on a substrate in the presence of a foam stabilizer such as 
ammonium stearate to about 2.5 to 3.5 times the initial volume. However, 
in this mechanical foaming method, the foam tends to decrease in volume in 
the course of drying and this decrease is particularly pronounced when an 
inorganic filler has been incorporated. In addition, in such mechanical 
foaming, the foaming rate of the product is influenced by the viscosity of 
the foam in such a manner that the larger the foaming rate, the higher is 
the viscosity of the foam, with the result that an open-cell foam having a 
fine cellular texture can hardly be obtained at any foaming rate in excess 
of 5 times. For this reason, whenever an open-cell foam having a higher 
foaming rate is demanded, it is imperative to lower the concentration of 
the emulsion and, so that the stability of the foam may be maintained 
throughout processing, to add an excess amount of a foam stabilizer. As a 
result, the product will have only an inadequate mechanical strength, have 
an insufficient bonding strength for substrates or develop surface cracks, 
thus failing to obtain the desired performance characteristics. 
After an intensive research to overcome the above-mentioned disadvantages, 
the present inventors have developed the novel technology of this 
invention. 
DETAILED DESCRIPTION OF THE INVENTION 
Thus, this invention, in one aspect, relates to a method of producing an 
open-cell polyurethane foam comprising heating a mixture of an aqueous 
emulsion of a polyurethane-foaming composition and a fluorocarbon compound 
of 1 to 3 carbon atoms having a boiling point of 5.degree. to 100.degree. 
C. In another aspect, this invention relates to a method wherein said 
aqueous emulsion further contains an ionic surfactant in a proportion of 
0.1 to 5 weight percent based on its solid content. 
The term "boiling point" as used herein stands for one under the 
atmospheric pressure. 
The term "polyurethane-foaming emulsion" as used in this specification and 
the claims appended thereto means any emulsion containing a polyhydroxy 
compound a polyisocyanate and, if necessary, a chain extender containing a 
plurality of reactive hydrogen atoms which may be known per se, and having 
a film-forming property. Preferably, it means a polyurethane-forming 
composition modified by the introduction of water-soluble groups of 
emulsified with an emulsifying agent. 
Specific examples of such emulsions are Implanil DLN, Implanil DLH, etc. in 
the Implanil D Series (Bayer A.G.), Alizelack S-1060, Alizelack S-2020, 
Alizelack S-4040N, etc. in the Alizelack S Series (Hodogaya Chemical Co., 
Ltd.) and the products in the Leathermin W Series (Dainichi Seika Kogyo, 
Ltd.). 
If required, such polyurethane emulsions can be used in combination with 
other synthetic resins. Among such other synthetic resins are 
solvent-soluble type, water-soluble type and aqueous emulsion type resins 
such as polyacrylic resins, polyamide resins, melamine reisns, polyvinyl 
acetate resins, polyvinyl alcohol resins, polyacetal resins, urea resins, 
polypropylene reisns,epoxy resins fluorocarbon resins, polycarbonate 
resins, etc., as well as solvent-soluble type and water-soluble 
polyurehtane resins. If necessary, fillers may also be incorporated in the 
emulsion. Among such fillers are various inorganic fillers, pigments, etc. 
such as clay, talc, mica, bentonite, diatomaceous earth, silicate, 
calcium, carbonate, aluminum hydroxide, magnesium hydroxide, antimony 
trioxide, magnesium carbonate, ultramarine, iron oxide and so on. 
The fluorocarbon compound employed in accordance with this invention has 1 
to 3 carbon atoms and a boiling point of 5.degree. to 100.degree. C. and, 
thus, includes such species as CCl.sub.3 F (b.p. 23.8.degree. C.), 
CHCl.sub.2 F (b.p. 8.9.degree. C.), C.sub.2 Cl.sub.3 F.sub.3 (b.p. 
47.6.degree. C.), C.sub.2 Br.sub.2 F.sub.4 (b.p. 47.3.degree. C.), etc. 
With any fluorocarbon compound whose boiling point is outside the range of 
5.degree. to 100.degree. C. and/or which ontains more than 3 carbon atoms, 
it is impossible to obtain the desired open-cell foam having a fine 
internal cellular structure. The level of addition of such fluorocarbon 
compound is 0.1 to 25 weight parts and preferably 1 to 5 weight parts to 
every 100 weight parts of the nonvolatile matter contained in the 
polyurethane-forming emulsion. If the amount of the fluorocarbon compound 
is outside the range of 0.1 to 25 weight parts, it is impossible to obtain 
an open-cell foam of fine cellular structure, either. If necessary, it is 
possible to add water-miscible solvents with boiling points below 
200.degree. C., such as alcohols (e.g. isopropyl alcohol), ethers (e.g. 
dimethyl ether), esters (e.g. ethyl acetate), ketones (e.g. acetone), and 
amides (e.g. dimethylformamide). 
The polyurethane-forming emulsion employed according to this invention 
generally contains 15 to 80 weight percent of solids (nonvolatile matter) 
in water, wherein said solids have been evenly dispersed as fine particles 
of 0.05 to 10.mu. in diameter either with the aid of an emulsifier or 
without an emulsifier. Accordingly, the emulsion is suitable for 
dispersing the fluorocarbon compound uniformly therein. However, to 
disperse and emulsify the fluorocarbon compound evenly, a 
polyurethane-forming emulsion alone is sometimes insufficient. Thus, in 
mechanical foaming, it is sometimes necessary to use an auxiliary compound 
which would assist in accomplishing a uniform dispersion and emulsifying 
and yielding a stable high-volume foam. Therefore, in such cases, an ionic 
surfactant is additionally employed. The ionic surfactant according to 
this invention may be selected from among those anionic surfactants, 
cationic surfactants and amphoteric surfactants which are known per se, as 
well as the corresponding fluorinated surfactants. The anionic surfactants 
mentioned above may for example be RCOOM, ROSO.sub.3 M, 
##STR1## 
[wherein R is a C.sub.8-18 alkyl group; M is an alkali metal, NH.sub.4 or 
the like]. The cationic surfactants include, for example, 
##STR2## 
[wherein R' is a C.sub.8-18 alkyl group; R.sub.1, R.sub.2 and R.sub.3 each 
is a C.sub.1-18 alkyl group; X is a halogen atom]. The amphoteric 
surfactants may for example be R"NHR.sub.4 COOH [wherein R" is a 
C.sub.8-18 alkyl group; R.sub.4 is --CnH.sub.2 n-- (wherein n is 1 to 8]. 
The anionic fluorinated surfactants include, among others, R'.sub.f 
OC.sub.6 H.sub.4 SO.sub.3 M, R'.sub.f OC.sub.6 H.sub.4 COOM, R'.sub.f 
OC.sub.6 H.sub.4 SO.sub.2 N(CH.sub.3)CH.sub.2 COOM, R.sub.f COOM, R.sub.f 
SO.sub.2 N(C.sub.2 H.sub.5)CH.sub.2 COOM, R.sub.f CH.sub.2 CH.sub.2 
O(C.sub.2 H.sub.5).sub.n SO.sub.3 M, R.sub.f CH.sub.2 CH.sub.2 SCH.sub.2 
CH.sub.2 CONHCH.sub.2 CH.sub.2 SO.sub.3 M, R.sub.f SO.sub.2 N(C.sub.2 
H.sub.5)(C.sub.2 H.sub.4 O).sub.n SO.sub.3 M, R'.sub.f OC.sub.6 H.sub.4 
COO(C.sub.2 H.sub.4 O).sub.n SO.sub.3 M, R'.sub.f OC.sub.6 H.sub.4 
CH.sub.2 OPO.sub.3 M.sub.2, R'.sub.f OC.sub.6 H.sub.4 SO.sub.2 N(R) 
(CH.sub.2 CH.sub.2 O).sub.n SO.sub.3 M, R.sub.f SO.sub.3 M, R.sub.f 
CH.sub.2 CH.sub.2 OSO.sub.3 M, R'.sub.f OC.sub.6 H.sub.4 S, R'.sub.f 
OC.sub.6 H.sub.4 CON(CH.sub.3)CH.sub.2 COOM, R'.sub.f OC.sub.6 H.sub.4 
CON(CH.sub.3)CH.sub.2 CH.sub.2 SO.sub.3 M, R.sub.f CH.sub.2 CH.sub.2 COOM 
[wherein R'.sub.f is a C.sub.6, C.sub.8, C.sub.9, C.sub.10, C.sub.12 
fluoroalkenyl group; M is a monovalent metal, NH.sub.4, NH.sub.3 CH.sub.2 
CH.sub.2 OH or NH.sub.2 (CH.sub.2 CH.sub.2 OH).sub.2 ; R.sub.f is a 
C.sub.6- C.sub.12 fluoroalkyl group; R is a C.sub.1 -C.sub.2 alkyl group; 
n is 1 to 10]. 
The cationic fluorinated surfactants may for example be R'.sub.f (OCH.sub.2 
CH.sub.2).sub.n N.sup..sym. (CH.sub.3).sub.3 I.sup..crclbar., R'.sub.f 
OC.sub.6 H.sub.4 CONHCH.sub.2 CH.sub.2 CH.sub.2 N.sup..sym. 
(CH.sub.3).sub.3 I.sup..crclbar., R.sub.f CONHCH.sub.2 CH.sub.2 
N.sup..sym. (CH.sub.3).sub.3 I.sup..sym., R.sub.f CH.sub.2 CH.sub.2 
SCH.sub.2 COOC.sub.2 H.sub.4 N.sup..sym. (CH.sub.3).sub.3 I.sup..crclbar., 
R.sub.f SO.sub.2 NHCH.sub.2 CH.sub.2 CH.sub.2 N.sup..sym. (CH.sub.3).sub.3 
I.sup..crclbar., R'.sub.f OC.sub.6 H.sub.4 SO.sub.2 NHCH.sub.2 CH.sub.2 
CH.sub.2 N.sup..sym. (CH.sub.3).sub.3 I.sup..crclbar., R'.sub.f OC.sub.6 
H.sub.4 CH.sub.2 N.sup..sym. (CH.sub.3).sub.3 I.sup..crclbar. [R'.sub.f 
is a C.sub.6, C.sub.8, C.sub.9, C.sub.10, C.sub.12 fluoroalkenyl group; 
R.sub.f is a C.sub.6 -C.sub.12 fluoroalkyl group; n is 1 to 8]. 
The amphoteric surfactants may for example be R.sub.f CONH CH.sub.2 
CH.sub.2 CH.sub.2 N.sup..sym. (CH.sub.3).sub.2 CH.sub.2 CH.sub.2 
COO.sup..crclbar., R.sub.f SO.sub.2 NHCH.sub.2 CH.sub.2 CH.sub.2 
N.sup..crclbar. (CH.sub.3).sub.2 CH.sub.2 CH.sub.2 COO.sup..crclbar., 
R'.sub.f OC.sub.6 H.sub.4 CH.sub.2 N.sup..crclbar. (CH.sub.3).sub.2 
CH.sub.2 COO.sup..crclbar., [R'.sub.f is a C.sub.6, C.sub.8, C.sub.9, 
C.sub.10, C.sub.12 fluoroalkenyl group; R.sub.f is a C.sub.6 -C.sub.12 
fluoroalkyl group]. 
Selection of these ionic surfactants depends on the type and amount of the 
polyurethane-forming emulsion and, to a larger extent, on the type and 
amount of the fluorocarbon compound. When, for instance, a fluorocarbon 
compound boiling at 5.degree. to 40.degree. C. is employed, it is 
advantageous to use a fluorinated ionic surfactant having 
vaporization-suppressive and high emulsifying activities. In case a 
fluorocarbon compound boiling at 40.degree. to 100.degree. C. is employed, 
it is advisable to use such ionic surfactants as ammonium stearate, 
alkylphenol polyethylene glycol sulfate esters, etc. The amount of such 
ionic surfactant is virtually optional but preferably within the range of 
0.1 to 5 weight parts to each 100 weight parts of the nonvolatile content 
of the polyurethane-forming emulsion. The ionic surfactant is first 
dissolved in water or in a co-solvent such as alcohol and after the 
fluorocarbon compound has been either dispersed and emulsified or 
dissolved therein, is added to the polyurethane-forming composition. 
Generally, the ionic surfactant is preferably added to the 
polyurethane-forming composition before the mechanical beating operating 
is initiated. 
To obtain an open-cell foam from the aqueous emulsion containing a 
polyurethane-forming composition according to this invention, the emulsion 
is preliminarily foamed by mechanical stirring to a foaming rate of 1.5 to 
5 times and, then, the fluorocarbon compound is vaporized by heating to 
achieve a foaming rate of 2 to 15 times. 
Compared with the conventional mechanically foamed product, the open-cell 
foam obtainable from the aqueous emulsion of polyurethane-forming 
composition in accordance with this invention features a higher foaming 
rate, a finer internal cellular structure, a reduced weight, a soft 
feeling or handle, and improved gas permeability and water absorption 
characteristics. Therefore, improved grades of synthetic leather, carpet 
backing, etc. can be easily produced by mere application of the aqueous 
emulsion of this invention to a flexible substrate followed by heating. 
Moreover, the method is by far simpler and more economical than the 
conventional production methods. Furthermore, when the aqueous emulsion of 
polyurethane-forming composition according to this invention is applied in 
the print dyeing of paper, textile fabrics, etc., improved 
three-dimensional prints can be accomplished. Thus, three-dimensional 
patterns can be reproduced on wall paper, T shirts, bags, etc. 
To obtain such three-dimensional prints, it is common practice to 
incorporate a foaming agent in a polyvinyl chloride resin and, after a 
foaming reaction, imprint the desired pattern under the pressure of a 
patterned roll. However, since the method produces a three-dimensional 
pattern by pressing a previously foamed layer, the cells are partially 
collapsed to leave only a reduced thickness and detract from the soft 
feeling which is a desired quality in any foam. 
By using a polyurethane emulsion instead of the polyvinyl chloride resin 
which is inherently less soft, this invention overcomes the 
above-mentioned disadvantages. The aqueous emulsion of 
polyurethane-foaming composition according to this invention is 
mechanically foamed, applied directly to a flexible substrate such as 
paper or cloth by means of a printing roll or a gravure-printing roll to 
reproduce a desired pattern thereon, and only then, the coating is foamed. 
It is, therefore, evident that the invention provides a soft product 
having a three-dimensional pattern that has never been obtainable by the 
prior art process. Furthermore, the aqueous emulsion of 
polyurethane-forming composition according to this invention is useful in 
such industrial applications as industrial adsorbents, filters, etc. 
The following examples are intended to illustrate this invention in further 
detail. In these examples, all parts and percents are by weight.

EXAMPLE 1 
(1) Production of an aqueous emulsion containing a polyurethane-forming 
composition 
______________________________________ 
Polyurethane-forming 
Impranil DLN 70 parts 
composition: (nonvolatile 40%, 
Bayer A.G.) 
Impranil DLH 10 parts 
(nonvolatile 45%, 
Bayer A.G.) 
Fluorocarbon: C.sub.2 Cl.sub.3 C.sub.3 
0.5 part 
Others: Elastron C-9 5 parts 
(aqueous polyurethane 
solution, Dai-ichi 
Kogyo Seiyaku Co., Ltd.) 
Boncoat 3750 3 parts 
(aqueous polyacrylic 
resin emulsion, 
Dainippon Ink & 
Chemicals, Inc. 
Sodium monohydrogen 
0.2 part 
phosphate 
Aluminum dust 40 parts 
Isopropyl alcohol 2 parts 
______________________________________ 
(2) Production of an open-cell foam in synthetic leather and its properties 
The above aqueous emulsion was stirred well to be well foamable and, then, 
mechanically foamed to a foaming rate of 3.5 times with a household 
electric mixer. The partially foamed composition was applied in a 
thickness of 0.3 mm to a polyurethane-pretreated polyester nonwoven 
fabric. The coating was then dried by heating at 120.degree. C. for 20 
minutes to give a synthetic leather having an open-cell coating. 
The foam had a satisfactory open-cell structure ensuring a high 
air-permeability and an excellent feeling. 
EXAMPLE 2 
(1) Production of an aqueous emulsion containing a polyurethane-forming 
composition 
An aqueous emulsion containing a polyurethane-forming composition was 
prepared according to the following formula. A control aqueous emulsion 
was also prepared using the same formula except for the omission of the 
fluorocarbon compound. 
______________________________________ 
Polyurethane-forming 
Impranil DLN 100 parts 
composition: (nonvolatile 40%, 
Bayer A.G.) 
Fluorocarbon: C.sub.2 Cl.sub.3 F.sub.3 
8 parts 
Ionic surfactant: 
Ammonium lauryl 1 part 
sulfate 
Others: Sumitex Resin M-3 
4 parts 
(Water-soluble 
melamine resin, 
Sumitomo Chemical 
Co., Ltd.) 
Sumitex Accelerator 
0.5 part 
ACX (Catalyst, 
Sumitomo Chemical 
Co., Ltd.) 
Boncoat 3750 4 parts 
(Aqueous polyacrylic 
resin emulsion, 
Dainippon Ink & 
Chemicals, Inc.) 
Water 30 parts 
______________________________________ 
(2) Production and properties of an open-cell foam 
The above aqueous emulsion containing a poly-urethane forming composition 
was stirred well to be foamable and, then, mechanically foamed to 3.5 
times by means of a household electric mixer. The emulsion was applied in 
a thickness of 0.5 mm to a sheet of mold-release paper. The coating was 
then heated at 115.degree. C. for 5 minutes to give an open-cell foam. The 
control emulsion was treated similarly to give a foam. The properties of 
these foams are shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
(Note 1) 
Water 
(Note 2) 
Specific 
Condition of absorp- 
Permeability 
Thickness gravity 
foam Feeling 
tion to air 
__________________________________________________________________________ 
This 3.2 m/m 
0.042 
Open-cell, 
Chamois-like, 
o 7,400 ml/cm.sup.2 min 
inven- fine cellular 
soft and 
tion structure 
flexible 
Control 
0.42 m/m 
0.162 
Smooth sur- 
Resilient 
x 4,500 ml/cm.sup.2 min 
face with 
and slimy 
coarse 
underlying 
structure 
__________________________________________________________________________ 
Note 1 
Water absorbency The absorption of water is measured by dripping 0.1 ml 
of inkcolored water on the opencell foam. o: waterabsorbent; x: not 
waterabsorbent. 
Note 2 
Air permeability An N.sub.2 gas bomb, a pressurereducing valve, a 
threeway cock, a sample mount, and a watercontaining flask are assembled 
in that sequency using a pressureresistant rubber tubing. The flask is 
open to the atmosphere. After the flow of N.sub.2 gas is accurately set t 
10 l/cm.sup.2 /min. with the pressurereducing valve, the threeway cock is 
communicated with the sample mount and the volume of water emerging in a 
period of 20 sec. is measured. The volume of permeating air per cm.sup.2 
of the specimen is calculated. 
EXAMPLE 3 
______________________________________ 
Polyurethane-forming 
Aizelack S-2020 
70 parts 
composition: (nonvolatile 40%, 
Hodogaya Chemical 
Co., Ltd.) 
Fluorocarbon: C.sub.2 Br.sub.2 F.sub.4 
10 parts 
Ionic surfactant: 
Sodium lauroyl 1 part 
sarcosinate 
Others: Sumitex Resin M-3 
4 parts 
(water-soluble 
melamine resin, 
Sumitomo Chemical 
Co., Ltd.) 
Sumitex Accelerator 
0.5 part 
ACX (catalyst, 
Sumitomo Chemical 
Co., Ltd.) 
Aluminum oxide 40 parts 
Isopropyl alcohol 
3 parts 
Water 5 parts 
______________________________________ 
The foamable aqueous emulsion of a polyurethaneforming composition 
according to the above formula was mechanically foamed to a foaming rate 
of 3.0 times by means of a household electric mixer and coated in a 
thickness of 2 mm on a sheet of nonflammable wall paper. The coating was 
dried by heating at 120.degree. C. for 10 minutes to give a wall paper 
having an open-cell foam backing. The foam had a fine open-cell structure, 
a thickness of 4.8 mm, a foaming rate of about 7 times, and a specific 
gravity of 0.13. 
The wall paper backed by the above open-cell foam was lightweight, 
nonflammable and excellent in sound- and heat-insulation properties. 
EXAMPLE 4 
______________________________________ 
Polyurethane-forming 
Aizelack S-4040N 
100 parts 
composition: (nonvolatile 45%, 
Hodogaya Chemical 
Co., Ltd.) 
Fluorocarbon: C.sub.2 Cl.sub.3 F.sub.3 
5 parts 
Ionic surfactant: 
Ammonium stearate 
5 parts 
(20% solution) 
Others: Sumitex Resin M-3 
6 parts 
(water-soluble 
melamine resin, 
Sumitomo Chemical 
Co., Ltd.) 
Sumitex Accelerator 
0.7 part 
ACX (catalyst, 
Sumitomo Chemical 
Co., Ltd.) 
Boncoat 3750 4 parts 
(Aqueous polyacrylic 
resin emulsion, 
Dainippon Ink & 
Chemicals, Inc.) 
Ultramarine 10 parts 
Water 5 parts 
______________________________________ 
The foamable aqueous emulsion of polyurethane-forming composition according 
to the above formula was mechanically foamed to a foaming rate of 3.0 
times by means of a household electric mixer and applied to a knitted 
polyester coton fabric by the rotary screen printing technique. The fabric 
was dried at 120.degree. C. for 7 minutes to give a knitted fabric having 
a three-dimensional patterns. 
This product had a deep relief pattern, a soft feeling and a high degree of 
flexibility. 
The shirt made from the fabric had excellent laundering resistance, an 
attractive appearance and, therefore, an excellent marketablity. 
EXAMPLE 5 
______________________________________ 
Polyurethane-forming 
Impranil DLN 100 parts 
composition: (nonvolatile 40%, 
Bayer A.G.) 
Fluorocarbon: C.sub.2 Cl.sub.3 F.sub.3 
5 parts 
Ionic surfactant: 
Sodium lauryl 1 part 
sulfate 
C.sub.8 F.sub.17 SO.sub.3 Na 
0.2 part 
Others: Sumitex Resin M-3 
7 parts 
(water-soluble 
melamine resin, 
Sumitomo Chemical 
Co., Ltd.) 
Sumitex Accelerator 
1 part 
ACX (catalyst, 
Sumitomo Chemical 
Co., Ltd.) 
Ultramarine 3 parts 
Calcium carbonate 
20 parts 
Water 10 parts 
______________________________________ 
The foamable aqueous emulsion containing a polyurethane-forming composition 
in accordance with the above formula was mechanically foamed to a foaming 
rate of 5.0 times by means of a household electric mixer and coated on the 
reverse side of a nylon-tufted fabric, the thickness of the coating being 
adjusted to 2 mm with a doctor knife. The coating was then dried by 
heating at 120.degree. C. for 10 minutes to give a finished carpet. The 
backing of the carpet was a lightweight, soft, air-permeable open-cell 
structure having a thickness of 4.5 mm and a specific gravity of 0.06. 
This carpet fitted intimately to the installation surface, would not slip, 
and had high resilient recovery and cushioning properties.