Process for producing antibacterial flexible polyurethane foam

The present invention provides a process for producing an antibacterial flexible polyurethane foam containing an antibacterial agent dispersed therein from a foaming mixture composed of polyols, organic isocyanates, catalysts, and blowing agents. The process is characterized in that the antibacterial agent is added to the foaming mixture and the catalyst is an organic amine which is used alone or in combination with a tin compound. In the latter case, the tin compound is a tetravalent tin compound or a divalent tin compound which is used in an amount less than 1 part by weight for 1 part by weight of the antibacterial agent. The antibacterial flexible polyurethane foam retains the antibacterial action for a long time and is safe because it contains an inorganic antibacterial agent dispersed therein which does not yield resistant bacteria.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a process for producing a flexible 
polyurethane foam having an antibacterial property. 
2. Description of the Prior Art 
Heretofore, flexible polyurethane foams have found a variety of uses 
including uses in kitchen cleaners, body sponges, puffs, filter elements, 
and mattresses. These polyurethane foams, are often required to have an 
antibacterial property. A possible way to impart an antibacterial property 
to flexible polyurethane foams is to impregnate the foam with an 
antibacterial agent by utilizing the open-cell structure characteristic of 
flexible polyurethane foam. The antibacterial foam prepared in this manner 
does not retain the antibacterial action for a long period of time because 
the antibacterial agent will soon escape from the open cells. Thus, there 
has been a demand for antibacterial flexible polyurethane foam which 
maintains its antibacterial effect for a long period of time. 
The present invention was completed to meet such a demand. 
SUMMARY OF THE INVENTION 
Therefore, it is an object of the present invention to provide a process 
for producing an antibacterial flexible polyurethane foam which stably 
retains a good antibacterial effect for a long period of time. 
To achieve the above-mentioned object, the present inventors carried out a 
series of research which led to the finding that it is possible to produce 
a flexible polyurethane foam containing an antibacterial agent integrally 
dispersed therein, exerting an outstanding antibacterial effect, and 
maintaining the antibacterial effect for a long time, from a foaming 
mixture composed of polyol, organic isocyanate, catalyst, and blowing 
agent, if the foaming mixture is incorporated with an inorganic 
antibacterial agent, especially powdery metal ion (such as silver ion, 
copper ion, and zinc ion), antibacterial agent, preferably one in which 
the metal ion is supported on zeolite. 
According to the present invention, an inorganic antibacterial agent is 
used because organic antibacterial agents are deactivated during the 
foaming process or leached out gradually during use. In addition, organic 
antibacterial agents are liable to yield resistant bacteria. 
An inorganic antibacterial agent, especially a metal ion antibacterial 
agent supported on zeolite, imparts a good antibacterial action to 
flexible polyurethane foam even when it is added to the foaming mixture 
and subjected to the foaming reaction. The thus obtained flexible 
polyurethane foam has a good antibacterial action which lasts for a long 
time. In addition, it is safe and it does not yield resistant bacteria. 
Therefore, it is suitable for use as a kitchen cleaner, body sponge, puff, 
filter element, and mattress. 
Usually, the production of flexible polyurethane foam is catalyzed by an 
organic amine and a divalent tin compound in combination. This practice, 
however, is not adequate in the present invention. The results of the 
present inventors' investigation indicate that a divalent tin compound 
used in an ordinary catalytic amount easily deactivates the metal ion 
antibacterial agent added to the foaming raw material. For the 
antibacterial agent to produce its effect, it is necessary that an organic 
amine should be used alone as the catalyst or a tetravalent tin compound 
or a small amount of a divalent tin compound should be used in combination 
with an organic amine catalyst. The amount of a divalent tin compound 
should be less than 1 part by weight for 1 part by weight of the 
antibacterial agent. 
Accordingly, the present invention provides a process for producing an 
antibacterial flexible polyurethane foam containing an antibacterial agent 
dispersed therein from a foaming mixture composed of polyol, organic 
isocyanate, catalyst, and blowing agent. The process is characterized in 
that the antibacterial agent is added to the foaming mixture and the 
catalyst is an organic amine which is used along or in combination with a 
tin compound. In the latter case, the tin compound is a tetravalent tin 
compound, or a divalent tin compound which is used in an amount less than 
1 part by weight for 1 part by weight of the antibacterial agent. 
The above and other objects, features and advantages of the present 
invention will be more apparent from the following description. 
DETAILED DESCRIPTION OF THE INVENTION 
The polyols, organic isocyanates, and blowing agents that can be used in 
the present invention are not specifically limited; but they can be 
selected from those which are commonly used for the production of flexible 
polyurethane foam. In addition, they can be used according to the ordinary 
formulation. These raw materials may be incorporated with other components 
which are commonly used for the production of flexible polyurethane foam. 
More specifically either polyether polyol or polyester polyol can be used 
as a polyol in the present invention. Examples of polyether polyols 
include adducts of polyhydric alcohols (such as ethylene glycol, propylene 
glycol, glycerin, trimethylolpropane, pentaerythritol and sucrose) with 
alkylene oxide (such as ethylen oxide, propylene oxide and butylene 
oxide); adducts of amines (such as diethanolamine, triethanolamine, and 
ethylenediamine) with alkylene oxide (such as ethylen oxide, propylene 
oxide and butylene oxide); and graft-type polymer polyol derived from 
styrene of acrylonitrile. Examples of polyester polyols include 
hydroxyl-terminated polyester polyol and polycaprolactone. The former is 
produced by polymerizing an aliphatic carboxylic acid (such as malonic 
acid, succinic acid, and adipic acid) or an aromatic carboxylic acid (such 
as phthalic acid and terephthalic acid) or a mixture thereof with an 
aliphatic glycol (such as ethylene glycol, propylene glycol and diethylene 
glycol) or a triol (such as trimethylolpropane and glycerin). The latter 
is obtained by the ring opening polymerization of lactone. 
The polyol should preferably have a molecular weight of 600 to 6000, more 
preferably 1000 to 5000. 
The organic isocyanate that can be used in the present invention is an 
organic compound containing two or more isocyanate groups in the one 
molecule. It includes aliphatic isocyanates, aromatic isocyanates, 
polyisocyanate monomer, mixtures thereof, and modified products thereof. 
Examples of aliphatic isocyanates include hexamethylene diisocyanate, 
isophore one diisosyanate, and methylcyclohexane diisocyanate. Examples of 
aromatic isocyanates include tolylene diisocyanate, (2,4- and/or 
2,6-isomers), diphenylmethane diisocyanate, and bitolylene diisocyanate. 
The organic isocyanate should preferably be used in an amount of 15 to 70 
parts by weight for 100 parts by weight of the polyol. 
The blowing agent that can be used in the present invention is water which 
reacts with the organic isocyanate to form carbon dioxide gas. If 
necessary, it can be used in combination with a low-boiling organic 
compound (such a halogenated hydrocarbon including 
trichloromonofluoromethane and methylene chloride) or a gas (such as air 
and carbon dioxide). 
The formulation for the flexible polyurethane foam may contain flame 
retardant (e.g., halogenated phosphate ester), antioxidant, plasticizer, 
filler, and coloring agent, in an amount not harmful to the effect of the 
present invention. 
The process of the present invention is catalyzed by an organic amine or 
tin catalyst. The organic amine is used alone or in combination with a tin 
catalyst. The tin catalyst is a tetravalent tin compound or a divalent tin 
compound. Incidentally, the organic amine should preferably be used in an 
amount of 0.1 to 10 parts by weight for 100 parts by weight of polyol. The 
tetravalent tin compound should preferably be used in an amount of 0.1 to 
2 parts, more preferably 0.1 to 1 parts, by weight for 100 parts by weight 
of polyol. The divalent tin compound, should be used in an amount less 
than 1 part, more preferably less than 0.7 parts, by weight for 1 part by 
weight of the antibacterial agent. 
Examples of the organic amine that can be used in the present invention 
include triethylenediamine, N-methylmorpholine, N-ethyl-morpholine, 
tetramethyl-1,4-butanediamine, dimethylethanolamine, diethylethanolamine, 
triethylamine, dimethylbenzylamine, triethanol-amine, 
1,8-diazacyclo(5.4.0)undecene-7, bis(2-dimethylaminoethyl)ether, 
trimethylaminoethyl piperagine, methylhydroxyethyl piperazin, 
N,N,N',N'-tetramethylhexamethylenediamine, 
N,N,N',N'-tetramethylpropylenediamine, 
N,N,N',N',N"-pentamethyldiethylenetriamine, 
N-trioxyethylene-N,N-dimethylamine, and N,N,N'-trimethylaminoethyl 
ethanolamine. Examples of the tetravalent tin compound include dibutyltin 
dilaurate and dibutyltin diacetate. Examples of the divalent tin compound 
include stannous octoate and stannous oleate. 
According to the present invention, the foaming mixture is incorporated 
with an antibacterial agent. A preferred antibacterial agent is an 
inorganic one, especially a metal ion (such as silver ion, copper ion, and 
zinc ion) antibacterial agent. The more desirable antibacterial agent is a 
metal ion (such as silver ion, copper ion, and zinc ion) antibacterial 
agent supported on zeolite. More detailedly, the most preferable 
antibacterial agent is one obtained by mixing a natural or synthetic 
zeolite with a solution containing at least one kind of ions selected from 
the group consisting of silver ions, copper ions and zinc ions which may 
be prepared by dissolving at least one water-soluble salt selected from 
the group consisting of silver salts (e.g., silver nitrate, etc.), copper 
salts (e.g., copper nitrate, etc.) and zinc salts (e.g., zinc chloride, 
zinc nitrate, etc.), and ion exchanging a part or all of ion-exchangable 
metal ions contained in zeolite to at least one kind of ions selected from 
the group consisting of silver ions, copper ions and zinc ions. In the 
zeolite antibacterial agent, silver content should preferably be 0.0006 to 
4% by weight, copper content should preferably be 0.03 to 10% by weight 
and zinc content should preferably be 0.04 to 14% by weight of the total 
weight of the agent. An example of such antibacterial agents is disclosed 
in Japanese Patent Laid-open No. 181002/1985. A commercial product is 
available under the trade name of Zeomic.RTM. from Cinnanen New Ceramics 
Co., Ltd. It is also possible to use an antibacterial agent in which the 
above-mentioned metal ion is supported on activated carbon. 
The inorganic antibacterial agent should preferably be used in the form of 
powder having an average particle diameter of 0.1 to 1 .mu.m. The 
inorganic antibacterial agent may be used in a proper amount according to 
the intended application of flexible polyurethane foam. A preferred amount 
should be more tha 0.1 parts by weight, more preferably 0.1 to 3 parts by 
weight for 100 parts by weight of polyol. 
The foaming mixture incorporated with the avobe-mentioned antibacterial 
agent can be made into an antibacterial flexible polyurethane foam by 
either a one-shot process or a prepolymer process under ordinary foaming 
conditions. In the one-shot process, a polyol, isocyanate, water, amine 
catalyst, tin catalyst, antibacterial agent and, if necessary, an 
auxiliary agent are independently introduced into a mixing room. Then the 
components are mixed and the mixture is provided on a conveyor belt and 
allowed to foam. In the prepolymer process, a prepolymer having an 
isocyanate terminating group is prepared by reacting a polyol with an 
excess of a isocyanate, and the thus prepared prepolymer is used as an 
isocyanate in the one-shot process. 
The flexible polyurethane foam produced according to the process of the 
present invention may be used in various application areas such as a 
kitchen cleaner, body sponge, puff, filter element, and mattress. These 
are exemplary only and the application areas are not limited to them. 
As mentioned above, the process of the present invention permits the 
production of an antibacterial flexible polyurethane foam which stably 
retains high antibacterial action for a long time. The antibacterial 
flexible polyurethane foam is safe because it contains an inorganic 
antibacterial agent dispersed therein which does not yield resistant 
bacteria. 
The invention will be explained in more detail with reference to the 
following examples and comparative examples, which are not intended to 
limit the scope of the invention. In the examples, "parts" means "parts by 
weight".

EXAMPLES 1 AND COMATIVE EXAMPLES 1 
Flexible polyurethane foams were prepared in the usual way according to the 
formulations shown in Table 1. The polyol, TDI the mixture of 
triethylenediamine and water, L-6202, tin catalyst, 
trichloromonofruolomethane, and antibacterial agent were introduced into 
the mixing room at predetermined flow rates where the flow rate of polyol 
is 50 kg/m.sup.3. Then, the components were mixed at a high agitation 
speed of 4500 rpm and the mixture was provided on a conveyor belt having a 
width of 2100 mm and continuously moving in one direction to prepare a 
polyurethane foam. The foaming mixture contains Zeomic.RTM. AZl0N which is 
an antibacterial agent available frrom Cinnanen New Ceramics Co., Ltd. The 
foam mixture contains 3.65% by weight of Ag and 6.35% by weight of Zn 
supported on zeolite. The resulting polyurethane foams were tested for 
antibacterial action in the following manner. The results are shown in 
Table 1. 
Method For Testing the Antibacterial Action 
40 ml of sterile physiological saline placed in a 300-ml Erlenmeyer flask 
is inoculated with Escherichia coli (about 100,000 per ml). The number of 
the bacteria is counted at certain time intervals while the medium is 
shaken at 20.degree. C. The values in Table 1 indicate the number of the 
bacteria in 1 ml of the medium. The medium contains small foam pieces 
(about 5 mm cube) cut from a specimen measuring 2.times.2.times.5 cm. 
TABLE 1 
______________________________________ 
Example Comparative 
Formulation (parts) 
1 2 Example 1 
______________________________________ 
Triol (MW = 3000) (*1) 
100 100 100 
TDI (*2) 64.6 64.1 65.1 
Water 4.9 5.3 5.3 
Triethylenediamine 
0.36 0.46 0.46 
Stannous octoate 0.07 -- 0.46 
(divalent tin catalyst) 
Dibutyltin dilaurate 
-- 0.2 -- 
(tetravalent tin catalyst) 
L-6202 (*3) 1.7 1.7 1.7 
Trichloromonofluoromethane 
3.0 10.0 10.0 
Zeomic AZ10N 0.3 0.3 0.3 
Antibacterial test 
0 hour (initial) 110,000 68,000 100,000 
24 hours 19,000 150 19,000,000 
48 hours 0 0 42,000,000 
Antibacterial action 
yes yes none 
______________________________________ 
Notes to Table 1 
(*1) Polyol prepared by addition polymerization of glycerin with propylen 
oxide and ehtylene oxide 
(*2) Tolylene diisocyanate (Ratio of 2,4/2,6-isomers = 80/20) 
(*3) Dimethylpolysiloxanepolyoxyethylene-polyoxy-propylene copolymer (a 
product of Nippon Unicar Co., Ltd.) 
EXAMPLE 3 AND COMATIVE EXAMPLE 2 
Flexible polyurethane foams were prepared in the same way as Example 1 
according to the formulations shown in Table 2 except that the flow rate 
of polyol is 40 kg/m.sup.3, and the width of conveyor belt is 1100 mm. The 
foaming mixture contains the same antibacterial agent as used in Examples 
1 and 2. The resulting polyurethane foams were tested for antibacterial 
action in the same manner as in Examples 1 and 2. In this example, the 
antibacterial action was tested for not only Escherichia coli but also 
Staphylococcus and Psudomonas aeruginosa. The results are shown in Table 
2. 
TABLE 2 
______________________________________ 
Comparative 
Formulation (parts) 
Example 3 Example 2 
______________________________________ 
Polyester polyol (*3) 
100 100 
TDI (*1) 47.2 47.2 
Water 3.8 3.8 
AX-31 (*4) 1.0 1.0 
Fomres 7786 (*5) 1.0 1.0 
PRX-607 (*6) 0.5 0.5 
N-ethylmorpholine 
2.4 2.4 
Zeomix AZ10N 0.25 -- 
Antibacterial test 
Escherichia coli 
0 hour (initial) 100,000 110,000 
24 hours 240 4,600,000 
48 hours 0 18,000,000 
Staphylococcus 
0 hour (initial) 61,000 90,000 
24 hours 1,000 60,000 
48 hours 0 420,000 
Psudomonas aeruginosa 
0 hour (initial) 120,000 60,000 
24 hours 0 120,000 
48 hours 0 230,000 
______________________________________ 
Notes to Table 2 
(*3) Polycondensate of adipic acid with diethylene glycol and 
trimethylolpropane. OH number = 51 (KOH mg/g) (a product of Nippon 
Polyurethane Co., Ltd.) 
(*4) Anionic surface active agent (a product of Sanyo Kasei Co., Ltd.) 
(*5) Nonionic surface active agent (a product of Witco Chemical) 
(*6) Silicone surface active agent (a product of Toray Silicone Co., Ltd. 
 
Preparation Example of the Antibacterial Agent 
0.91 kg of dry A-type zeolite powder (1.03 Na.sub.2 O.Al.sub.2 O.sub.3.1.91 
SiO.sub.2.zH.sub.2 O) are mixed with an aqueous solution containing 0.11 
mol AgNO.sub.3 and 0.98 mol Zn(NO.sub.3).sub.2 to obtain about 3.2 l of 
slurry having a pH of 4.1 and the slurry is maintained at about 25.degree. 
C. for 6 hours under agitation. After the completion of the ion exchange, 
the zeolite is recovered by filtration and washed with water. Then, the 
silver and zinc ions-changed zeolite is dried under vacuum, pulverized and 
classified. The thus obtained zeolite has an average particle size of 1.1 
.mu.m and a specific surface area of 718 m.sup.2 /g, and contains 1.48% 
by weight of Ag and 6.82% by weight of Zn.