JP7123483B2 - Polyurethane foam, pad, method for producing polyurethane foam, and method for producing pad - Google Patents

Description

TECHNICAL FIELD The present disclosure relates to polyurethane foams, pads made from the polyurethane foams, and methods for making them.

BACKGROUND ART Conventionally, there is known a method of producing polyurethane foam by reacting raw materials containing a polyol, a polyisocyanate and a foaming agent in the presence of a tin catalyst (see, for example, Patent Document 1). Moreover, hot press molding of flexible polyurethane foams with a thermoforming mold is generally performed. Heat press molding also causes a problem of yellowing of flexible polyurethane foam due to heat (see, for example, Patent Document 2).

Japanese Patent No. 4123421 (paragraph [0007]) Japanese Patent No. 4540545 (paragraph [0005])

Among the conventional polyurethane foams described above, those that are resistant to discoloration due to NOx are desired.

A first aspect of the invention made to solve the above problems is a polyurethane foam obtained by reacting raw materials containing a polyol, a polyisocyanate, and a blowing agent in the presence of a catalyst, wherein the catalyst contains an amine catalyst and a bismuth catalyst containing 40 to 50% by weight of free acid, and the amount of the bismuth catalyst is 0.05 to 0.3 parts by weight based on 100 parts by weight of the polyol; A polyurethane foam in which the ratio of the bismuth catalyst to the total catalyst is 5 to 34% by weight.

A second aspect of the invention is the polyurethane of the first aspect , wherein the amount of amine catalyst is 0.6 to 1.2 parts by weight relative to 100 parts by weight of the polyol, and the polyisocyanate is toluene diisocyanate. is a form.

A third aspect of the invention is the polyurethane foam of the first or second aspect , comprising an antioxidant.

A fourth aspect of the invention is that the change in yellow index, ΔYI, upon exposure to 200 ppm NOx for 2 hours is less than 10 and after hot pressing at 180° C. for 180 seconds followed by exposure to 200 ppm NOx for 2 hours. The polyurethane foam according to any one of the first to third aspects , wherein ΔYI, which is the change in yellow index when the time is applied, is less than 38.

A fifth aspect of the invention is the polyurethane foam according to any one of the first to fourth aspects , wherein the blowing agent is water.

A sixth aspect of the invention is the polyurethane foam according to any one of the first to fifth aspects , which has a pH value of 8.7 or less.

A seventh aspect of the invention is a pad for clothing or body wear, comprising the polyurethane foam according to the sixth aspect .

An eighth aspect of the invention is a method for producing a polyurethane foam by reacting raw materials containing a polyol, a polyisocyanate, and a blowing agent in the presence of a catalyst, wherein the catalyst comprises an amine catalyst and 40 free acids. 0.05 to 0.3 parts by weight of the bismuth catalyst is used with respect to 100 parts by weight of the polyol, and the ratio of the bismuth catalyst to the total catalyst is 5 to 34 parts by weight. %, a method for producing a polyurethane foam.

A ninth aspect of the invention is the polyurethane according to the eighth aspect , wherein the amount of the amine catalyst is 0.6 to 1.2 parts by weight with respect to 100 parts by weight of the polyol, and toluene diisocyanate is used as the polyisocyanate. A method of manufacturing a foam.

A tenth aspect of the invention is the method for producing a polyurethane foam according to the eighth aspect or the ninth aspect , wherein the raw material contains an antioxidant.

An eleventh aspect of the invention is the method for producing a polyurethane foam according to any one of the eighth to tenth aspects , wherein water is used as the foaming agent.

According to a twelfth aspect of the invention, the polyurethane foam produced by the production method according to any one of the eighth to eleventh aspects is provided with an uneven shape by hot pressing for clothing or body wear. A pad manufacturing method.

In the first aspect and the eighth aspect of the invention, a bismuth catalyst is used as a catalyst for reacting the raw materials of the polyurethane foam, and a tin catalyst is not used. It is possible to make the polyurethane foam less susceptible to NOx discoloration than when it is used. Moreover, according to the present invention, the free acid of the bismuth catalyst can prevent the polyurethane foam from becoming too alkaline, and the amine catalyst can prevent the polyurethane foam from becoming too acidic.

Toluene diisocyanate can be used as the polyisocyanate contained in the raw material of the polyurethane foam as in the second aspect of the invention , thereby obtaining a polyurethane foam with high industrial utility and excellent texture and elasticity. can be done.

According to the third aspect and the tenth aspect of the invention, the polyurethane foam can be made difficult to oxidize, leading to prevention of yellowing.

According to the fourth aspect of the invention, yellowing due to NOx becomes difficult, and yellowing after heating and compression can be reduced.

In the fifth aspect and the eleventh aspect of the invention, the foaming agent is water. According to the present invention, since flon is not used as a foaming agent, it is possible to produce a polyurethane foam that is excellent in the global environment. Moreover, by using a foaming agent that is harmless to the human body, the polyurethane foam can be suitably used for articles such as clothing that come into contact with the human body.

In the sixth aspect of the invention, since the pH value is 8.7 or less, it becomes possible to suitably use the polyurethane foam for applications such as clothing that come into contact with the body. For example, this polyurethane foam is suitably used for clothing and pads for wearing on the body ( seventh aspect of the invention ).

In the twelfth aspect of the invention, since the polyurethane foam is provided with an uneven shape by heat pressing, it is easy to form a pad for clothing or a body attachment in a shape that matches the shape of the body.

1 is a side cross-sectional view of a pad made of polyurethane foam according to an embodiment of the present disclosure; FIG. Table showing experimental examples of polyurethane foam

FIG. 1 shows a pad 10 according to one embodiment of the present disclosure. The pad 10 of this embodiment is made of polyurethane foam 11, and is used as a clothing pad that contacts the human body 90, such as a shoulder pad or underwear pad. In the present embodiment, the pad 10 is formed by heat-press molding a sheet-like polyurethane foam 11, and has, for example, a concave and convex shape in which the contact surface 12 in contact with the human body 90 is concave. It should be noted that contacting the human body 90 also includes the case where the pad 10 is wrapped in a woven, knitted, or non-woven fabric bag made of fibers and indirectly contacts the human body 90 via the fibers.

The polyurethane foam 11 of the present embodiment is obtained by reacting raw materials containing a polyol, a polyisocyanate, and a foaming agent in the presence of a catalyst.

Polyether polyols and polyester polyols can be used as polyols. Since polyester polyols hydrolyze, polyether polyols are preferable from the viewpoint of suppressing deterioration over time. Examples of polyether polyols include those obtained by adding an alkylene oxide such as ethylene oxide and propylene oxide to an active hydrogen-containing compound such as ethylene glycol, propylene glycol, glycerin and trimethylolpropane as a starting material. Polyester polyols include condensation polyester polyols obtained by reacting polycarboxylic acid with polyols such as ethylene glycol and glycerin, lactone polyester polyols, and polycarbonate polyols.

Polyisocyanates include aromatic isocyanates such as toluene diisocyanate, diphenylmethane diisocyanate, naphthalene diisocyanate, p-phenylene diisocyanate and xylene diisocyanate; alicyclic isocyanates such as isophorone diisocyanate and cyclohexyl diisocyanate; group isocyanates, and the like. Aromatic isocyanates are preferred from the viewpoint of raw material cost and water resistance, and toluene diisocyanate (eg, 2,4-toluene diisocyanate and 2,6-toluene diisocyanate) is particularly preferred from the viewpoint of texture and elasticity.

Examples of foaming agents include water. By using a foaming agent that is harmless to the human body, the polyurethane foam can be suitably used for articles such as clothing that come into contact with the human body. In addition, by not using flon as a foaming agent, it is possible to manufacture the polyurethane foam 11 that is environmentally friendly. Hydrocarbons such as cyclopentane and isopentane can also be used as the foaming agent.

As catalysts, metal catalysts and amine catalysts are used. In this embodiment, a bismuth catalyst is used as the metal catalyst. The amount of the bismuth catalyst is 0.05 to 0.30 parts by weight, more preferably 0.05 to 0.25 parts by weight, with respect to 100 parts by weight of the polyol that is the raw material of the polyurethane foam 11 . The bismuth catalyst accounts for 5 to 34% by weight, more preferably 5 to 26% by weight, of the total catalyst used for reacting the raw materials of the polyurethane foam 11 . If the bismuth catalyst content is less than 5% by weight, the polyurethane foam 11 will have a high pH value. Also, the free acid contained in the bismuth catalyst is 40 to 50% by weight. If the free acid of the bismuth catalyst is less than 40% by weight, the polyurethane foam 11 will have a high pH value. When the free acid content of the bismuth catalyst exceeds 50%, it becomes difficult to mold the polyurethane foam 11 .

Examples of bismuth catalysts include bismuth carboxylate, bismuth neodecanoate, bismuth sulfonate, bismuth octoate, and bismuth 2-ethylhexanoate.

The amine catalyst may be used together with the bismuth catalyst, and the amount of the amine catalyst is preferably more than 0.5 parts by weight and 1.2 parts by weight or less with respect to 100 parts by weight of the polyol. It is more preferably 0.6 to 1.0 parts by weight. Examples of amine catalysts include non-reactive monoamines such as dimethylcyclohexylamine, N-methyldicyclohexylamine, triethylamine, tripropylamine, tributylamine, N-methylmorpholine, N-ethylmorpholine and N-dimethylbenzylamine; triethylenediamine, tetramethylhexamethylenediamine, bisdimethylaminoethyl ether, tetramethylpropanediamine, dimethylaminoethylmorpholine, tetramethylethylenediamine, diazobicycloundecene, 2-methyl-1,4-diazo(2,2,2 ) non-reactive diamines such as bicyclooctane, non-reactive triamines such as pentamethyldiethylenetriamine and pentamethyldipropylenetriamine, dimethylethanolamine, N-trioxyethylene-N,N-dimethylamine, N,N-dimethyl-N - Reactive amines such as hexanolamine, and the like.

The polyurethane foam 11 also contains an antioxidant. The antioxidant makes it difficult for the polyurethane foam to oxidize, making it possible to prevent yellowing of the polyurethane foam. Examples of antioxidants include primary antioxidants such as amine-based antioxidants, and secondary antioxidants such as sulfur-based and phosphorus-based antioxidants. Specifically, hindered phenolic antioxidants (e.g., 4-methyl-2,6-di-tert-butylphenol (BHT), triethylene glycol-bis[3-(3-t-butyl-5-methyl -4-hydroxyphenyl) propionate], pentaerythritol tetrakis [3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate], etc.) and phosphorus antioxidants (e.g., bis(2,4 -di-t-butylphenyl) pentaerythritol diphosphite, tridecyl phosphite, tris(2-ethylhexyl) phosphite, etc.) and thiophene antioxidants (e.g., 2,5-thiophenediylbis(5-t- butyl-1,3-benzoxazole), etc.). Among such antioxidants, phosphorus-based antioxidants are preferred, and tris(tridecyl)phosphite is more preferred. As tris(tridecyl)phosphite, a commercially available product such as JP-333E manufactured by Johoku Kagaku Co., Ltd. can be used. These antioxidants can be used alone or in combination of two or more.

The polyurethane foam 11 may contain a foam stabilizer (for example, a silicone-based one) for stably forming a foam. Further, as other additives, a light stabilizer (for example, HALS), an ultraviolet absorber, and the like may be included.

Here, the polyurethane foam 11 is resistant to discoloration due to NOx. Specifically, ΔYI, which is the change in yellow index when exposed to 200 ppm NOx for 2 hours, is less than 10. Also, ΔYI, which is the change in yellow index when exposed to 200 ppm NOx for 2 hours after hot pressing at 180° C. for 180 seconds, is less than 38.

Moreover, the pH value of the polyurethane foam 11 is 8.7 or less. As a result, the polyurethane foam 11 can be suitably used for items that come into contact with the body and require weak acidity, such as pads for clothing. The pH value of the polyurethane foam 11 is preferably 4.0 or higher. As will be confirmed by experiments described later, in the polyurethane foam 11, when the content of the bismuth catalyst (that is, the content of the free acid) increases, the pH value of the polyurethane foam 11 decreases (that is, the acidity increases). , the higher the content of the amine catalyst, the higher the pH value of the polyurethane foam 11 (that is, the stronger the alkalinity).

The polyurethane foam 11 and pad 10 of this embodiment are manufactured, for example, as follows. First, a liquid A is prepared by mixing a polyol, a foaming agent, a foam stabilizer, and the like. Next, a liquid raw material obtained by mixing the A liquid and the B liquid containing the polyisocyanate is continuously discharged onto the conveyor. At this time, the catalyst used for the reaction of the raw materials is also mixed with the raw materials (for example, mixed with liquid A in advance). The raw materials react and foam on the conveyor to obtain a sheet-like polyurethane foam 11 . The sheet-shaped polyurethane foam 11 is cut into a predetermined size.

Next, the cut polyurethane foam 11 is heat-press molded in a press molding die (for example, the molding conditions are a molding temperature of 180° C. and a molding time of 180 seconds). A press molding die is composed of, for example, an upper die and a lower die, and between the upper die and the lower die, the polyurethane foam 11 is formed into a desired shape (for example, as shown in FIG. It has a cavity for molding into a concave and convex shape curved so that the contact surface 11 side becomes a concave surface. Then, the polyurethane foam 11 is shaped by being pressed by the upper mold and the lower mold, and is given an uneven shape, for example. Pad 10 is thus obtained.

In the polyurethane foam 11 of the present embodiment, a bismuth catalyst is used as a catalyst for reacting the raw materials of the polyurethane foam 11. Therefore, as will be confirmed in experiments described later, compared to the case where a tin catalyst is used, polyurethane It is possible to make the foam 11 difficult to discolor due to NOx. Further, according to the present embodiment, the free acid of the bismuth catalyst can prevent the polyurethane foam 11 from becoming too alkaline, and the amine catalyst can prevent the polyurethane foam 11 from becoming too acidic.

In this embodiment, since the polyurethane foam 11 is provided with an uneven shape by hot pressing, it is possible to easily manufacture the pad 10 for clothing or body wear in a shape that matches the shape of the body, for example. Furthermore, according to the polyurethane foam 11 of the present embodiment, it is possible to make the polyurethane foam less susceptible to NOx discoloration even after hot press molding.

[Confirmation experiment]
Pads made of polyurethane foam of Experimental Examples 1 to 8 shown in FIG. 2 were produced by the above-described production method, and moldability, discoloration against NOx, etc. were confirmed for these pads.

[Polyurethane foams of Experimental Examples 1 to 4, 7 and 8]
In Experimental Examples 1 to 4, 7, and 8 shown in FIG. 2, polyurethane foams were produced by foaming a raw material mixed with a bismuth catalyst. The compositions and compounding ratios of liquids A and B as foaming raw materials for the polyurethane foams of Experimental Examples 1 to 4, 7, and 8 are shown in FIG. 2 and shown below. In Experimental Example 8, both amine catalysts A and B were not included. In each experimental example, A liquid and B liquid were mixed so that the isocyanate index was 106. The isocyanate index is a value obtained by dividing the number of moles of isocyanate groups in polyisocyanate by the number of moles of all active hydrogen groups in polyol, blowing agent (water), etc. and multiplying the result by 100. In addition, the cream time in FIG. 2 is the time from the start of mixing liquids A and B to the start of foaming, and the rise time is the time from the start of mixing liquids A and B. , is the time until the expansion of the polyurethane foam stops due to foaming.

<Liquid A>
Polyol A; trade name "GP-3050" manufactured by Sanyo Kasei Co., Ltd.
Polyol B; trade name "PP-2000" manufactured by Sanyo Kasei Co., Ltd.
Foam stabilizer; Silicone-based foam stabilizer. Trade name "SZ-1136" manufactured by Dow Corning Toray Co., Ltd.
Foaming agent; Water Antioxidant; trade name "JP-333E" manufactured by Johoku Chemical Co., Ltd.
<Liquid B>
Polyisocyanate; trade name "Coronate T-80" manufactured by Tosoh Corporation
<Catalyst>
Amine catalyst A; trade name "Amino Alcohol 2Mabs" manufactured by Nippon Nyukazai Co., Ltd.
Amine catalyst B; trade name "33LSI" manufactured by Evonik
Bismuth catalyst; bismuth neodecanoate. Borchers trade name "Kat-315" (containing 45% by weight of free acid)

[Polyurethane foam of Experimental Example 5]
The formulation of Example 5 differs from the other Examples in that it does not contain a metal catalyst (bismuth catalyst, tin catalyst).

[Polyurethane foam of Experimental Example 6]
As described above, the formulations of Experimental Examples 1 to 4, 7 and 8 use a bismuth catalyst as the metal catalyst. On the other hand, the formulation of Experimental Example 6 differs in that it contains a tin catalyst (stannus octoate, trade name "MRH-110" manufactured by Johoku Kagaku Co., Ltd.) instead of the bismuth catalyst.

In this confirmatory experiment, the polyurethane foams of Experimental Examples 1 to 4 correspond to the polyurethane foam 11 forming the pad 10 of the above embodiment.

[Evaluation method]
<NOx discoloration>
As the discoloration property against NOx, the yellow index (YI) of the polyurethane foam before and after the test exposed to NOx gas was measured, and the change ΔYI was evaluated. Specifically, the polyurethane foam 11 was subjected to a test in which it was exposed to a NOx gas atmosphere of 200 ppm for 2 hours in a closed container, and the difference between the YI after the exposure test and the YI in the initial state before the exposure test was ΔYI. (first test). In addition, a 10 mm thick polyurethane foam test sample was hot press molded (50% compression) to a thickness of 5 mm at 180°C for 180 seconds using a hot plate of 550 mm long x 500 mm wide, and the polyurethane foam after hot press molding. 11 was subjected to a test in which it was exposed to a 200 ppm NOx gas atmosphere for 2 hours in a closed container, and the difference between the YI after the exposure test and the YI in the initial state before hot press molding was defined as ΔYI (second test). . Furthermore, as an index of NOx gas discoloration after hot pressing, relative evaluation of ΔYI of each experimental example based on ΔYI (32.6) of NOx gas discoloration after hot pressing in Experimental Example 5 that does not use a metal catalyst was also evaluated. Specifically, the rate of increase=(ΔYI of each experimental example−ΔYI of experimental example 5)/(ΔYI of experimental example 5)×100. The yellow index was measured using a color difference meter (model number: SM-T) manufactured by Suga Test Instruments Co., Ltd.

Evaluation of yellowing (discoloration) was performed as follows. ◎ Evaluation is as follows: ΔYI for the first test (exposure test without hot press molding) is less than 10, and ΔYI for the second test (exposure test after hot press molding) is less than 38, Furthermore, the increase rate of NOx gas discoloration after hot press molding was less than 10%. ○ Evaluation is that ΔYI for the first test (exposure test without hot press molding) is less than 10, and ΔYI for the second test (exposure test after hot press molding) is less than 38, Furthermore, the rate of increase in NOx gas discoloration after hot press molding was set to be 10% or more. × Evaluation is when ΔYI for the first test (exposure test without hot press molding) is 10 or more, or when ΔYI for the second test (exposure test after hot press molding) is 38 or more and

<pH value test>
Measured according to ISO3071. Specifically, 2 g of polyurethane foam was finely cut, placed in a flask with 100 mL of water, sealed, and shaken for 2 hours. The pH value of the extract was then measured with a pH meter.

When the measurement result of the pH value was 8.7 or more, it was evaluated as ◯, and when it was more than 8.7, it was evaluated as x.

<Moldability, Appearance>
Observe the appearance of the molded polyurethane foam, and if there is foaming failure (for example, cracks in the urethane foam or punctured cells), it is evaluated as x, and there is no molding failure. The case was rated as 0.

<Hardness>
Measured according to JIS K6400-55.
<Tensile strength>
Measured according to JIS K6400-56B method.
<Elongation>
Measured according to JIS K6400-55.
<Tear strength>
Measured according to JIS K6400-56B method.
<Compression strain>
Measured according to JIS K6400-4 4.5.2 A method. At this time, the polyurethane foam was compressed by 50% at 70°C.

[Evaluation results]
For each experimental example, if the measurement items listed in FIG. , and when there was an evaluation of x, the overall evaluation was x.

As shown in FIG. 2, from a comparison of Experimental Examples 1 to 4, 7 and Experimental Example 6, it was found that using a bismuth catalyst as a metal catalyst rather than a tin catalyst caused discoloration of NOx, especially NOx after heat molding. It was confirmed that the discoloration property was improved. Specifically, in the second NOx discoloration test (NOx exposure test after hot pressing), the polyurethane foams of Experimental Examples 1 to 4 containing a bismuth catalyst had a ΔYI of 38 or less. In particular, in Experimental Examples 1 to 3, the ΔYI in this second test was as good as 32 or less, and in the first test of NOx discoloration (NOx exposure test without hot press molding), ΔYI was 9. .0 or less (NOx discoloration evaluation: ⊚). On the other hand, in Experimental Example 6 using a tin catalyst, the ΔYI value in the first test was 8.1, but the ΔYI value in the second test (NOx exposure test after hot pressing) was 46.0. The rate of increase in discoloration against NOx gas after hot press molding deteriorates to 41%. Incidentally, in Experimental Example 4 in which no metal catalyst was used, the ΔYI value in the first test was 7.4 and the ΔYI value in the second test was 32.6.

Thus, in Experimental Examples 1 to 4 in which 0.05 parts or more of the bismuth catalyst was used in combination with the amine catalyst, the ΔYI value in the first test was less than 10, and the ΔYI value in the second test was less than 38. In Examples 1 to 3, the NOx gas discoloration increase rate after hot press molding is less than 10%, which is better than Experimental Example 6 using a tin catalyst. Moreover, even when the amount of bismuth catalyst is between 0.2 parts by weight in Experimental Example 3 and 0.3 parts by weight in Experimental Example 4 (for example, 0.25 parts by weight), the evaluation of yellowing is ⊚.

A comparison of Experimental Examples 3 and 4 shows that increasing the amount of bismuth catalyst while maintaining the amount of amine catalyst lowers the pH value.

In Experimental Examples 1 to 4, in which the amount of the amine catalyst was 0.6 parts by weight or more, no defective foaming occurred, and good moldability and appearance were obtained. On the other hand, in Experimental Examples 7 and 8 in which the amount of the amine catalyst was 0.5 parts by weight or less, defective foaming and poor appearance occurred. In FIG. 2, the measurement items described as unmeasurable for Experimental Examples 7 and 8 were measurement items that could not be measured due to defective foaming, and for Example 7, yellowing was evaluated using sample fragments.

From the results of Experimental Examples 1 to 8, 0.05 to 0.30 parts by weight of the bismuth catalyst and 0.6 to 1.2 parts by weight of the amine catalyst were contained with respect to 100 parts by weight of the polyol, and the entire catalyst In Experimental Examples 1 to 3, in which the ratio of the bismuth catalyst is 5 to 25% by weight, the evaluation of NOx discoloration is ◎, the evaluation of moldability and appearance is also ◯, and the pH value is 8.7 or less ( The evaluation was ◯), and the overall evaluation was ⊚.

[Other embodiments]
(1) In the above embodiment, the polyurethane foam 11 constitutes the pad 10 for clothing or body wear, but it is also used for bedding such as mattresses and pillows, cushions, chairs, sofas, vehicle seats, and the like. good too.

(2) In the above embodiment, the pad 10 has an uneven shape, but it may have a shape that does not have unevenness, such as a flat plate shape. In this case, the polyurethane foam 11 may not be subjected to hot press molding.

(3) In the above embodiment, the polyurethane foam 11 may be formed in a foam mold. In this case, a raw material obtained by mixing a liquid A containing a polyol, a foaming agent, a foam stabilizer, etc. and a liquid B containing a polyisocyanate is injected into a foam molding die. At this time, the catalyst used for the reaction of the raw materials is also mixed with the raw materials (for example, pre-mixed with liquid A) and injected into the foam molding mold. Then, the polyurethane foam 11 is foam-molded by reacting the raw materials in this foam-molding mold. At this time, the polyurethane foam 11 may be given a shape such as an uneven shape using a foaming mold.

10 pad 11 polyurethane foam

Claims (8)

A polyurethane foam obtained by reacting raw materials containing a polyol, a polyisocyanate, and a foaming agent in the presence of a catalyst,
The catalyst includes an amine catalyst and a bismuth catalyst containing 40-50% by weight of free acid;
The amount of the bismuth catalyst is 0.05 to 0.3 parts by weight with respect to 100 parts by weight of the polyol,
A polyurethane foam, wherein the proportion of said bismuth catalyst to said total catalyst is 5-34% by weight. The polyurethane foam of Claim 1, wherein the amount of amine catalyst is 0.6 to 1.2 parts by weight relative to 100 parts by weight of said polyol, and said polyisocyanate is toluene diisocyanate. 3. Polyurethane foam according to claim 1 or 2, comprising an antioxidant. ΔYI, the change in yellow index upon exposure to 200 ppm NOx for 2 hours, is less than 10;
4. The method of any one of claims 1 to 3, wherein after hot pressing at 180° C. for 180 seconds, the change in yellow index, ΔYI, upon exposure to 200 ppm NOx for 2 hours is less than 38. of polyurethane foam. 5. The method according to any one of claims 1 to 4, wherein 2 g of the polyurethane foam is finely cut, placed in a flask with 100 mL of water, sealed, and shaken for 2 hours. A polyurethane foam according to claim. A pad for clothing or body wear, comprising the polyurethane foam according to claim 5 . A method for producing a polyurethane foam by reacting raw materials containing a polyol, a polyisocyanate, and a blowing agent in the presence of a catalyst,
Using an amine catalyst and a bismuth catalyst containing 40 to 50% by weight of free acid as the catalyst,
Using 0.05 to 0.3 parts by weight of the bismuth catalyst with respect to 100 parts by weight of the polyol,
A method for producing polyurethane foam, wherein the ratio of the bismuth catalyst to the total catalyst is 5 to 34% by weight. A method for producing a pad for clothing or body wear, wherein the polyurethane foam produced by the production method according to claim 7 is provided with an uneven shape by hot pressing.

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