JP4589730B2 - Hydrophilic ester polyurethane foam - Google Patents

Description

The present invention relates to a specific ester-based polyurethane foam whose liquid absorbency and wettability are improved unexpectedly by chemical modification and subsequent felting (compression under heat and pressure). This foam can be incorporated into articles used to wipe or absorb liquids such as household cleaning sponges and mop tips.

In general, polyurethane foams are prepared by reacting an active hydrogen-containing compound (ie, a polyol) with a polyisocyanate in the presence of a blowing agent such as water, and usually a reaction catalyst and a bubble stabilizer. The porous polymer structure of the polyurethane foam has a skeleton structure with relatively heavy chains, and this skeleton forms an outline of the cell structure. The chains of the skeletal structure are connected by a very thin film forming a cell wall, often called a window. In an open cell foam, the windows of each cell are somewhat open or broken, creating an interconnected network that allows fluid (liquid or gas) to flow freely. However, conventional polyurethane foams are not porous or open cell enough to allow a large amount of fluid to pass through.

There is a relationship between the network structure and the method of removing or destroying the windows of the cells of the polyurethane foam. As a method for reticulating a foam, a mechanical method, a chemical method, and a thermal method are known. As an example, the foam can be reticulated by melting the window with a hot flame tip or explosion to leave the chain network intact. Alternatively, the cell window may be etched away by the hydrolysis action of water in the presence of an alkali metal hydroxide. See Patent Literatures 1-5 for various methods of reticulating polyurethane foam.

The tip of a household cleaning sponge or mop is very commonly formed from cellulose. Paper pulp is the main raw material for cellulose sponge. By reacting the pulp with carbon disulfide, a soluble cellulose xanthate compound is produced. This compound is dissolved in honey-like liquid viscose and mixed with reinforcing fibers to give strength to the pulp mixture. Cellulose is formed to have a double cell structure that mimics the natural sponge. Sodium sulfate crystals are added to the pulp and the resulting mixture is heated in a mold to melt the crystals. The mixture is regenerated to pure cellulose by heating, and sponge pores are formed as traces in the portion where the crystals are not dissolved. Maintain the moisture content and color purity of the cellulose sponge with bleaching agents and wetting agents. Cellulose has good water absorbency and wettability, but has lower wet integrity than other materials. Also, since cellulose becomes hard and brittle when dried, it must be moistened before use for wiping.

Open cell type ester-based and ether-based polyurethane foams are more flexible and flexible than cellulose, and are flexible even when dried without using a wetting agent. Compared to cellulose, foam has better wet strength and wet integrity and less swelling when wet. The foam may also be formed with a double cell structure to resemble a more natural sponge. In general, polyurethane foam can be produced at a lower cost than cellulose. However, polyurethane foam is hydrophobic and not very high in liquid absorbency and wettability, so it is not very suitable as a tip for household sponges or mops. Even if the polyurethane foam is post-treated with a surfactant to improve water absorption and wettability, these properties are inferior to cellulose.

Reticulated polyurethane foam is used as a component of filters. Moreover, since this reticulated foam has a polishing surface in particular, it has been proposed to be used as a component of household sponges (see Patent Documents 6 and 7). However, there is still a need for polyurethane foams suitable for use in place of cellulosic materials as liquid absorbing and wetting elements at the tip of household sponges and mops.
U.S. Pat. 3125542 U.S. Pat. 3405217 U.S. Pat. 3423338 U.S. Pat. 3425890 U.S. Pat. 4670477 U.S. Pat. 3857133 U.S. Pat. 5640737

According to the present invention, a hydrophilic ester-based polyurethane foam is first prepared by mixing a specific foam-forming component to form a porous polyurethane foam having a network structure of at least some chains and cell windows. . Generally, polyurethane foam formulations are expressed in parts by weight per 100 parts polyol. Accordingly, the foam formulation of the present invention includes the following per 100 parts by weight of polyester polyol: 20.0 to 62.0 parts by weight of isocyanate; 1.5 to 5.0 parts of blowing agent such as water; ~ 2.0 parts; gel catalyst 0-0.3 parts; and stabilizing surfactants 1.0-3.0 parts such as silicone surfactants. Other additives such as antibacterial additives, double cell additives, dyes, pigments, colorants, cross-linking additives, fragrances, detergents and extenders can also be incorporated into the foam formulation.

After mixing the foam-forming components, the foam is expanded and cured, preferably at atmospheric temperature and pressure. The resulting foam is preferably 70-130 per inch (27.6-51.2 per cm), most preferably 70-90 per inch (27.6-35 per cm). .4) holes, but may have a double cell or spongy structure. As a preferable double cell structure, a large cell and a medium size cell are scattered while fine cells are dispersed. The large cell diameter may be 0.06 to 0.09 inch (1.52 to 2.29 mm).

The cured foam is cut into pieces and chemically treated by immersion in a heated caustic bath for 3-15 minutes, preferably 6-10 minutes. An example of a preferred corrosive bath is a sodium hydroxide solution (5.0-10) heated to 70 ° F-160 ° F (21-71 ° C), preferably 120 ° F-160 ° F (49-71 ° C). 0.0%, preferably 7.5% NaOH). The corrosive solution removes at least part of the cell window in the foam cell structure by etching, and a hydrophilic ester-based polyurethane foam is obtained. The foam thus treated is compressed between calendar rolls, thoroughly washed and dried in an oven.

The treated foam is compressed to 1/2 to 1/20 of the initial thickness, preferably 1/3 to 1/8 of the initial thickness, and the compressed foam is compressed to 340 to 380 ° F. (171 Felt by heating at ~ 193 ° C for 10-60 minutes.

The felted foam structure has excellent wetting properties capable of absorbing at least about 30 pounds per square foot per minute (1.44 kPa / min), preferably at least 35 pounds (1.68 kPa / min). It consists of a hydrophilic ester-based polyurethane foam. Moreover, the said foam is superior to cellulose in water retention and wet strength. The felted hydrophilic ester-based polyurethane foam does not swell much even if it absorbs and retains liquid, so it would be ideal as a component for the tip of household sponges and mops.

The hydrophilic ester foam of the present invention is preferably prepared by mixing a polyol component with a surfactant, a catalyst, a foaming agent and other additives to make a polyol premix. After adding the isocyanate component to this polyol premix, the resulting foam mixture is preferably expanded and cured under atmospheric conditions to form a hydrophilic ester-based polyurethane foam. The foam forming step may be performed batchwise, semi-continuously or continuously.

Polyester polyurethane foams are more hydrophilic than polyether polyurethane foams because of the high polarity of carboxylic acid groups. Polyester polyols suitable for the production of flexible polyester-based polyurethane foams are known in the industry. Examples of such suitable polyester polyols include, for example, adipic acid, glutaric acid, succinic acid, phthalic acid, and the like by reacting dicarboxylic acid and / or monocarboxylic acid with an excess of diol and / or polyhydroxy alcohol. Acids or anhydrides thereof and / or fatty acids (linoleic acid, oleic acid, etc.) and diethylene glycol, ethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, neopentyl glycol, trimethylolpropane, trimethylolethane and / or Or what is manufactured by making pentaerythritol react is mentioned. Examples of these polyols include LEXOREZ 1102-50 or LEXOREZ 1102-60 from Inolex Chemical or FOMREZ 50 or FOMREZ 60 from Crompton. Other suitable polyester polyols can be prepared by reacting a lactone with an excess of diol, such as caprolactan and propylene glycol. Suitable polyester polyols are described in US Pat. No. 4,331,555. Preferably, the polyester polyol is produced by reacting adipic acid and an ethylene glycol monomer using a glycerin initiator. The hydrophilic ester polyol is generally produced by a reaction between polyethylene glycol and adipic acid. For example, FOMREZ 45 from Crompton and LEXOREZ 1105-HV2 from Inolex Chemical. Most preferably, the foam-forming mixture of the present invention comprises at least 5 parts by weight, preferably 10 parts by weight of a hydrophilic ester polyol of 50 hydroxyl groups as a polyol component. Also preferred are ester polyols of hydroxyl group 60, mixtures of ester polyols of hydroxyl group 50 and ester polyols of hydroxyl group 60, and hydrophilic ester polyols of hydroxyl group 50.

The “number of hydroxyl groups” of a polyol is a measure of the number of reactive hydroxyl groups that can be used in the reaction. The numerical value indicates the number of mg of potassium hydroxide corresponding to the number of hydroxyl groups in 1 g of the sample. The “functionality” of a polyol is defined as the average number of hydroxyl sites per molecule. Preferably, the polyester polyol used to form the foam of the present invention has 20-150, more preferably 40-100, most preferably 50-60 hydroxyl groups.

The term “polyisocyanate” refers in particular to the isocyanates described above for use in the preparation of polyurethane foams. “Polyisocyanates” include di- and poly-isocyanates, as well as polyols and polyisocyanate prepolymers with excess isocyanate groups that can be used in the reaction with another polyol. The amount of polyisocyanate used is often expressed in terms of an “index” which is 100 times the amount of isocyanate actually required to react with all active hydrogen-containing compounds present in the reaction mixture. For most foam applications, the isocyanate index is about 75-140. In the present invention, the isocyanate index is preferably 90 to 110, most preferably 100 or less, and particularly preferably 95 to 98.

The polyester-based polyurethane foam is prepared using any suitable organic polyisocyanate known in the art, such as hexamethylene diisocyanate, phenylene diisocyanate, toluene diisocyanate (TDI) and 4,4'-diphenylmethane diisocyanate (MDI). The methylene diisocyanate preferably used is a mixture of diphenylmethane diisocyanate and polymethylene polyphenyl isocyanate (sometimes referred to as “MDI” or “polymerizable MDI”). The MDI mixture may contain diphenylmethane-4,4′-diisocyanate, as well as 2,2′- and 2,4′-isomers, and high molecular weight oligomers and has an isocyanate functionality of about 2.1. ~ 2.7, preferably about 2.1-2.5. The isocyanate is preferably selected from commercially available mixtures of 2,4- and 2,6-toluene diisocyanates. A known toluene diisocyanate that is commercially available is TD80, which is a mixture of 80% 2,4-toluene diisocyanate and 20% 2,6-toluene diisocyanate. The amount of polyisocyanate used depends on the OH content and water content of the polyol in the formulation and is generally 20-90 parts by weight per 100 parts of polyol.

One or more surfactants can be used in the foam-forming composition. Surfactants lower the overall surface tension, promote bubble nucleation, stabilize the expanding cell structure, and emulsify incompatible components, resulting in the hydrophilicity of the resulting foam. May have some impact. A commonly used surfactant for polyurethane foam applications is a polysiloxane-polyoxyalkylene copolymer, usually about 0.5 to 3 parts by weight per 100 parts polyol. In the present invention, the surfactant is preferably used in an amount of 1.0 to 3.0 parts by weight per 100 parts of polyol. The surfactant may be, for example, an organic or silicone surfactant such as FOMREZ M66-86A (Witco) and L532 (OSi Specialties), which stabilizes the cell structure and acts as an emulsifier. Used to assist. Most preferably, 1.5 to 2.5 parts by weight of an open cell silicone surfactant is used per 100 parts of polyol.

The catalyst is used to adjust the relative rates of water-polyisocyanate reaction (gas generation reaction or foaming reaction) and polyol-polyisocyanate reaction (gelation reaction). The catalyst may consist of one type, but in most cases it is a mixture of two or more types of compounds. Preferred catalysts for the production of polyurethane foam are organotin salts and tertiary amines. Amine catalysts are known to have a greater impact on the water-polyisocyanate reaction, and organotin catalysts are known to have a greater impact on the polyol-polyisocyanate reaction. The total amount of catalyst generally varies from 0 to 5.0 parts by weight per 100 parts of polyol. The amount of catalyst used depends on the formulation used and the type of catalyst, as is known to those skilled in the art. Although various types of catalysts can be used in the present invention, the inventors have found that the following range amounts of catalyst are sufficient: 0.5 to 2.0 parts amine catalyst per 100 parts polyol; polyol 100 0 to 0.7 part, preferably 0 to 0.3 part of organotin catalyst per part.

All urethane catalysts useful and suitable in the present invention are known to those skilled in the art, such as triethylenediamine, N-methylimidazole, 1,2-dimethylimidazole, N-methylmorpholine, N-ethylmorpholine, triethylamine, tributylamine, Tertiary amines such as triethanolamine, dimethylethanolamine and bisdimethylaminodiethyl ether, and organic tins such as tin octoate, tin acetate, tin oleate, tin laurate, dibutyltin dilaurate, and other tins Salt.

In order to resemble the appearance of a natural sponge, a double cell structure may be formed. Materials for forming the dual cell structure may be added to the foam-forming mixture. These include castor oil derivatives, stearic acid, acetic acid and low melting waxes. These materials form voids larger than normal bubbles in the resulting foam structure. In use, it is preferred to add 0.04 to 0.21 part of double cell additive per 100 parts of polyol.

A foaming agent may be included in the foam-forming composition. The most common blowing agent is water, which can be added from 1.5 to 5.0 parts per 100 parts polyol. Other blowing agents include volatile organic compounds such as liquid carbon dioxide, pentane and acetone, and chlorinated compounds such as methylene chloride, HFC, HCFC and CFC.

Optionally other additives can be included in the foam-forming composition. Optional additives include, but are not limited to, antibacterial compounds, stabilizers, extenders, dyes, pigments, cross-linking additives, fragrances, cleaning agents and antistatic agents. Such additives should not adversely affect the properties of the final polyurethane foam. When used at the tip of a sponge or mop, it is preferable to add 0.5 to 1.5 parts of an antibacterial compound per 100 parts of polyol.

The hydrophilic ester-based polyurethane foam is preferably 70 to 130 per inch (27.6 to 51 per cm), most preferably 70 to 90 per inch (27.6 to 17.6 cm). 35.4) holes, but may have a double cell or spongy structure. As a preferable double cell structure, a large cell and a medium size cell are scattered while fine cells are dispersed. The large cell diameter may be 0.06-0.09 inch (1.5-2.3 mm).

The foam is then chemically reticulated and the cell pieces are removed by soaking the foam pieces in a heated caustic bath for 3-15 minutes, preferably 6-10 minutes. An example of a preferred corrosive bath is a sodium hydroxide solution (5.0-10) heated to 70 ° F-160 ° F (21-71 ° C), preferably 120 ° F-160 ° F (49-71 ° C). 0.0%, preferably 7.5% NaOH). The corrosive solution removes at least part of the cell window in the foam cell structure by etching, and a hydrophilic ester-based polyurethane foam is obtained. The foam thus treated is compressed between calendar rolls, thoroughly washed and dried in an oven.

The treated foam is compressed to 1/2 to 1/20 of the initial thickness, preferably 1/3 to 1/8 of the initial thickness, and the compressed foam is compressed to 340 to 380 ° F. (171 Felt by heating at ~ 193 ° C for 10-60 minutes. The compression ratio is generally called firmness. For example, a foam compressed to 1/3 of its original thickness has a stiffness of 3 felt. Moreover, the foam compressed to 1/5 of the original thickness has a firmness of 5 felt.

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

A cellulose sponge was obtained. The cellulose sponges of Examples C1, C2 and C3 were obtained from 3M, Nylonge and Spontex, respectively. According to the applicant's test, the water absorption of cellulose is 29-35 pounds (water) / ft ² / min (1.39-1.68 kPa / min), and the effective water absorption exceeds 40%. (44%).

The foam-forming material is mixed and poured into a 15 "x 15" (38.1 x 38.1 cm) cardboard box and the foam is formed at atmospheric pressure (eg, 1 atmosphere) and ambient temperature (approximately 75 ° F (24 ° C)). Polyurethane foams were prepared on a laboratory scale by making small lumps. The foam material was mixed in the proportions shown in Table 1. The unit of quantity is kg and is based on parts by weight per 100 parts of polyol. The foams of Examples C4-C6 are not prepared according to the present invention, but are comparative foams. The foams of Examples 1-7 were prepared according to the formulation according to the invention, but were not felted. Example form

A portion of each example foam blob was cut flat and thick and chemically treated or modified. The foam pieces were immersed in heated 7.5% aqueous sodium hydroxide (at least to 120 ° F. (49 ° C.)) for 8 minutes. Thereafter, the corrosive solution was mostly squeezed out by compression between calender rolls. Furthermore, the remaining corrosive solution was removed by washing and dried in an oven.

Example C4 was prepared as a standard for ester-based polyurethane foam. The foam of Example C5 was prepared using a hydrophilic polyol. Both the foams of Examples C4 and C5 were not chemically modified. Example C6 is a hydrophilic ester foam reticulated by heat. The foam of Example C6 had a completely open cell, but the liquid absorption of this foam was very low.

LEXOREZ 1102-50A is an ester polyol of hydroxyl group 50 from Inolex Chemical. F45 is FOMREZ 45, which is a hydrophilic ester polyol of the hydroxyl group 50 of Crompton. TEGOSTAB B8301 is an open cell silicone surfactant from Goldschmidt Chemical. NIAX silicone Y6353 is an open cell silicone surfactant from OSi Specialties. ULTRAFRESH DM50 is an antibacterial additive from Thomson Research. A dual cell additive (“DC additive”) is a castor oil derivative used to make the foam into any spongy tissue. KOSMOS K5N is a tin octoate catalyst (tin catalyst) manufactured by Goldschmidt Chemical. NEM is the amine catalyst n-ethylmorpholine. TD80 is a toluene diisocyanate mixture of 80% 2,4-toluene diisocyanate and 20% 2,6-toluene diisocyanate. “Index” is the isocyanate index. The cell structure of the foam may be uniform or cells of different sizes may be distributed. A uniform cell structure is indicated by the number of holes per inch in length. This number is derived from a visual comparison between foam and standard. Double cell foams have cells of various sizes. Large cell pores are within the stated range.

The sponge was cut to the desired size of 4.75 inches x 3.0 inches x 0.625 inches (12.1 cm x 7.6 cm x 1.6 cm). Before the test, the cellulose sponge was washed in a washing machine for two cycles to remove water-soluble substances or additives (for example, wetting agents). The polyurethane foam sample was not washed beforehand.

The liquid absorption rate (or wet rate) was measured by the following test method. Measure the weight and dimensions of the wet sponge sample. Sponges are generally rectangular on the front and back and have some thickness. Measure the length and thickness of the sponge to the nearest 0.01 inch (0.25 mm). Squeeze the sponge and record the weight after squeezing. Place the perforated plate on the bottom of the solid tray. Water is added on the perforated plate to a depth of 1/8 inch (3 mm). A sponge is placed in the water pooled on the perforated plate surface. Hold one side of the sponge in the water so that the front and back of the sponge are perpendicular to the water surface. Remove the sponge after 5 seconds and weigh the sponge so that there is no water loss. Record the wet weight to the nearest 0.01 g. Water absorption is expressed in weight of water per square foot per minute (pounds). The calculation method is as follows. (Wet weight-weight after squeezing) ÷ (sponge length × thickness).

The effective absorption rate indicates the volume% of water retained by the wet sponge after draining for 5 minutes after saturation. Absorption is expressed as the amount of water retained per cubic inch of sponge (cubic inches). The wet sponge dimensions (length, width and thickness) are measured to the nearest 0.01 inch (0.25 mm). Calculate the wet capacity. Squeeze the sponge and record the weight after squeezing to the nearest 0.01 g. Thereafter, the sponge is completely immersed in warm water and crushed to remove air in the sponge and absorb water for 1 minute. Take out the sponge using a hook and hang it vertically for 5 minutes to drain the water. Thereafter, the weight of the sponge is again measured in units of 0.01 g: this is referred to as wet weight. Calculate the volume% of water retained. The effective absorption rate is obtained from “(wet weight−weight after squeezing) ÷ wet capacity”.

Total absorption indicates the total amount of water that the sponge can hold after being drained vertically for 5 minutes and expressed as a percentage of the initial dry weight. Immerse the sponge in warm water and squeeze it to remove the air in the sponge and allow it to absorb water for 1 minute. Then take the sponge out of the water using a hook, hang it vertically and drain the water for 5 minutes. Thereafter, the weight of the sponge is measured, and the weight after draining is recorded in units of 0.01 g. Remove excess water by squeezing the sponge by hand. The sponge is then dried in an air circulation oven at 220 ° C. for at least 4 hours, cooled to room temperature and weighed again. Record the dry weight of the sponge to the nearest 0.01 g. The total absorption rate is represented by “{water retention after draining water (weight after draining-dry weight) ÷ dry weight of sponge} × 100”.

The time required for absorption is a measure of the time required for a drop of water to be completely absorbed by a moist sponge sample. The sponge sample is immersed in water and crushed in water to remove air in the sponge. Squeeze out sponge water as much as possible when removing from the water. Place a drop of water on the surface of a damp sponge. Record the time that the water is absorbed by the damp sponge. The average absorption time was calculated after 5 trials.

The wiping and drying performance is evaluated as follows. Pour 50 g of water onto a clean horizontal surface. Weigh sponge samples before testing and every time they pass through water. Continue until no more water can be absorbed. Do not squeeze the sponge before and after weighing. Record the weight of water absorbed by the sponge each time it passes through the water.

The dry sponge is weighed, the sponge sample is immersed in water, crushed to remove the air in the sponge, and then immersed in water for 5 minutes to measure the weight of the saturated sponge, thereby examining the water retention ability. The water holding capacity is the water holding weight per 1 g of sponge.

For the data in Tables 2 and 3, the non-felt foams (Examples 1-7) had excellent absorption similar to cellulose sponges (Examples C1, C2 and C3). The foam of Example 1 consisted of a low index conventional polyester formulation and was chemically modified in a corrosive solution. The foam of Example 1 was moistened and wiped off with water in the same manner as the cellulose sponge, and had a water retaining power superior to this. The foam of Example 1 had unexpectedly superior performance than the foam of the same composition that was not chemically modified (Example C4) and the hydrophilic ester foam (Example C5). Thus, by combining the low index and the chemical treatment, a hydrophilic ester polyurethane foam which is unexpectedly excellent can be obtained particularly when a foam is made using an open cell type silicone surfactant. The foams of Examples 2-7 showed performance equivalent to that of Example 1.

Other observations are also evident from the data shown. Example 2 shows that the addition of 10 parts of hydrophilic polyol per 100 parts can increase the total absorption of the resulting foam. The finer cell structure of Example 4 increased the effective absorption rate and total absorption rate of the foam and improved the wiping and drying performance. Examples 5 and 6 show a density increasing effect. Example 7 shows the effect of different surfactants on water absorption.

When the foam was felted, the water absorption was further improved. In Tables 4 and 5, Examples 8 to 13 are according to the present invention, and Comparative Examples C5 to C9 represent conventional cellulose or ester polyurethane foams. Comparative examples C5, C7 and C8 were not felted. Examples 8, 9, and 10 incorporate the same ester-based polyurethane formulation containing at least 5 parts by weight of a hydrophilic polyester polyol made from adipic acid and polyethylene glycol. However, the foams of Examples 9 and 10 felted.

ACQUELL is a formex L. P. Is a registered trademark of the company.

By making the foam felt according to the present invention, the water absorption rate and the effective water absorption rate were unexpectedly increased. The water absorption of the foams of Examples 9 and 10 of the present invention felted with various felting firmness exceeded that of other polyurethane foams and cellulose. Examples 9 and 10 are compared to Example 8 and Comparative Example C5 is compared to C9.

The invention has been described in terms of the detailed description of the preferred embodiments and examples. Various changes in form and detail will be within the skill of those in the art. Accordingly, the invention is to be evaluated by the following claims and not by the detailed description of the examples or the preferred forms.

Claims (12)

A method for producing a hydrophilic ester-based polyurethane foam,
(A) The following ingredients:
(I) 100 parts by weight of ester polyol (of which at least 5 parts by weight is composed of a hydrophilic polyester polyol produced from adipic acid and polyethylene glycol),
(Ii) 20.0-62.0 parts by weight of isocyanate (isocyanate index is 120 or less) per 100 parts of polyol, and
(Iii) 1.0-3.0 parts by weight of stabilizing surfactant per 100 parts of polyol:
To form a polyurethane foam,
(B) treating the polyurethane foam in a corrosive bath to form a hydrophilic ester polyurethane foam;
(C) A manufacturing method comprising felting the foam after the treatment,
The hydrophilic ester polyurethane foam has a water absorption of at least 98 kilograms per square meter per minute,
A process for producing a felt by compressing the treated foam while heating at 340 to 380 ° F. (171 to 193 ° C.). The method according to claim 1, wherein the stabilizing surfactant is a silicone-based surfactant. 2. The method according to claim 1, further comprising 1.0 to 5.0 parts by weight of a blowing agent as a component per 100 parts of polyol. The manufacturing method according to claim 3, wherein the foaming agent is water. The method according to claim 1, further comprising as a component a catalyst selected from the group consisting of a gel catalyst, a gas generating catalyst, and a mixture thereof. The production method according to claim 1, further comprising 0.5 to 2.0 parts of a foaming catalyst and 0 to 0.3 part of a gel catalyst as components. The method according to claim 1, further comprising an antibacterial additive as a component. The manufacturing method according to claim 1, wherein the caustic bath is made as a solution containing sodium hydroxide. The manufacturing method according to claim 1, wherein the foam after the treatment is felted by compressing the foam to 1/3 to 1/8 of the original thickness. The method according to claim 1, wherein the hydrophilic ester-based polyurethane foam has 70 to 130 holes per inch (27.6 to 51 holes per cm) before felting. The manufacturing method according to claim 1, wherein the isocyanate index is 100 or less. A hydrophilic ester-based polyurethane foam produced by the production method according to claim 1.