JPH08259657A - Production of polyurethane resin - Google Patents

Abstract

PURPOSE: To obtain a transparent polyurethane resin having excellent fog resistance for protection of a transparent base material by using a raw material mixture of a polyol component and a polyisocyanate component in combination with two kinds of surfactants.

CONSTITUTION: The polyurethane resin is obtained by using a raw material mixture which comprises (A) a polyol component (preferably a polyester polyol and/or a polyoxyalkylene polyol), (B) a polyisocyanate component, (C) a polyoxyethylene glycol monoalkylether based surfactant (preferably with an average molecular weight of 250-1,700) and (D) a polyoxyalkylene chain- containing polysiloxane based surfactant (preferably with an average molecular weight of 500-2,000). It is preferable that the component C constitutes 5-12 (weight) % of the raw material mixture and the component D constitutes 1-10% thereof.

COPYRIGHT: (C)1996,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent polyurethane resin having excellent antifogging property for protecting a transparent substrate.

[0002]

2. Description of the Related Art Various attempts have been made so far with respect to antifogging treatment of transparent substrates, but a treatment method balanced with surface performance such as scratch resistance has not been established. On the other hand, it has been attempted in the past to attach a transparent polyurethane resin sheet or to coat the base material directly on the substrate in order to prevent glass from scattering, and it has been effective in some cases.

[0003]

However, the surface of the polyurethane resin is usually more hydrophobic than the glass surface and is less likely to get wet with water. For this reason, when exposed to a humid atmosphere, dew condensation is likely to occur and visibility is likely to be impaired. Therefore, attempts have been made to improve the antifogging property by making the polyurethane resin film itself hydrophilic or kneading a surfactant.
If the film itself is made hydrophilic, the film strength tends to decrease, it tends to become dirty, and the durability tends to be impaired.

Further, it has been recognized that when a surfactant is kneaded, the surfactant bleeds out to the resin surface in a humid atmosphere to contaminate the surface. Therefore, it has been a difficult problem to achieve both transparency and anti-scattering ability of the polyurethane resin, scratch resistance and anti-fogging property. The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art.

[0005]

The present invention is a method for producing a transparent polyurethane resin from a raw material mixture containing a polyol component and a polyisocyanate component, which comprises a polyoxyethylene glycol monoalkyl ether surfactant and polyoxyethylene glycol. A method for producing a polyurethane resin, which comprises using a raw material mixture containing an alkylene chain-containing polysiloxane-based surfactant.

A feature of the present invention is to use a polyoxyethylene glycol monoalkyl ether type surfactant and a polyoxyalkylene chain-containing polysiloxane type surfactant.

The polyoxyethylene glycol monoalkyl ether type surfactant has an average molecular weight of 250.
It is preferably ˜1700. The polyoxyethylene glycol monoalkyl ether-based surfactant is preferably represented by the following formula (1). In the formula (1), R represents an alkyl group having 1 to 35 carbon atoms, and s represents an integer of 1 or more.

R—O— (C ₂ H ₄ O) _s H ··· (1)

If R is an alkyl group having a carbon number of more than 35, the compatibility with the polyurethane resin is extremely lowered and bleeding out becomes severe, which is not preferable. Carbon number 1
It is preferably an alkyl group of 0 to 20. Further, a linear alkyl group is particularly preferable. s is 3 to 3
It is preferably 0. When s exceeds 30, the entire polyurethane resin is excessively hydrophilized, and the polyurethane resin is whitened when exposed to high humidity, which is not preferable. The polyoxyethylene glycol monoalkyl ether surfactant is preferably contained in the raw material mixture in an amount of 5 to 12% by weight.

The polyoxyalkylene chain-containing polysiloxane surfactant in the present invention is preferably a linear or branched polydiorganosiloxane compound. A typical example of polydiorganosiloxane is polydimethylsiloxane, and a structure in which a part or all of the methyl group thereof is substituted with a polyoxyalkylene chain is preferable.

Examples of polyoxyalkylene chains include polyoxyethylene chains, polyoxypropylene chains, polyoxytetramethylene chains, poly (oxyethyleneoxypropylene) chains, and the like.

The end of the polyoxyalkylene chain is preferably a hydroxyl group, a carboxyl group, an alkyloxy group, an acyloxy group or the like. In particular, a non-reactive group such as an alkyloxy group or an acyloxy group is preferable.

The oxyalkylene chain is usually bonded to the silicon atom via an alkylene group such as a dimethylene group or a trimethylene group, but is not limited thereto.

It is particularly preferable that the structure of the polyoxyalkylene chain-containing polysiloxane of the present invention is represented by the following formula (2). In addition, in Formula (2), x is an integer of 0-10, y is an integer of 1-10, m is an integer of 4-40,
n represents an integer of 0 to 20 and R ¹ represents an alkyl group having 1 to 20 carbon atoms. However, the formula (2) does not represent only the block copolymer, but also a copolymer in which dimethylsiloxy units and polyoxyalkylene chain-containing siloxy units are randomly copolymerized.

[0015]

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In the formula (2), x is an integer of 0 to 5 and y is 1 to
5 is an integer, m is an integer of 4 to 40, n is an integer of 0 to 5, R
Particularly preferably, ¹ is a methyl group. x, y,
When n exceeds 5, the compatibility with the polyurethane resin decreases and the polyurethane resin becomes white. Further, m can be compatibilized with the polyurethane resin in a wide range.

The content of the polyoxyalkylene chain-containing polysiloxane-based surfactant in the raw material mixture is preferably 1 to 10% by weight. If it is less than 1% by weight, the antifogging effect is insufficient, and if it exceeds 10% by weight, bleeding out is excessive and the surface becomes sticky, which is not preferable in practice.

The polyol component is preferably polyester polyol and / or polyoxyalkylene polyol. Examples of the polyester polyol include a reaction product of a polyhydric dicarboxylic acid and a polyhydric alcohol, and a product obtained by ring-opening polymerization of a cyclic ester in the presence of an initiator.

Examples of polycarboxylic acids include adipic acid and phthalic acid. Examples of the polyhydric alcohol include ethylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol and neopentyl glycol. Cyclic esters include lactones such as caprolactone.

The number of functional groups of the polyester polyol is preferably 2 or more, and in some cases, more than 2. Therefore, a polyester polyol such as polycaprolactone polyether obtained by ring-opening polymerization of a cyclic ester is preferable because a polyester polyol having more than 2 functional groups can be obtained.

The average hydroxyl value of the polyester polyol is preferably 110 to 570.

The polyoxyalkylene polyol is preferably one obtained by ring-opening polymerization of a cyclic ether in the presence of an initiator. As the cyclic ether, alkylene oxides such as ethylene oxide and propylene oxide, and tetrahydrofuran are particularly preferable. The number of functional groups is preferably 2 or more, and in some cases, more than 2.

As the polyoxyalkylene polyol, those having particularly high hydrophilicity are particularly preferable. Examples of the highly hydrophilic polyoxyalkylene polyol include polyoxyalkylene polyols containing a polyoxyethylene group. The oxyethylene group content in the polyoxyalkylene polyol is 30% by weight or more, and particularly 50
It is preferably at least wt%. Polyoxyethylene polyols are preferred.

The average hydroxyl value of the polyoxyalkylene polyol is preferably 110 to 570, more preferably 110 to 400.

In the present invention, the polyol component is preferably a combination of polyester polyol and polyoxyalkylene polyol. Polycaprolactone polyol is particularly preferable as the polyester polyol, and polyoxyethylene polyol is preferable as the polyether polyol. Further, it is preferable that the total number of functional groups in the polyol component exceeds 2.

As the polyisocyanate component, non-yellowing polyisocyanate is preferable. Specifically, 1,6
-Hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, xylylene diisocyanate and the like.

They may be modified, and may be buret-modified, isocyanurate-modified or urethane-modified. As the polyisocyanate, it is preferable to use a modified polyisocyanate or a polyisocyanate which is reacted with a polyol to form an isocyanate group-terminated prepolymer or a hydroxyl group-terminated prepolymer.

In the present invention, isophorone diisocyanate and / or hexamethylene diisocyanate are preferred. More preferably, a part of polycaprolactone polyol is reacted with isophorone diisocyanate to form an isocyanate group-terminated prepolymer or a hydroxyl group-terminated prepolymer. This is because it is safer to use the prepolymer in a pre-controlled process before using the isocyanate alone, which may cause a rash or the like on the human body, alone at the production site. Further, it is preferable to use buret-modified or isocyanurate-modified 1,6-hexamethylene diisocyanate.

The ratio of total free isocyanate groups / total free hydroxyl groups is preferably 0.9 to 2.5. If it is less than 0.9, the resin becomes brittle, and if it exceeds 2.5, the surface of the polyurethane resin becomes hard and the scratch resistance is lowered. When it is desired to obtain a polyurethane resin having a thin film thickness, it is effective to dissolve these raw material mixtures in an appropriate organic solvent and then laminate them on a substrate.

In the present invention, transparency, anti-fogging property, anti-fog property and other physical properties of the film, particularly scratch resistance and stain resistance, can be made compatible because two surfactants are used in combination. . More specifically, these surfactants can partially or completely dissolve in the water adhering to the film surface, thereby lowering the surface energy of water and forming a good water film on the film surface.

The surfactant of the present invention is unlikely to bleed out. Further, in the present invention, since two kinds of surfactants are used in combination, not only the initial antifogging property but also the sustainability of the antifogging effect can be achieved.

As the molding method, a spray coating method, a knife coating method, a calender molding method and the like can be adopted. In particular, those obtained by the reactive casting method as described in JP-A-1-56717 are most preferable from the viewpoint of the optical quality of the polyurethane resin and that the cross-linkable resin can be molded.

The polyurethane resin according to the present invention is transparent, has excellent antifogging property, and is excellent in self-healing property and scratch resistance. Therefore, by laminating and using it on a transparent substrate such as glass or transparent synthetic resin, or on a mirror, it is possible to protect them and impart antifogging property, self-healing property, scratch resistance and the like. Since it is particularly excellent in anti-fogging property, it can be used as a transparent substrate such as glass and transparent synthetic resin, as a mirror, or in a humid place.

The transparent polyurethane resin in the present invention can be produced in advance in the form of a film or sheet and can be attached to the surface of glass via an adhesive layer or an adhesive layer. Alternatively, a raw material mixture of transparent polyurethane resin may be directly laminated on the glass and the raw materials may be laminated and cured (casting).

If necessary, stabilizers such as UV absorbers, antioxidants and light stabilizers, urethanization catalysts, extenders, colorants, flame retardants and other additives can be added to the transparent polyurethane resin raw material mixture. .

If desired, it may be colored or may have a pattern. It can also be colored or printed directly on the polyurethane resin, colored or a new film with a pattern can be glued or laminated to the polyurethane resin.

[0037]

EXAMPLES The present invention will be described below with reference to examples and the like, but the present invention is not limited to these. Moreover, a part shows a weight part. In addition, as a representative property for evaluating the mechanical and physical properties of the polyurethane film obtained in Examples, self-repairing property, tensile strength, tensile elongation, light transmittance, Taber abrasion, stain resistance, and moisture resistance. The degree of bleed out of the additive under the conditions and the antifogging property were measured. Each evaluation method is as follows.

Self-repairing property: The maximum load at which scratches formed within 5 minutes at 23 ° C. can be eliminated by scratching the surface of the polyurethane film resin with a loaded diamond tip having a diameter of 15 μm. The disappearance of the scratch was performed visually. In the case of non-self-healing inorganic glass, this method caused scratches under a load of about 5 g.

Tensile strength, tensile elongation, light transmittance, Taber abrasion: According to JIS K6301.

Contamination resistance: Marking was made on the surface of the polyurethane film with a felt-tipped pen and wiped with ethanol after 1 hour, the condition of the mark removal was expressed by the ratio of the loss fraction of the amount of transmitted light.

Bleedout resistance: The sample was placed in a constant temperature and humidity oven at 40 ° C. and 85% for 1 week, and then the haze value of the sample was measured to check the degree of bleed out of the additive.

Anti-fogging property: A unique evaluation device was devised to quantitatively express the haze resistance of the sample. In principle, the sample is exposed to an arbitrary high humidity condition, and the transition of the light transmittance from the moment when the exposure is started is recorded for 50 seconds.
On the other hand, changes in light transmittance when ordinary glass is exposed to the same conditions are also recorded. The area between the curve and the baseline showing the transition of each light transmittance thus obtained is obtained (shown in FIG. 1 below).

[A] of FIG. 1 shows the transition of the light transmittance of glass. The area of the shaded area is S ₁ . [B] shows the transition of the light transmittance of the sample. The area of the shaded area is S ₂ . [C] shows the transition of the light transmittance on the assumption that the sample is not clouded at all. The area of the shaded area is S ₀
And The antifogging value (AF, unit:%) is represented by the following formula (3).

[0044]

[Number 1] _{AF = 100 (S 2 -S 1} ) / (S 0 -S 1) ···· (3)

The antifogging value (AF) thus obtained was used as a measure of antifogging property. The apparatus shown in Table 5 was used for this measurement.

The polysiloxane-based surfactants A to C used in the examples are the polyoxyalkylene chain-containing polysiloxanes shown in Table 3.

Table 4 shows the structures of polyoxyethylene glycol monoalkyl ethers a to d. However, r, t
Represents a variable in the following formula (4).

CH ₃ (CH ₂ ) _r O (C ₂ H ₄ ) _t H ··· (4)

In the following Examples 1 to 7, 0.3% by weight of the silicone-based extender (BYK
-300), 0.2 wt% light stabilizer (MARK LA
-7H), 0.2% by weight of antioxidant (IRGANOX
1010), and 0.3% by weight of benzotriazole-based UV absorber (TINUVIN 328) was added to the polyol mixture. And, to the total weight of resin, 30
ppm of dibutyltin dilaurate was added to the polyisocyanate mixture.

Example 1 Polycaprolactone triol having a hydroxyl value of 196.4; 11.18 parts, hydroxyl value of 54
1.4 polycaprolactone triol; 9.70 parts,
Polysiloxane-based surfactant A; 7.45 parts, polyethylene glycol having a hydroxyl value of 280.5; 9.93 parts, and polyoxyethylene glycol monoalkyl ether a; 7.94 parts, at 80 ° C. for 3.0 hours. Stirring and mixing under heating and melting gave a uniform polyol mixture.

On the other hand, isophorone diisocyanate; 1
7.88 parts and polycaprolactone triol having a hydroxyl value of 541.8; 8.41 parts were heated and stirred at 80 ° C. for 5 hours to obtain a uniform prepolymer having an isocyanate group terminal.

NCO was added to the prepolymer thus obtained.
A polyisocyanate mixture was obtained by adding 26.82 parts of a nurate-modified hexamethylene isocyanate having a group content of 21.3% by weight.

Using a die while continuously discharging and stirring and mixing the polyol mixture and the polyisocyanate mixture, a continuously supplied release-treated smooth polyethylene terephthalate film base material (having a thickness of 0.1 m) is used.
m) was evenly coated to a film thickness of 0.3 mm.

This liquid film was heated at 120 ° C. in a continuous polymerization oven.
After heating at 40 ° C. for 40 minutes to essentially complete the polymerization, the film was wound with a base film. The base film and the polyurethane film were separated while paying out the obtained roll-shaped two-layer film to obtain a polyurethane film having excellent antifogging property, transparency, self-healing property, and scratch resistance.

Example 2 A polyurethane film having the following composition was produced by the same method as in Example 1.

(Polyol mixture) Hydroxyl value 196.4
Polycaprolactone triol; 11.61 parts, polycaprolactone triol having a hydroxyl value of 541.4; 1
0.14 parts, polysiloxane surfactant A; 4.97
Part, polyethylene glycol having a hydroxyl value of 280.5;
9.93 parts, polyoxyethylene glycol monoalkyl ether a; 7.94 parts.

(Polyisocyanate mixture) Isophorone diisocyanate; 18.42 parts, hydroxyl value 541.8
Polycaprolactone triol; 8.66 parts, NCO
Nurate-modified hexamethylene isocyanate having a group content of 21.3% by weight; 27.63 parts.

Example 3 By the same method as in Example 1, a polyurethane film having the following composition was produced.

(Polyol mixture) Hydroxyl value 196.4
Polycaprolactone triol; 10.51 parts, polycaprolactone triol having a hydroxyl value of 541.4; 8.
28 parts, polysiloxane surfactant B; 7.45 parts,
Polyethylene glycol having a hydroxyl value of 187.0; 9.9
3 parts, polyoxyethylene glycol monoalkyl ether b; 7.94 parts.

(Polyisocyanate mixture) isophorone diisocyanate; 18.58 parts, hydroxyl value 541.8
Polycaprolactone triol; 8.74 parts, NCO
Nurate-modified hexamethylene isocyanate having a group content of 21.3%; 27.87 parts.

Example 4 A polyurethane film having the following composition was produced in the same manner as in Example 1.

(Polyol mixture) Hydroxyl value 196.4
Polycaprolactone triol of 10.84 parts, polycaprolactone triol having a hydroxyl value of 541.4; 6.
96 parts, polysiloxane-based surfactant C; 2.98 parts,
Polyethylene glycol having a hydroxyl value of 187.0; 14.
90 parts, polyoxyethylene glycol monoalkyl ether c; 7.94 parts.

(Polyisocyanate mixture) Isophorone diisocyanate; 22.54 parts, hydroxyl value 541.8
Polycaprolactone triol; 10.60 parts, NC
Nurate-modified hexamethylene isocyanate having an O group content of 21.3%; 22.54 parts.

Example 5 A polyurethane film having the following composition was produced in the same manner as in Example 1.

(Polyol mixture) Hydroxyl value 196.4
Polycaprolactone triol; 11.72 parts, polycaprolactone triol having a hydroxyl value of 541.4; 1
4. 28 parts, polysiloxane surfactant C; 2.98
Part, polyethylene glycol having a hydroxyl value of 187.0;
9.93 parts, polyoxyethylene glycol monoalkyl ether d; 9.93 parts.

(Polyisocyanate mixture) Isophorone diisocyanate; 16.99 parts, hydroxyl value 541.8
Polycaprolactone triol; 799 parts, NCO
Nurate-modified hexamethylene isocyanate having a group content of 21.3%; 25.49 parts.

[Example 6] A mixture of a polyol and a polyisocyanate prepared in the following composition was added to 44.6 /
It was fed to a continuously rotating spray head at a ratio of 55.4, stirred and mixed in the spray head, sprayed on a glass substrate, and heated at 120 ° C. for 40 minutes to obtain 0.15 mm. A polyurethane film having a uniform thickness was obtained.

(Polyol mixture) Hydroxyl value 196.4
Polycaprolactone triol; 11.61 parts, polycaprolactone triol having a hydroxyl value of 541.4; 1
0.14 parts, polysiloxane surfactant A; 4.97
Part, polyethylene glycol having a hydroxyl value of 280.5;
9.93 parts, polyoxyethylene glycol monoalkyl ether a; 7.94 parts, ethyl methyl ketone; 1
9/11 copies.

(Polyisocyanate mixture) Isophorone diisocyanate; 18.42 parts, hydroxyl value 541.8
Polycaprolactone triol; 8.66 parts, NCO
Nurate-modified hexamethylene isocyanate having a group content of 21.3%; 27.63 parts, ethyl methyl ketone; 23.
75 copies.

[Example 7] The same method as in Example 1 except that a polyethylene terephthalate film (thickness: 0.05 mm) treated with a release agent was used as the substrate instead of the polyethylene terephthalate film having a thickness of 0.1 mm. Then, a polyurethane film was obtained. An acrylic adhesive was applied to this one surface in a solution form, dried, and then used as a release film, which was a low-density polyethylene film (thickness 0.01 m).
m) was laminated. The obtained polyurethane film could be easily adhered to the glass plate after peeling the release film.

Comparative Example 1 Polycaprolactone triol having a hydroxyl value of 196.4; 5.40 parts, hydroxyl value 54
1.4 polycaprolactone triol; 49.04
Part, polyethylene glycol having a hydroxyl value of 280.6; 2
0.78 parts, anionic surfactant (GoldSchm
idt Tegomer DS3117); 16.62
Parts, polysiloxane-based surfactant (Silwet L-77 manufactured by Nippon Unicar); 6.24 parts, 0.58 parts of extender, 0.38 parts of light stabilizer, 0.38 parts of antioxidant,
And 0.58 parts of a benzotriazole-based UV absorber (the same extender to UV absorber as in Example 1 are used) under heating and melting at 80 ° C. for 3 hours with stirring and mixing to obtain a uniform polyol. A mixture was obtained.

Then dibutyltin dilaurate; 0.03
Parts, nurate-modified hexamethylene isocyanate having an NCO group content of 21.3%; 100.00 parts under heating at 80 ° C. for 3 hours with stirring to obtain a uniform isocyanate mixture.

The polyol mixture and the polyisocyanate mixture were continuously discharged and stirred and mixed at a weight ratio of 100 / 1132.37 by using a die and continuously supplied with a release-treated smooth polyethylene terephthalate film ( A uniform film thickness of 0.3 mm was applied on the surface (0.1 mm in thickness). This liquid film was heated in a continuous polymerization oven at 120 ° C. for 20 minutes to essentially complete the polymerization, and then wound together with the substrate film. The base film and the product film were separated while paying out the obtained roll-shaped two-layer film to obtain a polyurethane film.

Comparative Example 2 Isophorone diisocyanate; 18.44 parts, anionic surfactant (Gold
Schmidt Tegomer DS3117);
0.99 parts and dibutyltin dilaurate; 0.03 parts were heated and stirred at 80 ° C. for 3 hours to obtain a uniform isocyanate-terminated prepolymer.

Subsequently, polycaprolactone triol having a hydroxyl value of 196.4; 37.43 parts, 0.58 part of an extender, 0.38 part of a light stabilizer, 0.38 part of an antioxidant,
0.58 parts of a benzotriazole-based UV absorber (the same extender to UV absorber as in Example 1 are used) is added, and the mixture is stirred and mixed under heating and melting at 80 ° C. for 3.0 hours to obtain a uniform mixture. An isocyanate group-terminated prepolymer was obtained.

The isocyanate group prepolymer thus obtained was slowly added to a reaction vessel containing 1,4-butanediol; 7.49 parts with stirring. Then 6
The reaction was completed by heating with stirring at 0 ° C. Thus, a hydroxyl-terminated prepolymer was obtained.

This prepolymer and NCO group content 21.3
% Of nurate-modified hexamethylene isocyanate; 3
While continuously discharging and stirring and mixing 4.5 parts, a die is used to continuously supply a release-treated smooth polyethylene terephthalate film base material (thickness 0.1 m).
m) was evenly coated to a film thickness of 0.3 mm.

This liquid film was heated at 120 ° C. in a continuous polymerization oven.
After heating for 20 minutes at the temperature to essentially complete the polymerization, the film was wound together with the base film. The base film and the polyurethane film were separated while paying out the obtained roll-shaped two-layer film.

Tables 1 and 2 show the evaluation results of the film thickness and physical properties of the polyurethane films obtained in Examples and Comparative Examples.
The results of the same evaluation of the glass plate itself are also shown.

[0080]

[Table 1]

[0081]

[Table 2]

[0082]

[Table 3]

[0083]

[Table 4]

[0084]

[Table 5]

[0085]

EFFECTS OF THE INVENTION By applying the transparent polyurethane resin according to the present invention to a transparent base material which is desired to have an antifogging effect, a scattering prevention effect when the base material is broken, and a scratch resistance effect, It is possible to achieve both the antifogging effect, the scattering prevention effect, and the scratch resistance effect.

[Brief description of drawings]

FIG. 1 is a graph showing how light transmittance changes with time, which is used for evaluation of antifogging property.

Claims (6)

[Claims] 1. A method for producing a transparent polyurethane resin from a raw material mixture containing a polyol component and a polyisocyanate component, which comprises a polyoxyethylene glycol monoalkyl ether surfactant and a polyoxyalkylene chain-containing polysiloxane surfactant. A method for producing a polyurethane resin, which comprises using a raw material mixture containing an agent. 2. A polyoxyethylene glycol monoalkyl ether surfactant having an average molecular weight of 250 to 170.
The manufacturing method according to claim 1, wherein the manufacturing method is 0. 3. The method according to claim 1 or 2, wherein the polyoxyalkylene chain-containing polysiloxane-based surfactant has an average molecular weight of 500 to 2,000. 4. The method according to claim 1, wherein the polyol component is a polyester polyol and / or a polyoxyalkylene polyol. 5. The method according to claim 4, wherein the polyoxyalkylene polyol is a highly hydrophilic polyoxyalkylene polyol. 6. The method according to claim 5, wherein the highly hydrophilic polyoxyalkylene polyol is a polyoxyalkylene polyol containing a polyoxyethylene group.