JPH09202819A - Method for modifying thermoplastic polyurethane resin - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To maintain excellent performance such as good moldability and breaking elongation of thermoplastic polyurethane resin in thermoforming such as extrusion molding, injection molding and melt spinning. And a method for improving the heat resistance of a molded article, particularly the recovery from deformation at high temperatures. When modifying a thermoplastic polyurethane resin (A), the polyisocyanate (B) having a terminal isocyanate group is (B) / (A) 3/97 to 25/7.
Melt kneading at a weight ratio of 5 to give polyisocyanate (B)
Is isocyanate equivalent (NCO equivalent) 500 to 3000
Of bifunctional polyisocyanate (B1) and NCO equivalent of 8
A polyisocyanate (B2) having an average number of functional groups of 0 to 250 of at least 2 (B2) / (B1)
Is 1/99 to 20/80 in weight ratio, and the molded product is subjected to heat treatment after melt-kneading at a temperature of 70 to 130 ° C. for 2 to 24 hours, which is a method for modifying a polyurethane elastomer.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a thermoplastic polyurethane resin having good melt fluidity in a molded article when the thermoplastic polyurethane resin is subjected to thermoforming such as extrusion molding, injection molding and melt spinning. The present invention relates to a method for modifying a thermoplastic polyurethane resin, which makes it possible to obtain a molded product having improved heat resistance, which is a drawback of the molded product obtained from the thermoplastic polyurethane resin, and particularly recovery from deformation at high temperatures.

[0002]

2. Description of the Related Art There are many proposals for improving the heat resistance of thermoplastic polyurethane resins. These can be technically classified as follows. (1) A method of increasing the melting point of a hard segment component in a linear urethane molecule. (2) A method of introducing a partial cross-linkage between linear urethane molecules.

However, since the thermal decomposition temperature of the urethane bond is usually around 230 ° C., molding at a temperature lower than that is required, and at the molding temperature, it is required to have a substantially linear structure. . Therefore, any polyurethane resin having a hard segment component having a melting point higher than the molding temperature or a partial cross-linking bond having a decomposition temperature higher than the molding temperature introduced in advance adversely affects good melt fluidity of the thermoplastic polyurethane, and a satisfactory molded product is obtained. Hard to get.

On the other hand, Japanese Patent Publication No. 34539/1989 discloses that moldability is good and the softening point can be increased by 20 to 30 ° C. by a method of adding and mixing polyisocyanate in a molten state to a molten thermoplastic polyurethane resin. Is disclosed. The polyisocyanate used here has a molecular weight of 300 to 6000, and among them, it is described that bifunctionality is particularly preferable. It is intended to improve the heat resistance of the molded product by cross-linking allophanate in the polymer.

Similarly, in JP-B-58-46573, in a method for producing a polyurethane elastic yarn, by adding a polyisocyanate having a molecular weight of 400 or more to a molten thermoplastic polyurethane elastic body and spinning it, excellent heat resistance is obtained. A method of stably melt spinning a polyurethane elastic yarn over a long period of time is disclosed. Here too, it is stated that the polyisocyanates are particularly preferably bifunctional.

On the other hand, in Japanese Patent Laid-Open No. 2-127515,
In a method for producing a heat-resistant urethane yarn, a molten thermoplastic polyurethane elastomer is polymerized from a bifunctional polyol component, a trifunctional polyol component and an isocyanate component, and the molar ratio of the isocyanate component to the OH group of the polyol component is 2 to 4 It is described that a polyurethane elastic yarn having heat resistance further superior to the above can be obtained by adding a prepolymer compound in the range of.

However, in Japanese Examined Patent Publication No. 1-34539 and Japanese Examined Patent Publication No. 58-46573, when a bifunctional polyisocyanate is used, the heat resistance of the molded article is still insufficient, and it is more than bifunctional. When a polyisocyanate having a large number of functional groups was used, the melt flowability at the time of molding was greatly reduced, and the moldability or spinnability was poor. Also in the method according to Japanese Patent Publication No. 2-127515, the melt fluidity at the time of molding was largely reduced and the moldability was poor. Also, the obtained urethane molded product is
Although it was superior in heat resistance to a molded article made of a thermoplastic polyurethane resin alone, it was inferior in elongation at break.

These results indicate that cross-linking by allophanate bonds is not sufficient to improve heat resistance, whereas polyisocyanates having a functionality higher than bifunctional have the linear structure required for the molten polymer composition during molding. It is considered to have an adverse effect.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a thermoplastic polyurethane resin with good melt fluidity while maintaining good melt fluidity during thermoforming such as extrusion molding, injection molding and melt spinning. Heat resistance, recoverability, which is a drawback of molded products obtained from plastic polyurethane resin,
It is an object of the present invention to provide a reforming method capable of obtaining a molded product having remarkably improved breaking elongation.

More specifically, it has better moldability and recoverability from deformation of the molded article at high temperature, as compared with the modification method by adding polyisocyanate to a thermoplastic polyurethane resin as proposed so far. It is an object of the present invention to provide a reforming method which is excellent in a good balance in all of the elongation at break.

[0011]

As a result of intensive studies to solve the above problems, the present inventors added at least two kinds of polyisocyanates having a specific number of functional groups and NCO equivalent to a thermoplastic polyurethane resin. Thus, the moldability was good, and it was found that the molded product was excellent in recoverability from deformation at high temperature and elongation at break by further heat treatment after molding, and completed the present invention.

That is, according to the present invention, when the thermoplastic polyurethane resin (A) is modified, the polyisocyanate (B) having a terminal isocyanate group is (B) / (A) 3 /
Melt-kneading at a weight ratio of 97 to 25/75, and polyisocyanate (B) has an isocyanate equivalent (NCO equivalent) of 5
00-3000 difunctional polyisocyanate (B1)
And a polyisocyanate (B2) having an NCO equivalent of 80 to 250 and an average number of functional groups of at least 2 (B2),
2) / (B1) is 1/99 to 20/80 in weight ratio, and the molded product after melt-kneading is 2 to 2 at a temperature of 70 to 130 ° C.
A method for modifying a thermoplastic polyurethane resin, which comprises performing heat treatment for 4 hours, preferably a bifunctional polyisocyanate (B1) is prepared from a polymer diol having a molecular weight of 500 to 4000 and an organic diisocyanate having a molecular weight of 150 to 300. And polyisocyanate having an NCO equivalent of 80 to 250 and an average number of functional groups of at least 2 which is obtained by a reaction of an organic disocyanate / polymer diol molar ratio of 1.5 / 1 to 4.5 / 1. The compound (B2) containing is a polymeric diphenylmethane diisocyanate, and the molded article is a urethane elastic yarn, which provides a method for modifying a thermoplastic polyurethane resin.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The thermoplastic polyurethane resin (A) used in the present invention preferably has a number average molecular weight of 500 to 500.
6000 polyols, such as bifunctional polyester polyols, polyether polyols, polycarbonate polyols and block copolymers thereof, with a molecular weight of 5
00 or less organic diisocyanate, for example, diphenylmethane diisocyanate (abbreviated as MDI), tolylene diisocyanate (abbreviated as TDI), dicyclohexylmethane diisocyanate (hydrogenated MDI), hexamethylene diisocyanate (HDI), xylylene diisocyanate (XDI), isophorone diisocyanate (IPD
It is a polymer obtained by polyaddition reaction of I) and the like with a chain extender such as glycol, triol, diamine, hydrazine and water at an NCO / OH ratio of about 1.

Among these polymer raw materials, as a polyol, polytetramethylene glycol or polycaprolactone diol, polycarbonate diol, polybutylene adipate, polymethylpentylene adipate,
Polyols containing at least one selected from the group consisting of polyhexamethylene / butylene adipate copolymers and polyneopentylene / hexamethylene adipate copolymers are preferred. As the organic diisocyanate, M
DI is preferred. Glycol is suitable as the chain extender, and 1,4-butanediol (1,4B
G) and bishydroxyethoxybenzene (BHEB) are particularly preferred.

As the thermoplastic polyurethane resin (A) used in the present invention, it is preferable to use a polymer having a substantially linear molecular structure. As a result, it becomes possible to achieve good moldability from excellent melt flow characteristics. Therefore, as a raw material of the thermoplastic polyurethane resin (A), a branching agent or a cross-linking agent is not necessary, but of course,
A polymer having a branch or a crosslink may be used as long as the moldability is not significantly reduced.

Thermoplastic polyurethane resin (A) of the present invention
As a method of synthesizing the above, any method of so-called prepolymer method of reacting a polyol and organic diisocyanate in advance and then reacting a chain extender or so-called one-shot method of mixing all reaction raw materials at once can be adopted. . As an industrial production method, a method of continuously producing using a mixer and / or a twin-screw extruder and / or a conveyor belt, or a method of obtaining a block-like, flake-like or powder-like polymer by a batch reaction Is preferably used.

NCO equivalent used in the present invention 500-3
000 difunctional polyisocyanates (B1) can be synthesized by reacting at least one difunctional polyol with a molar excess of at least one organic diisocyanate. The NCO equivalent as used herein is an isocyanate equivalent obtained by reacting a terminal isocyanate group with an excess of dibutylamine and determining consumed dibutylamine by hydrochloric acid titration. Examples of the bifunctional polyol include, for example, bifunctional polyesters, polyethers, polycarbonates or block copolymers thereof.

Among them, polytetramethylene glycol or polycaprolactone diol, polycarbonate diol, polybutylene adipate, polymethylpentylene adipate, polyhexamethylene / butylene adipate copolymer, polyneopentylene / hexamethylene adipate copolymer A polyol containing at least one selected from the group consisting of The molecular weight of the bifunctional polyol is preferably in the range of 500 to 6000,
Those of 600 to 2500 are particularly preferable. The molecular weight of the bifunctional polyol is a value calculated by reacting the terminal hydroxyl group with an excess acetylating agent and calculating the amount of consumed acetylating agent from the hydroxyl value obtained by KOH titration.

Examples of organic diisocyanates include, for example, diphenylmethane diisocyanate (MDI), tolylene diisocyanate (TDI), dicyclohexylmethane diisocyanate (hydrogenated MDI), hexamethylene diisocyanate (HDI), xylylene diisocyanate (XDI), isophorone diisocyanate. (IP
DI) and the like. Of these, MDI is particularly preferred. The compounding ratio of the organic diisocyanate and the bifunctional polyol is designed so that isocyanate groups remain at both ends of the bifunctional polyisocyanate,
Among them, the range of 1.5 / 1 to 4.5 / 1 is preferable. When the NCO equivalent of the bifunctional polyisocyanate is smaller than 500, the uniform dispersibility in the thermoplastic polyurethane resin decreases, the melt flowability decreases during continuous molding, and the physical properties of the molded product tend to vary. . NCO equivalent of the bifunctional polyisocyanate is 300
When it exceeds 0, the viscosity of the compound is high and handling becomes difficult. Similarly, the bifunctional polyisocyanate obtained when the compounding ratio of the organic diisocyanate and the bifunctional polyol is less than 1.5 / 1 has a high viscosity and is difficult to handle. On the other hand, when the compounding ratio is more than 4.5 / 1, the uniform dispersibility in the thermoplastic polyurethane resin is lowered, the melt fluidity is lowered during continuous molding, and the physical properties of the molded product are apt to vary.

NCO equivalent used in the present invention 80 to 25
Examples of the polyisocyanate (B2) having an average number of functional groups of 0 of at least 2 include the above-mentioned compounds and compounds obtained by modification of the above-mentioned organic diisocyanates. For example, uretdione ring-containing dimer, isocyanurate ring-containing trimer or carbodiimide modified product, buret modified product,
Alternatively, an adduct to a low molecular weight polyol such as glycerin or trimethylolpropane is also included. In addition to the above, polymeric MDI, which is a by-product during the production of MDI, may be mentioned.

Of these, polymeric MDI and carbodiimide-modified MDI are particularly preferable. These compounds are well known mainly as a curing agent for a two-pack type urethane resin, and commercially available products can be used.

The polyisocyanate (B) is obtained by mixing (B2) / (B1) in the composition in a weight ratio of 1/99 to 20/80 in a molten state. The mixing may be carried out at the time of synthesizing (B1) or at the time of molding, but for uniform mixing, it is preferable to mix prior to molding. When (B2) is less than the above range, the heat resistance improving effect of the molded product is insufficient, and (B2)
Is more than the above range, melt flowability during continuous molding is lowered, cutting occurs, mold release is deteriorated, and breaking elongation of a molded product is significantly reduced, which is not preferable.

If the weight ratio of the polyisocyanate (B) to the thermoplastic polyurethane resin (A) is less than 3/97, the heat resistance improving effect is insufficient, and
When it is larger than / 75, the shape retention immediately after molding is lowered and the tackiness is increased, resulting in deterioration of moldability.

The method for modifying the polyurethane resin of the present invention comprises:
It is carried out by a method in which the polyisocyanate (B) is melt-kneaded when the thermoplastic polyurethane resin (A) is injection-molded, extruded or melt-spun. For kneading, the respective components can be supplied to, for example, a twin-screw extruder by a metering feeder or a metering pump. The kneading condition is 1
80 to 220 ° C. and 10 seconds to 15 minutes are preferable. The melting of the thermoplastic polyurethane resin (A) is preferably performed at 180 to 220 ° C, and the melting of the polyisocyanate (B) is preferably performed at 60 to 100 ° C. Further, as in Japanese Patent Publication No. 34539/1989, polyisocyanate (B) may be quantitatively added to polyurethane resin (A) melted in a molding machine and then mixed by a static mixer.

The heat treatment of the present invention is carried out at a temperature of 70 to 130 ° C. for 2 to 24 hours after the melt kneading and molding. Under this condition, most of the cross-linking reaction of the polyisocyanate occurs, so that the elastic recovery property is improved. If this heat treatment condition is a temperature lower than 70 ° C. or shorter than 2 hours, the elongation at break of the molded product is lowered, and the effect of improving the elastic recovery property becomes insufficient.

If the heat treatment temperature is higher than 130 ° C., deformation of the molded product due to softening is not preferable. If the heat treatment time is longer than 24 hours, the productivity may be reduced and a heat deterioration phenomenon may occur, which is not preferable.

In the present invention, the thermoplastic polyurethane resin (A) is converted into a self-crosslinking polymer having an isocyanate group in the molecule by a urethane exchange reaction with a polyisocyanate (B) in a molding machine and heated after molding. After stabilizing the intermolecular higher-order structure by the treatment, the intermolecular crosslink is formed by the moisture curing reaction between the isocyanate groups. Therefore, the cross-linking by the urea bond provides higher heat resistance than the cross-linking by the allophanate bond in the prior art, that is, the recoverability from the deformation at high temperature is obtained. In addition, since the intermolecular higher-order structure is formed before the crosslinking reaction, it can exhibit a high elongation at break like the thermoplastic polyurethane resin.

[0028]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples. The present invention is not limited to only these examples. Further, "part" and "%" in the text are based on weight unless otherwise specified.

(Synthesis Example 1) Dehydrated polyneopenthylene (NPG) having a hydroxyl value of 56.1 / hexamethylene (H)
G) Adipate copolymer (however, NPG / HG = 1/1)
Of 210 parts and 900 parts of MDI are reacted at a temperature of 70 to 80 ° C. for 3 hours to obtain a viscous polyisocyanate (B1-
1) was obtained. The isocyanate equivalent weight of this product is 575
Met.

5 in a separable flask equipped with a stirrer
75 parts of polyisocyanate (B1-1) was maintained at a temperature of 80 ° C., 43 parts of 1,4-butanediol at 60 ° C. was added, and the mixture was stirred at high speed for about 2 minutes. The mixture thickened with exotherm due to the reaction. After the stirring was stopped, the reaction product was cast on a metal vat coated with a release agent in advance, and then 140
The reaction was completed by aging at ℃ for 3 hours. After cooling the solidified resin to room temperature and crushing, pelletize with an extruder,
A thermoplastic polyurethane resin (A-1) was obtained.

9 in a separable flask equipped with a stirrer
0 parts of polyisocyanate (B1-1) was kept at a temperature of 80 ° C., and as (B2-1), a polymeric MDI (manufactured by Nippon Polyurethane Co., trade name Millionate MR-200,
10 parts by weight of NCO equivalent of 135 and average number of functional groups of 2.5 were added and uniformly mixed by stirring to obtain a polyisocyanate composition (B-
1) was obtained.

(Synthesis example 2) dehydrated hydroxyl value 112.2
112 parts of the polytetramethylene ether glycol of 1 and 250 parts of MDI were reacted at a temperature of 70 to 80 ° C. for 3 hours to obtain a viscous polyisocyanate (B1-2). The isocyanate equivalent weight of this product was 1250. As the thermoplastic polyurethane resin (A-2), Pandex T-8185 (polyether thermoplastic polyurethane resin manufactured by Dainippon Ink and Chemicals, hardness 87) was directly used in the form of pellets. As (B2-2), carbodiimide-modified MDI (Mitsubishi Chemical isonate 143L, NCO
An equivalent weight of 143 and an average number of functional groups of 2.2) were used as they were.

Example 1 About 90 parts of the thermoplastic polyurethane resin (A-1) produced in Synthesis Example 1 was dried in a vacuum dryer at 100 ° C. for 2 hours, and then the polyisocyanate composition in a molten state at 80 ° C. After 10 parts of the product (B-1) was added and mechanically kneaded, it was continuously fed from a feeder to a 25 mmφ twin-screw extruder. The temperature of the feeder was set to 100 ° C and the temperature of the extruder was set to 200 ± 10 ° C. A film die having a width of 35 mm and a thickness of 0.5 mm was equipped at the tip of the extruder to form a film. The molding condition was good, and a uniform transparent film having almost the same shape as the die was obtained. The obtained film was heat-treated in a hot air drier at 110 ° C. for 6 hours, allowed to stand at 25 ° C. under a relative humidity of 50% for 1 week, and then subjected to physical property measurement according to JIS K6301. The results are shown in Table 1.

Example 2 Approximately 85 parts of the thermoplastic polyurethane resin (A-2) shown in Synthesis Example 2 was dried in a vacuum dryer at 100 ° C. for 2 hours, and then it was melted at 80 ° C. to produce a bifunctional polyfunctional polyamine. After 13 parts of isocyanate (B1-2) and 2 parts of polyfunctional polyisocyanate (B2-2) were added and mechanically kneaded, they were continuously fed from a feeder to a 25 mmφ twin-screw extruder. A film was formed in the same manner as in Example 1. The molding condition was good, and a uniform transparent film having almost the same shape as the die was obtained. The obtained film is heat-treated in a hot air dryer at 110 ° C. for 6 hours, and then 2
After leaving for 1 week at 5 ° C and 50% relative humidity, JI
Physical properties were measured according to SK6301. The results are shown in Table 1.

(Comparative Example 1) The thermoplastic polyurethane resin (A-1) was changed to 97 parts and 10 parts of the polyisocyanate composition (B-1) was changed to 3 parts of B2-1. It was extruded under the same conditions as above. The pressure increased and the discharge amount decreased with time in the extruder. The obtained film had a non-uniform thickness, many unmelted parts were generated, and the appearance was extremely poor.

Comparative Example 2 A film was prepared and physical properties were measured in the same manner as in Example 2 except that the raw material mixture ratio and the heat treatment after molding were not carried out. Table 1 shows the results
It was shown to.

[0037]

[Table 1] * 1: Measured according to JIS6301. Permanent elongation (%) increased by 200%
Residual strain after 10 minutes. The smaller this value is, the better the recovery is. * 2: 100% stretched sample is left in a constant temperature room at 130 ° C for 10 minutes, then taken out, and after 30 minutes at room temperature, residual strain at the time of stress relief. The smaller the value, the better the recoverability * 3: Shimadzu Flow Tester CFT-500C, temperature rising method 3 ℃ / min, nozzle 1mmφ * 1m
Measured with ml and load of 30 kgf The higher this value, the higher the heat resistance.

From the results shown in Table 1, it can be seen that the examples of the present invention are excellent in moldability during extrusion, and are excellent in elongation at break, recoverability and heat resistance.

(Example 3) Thermoplastic polyurethane resin Melfine SPN-304 (Dainippon Ink) was used in a 30 mmφ single-screw extruder equipped with a polyisocyanate composition feeder, a melt-kneading section and a spinning nozzle at the tip of the extruder. A chemical polyester-based thermoplastic polyurethane resin, hardness 80) was supplied as (A-3). From the feeder, the polyisocyanate composition (B-1) obtained in Synthesis Example 1 is
The supply amount was 10% with respect to the discharge amount of (A-3). Temperature of extruder, spinning head and nozzle is 210 ± 5
Set to ° C. 500 molten resin discharged from the nozzle
It was wound on a yarn tube at a speed of m / min. The spinning condition was good and uniform elastic yarn was obtained. Subsequently, heat treatment was performed at 110 ° C. for 6 hours. The characteristics of the obtained urethane elastic yarn are shown in Table 2. The characteristics of urethane elastic yarn are the strength and elongation at room temperature,
The elastic recovery rate, the heat setting rate at 130 ° C., and the flow temperature were evaluated.

(Comparative Example 3-1) Except that 10 parts of the polyisocyanate composition (B-1) was changed to 10 parts of (B1-1) and the heat treatment of the elastic yarn was not carried out. The same process as in Example 3 was performed. The spinning state was good and uniform elastic yarn was obtained. The characteristics of the obtained urethane elastic yarn were evaluated in the same manner as in Example 3 and shown in Table 2.

(Comparative Example 3-2) The same treatment as in Example 3 was carried out except that 10 parts of the polyisocyanate composition (B-1) was changed to 10 parts of (B1-1). The spinning state was good and uniform elastic yarn was obtained. The characteristics of the obtained urethane elastic yarn were evaluated in the same manner as in Example 3 and shown in Table 2.

[0042]

[Table 2] * 4: Measured according to the polyurethane filament yarn test method (Japan Chemical Fiber Association).

Orientec Tensilon RTA100 is used, pulling speed 50
0mm / min Initial gripping interval 50mm * 5: Restoring stress at the second 50% elongation against the forward stress at the second 50% elongation when 100% elongation-relaxation is repeated twice at room temperature Numerical value that represents the percentage of. Orientec Tensilon RTA100 is used, pulling speed 500mm / min, initial gripping interval 50mm. The higher this value, the better the recoverability.

From the results of Table 2, it can be seen that in the examples of the present invention, urethane elastic yarns having excellent heat resistance, particularly recovery from deformation at high temperature, can be obtained.

Example 4 About 90 parts of the thermoplastic polyurethane resin (A-2) produced in Synthesis Example 2 was dried in a vacuum dryer at 100 ° C. for 2 hours, and 1 part of stearic acid bisamide was used as a lubricant. Then, 10 parts of polyisocyanate composition B-2 in a molten state at 80 ° C. was added, and after sufficiently mechanically kneading, the mixture was supplied to a 3.5 ounce injection molding machine. The temperature of the molding machine was set to 200 ± 10 ° C. The sheet was formed by injecting from a pin gate into a mold having a postcard-sized cavity with a thickness of 2 mm. The molding state was good, and a uniform sheet almost in the same shape as the mold was obtained. The obtained sheet was subjected to heat treatment at 110 ° C. for 6 hours in a hot air drier, allowed to stand for 1 week at 25 ° C. and 50% relative humidity, and then subjected to physical property measurement according to JIS K6301. The results are shown in Table 3.

(Comparative Example 4) 90 parts of the thermoplastic polyurethane resin (A-2) was used as 98 parts and 10 parts of the polyisocyanate composition (B-2) was used as 2 parts of MDI to prevent heat treatment of the sheet. Except for this, the other conditions were the same as in Example 4, and the physical properties of the molded sheet were measured. The results are shown in Table 3.

[0047]

[Table 3] * 6: Measured according to JIS6301. It depends on the treatment conditions of 70 ° C. and 22 hours.

The lower this value, the better the recoverability. From the results in Table 3, it can be seen that in the examples of the present invention, injection-molded articles having excellent elongation at break, recovery from deformation and heat resistance can be obtained.

[0049]

EFFECTS OF THE INVENTION According to the present invention, when the thermoplastic polyurethane resin is thermoformed by extrusion molding, injection molding, melt spinning, and the like, while maintaining good moldability of the thermoplastic polyurethane resin, in particular, melt fluidity, due to its constitution. , Heat resistance, which is a drawback of molded products obtained from thermoplastic polyurethane resin,
In particular, it is possible to obtain a molded article with significantly improved recovery from deformation at high temperatures.

Claims (4)

[Claims] 1. When modifying a thermoplastic polyurethane resin (A), the polyisocyanate (B) having a terminal isocyanate group is (B) / (A) 3/97 to 25/7.
Melt-kneading at a weight ratio of 5, and the polyisocyanate (B) has an isocyanate equivalent (NC
O equivalent) 500-3000 bifunctional polyisocyanate (B1) and NCO equivalent 80-250 polyisocyanate (B2) whose average number of functional groups exceeds at least 2, and (B2) / (B1) is a weight ratio. 1/99 to 20 /
80, and a method for modifying a thermoplastic polyurethane resin, which comprises subjecting a molded product after melt-kneading to a temperature of 70 to 130 ° C. for 2 to 24 hours. 2. A bifunctional polyisocyanate (B1)
Consists of a polymeric diol having a molecular weight of 500 to 4000 and an organic diisocyanate having a molecular weight of 150 to 300, and has a molar ratio of organic diisocyanate / polymeric diol of 1.5 / 1.
The method for modifying a thermoplastic polyurethane resin according to claim 1, which is obtained by a reaction of about 4.5 / 1. 3. The thermoplastic polyurethane resin according to claim 1, wherein the compound (B2) containing a polyisocyanate having an NCO equivalent of 80 to 250 and an average number of functional groups of which exceeds at least 2 is a polymeric diphenylmethane diisocyanate. Quality method. 4. The method for modifying a thermoplastic polyurethane resin according to claim 1, wherein the molded product is a urethane elastic yarn.