JP2024075451A - Polyurethane Resin - Google Patents

Abstract

To provide a resin excellent in flexibility and fatigue resistance and difficult to be hardened in a low temperature region.SOLUTION: A polyurethane-based resin of the present disclosure contains constituent units derived from a urethane prepolymer with an aromatic diisocyanate and a diol compound as constituent units thereof, and a structural portion derived from a curing agent, the urethane prepolymer having a k value of less than 5.00, the diol compound containing polytetramethylene ether glycol and polycaprolactone diol and/or a copolymer of polytetramethylene ether glycol and caprolactone diol, and a molar ratio of polytetramethylene ether glycol units to polycaprolactone units in the urethane prepolymer [polytetramethylene ether glycol/polycaprolactone] is 3/7 or more.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to polyurethane-based resins. More specifically, the present disclosure relates to polyurethane-based resins that are preferably used in the spokes of non-pneumatic tires.

Pneumatic tires' ability to support load, absorb impact with the ground, and transmit force (accelerating, stopping, and turning) makes them the preferred choice for many vehicles, especially bicycles, motorcycles, cars, and trucks.

In recent years, non-pneumatic tires have been used as an alternative to pneumatic tires. Non-pneumatic tires are supported by structure rather than by traditional air pressure.

Spokes for use in non-pneumatic tires are known, for example, from those disclosed in Patent Documents 1 to 3, and are primarily made of ether-based polyurethane materials. It is described that the spokes in Patent Document 1 have a specific structure that makes it easier to reduce distortion and fatigue in the spokes, and reduces the occurrence and propagation of cracks.

JP 2008-260514 A JP 2015-518448 A JP 2017-501922 A

In recent years, there has been a demand for thinner spokes in order to reduce the weight of non-pneumatic tires. However, when conventional spokes are made thinner, they become more prone to bending. For this reason, there is a demand for more flexible resins.

In addition, when a vehicle equipped with non-pneumatic tires travels long distances or is driven at high speeds, the tire rotation speed increases, so the resins that make up the non-pneumatic tires and their components are required to have higher fatigue resistance.

One way to increase flexibility and fatigue resistance is to use an ether-based polyurethane resin with long soft segments. However, making the soft segments longer causes the resin to crystallize in the low temperature range, making the resin hard and reducing fatigue resistance.

Therefore, the object of this disclosure is to provide a resin that is excellent in flexibility and fatigue resistance and does not harden easily in low temperature regions. In addition, the object of this disclosure is to provide spokes that are excellent in flex resistance and fatigue resistance, and a non-pneumatic tire that includes such spokes.

As a result of intensive research conducted by the inventors to solve the above problems, they discovered that a specific polyurethane resin can be used to obtain a resin that is excellent in flexibility and fatigue resistance and does not harden easily in low temperature ranges. The present disclosure relates to a product that has been completed based on these findings.

That is, the present disclosure relates to a polyurethane elastomer composition comprising a structural unit derived from a urethane prepolymer having an aromatic diisocyanate and a diol compound as structural units, and a structural portion derived from a curing agent,
the urethane prepolymer has a k value of less than 5.00;
The diol compound includes polytetramethylene ether glycol and polycaprolactone diol, and/or a copolymer of polytetramethylene ether glycol and caprolactone diol;
The polyurethane resin has a molar ratio of polytetramethylene ether glycol units to polycaprolactone units in the urethane prepolymer [polytetramethylene ether glycol/polycaprolactone] of 3/7 or more.

The aromatic diisocyanate preferably includes diphenylmethane diisocyanate.

The number average molecular weight of the diol compound is preferably 4,000 or less.

The polycaprolactone diol preferably contains polycaprolactone diol using diethylene glycol as an initiator.

The curing agent preferably contains 1,4-butanediol.

The molar ratio of isocyanate groups to hydroxyl groups [NCO/OH] is preferably 0.90 to 1.10.

The polyurethane resin is preferably used for the spokes of non-pneumatic tires.

The present disclosure also provides a spoke for a non-pneumatic tire that includes the polyurethane-based resin.

The present disclosure also provides a non-pneumatic tire comprising an outer reinforced annular band, a hub, and spokes extending radially inwardly of the annular band and between the hub.

The polyurethane resin of the present disclosure has excellent flexibility and fatigue resistance, and does not harden easily in low temperature ranges. Therefore, the polyurethane resin can be used to manufacture spokes with excellent flex resistance and fatigue resistance.

FIG. 1 is a schematic diagram illustrating one embodiment of a non-pneumatic tire having spokes using the polyurethane-based resin of the present disclosure. 1 is a graph showing DMA charts of Example 3 and Comparative Example 4.

[Polyurethane resin]
The polyurethane resin of the present disclosure contains at least a structural unit derived from a urethane prepolymer having an aromatic diisocyanate and a diol compound as structural units, and a structural part derived from a curing agent. That is, the polyurethane resin is a resin obtained by reacting a urethane prepolymer having an aromatic diisocyanate and a diol compound as structural units with a curing agent, and, if necessary, with other components.

(Urethane prepolymer)
The urethane prepolymer is a prepolymer obtained by reacting an isocyanate containing an aromatic diisocyanate, a polyol containing a diol compound, and, if necessary, other components.

The k value of the urethane prepolymer (i.e., the molar ratio of polyisocyanate to polyol constituting the urethane prepolymer [polyisocyanate/polyol]) is less than 5.00, preferably 4.80 or less, more preferably 4.50 or less, and even more preferably 4.30 or less. When the k value is less than 5.00, a polyurethane resin having high flexibility and fatigue resistance is obtained. The permanent deformation is small, and the temperature stability of the resin is excellent. The k value may be within a range that does not impair the curing of the present invention, and may be, for example, 3.50 or more, or 4.00 or more.

Examples of the aromatic diisocyanate include tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), 4,4'-diisocyanato-3,3'-dimethylbiphenyl (tolidine diisocyanate (TODI)), 4,4'-dibenzyl diisocyanate, 1,5-naphthylene diisocyanate (NDI), xylylene diisocyanate, 1,3-phenylene diisocyanate, and 1,4-phenylene diisocyanate (PPDI). Among these, TDI, MDI, TODI, NDI, and PPDI are preferred, and MDI is more preferred. Examples of MDI include 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, and 4,4'-diphenylmethane diisocyanate. The aromatic diisocyanates may be used alone or in combination of two or more.

The urethane prepolymer may contain, as a diisocyanate constituent unit, a diisocyanate other than the aromatic diisocyanate. Examples of the other diisocyanates include aliphatic diisocyanates and alicyclic diisocyanates. Only one type of the other diisocyanates may be used, or two or more types may be used.

Examples of the aliphatic diisocyanates include 1,4-tetramethylene diisocyanate, 1,5-pentamethylene diisocyanate, 1,6-hexamethylene diisocyanate, 1,7-heptamethylene diisocyanate, 1,8-octamethylene diisocyanate, 1,9-nonamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, 2,4,4-trimethylhexamethylene diisocyanate, and 1,10-decamethylene diisocyanate.

Examples of the alicyclic diisocyanates include 1,3-cyclohexane diisocyanate, 1,4-cyclohexane diisocyanate, 1,3-bis(isocyanatemethyl)cyclohexane, 1,4-bis(isocyanatemethyl)cyclohexane, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, and norbornene diisocyanate.

The proportion of aromatic diisocyanate (particularly MDI) in the isocyanate constituting the urethane prepolymer is preferably 60 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more, relative to 100 mol% of the total amount of the isocyanate.

The diol compound includes polytetramethylene ether glycol and polycaprolactone diol, and/or a copolymer of polytetramethylene ether glycol and caprolactone diol. That is, in one embodiment, the diol compound includes polytetramethylene ether glycol and polycaprolactone diol. In another embodiment, the diol compound includes a copolymer of polytetramethylene ether glycol and caprolactone diol. The diol compound may include all of polytetramethylene ether glycol, polycaprolactone diol, and a copolymer of polytetramethylene ether glycol and caprolactone diol. Only one type of the diol compound may be used, or two or more types may be used.

When the copolymer is used as the diol compound, the composition containing the urethane prepolymer and the curing agent described below has a lower viscosity and is excellent in workability, and thickening over time is suppressed, resulting in excellent storage stability, compared to when the polytetramethylene ether glycol and polycaprolactone diol are mixed. In addition, the polytetramethylene ether glycol and polycaprolactone diol may be incompatible, in which case the block arrangement in the prepolymer differs from lot to lot, causing variations in the physical properties of the polyurethane resin and making stable production difficult. In contrast, when the copolymer is used, there is no need to consider compatibility, the transparency of the urethane prepolymer is excellent, and variations in the diol compound between lots are unlikely to occur, resulting in excellent production stability.

The number average molecular weight of polytetramethylene ether glycol is preferably 4000 or less, more preferably 3000 or less, and even more preferably 2500 or less. If the number average molecular weight is 4000 or less, the polyurethane resin is less likely to harden in the low temperature range. The number average molecular weight is preferably 500 or more, more preferably 1000 or more, and even more preferably 1500 or more. If the number average molecular weight is 500 or more, the flexibility of the polyurethane resin is further improved.

The polycaprolactone diol is obtained by ring-opening polymerization of ε-caprolactone using a compound having two or more hydroxyl groups as an initiator. In other words, the polycaprolactone diol has a structure in which the initiator and (poly)caprolactone are bonded to two or more hydroxyl groups of the initiator.

As the above initiator, diols having four or less repeating units, such as ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, diethylene glycol, and dipropylene glycol, are preferred, and diethylene glycol is more preferred.

The number average molecular weight of the polycaprolactone diol is preferably 4000 or less, more preferably 3000 or less, and even more preferably 2500 or less. If the number average molecular weight is 4000 or less, the polyurethane resin is less likely to harden in the low temperature range. The number average molecular weight is preferably 500 or more, more preferably 1000 or more, and even more preferably 1500 or more. If the number average molecular weight is 500 or more, the flexibility of the polyurethane resin is further improved.

The copolymer of polytetramethylene ether glycol and caprolactone diol may be any known or conventional copolymer, and among these, polycaprolactone diol using polytetramethylene ether glycol as an initiator is preferred. The polycaprolactone diol is obtained by ring-opening polymerization of ε-caprolactone using polytetramethylene ether glycol as an initiator.

The number average molecular weight of the copolymer is preferably 4000 or less, more preferably 3000 or less, and even more preferably 2500 or less. If the number average molecular weight is 4000 or less, the polyurethane resin is less likely to harden in the low temperature range. The number average molecular weight is preferably 500 or more, more preferably 1000 or more, and even more preferably 1500 or more. If the number average molecular weight is 500 or more, the flexibility of the polyurethane resin is further improved.

The number average molecular weight of the diol compound is preferably 4000 or less, more preferably 3000 or less, and even more preferably 2500 or less. If the number average molecular weight is 4000 or less, the polyurethane resin is less likely to harden in the low temperature range. The number average molecular weight is preferably 500 or more, more preferably 1000 or more, and even more preferably 1500 or more. If the number average molecular weight is 500 or more, the flexibility of the polyurethane resin is further improved. The number average molecular weight of the diol compound is a value calculated as a weighted average of the multiple diol compounds that constitute the prepolymer.

The urethane prepolymer may contain, as a diol constituent unit, polytetramethylene ether glycol, polycaprolactone diol, and other diol compounds other than the copolymer. Only one type of the other diol compounds may be used, or two or more types may be used.

The proportion of the diol compound (particularly one or more selected from the group consisting of polytetramethylene ether glycol, polycaprolactone diol, and the above copolymer) in the polyol constituting the above urethane prepolymer is preferably 60 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more, relative to 100 mol% of the total amount of the above polyol.

The molar ratio of polytetramethylene ether glycol units to polycaprolactone units in the urethane prepolymer [polytetramethylene ether glycol/polycaprolactone] is 3/7 or more, preferably 5/5 or more, and more preferably 6/4 or more. When the molar ratio is 3/7 or more, the polyurethane resin has excellent flexibility and fatigue resistance. The molar ratio is preferably 9/1 or less.

The proportion of residual isocyanate groups in the urethane prepolymer (residual NCO) is preferably 5.0 to 13.0 mol %, more preferably 7.0 to 11.0 mol %, relative to the total amount (100 mol %) of isocyanate groups in all isocyanates used to form the urethane prepolymer. When the residual NCO is within the above range, the curing reaction by the curing agent proceeds appropriately.

The urethane prepolymer is obtained by reacting an isocyanate containing the aromatic diisocyanate with a polyol containing the diol compound, and, if necessary, other components. The reaction can be carried out by a known or conventional method.

(Hardening agent)
As the curing agent, a known or conventional chain extender used as a chain extender for polyurethane resins can be used. The curing agent may be used alone or in combination of two or more kinds.

Examples of the curing agent include diols such as ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,2-pentanediol, 2,3-pentanediol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, 1,4-cyclohexanediol, and 1,4-cyclohexanedimethanol; and diamines such as hexamethylenediamine, 3,3'-dimethyl-4,4'-diaminodicyclohexylmethane, and 4,4'-methylenebis-2-chloroaniline. Among these, diols are preferred, more preferably ethylene glycol, 1,3-propanediol, and 1,4-butanediol, and particularly preferably 1,4-butanediol.

The proportion of 1,4-butanediol in the curing agent is preferably 60 mol% or more, more preferably 80 mol% or more, even more preferably 90 mol% or more, and particularly preferably 95 mol% or more, relative to 100 mol% of the total amount of the curing agent.

The content of the curing agent (particularly 1,4-butanediol) is preferably 6 to 10 parts by mass, and more preferably 8 to 9 parts by mass, per 100 parts by mass of the total amount of the urethane prepolymer. If the content is within the above range, the flexibility of the polyurethane resin is superior.

(Polyurethane resin)
The molar ratio of isocyanate groups to hydroxyl groups in the polyurethane resin [NCO/OH] is preferably 0.90 to 1.10, more preferably 0.95 to 1.05. When the molar ratio is within the above range, a polyurethane resin that is flexible and has high fatigue resistance is easily obtained. The hydroxyl groups include the hydroxyl groups contained in the diol compound and the hydroxyl groups that the curing agent may have.

The polyurethane resin preferably has a tensile modulus of 45% or less, more preferably 40% or less, measured at 23°C and 10% elongation in accordance with JIS K7161. If the tensile modulus is 45% or less, the flexibility of the polyurethane resin is superior. From the viewpoint of having adequate strength, the tensile modulus is preferably 20% or more, more preferably 25% or more.

The polyurethane resin preferably has a storage modulus at 23°C (sometimes referred to as "E' (23°C)") of 70 to 130 MPa, more preferably 80 to 120 MPa, and even more preferably 90 to 110 MPa. If the E' (23°C) is 70 MPa or more, the hardness tends to be high and the function of supporting the vehicle body becomes more sufficient. If the E' (23°C) is 130 MPa or less, the flexibility becomes higher and the deformation becomes more difficult.

The polyurethane resin preferably has a storage modulus at 100°C (sometimes referred to as "E'(100°C)") of 40 to 90 MPa, more preferably 50 to 80 MPa. The maximum temperature experienced when heat is stored in the tire is around 100°C. When E'(100°C) is within the above range, the rate of change from the storage modulus at room temperature is low, and the thermal stability is excellent.

The rate of decrease in E'(100°C) relative to E'(23°C) (sometimes referred to as "E' decrease rate") is preferably less than 45%, more preferably 43% or less, and even more preferably 40% or less. When the E' decrease rate is less than 45%, the temperature stability of the elastic change is superior, and when the polyurethane resin is used as a constituent material of a non-pneumatic tire, the ride comfort of the vehicle is improved. The E' decrease rate is a value calculated by the following formula.
E' decrease rate = {E' (23°C) - E' (100°C)} / E' (23°C) x 100

The tan δ of the polyurethane resin at 23°C is preferably 0.080 or less, more preferably 0.070 or less, and even more preferably 0.064 or less. If the tan δ is low, there is a tendency for the resin to have excellent fatigue resistance because less heat is generated when it receives external energy. In addition, the tan δ is, for example, 0.040 or more. The tan δ can be measured using a known or commonly used viscoelasticity measuring device.

It is preferable that the polyurethane resin does not show a shoulder peak between -40°C and 40°C (preferably -60°C and 40°C) in the DMA chart obtained by viscoelasticity measurement. In this case, the polyurethane resin does not harden easily in the low temperature range.

The polyurethane resin preferably has a permanent tensile set of 15% or less, more preferably 14% or less, and even more preferably 12% or less, measured at 23°C and 10% elongation in accordance with JIS K7312. The lower the permanent tensile set, the better the durability against the load on the vehicle body when stopped and the fatigue resistance against bending while driving.

The polyurethane resin is preferably bent 120,000 times or more, more preferably 150,000 times or more, even more preferably 180,000 times or more, and particularly preferably 200,000 times or more, using a DeMatcha flex fatigue test in accordance with JIS K7312, in which a crack is first introduced into a test piece using a crack growth test method, until the crack grows and breaks. The higher the number of flexes, the better the fatigue resistance.

It is preferable that the polyurethane resin does not substantially contain any structural units derived from components other than the above-mentioned components (components other than polyisocyanate, polyol, and curing agent). In this specification, "substantially does not contain" means that no structural units are actively added except for impurities contained in the raw materials, and may be, for example, 1% by mass or less.

The polyurethane resin can be produced by a known or conventional molding method using a composition containing the urethane prepolymer and the curing agent. For example, it can be molded using a general molding machine for thermoplastic resins, such as extrusion molding, injection molding, or heat press molding.

The viscosity of the composition at 60°C is preferably 4000 mPa·s or less, more preferably 3000 mPa·s or less, and even more preferably 2000 mPa·s or less. If the viscosity is low, the composition is easier to handle, the viscosity during molding is low, and the arrangement in the resulting polyurethane resin can be maintained, resulting in stable quality. The viscosity is, for example, 500 mPa·s or more, and may be 1000 mPa·s or more.

The time it takes for the viscosity of the composition to increase to 100% torque is preferably 150 seconds or more, more preferably 200 seconds or more, and even more preferably 300 seconds or more.

The polyurethane resin may be blended with additives (such as release agents, plasticizers, colorants, antioxidants, UV stabilizers, heat stabilizers, crosslinking agents, foaming agents, foam stabilizers, urethane catalysts, and fillers) to form a polyurethane resin composition. The additives may be blended with the raw material components before the reaction of the urethane prepolymer and the curing agent, or may be blended by melt kneading the polyurethane resin obtained by the reaction.

[Molded body]
The polyurethane resin can be molded into a molded article, for example, by a method in which a liquid molding material before the reaction is shaped and then reacted and solidified to form a molded article, a method in which the material is softened and melted by heating after the reaction to form a molded article, or a method in which the material is dissolved in a solution after the reaction to form a molded article.

Specific examples of molding methods include, but are not limited to, known or commonly used molding methods such as coating, cast molding, vacuum molding, extrusion molding, calendar molding, blow molding, inflation molding, rotational molding, slush molding, foam molding, compression molding, stamping molding, casting, and dipping.

Specific examples of the above molded article include, but are not limited to, films, sheets, hoses, tubes, packing materials, vibration-proofing materials, bonding materials, paint films, coating materials, fibers, foams, synthetic leather, and elastic bodies. The above molded articles can be preferably used in a wide range of applications, such as clothing and non-clothing products, packaging materials, household and miscellaneous goods, furniture parts, machine parts, electrical and electronic parts, automobile and other vehicle parts, industrial product components, civil engineering and construction materials, agricultural products, fishing supplies, gardening supplies, sanitary products, medical and nursing care products, and sports and leisure products.

The molded article is preferably used for the spokes of non-pneumatic tires. That is, the polyurethane resin is preferably used for the spokes of non-pneumatic tires because it has excellent flexibility and fatigue resistance and does not harden easily in low temperature regions. In this case, the spokes of the non-pneumatic tire contain at least the polyurethane resin.

[Non-pneumatic tires]
The non-pneumatic tire may, for example, include a non-pneumatic tire including an outer reinforced annular band, a hub, and spokes extending radially inwardly of the annular band and between the hub, the spokes being formed from the polyurethane-based resin.

One embodiment of the non-pneumatic tire is shown in FIG. 1. The non-pneumatic tire 1 shown in FIG. 1 includes an annular band 2 with a reinforced outer ring, a hub 3, and spokes 4 extending between the radially inner side of the annular band 2 (i.e., the center side of the annular band 2) and the hub 3. The outer side of the annular band 2 is reinforced by a tread 5. The hub 3 is annular and is set on a wheel (not shown). A plurality of spokes 4 are provided radially from the center of the annular band 2 so as to connect the hub 3 and the annular band 2. The spokes 4 are formed from the polyurethane-based resin of the present disclosure.

The polyurethane resin of the present disclosure has excellent flexibility and fatigue resistance, and does not harden easily in the low temperature range. Therefore, the polyurethane resin can be used to manufacture spokes with excellent flex resistance and fatigue resistance. In addition, when a non-pneumatic tire rotates, heat may accumulate up to about 100°C. Therefore, the heat accumulation property and temperature change of the elastic modulus of a non-pneumatic tire affect not only fatigue resistance but also ride comfort. When the polyurethane resin has low distortion and low tan δ, it can improve the temperature stability of elasticity change. Therefore, when the polyurethane resin is used for the spokes, the ride comfort of the vehicle can also be excellent.

Each aspect disclosed in this specification may be combined with any other feature disclosed in this specification. Each configuration in each embodiment and their combinations are merely examples, and additions, omissions, substitutions, and other modifications of configurations are possible as appropriate within the scope of the spirit of this disclosure. Furthermore, each invention related to this disclosure is not limited by the embodiments or the following examples, but is limited only by the scope of the claims.

One embodiment of the present disclosure will be described in more detail below based on examples, but the present disclosure is not limited to these examples.

Example 1
(Preparation of Prepolymer)
Into the flask, polytetramethylene ether glycol (PTMG) (trade name "PTMG2000", theoretical molecular weight 2000, manufactured by Mitsubishi Chemical Corporation) and polycaprolactone diol (PCL) (trade name "PLACCEL 220UA", molecular weight 2000, initiator: diethylene glycol, manufactured by Daicel Corporation) were added as polyols so that the molar ratio [PTMG/PCL] was 4/6. Then, diphenylmethane diisocyanate (MDI) (trade name "Millionate MT", manufactured by Tosoh Corporation) was added to the flask so that the k value was 4.25, and the reaction was carried out at 80°C until the residual NCO% was 9.0%, to obtain a prepolymer.

(Preparation of polyurethane test pieces)
The prepolymer obtained above and 1,4-butanediol (1,4-BG) (manufactured by Mitsubishi Chemical Corporation) as a chain extender were charged into a cup container so that the molar ratio [NCO/OH] was 1.03, and the mixture was uniformly mixed and degassed using a planetary stirring device (product name "Thinner AR-250", manufactured by Thinky Corporation) to obtain a liquid molding material. The obtained liquid molding material was poured into a mold, and the mold was heated in an oven at 120°C for 16 hours to harden it, and then further aged in a constant temperature and humidity environment of 23°C and 50% RH for 48 hours to produce a polyurethane test piece (rectangular, length 13 mm, width 20 mm, thickness 2 mm).

Examples 2 to 3
Prepolymer and polyurethane test pieces were prepared in the same manner as in Example 1, except that the amounts of PTMG and PCL added were changed so that [PTMG/PCL] would have the values shown in Table 1.

Example 4
Prepolymer and polyurethane test pieces were prepared in the same manner as in Example 1, except that a copolymer of polytetramethylene ether glycol (PTMG) and polycaprolactone (product name "PLACCEL T2205T", molecular weight 2000, manufactured by Daicel Corporation) was used as the polyol.

Comparative Example 1
Polyurethane test pieces were prepared in the same manner as in Example 1, except that a PTMG-MDI prepolymer (product name "VIBRATHANE B836", manufactured by LANXESS) was used as the prepolymer.

Comparative Example 2
Prepolymer and polyurethane test pieces were prepared in the same manner as in Example 1, except that polytetramethylene ether glycol (PTMG) (product name "PTMG2000", theoretical molecular weight 2000, manufactured by Mitsubishi Chemical Corporation) was used as the polyol and the k value and residual NCO % were changed as shown in Table 1.

Comparative Example 3
Prepolymer and polyurethane test pieces were prepared in the same manner as in Example 1, except that the k value and the residual NCO % were changed as shown in Table 1.

Comparative Example 4
Prepolymer and polyurethane test pieces were prepared in the same manner as in Example 1, except that polytetramethylene ether glycol (PTMG) (product name "PTMG2000", theoretical molecular weight 2000, manufactured by Mitsubishi Chemical Corporation) was used as the polyol.

Example 5
Prepolymer and polyurethane test pieces were prepared in the same manner as in Example 1, except that the amounts of PTMG and PCL added were changed so that [PTMG/PCL] would have the values shown in Table 1.

<Evaluation>
The liquid molding materials, prepolymers, and polyurethane test pieces prepared in the examples and comparative examples were evaluated as follows. The results are shown in Table 2.

(1) Tensile Modulus of Elasticity: Measured in accordance with JIS K7161 at a temperature of 23° C. and at a 10% elongation.

(2) Storage Modulus Using a viscoelasticity measuring device (product name "DMA7100", manufactured by Hitachi High-Tech Science Corporation), a test piece of 40 mm × 10 mm × (t) 2 mm was measured under the following conditions: chuck distance 20 mm, temperature -100 to 200°C, heating rate 2°C/min, frequency 10 Hz, initial strain, dynamic strain 0.05, and tensile mode. E' and tan δ at each temperature were read, and the rate of decrease in E' was calculated.
E' decrease rate = {E' (23°C) - E' (100°C)} / E' (23°C) x 100

(3) Cold hardening
In the DMA chart obtained by the above-mentioned measurement of storage modulus, those in which a shoulder peak was confirmed between -60°C and 40°C were evaluated as "with cold hardening", and those in which a shoulder peak was not confirmed were evaluated as "without cold hardening". The DMA charts of Example 3 and Comparative Example 4 are shown in Figure 2. It should be noted that, since [PTMG/PCL] is smaller in Examples 1, 2, and 4 than in Example 3, the shoulder peak is less easily confirmed.

(4) Tensile Set: Measured in accordance with JIS K7312 at a temperature of 23° C. and at a 10% elongation.

(5) Fatigue resistance In accordance with JIS K7312, a DeMatia flexural fatigue test was used. A crack was first introduced into a test piece using the crack growth test method, and the test piece was flexed a total of 200,000 times. The number of times the crack grew until the test piece broke was counted and calculated every 10,000 times, and the number of flexures was recorded.

(6) Viscosity The viscosity of the liquid molding material was measured at 60° C. and 10 rpm using an E-type viscometer (product name "VISCOMETER TV-22", manufactured by Toki Sangyo Co., Ltd.).

(7) Pot Life The liquid molding material was continuously stirred at 60° C. and 10 rpm using an E-type viscometer (product name "VISCOMETER TV-22", manufactured by Toki Sangyo Co., Ltd.), and the time until the torque reached 100% was measured, which was taken as the pot life.

(8) Appearance of Prepolymer The degree of cloudiness of the prepolymer was evaluated by visual inspection.

As shown in Table 2, the polyurethane test pieces of the examples were judged to have a low tensile modulus and excellent flexibility. In addition, it was judged that there was no cold hardening and that it was difficult to harden in the low temperature range. In addition, the number of flexions was more than 120,000, and it was judged to have excellent fatigue resistance. In all of the examples, the effects of a low tensile modulus and excellent flexibility, a large number of flexions, and excellent fatigue resistance were confirmed compared to Comparative Example 1, which used a known prepolymer. And when polycaprolactone diol was not used as the polyol (Comparative Examples 2 and 4), when the k value was 5.00 or more (Comparative Example 3), and when [PTMG/PCL] was less than 3/7 (Comparative Example 5), it was judged that the number of flexions was low and fatigue resistance was poor.

In addition, Example 4, which used a copolymer of PTMG and polycaprolactone as the polyol, had a lower viscosity, a longer pot life, and a higher prepolymer transparency than the other Examples.

Variations of the invention according to the present disclosure are described below.
[Appendix 1] A polyurethane prepolymer having an aromatic diisocyanate and a diol compound as structural units, and a structural part derived from a curing agent,
the urethane prepolymer has a k value of less than 5.00;
the diol compound comprises polytetramethylene ether glycol and polycaprolactone diol, and/or a copolymer of polytetramethylene ether glycol and caprolactone diol;
A polyurethane resin in which the molar ratio of polytetramethylene ether glycol units to polycaprolactone units in the urethane prepolymer [polytetramethylene ether glycol/polycaprolactone] is 3/7 or more.
[Appendix 2] The polyurethane resin according to appendix 1, wherein the aromatic diisocyanate includes diphenylmethane diisocyanate.
[Appendix 3] The polyurethane resin according to appendix 1 or 2, wherein the diol compound has a number average molecular weight of 4,000 or less.
[Appendix 4] The polyurethane-based resin according to any one of Appendices 1 to 3, wherein the polycaprolactone diol contains polycaprolactone diol using diethylene glycol as an initiator.
[Appendix 5] The polyurethane-based resin according to any one of Appendices 1 to 4, wherein the curing agent comprises 1,4-butanediol.
[Appendix 6] The polyurethane-based resin according to any one of Appendices 1 to 5, wherein the molar ratio of isocyanate groups to hydroxyl groups [NCO/OH] is 0.90 to 1.10.
[Appendix 7] The polyurethane-based resin according to any one of Appendices 1 to 6, which is used for spokes of a non-pneumatic tire.
[Appendix 8] A spoke of a non-pneumatic tire comprising the polyurethane resin according to any one of appendices 1 to 6.
[Appendix 9] A non-pneumatic tire comprising an outer reinforced annular band, a hub, and spokes according to appendix 8 extending radially inwardly of the annular band and between the hub.

1 Non-pneumatic tire 2 Annular band 3 Hub 4 Spokes 5 Tread

Claims (9)

The polyurethane resin composition includes a structural unit derived from a urethane prepolymer having an aromatic diisocyanate and a diol compound as structural units, and a structural part derived from a curing agent,
the urethane prepolymer has a k value of less than 5.00;
the diol compound comprises polytetramethylene ether glycol and polycaprolactone diol, and/or a copolymer of polytetramethylene ether glycol and caprolactone diol;
A polyurethane resin in which the molar ratio of polytetramethylene ether glycol units to polycaprolactone units in the urethane prepolymer [polytetramethylene ether glycol/polycaprolactone] is 3/7 or more. The polyurethane resin according to claim 1, wherein the aromatic diisocyanate includes diphenylmethane diisocyanate. The polyurethane resin according to claim 1 or 2, wherein the number average molecular weight of the diol compound is 4,000 or less. The polyurethane resin according to claim 1 or 2, wherein the polycaprolactone diol includes polycaprolactone diol using diethylene glycol as an initiator. The polyurethane resin according to claim 1 or 2, wherein the curing agent contains 1,4-butanediol. The polyurethane resin according to claim 1 or 2, in which the molar ratio of isocyanate groups to hydroxyl groups [NCO/OH] is 0.90 to 1.10. The polyurethane resin according to claim 1 or 2, which is used for the spokes of non-pneumatic tires. A spoke of a non-pneumatic tire comprising the polyurethane resin according to claim 1 or 2. A non-pneumatic tire comprising an outer reinforced annular band, a hub, and spokes according to claim 8 extending radially inwardly of the annular band and between the hub.

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