JP6886354B2 - Polyurethane foam - Google Patents

Description

The present invention relates to a polyurethane foam suitable as a material for a shoe sole member, and more particularly to a polyurethane foam having durability, shock absorption, and resilience, and also having excellent bending resistance.

The midsole that makes up the sole has "shock absorption to absorb and mitigate the impact on the foot,""repulsion to assist kicking," and "anti-cracking due to flexion of the sole." (That is, bending resistance) "is required.
The ethylene-vinyl acetate copolymer (EVA) foam, which is often used as a material for the midsole, is lightweight and has shock absorption and bending resistance, but has insufficient resilience and large compression set. There were drawbacks such as. It should be noted that a material having a large compression set is inferior in durability because it will settle when used for a long period of time in an application where a constant load is applied.

Therefore, the applicant has developed a polyurethane foam having "durability", "shock absorption" and "repulsion" which is a performance contrary to the "durability" (see Patent Document 1), and further "tolerance". We have proposed a polyurethane foam with improved flexibility (see Patent Document 2).

On the other hand, as a sole, a midsole having shock absorption and a laminated structure in which an outsole having abrasion resistance and anti-slip property is provided on the ground contact surface side of the midsole are known. A rubber material is often used for the outsole, but the rubber material has a high specific gravity, and it is necessary to reduce the used area when reducing the weight of the shoe. For example, the outsole of an arbitrary shape may be arranged only in a place where wear resistance and anti-slip property are required, such as a toe part, a stepping part, and a heel part. Further, in a place where the shoe is easily bent such as a stepping portion, a part of the outsole is cut out to expose the midsole, so that the weight of the shoe and the flexibility can be improved.
However, in this way, when the outsole of any shape is placed at any place or the midsole is partially exposed on the ground contact surface side by cutting out a part of the outsole, the outsole A load is likely to be applied to the boundary portion with. Therefore, if the bending resistance of the midsole is insufficient, the midsole may be cracked depending on the usage conditions.

Japanese Unexamined Patent Publication No. 2016-069658 Japanese Patent Application No. 2015-240109

In consideration of the above situation, it is an object of the present invention to provide a polyurethane foam which is durable, has shock absorption and repulsion which is a performance contrary to the shock absorption, and is also excellent in bending resistance. To do.

In order to solve the above problems, the present inventors have conducted diligent studies, and as a result,
Focusing on the use of polytetramethylene ether glycol (PTMG) as the polyol component, this is obtained by reacting with a polyisocyanate component containing i) an isocyanate group-terminated prepolymer and ii) a modified MDI in a specific compounding ratio. Polyurethane foams that have a specific average cell size and are uniform with no variation in cell size not only have excellent shock absorption, high resilience, and durability, but also have improved bending resistance. We have found that this can be achieved, and have completed the present invention.

That is, the present invention has the following gist;
(1) A polyurethane foam made of a polyurethane raw material containing a polyol component, a polyisocyanate component, a foaming agent, a catalyst, and a foam stabilizer.
The polyol component is a polytetramethylene ether glycol having a number average molecular weight of 300 to 3000, an average number of functional groups of 2 , and an average hydroxyl value of 50 to 200 mgKOH / g.
The polyisocyanate component is
i) An isocyanate group-terminated prepolymer having a number average molecular weight of 500 to 2000, an average number of functional groups of 2 to 3, and an isocyanate group content of 3 to 10% by mass.
ii) Containing modified MDI having an isocyanate group content of 25 to 33% by mass,
The content ratio of the prepolymer of the above i) and the modified MDI of the above ii) is 97/3 to 80/20 by weight, and the isocyanate index is 0.80 to 0.95.
The average cell size is 30 to 100 μm, and cells with a cell size of 20 to 300 μm occupy 90% or more of all cells.
A polyurethane foam characterized by having a compression set of 20% or less measured in accordance with JIS K 6262 and having bending resistance.
(2) The polyurethane foam according to (1) above, which is a molded product.
(3) The operation of bending a polyurethane foam having a length of 120 mm, a width of 60 mm, and a thickness of 6 mm to which a resin-impregnated board having a thickness of 2 mm is adhered at 90 ° and returning immediately after that is performed 144 times / minute. The polyurethane foam according to any one of (1) and (2) above, which is repeated at a high speed and the number of times until cracks occur is 100,000 times or more.
(4) A shoe sole member using the polyurethane foam according to any one of (1) to (3) above.

In the present specification, the isocyanate group-terminated prepolymer refers to a prepolymer having an isocyanate group at the terminal, and the isocyanate index refers to a molar ratio of NCO group / OH group.

The polyurethane foam of the present invention reacts a polyurethane raw material containing a polyol component composed of PTMG, a polyisocyanate component containing an isocyanate group-terminated prepolymer and a modified MDI in a specific blending ratio, a foaming agent, a catalyst, and a foam stabilizer. It is obtained, and further, by setting a specific average cell size and forming a uniform foam with no variation in cell size, it is excellent in shock absorption, but has resilience and small compression set. In addition to being excellent in durability, it has strong bending resistance.

Such a polyurethane foam of the present invention is suitable for a sole member (for example, a midsole) that is constantly loaded and requires both shock absorbing and repulsive functions, and has been used for a long period of time. However, it is possible to obtain shoes whose soles are not easily deformed or broken and whose soles can always be bent appropriately. In particular, when the polyurethane foam of the present invention is used for the midsole and an outsole made of a rubber material is provided on the ground contact surface side of the midsole to form a sole with a laminated structure, an outsole having an arbitrary shape can be provided at any location. Even if the midsole on the ground surface side is partially exposed by arranging or cutting out a part of the outsole, the midsole cracks at the boundary with the outsole where a load is easily applied. do not.
Further, the shoes using the polyurethane foam as the sole member can reliably absorb the impact on the foot during walking or running, and can sufficiently support the kicking of the foot.

It is a figure explaining the shape of the weight used in the drop impact test.

The polyurethane foam of the present invention is obtained by reacting a polyurethane raw material containing a polyol component, a polyisocyanate component, a foaming agent, a catalyst, and a foam stabilizer.

[Polycarbonate component]
As the polyol component, polytetramethylene ether glycol having a number average molecular weight of 300 to 3000, an average number of functional groups of 2 to 3, and an average hydroxyl value of 50 to 200 mgKOH / g (hereinafter, number average molecular weight, average number of functional groups, average hydroxyl group). Polytetramethylene ether glycol having a value within the above range is also referred to as "PTMG-I").
In the present invention, two or more types of PTMG-I having different number average molecular weights may be mixed and used.

When the number average molecular weight of PTMG-I is less than 300 or the average hydroxyl value exceeds 200 mgKOH / g, the cell size of the obtained urethane foam tends to be non-uniform or the flexibility is likely to be impaired, resulting in the desired resistance. Flexibility cannot be obtained.
On the other hand, when the number average molecular weight exceeds 3000 or the average hydroxyl value is less than 50 mgKOH / g, the ratio of soft segments (parts where the bonds are relatively soft in the polymer chain; in the case of polyurethane, refers to alkyl chains, etc.) The amount of the polyurethane foam is increased, and the shock absorption of the obtained polyurethane foam is easily obtained, but the desired resilience cannot be obtained.
The preferred range is a number average molecular weight of 1000 to 2500, an average number of functional groups of 2 to 3, and an average hydroxyl value of 50 to 100 mgKOH / g.

In the present invention, it is preferable not to use a polyoxypropylene-based polyol or a diol together with the above-mentioned PTMG-I as the polyol component. If they are used together, the resulting foam will be inferior in elongation and tensile strength, and in applications such as shoe sole members, cracks are likely to occur during bending.
If necessary, a cross-linking agent may be added to the polyol component.
Examples of the cross-linking agent include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, neopentyl glycol, tetramethylene ether glycol, glycerin, pentaerythritol, trimethylolpropane, monoethanolamine, diethanolamine, isopropanolamine, and amino. Alcohols such as ethylethanolamine, sucrose, sorbitol and glucose can be used. In particular, among these, those having three or more functionalities are preferable.

[Polyisocyanate component]
The polyisocyanate component of the present invention contains i) an isocyanate group-terminated prepolymer described later and ii) a modified MDI described later in a blending ratio (weight ratio) of 97/3 to 80/20.
The modified MDI is obtained by modifying MDI (diphenylmethane diisocyanate), which is solid at room temperature, so as to be liquid at room temperature.
Since the i) isocyanate group-terminated prepolymer described later has a large molecular weight and a high viscosity, the viscosity can be lowered by mixing ii) modified MDI. Therefore, as a result of omitting the addition of the plasticizer, there is no risk of bleeding out of the plasticizer from the foam surface when it is actually used for a shoe sole member or the like. When bleed-out occurs, it becomes inferior in handleability, for example, it hinders adhesion to other members.
Further, since i) the isocyanate group-terminated prepolymer described later has a low isocyanate group content, i) alone is inferior in foamability, and it is difficult to reduce the density of the obtained polyurethane foam. Therefore, by mixing ii) modified MDI, the isocyanate group content can be increased, and the density of the polyurethane foam can be easily reduced.

In the present invention, by using i) and ii) in combination as described above, physical properties such as bending resistance, shock absorption, and resilience are ensured even if the density of the foam is reduced (weight reduction). Can be enhanced to.
If the blending ratio of ii) to i) is larger than this, not only the desired resilience cannot be obtained, but also the foam is liable to crack when repeatedly bent, resulting in a foam having poor bending resistance. On the contrary, even if the compounding ratio of ii) to i) is less than this, sufficient bending resistance cannot be obtained.

i) Isocyanate group-terminated prepolymer;
i) As the isocyanate group-terminated prepolymer, those having a number average molecular weight of 500 to 2000, an average number of functional groups of 2 to 3, and an isocyanate group content of 3 to 10% by mass are used.
If the number average molecular weight exceeds 2000 or the NCO group content is less than 3% by mass, the obtained polyurethane foam is difficult to foam and becomes too hard, and not only the desired bending resistance cannot be obtained. It has a high viscosity and tends to be difficult to mix with other materials. On the other hand, if the number average molecular weight is less than 500 or the NCO group content is more than 10% by mass, the obtained polyurethane foam is easily foamed and becomes too soft, and desired shock absorption and resilience can be obtained. I can't.

The above i) isocyanate group-terminated prepolymer can be obtained by reacting a polyol and a polyisocyanate so that the isocyanate group (NCO group) becomes excessive (NCO group content is 3 to 10% by mass).
As this polyol,
α) Polyether polyol, polyester polyol,
β) Polymer polyol (for example, a polyether polyol obtained by graft-copolymerizing polyacrylonitrile, acrylonitrile-styrene copolymer, etc.),
γ) Of the alcohols listed as examples of the cross-linking agent, bifunctional ones and the like can be used, and these may be used alone or in combination of two or more, but among them, a polyether polyol is preferable, and more preferably. It is polytetramethylene ether glycol (hereinafter, this is also referred to as "PTMG-II"). This "PTMG-II" is referred to as "PTMG-I (polytetramethylene ether glycol having a number average molecular weight of 300 to 3000, an average number of functional groups of 2 to 3, and an average hydroxyl value of 50 to 200 mgKOH / g)". , "Polytetramethylene ether glycol in which at least one of the number average molecular weight, the average number of functional groups, and the average hydroxyl value is out of the above range" is included.

As the polyisocyanate,
Fragrances such as diphenylmethane diisocyanate (4,4'-MDI), polypeptide MDI (Crude MDI), 2,4-toluene diisocyanate (2,4-TDI), 2,6-toluene diisocyanate (2,6-TDI) Examples thereof include group isocyanates, aliphatic diisocyanates such as tetramethylene diisocyanate and hexamethylene diisocyanate (HDI), isophorone diisocyanates, hydrogenated TDIs, alicyclic diisocyanates such as hydrogenated MDIs, etc. Although it can be used in combination, 4,4'-MDI is preferable.

That is, i) as the isocyanate group-terminated prepolymer, those obtained by reacting PTMG-II with 4,4'-MDI are preferable.
If it is a prepolymer obtained by reacting this PTMG-II with 4,4'-MDI,
-Since the crystallinity of the PTMG part is high in the first place, it is easy to obtain urethane foam with high resilience, and in addition,
-As a [polyisocyanate component], ii) not only has good compatibility when used in combination with modified MDI, but also
-The mixability at the time of reacting with PTMG-I, which is the [polyurethane component] of the present invention, is also good, the molecular structure tends to be uniform, and the quality of the obtained urethane foam can be stabilized.

ii) Modified MDI;
As the modified MDI capable of lowering the viscosity of the [polyisocyanate component] because it is a liquid at room temperature, one having an isocyanate group content of 25 to 33% by mass is used.
If the modified MDI has an NCO group content of less than 25% by mass, i) the effect of increasing the NCO group content when mixed with the prepolymer is small, so in order to sufficiently increase the foamability and reduce the foam density. Must be mixed in an extremely high proportion, and there is a risk that the desired bending resistance cannot be obtained.
On the other hand, if the modified MDI exceeds 33% by mass, the NCO group content can be increased with a very small amount, but since the amount is small, the viscosity of i) having a large molecular weight cannot be reduced, and [polypoly]. Ingredients] will be poorly mixed when reacted.

Specific examples of such a modified MDI that is liquid at room temperature include a polymeric (crude MDI), urethane modified, urea modified, allophanate modified, biuret modified, carbodiimide modified, uretonimine modified, and uretdione modified. , Isocyanurate modified product and the like.
Among them, a polypeptide (crude MDI) or a modified carbodiimide is preferable because the molecular (crosslinked) structure after the reaction with the above-mentioned [polyol component] is excellent.

In the present invention, the isocyanate index is in the range of 0.8 to 0.95 in order to obtain a foam having bending resistance in addition to shock absorption, resilience and durability.
If the isocyanate index is too small, the number of hydroxyl groups is large with respect to the isocyanate group, so that the polymerization does not proceed well and the urethane foam surface may not be cured. However, it tends to be inferior in bending resistance, and if it exceeds 0.95, it becomes difficult to obtain the bending resistance required by the present invention.
The bending resistance required by the present invention is the operation of bending a polyurethane foam having a length of 120 mm, a width of 60 mm, and a thickness of 6 mm to which a resin-impregnated board having a thickness of 2 mm is adhered at 90 ° and immediately returning the polyurethane foam 144 times. Repeated at a rate of / minute, the number of times until cracks occur (sempo bending test) is 100,000 times or more. If it is 100,000 times or more, even if the polyurethane foam is used as a shoe sole, cracking at the time of bending can be prevented.
Furthermore, if the isocyanate index is in the range of 0.8 or more and less than 0.9, the number of sempo bending tests of the obtained polyurethane foam will be 150,000 or more, and the bending resistance will be more excellent, so that it can be used in various applications. Is possible.
Here, the resin-impregnated board is a pulp board (impregnated paper) impregnated with synthetic resin, synthetic rubber, natural rubber, or the like, and is used as, for example, an insole or an insole core material. In the present invention, the trade name "# 347" manufactured by Bontex Co., Ltd. is used.

[Blowing agent]
Water (ion-exchanged water) can be used as the foaming agent. The amount to be added is preferably 0.5 to 3 parts by weight with respect to 100 parts by weight of the above-mentioned [polyol component].
If the amount added is less than 0.5 parts by weight, foaming is insufficient and resilience is exhibited, but shock absorption is inferior. If the amount added exceeds 3 parts by weight, the cells of the polyurethane foam obtained by over-foaming become rough, the inside of the foam is easily cracked, and the foam state is inferior, and the resilience tends to be inferior.

〔catalyst〕
The catalyst may be any conventionally used catalyst, and examples thereof include amine-based catalysts such as triethylenediamine and diethanolamine, and metal catalysts such as bismuth catalyst, but the catalyst is not particularly limited.
The amount to be added is preferably 0.1 to 5 parts by weight with respect to 100 parts by weight of the above-mentioned [polyol component].

[Foaming agent]
In the present invention, [a polyol component composed of "PTMG-I"] and [a polyisocyanate component containing "isocyanate group-terminated prepolymer" and "modified MDI" in a specific compounding ratio] are reacted to form a mold (a polyisocyanate component). By foaming and curing in the mold), a synergistic effect of the urethane reaction by the above three "compounds" and the compression action at the time of foaming is produced, and the cell size can be made uniform and fine.
Therefore, the foam stabilizer to be used is not particularly limited as long as it can be used with urethane foam, but when performing vigorous exercise such as sports shoes, higher resilience is required, so the viscosity is 300. It is preferable to use a silicone compound of ~ 2000 mPa · s (25 ° C.).
If the viscosity is less than 300 mPa · s, the foam-regulating action is weak, the cell becomes coarse, and it is difficult to obtain high resilience. On the other hand, if the viscosity exceeds 2000 mPa · s, it becomes difficult to disperse uniformly in the polyurethane raw material, and not only the cell size of the obtained foam becomes not uniform, but also the physical properties change locally (physical property values depending on the measurement location). Therefore, the preferable viscosity is 800 to 1000 mPa · s (25 ° C.). The viscosity is a value measured by a B-type rotational viscometer.

When the above-mentioned silicone compound is added as a defoaming agent, it may be 0.5 to 9 parts by weight with respect to 100 parts by weight of the above-mentioned [polyol component].
If it is less than 0.5 parts by weight, the foam-regulating action is weak, the cell size of the obtained polyurethane foam is large and non-uniform, the resilience is low, and it is difficult to obtain the desired shock absorption and durability.
On the other hand, if it exceeds 9 parts by weight, the resilience is inferior, and bleed-out occurs in which the defoaming agent exudes from the foam surface, which hinders adhesion to other members and is also inferior in handleability. In particular, if it exceeds 5 parts by weight, the desired resilience, shock absorption, and durability can be obtained, but a tacky feeling (sticky feeling) tends to occur to the extent that there is no problem in use, so 0 is preferable. .5 to 5 parts by weight.

The raw material of the polyurethane foam of the present invention includes a polyol component, an isocyanate component, a foaming agent, a catalyst, a foam stabilizer, as well as a plasticizer, a filler, an antioxidant, a defoaming agent, and a compatibilizer, if necessary. , Colorants, stabilizers, UV absorbers and other additives commonly used in the production of polyurethane foam may be used as long as the effects of the present invention can be obtained.

In the present invention, it is preferable that the above polyurethane raw materials are reacted by molding.
Mold molding is a method in which the polyurethane raw material (stock solution) is injected into a mold (molding mold), foamed and cured in the mold, and then demolded to obtain a foam.
In the case of mold molding, the cell size can be made uniform and fine due to the compression effect at the time of foaming, and the density can be easily adjusted by the injection amount of the polyurethane stock solution with respect to the volume in the mold.

Further, when mixing the polyurethane raw materials, it is preferable that the screw rotation speed is 2000 to 20000 rpm because a uniform foam with no variation in cell size can be obtained. If the rotation speed is less than 2000 rpm, the cell size varies widely and the bending resistance of the obtained polyurethane foam tends to be inferior, while if it exceeds 20000 rpm, the solidification rate becomes high and the injection into the mold remains incomplete. , Hardens.

The polyurethane foam of the present invention has a compression set of 20% or less measured according to JIS K 6262 under the conditions of a compressibility of 25%, 40 ° C., and 24 hours.
When the compression set exceeds 20%, the durability is inferior for applications such as shoe sole members, and therefore it is preferably 15% or less.

Further, the polyurethane foam of the present invention has bending resistance.
In the bending resistance test of a test piece obtained by cutting the polyurethane foam into a length of 120 mm, a width of 60 mm, and a thickness of 6 mm, the test piece was cut into a resin impregnated board having a thickness of 2 mm (trade name "# 347" manufactured by Bontex Co., Ltd. ), Then bend at an angle of 90 °, and immediately after that, when the operation of returning to the original state is repeated at a speed of 144 times / minute, the number of times until cracks occur is measured, and this is used as an index. To do. The larger the value (number of times), the more bending resistance is indicated, and in the present invention, the number of times is preferably 100,000 times or more.

Further, the polyurethane foam of the present invention has shock absorption and high resilience.
For shock absorption, in a drop impact test of a test piece obtained by cutting the polyurethane foam to a thickness of 12.5 mm, a bullet-shaped weight w (made of iron, 5.1 kg) as shown in FIG. 1 is made to collide from a height of 50 mm. At that time, the value of the maximum impact load measured by using the product name "dynatup GRC8200" manufactured by Instron is used as an index. The smaller the value of the maximum impact load, the more (impact) is absorbed, and in the present invention, it is preferably 1.5 kN or less.
Regarding the resilience, the elastic modulus of resilience measured in accordance with JIS K 6255 may be 55% or more, and particularly 60% or more, which is most suitable as a sole member of sports shoes and is preferable.

In the polyurethane foam of the present invention, cells having an average cell size of 30 to 100 μm and a cell size of 20 to 300 μm occupy 90% or more of all cells. The ratio of the number of cells having a certain range of cell size to the whole is an index for judging the degree of variation, and the fact that the number accounts for 90% or more indicates that the form is uniform and has no variation. ing.
As described above, since the polyurethane foam of the present invention has a specific average cell size and is a uniform foam without variation, it has shock absorption, resilience, durability, and is also excellent in bending resistance. It is a thing.
Here, in the present specification, the cell size is the diameter of the cell, and the average cell size is the number of cells existing in the range of 1.7 mm in length and 1.2 mm in width in the cross section of the urethane foam (all cells). The number of cells) and the size of each cell were measured and calculated using a microscope. Further, the number of all cells is a, the number of cells having a cell size of 20 to 300 μm is b, and the ratio of cells having a cell size of 20 to 300 μm to all cells is a formula of b / a × 100 (%). I asked for it.

The polyurethane foam of the present invention preferably has an apparent density of 0.25 to 0.5 g / cm ^{3 measured in accordance with JIS K 7222.}
If the density is too high, it is difficult to use it for applications such as shoe sole members where weight reduction is important. Further, if the density of the foam is too low, it is difficult to obtain desired physical properties (repulsion, bending resistance, etc.).

The polyurethane foam of the present invention is a material having both shock absorption and resilience, has low compression set, is excellent in durability, and has strong bending resistance, and is therefore suitable for a shoe sole member, for example. ..
The sole member is an outsole, a midsole, and an insole. Not only the polyurethane foam of the present invention is provided on the entire surface of the sole, but also a recess is formed in the midsole made of another material, and the book is formed therein. Partial placement is also possible, such as by inserting the polyurethane foam of the invention.
Further, as the sole, the polyurethane foam of the present invention may be used for the midsole, and an outsole made of a rubber material having anti-slip properties may be laminated on the ground contact surface side thereof. In that case, the outsole may be arranged at an arbitrary position on the contact patch side of the midsole, or the midsole on the contact patch side may be partially exposed by cutting out a part of the outsole. Good. Since the polyurethane foam of the present invention has excellent bending resistance, the midsole does not crack even when a load is applied to the boundary portion between the midsole and the outsole.

The polyurethane foam of the present invention is suitable for applications requiring shock absorption, resilience, durability, bending resistance, etc., such as inside a helmet, a protector, a cushioning material for a vehicle, and a floor material, in addition to a shoe sole member. Can be used.

Examples 1-10, Comparative Examples 1-11
As shown in Tables 1 and 2, the polyurethane raw material in which each material is mixed is injected into the mold while stirring at a screw rotation speed of 3500 rpm, reacted under the condition of a mold temperature of 40 ° C., and then demolded. Polyurethane foam was obtained.
The unit of the numerical value indicating the composition of the materials in Tables 1 and 2 is the part by weight.

The materials used in the table are shown below;
[Polycarbonate component]
-PTMG-I-1: Polytetramethylene ether glycol (number average molecular weight 2000, hydroxyl value 57.2 mgKOH / g, average number of functional groups 2)
-PTMG-I-2: Polytetramethylene ether glycol (number average molecular weight 850, hydroxyl value 132 mgKOH / g, average number of functional groups 2)
-PTMG-I'-1: Polytetramethylene ether glycol (number average molecular weight 280, hydroxyl value 400 mgKOH / g, average number of functional groups 2)
-PTMG-I'-2: Polytetramethylene ether glycol (number average molecular weight 3200, hydroxyl value 35 mgKOH / g, average number of functional groups 2)
-PPG: Polyoxypropylene glycol (number average molecular weight 2200, hydroxyl value 51 mgKOH / g, average number of functional groups 2)
Low molecular weight diol: 1,4-butanediol (molecular weight 90, hydroxyl value 1244 mgKOH / g, number of functional groups 2)

-Catalyst A: Triethylenediamine (manufactured by Tosoh Corporation, product name "TEDA-L33")
-Catalyst B: Bismuth catalyst (manufactured by Nihon Kagaku Sangyo Co., Ltd., product name "Pucat 25")
Defoamer A: Silicone compound (viscosity 900 mPa · s (25 ° C))
Defoamer B: Silicone compound (viscosity 250 mPa · s (25 ° C))
・ Foaming agent: Ion-exchanged water

[Polyisocyanate component]
-Isocyanate group-terminated prepolymer 1: Prepolymer obtained by reacting PTMG-II with 4,4'-MDI (number average molecular weight 1000, average number of functional groups 2, isocyanate group content 8.01% by mass)
-Isocyanate group-terminated prepolymer 2: Prepolymer obtained by reacting PTMG-II with 4,4'-MDI (number average molecular weight 2500, average number of functional groups 2, isocyanate group content 2.5% by mass)
-Modified MDI-1: Carbodiimide modified product (average number of functional groups 2 and isocyanate group content 28.2%)
-Modified MDI-2: Polymeric (crude MDI) (average number of functional groups 2.5, isocyanate group content 31.1% by mass)

Examples 11 and 12
The same composition as in Example 1 except that the amount of the polyurethane raw material injected into the mold is adjusted so that the apparent densities of the obtained urethane foams are the values shown in Table 1 (g / cm ^3). The polyurethane foams of Examples 11 and 12 were obtained.

Comparative Examples 12 to 13
Polyurethane foam was obtained in the same manner as in Example 1 except that the screw rotation speed was set to 1500 rpm and 22000 rpm.

The polyurethane foams obtained in Examples 1 to 12 and Comparative Examples 1 to 13 were appropriately cut to prepare test pieces, and the measurements shown below were carried out. In Comparative Example 13, the physical properties could not be measured because the raw material was solidified too quickly after being injected into the mold and solidified before the raw material spread in the mold, resulting in molding failure.
The results are also shown in Tables 1 and 2.

<Apparent density> A value measured in accordance with JIS K 7222 on a test piece cut into a rectangular parallelepiped having a length of 15 mm, a width of 15 mm, and a thickness of 10 mm.
<Average cell size> The number of cells (the number of all cells) existing within the range of 1.7 mm in length and 1.2 mm in width in the cross section of urethane foam, and the size of each cell (diameter of cells) are measured with a microscope. Average value calculated using.
<Variation of cell size> The number of all cells is a, the number of cells with a cell size of 20 to 300 μm is b, and the ratio of cells with a cell size of 20 to 300 μm to all cells is b / a × 100. The value calculated by the formula (%).

<Repulsive modulus> A value measured in accordance with JIS K 6255 on a test piece cut to a diameter of 12.5 mm and a thickness of 12.5 mm.
<Maximum impact load> A bullet-shaped weight as shown in FIG. 1 was used by a drop impact test on a test piece cut to a length of 70 mm, a width of 60 mm, and a thickness of 12.5 mm using a "dynatup GRC8200 (manufactured by Instron)". Maximum impact load when w (made of iron, 5.1 kg) is made to collide from a height of 50 mm.

<Compression permanent strain> A value measured according to JIS K 6262 under the conditions of a compression rate of 25%, 40 ° C., and 24 hours on a test piece cut to a diameter of 29.5 mm and a thickness of 12.5 mm.
<Sempo bending test> A resin-impregnated board with a thickness of 2 mm (trade name "# 347" manufactured by Bontex) is bonded to a test piece cut to a size of 120 mm in length, 60 mm in width, and 6 mm in thickness, and then bent into a sempo. According to the test, the number of times until a crack occurs when the operation of bending at 90 ° and returning immediately after that is repeated at a speed of 144 times / minute.
In Table 2, in Comparative Examples 4 and 10, cracks occurred less than 5000 times, and in Examples 1, 3 to 7, 10 in Table 1 and Comparative Example 1 in Table 2, cracks occurred 200,000 times or more. Indicates that did not occur.

<Bending test> The polyurethane foams obtained in Example 1 and Comparative Example 12 were cut into a size of 120 mm in length, 60 mm in width, and 6 mm in thickness to form a test piece, and a resin having a thickness of 2 mm was formed on one surface of the test piece. An impregnated board (trade name "# 347" manufactured by Bontex), with a rubber piece (SBR: styrene-butadiene rubber) with a thickness of 2 mm bonded to the other surface, and a width of 2 mm at the substantially central part of the rubber piece. , A cross-shaped punched hole with a length of 1.5 mm (with the test piece exposed) is bent so that the bending line and the punching hole are substantially parallel in the same manner as in the <Sempo bending test>. It was.
When the test piece of Example 1 was used, the test piece did not crack at the portion corresponding to the punched hole even when bent 100,000 times, but when the test piece of Comparative Example 12 was used, 20,000. At the time of bending, a crack occurred at the boundary between the polyurethane foam and the rubber piece.

From Table 1 (Examples 1 to 12), the polyurethane foam of the present invention contains [a polyol component composed of "PTMG-I"] and [a specific compounding ratio of "isocyanate group-terminated prepolymer" and "modified MDI". It is obtained by reacting with the polyisocyanate component contained in the above], and it is found that it is excellent in shock absorption and resilience, has small compression set, is excellent in durability, and has strong bending resistance. It was.

For example, when Example 1 using PTMG-I-1 as a polyol component and Comparative Examples 3, 4 and 5 using other components are compared, in Example 1, the rebound resilience is as high as 70%. It showed resilience and had a maximum impact load of 0.8 kN, which was excellent in impact absorption. In the Sempo bending test, bending resistance enough to withstand 200,000 times was obtained.
On the other hand, in Comparative Example 3 in which the number average molecular weight of PTMG was large and the average hydroxyl value was too small, although the shock absorption was excellent, the rebound resilience was 50%, and the desired repulsion could not be obtained. In Comparative Example 4 in which the number average molecular weight was small and the average hydroxyl value was too large, the elastic modulus was excellent at 60%, but the result of the sempo bending test was less than 5000 times, which was inferior in bending resistance. Further, in Comparative Example 5 in which PPG was used instead of PTMG, although the impact absorption was excellent, the desired elastic modulus was 50%, and the desired resilience could not be obtained, and the desired bending resistance could not be obtained. It was.

Further, in Comparative Example 6 using the isocyanate group-terminated prepolymer 2 having a larger number average molecular weight and a lower NCO group content than the isocyanate group-terminated prepolymer 1, the impact resilience was as high as 75%, and the impact was impacted. It was excellent in absorbency, but inferior in bending resistance.

In the present invention, the compounding ratio of the specific isocyanate group-terminated prepolymer and the specific modified MDI is 97/3 to 80/20.
As shown by the results of Examples 5, 7 and 10 and Comparative Examples 7 to 9, this is repulsive and shock absorbing in Comparative Example 7 containing only the prepolymer and Comparative Example 9 in which the compounding ratio of the modified MDI is small. Although it was excellent in properties, it was inferior in bending resistance. Further, in Comparative Example 8 in which the compounding ratio of the modified MDI was large, not only the bending resistance but also the resilience was inferior. That is, all of Examples 1 to 12 having a compounding ratio of 97/3 to 80/20 satisfied all the physical properties of resilience, shock absorption, and bending resistance.

In the present invention, the isocyanate index is 0.80 to 0.95.
This is because, as shown by the results of Examples 2 and 4 and Comparative Examples 1 and 2, in Comparative Example 1 in which the isocyanate index is too small, a flexible foam can be obtained and shock absorption is excellent, but compression permanent strain is obtained. In Comparative Example 2 in which the index was too large, the resilience was high, but the bending resistance was inferior. That is, all of Examples 1 to 12 having the index of 0.80 to 0.95 satisfied all the physical properties of resilience, shock absorption, and bending resistance.
In particular, except for Examples 2 and 9 in which the isocyanate index was 0.80 or more and less than 0.90, the bending resistance was 150,000 times or more, which was a more preferable result.

Then, when Example 1 and Comparative Example 12 were compared, the bending resistance was inferior in Comparative Example 12 having the same compounding ratio as that of Example 1 but having a low screw rotation speed. Further, in the <bending test>, when the test piece of Example 1 was used, the test piece at the portion corresponding to the punched hole did not crack even when bent 100,000 times, but the test piece of Comparative Example 12 was used. In the case of using, a crack occurred at the boundary between the polyurethane foam and the rubber piece when the polyurethane foam was bent 20,000 times.
This is considered to be due to the variation in cell size, and in the present invention, cells having an average cell size of 30 to 100 μm and a cell size of 20 to 300 μm occupy 90% or more of all cells. For example, it was shown that a uniform foam with no variation can be obtained, and the polyurethane foam of the present invention satisfying all physical characteristics can be obtained.

In addition, when the polyurethane foam of the present invention is used for the midsole, the midsole on the ground contact surface side is partially placed by arranging an outsole of an arbitrary shape at an arbitrary position or cutting out a part of the outsole. Even when it is exposed, it is possible to prevent the midsole at the boundary with the outsole, which is easily loaded, from cracking.

The present invention is a polyurethane foam having excellent shock absorption, resilience, durability and bending resistance, and is therefore suitable as a material for sole members (for example, midsole).
Further, in addition to the shoe sole member, it is suitable for applications requiring shock absorption, resilience, durability, bending resistance, etc., such as inside a helmet, a protector, a cushioning material for a vehicle, and a floor material.

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Claims (4)

A polyurethane foam made of a polyurethane raw material containing a polyol component, a polyisocyanate component, a foaming agent, a catalyst, and a foam stabilizer.
The polyol component is a polytetramethylene ether glycol having a number average molecular weight of 300 to 3000, an average number of functional groups of 2 , and an average hydroxyl value of 50 to 200 mgKOH / g.
The polyisocyanate component is
i) An isocyanate group-terminated prepolymer having a number average molecular weight of 500 to 2000, an average number of functional groups of 2 to 3, and an isocyanate group content of 3 to 10% by mass.
ii) Containing modified MDI having an isocyanate group content of 25 to 33% by mass,
The content ratio of the prepolymer of the above i) and the modified MDI of the above ii) is 97/3 to 80/20 by weight.
The isocyanate index is 0.80 to 0.95.
The average cell size is 30 to 100 μm, and cells with a cell size of 20 to 300 μm occupy 90% or more of all cells.
A polyurethane foam characterized by having a compression set of 20% or less measured in accordance with JIS K 6262 and having bending resistance. The polyurethane foam according to claim 1, wherein the polyurethane foam is a molded product. The operation of bending a polyurethane foam having a length of 120 mm, a width of 60 mm, and a thickness of 6 mm to which a resin-impregnated board having a thickness of 2 mm is adhered at 90 ° and returning immediately after that is repeated at a speed of 144 times / minute. The polyurethane foam according to claim 1 or 2, wherein the number of times until cracks occur is 100,000 times or more. A shoe sole member using the polyurethane foam according to any one of claims 1 to 3.

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