JP7564672B2 - Bound stopper and manufacturing method thereof - Google Patents

Description

The present invention relates to a bound stopper that is attached to the piston rod of a vehicle shock absorber and a method for manufacturing the same.

As shown in FIG. 7, a shock absorber 70 for a vehicle has a bound stopper 75 attached to a piston rod 72 of a cylinder. Reference numeral 71 denotes the cylinder body, and reference numeral 73 denotes a spring. The bound stopper 75 is made of an elastic foam molded into a bellows shape, and when the shock absorber 70 expands and contracts due to impact or vibration from the road surface and the cylinder body 71 collides with the bound stopper 75, the bound stopper 75 compresses and deforms to absorb the impact.

The bound stopper 75 is subject to repeated collisions with the cylinder body and the resulting compressive deformation, so it must have high mechanical strength and be durable against fatigue failure and settling when subjected to repeated heavy loads.

A conventional bound stopper that is durable and resistant to settling under high loads and large deformations while reducing costs has been proposed, which is made by injecting a urethane raw material containing polyester polyol as the polyol component and diphenylmethane diisocyanate as the isocyanate component into a mold and heating it to 70°C or higher for primary vulcanization, and then removing the molded body from the mold and heating it for secondary vulcanization, thereby forming a polyurethane foam so that the density (Da) and foam cell diameter (Ra) of the skin layer and the density (Db) and foam cell diameter (Rb) of the core satisfy specific formulas and relationships (Patent Document 1).

JP 2015-183832 A

However, the primary and secondary vulcanization processes must ensure that the density (Da) and foam cell diameter (Ra) of the skin layer and the density (Db) and foam cell diameter (Rb) of the core layer satisfy specific formulas and relationships, making it difficult to control the reaction.

Furthermore, vehicles require comfort (a good ride quality), but with conventional bounding stoppers, there was a feeling of being pushed up due to unevenness in the road surface while the vehicle was traveling, and no improvement in ride quality was achieved.

The present invention has been made in consideration of the above points, and aims to provide a bound stopper that has high mechanical strength, provides a comfortable ride, and is easy to manufacture, as well as a method for manufacturing the same.

The invention of claim 1 is a polyurethane foam bound stopper to be attached to a piston rod of a shock absorber for a vehicle, which is made of polyurethane foam obtained from a polyurethane foam composition containing at least an isocyanate component and a blowing agent, and is characterized in that the isocyanate component is made of a urethane prepolymer having an isocyanate group at its end, which is obtained from a polyol component, a polyrotaxane containing a cyclic molecule having an active hydrogen group as a constituent, and diphenylmethane diisocyanate.

The invention of claim 2 is the same as that of claim 1, in which the urethane prepolymer having an isocyanate group at its end has a blending amount of the polyrotaxane of 0.1 to 6.5 parts by weight per 100 parts by weight of the polyol component.

The invention of claim 3 is characterized in that in the invention of claim 1 or 2, the density of the polyurethane foam is 0.2 to 0.7 g/ ^cm3 .

The invention of claim 4 is a method for manufacturing a bound stopper made of polyurethane foam to be attached to a piston rod of a shock absorber for a vehicle, which comprises mixing a polyol component and a polyrotaxane containing cyclic molecules having active hydrogen groups as constituents in a molten state, then blending diphenylmethane diisocyanate to prepare a urethane prepolymer having an isocyanate group at its terminal, and injecting a polyurethane foam composition containing at least the urethane prepolymer having an isocyanate group at its terminal and a foaming agent into a mold and foaming the polyurethane foam to form a bound stopper.

The bound stopper of the present invention is composed of a polyurethane foam obtained from a polyurethane foam composition containing at least a urethane prepolymer having an isocyanate group at its terminal and a foaming agent. The urethane prepolymer having an isocyanate group at its terminal is obtained by mixing a polyol component and a polyrotaxane containing a cyclic molecule having an active hydrogen group in a molten state, and then adding diphenylmethane diisocyanate.

As shown in the schematic diagram of FIG. 2, the polyrotaxane 20 has an axial molecule 23 inserted in a skewer-like manner into the opening of the cyclic molecule 21, and the axial molecule 23 has blocking groups 25 at both ends. The blocking groups 25 prevent the cyclic molecule 21 from detaching from the axial molecule 23. According to the present invention, when preparing a urethane polymer having an isocyanate group at its end, the hydroxyl group of the polyol component and the active hydrogen group in the cyclic molecule 21 of the polyrotaxane 20 react with diphenylmethane diisocyanate to form a urethane bond. Then, a polyurethane foam is formed by a foaming reaction between at least the urethane prepolymer having an isocyanate group at its end and a foaming agent, and a bound stopper made of the polyurethane foam is obtained.

In the polyrotaxane 20, the cyclic molecules 21 can move relatively freely along the axial molecules 23, and in the polyurethane foam constituting the bound stopper, the urethane bonds (crosslinking points) formed in the cyclic molecules 21 of the polyrotaxane 20 can also move along the axial molecules 23 (pulley effect). Even if the polyurethane foam is repeatedly subjected to a large load from the outside, the pulley effect can disperse the load, preventing the crosslinking points from being destroyed. In addition, when the cyclic molecules 21 approach each other on the axial molecules 23, an air spring effect is generated in which the cyclic molecules 21 try to keep a constant distance between them, and the air spring effect gives the polyurethane foam excellent restorability. Due to these actions, the polyurethane foam of the present invention has increased mechanical strength, reduced dynamic energy applied from the outside, improved durability against destruction and sagging, and improved ride comfort.

In addition, according to the present invention, when preparing a urethane prepolymer having an isocyanate group at its end, polyrotaxane is added to a molten polyol component, and the polyol component and polyrotaxane are mixed in a molten state, so that the polyrotaxane can be uniformly dispersed in the polyol component. The polyol component and polyrotaxane are preferably mixed at a temperature equal to or higher than the melting point of the polyrotaxane. On the other hand, in the one-shot method in which the polyol component, the foaming agent, the isocyanate component, etc. are mixed at once and injected into a mold, the polyrotaxane, which is a solid at room temperature, needs to be melted at a temperature equal to or higher than the melting point, or dissolved or dispersed in a dispersion medium, but it is difficult to uniformly disperse the polyrotaxane due to differences in the temperature, viscosity, etc. of each component. Furthermore, it is difficult to reliably react all the active hydrogen groups of the polyrotaxane, which is an ultra-high molecular weight compound, with the isocyanate component, so that the pulley effect and air spring effect of the polyrotaxane cannot be fully obtained, and it is difficult to obtain a polyurethane foam that is excellent in mechanical strength and durability and provides a good ride.

In addition, in the present invention, a dispersion medium such as a surfactant is not required to disperse polyrotaxane in the polyurethane foam, and the decrease in mechanical strength and durability against breakage, sagging, etc., caused by the dispersion medium of the polyurethane foam can be prevented. If a compound that does not have an active hydrogen group in the molecule is used as the dispersion medium, a decrease in mechanical strength and bleeding, etc. may occur, and if a compound (monol) that contains one active hydrogen group in the molecule is used, a decrease in mechanical strength due to a decrease in crosslink density may occur.

In addition, the diphenylmethane diisocyanate used in the present invention is less expensive than 1,5-naphthalene diisocyanate (NDI), and compared to NDI, it is produced in larger quantities worldwide and can be procured globally.

FIG. 2 is a cross-sectional view of a bound stopper according to an embodiment of the present invention. FIG. 1 is a schematic diagram showing a structure of a polyrotaxane containing, as a constituent, a cyclic molecule having an active hydrogen group. 1A and 1B are cross-sectional views of a mold used in manufacturing the bound stopper of the present invention and a cross-sectional view of the mold during foaming. 4 is a cross-sectional view of a mold during demolding in the manufacture of the bound stopper of the present invention. FIG. 1 is a table showing the compositions and physical properties of Examples 1 to 9. 1 is a table showing the formulations and physical properties of Examples 10 to 16 and Comparative Examples 1 and 2. FIG. 4 is a cross-sectional view showing a state in which the bound stopper is attached.

The bound stopper 10 according to one embodiment of the present invention shown in FIG. 1 is attached to the piston rod 72 of a shock absorber of a vehicle, similar to the bound stopper 75 shown in FIG. 7.

The bound stopper 10 is made of a cylindrical polyurethane foam with the outer peripheral surface 10a molded into a bellows shape, and has a through hole 11 in the center through which the piston rod of the shock absorber can be inserted. The bound stopper 10 is formed so that the upper part 10b has a larger outer diameter than the lower part 10c. The length and diameter of the bound stopper 10 are determined according to the shock absorber.

The density (based on JIS K7222:2005) of the polyurethane foam constituting the bound stopper 10 is preferably 0.2 to 0.7 g/cm ^3. If the density is less than 0.2 g/cm ³ , the physical properties of the polyurethane foam are degraded, whereas if the density exceeds 0.7 g/cm ³ , the foaming pressure increases during foam molding of the polyurethane foam, making molding difficult.

The tensile strength (in accordance with JIS K6251:2017) of the polyurethane foam that constitutes the bound stopper 10 is preferably 3.5 MPa or more.

The polyurethane foam that constitutes the bound stopper 10 is obtained from a polyurethane foam composition. The polyurethane foam composition contains at least an isocyanate component and a foaming agent.

The isocyanate component is made of a urethane prepolymer having an isocyanate group at the end, which is obtained by mixing a polyol component and a polyrotaxane containing cyclic molecules with active hydrogen groups in a molten state, and then adding diphenylmethane diisocyanate.

The polyol component is a polyester polyol, preferably having an average carbon number of 3 to 8 between ester bonds.
Condensation polyester polyols or ring-opening polyester polyols are used as the polyester polyols having an average carbon number between ester bonds of 3 to 8. In addition, polytetramethylene ether glycol (PTMG) [HO-(CH ₂ CH ₂ CH ₂ CH ₂ O) _n -H] can also be used as the polyol component.

As the condensation polyester polyol, a polycondensation product of a diol having 2 to 6 carbon atoms between hydroxyl groups and a dicarboxylic acid having 4 to 10 carbon atoms between carboxyl groups is preferred.

Examples of diols having 2 to 6 carbon atoms between the hydroxyl groups include ethylene glycol [HO-CH ₂ CH ₂ -OH], 1,4-butanediol [HO-(CH ₂ ) ₄ -OH], and 1,6-hexanediol [HO-(CH ₂ ) ₆ -OH].
Examples of dicarboxylic acids having 4 to 10 carbon atoms between the carboxyl groups include adipic acid [HOOC-(CH ₂ ) ₄ -COOH], suberic acid [HOOC-(CH ₂ ) ₆ -COOH], sebacic acid [HOOC-(CH ₂ ) ₈ -COOH], and dodecanedioic acid [HOOC-(CH ₂ ) ₁₀ -COOH]. Note that the number of carbon atoms between the carboxyl groups does not include the number of carbons constituting the carboxyl groups.

As a ring-opening polyester polyol, polycaprolactone diol (PCL) obtained by ring-opening polymerization of ε-caprolactone is preferred.

The weight average molecular weight (Mw) of the polyol for the urethane prepolymer having an isocyanate group at the end is 800 to 5000, more preferably 1000 to 3000, and the hydroxyl value is 20 to 200 mgKOH/g, more preferably 35 to 180 mgKOH/g.

As shown in the schematic diagram of FIG. 2, the polyrotaxane containing a cyclic molecule having an active hydrogen group in its constituents is structured such that an axial molecule 23 is inserted in a skewer-like manner into the opening of a cyclic molecule 21 having an active hydrogen group, and blocking groups 25 at both ends of the axial molecule 23 prevent the cyclic molecule 21 from detaching. Examples of the active hydrogen group of the cyclic molecule 21 include a hydroxyl group and an amino group, and the hydroxyl group is particularly preferred. The polyrotaxane containing a cyclic molecule having an active hydrogen group in its constituents preferably has a hydroxyl value of 60 to 100 mg KOH/g, a molecular weight of the axial molecule of 10,000 to 40,000, and a total molecular weight of 150,000 to 800,000. The amount of the polyrotaxane containing a cyclic molecule having an active hydrogen group in its constituents is preferably 0.1 to 6.5 parts by weight, more preferably 0.5 to 6 parts by weight, per 100 parts by weight of the polyol component. If it is less than 0.1 part by weight, the effect of improving physical properties cannot be obtained. If it exceeds 6.5 parts by weight, the viscosity of the urethane prepolymer will be too high, making molding difficult.

Diphenylmethane diisocyanate (MDI) includes 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, and polymeric MDI (crude MDI). 4,4'-diphenylmethane diisocyanate is also called monomeric MDI or pure MDI. Polymeric MDI (crude MDI) is a mixture of monomeric MDI and high molecular weight polyisocyanate. Among them, 4,4'-diphenylmethane diisocyanate is preferred.
The diphenylmethane diisocyanate used in the present invention is less expensive than 1,5-naphthalene diisocyanate (NDI), and compared with NDI, it is produced in a larger amount worldwide and can be procured globally.

The NCO% of a urethane prepolymer having an isocyanate group at its end is preferably 2 to 7%, and more preferably 3 to 6%. If the NCO% is less than 2%, sufficient strength is not obtained and durability is also poor. On the other hand, if the NCO% is more than 7%, the flexibility is lost and the material becomes hard, brittle, and durability is also poor.

The blowing agent contained in the polyurethane foam composition can be water, a fluorocarbon substitute, or a hydrocarbon such as pentane, either alone or in combination. When water is used, carbon dioxide gas is generated during the reaction of the isocyanate component, and the foaming is caused by this carbon dioxide gas. The amount of water used as the blowing agent is preferably 0.2 to 5 parts by weight per 100 parts by weight of the urethane prepolymer having an isocyanate group at its terminal.

Polyurethane foam compositions can contain additives such as catalysts, foam stabilizers, hydrolysis stabilizers, crosslinking agents, flame retardants, colorants, stabilizers, and fillers.

The catalyst may be a known urethanization catalyst or a retardation catalyst (temperature-sensitive catalyst). Examples of urethanization catalysts include amine catalysts such as triethylamine, triethylenediamine, diethanolamine, dimethylaminomorpholine, N-ethylmorpholine, and tetramethylguanidine, tin catalysts such as stannous octoate and dibutyltin dilaurate, and metal catalysts (also called organometallic catalysts) such as phenylmercury propionate and lead octenate. Retarded catalysts are amine salts in which the active group of the urethanization catalyst is blocked with an acid such as formic acid or octylic acid, and examples of such catalysts include phenol salts of diazabicycloalkenes, octylic acid salts of diazabicycloalkenes, and tertiary amine salts.

The foam stabilizer may be any foam stabilizer that is used in polyurethane foam, and examples of such foam stabilizers include silicone-based foam stabilizers, fluorine-containing compound-based foam stabilizers, and known surfactants. If the foam stabilizer is added during the preparation of the urethane prepolymer having an isocyanate group at its end, it will disperse uniformly in the urethane prepolymer, improving the foam stabilization ability and allowing the production of polyurethane foam with fine and uniform cells.

Examples of hydrolysis stabilizers include carbodiimide compounds. In particular, when polyester polyol is used as the polyol component, the hydrolysis resistance of the polyurethane foam can be improved by adding a hydrolysis stabilizer. Since carbodiimide groups are reactive with active hydrogen groups, it is preferable to add them together with the blowing agent when producing the polyurethane foam.

Examples of crosslinking agents include ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,4-butanediol, glycerin, and trimethylolpropane. The crosslinking agent is preferably added when preparing the urethane prepolymer having an isocyanate group at its end. If the crosslinking agent is mixed in a molten state together with the polyol component and polyrotaxane, the crosslinking agent can be uniformly dispersed in the urethane prepolymer.

Examples of flame retardants include halogenated compounds such as polyvinyl chloride, chloroprene rubber, and chlorinated polyethylene; condensed phosphate compounds such as phosphate esters and halogenated phosphate esters; organic compounds such as melamine resins and urea resins; and inorganic compounds such as antimony oxide and aluminum hydroxide. If the flame retardant is added during the preparation of the urethane prepolymer having an isocyanate group at its end, it can be uniformly dispersed in the urethane prepolymer.

Examples of colorants include pigments and dyes. If the colorant is added during the preparation of the urethane prepolymer having an isocyanate group at its end, it can be uniformly dispersed in the urethane prepolymer.

Examples of stabilizers include antioxidants, ultraviolet absorbers, and light stabilizers. If the stabilizer is added during the preparation of the urethane prepolymer having an isocyanate group at its end, it can be uniformly dispersed in the urethane prepolymer.

The isocyanate index (INDEX) is preferably 90 to 120. If the isocyanate index is less than 90, the degree of crosslinking is low, and the polyurethane foam does not obtain sufficient mechanical strength and is prone to sagging when subjected to repeated loads. On the other hand, if the isocyanate index is more than 120, the degree of crosslinking is high, and the polyurethane foam becomes hard and has low elasticity. A more preferred isocyanate index is 95 to 115. The isocyanate index is an index used in the field of polyurethane foams, and is a numerical value that represents the equivalent ratio of isocyanate groups to active hydrogen groups in a polyurethane foam composition, expressed as a percentage [equivalent of NCO groups/equivalent of active hydrogen groups x 100].

The manufacturing method of the bound stopper is explained below. The manufacturing process of the bound stopper consists of a urethane prepolymer preparation process, a polyurethane foam composition injection and foaming process into a mold, and a demolding process.

In the urethane prepolymer production process, a polyrotaxane containing cyclic molecules with active hydrogen groups as constituents is added to a polyol component that has been heated to a specified temperature and put into a molten state, and after mixing in the molten state for a specified time, isocyanate is added, causing the active hydrogen groups of the polyol component and the cyclic molecules of the polyrotaxane to react with the isocyanate, producing a urethane prepolymer with an isocyanate group at its end.

To heat the polyol component and polyrotaxane to a molten state, it is preferable to heat them at 60 to 120°C, depending on the melting point of the polyol component used. Even if the polyol component and polyrotaxane are solid at room temperature, they can be mixed in a molten state and therefore uniformly dispersed.

It is preferable to add isocyanate and heat at 100 to 180°C to react the isocyanate with the active hydrogen groups of the polyol component and the cyclic molecules of the polyrotaxane.

In the step of injecting and foaming the polyurethane foam composition into a mold, the polyurethane foam composition, which contains at least a urethane prepolymer having an isocyanate group at its end, the foaming agent, and appropriate additives, is injected into a mold and foamed to form a bound stopper made of the polyurethane foam.

3(3-A) shows one embodiment of a bound stopper mold 30. The mold 30 comprises a lower mold 31, a middle mold 33, and an upper mold 35.
The lower die 31 is made up of a first lower die 31 a and a second lower die 31 b which can be separated into left and right halves, and has die surfaces 311 a and 311 b which form the side outer peripheral surface 10 a of the bound stopper 10 .
The middle die 33 is substantially rod-shaped and has a die surface 33a on its outer periphery that forms the through hole 11 of the bound stopper 10, and is disposed between the first lower die 31a and the second lower die 31b. The lower die 31 and the middle die 33 are combined to form a cavity 34 between the die surface 311a of the first lower die 31a and the die surface 311b of the second lower die 31b and the die surface 33a of the middle die 33.

After the polyurethane foam composition is injected into the cavity 34, as shown in FIG. 3 (3-B), the upper mold 35 is placed over the cavity 34 to close the mold, and the polyurethane foam composition 40 is reacted and foamed. The mold is left in the closed state for a predetermined time to cure (primary cure), forming a bound stopper 10 made of polyurethane foam. The primary cure is preferably performed at 60 to 120°C for 10 to 120 minutes.

In the demolding process, as shown in FIG. 4, the upper die 35 is removed, the first lower die 31a and the second lower die 31b are opened, and the middle die 33 is separated. The middle die 33 separated from the first lower die 31a and the second lower die 31b is fitted into the through hole 11 of the bound stopper 10 made of the polyurethane foam. The bound stopper 10 is then wiped off from the middle die 33 by utilizing its elasticity, and the bound stopper 10 is obtained. It is preferable to perform a secondary cure of the bound stopper 10 after demolding. The secondary cure is preferably performed at 90 to 180°C for 8 to 24 hours.

<Preparation of urethane prepolymer having isocyanate group at its terminal>
Polyester polyols PO-1 to PO-7 and isocyanate were used to prepare urethane prepolymers having isocyanate groups at their ends for use in the examples and comparative examples shown in FIGS.
The polyester polyols PO-1 to PO-7 and the isocyanate were as follows.

・Polyester polyol PO-1
The polyester polyol PO-1 is a condensation polyester polyol having an average of 3 carbon atoms between ester bonds, which is composed of adipic acid (AA) having 4 carbon atoms between the carboxylic acids and ethylene glycol (EG) having 2 carbon atoms between the hydroxyl groups, and has Mw; 2000, functionality; 2, hydroxyl value; 56 mgKOH/g, product name; Polylite OD-X-102, manufactured by DIC Corporation.

・Polyester polyol PO-2
The polyester polyol PO-2 is a condensation polyester polyol having an average of 4 carbon atoms between ester bonds, which is composed of adipic acid (AA) having 4 carbon atoms between the carboxylic acids and 1,4-butanediol (BG) having 4 carbon atoms between the hydroxyl groups, and has Mw; 2000, functionality; 2, hydroxyl value; 56 mgKOH/g, product name; Polylite OD-X-668, manufactured by DIC Corporation.

・Polyester polyol PO-3
The polyester polyol PO-3 is a condensation polyester polyol having an average of 5 carbon atoms between ester bonds, which is composed of adipic acid (AA) having 4 carbon atoms between the carboxylic acids and 1,6-hexanediol (HD) having 6 carbon atoms between the hydroxyl groups, and has Mw; 2000, functionality; 2, hydroxyl value; 56 mgKOH/g, product name; HS2H-201AP, manufactured by Toyokuni Oil Mills.

・Polyester polyol PO-4
The polyester polyol PO-4 is a condensation polyester polyol having an average of 7 carbon atoms between ester bonds, which is composed of sebacic acid (SA) having 8 carbon atoms between the carboxylic acids and 1,6-hexanediol (HD) having 6 carbon atoms between the hydroxyl groups, and has Mw; 2000, functionality; 2, hydroxyl value; 56 mgKOH/g, product name; HS2H-201AP, manufactured by Toyokuni Oil Mills.

・Polyester polyol PO-5
The polyester polyol PO-5 is a condensation polyester polyol having an average of 8 carbon atoms between ester bonds, which is composed of dodecanedioic acid (DDA) having 10 carbon atoms between the carboxylic acids and 1,6-hexanediol (HD) having 6 carbon atoms between the hydroxyl groups, and has Mw; 3700, functionality; 2, hydroxyl value; 30 mgKOH/g, product name: Polylite OD-X-2555, manufactured by Toyokuni Oil Mills.

・Polyester polyol PO-6
The polyester polyol PO-6 is a polycaprolactone diol (PCL) having an average carbon number of 5 between ester bonds obtained by ring-opening polymerization of ε-caprolactone, and has Mw; 2000, functionality; 2, hydroxyl value; 56 mgKOH/g, product name; PLACCEL 220, manufactured by Daicel Corporation.

・Polyester polyol PO-7
The polyester polyol PO-7 is polytetramethylene ether glycol (PTMG), having an average carbon number between ester bonds of 4, Mw of 2000, functionality of 2, hydroxyl value of 56 mgKOH/g, product name: PTMG2000, manufactured by Mitsubishi Chemical Corporation.

Polyrotaxane: Polyrotaxane containing cyclic molecules with hydroxyl groups in the structure, molecular weight: 180,000, hydroxyl value: 85 mg KOH/g, product name: Super Polymer SH1300P (melting point: approx. 40°C), manufactured by Advanced Materials Co., Ltd.

Isocyanate In Examples 1 to 16 and Comparative Example 2, the isocyanate was 4,4'-diphenylmethane diisocyanate (monomeric MDI), NCO %: 33.6%, product name: Cosmonate MT, manufactured by Tosoh Corporation.
In Comparative Example 1, the isocyanate is 1,5-naphthalene diisocyanate (NDI).

A urethane prepolymer having an isocyanate group at its end was prepared by blending the above-mentioned polyol, polyrotaxane, and isocyanate in the ratios shown in each example and comparative example in Figures 5 and 6 as follows. Examples 1 to 16 and Comparative Example 1 contain polyrotaxane in the urethane prepolymer having an isocyanate group at its end, and Comparative Example 2 does not contain polyrotaxane.

A 20-liter metal reaction vessel is charged with a specified amount of polyol (preliminarily heated to about 100°C to make it molten) according to the examples and comparative examples, and then heated to 130°C. In this state, a specified amount of polyrotaxane (solid state) according to the examples is charged into the reaction vessel, and mixed for 10 minutes while maintaining the temperature at 130°C to melt the polyrotaxane and disperse it uniformly in the polyol. With the reaction vessel maintained at 130°C, a specified amount of isocyanate according to the examples is charged and mixed for another 20 minutes. The reaction vessel is then left at room temperature and slowly cooled to produce a urethane prepolymer having an isocyanate group at its end. The urethane prepolymer having an isocyanate group at its end in Comparative Example 1 was produced only from polyol and isocyanate.

<Preparation of test pieces>
Using the prepared urethane polymer having an isocyanate group at its end and the following foaming liquid, test pieces of Examples 1 to 16 and Comparative Examples 1 to 3 were prepared by the methods described below.
Foaming liquid: water/castor oil = 50/50, product name: Advado SV, manufactured by Rhein Chemie Japan

A polyurethane foam composition was prepared by mixing a urethane polymer having an isocyanate group at the end, which had been adjusted to 80°C, with a foaming liquid, which had been adjusted to 40°C, in the ratios shown in Figures 5 and 6 for Examples 1 to 16 and Comparative Examples 1 and 2. The polyurethane foam composition was mixed and then poured into a test piece mold, which had been adjusted to 80°C, in a specified amount. The test piece mold had a cavity of 200 x 110 x 30 mm. The amount poured for each Example and Comparative Example is shown in Figures 5 and 6. The polyurethane foam was foamed in the mold, cured at 80°C for 30 minutes (primary curing), and then demolded. The polyurethane foam after demolding was further cured at 100°C for 12 hours (secondary curing) to obtain test pieces for Examples 1 to 16 and Comparative Examples 1 and 2.

<Product Creation>
The products (bound stoppers) of Examples 1 to 16 and Comparative Examples 1 to 3 were obtained in the same manner as in the preparation of the test pieces, except that the production mold (cavity volume: 152 ml) shown in FIGS. 3 and 4 was used and the injection amounts were those of the examples and comparative examples shown in FIGS. 5 and 6.

The density and tensile strength of the test pieces of each example and each comparative example were measured, and the ride comfort of the products was also measured. The measurement results are shown in Figures 5 and 6.

The density was measured in accordance with JIS K7222:2005 using a test piece (200 x 110 x 30 mm) as the measurement sample (with skin layers on all top, bottom and side surfaces).

Tensile strength was measured in accordance with JIS K6251:2017 by slicing a measurement sample of No. 2 dumbbell x 2 mm thickness (no skin layer on the top, bottom or sides) from the test piece. Tensile strength was judged as "x" if it was less than 3.5 MPa, "good" if it was between 3.5 MPa and less than 4 MPa, and "◎" if it was 4 MPa or more.

The ride comfort was evaluated by inserting the product (bound stopper 10) into a shaft, measuring (A) the load (N) at 1% compression (displacement) and (B) the load (N) at 5% compression (displacement) using an autograph (Shimadzu Corporation), and calculating the slope of the load change from the displacement of the bound stopper (the difference between the 5% compression and the 1% compression) and the load change using the following formula. The displacement of the bound stopper was 4 mm.
Load change slope = (B-A)/displacement

The smaller the gradient of the load change, the smaller the feeling of being pushed up by unevenness in the road surface while the vehicle is traveling, and the better the ride comfort. The gradient of the load change was judged as "x" if it was 10.0 or more, "good" if it was 8.5 to less than 10.0, and "excellent" if it was less than 8.5.

In addition, if either the tensile strength or ride comfort judgment is marked with an "X", the overall judgment is marked with an "X", if both judgments are marked with an "O" or if both are marked with an "O" and an "◎", the overall judgment is marked with an "O", and if both judgments are marked with an "◎", the overall judgment is marked with an "◎".

In Example 1, a polyurethane foam composition with an isocyanate index of 108 was prepared from 1000 g of polyester polyol PO-1 (AA/EG) having an average carbon number of 3 between ester bonds, 30 g of polyrotaxane, and 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 5.0%, which was prepared from 334 g of 4,4'-diphenylmethane diisocyanate, and 3.0 g of foaming liquid. The amounts of this composition injected into a test piece mold and a product mold were 323 g and 75 g, respectively, to prepare a test piece and a product.
Example 1 had a density of 0.49 g/cm ³ , a tensile strength of 3.5 MPa, a tensile strength rating of "good", a load change slope of 8.2, and a ride comfort rating of "excellent", resulting in an overall rating of "good".

In Example 2, a polyurethane foam composition with an isocyanate index of 108 was prepared from 1000 g of polyester polyol PO-2 (AA/BG) having an average carbon number between ester bonds of 4, 30 g of polyrotaxane, and 334 g of 4,4'-diphenylmethane diisocyanate, as well as 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 5.0%, and the prepolymer was mixed with 3.0 g of foaming liquid. The amounts of the mixture injected into a test piece mold and a product mold were 330 g and 76 g, respectively, to prepare a test piece and a product.
Example 2 had a density of 0.50 g/cm ³ , a tensile strength of 3.8 MPa, a tensile strength rating of "good", a load change slope of 8.0, and a ride comfort rating of "excellent", resulting in an overall rating of "good".

In Example 3, a polyurethane foam composition with an isocyanate index of 108 was prepared from 1000 g of polyester polyol PO-3 (AA/HD) having an average carbon number of 5 between ester bonds, 30 g of polyrotaxane, and 334 g of 4,4'-diphenylmethane diisocyanate, as well as 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 5.0%, and the prepolymer was mixed with 3.0 g of foaming liquid. The amounts of the mixture injected into the test piece mold and the product mold were 317 g and 73 g, respectively, to prepare a test piece and a product.
Example 3 had a density of 0.48 g/cm ³ , a tensile strength of 4.2 MPa, a tensile strength rating of "A", a load change slope of 7.5, and a ride comfort rating of "A", resulting in an overall rating of "A".

In Example 4, a polyurethane foam composition with an isocyanate index of 108 was prepared from 1000 g of polyester polyol PO-4 (SA/HD) having an average carbon number of 7 between ester bonds, 30 g of polyrotaxane, and 334 g of 4,4'-diphenylmethane diisocyanate, as well as 100 g of a urethane prepolymer having an isocyanate group at its terminal and an NCO% (theoretical value) of 5.0%, and the prepolymer was mixed with 3.0 g of foaming liquid. The amounts of the mixture injected into the test piece mold and the product mold were 343 g and 79 g, respectively, to prepare a test piece and a product.
Example 4 had a density of 0.52 g/cm ³ , a tensile strength of 4.8 MPa, a tensile strength rating of "A", a load change slope of 7.2, and a ride comfort rating of "A", resulting in an overall rating of "A".

In Example 5, a polyurethane foam composition with an isocyanate index of 108 was prepared from 1000 g of polyester polyol PO-5 (DDA/HD) having an average carbon number of 8 between ester bonds, 30 g of polyrotaxane, and 266 g of 4,4'-diphenylmethane diisocyanate, and 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 5.0%, and the prepolymer was mixed with 3.0 g of foaming liquid. The amounts of the mixture injected into the test piece mold and the product mold were 337 g and 78 g, respectively, to prepare a test piece and a product.
Example 5 had a density of 0.51 g/cm ³ , a tensile strength of 4.9 MPa, a tensile strength rating of "A", a load change slope of 7.0, and a ride comfort rating of "A", resulting in an overall rating of "A".

In Example 6, a polyurethane foam composition with an isocyanate index of 108 was prepared from 1000 g of polyester polyol PO-6 (PCL) having an average carbon number of 5 between ester bonds, 30 g of polyrotaxane, and 334 g of 4,4'-diphenylmethane diisocyanate, and 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 5.0%, and the prepolymer was injected in amounts of 323 g and 75 g into a test piece mold and a product mold to prepare a test piece and a product.
Example 6 had a density of 0.49 g/cm ³ , a tensile strength of 4.4 MPa, a tensile strength rating of "A", a load change slope of 7.6, and a ride comfort rating of "A", resulting in an overall rating of "A".

In Example 7, a polyurethane foam composition having an isocyanate index of 103 was prepared from 1000 g of polyester polyol PO-6 (PCL) having an average carbon number of 5 between ester bonds, 30 g of polyrotaxane, and 245 g of 4,4'-diphenylmethane diisocyanate, and 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 3.0%, and 1.9 g of foaming liquid. The amounts of the composition injected into a test piece mold and a product mold were 330 g and 76 g, respectively, to prepare a test piece and a product.
Example 7 had a density of 0.50 g/cm ³ , a tensile strength of 4.0 MPa, a tensile strength rating of "A", a load change slope of 7.3, and a ride comfort rating of "A", resulting in an overall rating of "A".

In Example 8, a polyurethane foam composition having an isocyanate index of 104 was prepared from 1000 g of polyester polyol PO-6 (PCL) having an average carbon number of 5 between ester bonds, 30 g of polyrotaxane, and 288 g of 4,4'-diphenylmethane diisocyanate, and 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 4.0%, and 2.5 g of foaming liquid. 337 g and 78 g were injected into a test piece mold and a product mold, respectively, to prepare a test piece and a product.
Example 8 had a density of 0.51 g/cm ³ , a tensile strength of 4.2 MPa, a tensile strength rating of "A", a load change slope of 7.4, and a ride comfort rating of "A", resulting in an overall rating of "A".

In Example 9, a polyurethane foam composition with an isocyanate index of 103 was prepared from 1000 g of polyester polyol PO-6 (PCL) having an average carbon number of 5 between ester bonds, 30 g of polyrotaxane, and 383 g of 4,4'-diphenylmethane diisocyanate, and 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 6.0%, and the prepolymer was injected in amounts of 323 g and 75 g into a test piece mold and a product mold to prepare a test piece and a product.
Example 9 had a density of 0.49 g/cm ³ , a tensile strength of 4.7 MPa, a tensile strength rating of "A", a load change slope of 7.8, and a ride comfort rating of "A", resulting in an overall rating of "A".

In Example 10, a polyurethane foam composition with an isocyanate index of 108 was prepared from 1000 g of polyester polyol PO-6 (PCL) having an average carbon number of 5 between ester bonds, 30 g of polyrotaxane, and 334 g of 4,4'-diphenylmethane diisocyanate, and 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 5.0%, and the prepolymer was mixed with 3.0 g of foaming liquid. The amounts of the mixture injected into the test piece mold and the product mold were 191 g and 45 g, respectively, to prepare a test piece and a product.
Example 10 had a density of 0.29 g/cm ³ , a tensile strength of 4.0 MPa, a tensile strength rating of "A", a load change slope of 7.0, and a ride comfort rating of "A", resulting in an overall rating of "A".

In Example 11, a polyurethane foam composition with an isocyanate index of 108 was prepared from 1000 g of polyester polyol PO-6 (PCL) having an average carbon number of 5 between ester bonds, 30 g of polyrotaxane, and 334 g of 4,4'-diphenylmethane diisocyanate, and 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 5.0%, and the prepolymer was injected in amounts of 271 g and 62 g into a test piece mold and a product mold to produce a test piece and a product.
Example 11 had a density of 0.41 g/cm ³ , a tensile strength of 4.2 MPa, a tensile strength rating of "A", a load change slope of 7.5, and a ride comfort rating of "A", resulting in an overall rating of "A".

In Example 12, a polyurethane foam composition with an isocyanate index of 108 was prepared from 1000 g of polyester polyol PO-6 (PCL) having an average carbon number of 5 between ester bonds, 30 g of polyrotaxane, and 334 g of 4,4'-diphenylmethane diisocyanate, and 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 5.0%, and the prepolymer was injected into a test piece mold and a product mold in amounts of 409 g and 94 g, respectively, to prepare a test piece and a product.
Example 12 had a density of 0.62 g/cm ³ , a tensile strength of 4.5 MPa, a tensile strength rating of "A", a load change slope of 8.0, and a ride comfort rating of "A", resulting in an overall rating of "A".

In Example 13, a polyurethane foam composition with an isocyanate index of 108 was prepared from 1000 g of polyester polyol PO-6 (PCL) having an average carbon number of 5 between ester bonds, 5 g of polyrotaxane, and 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 5.0%, which was prepared from 324 g of 4,4'-diphenylmethane diisocyanate, and 3.0 g of foaming liquid. The amounts of the composition injected into the test piece mold and the product mold were 323 g and 75 g, respectively, to prepare a test piece and a product.
Example 13 had a density of 0.49 g/cm ³ , a tensile strength of 4.0 MPa, a tensile strength rating of "A", a load change slope of 8.0, and a ride comfort rating of "A", resulting in an overall rating of "A".

In Example 14, a polyurethane foam composition with an isocyanate index of 108 was prepared from 1000 g of polyester polyol PO-6 (PCL) having an average carbon number of 5 between ester bonds, 10 g of polyrotaxane, and 10 g of 4,4'-diphenylmethane diisocyanate, and 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 5.0%, the prepolymer being made from 326 g of 4,4'-diphenylmethane diisocyanate. The amounts of the composition injected into a test piece mold and a product mold were 330 g and 76 g, respectively, to prepare a test piece and a product.
Example 14 had a density of 0.50 g/cm ³ , a tensile strength of 4.1 MPa, a tensile strength rating of "A", a load change slope of 7.9, and a ride comfort rating of "A", resulting in an overall rating of "A".

In Example 15, a polyurethane foam composition with an isocyanate index of 108 was prepared from 1000 g of polyester polyol PO-6 (PCL) having an average carbon number of 5 between ester bonds, 50 g of polyrotaxane, and 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 5.0%, which was prepared from 342 g of 4,4'-diphenylmethane diisocyanate, and 3.0 g of foaming liquid. The amounts of the composition injected into the test piece mold and the product mold were 337 g and 78 g, respectively, to prepare a test piece and a product.
Example 15 had a density of 0.51 g/cm ³ , a tensile strength of 4.7 MPa, a tensile strength rating of "A", a load change slope of 7.4, and a ride comfort rating of "A", resulting in an overall rating of "A".

In Example 16, a polyurethane foam composition with an isocyanate index of 102 was prepared from 1000 g of polyester polyol PO-7 made of polytetramethylene ether glycol (PTMG), 30 g of polyrotaxane, and 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 5.0%, which was made from 334 g of 4,4'-diphenylmethane diisocyanate, and 2.1 g of foaming liquid. 330 g and 76 g were injected into a test piece mold and a product mold to prepare a test piece and a product.
Example 16 had a density of 0.51 g/cm ³ , a tensile strength of 5.0 MPa, a tensile strength rating of "A", a load change slope of 9.6, and a ride comfort rating of "O", resulting in an overall rating of "O".

In Comparative Example 1, 1,5-naphthalene diisocyanate (NDI) was used as the isocyanate, and a polyurethane foam composition with an isocyanate index of 108 was prepared from 1000 g of polyester polyol PO-1 (AA/EG) having an average carbon number between ester bonds of 3, 30 g of polyrotaxane, and 273 g of 1,5-naphthalene diisocyanate (NDI), as well as 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 5.0%, and 3.0 g of foaming liquid. The amounts injected into the test piece mold and the product mold were 330 g and 76 g, respectively, to prepare a test piece and a product.
Comparative Example 1 had a density of 0.50 g/cm ³ , a tensile strength of 4.3 MPa, a tensile strength rating of "A", a load change slope of 11.3, and a ride comfort rating of "X", resulting in an overall rating of "X".

Comparative Example 2 is an example that does not contain polyrotaxane, and a polyurethane foam composition having an isocyanate index of 108 was prepared from 1000 g of polyester polyol PO-6 (PCL) having an average carbon number of 5 between ester bonds and 100 g of a urethane prepolymer having an isocyanate group at a terminal and an NCO% (theoretical value) of 5.0%, which was prepared from 334 g of 4,4'-diphenylmethane diisocyanate, and 3.0 g of foaming liquid. The amounts injected into the test piece mold and the product mold were 323 g and 75 g, respectively, to prepare a test piece and a product.
Comparative Example 2 had a density of 0.49 g/cm ³ , a tensile strength of 4.0 MPa, a tensile strength rating of "A", a load change slope of 10.1, and a ride comfort rating of "X", resulting in an overall rating of "X".

Thus, each of the Examples has high mechanical strength (tensile strength) and good ride comfort. In contrast, Comparative Example 1, which used 1,5-naphthalene diisocyanate (NDI) as the isocyanate, and Comparative Example 2, which did not contain polyrotaxane, are inferior in ride comfort to Examples 1 to 16.
The present invention is not limited to the embodiments, and can be modified without departing from the spirit of the invention.

REFERENCE SIGNS LIST 10 Bound stopper 20 Polyrotaxane containing cyclic molecules having active hydrogen groups in its constituents 30 Mold 31 Lower mold 33 Middle mold 35 Upper mold

Claims (4)

A polyurethane foam bound stopper is attached to a piston rod of a shock absorber for a vehicle.
The polyurethane foam is obtained from a polyurethane foam composition including at least an isocyanate component and a blowing agent.
the isocyanate component is composed of a urethane prepolymer having an isocyanate group at a terminal thereof , the urethane prepolymer being obtained from a polyol component, a polyrotaxane containing a cyclic molecule having an active hydrogen group as a constituent, and diphenylmethane diisocyanate;
The urethane prepolymer having an isocyanate group at its end has a blending amount of the polyrotaxane of 0.1 parts by weight or more per 100 parts by weight of the polyol component,
A bound stopper characterized in that the density of the polyurethane foam is 0.2 g/cm3 or more ^. The bound stopper according to claim 1, characterized in that the urethane prepolymer having an isocyanate group at its end has a blending amount of the polyrotaxane of 0.1 to 6.5 parts by weight per 100 parts by weight of the polyol component. 3. The bound stopper according to claim 1, wherein the polyurethane foam has a density of 0.2 to 0.7 g/cm ³ . A method for manufacturing a bound stopper made of polyurethane foam to be attached to a piston rod of a shock absorber for a vehicle, comprising the steps of:
A polyol component and a polyrotaxane containing, as a constituent, a cyclic molecule having an active hydrogen group are mixed in a molten state, and then diphenylmethane diisocyanate is added to the mixture to prepare a urethane prepolymer having an isocyanate group at its terminal.
a polyurethane foam composition including at least a urethane prepolymer having an isocyanate group at a terminal thereof and a foaming agent is injected into a mold and foamed to form a bound stopper made of the polyurethane foam;
The urethane prepolymer having an isocyanate group at its end has a blending amount of the polyrotaxane of 0.1 parts by weight or more per 100 parts by weight of the polyol component,
A method for manufacturing a bound stopper, wherein the density of the polyurethane foam constituting the bound stopper is 0.2 g/cm3 ^or more .

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