Flame-retardant soundproofing material for vehicle

Abstract

A flame-retardant soundproofing material for vehicles according to the present invention is provided with a polyurethane foam obtained by foam molding a urethane resin composition. The urethane resin composition has (A) an isocyanate component, (B) a polyol component, (C) a flame-retardant plasticizer, and (D) an antioxidant. The (A) isocyanate component has: a mixture of a 2,4'-diphenylmethane diisocyanate and a 4,4'-diphenylmethane diisocyanate; and one or more modified products selected from at least one of a carbodiimide-modified product and a uretonimine-modified product of the mixture.

Description

Flame-retardant soundproofing material for vehicles

[0001] The present disclosure relates to a flame-retardant soundproofing material for vehicles used in the engine compartment of a vehicle, etc.

[0002] In vehicles such as automobiles, various measures are taken to reduce noise leaking outside the vehicle or into the passenger compartment. For example, in the engine compartment of a vehicle, soundproofing materials such as engine covers, side covers, and oil pan covers are placed around the engine to reduce noise radiated from the engine, which is a noise source. In recent years, attempts have been made to further enhance soundproofing by placing soundproofing materials around fuel pipes, transmissions, and other components. For example, soundproofing materials placed near rotating bodies that make up a transmission must have a desired rigidity to prevent deformation and interference with the rotating bodies. Rigidity at high temperatures is particularly important, and they must not sag or deform even at high temperatures (droop resistance). Furthermore, in the operating environment around the engine, flame retardancy is also required in addition to soundproofing.

[0003] For example, Patent Document 1 describes a flame-retardant soundproofing and vibration-proofing material for vehicles that uses a flexible polyurethane foam obtained by reacting and foaming an isocyanate component and a polyol component. Patent Document 1 also describes that by using diphenylmethane diisocyanate and a monomeric MDI containing its carbodiimide-modified product and / or uretonimine-modified product as the main component of the isocyanate component, the heat degradation resistance and flame retardancy of the polyurethane foam are improved.

[0004] JP-A-2003-97645 JP-A-5-105811

[0005] The polyurethane foam described in Patent Document 1 uses one or more modified compounds selected from carbodiimide modified compounds and uretonimine modified compounds as the isocyanate component. The use of modified compounds increases intermolecular cohesion, thereby improving the rigidity of the polyurethane foam. However, as the rigidity increases, the foam becomes less soluble during combustion, which prolongs combustion and reduces flame retardancy. Thus, improving rigidity and improving flame retardancy are in a trade-off relationship.

[0006] The present disclosure has been made in view of the above circumstances, and an object of the present disclosure is to provide a flame-retardant soundproofing material for vehicles that has desired rigidity and flame retardancy in addition to soundproofing properties.

[0007] (1) In order to solve the above-mentioned problems, the present disclosure provides a flame-retardant soundproofing material for vehicles, which includes a polyurethane foam obtained by foam-molding a urethane resin composition, and the urethane resin composition includes (A) an isocyanate component, (B) a polyol component, (C) a flame-retardant plasticizer, and (D) an antioxidant, and the (A) isocyanate component includes a mixture of 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate and one or more modified products selected from a carbodiimide-modified product and a uretonimine-modified product of at least one of the mixture.

[0008] In the flame-retardant soundproofing material for vehicles disclosed herein, a polyurethane foam having the desired soundproofing properties, rigidity, and flame retardancy is realized by using a specific isocyanate component as a raw material and by using a flame-retardant plasticizer and an antioxidant in combination. Regarding the isocyanate component, hereinafter, diphenylmethane diisocyanate will be referred to as "MDI," 2,4'-diphenylmethane diisocyanate will be referred to as "2,4'-MDI," and 4,4'-diphenylmethane diisocyanate will be referred to as "4,4'-MDI."

[0009] By using a modified product as the isocyanate component, intermolecular cohesion is enhanced, enabling the production of polyurethane foams with high rigidity not only at room temperature but also at high temperatures. The modified product is produced by a carbodiimidation reaction in which the NCO groups of two MDIs condense with each other, followed by a uretonimination reaction in which one molecule of MDI is added to the resulting carbodiimidation product (carbodiimide modified product). As a secondary reaction of the carbodiimidation reaction of MDI, a uretonimination product (uretonimine modified product) is also produced in a chemical equilibrium reaction. Generally, as the carbodiimidation reaction progresses, most of the reaction product is considered to be a uretonimine modified product. In this specification, the term "modified product" refers to "one or more modified products selected from carbodiimide modified products and uretonimine modified products," so as to include all products obtained by the carbodiimidation reaction of either or both of 2,4'-MDI and 4,4'-MDI. This can also be expressed as a “carbodiimide-modified product and / or a uretonimine-modified product.” The carbodiimide-modified product and the uretonimine-modified product can be obtained by a known method, for example, by reacting a single-component MDI or a multi-component MDI including isomers using a catalyst such as a phosphoric acid ester.

[0010] The polyurethane foam constituting the flame-retardant soundproofing material for vehicles of the present disclosure (hereinafter referred to as "the polyurethane foam of the present disclosure") contains a flame-retardant plasticizer. The flame-retardant plasticizer penetrates between polyurethane crystals at high temperatures, softening the polyurethane foam and making it more soluble. For example, using a simple plasticizer without flame retardancy can make the polyurethane foam more soluble during combustion, but there is a risk that it may burn and increase the size of the fire. In this regard, the polyurethane foam of the present disclosure uses a flame-retardant plasticizer, so this risk is eliminated. Thus, in the polyurethane foam of the present disclosure, even if the rigidity of the foam is increased by using a modified isocyanate component, the incorporation of the flame-retardant plasticizer makes the foam more soluble during combustion, thereby suppressing a decrease in flame retardancy.

[0011] The incorporation of a flame-retardant plasticizer improves the flame retardancy of a polyurethane foam. However, increasing the amount of the additive from the viewpoint of improving flame retardancy may soften the polyurethane foam and reduce its rigidity. In this regard, the polyurethane foam of the present disclosure uses an antioxidant in combination to ensure flame retardancy while maintaining the rigidity of the polyurethane foam. The antioxidant has the following effect: When polyurethane thermally decomposes, its molecules are cleaved, generating low-molecular-weight components. Low-molecular-weight components are easily ignited, promoting sustained combustion. The incorporation of an antioxidant inhibits the thermal decomposition of polyurethane and the generation of low-molecular-weight components, thereby reducing ignition components. In other words, the polyurethane foam of the present disclosure can be imparted with flame retardancy without the incorporation of an excessive amount of flame-retardant plasticizer by incorporating an antioxidant to preventively reduce ignition-prone components. This achieves both rigidity and flame retardancy, which was previously difficult to achieve.

[0012] Incidentally, Patent Document 2 describes a liquid flame-retardant polyurethane composition comprising 50 to 99% by weight of a flame-retardant organophosphorus compound and 50 to 1% by weight of tribromoneopentyl alcohol (TBNPA). Patent Document 2 also describes a formulation in which an antioxidant, such as a hydroquinone compound or a trivalent organophosphorus compound, is further added to a mixture of the flame-retardant organophosphorus compound and TBNPA. Patent Document 2 aims to provide a low-viscosity liquid composition that can impart flame retardancy using TBNPA. Therefore, the use of an antioxidant is not essential, and the effects of combining the composition with a flame-retardant organophosphorus compound are not described. Furthermore, the only polyurethane foams described are those in which the isocyanate component is toluene diisocyanate (TDI), and Patent Document 2 does not include the technical idea of ​​increasing the rigidity of the polyurethane foam.

[0013] (2) In the above configuration, the content of the modified isocyanate component (A) may be 19% by mass or more, based on 100% by mass of the entire urethane resin composition. The content of the modified isocyanate component (A) may be 30% by mass or less. These configurations make it easier to achieve a balance between the rigidity and flame retardancy of the polyurethane foam.

[0014] (3) In any of the above configurations, the content of the flame-retardant plasticizer (C) may be 3.7% by mass or more, based on 100% by mass of the entire urethane resin composition. The content of the flame-retardant plasticizer may also be 6.5% by mass or less. These configurations facilitate achieving a balance between the rigidity and flame retardancy of the polyurethane foam.

[0015] (4) In any of the above configurations, the flame-retardant plasticizer (C) may contain a phosphate ester. This configuration allows the polyurethane foam to be softened with a relatively small amount of the flame-retardant plasticizer, and also provides good moldability.

[0016] (5) In any of the above configurations, the content of the antioxidant (D) may be 1.6% by mass or more, based on 100% by mass of the entire urethane resin composition. The content of the antioxidant may also be 2.4% by mass or less. These configurations effectively suppress the generation of low-molecular-weight components due to thermal decomposition of polyurethane. As a result, the desired flame retardancy is imparted even with a small amount of flame-retardant plasticizer. For example, combining this configuration with the above configurations (2) and (3) is effective in imparting the desired rigidity and flame retardancy to a polyurethane foam.

[0017] (6) In any of the above configurations, the antioxidant (D) may contain a hindered phenol compound. This configuration can enhance the effect of inhibiting thermal decomposition of polyurethane. For example, combining this configuration with the above configuration (4) can further enhance the rigidity and flame retardancy of the polyurethane foam. Furthermore, combining the above configurations (2), (3), and (5) is even more preferable.

[0018] The flame-retardant soundproofing material for vehicles of the present disclosure has desired rigidity and flame retardancy in addition to soundproofing properties.

[0019] Hereinafter, embodiments of the flame-retardant soundproofing material for vehicles according to the present disclosure will be described. Note that the embodiments are not limited to the following embodiments, and various modifications and improvements that can be made by those skilled in the art can be made.

[0020] In the flame-retardant soundproofing material for vehicles of the present disclosure, the components other than the polyurethane foam are not particularly limited. The flame-retardant soundproofing material for vehicles of the present disclosure may be composed of polyurethane foam alone, or may be composed of a combination of polyurethane foam and other components. For example, when the flame-retardant soundproofing material for vehicles of the present disclosure is embodied in an engine cover, the engine cover may have a single-layer structure of polyurethane foam, or a multi-layer structure having a soundproofing layer made of polyurethane foam and a skin layer covering the surface thereof. Furthermore, the term "vehicle" as used herein includes not only automobiles but also airplanes, trains, and the like.

[0021] <Components of Polyurethane Foam> The polyurethane foam of the present disclosure is a foam-molded product of a urethane resin composition having (A) an isocyanate component, (B) a polyol component, (C) a flame-retardant plasticizer, and (D) an antioxidant.

[0022] (A) Isocyanate Component The isocyanate component contains a mixture of 2,4'-MDI and 4,4'-MDI and one or more modified products selected from a carbodiimide-modified product and a uretonimine-modified product of at least one of the mixtures. The content ratio of 2,4'-MDI to 4,4'-MDI in the mixture may be appropriately determined taking into consideration rigidity, moldability, etc. As described above, the modified product includes a product obtained by the carbodiimidation reaction of 2,4'-MDI or 4,4'-MDI, and a product obtained by the carbodiimidation reaction of 2,4'-MDI and 4,4'-MDI.

[0023] From the viewpoint of increasing the rigidity of the polyurethane foam, it is desirable to maximize the content of the modified substance in the isocyanate component. For example, the content of the modified substance is desirably 19% by mass or more, where the entire urethane resin composition is taken as 100% by mass. 21% by mass or more is more preferable. On the other hand, if the content of the modified substance is too high, the foam will not melt easily during combustion, making it difficult for embers to fall. In consideration of this point, the content of the modified substance is desirably 30% by mass or less, and 28% by mass or more is more preferable.

[0024] In addition to the mixture and modified product, the isocyanate component may also contain a prepolymer obtained by reacting MDI with a polyol. When the prepolymer is contained, the viscosity of the urethane resin composition is higher and moldability is improved compared to when the prepolymer is not contained. The prepolymer content is preferably 18% by mass or more and 30% by mass or less, with the entire urethane resin composition being taken as 100% by mass. For example, when MDI is reacted with a polyol having three functional groups, a prepolymer having three urethane bonds is obtained. Among these, an isocyanate-terminated prepolymer obtained by reacting MDI with a bifunctional polyether polyol is preferred. Here, examples of bifunctional polyether polyols include polyether polyols having a molecular weight of approximately 1,000.

[0025] Although mixtures, modified compounds, and prepolymers have been described as isocyanate components, the inclusion of other isocyanate compounds is not excluded as long as the polyurethane foam of the present disclosure can be realized without impairing the effects of these components. Examples of such isocyanate compounds include polymeric MDI (polynuclear compounds) containing three or more isocyanate groups and three or more benzene rings per molecule. However, the inclusion of polymeric MDI forms a crosslinked structure in the polyurethane foam, making it less likely to melt during combustion. This is undesirable because it may result in reduced flame retardancy.

[0026] (B) Polyol Component Known polyol components include polyhydric hydroxy compounds, polyether polyols, polyester polyols, polyether polyamines, polyester polyamines, alkylene polyols, urea-dispersed polyols, melamine-modified polyols, polycarbonate polyols, acrylic polyols, polybutadiene polyols, and phenol-modified polyols. When producing the polyurethane foam of the present disclosure, polyether polyols are used as the main component. The term "main component" refers to a component that accounts for 60% by mass or more, assuming that the total polyol component is 100% by mass. Therefore, the polyol component may be polyether polyol alone, or may be used in combination with other polyols as the main component. For example, from the viewpoint of improving moldability, it is desirable to use polyester polyols in combination. Furthermore, even when using only polyether polyols, multiple types with different functional groups, molecular weights, compatibility, etc. may be used in combination.

[0027] The number of functional groups of the polyether polyol is preferably 2 or more and 4 or less. If the number of functional groups is less than 2, the chain reaction with the isocyanate component is easily interrupted, making it difficult to polymerize, resulting in reduced moldability. For example, a polyether polyol with a functionality of 2 is suitable in that it does not form a crosslinked structure, making it easier to extinguish the fire during combustion and improving flame retardancy. A polyether polyol with a functionality of 3 or more is suitable in that it forms a crosslinked structure, thereby hardening the polyurethane foam and increasing its rigidity. However, if the number of functional groups exceeds 4, the polyurethane foam will have reduced elongation, resulting in reduced soundproofing.

[0028] The mass-average molecular weight of the polyether polyol is preferably 5,000 or more and 8,000 or less. If the mass-average molecular weight is less than 5,000, the polyurethane foam becomes hard, resulting in a decrease in soundproofing. If the mass-average molecular weight exceeds 8,000, the viscosity of the urethane resin composition becomes too high, making it difficult to react with the isocyanate component and to foam.

[0029] (C) Flame-retardant plasticizer Examples of flame-retardant plasticizers include halogenated or non-halogenated phosphorus compounds used as flame retardants. Halogenated phosphorus compounds have poor plasticity and therefore require a large amount to be added, which may reduce foam moldability. For this reason, non-halogenated phosphorus compounds are preferred. Flame-retardant plasticizers may be liquid or solid, but liquid is preferable from the perspective of mixing with liquid materials such as isocyanate components. Suitable flame-retardant plasticizers include, for example, phosphate esters such as trimethyl phosphate and tributyl phosphate.

[0030] From the viewpoint of fully suppressing the decrease in flame retardancy, the content of the flame-retardant plasticizer is preferably 3.7% by mass or more, and more preferably 4.0% by mass or more, based on 100% by mass of the entire urethane resin composition. On the other hand, from the viewpoint of avoiding a decrease in rigidity due to the incorporation of the flame-retardant plasticizer, the content of the flame-retardant plasticizer is preferably 6.5% by mass or less, and more preferably 6.0% by mass or less.

[0031] (D) Antioxidant Examples of the antioxidant include hindered phenol compounds and hindered amine compounds. Among them, hindered phenol compounds are preferred because they are highly effective in suppressing thermal decomposition of polyurethane. Hindered phenol compounds are phenol compounds having a substituent exhibiting steric hindrance at one or both ortho positions of the phenolic hydroxyl group. The antioxidant may be liquid or solid, but liquid antioxidants have a relatively small molecular weight and tend to volatilize when heated, which may result in the risk of burning and increasing the fire potential. Therefore, from the viewpoint of improving flame retardancy, it is preferable that the antioxidant be solid.

[0032] In order to fully exert the effects of suppressing thermal decomposition of polyurethane and reducing low-molecular-weight components that can become ignition components, the content of the antioxidant is desirably 1.6% by mass or more, and more preferably 1.8% by mass or more, based on 100% by mass of the entire urethane resin composition. On the other hand, from the viewpoint of avoiding a decrease in flame retardancy due to combustion of the antioxidant itself, the content of the antioxidant is desirably 2.4% by mass or less, and more preferably 2.2% by mass or less.

[0033] (E) Other Components In addition to the components (A) to (D) above, the urethane resin composition may contain, as appropriate, known materials used in producing polyurethane foams, such as catalysts, blowing agents, foam stabilizers, crosslinking agents, antistatic agents, viscosity reducers, stabilizers, fillers, and pigments. Among these, catalysts include amine catalysts such as tetramethylethylenediamine, bis(2-dimethylaminoethyl)ether, triethylenediamine, triethylamine, N,N,N',N'-tetramethylhexane-1,6-diamine, N,N,N',N'',N''-pentamethyl-diethylenetriamine, N,N,N',N'',N''',N'''-hexamethyltriethylenetetraamine, and N,N',N'-trimethylaminoethylpiperazine; acids such as formic acid, citric acid, butylic acid, and 2-ethylhexanoic acid; and organometallic catalysts such as tin laurate and tin octoate. Water is a preferred blowing agent. In addition to water, other suitable blowing agents include methylene chloride, CO ２ Suitable foam stabilizers include silicone-based foam stabilizers, and suitable crosslinking agents include diethylene glycol, triethanolamine, and diethanolamine.

[0034] <Properties of Polyurethane Foam> (1) Rigidity The rigidity of the polyurethane foam of the present disclosure is preferably, for example, an Asker C hardness of 63 or more. An Asker C hardness of 65 or more is more preferable. The Asker C hardness may be measured using an "Asker Rubber Hardness Tester Type C" manufactured by Kobunshi Keiki Co., Ltd., based on the spring hardness test type C specified in JIS K7312-1996.

[0035] (2) Flame Retardancy The flame retardancy of a polyurethane foam can be determined, for example, by conducting a horizontal burn test according to the UL94 standard. The horizontal burn test is performed by fixing one end of a sample and holding it horizontally, and applying a gas burner flame to the free end for 30 seconds. If the sample continues to burn after the flame is removed, the burning rate is measured. The polyurethane foam of the present disclosure preferably has HB level flame retardancy according to the UL94 standard. The criteria for determining whether or not a sample has HB level flame retardancy are as follows: (1) For samples with a thickness of 3.05 mm or more, the burning rate does not exceed 38.1 mm per minute. (2) For samples with a thickness of 3.05 mm or less, the burning rate does not exceed 76.2 mm per minute, or the burning stops before the flame reaches a point 102 mm from the end of the sample. The polyurethane foam of the present disclosure desirably has flame retardancy at the HB level of the UL94 standard not only in its normal state, i.e., the state in which it is produced, but also after heat aging at 135° C. for 168 hours. It also desirably maintains flame retardancy at the HB level of the UL94 standard even after heat aging at 135° C. for 336 hours and even after heat aging at 135° C. for 600 hours. Heat aging can be performed by placing a sample in an oven at 135° C. and maintaining it for a predetermined period of time.

[0036] <Method for Producing Polyurethane Foam> The polyurethane foam of the present disclosure is produced by foam molding a urethane resin composition. First, a premix polyol is prepared by premixing a polyol component with an antioxidant and other components, such as a catalyst, a blowing agent, and a foam stabilizer. Next, the prepared premix polyol is mixed with an isocyanate component and a flame-retardant plasticizer, followed by foam molding. For example, the premix polyol, the isocyanate component, and the flame-retardant plasticizer may be mechanically stirred using a propeller or the like, and then injected into a mold for foam molding. Alternatively, a mixed raw material containing the isocyanate component and the flame-retardant plasticizer may be prepared in advance. The premix polyol and the mixed raw material may then be ejected at high pressure using a high-pressure injector or the like, causing the two components to collide and mix, resulting in foam molding (impingement mixing method). The impingement mixing method enables continuous production, making it suitable for mass production. Furthermore, compared to mechanical stirring methods, the collision stirring method eliminates the need for a container cleaning step that is required after each mixing, improving yield and reducing manufacturing costs.

[0037] The premix polyol and the isocyanate component are preferably blended so that the isocyanate index (equivalent ratio of isocyanate groups to active hydrogen groups) is 1.0 to 1.5, preferably 1.0 to 1.2. If the isocyanate index is less than 1.0, flame retardancy decreases. If it exceeds 1.5, moldability decreases.

[0038] Next, the present disclosure will be described more specifically with reference to examples.

[0039] <Production of Polyurethane Foam Sample> First, 100 parts by mass of polyether polyol (SBU Polyol 0248 manufactured by Sumika Covestro Urethane Co., Ltd., average molecular weight 6000, number of functional groups 3) as the polyol component (B) was appropriately blended with a hindered phenol compound (IRGANOX (registered trademark) 1010 manufactured by BASF) as the antioxidant, and further 3 parts by mass of diethanolamine as a crosslinking agent, 5 parts by mass of water as a blowing agent, 0.6 parts by mass of amine catalyst A (Kao Raiser (registered trademark) No. 31 manufactured by Kao Corporation), 0.4 parts by mass of amine catalyst B (TOYOCAT (registered trademark) MR manufactured by Tosoh Corporation), 0.3 parts by mass of a silicone foam stabilizer (VORASURF (registered trademark) SZ-1336 manufactured by Dow-Toray Industries, Inc.), 0.3 parts by mass of a pigment (FTIRGANOX (registered trademark) manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd.), and 2 parts by mass of "1576 Black" was added and mixed to prepare a premix polyol.

[0040] Next, as the isocyanate component (A), an isocyanate raw material was prepared by appropriately mixing a mixture of 2,4'-MDI and 4,4'-MDI, a modified MDI containing a modified product obtained by carbodiimidizing 4,4'-MDI (manufactured by Sumika Bayer Urethane Co., Ltd., "SBU Isocyanate 0632"), and an MDI prepolymer (manufactured by the same company, "SBU Isocyanate S234")

[0041] Next, the prepared premix polyol and an isocyanate raw material were mixed so that the isocyanate index was 1.0 to 1.1, and then (C) a phosphate ester of a flame-retardant plasticizer ("ADEKA STAB (registered trademark) PFR" manufactured by ADEKA Corporation) was appropriately added and mixed to prepare a urethane resin composition. The blending amounts of each component in the urethane resin composition are as shown in Table 1 below. The urethane resin composition was then injected into the cavity of a mold, sealed, and foam-molded at a mold temperature of 50°C for 5 minutes to produce 13 types of polyurethane foam samples. The density of the polyurethane foam samples was 0.12 g / cm. ３ It was decided.

[0042] <Evaluation of Polyurethane Foam> The produced samples were evaluated for rigidity, flame retardancy and soundproofing.

[0043] [Evaluation Method] (1) Rigidity The Asker C hardness of the sample was measured using an Asker Rubber Hardness Tester Type C manufactured by Kobunshi Keiki Co., Ltd.

[0044] (2) Flame Retardancy: Strip-shaped test specimens (normal test specimens) measuring 127 mm in length, 12.7 mm in width, and 12.7 mm in thickness were prepared from the prepared samples. First, the normal test specimens were subjected to a horizontal combustion test according to the UL94 standard. Next, the normal test specimens were placed in an oven at 135°C and subjected to heat aging for 168 hours (first heat aging), and then the same test was performed. Separately, the normal test specimens were placed in an oven at 135°C and subjected to heat aging for 336 hours (second heat aging), and then the same test was performed. Furthermore, the normal test specimens were placed in an oven at 135°C and subjected to heat aging for 600 hours (third heat aging), and then the same test was performed. The samples were evaluated as having high flame retardancy (indicated by a circle in Table 1) if they met the HB level criteria (burning rate not exceeding 38.1 mm per minute), and as having insufficient flame retardancy (indicated by an x ​​in Table 1) if they did not meet the criteria.

[0045] (3) Soundproofing The cross section of the polyurethane foam was observed using a microscope, and if open cells were formed, it was evaluated as having the desired soundproofing. In the evaluation column of Table 1, if open cells were formed, the soundproofing was evaluated as "present."

[0046] [Evaluation Results] Table 1 shows the components of the urethane resin composition and the evaluation results of the polyurethane foam.

[0047] As shown in Table 1, Samples 1 to 7 had high rigidity in addition to soundproofing properties. Furthermore, they had flame retardancy at the UL94 HB level not only in the normal state but also after heat aging. Samples 8 to 13 had sound absorption properties, but were inferior to Samples 1 to 7 in either rigidity or flame retardancy. Specifically, Sample 8, which contained a higher proportion of modified substance than Samples 1 to 7, had reduced flame retardancy. Conversely, Sample 9, which contained a lower proportion of modified substance, had reduced rigidity. Sample 10, which contained a higher proportion of flame-retardant plasticizer than Samples 1 to 7, had reduced rigidity. Conversely, Sample 11, which contained a lower proportion of flame-retardant plasticizer, had reduced flame retardancy. Sample 12, which contained a higher proportion of antioxidant than Samples 1 to 7, had high flame retardancy after heat aging but reduced flame retardancy in the normal state. On the other hand, sample 13, which contained a small amount of antioxidant, had high flame retardancy both at room temperature and after 168 hours of heat aging, but the effect of inhibiting the thermal decomposition of polyurethane was insufficient, and the flame retardancy decreased after heat aging for 336 hours or more.

[0048] The flame-retardant soundproofing material for vehicles of the present disclosure is useful as a soundproofing material to be placed around engine covers, side covers, oil pan covers, as well as fuel pipes, transmissions, etc.

Claims

1. A flame-retardant soundproofing material for vehicles comprising a polyurethane foam obtained by foam molding a urethane resin composition, the urethane resin composition comprising (A) an isocyanate component, (B) a polyol component, (C) a flame-retardant plasticizer, and (D) an antioxidant, the (A) isocyanate component comprising a mixture of 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate, and one or more modified products selected from a carbodiimide modified product and a uretonimine modified product of at least one of the mixture.

2. A flame-retardant soundproofing material for vehicles as described in claim 1, wherein the content of the modified form of the (A) isocyanate component is 19% by mass or more and 30% by mass or less, when the entire urethane resin composition is 100% by mass.

3. A flame-retardant soundproofing material for vehicles as described in claim 1, wherein the content of the flame-retardant plasticizer (C) is 3.7 mass% or more and 6.5 mass% or less, when the entire urethane resin composition is 100 mass%.

4. The flame-retardant soundproofing material for vehicles according to claim 1, wherein the flame-retardant plasticizer (C) comprises a phosphate ester.

5. A flame-retardant soundproofing material for vehicles as described in claim 1, wherein the content of the (D) antioxidant is 1.6 mass% or more and 2.4 mass% or less, when the entire urethane resin composition is 100 mass%.

6. The flame-retardant soundproofing material for vehicles according to claim 1, wherein the antioxidant (D) comprises a hindered phenol compound.

7. The flame-retardant soundproofing material for vehicles according to claim 1, wherein the (C) flame-retardant plasticizer comprises a phosphoric acid ester, and the (D) antioxidant comprises a hindered phenol compound.

8. A flame-retardant soundproofing material for vehicles as described in claim 1, wherein, when the entire urethane resin composition is taken as 100 mass%, the content of the modified form of the isocyanate component (A) is 19 mass% or more and 30 mass% or less, the content of the flame-retardant plasticizer (C) is 3.7 mass% or more and 6.5 mass% or less, and the content of the antioxidant (D) is 1.6 mass% or more and 2.4 mass% or less.

9. The flame-retardant soundproofing material for vehicles according to claim 8, wherein the flame-retardant plasticizer (C) comprises a phosphoric acid ester, and the antioxidant (D) comprises a hindered phenol compound.

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