Hot melt adhesive and method for manufacturing hot melt adhesive

Abstract

To provide a hot melt adhesive that can be used in a wide range of applications. [Solution] The hot melt pressure-sensitive adhesive is made from an amine hydrolyzate of polyurethane with polyetheramine having a molecular weight or number average molecular weight of 150 to 800, and at least one selected from the group consisting of carboxylic acids and carboxylic acid anhydrides.

Description

[Technical Field]

[0001] The present disclosure relates to a hot melt adhesive and a method for producing the hot melt adhesive. [Background technology]

[0002] Effective utilization of waste polyurethane materials, etc. has been studied. For example, Patent Document 1 discloses a hot melt adhesive that utilizes waste polyurethane materials, etc. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-131602 Summary of the Invention [Problem to be solved by the invention]

[0004] However, this hot melt adhesive has limited uses, for example, it is not very effective for joining plastic vehicle parts.

[0005] The present disclosure has been made in view of the above circumstances, and aims to provide a hot melt pressure-sensitive adhesive that can be used in a wide range of applications by effectively utilizing polyurethane waste, etc. The present disclosure can be realized in the following aspects. [Means for solving the problem]

[0006] [1] an amine hydrolyzate of polyurethane with a polyetheramine having a molecular weight or number average molecular weight of 150 or more and 800 or less; At least one selected from carboxylic acids and carboxylic acid anhydrides; A hot melt adhesive made from the raw material. [Effects of the Invention]

[0007] According to the present disclosure, a hot melt pressure sensitive adhesive that can be used in a wide range of applications can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a conceptual diagram for explaining an example of the first step of the embodiment. [Figure 2] FIG. 2 is a conceptual diagram for explaining an example of the second step of the embodiment. [Figure 3] FIG. 3 is a conceptual diagram for explaining an example of the third step of the embodiment. [Figure 4] FIG. 4 is a conceptual diagram showing the procedure for producing an evaluation sample. [Figure 5] FIG. 5 is a conceptual diagram showing the procedure for producing an evaluation sample. [Figure 6] Fig. 6(A) is a conceptual diagram showing the evaluation results of an example, and Fig. 6(B) is a conceptual diagram showing the evaluation results of a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0009] Here, a preferred example of the present disclosure will be described. [2] The hot melt pressure-sensitive adhesive according to [1], which contains a tackifier resin. [3] The hot melt pressure-sensitive adhesive according to [1] or [2], which contains a polyhydric alcohol. [4] an amine decomposition step in which polyurethane is decomposed using a polyetheramine having a molecular weight or number average molecular weight of 150 to 800 to obtain an amine decomposition product; a reaction step of reacting the amine decomposition product with at least one selected from a carboxylic acid and a carboxylic acid anhydride; A method for producing a hot melt adhesive, comprising: [5] The method for producing a hot melt pressure-sensitive adhesive according to [4], further comprising the step of adding a tackifier resin. [6] The method for producing a hot melt pressure-sensitive adhesive according to [4] or [5], wherein the aminolysis step is carried out in the presence of a polyhydric alcohol.

[0010] The present disclosure will be described in detail below. In this specification, when a numerical range is indicated using "-", it is intended to include both the lower limit and the upper limit unless otherwise specified. For example, the expression "10-20" includes both the lower limit "10" and the upper limit "20". In other words, "10-20" has the same meaning as "10 or more and 20 or less". In addition, in this specification, the upper limit and lower limit of each numerical range can be combined in any way.

[0011] 1. Hot melt adhesive The hot melt pressure sensitive adhesive is made from an amine decomposition product of polyurethane and at least one selected from carboxylic acids and carboxylic acid anhydrides.

[0012] (1) Amine decomposition products of polyurethane The amine hydrolyzed product of polyurethane is obtained by hydrolyzing polyurethane with a polyetheramine having a molecular weight or number average molecular weight of 150 or more and 800 or less.

[0013] (1.1) Polyurethane The polyurethane may be any of flexible polyurethane foam, semi-rigid polyurethane foam, and rigid polyurethane foam. The polyurethane may be a polyurethane foam with an open cell structure or a polyurethane foam with a closed cell structure. The polyurethane may be a pulverized product pulverized to a predetermined size. The polyurethane may also be a cut product cut to a predetermined size. Examples of polyurethane include scraps discarded during the polyurethane foam manufacturing process and used polyurethane foam to be discarded.

[0014] The polyurethane to be decomposed may be, for example, polyurethane contained in a vehicle ceiling material. The vehicle ceiling material is, for example, a laminate including a urethane foam sheet. Specifically, the vehicle ceiling material is made of a laminate obtained by laminating and compression-molding a slabstock foamed soft urethane foam sheet, a glass fiber sheet coated with a urethane moisture-curing adhesive, and an olefin synthetic resin nonwoven fabric. The polyurethane to be decomposed may or may not be separated from the vehicle ceiling material. In addition, in JP 2018-131602 A and JP 2018-141163 A, synthetic wood, which is a hard polyurethane composite material, is the main target of decomposition.

[0015] (1.2) Polyetheramine Using polyetheramines for amine decomposition suppresses unpleasant odors (e.g., alcohol odor, ammonia odor) from hot-melt adhesives. Using low-molecular-weight amines such as benzylamine or diethanolamine instead of polyetheramines results in odors (e.g., ammonia odor) from the hot-melt adhesive, limiting the applications of the hot-melt adhesive. For example, using low-molecular-weight amines makes it difficult to use them for adhering automotive components. In contrast, using polyetheramines for amine decomposition allows hot-melt adhesives to be used for a wide range of applications, including adhering automotive components. The polyetheramine has a molecular weight or number average molecular weight of 150 or more and 800 or less. The molecular weight or number average molecular weight of the polyetheramine is 150 or more, preferably 230 or more, and more preferably 400 or more, from the viewpoint of suppressing the odor of the hot-melt pressure-sensitive adhesive and suppressing cracking or disintegration when a solidified hot-melt pressure-sensitive adhesive is subjected to vibration or impact. The molecular weight or number average molecular weight of the polyetheramine is 800 or less, preferably 700 or less, and more preferably 600 or less, from the viewpoint of at least one of sufficiently decomposing polyurethane with amino groups at a practical rate, suppressing residual odors, and suppressing adverse effects of residual catalysts. From these viewpoints, the molecular weight or number average molecular weight of the polyetheramine is 150 or more and 800 or less, preferably 230 or more and 700 or less, and more preferably 400 or more and 600 or less. The number average molecular weight can be measured by a known method. For example, it can be measured by using gel permeation chromatography (GPC) with tetrahydrofuran (THF) as an eluent and detecting the differential refractive index. The number average molecular weight is calculated by creating a calibration curve based on the GPC measurement results of a standard sample, polystyrene, and calculating the measurement results of the measurement sample as a polystyrene equivalent value.

[0016] In addition, if a low molecular weight amine such as benzylamine or diethanolamine is used instead of polyetheramine, the hot melt adhesive will emit an odor, limiting the applications of the hot melt adhesive. For example, if a low molecular weight amine is used, it will be difficult to use it for adhering automotive parts. The reason for this is that if a low molecular weight amine is used, the physical properties of the hot melt adhesive will become unstable, making it necessary to take measures against hydrolysis. When the molecular weight of the polyetheramine is increased, the effects of improving the melt viscosity of the hot melt pressure sensitive adhesive and improving the strength of the cured product can be expected. One reason for using polyetheramines to increase the molecular weight of hot-melt adhesives is to improve the impact resistance of the cured hot-melt adhesive, thereby suppressing cracking due to vibration and improving its suitability as an adhesive for automotive parts. Another reason is to improve the mechanical strength (peel strength) of the cured hot-melt adhesive, improving its suitability as an adhesive for automotive parts. Another reason is to ensure a melt viscosity (or high softening temperature) that prevents the hot-melt adhesive from flowing at the required heat resistance temperature (80°C). If the molecular weight of the polyetheramine is too high, there is a risk that undissolved polyetheramine may be produced.

[0017] The amount of polyetheramine added is not particularly limited. The amount of polyetheramine added is preferably 65 parts by mass or more, more preferably 70 parts by mass or more, and even more preferably 75 parts by mass or more, per 100 parts by mass of polyurethane, from the viewpoint of sufficiently decomposing the polyurethane. The amount of polyetheramine added is preferably 100 parts by mass or less, more preferably 95 parts by mass or less, and even more preferably 90 parts by mass or less, per 100 parts by mass of polyurethane, from the viewpoint of reducing unreacted polyetheramine even after hot melting and sufficiently solidifying the hot melt pressure-sensitive adhesive after cooling. From these viewpoints, the amount of polyetheramine added is preferably 65 parts by mass or more and 100 parts by mass or less, more preferably 70 parts by mass or more and 95 parts by mass or less, and even more preferably 75 parts by mass or more and 90 parts by mass or less.

[0018] (2) Carboxylic acids and carboxylic anhydrides The carboxylic acid or carboxylic anhydride reacts with the polyol contained in the amine decomposition product to produce an ester. It is believed that this esterification causes a dehydration condensation reaction in the polyol. As a result, the molecular weight of the polyol increases, and even when the solidified hot-melt adhesive is heated, low-molecular-weight reaction products are less likely to be produced, thereby suppressing evaporation loss and thermal degradation. In other words, the thermal softening temperature of the solidified hot-melt adhesive increases, expanding the uses of the hot-melt adhesive to include adhesion to components that may be exposed to high temperatures. In addition, carboxylic acids or carboxylic anhydrides can neutralize methylenedianiline (MDA), which is generated during the thermal decomposition process of MDI, the main raw material that makes up rigid urethane, thereby suppressing the generation of MDA. Since the esterification reaction is a reversible equilibrium reaction, it is necessary to suppress the reverse reaction (hydrolysis reaction). Therefore, it is desirable to remove the water generated during the esterification reaction as quickly as possible. For example, it is desirable to adopt a nitrogen substitution method in which the steam generated in the reaction vessel is replaced with nitrogen.

[0019] The type of carboxylic acid is not particularly limited. From the viewpoint of promoting the dehydration condensation reaction, a carboxylic acid having 2 to 10 carbon atoms is preferred as the carboxylic acid. Among these, a saturated or unsaturated aliphatic dicarboxylic acid having 2 to 8 carbon atoms is preferred from the viewpoint of increasing the molecular weight of the decomposition product by reacting with the amino group contained in the amine decomposition product to form an amide, thereby suppressing cracking or disintegration when the solidified hot-melt pressure-sensitive adhesive is subjected to vibration or impact. The saturated or unsaturated aliphatic dicarboxylic acid having 2 to 8 carbon atoms is preferably one or more selected from the group consisting of oxalic acid, maleic acid, fumaric acid, malonic acid, succinic acid, glutaric acid, adipic acid, and sebacic acid. The type of carboxylic acid anhydride is not particularly limited. As the carboxylic acid anhydride, a carboxylic acid anhydride having 2 to 10 carbon atoms is preferred. Among these, a saturated or unsaturated aliphatic dicarboxylic acid anhydride having 4 to 8 carbon atoms is preferred, from the viewpoint of increasing the molecular weight of the decomposition product by generating an amide through reaction with an amino group contained in the amine decomposition product, and suppressing cracking or disintegration when the solidified hot-melt pressure-sensitive adhesive is subjected to vibration or impact. The saturated or unsaturated aliphatic dicarboxylic acid having 4 to 8 carbon atoms is preferably one or more selected from the group consisting of maleic anhydride, fumaric anhydride, malonic anhydride, succinic anhydride, glutaric anhydride, and adipic anhydride. The carboxylic acids and carboxylic anhydrides can be used in combination. Furthermore, since both carboxylic acids and carboxylic anhydrides are weak acids, they also have the function of neutralizing the MDA contained in the amine decomposition product. As a result of the neutralization of MDA, the amount of MDA in the hot melt adhesive can be significantly reduced.

[0020] The amount of at least one selected from carboxylic acids and carboxylic acid anhydrides added is preferably 25 to 30 parts by mass per 100 parts by mass of polyurethane, from the viewpoint of increasing the molecular weight of the decomposition products, sufficiently neutralizing MDA (methylenedianiline), suppressing the generation of carboxylate salts, and cost.

[0021] (3) Tackifying resin From the viewpoint of improving adhesive strength, the hot melt adhesive preferably contains a tackifying resin. The tackifier resin is not particularly limited, and examples of the tackifier resin that can be used include one or more selected from the group consisting of rosin-based tackifier resins, terpene-based tackifier resins, hydrocarbon-based tackifier resins, epoxy-based tackifier resins, polyamide-based tackifier resins, elastomer-based tackifier resins, phenol-based tackifier resins, and ketone-based tackifier resins.

[0022] As the tackifying resin, it is preferable to use at least a rosin-based tackifying resin from the viewpoint of ensuring adhesion to PE materials such as automobile parts while taking the environment into consideration. Rosin-based tackifiers are derived from natural products and are therefore preferred from the perspective of recent carbon neutrality. Furthermore, rosin-based tackifier resins have good compatibility with hydroxyl groups, so they are more likely to bond with the hydroxyl groups of unreacted polyols in an ester reaction than petroleum-based tackifier resins. Therefore, the use of rosin-based tackifier resins makes it easier to prepare uniform hot-melt adhesives. The rosin-based tackifying resin is not particularly limited. Examples of rosin-based tackifying resins include unmodified rosins (raw rosins) such as gum rosin, wood rosin, and tall oil rosin; modified rosins (hydrogenated rosin, disproportionated rosin, polymerized rosin, and other chemically modified rosins) obtained by modifying these unmodified rosins through hydrogenation, disproportionation, polymerization, etc.; and various other rosin derivatives. Examples of the rosin derivatives include rosin esters such as those obtained by esterifying unmodified rosin with alcohols (i.e., rosin esters), and those obtained by esterifying modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, and other chemically modified rosins) with alcohols (i.e., modified rosin esters); unsaturated fatty acid-modified rosins obtained by modifying unmodified rosin or modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, and other) with unsaturated fatty acids; and unsaturated fatty acid-modified rosins obtained by modifying rosin esters with unsaturated fatty acids. rosin esters; rosin alcohols obtained by reducing the carboxyl groups in unmodified rosin, modified rosin (hydrogenated rosin, disproportionated rosin, polymerized rosin, etc.), unsaturated fatty acid modified rosins, or unsaturated fatty acid modified rosin esters; metal salts of rosins (particularly rosin esters) such as unmodified rosin, modified rosin, and various rosin derivatives; rosin phenolic resins obtained by adding phenol to rosins (unmodified rosin, modified rosin, various rosin derivatives, etc.) using an acid catalyst and then thermally polymerizing the resulting rosin. The softening temperature of the rosin-based tackifier resin is not particularly limited. From the viewpoint of ensuring sufficient heat resistance of the cured product of the hot-melt pressure-sensitive adhesive, the softening temperature of the rosin-based tackifier resin is preferably 80°C or higher and 150°C or lower. For example, taking into consideration the temperature on a vehicle dashboard, the softening temperature of the rosin-based tackifier resin is more preferably 120°C or higher and 150°C or lower. When the softening temperature of the rosin-based tackifier resin is within the above-mentioned preferred range, the cured product of the hot-melt pressure-sensitive adhesive is less likely to soften even at high temperatures, and peeling of the cured product from the adherend at high temperatures is suppressed. As a result, hot-melt pressure-sensitive adhesives using rosin-based tackifier resins having such softening temperatures are suitable for use in adhesion to components exposed to high temperatures, such as automotive interior materials.

[0023] The softening temperature of the rosin-based tackifying resin is measured using the ring and ball method in accordance with JIS K5903. Specifically, (B) the rosin-based tackifying resin is dissolved in an evaporating dish at the lowest possible temperature and poured into a preheated ring. After cooling, the raised portion of the ring, including the top edge, is cut off with a slightly heated knife. The ring filled with the tackifying resin is then inserted into a designated hole in a holder and placed in a glass container (diameter 85 mm, height 127 mm or more). The temperature of the glycerin liquid, which serves as the heat transfer medium in the glass container, is maintained for 15 minutes so that it does not drop by more than 45°C below the designated softening point. Next, a steel ball is placed in the center of the tackifying resin in the ring and placed in a fixed position on the holder. Heating is performed while maintaining a distance of 50 mm or more from the top edge of the ring to the glycerin liquid. After heating begins, the temperature is raised at a rate of 5.0±0.5°C per minute from 45°C before the specified softening point, and the temperature at which the tackifier resin softens and comes into contact with the bottom plate is taken as the softening temperature.

[0024] The amount of tackifier resin added is preferably 10% by mass or more, where the entire hot melt adhesive is taken as 100% by mass, from the viewpoint of ensuring sufficient adhesion to flat surfaces such as sound-absorbing materials, and more preferably 20% by mass or more, from the viewpoint of ensuring sufficient adhesion to curved surfaces and ensuring adhesive strength that will not peel even in high-temperature environments of 80°C or higher. From the viewpoint of cost, the amount of the tackifier resin added is preferably 60% by mass or less, where the total amount of the hot melt adhesive is 100% by mass. From these viewpoints, the amount of the tackifier resin added is preferably 10% by mass or more and 60% by mass or less, and more preferably 20% by mass or more and 50% by mass or less.

[0025] (4) Polyhydric alcohol The hot melt pressure sensitive adhesive preferably contains a polyhydric alcohol from the viewpoint of ensuring flexibility of the solidified hot melt pressure sensitive adhesive and suppressing cracking or disintegration when subjected to vibration or impact. The polyhydric alcohol is not particularly limited. The polyhydric alcohol may be a dihydric polyhydric alcohol or a trihydric or higher polyhydric alcohol. The polyhydric alcohols may be used alone or in combination of two or more kinds. As the dihydric polyalcohol, a diol having a branched structure is preferred. As the diol having a branched structure, a diol having 6 to 20 carbon atoms is preferred, a diol having 6 to 12 carbon atoms is more preferred, and a diol having 8 to 10 carbon atoms is even more preferred. A suitable example of a diol having a branched structure is butylethylpropanediol (BEPG, 2-butyl-2-ethyl-1,3-propanediol). Examples of trihydric or higher polyhydric alcohols include glycerin, trimethylolpropane, trialkanolamine, pentaerythritol, diglycerin, triglycerin, dipentaerythritol, sorbit, sorbitan, and sorbide.

[0026] As the polyhydric alcohol, butyl ethyl propanediol and glycerin are preferred from the viewpoint of compatibility with the rosin-based tackifying resin. As the polyhydric alcohol, butyl ethyl propanediol is more preferred from the viewpoint of compatibility with the rosin-based tackifying resin.

[0027] From the viewpoint of ensuring sufficient adhesiveness, the amount of polyhydric alcohol added is preferably 10 parts by mass or more and 45 parts by mass or less, more preferably 15 parts by mass or more and 35 parts by mass or less, and even more preferably 20 parts by mass or more and 25 parts by mass or less, relative to 100 parts by mass of the total of the "polyurethane used for decomposition," the "polyetheramine," and the "at least one selected from carboxylic acids and carboxylic acid anhydrides."

[0028] (5) Uses of hot melt adhesives The use of the hot melt adhesive of the present disclosure is not particularly limited. This hot melt adhesive has high heat resistance, impact resistance, and vibration resistance, making it suitable for use in adhering automobile components. In addition, this hot melt adhesive has little odor (low VOC volatilization), making it suitable for use in adhering automobile interior materials. Examples of interior materials include ceiling materials and floor materials. The hot melt pressure sensitive adhesive of the present disclosure can also be applied to PP-based members (PP-based molded articles) and PE-based members (PE-based molded articles), which have traditionally been difficult to adhere to.

[0029] (6) Effect of hot melt adhesive The hot melt adhesive of the present disclosure can effectively utilize polyurethane-containing scrap materials, which have traditionally been discarded or used as RPF fuel, as hot melt adhesives that can be used in a wide range of applications. For example, polyurethane-containing scrap materials can be chemically recycled and utilized as adhesives for vehicle components. Examples of vehicle components include automotive air conditioning ducts, automotive instrument panel ducts, and automotive sound-absorbing components. The hot melt pressure sensitive adhesive of the present disclosure can suppress as much as possible the production of MDA, which is a harmful substance to the human body. According to the hot melt adhesive of the present disclosure, even after components are adhered to each other, the components can be separated by softening the adhesive portion with heat. Therefore, it is possible to provide components that can be disassembled relatively easily. In other words, such components are easy to disassemble after use. For example, a component in which a sound-absorbing material is adhered to a substrate with the hot melt adhesive of the present disclosure is easy to disassemble. Use of a rosin-based tackifier in the hot melt pressure-sensitive adhesive of the present disclosure results in an environmentally friendly hot melt pressure-sensitive adhesive. The hot melt adhesive of the present disclosure does not use organic solvents and therefore does not generate VOCs such as aldehydes, toluene, or xylene. The hot melt adhesive of the present disclosure is a hot melt adhesive made primarily from urethane, and therefore melts and softens slowly as the temperature rises. Therefore, the temperature range in which the adhesive can remain softened is wide, ensuring a long open time. This makes it easy to adapt to various work environments. In other words, the application and application procedures must be adjusted depending on the type of material to be adhered, but this adhesive is also easy to adapt to these adjustments. The characteristics of this hot melt adhesive are a significant difference from PP-based hot melt adhesives. The hot melt pressure sensitive adhesive of the present disclosure does not require a catalyst, and therefore can suppress the irritating odor caused by the catalyst. The hot melt pressure sensitive adhesive of the present disclosure does not require a catalyst, and is therefore advantageous in terms of cost since no expensive catalyst is used. The hot melt pressure sensitive adhesive of the present disclosure does not require a catalyst, and therefore there is no concern about secondary reactions caused by catalyst remaining in the hot melt pressure sensitive adhesive.

[0030] 2. Manufacturing method of hot melt adhesive The manufacturing method of a hot melt adhesive includes the following steps [1] [2]. Step [1]: An amine decomposition step in which polyurethane is decomposed using a polyetheramine having a molecular weight or number average molecular weight of 150 or more and 800 or less to produce an amine decomposition product. Step [2]: A reaction step in which the amine decomposition product is reacted with at least one selected from a carboxylic acid and a carboxylic acid anhydride. The method for producing a hot melt pressure sensitive adhesive of the present disclosure involves chemical recycling of polyurethane.

[0031] (1) Process [1] Regarding the terms "polyetheramine," "polyurethane," and "polyhydric alcohol" in step [1], the explanations for "(1.2) polyetheramine," "(1.1) polyurethane," and "(1.5) polyhydric alcohol" in the "1. Hot melt adhesive" section shall apply as is, and the description thereof shall be omitted.

[0032] The amount of polyetheramine added in step [1] is preferably 25 parts by mass or more and 100 parts by mass or less per 100 parts by mass of polyurethane, since it sufficiently decomposes the polyurethane.

[0033] The decomposition temperature in step [1] is preferably 150°C or higher and 210°C or lower, more preferably 160°C or higher and 200°C or lower, and even more preferably 170°C or higher and 190°C or lower, from the viewpoint of promoting the thermal decomposition of polyurethane while suppressing the generation of MDA. The decomposition treatment time is not particularly limited, but may be, for example, 10 minutes to 24 hours, or 30 minutes to 10 hours. The end point of the decomposition treatment time may be appropriately set while checking the progress of decomposition of the polyurethane depending on the size of the polyurethane, whether stirring is performed, etc.

[0034] Step [1] is preferably carried out in the presence of a polyhydric alcohol, from the viewpoint of ensuring flexibility of the solidified hot-melt pressure-sensitive adhesive and suppressing cracking or disintegration when subjected to vibration or impact.

[0035] From the viewpoint of ensuring sufficient adhesiveness, the amount of polyhydric alcohol added is preferably 2 to 20 parts by mass, more preferably 7 to 18 parts by mass, and even more preferably 12 to 15 parts by mass, per 100 parts by mass of the total of the "polyurethane used for decomposition," the "polyetheramine," and "at least one selected from carboxylic acids and carboxylic acid anhydrides."

[0036] (2) Process [2] Regarding the terms "carboxylic acid" and "carboxylic acid anhydride" in step [2], the explanation for "(2) Carboxylic acid, carboxylic acid anhydride" in the section "1. Hot melt adhesive" applies as is, and the description thereof will be omitted.

[0037] The amount of at least one selected from carboxylic acids and carboxylic acid anhydrides is preferably 25 parts by mass or more and 30 parts by mass or less per 100 parts by mass of polyurethane, from the viewpoint of increasing the molecular weight of the decomposition product, sufficiently neutralizing MDA (methylenedianiline), and suppressing the generation of carboxylate salts.

[0038] The temperature in step [2] is preferably 150°C or higher and 210°C or lower, more preferably 160°C or higher and 200°C or lower, and even more preferably 170°C or higher and 190°C or lower, from the viewpoint of increasing the molecular weight of the amine decomposition product by the amidation reaction. The time for step [2] is not particularly limited, but may be, for example, from 10 minutes to 24 hours, or from 30 minutes to 10 hours.

[0039] (3) Process [3] The method for producing a hot melt pressure sensitive adhesive may further include a step [3] of adding a tackifier resin in addition to the steps [1] and [2]. Regarding the term "tackifier resin" in step [3], the explanation for "(3) tackifier resin" in the section "1. Hot melt adhesive" applies as is, and the description thereof will be omitted.

[0040] In order to ensure sufficient adhesion of the hot melt adhesive at high temperatures (80°C or higher), the amount of tackifier resin added is preferably 2% by mass or more and 60% by mass or less, more preferably 5% by mass or more and 50% by mass or less, and even more preferably 10% by mass or more and 40% by mass or less, when the entire hot melt adhesive is taken as 100% by mass.

[0041] The temperature in step [3] is preferably 150°C or higher and 210°C or lower, more preferably 160°C or higher and 200°C or lower, and even more preferably 170°C or higher and 190°C or lower, from the viewpoint of improving the dispersibility of the tackifier resin in the hot-melt adhesive. The time for step [3] is not particularly limited, but may be, for example, from 10 minutes to 24 hours, or from 30 minutes to 10 hours.

[0042] (4) Effects of the manufacturing method of hot melt adhesive According to the manufacturing method of the present disclosure, polyurethane-containing scraps, which have traditionally been discarded or used as RPF fuel, can be effectively utilized as hot-melt adhesives that can be used in a wide range of applications. For example, polyurethane-containing scraps can be chemically recycled and utilized as adhesives for vehicle components. Examples of vehicle components include, but are not limited to, automotive air conditioning ducts, automotive instrument panel ducts, and automotive sound-absorbing components. According to the manufacturing method of the present disclosure, it is possible to suppress as much as possible the production of MDA, which is a burden on the human body. According to the manufacturing method of the present disclosure, it is possible to manufacture a hot melt adhesive that allows components to be separated from each other by softening the adhesive portion with heat even after bonding them together. Therefore, it is possible to provide components that can be disassembled relatively easily. In other words, such components are easy to disassemble after use. For example, a component in which a sound-absorbing material is bonded to a substrate with the hot melt adhesive of the present disclosure is easy to disassemble. By using a rosin-based tackifier in the production method of the present disclosure, an environmentally friendly hot melt pressure sensitive adhesive can be produced. The manufacturing method of the present disclosure does not use organic solvents, and therefore does not generate VOCs such as aldehydes, toluene, or xylene, making it environmentally friendly. The hot melt adhesive produced by the manufacturing method of the present disclosure is a hot melt adhesive made primarily from urethane, and therefore melts and softens slowly as the temperature rises. Therefore, the temperature range over which the adhesive can remain softened is wide, ensuring a long open time. This makes it easy to adapt to various work environments. In other words, the application and application procedures must be adjusted depending on the type of material to be adhered, but this method is also easy to adapt to these adjustments. The characteristics of this hot melt adhesive are a significant difference from PP-based hot melt adhesives. [Example]

[0043] A. Working Example 1. Manufacturing of hot melt adhesives The manufacturing method of the hot melt pressure sensitive adhesive in the examples will be described with reference to Figures 1 to 3. Note that the drawings in this disclosure conceptually show a manufacturing apparatus for carrying out the manufacturing method, and do not accurately show the configuration of the manufacturing apparatus. (1) First step (see Figure 1) 115 g of polyetheramine 3 (PEA, number average molecular weight 400) was placed in a lidded container 1 and heated. After confirming that the temperature of the PEA had reached 180°C, 148 g of polyurethane scrap 5 was added so that it was immersed in the PEA. When the polyurethane scrap 5 had decomposed and the solid matter was almost no longer visible, 38 g of BEPG7 was added to the contents of the container. (2) Second step (see Figure 2) Thereafter, nitrogen was continuously flowed into the vessel 1 to continuously discharge the gas (water vapor) in the vessel 1, while 40 g of succinic anhydride 9 was added to the content in the vessel 1. The temperature of the content in the vessel 1 in the second step was set to 180°C. (3) Third step (see Figure 3) Thereafter, 50 g of rosin resin 11 was mixed with the content in vessel 1 to produce a hot melt adhesive. The temperature of the content in the vessel in the third step was set to 180°C.

[0044] 2. Evaluation of hot melt adhesives (1) Evaluation of adhesiveness (1.1) Evaluation Method Here, a polyurethane sound absorbing material, which is an example of a vehicle part, was adhered to a polyethylene substrate to check the adhesive strength. A molten hot-melt adhesive was applied to a polyethylene substrate, and then a polyurethane sound-absorbing material was attached to the hot-melt adhesive and pressed against the substrate. After the hot melt adhesive had cooled, an attempt was made to peel the sound absorbing material from the substrate.

[0045] (1.2) Evaluation results When a composite of a sound-absorbing material and a substrate bonded with a hot melt adhesive was peeled off from the substrate, the sound-absorbing material itself underwent material failure. In other words, the sound-absorbing material did not peel off from the substrate at the adhesive joint between the two. This confirmed that the hot melt adhesive exerted sufficient adhesive strength. In addition, a hot-melt adhesive produced by the same process as above, except that glycerin was used instead of BEPG, was evaluated in the same manner as above. It was confirmed that the hot-melt adhesive also exhibited sufficient adhesive strength in this case.

[0046] (2) Evaluation of various physical properties The number average molecular weight (Mn) of the hot melt adhesive was 731, and the weight average molecular weight (Mw) was 2241. The number average molecular weight (Mn) and the weight average molecular weight (Mw) were measured using a gel permeation chromatograph (GPC) EXTREMA manufactured by JASCO Corporation. THF was used as the dispersion medium.

[0047] (3) Vibration resistance evaluation of solidified hot melt adhesive As shown in Figure 4, a hot melt adhesive 17 was applied in a C-shape to the top surface of an open-cell urethane foam 13 (50 mm x 50 mm square, 3 mm thick) used as a sound-absorbing material using a φ3 mm diameter glue gun applicator 15. Then, as shown in Figure 5, the surface of the open-cell urethane foam 13 to which the hot melt adhesive 17 was applied was attached to a substrate 19 (PE plate) to form a laminate 21. The laminate 21 was then turned over so that the open-cell urethane foam 13 was on top, and a 5 kg iron plate 23 was placed on top of the laminate 21 while pressing it against the surface. This was left in this state for 60 minutes, allowing the hot melt adhesive 17 to cool and solidify. Thereafter, as shown in FIG. 6(A), the laminate 21 was folded 90 degrees with the substrate 19 facing inward. No cracks occurred in the hot melt adhesive 17 at the folded portion. This is because the solidified hot melt adhesive 17 was able to follow the bending even at the folded portion. As such, it was found that the solidified hot melt adhesive 17 has flexibility and is less likely to break or crack even when subjected to vibration or impact loads.

[0048] (4) Summary of evaluation results From the above evaluation results, it was confirmed that the examples provide hot melt pressure sensitive adhesives that can be used in a wide range of applications.

[0049] B. Comparative example 1. Manufacturing of hot melt adhesives A method for producing a hot melt pressure sensitive adhesive in a comparative example will be described. (1) First step 50 g of benzylamine, 10 g of diamine, and 100 g of rigid polyurethane were placed in a flask. The contents of the flask were heated to 180°C in an oil bath and stirred for 1 hour to prepare a decomposition solution. (2)Second process Impurities (undissolved solids) were removed from the decomposition liquid (contents of the flask). (3) Third step To the decomposition liquid (contents of the flask) was added 24 g of 3,3',4,4'-diphenylsulfonetetracarboxylic acid dihydrate, and the mixture was heated in an oil bath at 120°C, and the contents of the flask were stirred for 1 hour. (4) 4th step A rosin-based adhesive manufactured by Harima Chemicals was further added to the contents of the flask, and the mixture was heated in a 120°C oil bath and stirred to produce a hot-melt adhesive.

[0050] 2. Vibration resistance evaluation of solidified hot melt adhesive For the comparative example, the laminate 21 was prepared and evaluated in the same manner as in the example. As shown in FIG. 6(B), the laminate 21 was bent at 90 degrees with the substrate 19 facing inward. Cracks 25 occurred in the hot melt adhesive 17 at the bend. This is because the solidified hot melt adhesive 17 was unable to conform to the bending at the bend. As such, it was found that the solidified hot melt adhesive 17 is inflexible and is prone to fracture and cracking when subjected to vibration or impact loads.

[0051] The present disclosure is not limited to the above-described embodiments, and various modifications and variations are possible. [Explanation of symbols]

[0052] 1...container 3...Polyetheramine 5...Polyurethane scraps 7...BEPG (butyl ethyl propanediol) 9...Succinic anhydride 11...rosin resin 13...Open-cell urethane foam 15...Glue gun applicator 17...Hot melt adhesive 19...Base material 21...Laminate 23...Iron plate 25...Crack

Claims

1. an amine decomposition product of polyurethane with a polyetheramine having a molecular weight or number average molecular weight of 150 or more and 800 or less; At least one selected from carboxylic acids and carboxylic acid anhydrides; A hot melt adhesive made from the raw material.

2. The hot melt adhesive of claim 1 , comprising a tackifying resin.

3. The hot melt pressure-sensitive adhesive according to claim 1 or 2, which comprises a polyhydric alcohol.

4. an amine decomposition step in which polyurethane is decomposed using a polyetheramine having a molecular weight or number average molecular weight of 150 to 800 to obtain an amine decomposition product; a reaction step of reacting the amine decomposition product with at least one selected from a carboxylic acid and a carboxylic acid anhydride; A method for producing a hot melt adhesive, comprising:

5. The method for producing a hot melt pressure sensitive adhesive according to claim 4 , further comprising the step of adding a tackifier resin.

6. The method for producing a hot melt pressure-sensitive adhesive according to claim 4 or 5, wherein the aminolysis step is carried out in the presence of a polyhydric alcohol.

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