Benzoxazine type adhesive easy to peel after being heated as well as preparation method and use method of benzoxazine type adhesive

Abstract

The invention relates to a benzoxazine type adhesive easy to peel after being heated as well as a preparation method and a use method of the benzoxazine type adhesive. The molecular structure of the benzoxazine type adhesive comprises an organic silicon component and carboxyl-containing benzoxazine. The adhesive based on the benzoxazine structure can be prepared through one-step reaction. The method is simple and controllable in synthesis condition, high in synthesis efficiency and convenient to separate and purify; the organic silicon adhesive disclosed by the invention is used for bonding at medium and low temperatures, and is subjected to decarboxylation reaction after being further heated, so that the adhesive is expanded, and debonding is realized. The adhesive disclosed by the invention not only can be directly used as an adhesive, but also can be added with a filler according to requirements, so that different requirements under various special occasions are met.

Description

Technical Field

[0001] The invention relates to a benzoxazine adhesive that is easily peeled when heated and a preparation and use method thereof, belonging to the field of polymer material preparation and application. Background Art

[0002] Benzoxazine resin is a novel thermosetting resin developed from traditional phenolic resins. Its characteristic monomer structure contains an oxazine ring structure characterized by nitrogen and oxygen. The benzoxazine monomer is synthesized by a Mannich reaction using a phenolic compound, formaldehyde, and an amine in a molar ratio of 1:2:1. At a certain temperature, the benzoxazine monomer undergoes ring-opening polymerization, forming phenolic hydroxyl groups, which catalyze the formation of a polyphenolic-like structure, resulting in a three-dimensional cross-linked network. The cured benzoxazine polymer contains numerous phenolic hydroxyl groups, which can form numerous intramolecular and intermolecular hydrogen bonds, enabling excellent interaction with substrates and thus serving as an adhesive. In addition to the excellent mechanical properties, heat resistance, and electrical insulation properties of traditional phenolic resins, benzoxazine resins offer unique advantages, such as the absence of a catalyst during curing, the absence of small molecule release, and near-zero volume shrinkage. Currently, benzoxazine adhesives have been successfully used in bonding applications such as aerospace and rail transportation, and have broad potential applications.

[0003] The chemical bonding mechanisms of current adhesives mainly include chemical bonding, van der Waals force, hydrogen bonding, etc. Chemical bonding adhesives mainly achieve bonding effects by forming chemical bonds between the adhesive and the surface of the adhered object, including ionic bonds, covalent bonds, and coordination bonds. This type of adhesive is usually used on metal surfaces, glass surfaces, etc., and has high bonding strength, but the high bonding strength makes the bond difficult to peel off, the bonding process has no redundancy for operational errors, and it is difficult to remove, which is not conducive to practical operation. Unlike chemical bonding adhesives, van der Waals force adhesives achieve bonding through van der Waals forces. Therefore, this type of adhesive is usually simple to operate and easy to clean and remove, but affected by the strength of the intermolecular force itself, the initial bonding strength of the adhesive is insufficient, making it difficult to apply to high-strength bonding scenarios.

[0004] Hydrogen bonding is characterized by intramolecular and intermolecular hydrogen bonds and is primarily used in applications such as hydrogel bonding, underwater bonding, and polar surface bonding. When exposed to high temperatures, hydrogen bonds dissociate, allowing the adhesive to easily peel from the bonded area, achieving both bonding and peeling. However, hydrogen bonding adhesives typically have low bond strength and can even cause the bonded structure to debond during daily use, posing a safety hazard.

[0005] Furthermore, CN119463801A reports on a silicone adhesive and its preparation method. The adhesive's main components include hydroxyl-terminated polydimethylsiloxane, dimethyl silicone oil, surface-modified nano-calcium carbonate, alkoxy-modified MQ resin, a crosslinker, a silane coupling agent, and a catalyst. CN119351014A reports on a bio-based benzoxazine adhesive and its preparation method. The adhesive has a bonding strength of 6.41 MPa and requires 365 nm UV irradiation for 30 minutes, with a curing temperature of up to 200°C. CN117777946A discloses a formula and method for using a high-strength benzoxazine-based silicone adhesive that can be cured at medium and low temperatures. However, none of the above-mentioned prior art methods consider the subsequent debonding issue.

[0006] Therefore, how to achieve high-strength bonding while conveniently and controllably debonding has become an urgent problem to be solved. Summary of the Invention

[0007] In view of the above-mentioned state of the prior art, especially the low initial bonding strength of hydrogen bonding type adhesives, it is difficult to achieve strong bonding and controllable debonding at the same time. The present invention further studies on the basis of previous work, redesigns the formula and molecular structure, optimizes the bonding and debonding process, and achieves a balance between the two. The present invention introduces an organosilicon component into the carboxyl-containing benzoxazine structure, and utilizes the characteristics of the organosilicon compound chain segments being flexible and having low surface energy to reduce the polymerization temperature of benzoxazine, thereby achieving bonding at a lower temperature. At the same time, under further heating conditions, the carboxyl groups in the adhesive molecules undergo a decarboxylation reaction, releasing carbon dioxide, and the volume expands significantly. The volume expansion causes the cross-linked network of the bond to be destroyed, thereby achieving a debonding effect. The combination of the above two simultaneously achieves higher-strength bonding and controllable debonding.

[0008] Therefore, one objective of the present invention is to provide a benzoxazine-based adhesive that is easily peelable upon heating. By incorporating an organosilicon component into the carboxyl-containing benzoxazine structure, this adhesive achieves adhesion at relatively low temperatures. Simultaneously, upon further heating, the carboxyl groups in the adhesive molecules undergo decarboxylation, releasing carbon dioxide, enabling controlled debonding.

[0009] A second object of the present invention is to provide a method for preparing and using a benzoxazine-based adhesive that is easily peelable upon heating. The present invention utilizes a one-pot reaction method to produce an adhesive based on a benzoxazine structure. This method offers simple and controllable synthesis conditions, high synthesis efficiency, and convenient separation and purification. The benzoxazine-based adhesive prepared by the present invention can be used directly as an adhesive, as a primer, or as a base formulation for use as an adhesive after adding other fillers to meet the bonding requirements of various special occasions.

[0010] The technical solution for achieving the above-mentioned invention object can be summarized as follows:

[0011] A benzoxazine adhesive which is easily peelable when heated, wherein the molecular structure of the adhesive contains silicon-oxygen bonds, benzoxazine groups and carboxyl groups.

[0012] According to the present invention, preferably, the molecular structure of the benzoxazine-type adhesive that is easily peelable upon heating contains at least a structural unit represented by formula (I) and at least one structural unit represented by formula (II):

[0013]

[0014] Formula (I);

[0015]

[0016] Formula (II);

[0017] In formula (I) and formula (II), R', R'', R1 and R2 are independently selected from various organic groups, including various aliphatic hydrocarbon groups, aromatic hydrocarbon groups and / or organosilicon groups; and R1 should contain at least one carboxyl group; and n is 1-3000.

[0018] According to the present invention, preferably, the aliphatic hydrocarbon group is selected from C1-C 10 alkyl or halogenated alkane, more preferably methyl or trifluoropropyl.

[0019] According to the present invention, preferably, the aromatic hydrocarbon group is selected from phenyl, phenethyl, methylphenyl, phenolic phenyl, and more preferably phenyl.

[0020] According to the present invention, preferably, the organosilicon group is selected from trialkylsiloxy, trialkoxysilyl, short-chain polysiloxane, dendritic polysiloxane, and disiloxane, and short-chain polysiloxane and disiloxane are further preferred; more preferably, the number of chain segments of the short-chain polysiloxane is 2-3000.

[0021] According to the present invention, preferably, the benzoxazine adhesive that is easily peelable when heated has a structure represented by formula (III), formula (IV) or formula (V):

[0022]

[0023] Formula (III);

[0024]

[0025] Formula (IV);

[0026]

[0027] Formula (V);

[0028] In the formula, R`, R``, R1, and R2 have the same meanings as in formula (I) and formula (II), the selectors of R```, R````, and R3 are the same as those of R` and R``, n is 0-3000, and m is 1-3000.

[0029] According to the present invention, the method for preparing the above-mentioned benzoxazine-type adhesive that is easily peelable when heated comprises the following steps:

[0030] An amino-containing organosilicon compound is mixed with an aldehyde compound and a carboxylic acid containing at least one phenolic hydroxyl group, and the mixture is reacted in a solvent. After purification, a benzoxazine adhesive that is easily peeled when heated is obtained.

[0031] According to the present invention, preferably, the amino-containing organosilicon compound includes amino-terminated organosilicon polymers, side chain amino-containing organosilicon polymers, and amino-containing organosilicon small molecules, preferably amino-terminated organosilicon polymers and amino-containing organosilicon small molecules, and further preferably diaminopropyltetramethyldisiloxane.

[0032] According to the present invention, preferably, the aldehyde compound is various aldehyde organic compounds that can be dissolved in this system; further preferably, the aldehyde compound is a small molecule aldehyde compound or polyformaldehyde; more preferably, the aldehyde compound is formaldehyde or trioxymethylene.

[0033] According to the present invention, preferably, the carboxylic acid containing at least one phenolic hydroxyl group includes various carboxylic acids containing at least one phenolic hydroxyl group and at least one carboxyl group in their molecular structures. Further preferably, the carboxylic acid is diphenolic acid, vanillic acid or p-hydroxyphenylacetic acid.

[0034] According to the present invention, preferably, the solvent is a variety of polar or non-polar solvents that can dissolve the reactants and do not chemically react with the reactants; further preferably, toluene, dioxane, tetrahydrofuran, chloroform, methanol, diphenyl ether, dimethyl sulfoxide, N,N-dimethylformamide; more preferably, dioxane and toluene.

[0035] According to the present invention, preferably, the ratio of the molar number of amino groups in the amino-containing organosilicon compound, the molar number of aldehyde groups in the aldehyde compound, and the molar number of phenolic hydroxyl groups in the carboxylic acid containing at least one phenolic hydroxyl group is 1:(0.1-15):(0.1-20), and more preferably 1:(2-15):(1-10).

[0036] According to the present invention, preferably, the reaction temperature of the amino-containing organosilicon compound, the aldehyde compound, and the carboxylic acid containing at least one phenolic hydroxyl group is 30-150° C., more preferably 50-80° C.; and the reaction time is 1-24 h.

[0037] According to the present invention, there is also provided a benzoxazine adhesive composition that is easily peelable when heated, comprising the following components in parts by weight:

[0038] 100 parts of the above-mentioned benzoxazine adhesive that is easily peeled when heated, 0-10 parts of catalyst A, 0-400 parts of filler, and 0-200 parts of auxiliary agent.

[0039] According to the present invention, preferably, the catalyst A is a compound that can catalyze the ring-opening polymerization reaction of benzoxazine, including various types of Lewis acids and bases in a broad sense; further preferably, benzenesulfonic acid, acetic acid, hexamethylenediamine and sodium hydroxide, and the amount used is preferably 0-3 parts.

[0040] According to the present invention, the filler is preferably any additive capable of improving the performance of benzoxazine-based adhesives. Further preferred are fumed silica, precipitated silica, carbon black, calcium carbonate, aluminum hydroxide and / or magnesium hydroxide, and various specially treated compounds thereof. Silazane-treated silica is even more preferred. The filler is used in an amount of 0-400 parts, preferably 0-30 parts.

[0041] According to the present invention, preferably, the auxiliary agent is various auxiliary agents that do not significantly reduce the performance of the adhesive after addition, including various functional components and non-functional components, further preferably thermal oxygen stabilizers, flame retardants, conductive agents, deep curing agents, pigments and / or plasticizers; further preferably, iron red, and the number of parts used is preferably 0-10 parts.

[0042] According to the present invention, preferably, the heat-strippable benzoxazine adhesive composition comprises the following components in parts by mass:

[0043] 100 parts of the above-mentioned benzoxazine adhesive that is easily peeled when heated, 1-3 parts of catalyst A, 1-30 parts of filler, and 1-10 parts of auxiliary agent.

[0044] According to the present invention, the method for using the heat-peelable benzoxazine adhesive comprises the following two steps:

[0045] (1) The benzoxazine adhesive that is easily peeled when heated is evenly applied to the surface of the adherends. After the two adherends are fixed, the temperature is raised to achieve bonding.

[0046] (2) The bonded adherend obtained in step (1) is further heated to the foaming temperature and maintained for a period of time to achieve debonding.

[0047] According to the present invention, preferably, the programmed temperature increase is a temperature increase process from an initial temperature to a final temperature through multiple "temperature increase-constant temperature" steps with a certain temperature difference as a gradient;

[0048] Preferably, the temperature difference includes any temperature difference between 5°C and 100°C, the heating rate is any heating rate between 0.1°C / min and 20°C / min, and in the "heating-constant temperature" link, the constant temperature time is any time between 1 minute and 180 minutes. The termination temperature of the heating program is the time when the benzoxazine resin is cured, including any temperature between 50°C and 200°C.

[0049] According to the present invention, preferably, the high-temperature foaming is a process of foaming the polybenzoxazine resin obtained in step (1) at a set temperature for a certain period of time; preferably, the temperature of the high-temperature foaming is greater than the temperature at which the heating program ends.

[0050] The beneficial effects of the present invention are as follows:

[0051] 1. This invention utilizes flexible molecular design to introduce an organosilicon component into the carboxyl-containing benzoxazine structure. Leveraging the flexible chain segments and low surface energy of organosilicon compounds, the polymerization temperature of the benzoxazine is lowered, enabling bonding at relatively low temperatures. Simultaneously, as the temperature rises, the carboxyl groups in the adhesive molecules undergo decarboxylation, releasing carbon dioxide and significantly expanding in volume. This volume expansion disrupts the cross-linked network, achieving a debonding effect. This combination of the two achieves both high-strength bonding and controllable debonding.

[0052] 2. The heat-peelable benzoxazine adhesive of this invention undergoes ring-opening polymerization of benzoxazine to generate numerous phenolic hydroxyl groups, providing numerous sites for surface bonding. Cross-linking within the adhesive enhances bulk strength, achieving high-strength hydrogen-bonding adhesion. The carboxyl groups within the adhesive's molecular structure catalyze the ring-opening of benzoxazine and, to a certain extent, also lower its curing temperature.

[0053] 3. This invention leverages the convenience and efficiency of the Mannich reaction. By optimizing and selecting reactants, a simple, one-step reaction can be used to prepare a benzoxazine-based adhesive that is easily peelable upon heating. The mild reaction conditions avoid side reactions associated with high-temperature reactions. This reaction also offers advantages over the hydrosilylation process for preparing organosilicon-modified benzoxazines, avoiding the drawbacks of catalyst deactivation and a low addition ratio.

[0054] 4. The present invention introduces siloxane chains into the benzoxazine monomer. The flexibility and low intermolecular forces of the -Si-O-Si- chains make benzoxazine more susceptible to ring-opening reactions. At the same time, the carboxyl groups contained in the carboxyl-containing phenol source also catalyze the ring-opening reaction to a certain extent. The two together promote the ring-opening reaction of benzoxazine, successfully achieving low-temperature curing and high-temperature controllable debonding of benzoxazine.

[0055] 5. The heat-peelable benzoxazine adhesive of the present invention can cure at low temperatures for bonding and controllably debond at high temperatures. It can meet the needs of various applications and has broad application prospects and a promising market outlook. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 The benzoxazine compound prepared in Example 1 1 HNMR spectrum.

[0057] Figure 2 The benzoxazine compound prepared in Example 2 1 HNMR spectrum.

[0058] Figure 3 This is the Fourier near-infrared spectrum of the benzoxazine compound prepared in Example 1.

[0059] Figure 4 This is the Fourier near-infrared spectrum of the benzoxazine compound prepared in Example 2.

[0060] Figure 5 This is the thermogravimetric analysis curve of the benzoxazine adhesive prepared in Example 1.

[0061] Figure 6 This is the DSC curve of the benzoxazine compound prepared in Example 1.

[0062] Figure 7 This is the DSC curve of the benzoxazine compound prepared in Example 1 after curing.

[0063] Figure 8 This is a picture of the benzoxazine adhesive prepared in Example 1 being pulled apart after bonding.

[0064] Figure 9 This is a picture of the foaming and debonding of the adhesive part prepared in Example 13.

[0065] Figure 10 This is a picture of the foaming and debonding of the adhesive part prepared in Example 14.

[0066] Figure 11 This is a picture of the foaming and debonding of the adhesive part prepared in Example 15.

[0067] Figure 12 This is a picture of the foaming and debonding of the adhesive part prepared in Example 16. DETAILED DESCRIPTION

[0068] The present invention introduces an organosilicon component into the carboxyl-containing benzoxazine structure, and utilizes the characteristics of the organosilicon compound chain segments being flexible and having low surface energy to reduce the polymerization temperature of the benzoxazine and achieve bonding at a relatively low temperature. At the same time, under further elevated temperature conditions, the carboxyl groups in the adhesive molecules undergo a decarboxylation reaction, releasing carbon dioxide, significantly expanding the volume, and destroying the hydrogen bonds under high temperature and physical action, thereby achieving both high-strength bonding and controllable debonding. The present invention can produce a benzoxazine-type adhesive that is easily peeled when heated through a one-step reaction using a "one-pot method". The method has simple and controllable synthesis conditions, high synthesis efficiency, and convenient separation and purification. The benzoxazine-type adhesive prepared by the present invention can be used directly as an adhesive, can also be used as a primer, can also be used as a basic formula, and can be used as an adhesive after adding other fillers to meet the bonding needs of various special occasions.

[0069] The benzoxazine adhesive that is easily peelable when heated contains silicon-oxygen bonds, benzoxazine groups and carboxyl groups in its molecular structure.

[0070] In one or more preferred embodiments, the molecular structure of the heat-peelable benzoxazine adhesive contains at least a structural unit represented by formula (I) and at least one structural unit represented by formula (II):

[0071]

[0072] Formula (I);

[0073]

[0074] Formula (II);

[0075] In formula (I) and formula (II), R', R'', R1 and R2 are independently selected from various organic groups, including various aliphatic hydrocarbon groups, aromatic hydrocarbon groups and / or organosilicon groups; and R1 should contain at least one carboxyl group; and n is 1-3000.

[0076] According to the present invention, the molecular structure of the adhesive contains both silicon-oxygen bonds and benzoxazine groups. The flexible chain segments and low surface energy of the organosilicon compound reduce the polymerization temperature of the benzoxazine, enabling bonding at relatively low temperatures. The molecular structure of the adhesive also contains carboxyl groups. Under further elevated temperature conditions, the carboxyl groups in the adhesive molecules undergo a decarboxylation reaction, releasing carbon dioxide and significantly expanding in volume. This volume expansion causes the cross-linked network of the bond to be destroyed, achieving a debonding effect. This combination of the two simultaneously achieves high-strength bonding and controlled debonding.

[0077] According to the present invention, there is no special requirement for the siloxane bond unit and the benzoxazine group unit in the molecular structure of the adhesive. In one or more preferred embodiments, the aliphatic hydrocarbon group is selected from C1-C10 alkyl or halogenated alkane, more preferably methyl or trifluoropropyl.

[0078] In one or more preferred embodiments, the aromatic hydrocarbon group is selected from phenyl, phenethyl, methylphenyl, phenolic phenyl, and more preferably phenyl.

[0079] In one or more preferred embodiments, the organosilicon group is selected from trialkylsiloxy, trialkoxysilyl, short-chain polysiloxane, dendritic polysiloxane, and disiloxane, with short-chain polysiloxane and disiloxane being further preferred; more preferably, the number of chain segments of the short-chain polysiloxane is 2-3000.

[0080] In one or more preferred embodiments, the heat-peelable benzoxazine adhesive has a structure represented by formula (III), formula (IV) or formula (V):

[0081]

[0082] Formula (III);

[0083]

[0084] Formula (IV);

[0085]

[0086] Formula (V);

[0087] In the formula, R`, R``, R1, and R2 have the same meanings as in formula (I) and formula (II), the selectors of R```, R````, and R3 are the same as those of R` and R``, n is 0-3000, and m is 1-3000.

[0088] According to the present invention, the method for preparing the above-mentioned benzoxazine-type adhesive that is easily peelable when heated comprises the following steps:

[0089] An amino-containing organic silicon compound is mixed with an aldehyde compound and a carboxylic acid containing at least one phenolic hydroxyl group, and the mixture is reacted in a solvent. After purification, a benzoxazine-type adhesive that is easily peeled when heated is obtained.

[0090] According to the present invention, an amino-containing organosilicon compound, an aldehyde compound, and a carboxylic acid containing at least one phenolic hydroxyl group are subjected to a Mannich reaction in a solvent in a one-pot method, which is convenient, efficient, and has mild conditions.

[0091] In one or more preferred embodiments, the amino-containing organosilicon compound includes amino-terminated organosilicon polymers, side chain amino-containing organosilicon polymers, and amino-containing organosilicon small molecules, preferably amino-terminated organosilicon polymers and amino-containing organosilicon small molecules, and further preferably diaminopropyltetramethyldisiloxane.

[0092] According to the present invention, the aldehyde compound is any organic aldehyde compound that is soluble in the system. In one or more preferred embodiments, the aldehyde compound is a small molecule aldehyde compound or paraformaldehyde; more preferably, the aldehyde compound is formaldehyde or trioxymethylene.

[0093] According to the present invention, the carboxylic acid containing at least one phenolic hydroxyl group includes any carboxylic acid having both at least one phenolic hydroxyl group and at least one carboxyl group in its molecular structure. In one or more preferred embodiments, the carboxylic acid is diphenolic acid, vanillic acid, or p-hydroxyphenylacetic acid.

[0094] According to the present invention, the solvent is any polar or non-polar solvent that can dissolve the reactants and does not chemically react with them. In one or more preferred embodiments, the solvent is toluene, dioxane, tetrahydrofuran, chloroform, methanol, diphenyl ether, dimethyl sulfoxide, or N,N-dimethylformamide; more preferably, dioxane or toluene.

[0095] According to the present invention, an amino-containing organosilicon compound, an aldehyde compound, and a carboxylic acid containing at least one phenolic hydroxyl group are reacted according to the Mannich reaction ratio. In one or more preferred embodiments, the ratio of the molar number of amino groups in the amino-containing organosilicon compound, the molar number of aldehyde groups in the aldehyde compound, and the molar number of phenolic hydroxyl groups in the carboxylic acid containing at least one phenolic hydroxyl group is 1:(0.1-15):(0.1-20), more preferably 1:(2-15):(1-10).

[0096] According to the present invention, siloxane chains are introduced into benzoxazine monomers. The flexibility and low intermolecular forces of the -Si-O-Si- chains make benzoxazine more susceptible to ring-opening reactions. At the same time, the carboxyl groups contained in the carboxyl-containing phenol source also catalyze the ring-opening reaction to a certain extent. The two together promote the ring-opening reaction of benzoxazine, successfully achieving low-temperature curing and high-temperature controllable debonding of benzoxazine.

[0097] In one or more preferred embodiments, the reaction temperature of the amino-containing organosilicon compound, the aldehyde compound, and the carboxylic acid containing at least one phenolic hydroxyl group is 30-150° C., more preferably 50-80° C., and the reaction time is 1-24 h.

[0098] According to the present invention, there is also provided a benzoxazine adhesive composition that is easily peelable when heated, comprising the following components in parts by weight:

[0099] 100 parts of the above-mentioned benzoxazine adhesive that is easily peeled when heated, 0-10 parts of catalyst A, 0-400 parts of filler, and 0-200 parts of auxiliary agent.

[0100] According to the present invention, the catalyst A is a compound capable of catalyzing the ring-opening polymerization reaction of benzoxazine, including various Lewis acids and bases in a broad sense. In one or more preferred embodiments, the catalyst A is benzenesulfonic acid, acetic acid, hexamethylenediamine, and sodium hydroxide, preferably used in 0-3 parts.

[0101] According to the present invention, the filler is any additive capable of improving the performance of benzoxazine-based adhesives. In one or more preferred embodiments, the filler is fumed silica, precipitated silica, carbon black, calcium carbonate, aluminum hydroxide, and / or magnesium hydroxide, as well as any of these compounds that have undergone special treatments, more preferably silazane-treated silica. The filler is used in an amount of 0-400 parts, preferably 0-30 parts.

[0102] According to the present invention, the additives are various additives that do not significantly reduce the performance of the adhesive upon addition, including various functional and non-functional components. In one or more preferred embodiments, the additives are a thermal stabilizer, a flame retardant, a conductive agent, a deep curing agent, a pigment, and / or a plasticizer; iron oxide red is further preferred, and the amount used is preferably 0-10 parts.

[0103] In one or more preferred embodiments, the heat-strippable benzoxazine adhesive composition comprises the following components in parts by weight:

[0104] 100 parts of the above-mentioned benzoxazine adhesive that is easily peeled when heated, 1-3 parts of catalyst A, 1-30 parts of filler, and 1-10 parts of auxiliary agent.

[0105] According to the present invention, the method for using the heat-peelable benzoxazine adhesive comprises the following two steps:

[0106] (1) The benzoxazine adhesive that is easily peeled when heated is evenly applied to the surface of the adherends. After the two adherends are fixed, the temperature is raised to achieve bonding.

[0107] (2) The bonded adherend obtained in step (1) is further heated to the foaming temperature and maintained for a period of time to achieve debonding.

[0108] According to the present invention, the programmed temperature rise is a temperature rise process from an initial temperature to a final temperature through multiple "heating-maintaining temperature" steps with a certain temperature difference as a gradient. The temperature difference includes any temperature difference between 5°C and 100°C, preferably 10°C according to the present invention; the heating rate in the "heating-maintaining temperature" step is any heating rate between 0.1°C / min and 20°C / min, preferably 10°C / min; the constant temperature time in the "heating-maintaining temperature" step is any time between 1 minute and 180 minutes, preferably any time between 30 minutes and 120 minutes, more preferably 60 minutes; the initial temperature is any temperature between room temperature and the final temperature, preferably 50-150°C, more preferably 100°C; and the final temperature is the time when the benzoxazine resin is cured, including an optimal curing temperature between 50°C and 200°C obtained through actual experiments.

[0109] According to the present invention, the high-temperature foaming is a process of foaming the polybenzoxazine resin obtained in step (1) at a set temperature for a set time. The temperature is a temperature higher than the set temperature in step (1) obtained through experimental testing; the set time is a time value required to ensure the application performance of the foamed material, obtained through experimental testing. Preferably, the temperature for high-temperature foaming is greater than the temperature at which the heating program terminates.

[0110] Anything not described in detail in the present invention is based on the existing technology.

[0111] Principle of the present invention:

[0112] This invention utilizes flexible molecular design to introduce an organosilicon component into the carboxyl-containing benzoxazine structure. By leveraging the flexible chain segments and low surface energy of organosilicon compounds, the polymerization temperature of the benzoxazine is lowered, enabling bonding at relatively low temperatures. Simultaneously, as the temperature rises, the carboxyl groups in the adhesive molecules undergo decarboxylation, releasing carbon dioxide and significantly expanding in volume. This volume expansion disrupts the cross-linked bonding network, achieving a debonding effect. This combination of the two achieves both high-strength bonding and controlled debonding.

[0113] Benzoxazine ring-opening polymerization generates numerous phenolic hydroxyl groups, which provide numerous sites for surface bonding. Cross-linking within the adhesive enhances bulk strength, achieving high-strength hydrogen-bonding adhesion. Furthermore, the carboxyl groups within the adhesive's molecular structure catalyze the ring-opening of benzoxazine, which also reduces its curing temperature to a certain extent.

[0114] This invention leverages the convenience and efficiency of the Mannich reaction. By optimizing and screening reactants, a simple, one-step reaction is used to prepare a benzoxazine-based adhesive that is easily peelable upon heating. The mild reaction conditions avoid side reactions associated with high-temperature reactions. This reaction also offers advantages over the hydrosilylation process for preparing organosilicon-modified benzoxazines, avoiding the drawbacks of catalyst deactivation and a low addition ratio.

[0115] The present invention introduces siloxane chains into the benzoxazine monomer. The flexibility and low intermolecular force of the -Si-O-Si- chains make benzoxazine more susceptible to ring-opening reactions. At the same time, the carboxyl groups contained in the carboxyl-containing phenol source also catalyze the ring-opening reaction to a certain extent. The two together promote the ring-opening reaction of benzoxazine, successfully achieving low-temperature curing and high-temperature controllable debonding of benzoxazine.

[0116] Adding various additives to the formula involved in the present invention can further improve its performance and expand its application, such as thermal oxygen stabilizers, flame retardants, conductive agents, foaming agents, deep curing agents, pigments, plasticizers, etc. Certain additives can play multiple roles, such as iron oxide red can simultaneously play the role of thermal oxygen stabilizer, pigment, and reinforcing filler. Adding special polymers can improve the wetting performance of such adhesives with specific interfaces. Adding special coupling agents can improve the adhesion performance of such adhesives with special interfaces. In short, by changing the dosage of additives and using multiple additives together, high-performance adhesives that meet the needs of various occasions can be prepared, which has broad application prospects and good market prospects.

[0117] The present invention will be further described below with reference to specific examples, but is not limited thereto.

[0118] The raw materials used in the examples are all conventional commercially available raw materials.

[0119] The molar ratios described in the examples are ratios by amount of substance, and the proportions described are ratios by mass.

[0120] Example 1

[0121] 2.49 g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, 1.26 g of paraformaldehyde, and 100 ml of dioxane were weighed into a three-necked flask and stirred for 0.5 h. 2.86 g of diphenolic acid was dissolved in 50 ml of dioxane and reacted at 90°C for 8 h. After completion of the reaction, the solvent was partially removed using a rotary evaporator and further purified. The product was then vacuum-dried to constant weight to obtain an aminopropyl double-capped-diphenolic acid benzoxazine adhesive with a yield of 64.6%.

[0122] The benzoxazine compound prepared in this example 1 HNMR diagram, such as Figure 1 As shown. NMR data:

[0123] 1 HNMR(400MHz,DMSO-d6),δ:-0.09-0.08(s,12,-Si-CH3),0.39-0.52(t,4,-Si-CH2-CH2),1.37-1.5 2(m,7,-C-CH3,-CH2-CH2-CH2),1.87-1.95(t,2,CH2-CH2-COOH),2.15-2.25(t,2,-CH2-CH2-COOH), 2.54-2.64 (t, 4, N-CH2-CH2), 3.77-3.87(s,Ph-CH2-N), 4.64-4.79(s,N-CH2-O), 6.50-6.85(m,Ph).

[0124] The infrared spectrum of the benzoxazine compound prepared in this example is as follows: Figure 3 shown.

[0125] Example 2

[0126] Weigh 1.12g of hexamethylenediamine, 1.26g of paraformaldehyde, and 100ml of dioxane in a three-necked flask and stir for 0.5h. Then, dissolve 2.86g of diphenolic acid in 50ml of dioxane and react at 80°C for 6h. After the reaction, remove some of the solvent using a rotary evaporator, further purify the mixture, and then vacuum dry it to constant weight to obtain a hexamethylenediamine-diphenolic acid benzoxazine adhesive.

[0127] The benzoxazine compound prepared in this example 1 HNMR diagram, such as Figure 2 As shown. NMR data:

[0128] 1 HNMR(400MHz,DMSO-d6),δ:1.15-1.53(t,8,-CH2-CH2-CH2-,-CH2-CH2-CH2-),1.85-1.95(t,2,-CH2-CH2-COOH),2.13-2.25( t,2,-CH2-CH2-COOH),2.50-2.61(t,4,-N-CH2-CH2),3.74-3.89(s,-N-CH2-Ph),4.63-4.78(s,-N-CH2-N),6.50-6.88(m,Ph) .

[0129] The infrared spectrum of the benzoxazine compound prepared in this example is as follows: Figure 4 shown.

[0130] Example 3

[0131] 5g of 3-aminopropyl-terminated polydimethylsiloxane (molecular weight 500), 1.26g of paraformaldehyde, and 100ml of dioxane were weighed and placed in a three-necked flask. The mixture was stirred for 2 hours. 2.86g of diphenolic acid was dissolved in 50ml of dioxane and reacted at 80°C for 9 hours. After the reaction, the solvent was partially removed using a rotary evaporator, and the mixture was further purified and then vacuum-dried to constant weight to obtain an aminopropyl-terminated polydimethylsiloxane-diphenolic acid benzoxazine adhesive.

[0132] Example 4

[0133] Weigh 2.49 g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, 1.6 g of paraformaldehyde, and 3.04 g of p-hydroxyphenylacetic acid into a three-necked flask, add 100 ml of toluene, and react at 90°C for 8 h. The reaction solution is cooled, filtered, evaporated under reduced pressure, washed three times with ether solution, and vacuum dried to obtain an "aminopropyl double-capped-p-hydroxyphenylacetic acid" benzoxazine-type adhesive.

[0134] Example 5

[0135] 5 g of 3-aminopropyl-terminated polydimethylsiloxane (molecular weight, 500), 1.6 g of paraformaldehyde, and 3.04 g of p-hydroxyphenylacetic acid were weighed into a three-necked flask, and 100 ml of toluene was added. The mixture was reacted at 100°C for 16 h. The reaction solution was cooled, filtered, evaporated under reduced pressure, washed three times with cold ether solution, and dried in vacuo to obtain an "aminopropyl-terminated polydimethylsiloxane-p-hydroxyphenylacetic acid" benzoxazine-type adhesive.

[0136] Example 6

[0137] 1.16g of hexamethylenediamine, 9g of paraformaldehyde, and 100ml of dioxane were weighed into a three-necked flask and heated to 90°C with stirring for 2 hours. 30.43g of p-hydroxyphenylacetic acid was dissolved in 50ml of toluene and reacted at 80°C for 6 hours. After completion of the reaction, the solvent was partially removed using a rotary evaporator, further purified, and then vacuum-dried to constant weight to obtain a hexamethylenediamine-p-hydroxyphenylacetic acid benzoxazine adhesive.

[0138] Example 7

[0139] Similar to Example 4, p-hydroxyphenylacetic acid was replaced with an equimolar amount of vanillic acid to obtain an "aminopropyl double-capped-vanillic acid" benzoxazine adhesive.

[0140] Example 8

[0141] Similar to Example 5, p-hydroxyphenylacetic acid was replaced with an equimolar amount of vanillic acid to obtain an "aminopropyl polydimethylsiloxane-vanillic acid" benzoxazine adhesive.

[0142] Example 9

[0143] Similar to Example 6, p-hydroxyphenylacetic acid was replaced with an equimolar amount of vanillic acid to obtain a "hexamethylenediamine-vanillic acid" benzoxazine adhesive.

[0144] Example 10

[0145] The "aminopropyl double-head-bisphenol acid" benzoxazine adhesive obtained in Example 1 was applied to the surface of the polished iron sheet and cured in an oven using a staged heating curing method. The specific heating program was: 115°C / 2h, 125°C / 2h, 135°C / 2h to obtain a bonded component.

[0146] Example 11

[0147] The "aminopropyl double-head-bisphenol acid" benzoxazine adhesive obtained in Example 1 was applied to the surface of the polished iron sheet and cured in an oven using a staged heating curing method. The specific heating program was: 125°C / 2h, 135°C / 2h, 145°C / 2h to obtain a bonded component.

[0148] Example 12

[0149] The "aminopropyl double-head-bisphenol acid" benzoxazine adhesive obtained in Example 1 was applied to the surface of the polished iron sheet and cured in an oven using a staged heating curing method. The specific heating program was: 135°C / 2h, 145°C / 2h, 155°C / 2h to obtain a bonded component.

[0150] Example 13

[0151] The adhesive component obtained in Example 10 was subjected to a temperature-raising foaming process in an oven, with a specific temperature-raising procedure of 200° C. / 4 h, to obtain an easily peelable adhesive component.

[0152] Example 14

[0153] The adhesive component obtained in Example 10 was subjected to a temperature-raising foaming process in an oven, with a specific temperature-raising procedure of 210° C. / 4 h, to obtain an easily peelable adhesive component.

[0154] Example 15

[0155] The adhesive component obtained in Example 10 was subjected to a temperature-raising foaming process in an oven, with a specific temperature-raising procedure of 220° C. / 4 h, to obtain an easily peelable adhesive component.

[0156] Example 16

[0157] The adhesive component obtained in Example 10 was subjected to a temperature-raising foaming process in an oven, with a specific temperature-raising procedure of 230° C. / 4 h, to obtain an easily peelable adhesive component.

[0158] Example 17

[0159] The "hexamethylenediamine-bisphenol acid" benzoxazine adhesive obtained in Example 2 was applied to the polished surface of the iron sheet, and the curing and debonding procedures described in Example 10 were followed.

[0160] Example 18

[0161] The "aminopropyl polydimethylsiloxane-bisphenol acid" benzoxazine adhesive obtained in Example 3 was applied to the polished iron sheet surface, and the curing and debonding procedures described in Example 10 were followed.

[0162] Example 19

[0163] The aminopropyl double-capped p-hydroxyphenylacetic acid benzoxazine adhesive obtained in Example 4 was applied to the polished iron sheet surface. The curing and debonding procedures were similar to those described in Example 11. The differences were: the curing temperature was 100°C / 2h, 120°C / 2h, and 140°C / 2h; and the foaming temperature was 210°C for 3h.

[0164] Example 20

[0165] The aminopropyl-terminated polydimethylsiloxane-p-hydroxyphenylacetic acid benzoxazine adhesive obtained in Example 5 was applied to the polished iron sheet surface. The curing and debonding procedures were similar to those described in Example 10. The differences were: the curing temperature was 100°C / 1 hour, 120°C / 2 hours, and 140°C / 2 hours; and the foaming temperature was 200°C for 4 hours.

[0166] Test Example 1

[0167] According to the "Determination of tensile shear strength of adhesives (rigid material to rigid material)" (national standard: GB / T7124-2008), the bonding strength between the adhesives in Examples 10-12 and the iron sheet was tested. The results are shown in Table 1.

[0168] Table 1 shows the bonding strength test results of the benzoxazine adhesive prepared in Example 1.

[0169]

[0170] Reference document 1 (CN119463801A) reports an organic silicone adhesive and its preparation method. The adhesive's main components include hydroxyl-terminated polydimethylsiloxane, dimethyl silicone oil, surface-modified nano-calcium carbonate, alkoxy-modified MQ resin, a crosslinker, a silane coupling agent, and a catalyst. However, its bonding strength is only 3.06 MPa, and its complex composition results in high production costs and significant energy consumption. In contrast, the present invention provides a benzoxazine-based organic silicone adhesive that can be prepared in a single step. While its strength far exceeds that of the referenced adhesive, it also features a simpler process and more efficient production.

[0171] Reference document 2 (CN119351014 A) reports a bio-based benzoxazine adhesive and its preparation method. The adhesive has a bond strength of 6.41 MPa and requires 30 minutes of 365 nm UV irradiation and a curing temperature of up to 200°C. In comparison, the adhesive obtained in the present invention has a simpler preparation method and curing procedure, a more practical process, and higher bond strength.

[0172] Reference Document 3 (CN117777946 A) describes the formula and method for use of a high-strength benzoxazine-based silicone adhesive that cures at medium and low temperatures, as previously proposed by the present inventors. Building on previous work, the present inventors have redesigned the formula and molecular structure to achieve higher bonding strength without the need for a catalyst. Furthermore, the preparation and bonding procedures are simplified, and the raw materials are sourced from environmentally friendly sources.

[0173] Test Example 2

[0174] The debonding effect of the benzoxazine-based adhesive prepared in Example 1 was tested, and the results are shown in Table 2.

[0175] Table 2 is the debonding effect test of the benzoxazine adhesive prepared in Example 1

[0176]

[0177] Table 2 shows the debonding effect of the adhesive obtained by the present invention after bonding. After the foaming process, the bonding strength of the bonded components is significantly reduced, achieving an easy peeling effect. The peeling effect photo is shown in FIG. Figures 9-12 shown.

[0178] Through Table 1, Table 2 and Figures 9-12 As shown, the benzoxazine-based adhesive obtained by the present invention has the advantages of low curing temperature, high bonding strength, a wide range of raw material sources, and a simple synthesis process after curing. Furthermore, users can adjust the bonding strength by adjusting the decarboxylation temperature and reaction time according to the application scenario, making the adhesive excellent for multi-scenario applications.

Claims

1. A benzoxazine adhesive that is easily peelable when heated, characterized in that: The molecular structure of the adhesive contains silicon-oxygen bonds, benzoxazine groups and carboxyl groups.

2. The heat-peelable benzoxazine adhesive according to claim 1, wherein: The molecular structure of the benzoxazine-type adhesive that is easily peelable when heated contains at least a structural unit represented by formula (I) and at least one structural unit represented by formula (II): Formula (I); Formula (II); In formula (I) and formula (II), R', R'', R1 and R2 are independently selected from various organic groups, including various aliphatic hydrocarbon groups, aromatic hydrocarbon groups and / or organosilicon groups; and R1 should contain at least one carboxyl group; and n is 1-3000.

3. The heat-peelable benzoxazine adhesive according to claim 2, wherein: The aliphatic hydrocarbon group is selected from C1-C 10 Alkane or halogenated alkane, preferably methyl or trifluoropropyl; Preferably, the aromatic hydrocarbon group is selected from phenyl, phenethyl, methylphenyl, and phenolic phenyl; Preferably, the organosilicon group is selected from trialkylsiloxy, trialkoxysilyl, short-chain polysiloxane, dendritic polysiloxane, and disiloxane; more preferably, the number of chain segments of the short-chain polysiloxane is 2-3000.

4. The heat-peelable benzoxazine adhesive according to claim 2, wherein: The benzoxazine adhesive that is easily peelable when heated has a structure represented by formula (III), formula (IV) or formula (V): Formula (III); Formula (IV); Formula (V); In the formula, R`, R``, R1, and R2 have the same meanings as in formula (I) and formula (II), the selectors of R```, R````, and R3 are the same as those of R` and R``, n is 0-3000, and m is 1-3000.

5. A method for preparing the heat-peelable benzoxazine adhesive according to any one of claims 1 to 4, comprising the following steps: An amino-containing organosilicon compound is mixed with an aldehyde compound and a carboxylic acid containing at least one phenolic hydroxyl group, and the mixture is reacted in a solvent. After purification, a benzoxazine adhesive that is easily peeled when heated is obtained.

6. The method for preparing the heat-strippable benzoxazine adhesive according to claim 5, wherein: The amino-containing organosilicon compounds include amino-terminated organosilicon polymers, organosilicon polymers containing amino groups on the side chains, and amino-containing organosilicon small molecules; Preferably, the aldehyde compound is any aldehyde organic compound that can be dissolved in the system; further preferably, the aldehyde compound is a small molecule aldehyde compound or paraformaldehyde; Preferably, the carboxylic acid containing at least one phenolic hydroxyl group includes various carboxylic acids containing at least one phenolic hydroxyl group and at least one carboxyl group in their molecular structures. Further preferably, the carboxylic acid is diphenolic acid, vanillic acid or p-hydroxyphenylacetic acid.

7. The method for preparing the heat-strippable benzoxazine adhesive according to claim 5, wherein: The ratio of the molar number of amino groups in the amino-containing organosilicon compound, the molar number of aldehyde groups in the aldehyde compound, and the molar number of phenolic hydroxyl groups in the carboxylic acid containing at least one phenolic hydroxyl group is 1:(0.1-15):(0.1-20), preferably 1:(2-15):(1-10).

8. The method for preparing a benzoxazine adhesive that is easily peelable when heated according to claim 5, wherein: The reaction temperature of the amino-containing organosilicon compound, the aldehyde compound and the carboxylic acid containing at least one phenolic hydroxyl group is 30-150°C, preferably 50-80°C.

9. A benzoxazine adhesive composition that is easily peelable when heated, characterized in that: The combination comprises the following components in parts by mass: 100 parts of the heat-strippable benzoxazine adhesive according to any one of claims 1 to 4, 0-10 parts of catalyst A, 0-400 parts of filler, and 0-200 parts of additive; Preferably, the catalyst A is a compound that can catalyze the ring-opening polymerization reaction of benzoxazine, including various Lewis acids and bases in a broad sense; more preferably, benzenesulfonic acid, acetic acid, hexamethylenediamine and sodium hydroxide; Preferably, the filler is various additives that can improve the performance of adhesives based on benzoxazine structures, and more preferably, fumed silica, precipitated silica, carbon black, calcium carbonate, aluminum hydroxide and / or magnesium hydroxide, and various specially treated compounds thereof; Preferably, the auxiliary agent is a thermal oxygen stabilizer, a flame retardant, a conductive agent, a deep curing agent, a pigment and / or a plasticizer.

10. A method for using the heat-peelable benzoxazine adhesive according to any one of claims 1 to 4, comprising the following two steps: (1) The benzoxazine adhesive that is easily peeled when heated is evenly applied to the surface of the adherends. After the two adherends are fixed, the temperature is raised to achieve bonding. Preferably, the programmed temperature rise is a temperature rise process from an initial temperature to a terminal temperature through multiple "heating-constant temperature" steps with a certain temperature difference as a gradient; further preferably, the temperature difference includes any temperature difference between 5°C and 100°C, the heating rate is any heating rate between 0.1°C / min and 20°C / min, the constant temperature time in the "heating-constant temperature" step is any time between 1 minute and 180 minutes, and the terminal temperature of the temperature rise program is the time when the benzoxazine resin is cured, including any temperature between 50°C and 200°C; (2) The bonded adherend obtained in step (1) is further heated to the foaming temperature and maintained for a period of time to achieve debonding; Preferably, the high-temperature foaming is a process of foaming the polybenzoxazine resin obtained in step (1) at a set temperature for a certain period of time; preferably, the temperature of the high-temperature foaming is greater than the temperature at which the heating program ends.

Images