Hot melt adhesive, preparation method thereof and application of hot melt adhesive in air conditioner filter

Abstract

The invention relates to a hot melt adhesive and a preparation method and application thereof in an air conditioner filter, and the preparation method of the hot melt adhesive comprises the following steps: S1, placing an acrylic acid soft monomer, an acrylic acid hard monomer and a functional monomer in a reactor, adding a first type of initiator, and carrying out a prepolymerization reaction at a first temperature to obtain a prepolymer; the functional monomer comprises carboxyl; s2, adding silicon dioxide, polyfunctional isocyanate, a second type of initiator and a catalyst into the prepolymer, and carrying out polymerization reaction at a second temperature to obtain a hot melt adhesive; the second temperature is higher than the first temperature. In this way, the prepared hot melt adhesive can achieve low odor, and when the hot melt adhesive is applied to the field of passenger car interiors, the quality of air in a car cannot be affected; meanwhile, the adhesive also has relatively high cohesiveness, relatively high high-temperature resistance, relatively high low-temperature resistance and relatively good processability.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, in particular to a hot melt adhesive and a preparation method thereof and application in air conditioning filters. Background Art

[0002] Hot melt adhesive is a special adhesive that is solid at room temperature. When heated, it melts and turns into a liquid. Based on the different curing methods, hot melt adhesives can be mainly divided into two categories: reactive hot melt adhesives and non-reactive hot melt adhesives. Among reactive hot melt adhesives, moisture-curing polyurethane hot melt adhesives occupy an important position. It is made of NCO (isocyanate group)-terminated prepolymers as the base material, supplemented with thermoplastic resins, tackifying resins, antioxidants, catalysts, fillers and other additives. During application, this type of hot melt adhesive chemically reacts with moisture in the air to form reliable bonding strength to meet the bonding requirements in different scenarios. Non-reactive hot melt adhesives are mainly composed of thermoplastic polymers, tackifying resins, plasticizers, antioxidants and other ingredients. After heating and application, as the temperature drops and cools, bonding strength can be quickly formed, achieving a firm connection between materials.

[0003] Hot melt adhesives are widely used in passenger car interiors due to their high processing efficiency and better environmental performance compared to other adhesives. For example, they are used as adhesives in components such as air conditioners, ceilings, seats, door panels, dashboards, and carpets. Commonly used PUR (Polyurethane Reactive) and thermoplastic elastomer hot melt adhesives inevitably produce odors during use due to the effects of added tackifying resins, residual small-molecule monomers, and residual solvents. This is especially true during the hot summer months, when vehicle temperatures can reach as high as 70°C. Under prolonged high-temperature conditions, the tackifying resins (rosin resin, terpene resin, C5 petroleum resin, C9 petroleum resin, etc.), plasticizers (paraffin wax, polyethylene wax, mineral oil, etc.), residual solvents, and small-molecule organic compounds in the base resin in the hot melt adhesive are more likely to precipitate, and the released odor can seriously impact vehicle air quality. Summary of the Invention

[0004] In view of this, embodiments of the present application provide a hot melt adhesive, a preparation method thereof, and an application in an air conditioning filter to solve at least one problem existing in the background technology.

[0005] In a first aspect, an embodiment of the present application provides a method for preparing a hot melt adhesive, the method comprising the following steps:

[0006] S1: placing an acrylic soft monomer, an acrylic hard monomer, and a functional monomer in a reactor, adding a first type of initiator, and performing a prepolymerization reaction at a first temperature to obtain a prepolymer; the functional monomer includes a carboxyl group;

[0007] S2: adding silicon dioxide, multifunctional isocyanate, a second type of initiator and a catalyst to the prepolymer, and performing a polymerization reaction at a second temperature to obtain the hot melt adhesive; the second temperature is higher than the first temperature.

[0008] In combination with the first aspect of the present application, in an optional embodiment, the amount of the acrylic soft monomer added is 43 to 57 parts by weight; the amount of the acrylic hard monomer added is 28 to 32 parts; the amount of the functional monomer added is 10 to 20 parts; the amount of the silica added is 15 to 20 parts; the amount of the multifunctional isocyanate added is 0.5 to 1 part; the amount of the first type of initiator added is 0.3 to 0.6 parts; the amount of the second type of initiator added is 0.3 to 0.5 parts; and the amount of the catalyst added is 0.1 to 0.15 parts.

[0009] In conjunction with the first aspect of the present application, in an optional embodiment, the method satisfies at least one of the following features:

[0010] (1) The acrylic soft monomer includes at least one of isooctyl acrylate, butyl acrylate, lauryl acrylate, octadecyl acrylate, and isobutyl acrylate; preferably, the acrylic soft monomer includes isooctyl acrylate and butyl acrylate, and the mass ratio of the isooctyl acrylate to the butyl acrylate is (18-22): (25-35);

[0011] (2) the acrylic hard monomer comprises at least one of isobornyl methacrylate, cyclohexyl methacrylate, isobornyl acrylate, cyclohexyl acrylate, tetrahydrofuran methacrylate, and tetrahydrofuran methacrylate;

[0012] (3) The functional monomer includes at least one of methacrylic acid, acrylic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid;

[0013] (4) The polyfunctional isocyanate includes at least one of isophorone diisocyanate trimer, hexamethylene diisocyanate trimer, hexamethylene diisocyanate biuret, diphenylmethane diisocyanate oligomer, and toluene diisocyanate;

[0014] (5) The glass transition temperature of the hot melt adhesive is -5°C to 0°C;

[0015] (6) The colloid viscosity of the hot melt adhesive at 150° C. is less than or equal to 7000 mPa·s.

[0016] In conjunction with the first aspect of the present application, in an optional embodiment, the first temperature is 50° C. to 95° C.; step S1 includes:

[0017] S11: placing the acrylic soft monomer, the acrylic hard monomer, and the functional monomer in a reactor, adding a first initiator, and stirring at 50° C. to 70° C. to perform a first prepolymerization reaction;

[0018] Preferably, the first prepolymerization reaction time is 3 hours to 4 hours; preferably, the amount of the first initiator added is 0.15 to 0.3 parts by weight; preferably, the first initiator includes an azo compound, which can be selected from at least one of azobisisobutyronitrile, azobisisoheptanenitrile, azobisisovaleronitrile, azobiscyclohexylcarbonitrile, and dimethyl azobisisobutyrate;

[0019] S12: adding a second initiator and a molecular weight regulator at 75° C. to 95° C. and performing a second prepolymerization reaction under stirring;

[0020] Preferably, the time of the second prepolymerization reaction is 3h to 4h; preferably, the amount of the second initiator added is 0.15 to 0.3 parts by weight; preferably, the second initiator includes benzoyl peroxide; preferably, the amount of the molecular weight regulator added is 0.3 to 0.5 parts by weight; preferably, the molecular weight regulator includes at least one of n-dodecyl mercaptan, 3-isooctyl mercaptan and methyl styrene dimer.

[0021] In conjunction with the first aspect of the present application, in an optional implementation manner, step S2 satisfies at least one of the following characteristics:

[0022] (1) The second temperature is 110°C to 130°C;

[0023] (2) The polymerization reaction time is 10 h to 20 h;

[0024] (3) The second type of initiator includes tert-amyl peroxy-2-ethylhexanoate and / or 1,1-di-tert-amyl peroxycyclohexane;

[0025] (4) The catalyst includes an organotin catalyst and / or a tertiary amine catalyst.

[0026] In conjunction with the first aspect of the present application, in an optional embodiment, after the polymerization reaction in step S2 is completed, the method further includes:

[0027] Under vacuum conditions at 150° C. to 170° C., removing unreacted acrylic soft monomer, acrylic hard monomer, and functional monomer;

[0028] Preferably, the vacuum condition is evacuated to -0.09 MPa to -0.07 MPa; preferably, the vacuum condition is maintained for 20 min to 40 min.

[0029] In a second aspect, an embodiment of the present application provides a hot melt adhesive, wherein raw materials for preparing the hot melt adhesive include acrylic soft monomers, acrylic hard monomers, functional monomers, silica and multifunctional isocyanate; the functional monomers include carboxyl groups.

[0030] In conjunction with the second aspect of the present application, in an optional embodiment, the raw materials for preparing the hot melt adhesive include, in parts by weight:

[0031] 43-57 parts of acrylic soft monomer

[0032] 28-32 parts of acrylic hard monomer

[0033] 10-20 parts of functional monomer

[0034] 15-20 parts of silicon dioxide

[0035] 0.5-1 part of multifunctional isocyanate;

[0036] Preferably, the raw materials for preparing the hot melt adhesive further include an initiator, a catalyst and a molecular weight regulator; in parts by weight, the initiator is 0.6 to 1.1 parts; the catalyst is 0.1 to 0.15 parts; and the molecular weight regulator is 0.3 to 0.5 parts.

[0037] In conjunction with the second aspect of the present application, in an optional embodiment, the hot melt adhesive satisfies at least one of the following characteristics:

[0038] (1) The acrylic soft monomer includes at least one of isooctyl acrylate, butyl acrylate, lauryl acrylate, octadecyl acrylate, and isobutyl acrylate; preferably, the acrylic soft monomer includes isooctyl acrylate and butyl acrylate, and the mass ratio of the isooctyl acrylate to the butyl acrylate is (18-22): (25-35);

[0039] (2) the acrylic hard monomer comprises at least one of isobornyl methacrylate, cyclohexyl methacrylate, isobornyl acrylate, cyclohexyl acrylate, tetrahydrofuran methacrylate, and tetrahydrofuran methacrylate;

[0040] (3) The functional monomer includes at least one of methacrylic acid, acrylic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid;

[0041] (4) The polyfunctional isocyanate includes at least one of isophorone diisocyanate trimer, hexamethylene diisocyanate trimer, hexamethylene diisocyanate biuret, diphenylmethane diisocyanate oligomer, and toluene diisocyanate;

[0042] (5) The glass transition temperature of the hot melt adhesive is -5°C to 0°C;

[0043] (6) The colloid viscosity of the hot melt adhesive at 150° C. is less than or equal to 7000 mPa·s.

[0044] In a third aspect, embodiments of the present application provide the use of the hot melt adhesive prepared by the hot melt adhesive preparation method as described in any one of the first aspects or the hot melt adhesive as described in any one of the second aspects in an air conditioning filter.

[0045] Compared with the prior art, the embodiments of the present application have the following beneficial effects:

[0046] The hot melt adhesive and its preparation method and application in air conditioning filters provided in the embodiment of the present application, the preparation method of the hot melt adhesive includes the following steps: S1: placing an acrylic soft monomer, an acrylic hard monomer and a functional monomer in a reactor, adding a first type of initiator, and performing a prepolymerization reaction at a first temperature to obtain a prepolymer; the functional monomer includes a carboxyl group; S2: adding silica, a multifunctional isocyanate, a second type of initiator and a catalyst to the prepolymer, and performing a polymerization reaction at a second temperature to obtain a hot melt adhesive; the second temperature is higher than the first temperature. In the embodiment of the present application, first, a bulk polymerization process is adopted to obtain a prepolymer by a prepolymerization reaction of an acrylic soft monomer, an acrylic hard monomer and a functional monomer at a first temperature. In this step, there is no need to provide a reaction environment by a solvent, which can avoid the odor of the prepared hot melt adhesive caused by residual solvent; and the combination of the acrylic soft monomer and the acrylic hard monomer can form a hot melt adhesive with good flexibility, wettability and adhesion, and can also avoid the problem that the hot melt adhesive produced by the use of a tackifying resin is prone to odor; since the functional monomer including a carboxyl group can introduce a carboxyl group into the prepolymer, the subsequent polymerization at the second temperature is carried out. During the polymerization reaction, the multifunctional isocyanate can form covalent bonds with the carboxyl groups in the prepolymer and the silanol groups on the surface of the silica. The silanol groups on the surface of the silica can also form hydrogen bonds with the carboxyl groups in the prepolymer, thereby facilitating the formation of a stable three-dimensional cross-linked structure and improving the bonding strength of the hot melt adhesive. At high processing temperatures (approximately 140°C to 160°C), the hydrogen bonds break, and the hot melt adhesive can restore its fluidity, ensuring the processing performance of the hot melt adhesive. After the processing is completed and the temperature is cooled, a stable three-dimensional cross-linked structure can be regenerated in the hot melt adhesive, resulting in the hot melt adhesive having high high-temperature and low-temperature resistance. In other words, the hot melt adhesive prepared in the embodiment of the present application can achieve low odor and will not affect the air quality in the vehicle when used in the field of passenger car interiors. At the same time, it also has high adhesion, high high-temperature and low-temperature resistance, and good processing performance. In addition, in the embodiment of the present application, the staged polymerization at low temperature (first temperature) and high temperature (second temperature) is conducive to polymerization heat dissipation, which can better improve the controllability and safety of the polymerization process, thereby facilitating its application in actual production.

[0047] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The drawings described herein are used to provide a further understanding of the present application and constitute a part of the present application. The illustrative embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0049] Figure 1 A schematic flow chart of a method for preparing a hot melt adhesive provided in an embodiment of the present application;

[0050] Figure 2 A schematic structural diagram of a passenger car air conditioning filter provided in an embodiment of the present application;

[0051] Figure 3 The TGA curves obtained by thermogravimetric analysis of the hot melt adhesive prepared in Example 1 and the hot melt adhesive prepared in Comparative Example 2 are shown;

[0052] Figure 4 The DGT curves are obtained by thermogravimetric analysis of the hot melt adhesive prepared in Example 1 and the hot melt adhesive prepared in Comparative Example 2. DETAILED DESCRIPTION

[0053] In order to make the technical solutions and beneficial effects of the present invention more clearly understood, the following is a detailed description of the invention by referring to the accompanying drawings and listing specific embodiments. It should be understood that these embodiments are intended only to illustrate the present invention and are not intended to limit the scope of the invention. The experimental methods in the following examples where specific conditions are not specified are generally based on conventional experimental conditions. Unless otherwise specified, the reagents and raw materials used in the present invention are commercially available.

[0054] In the following description, numerous specific details are provided to provide a more thorough understanding of the present application. However, it will be apparent to those skilled in the art that the present application can be practiced without one or more of these details. In other instances, certain technical features known in the art are not described to avoid confusion with the present application; that is, all features of actual embodiments are not described herein, nor are well-known functions and steps described in detail.

[0055] The purpose of the terms used herein is only to describe specific embodiments and is not intended to limit the present application. When used herein, the singular forms "a", "an", and "the" are also intended to include the plural forms, unless the context clearly indicates otherwise. The terms "comprising" and / or "including", when used in this specification, determine the presence of the features, integers, steps, operations, elements and / or parts, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, parts and / or groups. When used herein, the term "and / or" includes any and all combinations of the relevant listed items.

[0056] In order to fully understand the present application, detailed steps and detailed structures will be presented in the following description to illustrate the technical solution of the present application. The preferred embodiments of the present application are described in detail below. However, in addition to these detailed descriptions, the present application may also have other implementation methods.

[0057] Unless otherwise defined, technical and scientific terms used in this application have the same meanings as those in the technical field to which this application belongs.

[0058] In the following examples, if no specific techniques or conditions are specified, the methods are generally carried out according to conventional techniques or conditions described in the literature in the field, or according to the product instructions and the conditions recommended by the manufacturer. The numerical ranges in the following examples are all inclusive.

[0059] To address the odor problem of hot melt adhesives, related technologies include: improving the hot melt adhesive's high-temperature resistance by adding a high-styrene-content main polymer and solid petroleum resin, thereby reducing the volatilization of small molecule gases from the hot melt adhesive; or, during the hot melt adhesive preparation process, removing small molecules from the polyol by using a pore-opening agent and nitrogen gas flow through the bottom of the reactor, using high temperature and vacuum, and controlling the odor of the isocyanate component, thereby producing a low-odor hot melt adhesive. While these methods can reduce the odor of hot melt adhesives, their effectiveness is limited and they can easily affect the adhesive's inherent bonding and processing properties.

[0060] Based on this, the present application embodiment provides a method for preparing hot melt adhesive, please refer to Figure 1 The preparation method of the hot melt adhesive provided in the embodiment of the present application includes the following steps:

[0061] S1: placing an acrylic soft monomer, an acrylic hard monomer, and a functional monomer in a reactor, adding a first type of initiator, and performing a prepolymerization reaction at a first temperature to obtain a prepolymer; the functional monomer includes a carboxyl group;

[0062] S2: adding silica, multifunctional isocyanate, a second type of initiator and a catalyst to the prepolymer, and performing a polymerization reaction at a second temperature to obtain a hot melt adhesive; the second temperature is higher than the first temperature.

[0063] In an embodiment of the present application, in step S1, a bulk polymerization process is adopted, and a prepolymer is obtained by a prepolymerization reaction of an acrylic soft monomer, an acrylic hard monomer and a functional monomer at a first temperature. In this step, there is no need to provide a reaction environment through a solvent, which can avoid the odor of the hot melt adhesive caused by solvent residue; and the combination of the acrylic soft monomer and the acrylic hard monomer can form a hot melt adhesive with good flexibility, wettability and adhesion, and can also avoid the problem of the hot melt adhesive easily generating odor due to the use of a tackifying resin. Since the functional monomer including a carboxyl group can introduce a carboxyl group into the prepolymer, in step S2, during the polymerization reaction at the second temperature, the multifunctional isocyanate can form a covalent bond with the carboxyl group in the prepolymer and the silanol group on the surface of the silica. The silanol group on the surface of the silica can also form a hydrogen bond with the carboxyl group in the prepolymer, thereby facilitating the formation of a stable three-dimensional cross-linked structure and improving the bonding strength of the hot melt adhesive. At high processing temperatures (approximately 140°C to 160°C), the hydrogen bonds break, and the hot melt adhesive can restore its fluidity, ensuring the processing performance of the hot melt adhesive. After the processing is completed and the temperature is lowered, a stable three-dimensional cross-linked structure can be regenerated in the hot melt adhesive, thereby making the prepared hot melt adhesive have high high-temperature and low-temperature resistance. That is, the hot melt adhesive prepared in the embodiment of the present application can achieve low odor and will not affect the air quality inside the vehicle when used in the field of passenger car interiors. At the same time, it also has high adhesion, high high-temperature and low-temperature resistance, and good processing performance. In addition, in the embodiment of the present application, polymerization is carried out in stages at low temperature (first temperature) and high temperature (second temperature), which is beneficial to polymerization heat dissipation and can better improve the controllability and safety of the polymerization process, thereby facilitating application in actual production.

[0064] In the embodiment of the present application, acrylic soft monomer can provide flexibility for the hot melt adhesive finally obtained, acrylic hard monomer can provide hardness for the hot melt adhesive finally obtained, and functional monomer can introduce carboxyl group into prepolymer, thereby improving the adhesion and high temperature and low temperature resistance of the hot melt adhesive finally obtained. It can be understood that the addition amount of acrylic soft monomer, acrylic hard monomer and functional monomer will have a direct impact on the comprehensive performance of the hot melt adhesive obtained. In step S2, when the amount of silica added is too little and the amount of multifunctional isocyanate added is too much, the hydrogen bond formed between the carboxyl group in the prepolymer and the silanol group on the surface of silica is reduced, and the carboxyl group on the prepolymer mainly undergoes cross-linking reaction with the multifunctional isocyanate to form a covalent bond, so that the degree of cross-linking is significantly increased, and the fluidity of the hot melt adhesive obtained deteriorates at low temperatures, and the adhesion is affected at low temperatures, and the risk of debonding increases, and the fluidity of the hot melt adhesive in a high temperature molten state will also significantly decrease, and the melt viscosity and softening point will increase, which is not conducive to processing and dispensing; ... When too much silicon dioxide is added and too little multifunctional isocyanate is added, the covalent bond connection formed by the multifunctional isocyanate and the carboxyl group in the prepolymer and the silanol group on the surface of silica is easily reduced. The internal cross-linking structure of the hot melt adhesive obtained is insufficient, which is not conducive to the formation of a stable three-dimensional cross-linking structure. The cohesive force is mainly provided by the hydrogen bond between the silanol group on the surface of silica and the carboxyl group in the prepolymer. At high temperatures, when the hydrogen bonds are broken, the linear molecular structure in the hot melt adhesive will be easily moved, and the softening point, high-temperature peel strength and moisture-heat aging resistance of the hot melt adhesive will all decrease.

[0065] Therefore, in order to improve the comprehensive performance of the prepared hot melt adhesive, in some embodiments, the addition amount of acrylic soft monomer can be 43 to 57 parts by weight, for example, 43 parts, 45 parts, 47 parts, 49 parts, 51 parts, 53 parts, 55 parts, 57 parts or any value between any two of the above numerical ranges; the addition amount of acrylic hard monomer can be 28 to 32 parts, for example, 28 parts, 29 parts, 30 parts, 31 parts, 32 parts or any value between any two of the above numerical ranges; the addition amount of functional monomer can be 10 to 20 parts, for example, 10 parts, 12 parts, 14 parts, 16 parts, 18 parts, 20 parts or any value between any two of the above numerical ranges; the addition amount of the first type initiator can be 0.3 to 0.6 parts, for example, 0.3 parts, 0.4 parts, 0.5 parts, 0.6 parts or any value between the above any value between the two numerical ranges; the amount of silicon dioxide added can be 15 to 20 parts, for example, 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts or any value between any two of the above numerical ranges; the amount of multifunctional isocyanate added can be 0.5 to 1 part, for example, 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part or any value between any two of the above numerical ranges; the amount of the second type of initiator added can be 0.3 to 0.5 parts, for example, 0.3 parts, 0.4 parts, 0.5 parts or any value between any two of the above numerical ranges; the amount of the catalyst added can be 0.1 to 0.15 parts, for example, 0.1 parts, 0.11 parts, 0.12 parts, 0.13 parts, 0.14 parts, 0.15 parts or any value between any two of the above numerical ranges. This is conducive to the full prepolymerization reaction of acrylic soft monomers, acrylic hard monomers and functional monomers initiated by the first type of initiator, and the full polymerization reaction between the prepolymer, silica and multifunctional isocyanate is ensured by the second type of initiator and catalyst, thereby giving full play to the role of each raw material, while reducing the odor of the hot melt adhesive, and effectively improving the flexibility, wettability, adhesion, low temperature resistance and high temperature resistance of the hot melt adhesive.

[0066] Exemplarily, the acrylic soft monomer may include at least one of isooctyl acrylate, butyl acrylate, lauryl acrylate, octadecyl acrylate, and isobutyl acrylate. In some specific embodiments, the acrylic soft monomer may include isooctyl acrylate and butyl acrylate, and the mass ratio of isooctyl acrylate to butyl acrylate may be (18-22):(25-35), for example, 18:25, 20:30, 20:35, 22:25, 22:35, 18:35, or any ratio within the above ratio range. By controlling the mass ratio of isooctyl acrylate to butyl acrylate within the above range, the combination of isooctyl acrylate and butyl acrylate is conducive to obtaining a hot melt adhesive with a suitable glass transition temperature, thereby improving the overall performance of the hot melt adhesive. Specifically, in step S1, the amount of isooctyl acrylate added can be 18 to 22 parts by weight; the amount of butyl acrylate added can be 25 to 35 parts by weight; the amount of acrylic hard monomer added can be 28 to 32 parts by weight; the amount of functional monomer added can be 10 to 20 parts by weight; and the amount of the first type initiator added can be 0.3 to 0.6 parts by weight.

[0067] If the glass transition temperature of the hot melt adhesive is too high, its low-temperature resistance will deteriorate, and it will easily debond at low temperatures. If the glass transition temperature of the hot melt adhesive is too low, its high-temperature resistance will deteriorate, and it will easily overflow and separate at high temperatures. Therefore, in some specific embodiments, the glass transition temperature of the hot melt adhesive can be between -5°C and 0°C, for example, -5°C, -4°C, -3°C, -2°C, -1°C, 0°C, or any value between any two of the above ranges. This helps to balance the low-temperature resistance and high-temperature resistance of the hot melt adhesive.

[0068] It should be noted that the glass transition temperature of the hot melt adhesive described in the embodiments of the present application refers to the theoretical glass transition temperature of the hot melt adhesive, which can be calculated by the Fox equation or the Gordon-Taylor equation based on the raw materials used in the preparation of the hot melt adhesive.

[0069] For example, the acrylic hard monomer may include at least one of isobornyl methacrylate, cyclohexyl methacrylate, isobornyl acrylate, cyclohexyl acrylate, tetrahydrofuranyl methacrylate, and tetrahydrofuranyl methacrylate. In some specific embodiments, the acrylic hard monomer may include isobornyl methacrylate and / or cyclohexyl methacrylate. Because isobornyl methacrylate and cyclohexyl methacrylate have large non-polar side chains and exhibit a steric effect, they can provide good steric hindrance, which helps reduce the viscosity of the hot melt adhesive in a high-temperature molten state, thereby facilitating dispensing and processing.

[0070] In some specific embodiments, the hot melt adhesive can have a viscosity of 7000 mPa·s or less at 150°C. By controlling the type and amount of raw materials used to prepare the hot melt adhesive, the viscosity of the hot melt adhesive at 150°C can be controlled within the above range, effectively improving the processing performance of the hot melt adhesive and facilitating dispensing.

[0071] For example, the functional monomer may include at least one of methacrylic acid, acrylic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid. These functional monomers can effectively crosslink and polymerize with the acrylic soft monomer and the acrylic hard monomer, introducing carboxyl groups into the prepolymer and improving the adhesive properties of the resulting hot melt adhesive.

[0072] In some embodiments, the first temperature in step S1 may be 50° C. to 95° C.; step S1 may include:

[0073] S11: placing an acrylic soft monomer, an acrylic hard monomer, and a functional monomer in a reactor, adding a first initiator, and stirring at 50° C. to 70° C. to perform a first prepolymerization reaction;

[0074] Specifically, the first prepolymerization reaction time can be 3 to 4 hours. The first initiator can be added in an amount of 0.15 to 0.3 parts by weight. For example, the first initiator can include an azo compound, such as at least one of azobisisobutyronitrile, azobisisoheptanenitrile, azobisisovaleronitrile, azobiscyclohexylcarbonitrile, and dimethyl azobisisobutyrate. The above-mentioned first initiator is stable at 50°C to 70°C, which is conducive to effectively initiating the first prepolymerization reaction.

[0075] S12: adding a second initiator and a molecular weight regulator at a temperature of 75° C. to 95° C., and performing a second prepolymerization reaction under stirring.

[0076] Specifically, the time of the second prepolymerization reaction can be 3h to 4h; the amount of the second initiator added can be 0.15 to 0.3 parts by weight; illustratively, the second initiator can include benzoyl peroxide. The above-mentioned type of second initiator is stable under the conditions of 75°C to 95°C, which is conducive to better initiation of the second prepolymerization reaction. Furthermore, the amount of the molecular weight regulator added can be 0.3 to 0.5 parts by weight, for example, it can be 0.3 parts, 0.4 parts, 0.5 parts or any value between any two of the above numerical ranges. Exemplarily, the molecular weight regulator can include at least one of n-dodecyl mercaptan, 3-isooctyl mercaptan and methyl styrene dimer. The above-mentioned type of molecular weight regulator can make the final hot melt adhesive have low odor, solvent solubility and good leveling properties.

[0077] In the embodiment of the present application, the prepolymerization reaction is divided into a first prepolymerization reaction and a second prepolymerization reaction at two temperatures. A two-step bulk polymerization process is adopted, and suitable initiator types are selected for different reaction temperatures to achieve staged polymerization at different temperatures. This is beneficial to improving the sufficiency of the prepolymerization reaction, thereby improving the quality of the obtained prepolymer. It is also beneficial to the heat dissipation of the prepolymerization, which can better improve the controllability and safety of the prepolymerization process.

[0078] In step S2, silicon dioxide, multifunctional isocyanate, a second type of initiator and a catalyst are added to the prepolymer, and a polymerization reaction is carried out at a second temperature to obtain a hot melt adhesive.

[0079] In an actual preparation process, step S2 may include: after the second prepolymerization reaction is completed in step S12, while the temperature is maintained at 75°C to 95°C, first adding silica to the prepolymer and stirring and mixing. Specifically, the stirring time may be 30 minutes to 50 minutes to ensure uniform mixing; next, when the temperature drops below 45°C, adding a multifunctional isocyanate, a second type initiator, and a catalyst, stirring and mixing to obtain a glycerol-like prepolymer, and then heating to the second temperature to carry out a polymerization reaction to obtain a hot melt adhesive. In this way, adding silica at a high temperature of 75°C to 95°C is conducive to uniform mixing of silica, and then lowering the temperature to below 45°C before adding the multifunctional isocyanate, the second type initiator, and the catalyst can avoid the problem of starting the polymerization reaction before the multifunctional isocyanate, the second type initiator, and the catalyst are evenly mixed, resulting in uneven polymerization and affecting the performance of the obtained hot melt adhesive. By first fully mixing the reactants at a low temperature below 45°C and then heating to the second temperature for polymerization, it can be better ensured that the polymerization reaction is carried out more uniformly, fully and completely, which is beneficial to improving the comprehensive performance of the hot melt adhesive produced.

[0080] It is understood that when the second temperature is too low, it is not conducive to the full progress of the polymerization reaction, which in turn affects the quality of the hot melt adhesive produced; when the second temperature is too high, the controllability of the polymerization reaction is reduced, and it may affect the function of the second type of initiator and catalyst, which in turn also affects the quality of the hot melt adhesive produced. Therefore, in some embodiments, the second temperature can be 110°C to 130°C, for example, it can be 110°C, 120°C, 130°C, or any value between any two of the above numerical ranges. This is conducive to promoting the full, complete and more controllable progress of the polymerization reaction, reducing the residual reaction monomer, thereby improving the quality of the hot melt adhesive produced and reducing the odor of the hot melt adhesive.

[0081] Furthermore, the polymerization reaction time can be 10 to 20 hours, for example, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, or any value between any two of the above ranges. This helps promote a more complete polymerization reaction, reduces residual monomers, and thus improves the quality of the hot melt adhesive and reduces the odor of the hot melt adhesive.

[0082] For example, the multifunctional isocyanate may include at least one of isophorone diisocyanate trimer, hexamethylene diisocyanate trimer, hexamethylene diisocyanate biuret, diphenylmethane diisocyanate oligomer, and toluene diisocyanate. The silicon dioxide may include nano silicon dioxide.

[0083] The second type of initiator and catalyst can be selected based on the second temperature range. For example, the second type of initiator can include tert-amyl peroxy-2-ethylhexanoate and / or 1,1-di-tert-amyl cyclohexane peroxide. The catalyst can include an organotin catalyst and / or a tertiary amine catalyst, where organotin catalysts include, for example, dibutyltin dilaurate and / or stannous octoate, and tertiary amine catalysts include, for example, at least one of triethylamine, diethylenediamine, and dimethylcyclohexylamine. These second type of initiators and catalysts are stable at high temperatures, which helps ensure the polymerization reaction proceeds smoothly.

[0084] In some embodiments, after the polymerization reaction in step S2 is completed, the method for preparing the hot melt adhesive further comprises: removing unreacted acrylic soft monomer, acrylic hard monomer, and functional monomer under vacuum conditions at 150° C. to 170° C.

[0085] In an embodiment of the present application, by heating and softening the hot melt adhesive under high temperature conditions and removing unreacted acrylic soft monomers, acrylic hard monomers and functional monomers under vacuum conditions, the residual reactive monomers in the prepared hot melt adhesive can be reduced, further reducing the odor of the hot melt adhesive.

[0086] In the actual preparation process, the vacuum condition can be evacuated to -0.09 MPa to -0.07 MPa; optionally, the vacuum condition is maintained for 20 min to 40 min to ensure more thorough removal of unreacted acrylic soft monomer, acrylic hard monomer and functional monomer.

[0087] An embodiment of the present application also provides a hot melt adhesive, the raw materials for preparing the hot melt adhesive include acrylic soft monomer, acrylic hard monomer, functional monomer, silicon dioxide and multifunctional isocyanate; the functional monomer includes carboxyl group.

[0088] The hot melt adhesive provided in the embodiment of the present application can form a hot melt adhesive with good flexibility, wettability and adhesion by combining acrylic soft monomers and acrylic hard monomers, which can avoid the problem that the hot melt adhesive produced by using a tackifying resin is prone to odor. In the actual preparation process, a bulk polymerization process can be used to achieve a prepolymerization reaction between acrylic soft monomers, acrylic hard monomers, and functional monomers, without the need to provide a reaction environment through a solvent, which can avoid the odor of the hot melt adhesive produced due to solvent residue. The functional monomer includes a carboxyl group. In the actual preparation process, the multifunctional isocyanate can form a covalent bond with the carboxyl group and the silanol group on the surface of the silica. The silanol group on the surface of the silica can also form a hydrogen bond with the carboxyl group, which is conducive to forming a stable three-dimensional cross-linked structure and improving the bonding strength of the hot melt adhesive. At high processing temperatures (about 140°C to 160°C), the hydrogen bonds break and the hot melt adhesive can restore its fluidity, ensuring the processing performance of the hot melt adhesive. After the processing is completed and the temperature is lowered, a stable three-dimensional cross-linked structure can be regenerated in the hot melt adhesive, so that the prepared hot melt adhesive has higher high temperature and low temperature resistance.

[0089] In some embodiments, the raw materials for preparing the hot melt adhesive include, by weight:

[0090] 43-57 parts of acrylic soft monomer

[0091] 28-32 parts of acrylic hard monomer

[0092] 10-20 parts of functional monomer

[0093] 15-20 parts of silicon dioxide

[0094] 0.5-1 part of multifunctional isocyanate.

[0095] Furthermore, the raw materials for preparing the hot melt adhesive also include an initiator, a catalyst and a molecular weight regulator; in parts by weight, the initiator is 0.6 to 1.1 parts; the catalyst is 0.1 to 0.15 parts; and the molecular weight regulator is 0.3 to 0.5 parts.

[0096] In some specific embodiments, the raw materials for preparing the hot melt adhesive include 43 parts, 45 parts, 47 parts, 49 parts, 51 parts, 53 parts, 55 parts, 57 parts of acrylic soft monomer or any value between any two of the above numerical ranges, in parts by weight.

[0097] In some specific embodiments, the raw materials for preparing the hot melt adhesive include 28 parts, 29 parts, 30 parts, 31 parts, 32 parts of acrylic hard monomer, or any value between any two of the above numerical ranges, in parts by weight.

[0098] In some specific embodiments, the raw materials for preparing the hot melt adhesive include 10 parts, 12 parts, 14 parts, 16 parts, 18 parts, 20 parts of the functional monomer, or any value between any two of the above numerical ranges, in parts by weight.

[0099] In some specific embodiments, the raw materials for preparing the hot melt adhesive include 15 parts, 16 parts, 17 parts, 18 parts, 19 parts, 20 parts of silicon dioxide, or any value between any two of the above numerical ranges, in parts by weight.

[0100] In some specific embodiments, the raw materials for preparing the hot melt adhesive include 0.5 parts, 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part or any value between any two of the above numerical ranges of multifunctional isocyanate in parts by weight.

[0101] In some specific embodiments, the raw materials for preparing the hot melt adhesive include 0.6 parts, 0.7 parts, 0.8 parts, 0.9 parts, 1 part, 1.1 parts of the initiator, or any value between any two of the above numerical ranges, in parts by weight.

[0102] In some specific embodiments, the raw materials for preparing the hot melt adhesive include 0.1 parts, 0.11 parts, 0.12 parts, 0.13 parts, 0.14 parts, 0.15 parts of the catalyst, or any value between any two of the above numerical ranges, in parts by weight.

[0103] In some specific embodiments, the raw materials for preparing the hot melt adhesive include 0.3 parts, 0.4 parts, 0.5 parts or any value between any two parts of the above numerical ranges of the molecular weight regulator, calculated by weight.

[0104] Controlling the addition amount of each raw material within the above-mentioned range is conducive to the full prepolymerization reaction of acrylic soft monomer, acrylic hard monomer and functional monomer initiated by the first type initiator to form a high-quality prepolymer, and the full polymerization reaction between the prepolymer, silica and multifunctional isocyanate is ensured by the second type initiator and catalyst, thereby giving full play to the role of each raw material, thereby effectively improving the flexibility, wettability, adhesion, low-temperature resistance and high-temperature resistance of the hot melt adhesive while reducing the odor of the hot melt adhesive.

[0105] Exemplarily, the acrylic soft monomer may include at least one of isooctyl acrylate, butyl acrylate, lauryl acrylate, octadecyl acrylate, and isobutyl acrylate. In some specific embodiments, the acrylic soft monomer may include isooctyl acrylate and butyl acrylate, and the mass ratio of isooctyl acrylate to butyl acrylate may be (18-22):(25-35), for example, 18:25, 20:30, 20:35, 22:25, 22:35, 18:35, or any ratio within the above ratio range. By controlling the mass ratio of isooctyl acrylate to butyl acrylate within the above range, the combination of isooctyl acrylate and butyl acrylate is conducive to obtaining a hot melt adhesive with a suitable glass transition temperature, thereby improving the overall performance of the hot melt adhesive.

[0106] Specifically, in parts by weight, the raw materials for preparing the hot melt adhesive may include:

[0107] 18-22 parts of 2-ethylhexyl acrylate

[0108] 25-35 parts of butyl acrylate

[0109] 28-32 parts of acrylic hard monomer

[0110] 10-20 parts of functional monomer

[0111] 15-20 parts of silicon dioxide

[0112] 0.5-1 part of multifunctional isocyanate.

[0113] Furthermore, the raw materials for preparing the hot melt adhesive may include, in parts by weight:

[0114] 18-22 parts of 2-ethylhexyl acrylate

[0115] 25-35 parts of butyl acrylate

[0116] 28-32 parts of acrylic hard monomer

[0117] 10-20 parts of functional monomer

[0118] 15-20 parts of silicon dioxide

[0119] 0.5-1 part of multifunctional isocyanate

[0120] Initiator: 0.6-1.1 parts

[0121] Catalyst is 0.1~0.15 parts

[0122] The molecular weight regulator is 0.3 to 0.5 parts.

[0123] For example, the acrylic hard monomer may include at least one of isobornyl methacrylate, cyclohexyl methacrylate, isobornyl acrylate, cyclohexyl acrylate, tetrahydrofuranyl methacrylate, and tetrahydrofuranyl methacrylate. In some specific embodiments, the acrylic hard monomer may include isobornyl methacrylate and / or cyclohexyl methacrylate. Because isobornyl methacrylate and cyclohexyl methacrylate have large non-polar side chains and exhibit a steric effect, they can provide good steric hindrance, which helps reduce the viscosity of the hot melt adhesive in a high-temperature molten state, thereby facilitating dispensing and processing.

[0124] For example, the functional monomer may include at least one of methacrylic acid, acrylic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid. These functional monomers can effectively crosslink and polymerize with the acrylic soft monomer and the acrylic hard monomer, introducing carboxyl groups into the prepolymer and improving the adhesive properties of the resulting hot melt adhesive.

[0125] For example, the multifunctional isocyanate may include at least one of isophorone diisocyanate trimer, hexamethylene diisocyanate trimer, hexamethylene diisocyanate biuret, diphenylmethane diisocyanate oligomer, and toluene diisocyanate.

[0126] Exemplarily, the catalyst may include an organotin catalyst and / or a tertiary amine catalyst, wherein the organotin catalyst includes, for example, dibutyltin dilaurate and / or stannous octoate, and the tertiary amine catalyst includes, for example, at least one of triethylamine, diethylenediamine, and dimethylcyclohexylamine.

[0127] For example, the molecular weight regulator may include at least one of n-dodecyl mercaptan, isooctyl 3-mercaptopropionate, and methyl styrene dimer. The molecular weight regulator of the above type can make the final hot melt adhesive have low odor, good solvent solubility, and good leveling properties.

[0128] In some embodiments, the initiator may include a first type of initiator and a second type of initiator. Specifically, the first type of initiator may include a first initiator and a second initiator, wherein the first initiator, for example, includes an azo compound, specifically at least one of azobisisobutyronitrile, azobisisoheptanenitrile, azobisisovaleronitrile, azobiscyclohexylcarbonitrile, and dimethyl azobisisobutyrate; and the second initiator may include benzoyl peroxide. The second type of initiator may include tert-amyl peroxy-2-ethylhexanoate and / or 1,1-di-tert-amyl cyclohexane peroxide.

[0129] In the embodiments of the present application, the combination of multiple initiators is beneficial to selecting the appropriate initiator type according to the actual process conditions in the actual preparation process, thereby promoting the initiator to play a stabilizing role, promoting the full progress of the polymerization reaction, and thus improving the comprehensive performance of the hot melt adhesive.

[0130] In some embodiments, the raw materials for preparing the hot melt adhesive may include, by weight:

[0131] 18-22 parts of 2-ethylhexyl acrylate

[0132] 25-35 parts of butyl acrylate

[0133] 28-32 parts of acrylic hard monomer

[0134] 10-20 parts of functional monomer

[0135] 15-20 parts of silicon dioxide

[0136] 0.5-1 part of multifunctional isocyanate

[0137] 0.3-0.6 parts of the first type initiator

[0138] 0.3-0.5 parts of the second type initiator

[0139] Catalyst is 0.1~0.15 parts

[0140] The molecular weight regulator is 0.3 to 0.5 parts.

[0141] Furthermore, the raw materials for preparing the hot melt adhesive may include, in parts by weight:

[0142] 18-22 parts of 2-ethylhexyl acrylate

[0143] 25-35 parts of butyl acrylate

[0144] 28-32 parts of acrylic hard monomer

[0145] 10-20 parts of functional monomer

[0146] 15-20 parts of silicon dioxide

[0147] 0.5-1 part of multifunctional isocyanate

[0148] 0.15-0.3 parts of the first initiator

[0149] 0.15-0.3 parts of the second initiator

[0150] 0.3-0.5 parts of the second type initiator

[0151] Catalyst is 0.1~0.15 parts

[0152] The molecular weight regulator is 0.3 to 0.5 parts.

[0153] If the glass transition temperature of the hot melt adhesive is too high, its low-temperature resistance will deteriorate, and it will easily debond at low temperatures. If the glass transition temperature of the hot melt adhesive is too low, its high-temperature resistance will deteriorate, and it will easily overflow and separate at high temperatures. Therefore, in some specific embodiments, the glass transition temperature of the hot melt adhesive can be between -5°C and 0°C, for example, -5°C, -4°C, -3°C, -2°C, -1°C, 0°C, or any value between any two of the above ranges. This helps to balance the low-temperature resistance and high-temperature resistance of the hot melt adhesive.

[0154] It should be noted that the glass transition temperature of the hot melt adhesive described in the embodiments of the present application refers to the theoretical glass transition temperature of the hot melt adhesive, which can be calculated by the Fox equation or the Gordon-Taylor equation based on the raw materials used in the preparation of the hot melt adhesive.

[0155] In some specific embodiments, the hot melt adhesive can have a viscosity of 7000 mPa·s or less at 150°C. By controlling the type and amount of raw materials used to prepare the hot melt adhesive, the viscosity of the hot melt adhesive at 150°C can be controlled within the above range, effectively improving the processing performance of the hot melt adhesive and facilitating dispensing.

[0156] The embodiments of the present application also provide a hot melt adhesive prepared by the method for preparing the hot melt adhesive as described in any of the above embodiments, or the use of the hot melt adhesive as described in any of the above embodiments in an air conditioning filter.

[0157] It is understood that the hot melt adhesive produced by the hot melt adhesive preparation method described in any of the above embodiments, or the hot melt adhesive described in any of the above embodiments, can achieve low odor, while also exhibiting high adhesion, high high and low temperature resistance, and good processability. Therefore, when used in air conditioning filters, the hot melt adhesive not only ensures good adhesion in both high and low temperature environments, but also effectively reduces odor.

[0158] The cabin air filter may include a passenger car cabin air filter, for example. Figure 2 The passenger car air conditioning filter includes a filter frame 100 and a filter element 200 fixed in the filter frame 100 by hot melt adhesive. When the hot melt adhesive prepared by the preparation method of the hot melt adhesive described in any of the above embodiments or the hot melt adhesive described in any of the above embodiments is used in the passenger car air conditioning filter, it can not only enhance the bonding force between the filter frame 100 and the filter element 200, but also significantly reduce the odor in the car, greatly reducing the impact on the air quality in the car.

[0159] Specifically, the preparation method of the passenger car cabin filter may include the following steps:

[0160] 1) Folding the entire roll of filter paper using a paper folding machine to obtain a wavy filter element 200;

[0161] 2) Cut the wavy filter element 200 to the required size, heat the hot melt adhesive to the processing temperature (140°C), and dispense adhesive on the inner surface of the filter frame 100 using an automatic adhesive dispenser. Then, bond the cut wavy filter element 200 to the filter frame 100 and fill the frame. After the sealing molding is completed, the passenger car air conditioning filter is obtained.

[0162] Because the hot melt adhesive prepared by the hot melt adhesive preparation method described in any of the above embodiments, or the hot melt adhesive described in any of the above embodiments, is low-odor, has high adhesion, high high- and low-temperature resistance, and good processing properties, the use of the hot melt adhesive is not only convenient for dispensing and processing, but also ensures a secure bond between the filter element 200 and the filter frame 100 while effectively reducing odor inside the vehicle.

[0163] The technical solution of the present application is further described below with reference to a number of embodiments and comparative examples.

[0164] Example 1

[0165] The raw materials and mass ratios for preparing the hot melt adhesive in this embodiment are shown in Table 1. The preparation method of the hot melt adhesive includes the following steps:

[0166] S101: adding functional monomers, acrylic acid hard monomers and acrylic acid soft monomers to a reactor, introducing nitrogen to replace air, adding a first initiator, raising the temperature to 60° C., and continuing the reaction with stirring at 100 rpm for 3.5 hours (first prepolymerization reaction);

[0167] S102: Raise the temperature to 85° C., add a second initiator and a molecular weight regulator to the reaction product of step S101, and continue the reaction for 3.5 hours under stirring at 100 rpm (second prepolymerization reaction);

[0168] S103: Adding silicon dioxide to the reaction product of step S102 at 85°C and stirring continuously for 40 minutes; cooling to 45°C, adding a multifunctional isocyanate, a second type initiator, and a catalyst, and mixing uniformly to obtain a glycerin-like prepolymer; then heating to 120°C and maintaining the temperature for 15 hours to complete the polymerization reaction and obtain a hot melt adhesive;

[0169] S104: At a temperature of 160° C., evacuate to a gauge pressure of −0.08 MPa and maintain for 30 minutes to remove small molecules (unreacted acrylic soft monomer, acrylic hard monomer, and functional monomer) in the hot melt adhesive prepared in step S103 .

[0170] The raw materials and mass ratios for preparing the hot melt adhesives in Examples 2 to 5 and Comparative Example 1 are shown in Table 1. The preparation methods of the hot melt adhesives are the same as those in Example 1.

[0171] The hot melt adhesive in Comparative Example 2 is a commercially available polyolefin hot melt adhesive.

[0172] Table 1

[0173]

[0174]

[0175]

[0176] The properties of the hot melt adhesives prepared in the above embodiments and comparative examples were tested. The specific tests are as follows:

[0177] 1) Melt viscosity test at 150°C: The test is performed using a rotational viscometer. The measurement method is to place a 500ml pre-melted hot melt adhesive sample into the test tank of the rotational viscometer, set the temperature to 150°C, maintain it for 20 minutes, and rotate the rotor for 60 seconds before reading the value to determine the melt viscosity of the hot melt adhesive at 150°C.

[0178] 2) Odor Level Test: Place 10 grams of hot melt adhesive into a 1L odor bottle, seal it, and place it in a constant temperature forced air oven heated to 80±2°C for 2 hours. Remove the odor bottle from the oven, return it to 25±2°C, and then manually smell the sample. Assess the odor level according to the criteria in Table 2.

[0179] Table 2 Odor rating standards

[0180]

[0181]

[0182] 3) VOCs (Volatile Organic Compounds) Test: Place a 10g hot melt adhesive block inside a scent bottle. After sealing, place the bottle in a constant temperature forced air oven heated to 80±2°C for 2 hours. Then, remove the scent bottle from the oven, return the temperature to 25±2°C, and quickly insert the VOC tester into the scent bottle for testing.

[0183] 4) Ball and Ball Softening Point Test: According to ASTM D36, the temperature at which the steel ball penetrates the specimen and contacts the metal plate is recorded. This is the ball and ball softening point of the specimen.

[0184] 5) High-temperature resistance test: First, use an automatic dispensing machine to dispense hot melt adhesive on the inner surface of the filter frame. The filter element is bonded and fixed to the filter frame with the hot melt adhesive. After the frame is filled and the sealing molding is completed, the air conditioning filter is obtained. Then, the obtained air conditioning filter is placed in an oven at 80±2℃ for 24 hours. After removal, observe for glue overflow, detachment, and debonding.

[0185] 6) Low-temperature resistance test: First, prepare an air conditioning filter using the same method as in step 5) above. Then, place the prepared air conditioning filter in a low-temperature box at -40±2°C for 24 hours. After removal, observe for glue overflow, detachment, and debonding.

[0186] 7) T-peel strength test at different temperatures: After the hot melt adhesive is placed at a constant temperature of 85°C, 25°C, and -40°C for 30 minutes, the peel strength is tested according to GB / T2792-2016.

[0187] 8) After aging for 500 hours, T-type peel strength test at 25°C: The aging test conditions for the double 85 are as follows: the hot melt adhesive is stored at a temperature of 85±2°C and a humidity of 85% RH±5% RH for 500 hours, and then the peel strength is tested at 25°C according to GB / T2792-2016.

[0188] The above test results are shown in Table 1.

[0189] 9) Thermo-Gravimetric Analysis (TGA) test: The test was performed using a thermogravimetric analyzer in an air atmosphere at a heating rate of 10°C / min. The test results are shown in Figure 3 and Figure 4 .

[0190] Depend on Figure 3 The TGA curve (thermogravimetric curve) and Figure 4It can be seen from the DTG curve (derivative thermogravimetric curve) in that the hot melt adhesive of comparative example 2 contains migratory small molecule components such as tackifying resin, antioxidant, and plasticizer. Under the conditions of the thermogravimetric analysis experiment, the hot melt adhesive begins to lose mass when the temperature rises to 150°C. When the temperature rises to 200°C, the mass loss rate reaches 1.0%. This shows that the hot melt adhesive of comparative example 2 has higher VOC (volatile organic compound) emissions in actual production and use scenarios, which will cause the air quality in the processing environment and the surrounding and vehicle spaces to deteriorate. The hot melt adhesive in Example 1 has good thermal stability within 200°C because it does not contain migratory small molecules. Therefore, when compared under the same test conditions, the hot melt adhesive in Example 1 has lower VOC emissions and lower odor levels. It can be seen that the hot melt adhesive prepared in this application has good high-temperature stability, which can prevent thermal oxidation degradation caused by high processing temperature and long processing time, thereby preventing the generation of odorous small molecule organic matter during the processing process.

[0191] As can be seen from the data in Table 1, the VOCs test values of the hot melt adhesives prepared in Examples 1 to 5 were all low, with an odor rating of 2.0, which is significantly lower than the odor level of the hot melt adhesive in Comparative Example 2. This shows that in the present application, a bulk polymerization process is used to obtain the prepolymer through the prepolymerization reaction of acrylic soft monomers, acrylic hard monomers, and functional monomers. Since no solvent is required to provide a reaction environment in this step, the odor caused by residual solvent in the prepared hot melt adhesive can be avoided. Moreover, the combination of acrylic soft monomers and acrylic hard monomers can form a hot melt adhesive with good flexibility, wettability, and adhesion, and the problem of hot melt adhesives easily generating odor due to the use of tackifying resins is also avoided, resulting in a low odor level for the prepared hot melt adhesives. In addition, the hot melt adhesives prepared in Examples 1 to 5 showed no obvious debonding, overflowing, or detachment in the high-temperature resistance and low-temperature resistance tests at 85°C and -40°C. Moreover, the T-peel strength of the hot melt adhesives prepared in Examples 1 to 5 at 85°C, 25°C, and -40°C was relatively high. This shows that in the present application, not only can a hot melt adhesive with good flexibility, wettability and adhesion be formed by combining acrylic soft monomers and acrylic hard monomers, but also the functional monomer including carboxyl groups can introduce carboxyl groups into the prepolymer, so that during the polymerization reaction, the multifunctional isocyanate can form a covalent bond with the carboxyl groups in the prepolymer and the silanol groups on the surface of silica, and the silanol groups on the surface of silica can also form hydrogen bonds with the carboxyl groups in the prepolymer, thereby facilitating the formation of a stable three-dimensional cross-linked structure and improving the bonding strength of the hot melt adhesive. At high processing temperatures (about 140°C to 160°C), the hydrogen bonds break and the hot melt adhesive can restore its fluidity, ensuring the processing performance of the hot melt adhesive. After the processing is completed and the temperature is lowered, a stable three-dimensional cross-linked structure can be regenerated in the hot melt adhesive, so that the prepared hot melt adhesive has high high temperature and low temperature resistance. That is, the hot melt adhesive prepared in the embodiment of the present application can achieve low odor, while also having high adhesion, high high temperature and low temperature resistance, and good processing performance.

[0192] A comparison of the data from Examples 1 to 3 in Table 1 shows that, compared to Example 1, due to the reduced silica addition in Example 2, hydrogen bonds between the carboxyl groups in the prepolymer and the silanol groups on the silica surface decreased. The carboxyl groups on the prepolymer primarily cross-linked with the multifunctional isocyanate, forming covalent bonds. This significantly increased the degree of cross-linking, significantly reduced the fluidity of the resulting hot melt adhesive, and increased its melt viscosity and spheroidization softening point at 150°C, making it difficult to process and dispense. Furthermore, due to the increased degree of cross-linking, the hot melt adhesive's adhesion to the relatively smooth filter plate decreased at temperatures as low as -40°C, resulting in slight debonding. Compared with Example 1, the amount of silica added in Example 3 is increased and the amount of multifunctional isocyanate added is reduced, which easily leads to a decrease in the covalent bond connection formed between the multifunctional isocyanate and the carboxyl groups in the prepolymer and the silanol groups on the surface of silica. The internal cross-linking structure of the obtained hot melt adhesive is insufficient, which is not conducive to the formation of a stable three-dimensional cross-linking structure. The cohesive force is mainly provided by the hydrogen bonding between the silanol groups on the surface of silica and the carboxyl groups in the prepolymer. At high temperatures, when the hydrogen bonds are broken, the linear molecular structure in the hot melt adhesive will be easily moved, and the softening point, high-temperature peel strength and moisture-heat aging resistance of the hot melt adhesive will all decrease.

[0193] Compared to Example 1, Example 4 adjusted the amounts of functional monomers, acrylic hard monomers, and acrylic soft monomers. This reduced the proportion of soft segments in the reactive monomers and increased the proportion of hard segments, resulting in an increase in the glass transition temperature of the resulting hot melt adhesive. This resulted in reduced adhesion to smooth filter plates at low temperatures, and thus reduced low-temperature resistance. Furthermore, in Example 4, the increased proportion of functional monomers led to an increase in the unneutralized carboxyl group content, resulting in a decrease in the hot melt adhesive's long-term resistance to wet-heat aging.

[0194] In Example 5, compared with Example 1, the addition amounts of the functional monomer, acrylic hard monomer, and acrylic soft monomer were adjusted, the proportion of the hard segment in the reaction monomer decreased, and the proportion of the soft segment increased, so that the glass transition temperature of the prepared hot melt adhesive decreased; at the same time, due to the decrease in the proportion of the functional monomer methacrylic acid, the melt viscosity and the ring softening point of the hot melt adhesive at 150°C were reduced, affecting the high-temperature bonding performance and reducing the high-temperature resistance.

[0195] As can be seen from the above, in this application, the raw materials for preparing the hot melt adhesive include, by weight, 43-57 parts of acrylic soft monomer, 28-32 parts of acrylic hard monomer, 10-20 parts of functional monomer, 15-20 parts of silica, and 0.5-1 part of multifunctional isocyanate, which is a more preferred solution. Furthermore, it is more preferred that the glass transition temperature of the hot melt adhesive be between -5°C and 0°C.

[0196] In Comparative Example 1, methyl methacrylate is used as an acrylic hard monomer. Since methyl methacrylate does not have the non-polar large side chain structure of isobornyl methacrylate, it cannot provide effective steric hindrance. Compared with Example 1, the melt viscosity of the hot melt adhesive prepared in Comparative Example 1 at 150°C increases significantly, reaching as high as 14500mPa·s. Severe stringing occurs during the dispensing process, making it difficult to process. Therefore, it is a more preferred option to use acrylic hard monomers such as isobornyl methacrylate and / or cyclohexyl methacrylate with a non-polar large side chain structure in this application. Furthermore, it is a more preferred option for the hot melt adhesive to have a colloidal viscosity of less than or equal to 7000mPa·s at 150°C.

[0197] In the present invention, acrylic soft monomers, acrylic hard monomers, functional monomers including carboxyl groups, silica and multifunctional isocyanates are used in combination, so that the prepared hot melt adhesive has high temperature resistance (≥100°C), and the hot melt adhesive does not creep under long-term use conditions. The hot melt adhesive in this application is applied to passenger car air conditioning filters, which can meet the long-term use requirements under the vehicle operating environment. The hot melt adhesive has low odor and can effectively reduce the impact on the air quality in the car.

[0198] It should be noted that the hot melt adhesive embodiments, hot melt adhesive preparation method embodiments and application embodiments in air conditioning filters provided in this application belong to the same concept; the technical features in the technical solutions recorded in each embodiment can be arbitrarily combined without conflict.

[0199] It should be understood that the above embodiments are exemplary and are not intended to encompass all possible implementations of the present application. Various modifications and variations may be made based on the above embodiments without departing from the scope of the present disclosure. Similarly, the various technical features of the above embodiments may be arbitrarily combined to form other embodiments of the present invention that may not be explicitly described. Therefore, the above embodiments merely illustrate several implementations of the present invention and do not limit the scope of protection of the patent of the present invention.

Claims

1. A method for preparing a hot melt adhesive, characterized in that: The method comprises the following steps: S1: placing an acrylic soft monomer, an acrylic hard monomer, and a functional monomer in a reactor, adding a first type of initiator, and performing a prepolymerization reaction at a first temperature to obtain a prepolymer; the functional monomer includes a carboxyl group; S2: adding silicon dioxide, multifunctional isocyanate, a second type of initiator and a catalyst to the prepolymer, and performing a polymerization reaction at a second temperature to obtain the hot melt adhesive; the second temperature is higher than the first temperature.

2. The method for preparing the hot melt adhesive according to claim 1, wherein: In parts by weight, the added amount of the acrylic soft monomer is 43 to 57 parts; the added amount of the acrylic hard monomer is 28 to 32 parts; the added amount of the functional monomer is 10 to 20 parts; the added amount of the silica is 15 to 20 parts; the added amount of the multifunctional isocyanate is 0.5 to 1 part; the added amount of the first type initiator is 0.3 to 0.6 part; the added amount of the second type initiator is 0.3 to 0.5 part; and the added amount of the catalyst is 0.1 to 0.15 part.

3. The method for preparing the hot melt adhesive according to claim 1, wherein: The method satisfies at least one of the following characteristics: (1) The acrylic soft monomer includes at least one of isooctyl acrylate, butyl acrylate, lauryl acrylate, octadecyl acrylate, and isobutyl acrylate; preferably, the acrylic soft monomer includes isooctyl acrylate and butyl acrylate, and the mass ratio of the isooctyl acrylate to the butyl acrylate is (18-22): (25-35); (2) the acrylic hard monomer comprises at least one of isobornyl methacrylate, cyclohexyl methacrylate, isobornyl acrylate, cyclohexyl acrylate, tetrahydrofuran methacrylate, and tetrahydrofuran methacrylate; (3) The functional monomer includes at least one of methacrylic acid, acrylic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid; (4) The polyfunctional isocyanate includes at least one of isophorone diisocyanate trimer, hexamethylene diisocyanate trimer, hexamethylene diisocyanate biuret, diphenylmethane diisocyanate oligomer, and toluene diisocyanate; (5) The glass transition temperature of the hot melt adhesive is -5°C to 0°C; (6) The colloid viscosity of the hot melt adhesive at 150° C. is less than or equal to 7000 mPa·s.

4. The method for preparing a hot melt adhesive according to any one of claims 1 to 3, characterized in that: The first temperature is 50° C. to 95° C.; step S1 comprises: S11: placing the acrylic soft monomer, the acrylic hard monomer, and the functional monomer in a reactor, adding a first initiator, and stirring at 50° C. to 70° C. to perform a first prepolymerization reaction; Preferably, the first prepolymerization reaction time is 3 hours to 4 hours; preferably, the amount of the first initiator added is 0.15 to 0.3 parts by weight; preferably, the first initiator includes an azo compound, which can be selected from at least one of azobisisobutyronitrile, azobisisoheptanenitrile, azobisisovaleronitrile, azobiscyclohexylcarbonitrile, and dimethyl azobisisobutyrate; S12: adding a second initiator and a molecular weight regulator at 75° C. to 95° C. and performing a second prepolymerization reaction under stirring; Preferably, the time of the second prepolymerization reaction is 3h to 4h; preferably, the amount of the second initiator added is 0.15 to 0.3 parts by weight; preferably, the second initiator includes benzoyl peroxide; preferably, the amount of the molecular weight regulator added is 0.3 to 0.5 parts by weight; preferably, the molecular weight regulator includes at least one of n-dodecyl mercaptan, 3-isooctyl mercaptan and methyl styrene dimer.

5. The method for preparing a hot melt adhesive according to any one of claims 1 to 3, characterized in that: Step S2 satisfies at least one of the following characteristics: (1) The second temperature is 110°C to 130°C; (2) The polymerization reaction time is 10 h to 20 h; (3) The second type of initiator includes tert-amyl peroxy-2-ethylhexanoate and / or 1,1-di-tert-amyl peroxycyclohexane; (4) The catalyst includes an organotin catalyst and / or a tertiary amine catalyst.

6. The method for preparing hot melt adhesive according to claim 1, characterized in that: After the polymerization reaction in step S2 is completed, the method further comprises: Under vacuum conditions at 150° C. to 170° C., removing unreacted acrylic soft monomer, acrylic hard monomer, and functional monomer; Preferably, the vacuum condition is evacuated to -0.09 MPa to -0.07 MPa; preferably, the vacuum condition is maintained for 20 min to 40 min.

7. A hot melt adhesive, characterized in that: The raw materials for preparing the hot melt adhesive include acrylic soft monomer, acrylic hard monomer, functional monomer, silicon dioxide and multifunctional isocyanate; the functional monomer includes carboxyl group.

8. The hot melt adhesive according to claim 7, characterized in that: In parts by weight, the raw materials for preparing the hot melt adhesive include: 43-57 parts of acrylic soft monomer 28-32 parts of acrylic hard monomer 10-20 parts of functional monomer 15-20 parts of silicon dioxide 0.5-1 part of multifunctional isocyanate; Preferably, the raw materials for preparing the hot melt adhesive further include an initiator, a catalyst and a molecular weight regulator; in parts by weight, the initiator is 0.6 to 1.1 parts; the catalyst is 0.1 to 0.15 parts; and the molecular weight regulator is 0.3 to 0.5 parts.

9. The hot melt adhesive according to claim 7 or 8, characterized in that: The hot melt adhesive satisfies at least one of the following characteristics: (1) The acrylic soft monomer includes at least one of isooctyl acrylate, butyl acrylate, lauryl acrylate, octadecyl acrylate, and isobutyl acrylate; preferably, the acrylic soft monomer includes isooctyl acrylate and butyl acrylate, and the mass ratio of the isooctyl acrylate to the butyl acrylate is (18-22): (25-35); (2) the acrylic hard monomer comprises at least one of isobornyl methacrylate, cyclohexyl methacrylate, isobornyl acrylate, cyclohexyl acrylate, tetrahydrofuran methacrylate, and tetrahydrofuran methacrylate; (3) The functional monomer includes at least one of methacrylic acid, acrylic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid; (4) The polyfunctional isocyanate includes at least one of isophorone diisocyanate trimer, hexamethylene diisocyanate trimer, hexamethylene diisocyanate biuret, diphenylmethane diisocyanate oligomer, and toluene diisocyanate; (5) The glass transition temperature of the hot melt adhesive is -5°C to 0°C; (6) The colloid viscosity of the hot melt adhesive at 150° C. is less than or equal to 7000 mPa·s.

10. Use of the hot melt adhesive prepared by the method for preparing the hot melt adhesive according to any one of claims 1 to 6 or the hot melt adhesive according to any one of claims 7 to 9 in an air conditioning filter.

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