Hot melt adhesive and preparation method thereof

Abstract

The embodiment of the invention provides a hot melt adhesive and a preparation method thereof. The hot melt adhesive comprises the following components in parts by weight: 5-15 parts of polybutadiene polyol; 15 to 30 parts of polyester polyol; 35 to 45 parts of tackifying resin; 10-15 parts of a thermoplastic elastomer; 5 to 10 parts of diisocyanate; 5 to 10 parts of a first prepolymer; 0.2 to 0.5 part of an antioxidant; 0.5 to 2.0 parts of a catalyst; at most 0.2 part of a defoaming agent; up to 0.1 part of a stabilizer; wherein the preparation raw material of the first prepolymer comprises liquid polybutadiene resin. According to the hot melt adhesive and the preparation method thereof provided by the embodiment of the invention, the low-temperature bonding stability of a product is improved by adopting the hydroxyl-terminated polybutadiene and the liquid polybutadiene resin, and the high-temperature bonding strength of the product is improved by introducing the high-softening-point tackifying resin and the polyfunctional prepolymer.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hot melt adhesives, and particularly relates to a hot melt adhesive and a preparation method thereof. BACKGROUND

[0002] With the rapid development of intelligent vehicles and new energy vehicles, vehicle-mounted display screens evolve towards large size, curved surface and high resolution, which puts forward higher requirements for bonding materials. For example, it is required to work stably at-60 DEG C to 120 DEG C for a long time, resist delamination caused by cold and hot cycles, have high toughness in high-frequency vibration during vehicle driving, meet vehicle-grade environmental protection standards, and be suitable for strength and glue overflow control in ultrathin bonding (glue layer thickness is less than or equal to 0.3 mm), and be convenient for disassembly and recycling of parts at 100 DEG C to 120 DEG C and repeated use.

[0003] However, traditional adhesives (such as epoxy resin and acrylate) have problems such as slow curing, high brittleness and high concentration of volatile organic compounds, and ordinary hot melt adhesives have insufficient heat resistance (softening point < 80 DEG C), which are difficult to meet the requirements. Specifically, the current vehicle-mounted display screen bonding mainly adopts the following technologies, but all have corresponding limitations. For example, the disadvantages of acrylic pressure-sensitive adhesive are creep failure at high temperature (> 85 DEG C) and poor long-term durability; the defects of ordinary moisture-curing reaction type polyurethane hot melt adhesive are poor low-temperature adhesion, insufficient initial adhesion strength and easy to produce bubbles, which requires long time pressure preservation; and the disadvantages of UV curing adhesive are incomplete curing in shadow area, easy to flow, and yellowing after UV aging.

[0004] In summary, the performance of the current hot melt adhesive is difficult to meet the production needs, and it is urgent to develop a hot melt adhesive to solve the above problems. SUMMARY

[0005] Therefore, the application provides a hot melt adhesive and a preparation method thereof to solve the technical problem that the performance of the existing hot melt adhesive is poor and difficult to meet the production needs.

[0006] In a first aspect, the application provides a hot melt adhesive, which comprises the following components by weight:

[0007] 5 to 15 parts of polybutadiene polyol;

[0008] 15 to 30 parts of polyester polyol;

[0009] 35 to 45 parts of tackifying resin;

[0010] 10 to 15 parts of thermoplastic elastomer;

[0011] 5 to 10 parts of diisocyanate;

[0012] 5 to 10 parts of first prepolymer;

[0013] Antioxidant 0.2-0.5 parts;

[0014] Catalyst 0.5-2.0 parts;

[0015] Up to 0.2 parts of a defoaming agent;

[0016] Up to 0.1 parts of a stabilizer;

[0017] The first prepolymer is prepared from a liquid polybutadiene resin.

[0018] In some embodiments, the polybutadiene polyol has a number average molecular weight of between 2000 and 3000, and the polybutadiene polyol has a glass transition temperature of < -55°C.

[0019] In some embodiments, the polyester polyol has a number average molecular weight of between 2000 and 4000.

[0020] In some embodiments, the polyester polyol has a hydroxyl value of between 30 and 60 mg KOH / g.

[0021] In some embodiments, the polyester polyol has a melting temperature of between 60 and 90°C.

[0022] In some embodiments, the polyester polyol has a crystallinity of > 40%.

[0023] In some embodiments, the tackifying resin has a softening point of between 100 and 120°C.

[0024] In some embodiments, the polybutadiene polyol is at least one of a primary hydroxyl liquid polybutadiene, a secondary hydroxyl liquid polybutadiene, a hydrogenated primary hydroxyl liquid polybutadiene, a hydrogenated secondary hydroxyl liquid polybutadiene.

[0025] In some embodiments, the polyester polyol is a crystalline polyester polyol, which is prepared by condensation polymerization of an aromatic diacid and a linear aliphatic diol.

[0026] In some embodiments, the tackifying resin includes at least one of a petroleum resin, a rosin resin, a terpene resin, a methylstyrene resin, and a modified resin thereof.

[0027] In some embodiments, the thermoplastic elastomer is a styrene-isoprene-styrene.

[0028] In some embodiments, the diisocyanate includes at least one of diphenylmethane diisocyanate, toluene diisocyanate, p-phenylene diisocyanate, isophorone diisocyanate.

[0029] In some embodiments, the antioxidant is at least one of antioxidant 1010, antioxidant 1076, antioxidant 164, antioxidant 264.

[0030] In some embodiments, the defoaming agent is one of BYK-A530, BYK-A535, BYK-A550, BYK-A555, BYK-A560, BYK-A595.

[0031] In some embodiments, the stabilizer is at least one of phosphoric acid or polyphosphoric acid.

[0032] In some embodiments, the catalyst is at least one of dimorpholinyl diethyl ether, triethylenediamine.

[0033] In a second aspect, the embodiments of the present application provide a preparation method of the hot melt adhesive, comprising:

[0034] Preparation of the first prepolymer, raw materials of the first prepolymer comprising liquid polybutadiene resin;

[0035] Preparation of the second prepolymer, the second prepolymer being an end-isocyanate polyurethane / polyester prepolymer;

[0036] Adding the first prepolymer and the catalyst into the second prepolymer, and reacting to obtain the hot melt adhesive.

[0037] In some embodiments, the preparation of the first prepolymer comprises:

[0038] Providing polybutadiene polyol, tri-functional chain extender, liquid polybutadiene, auxiliary agent and isocyanate;

[0039] Mixing the tri-functional chain extender, the polybutadiene polyol, the liquid polybutadiene and the auxiliary agent, and dehydrating under vacuum to obtain a first mixture;

[0040] Cooling the first mixture to 60-80℃, and adding the isocyanate into the first mixture, and reacting to a first theoretical isocyanate value to obtain the first prepolymer.

[0041] In some embodiments, the dehydrating under vacuum comprises:

[0042] Vacuum stirring at 120-140℃ for 1.5-2h.

[0043] In some embodiments, reacting under nitrogen for 1-2h, then heating to 110-120℃, and stirring and reacting under vacuum for 1-2h, and the first theoretical isocyanate value is 4.0±0.1%.

[0044] In some embodiments, the tri-functional chain extender is trimethylolpropane, the auxiliary agent is phosphoric acid, and the isocyanate is toluene diisocyanate.

[0045] In some embodiments, the preparing the second prepolymer comprises:

[0046] providing tackifying resin, antioxidant, thermoplastic elastomer, polybutadiene polyol, polyester polyol, stabilizer, defoaming agent, and diisocyanate;

[0047] placing the tackifying resin, the antioxidant, and the thermoplastic elastomer in a reaction kettle, and sufficiently dispersing and uniformly mixing to obtain a second mixture;

[0048] cooling the second mixture to 130-160°C, mixing the polybutadiene polyol, the polyester polyol, the stabilizer, and the defoaming agent, and then adding diisocyanate, and reacting to a second theoretical isocyanate value to obtain the second prepolymer.

[0049] In some embodiments, the placing the tackifying resin, the antioxidant, and the thermoplastic elastomer in a reaction kettle, and sufficiently dispersing and uniformly mixing to obtain a second mixture comprises:

[0050] stirring at 200-220°C for 0.5-1h to sufficiently disperse and uniformly mix.

[0051] In some embodiments, the cooling the second mixture to 130-160°C, mixing the polybutadiene polyol, the polyester polyol, the stabilizer, and the defoaming agent, and then adding diisocyanate comprises:

[0052] firstly dehydrating at 130-140°C under vacuum for 1.5-2h, and then cooling to 110-120°C and adding the diisocyanate.

[0053] In some embodiments, the second theoretical isocyanate value is 1.9%±0.1%.

[0054] In some embodiments, the adding the first prepolymer and a catalyst to the second prepolymer, and reacting to obtain the hot melt adhesive comprises:

[0055] increasing the temperature to 140-150°C, adding the first prepolymer and the catalyst to the second prepolymer, and stirring and dispersing under vacuum for 20-30min.

[0056] The hot melt adhesive and the preparation method thereof provided by the embodiments of the present application, by molecular structure design, i.e., using low-temperature-resistant polybutadiene polyol, crystalline polyester polyol, and isocyanate reaction, while introducing a multifunctional prepolymer, improving high-temperature creep resistance, and introducing low-temperature-resistant liquid polybutadiene resin and low-glass-transition-temperature polybutadiene polyol, under the joint action of the above components, the low-temperature wetting and bonding performance is effectively improved. By controlling the reaction components of the hot melt adhesive, the problem of bubbles is solved, and sufficient initial adhesion strength is provided to meet the requirements of the automatic production line. Attached Figure Description

[0057] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0058] Figure 1 This is a schematic flowchart of the hot melt adhesive preparation method provided in the embodiments of this application. Detailed Implementation

[0059] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that the embodiments of this application can also be implemented in other embodiments without these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted so as not to obscure the description of the embodiments of this application with unnecessary detail.

[0060] It should also be understood that the term "and / or" as used in the specification of embodiments of this application and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0061] It should be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on or indirectly on that other component. When a component is referred to as being "connected to" another component, it can be directly connected to or indirectly connected to that other component.

[0062] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0063] Furthermore, in the description of the embodiments and the appended claims of this application, the terms "first," "second," "third," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance.

[0064] Reference to "some embodiments," "certain embodiments," "certain embodiments" or the like, described in the present application specification means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present application. The appearances of the phrases "in some embodiments," "in certain embodiments," "in other embodiments," "in yet other embodiments," or the like, in various places in the specification are not necessarily all referring to the same embodiments, although the phrases can be so referring in some cases. The terms "including," "comprising," "having," and variations thereof, mean "including but not limited to," unless expressly specified otherwise. "Plural" includes two or more.

[0065] The first aspect of the present application provides a hot melt adhesive, comprising the following components by weight:

[0066] polybutadiene polyol 5-15 parts;

[0067] polyester polyol 15-30 parts;

[0068] tackifying resin 35-45 parts;

[0069] thermoplastic elastomer 10-15 parts;

[0070] diisocyanate 5-10 parts;

[0071] first prepolymer 5-10 parts;

[0072] antioxidant 0.2-0.5 parts;

[0073] catalyst 0.5-2.0 parts;

[0074] up to 0.2 parts of defoaming agent;

[0075] up to 0.1 parts of stabilizer;

[0076] wherein the raw material for the first prepolymer comprises liquid polybutadiene resin.

[0077] The hot melt adhesive provided by the present application uses macromolecular thermoplastic polyolefin resin, reduces the amount of reactive components in the system to ensure the thermal stability of the entire system, uses polybutadiene polyol and liquid polybutadiene resin to improve the low-temperature bonding performance, and introduces multifunctional prepolymer to provide crosslinking degree, so that it has good heat resistance.

[0078] Specifically, the polybutadiene polyol and the liquid polybutadiene resin cooperate with each other to ensure the bonding performance of the hot melt adhesive at low temperature. The principle is that the low-temperature toughness of polybutadiene is derived from the intrinsic characteristics of its molecular chain. The dense methylene groups on the main chain form a structure similar to a "spring", and the carbon-carbon single bond has a very low internal rotation energy barrier, which can still move freely even at -70°C. However, the molecular chain movement ability of ordinary rubber such as natural rubber (Tg-60°C) is much poorer due to the presence of polar groups or side chains. It is worth mentioning that the formulation of the embodiment of the present application uses a double polybutadiene strategy, directly adding a polyol to provide active terminal hydroxyl groups for crosslinking, and a liquid polybutadiene resin introduces long flexible chains in the form of a prepolymer. The latter is particularly critical - the isocyanate groups remaining in the prepolymer act as "anchor points" to weave ultra-long flexible chains into the crosslinked network, avoiding phase separation and ensuring that stress is evenly distributed during deformation.

[0079] In some embodiments, the number average molecular weight of the polybutadiene polyol is between 2000 and 3000, and the polybutadiene polyol has a glass transition temperature of less than -55°C. A molecular weight of less than 2000 for the polybutadiene polyol results in a molecular chain that is too short and insufficiently entangled, while a molecular weight of more than 3000 results in poor solubility. Between the above range, corresponding to about 35-55 repeating units, is near the "critical entanglement molecular weight" of polymer physics, and a moderate entanglement network can be formed. When the molecular weight is 2000-3000, each polybutadiene polyol molecule contains 2.0-2.2 terminal hydroxyl groups (functionality), which is conducive to the construction of a rigid-flexible network structure. A Tg of less than -55°C means that at -40°C (the minimum operating temperature of an on-board screen), the chain segment movement ability remains active, the free volume fraction is greater than 12%, and the chain segment can quickly adjust its conformation under external force impact, avoiding stress concentration.

[0080] In some embodiments, the number average molecular weight of the polyester polyol is between 2000 and 4000. Specifically, the number average molecular weight of the polyester polyol can be 2000, 2200, 2500, 2800, 3000, 3200, 3300, 3400, 3500, 3600, 3700, 3800, 3900, 4000, or any value within the range of 2000-4000. A molecular weight of less than 2000 results in a chain segment that is too short, and a high crosslinking density causes the adhesive to become brittle; a molecular weight of more than 4000 results in a chain segment that is too long, and the intermolecular force is weakened, resulting in a decrease in high-temperature strength. The close molecular weight of the polybutadiene polyol (2000-3000) improves the compatibility of polar / non-polar chain segments. It ensures that the molecular chain is long enough to form a crystalline region, while avoiding excessively high melt viscosity.

[0081] In some embodiments, the polyester polyol has a hydroxyl value of 30-60 mg KOH / g. Specifically, the hydroxyl value can be 30 mg KOH / g, 40 mg KOH / g, 45 mg KOH / g, 50 mg KOH / g, 55 mg KOH / g, 60 mg KOH / g, or any value within the range of 30-60 mg KOH / g. If the hydroxyl value is too low (<30), there are not enough crosslinking points, leading to high-temperature creep; if the hydroxyl value is too high (>60), there are too many crosslinking points, leading to low-temperature brittle fracture. Within the above range, the crosslinking network spacing can be ensured to be 10-20 nm after reaction with diisocyanate.

[0082] In some embodiments, the polyester polyol has a melting temperature of 60-90°C. In some embodiments, the polyester polyol has a melting temperature of 60°C, 62°C, 65°C, 70°C, 75°C, 80°C, 82°C, 85°C, 88°C, 90°C, or any value within the range of 60-90°C. Tm>60°C ensures that the crystalline region does not melt at the normal working temperature of the vehicle-mounted screen (-40-85°C), thereby maintaining the strength of the skeleton; Tm<90°C avoids excessively high processing temperature. The shear strength retention rate is >90% after 1000 h of thermal aging at 85°C.

[0083] In some embodiments, the polyester polyol has a crystallinity of ≥40%. Specifically, the polyester polyol has a crystallinity of 40%, 45%, 50%, 60%, 70%, 80%, etc. The crystalline region acts as a "physical crosslinking point" and is more resistant to high temperatures than chemical crosslinking. The tensile strength and high-temperature shear strength are effectively improved.

[0084] In application, the polyester polyol serves as a rigid component, complementing the flexibility of polybutadiene. These four parameters actually constitute a complete performance regulation chain: molecular weight determines chain length, hydroxyl value reflects reactivity, melting temperature is related to processability, and crystallinity affects mechanical strength. It is particularly important to emphasize that these parameters can synergistically address the specific needs of vehicle-mounted screens, such as not softening at high temperatures and not cracking during cold-heat cycling.

[0085] In some embodiments, the tackifying resin has a softening point of 100-120°C. Higher than the working temperature (the upper limit of the working temperature of the vehicle-mounted screen is usually 85°C), thereby locking the cohesive strength. Match the construction viscosity window to lock the process feasibility; link the polyester melting interval to lock the stability of the composite structure. This parameter ensures that the hot melt adhesive maintains reliable adhesion under full working conditions of -40-85°C, while meeting the requirements of 180°C high-speed coating process, becoming the uncompromising core indicator of the vehicle-mounted screen adhesive.

[0086] In some embodiments, the polybutadiene polyol is at least one of a primary hydroxyl liquid polybutadiene, a secondary hydroxyl liquid polybutadiene, a hydrogenated primary hydroxyl liquid polybutadiene, a hydrogenated secondary hydroxyl liquid polybutadiene. The polybutadiene polyol serves to provide a flexible segment with terminal hydroxyl groups to participate in the reaction. It provides low temperature toughness (anti-40°C brittle fracture), hydrolysis resistance, and soft elasticity to balance the rigidity of the crosslinked network.

[0087] In some embodiments, the polyester polyol is a crystalline polyester polyol, which is obtained by condensation polymerization of aromatic diacid and linear aliphatic diol. It builds a rigid segment with high-polarity hydroxyl groups. It provides high strength, heat resistance (anti-150°C softening), adhesion, and crystallinity to enhance the adhesion of metal / plastic substrates.

[0088] In some embodiments, the tackifying resin includes at least one of petroleum resin, rosin resin, terpene resin, methylstyrene resin, and modified resin thereof. It is used to improve the interfacial wettability and initial adhesion, improve the instantaneous adhesion to glass / metal, reduce the melt viscosity to facilitate construction, and adjust the peel strength.

[0089] In some embodiments, the thermoplastic elastomer is styrene-isoprene-styrene. It physically toughens the backbone of the prepolymer. It provides melt flowability, film formability, and elastic recovery, and reduces the cold flow phenomenon.

[0090] In some embodiments, the diisocyanate includes at least one of diphenylmethane diisocyanate, toluene diisocyanate, p-phenylene diisocyanate, isophorone diisocyanate. It reacts with the polyol to form a polyurethane backbone. It introduces a flexible long segment and a reaction site, avoids phase separation caused by direct addition of liquid resin, and improves low temperature performance and dispersion uniformity.

[0091] In some embodiments, the antioxidant is at least one of antioxidant 1010, antioxidant 1076, antioxidant 164, antioxidant 264. It inhibits high-temperature oxidative degradation, prolongs the life of the adhesive, and prevents yellowing.

[0092] In some embodiments, the defoaming agent is one of BYK-A530, BYK-A535, BYK-A550, BYK-A555, BYK-A560, BYK-A595. It is used to eliminate mixing bubbles, prevent the formation of micropores in the adhesive layer, and improve the sealing performance and appearance flatness.

[0093] In some embodiments, the stabilizer is at least one of phosphoric acid or polyphosphoric acid. It shields ultraviolet rays or heat, resists UV aging (meets the 10-year life requirement of vehicle-mounted screens), and inhibits high-temperature discoloration.

[0094] In some embodiments, the catalyst is at least one of bismorpholino diethyl ether and triethylenediamine. This accelerates the reaction, shortens the curing time (30 min surface drying at 120°C), and regulates the degree of reaction to avoid excessive crosslinking.

[0095] In applications, the hot melt adhesive provided in this application embodiment has higher initial tack strength—reaching 0.5 MPa in 2 minutes and 2.0 MPa in 20 minutes—compared to existing polyurethane hot melt adhesives. It also exhibits high thermal stability, solving the problem of viscosity increase due to prolonged heating and the need for frequent adjustments to dispensing parameters. Furthermore, it is suitable for sealing and bonding various types of automotive displays and structural bonding, as well as bonding low-polarity materials, greatly expanding its applicability to a wider range of scenarios.

[0096] This application also provides a method for preparing hot melt adhesive, such as... Figure 1 As shown, it includes:

[0097] S10. Prepare the first prepolymer, wherein the raw material for preparing the first prepolymer includes liquid polybutadiene resin;

[0098] S20. Prepare a second prepolymer, which is a terminal isocyanate polyurethane / polyester prepolymer;

[0099] S30. Add the first prepolymer and catalyst to the second prepolymer and react to obtain hot melt adhesive.

[0100] The first step, preparing the prepolymer from liquid polybutadiene resin, is ingenious. Directly adding liquid resin easily leads to phase separation, but by creating the prepolymer and sealing it with crosslinking points and isocyanate groups, the flexibility of the polybutadiene chain is preserved while achieving chemical compatibility with subsequent components. The second step, designing the polyurethane / polyester prepolymer, is even more skillful. Pre-forming easily crystallizing polyester polyols and tackifying resins into prepolymers is equivalent to pre-assembling the physical crosslinking points (crystallization zones) and chemical crosslinking points. The most brilliant part is the third step, the low-temperature catalytic reaction. Traditional processes often lead to over-reaction of isocyanate groups when mixing at high temperatures. By utilizing the properties of the catalyst, while ensuring reaction efficiency, the long-chain buffering effect of the first prepolymer prevents localized gelation.

[0101] In step S10, the preparation of the first prepolymer includes:

[0102] S11 provides polybutadiene polyols, trifunctional chain extenders, liquid polybutadiene, additives and isocyanates;

[0103] S12. Mix the trifunctional chain extender, polybutadiene polyol, liquid polybutadiene and additives, and dehydrate under vacuum to obtain the first mixture;

[0104] S13, cooling the first mixture to 60-80℃, and adding isocyanate to the first mixture, and reacting until the first theoretical isocyanate value is reached to obtain a first prepolymer.

[0105] The difference in reactivity of the secondary hydroxyl group of the trifunctional chain extender and the terminal hydroxyl group of the liquid polybutadiene is the key as a trifunctional crosslinking agent, which needs to be dehydrated first and then cooled to add isocyanate. The molecular weight distribution of the liquid polybutadiene will affect the viscosity of the prepolymer. When the temperature is lower than 60℃, the viscosity of the system is too large and is not uniform; when the temperature is higher than 80℃, the side reaction of the primary amine is intensified.

[0106] In some embodiments, the dehydration is performed under vacuum, including: vacuum stirring for 1.5-2h at 120-140℃; specifically, at 120℃, 122℃, 125℃, 130℃, 132℃, 135℃, 140℃, etc. within the range of 120-140℃. This temperature range can just break through the water molecule binding energy without destroying the double bond of polybutadiene. Catalytic esterification with phosphoric acid reduces the carboxyl content from 300ppm to <50ppm.

[0107] In some embodiments, the reaction is performed until the theoretical isocyanate value reaches a preset value, including: reacting for 1-2h under nitrogen, then heating to 110-120℃, and stirring for 1-2h under vacuum negative pressure. The first theoretical isocyanate value is 4.0±0.1%. The reaction kinetics is controlled, the 4-NCO site is selectively activated at 60-80℃ (occupancy >80%), and branching and crosslinking are avoided. The temperature of 110-120℃ promotes the reaction of the 1-NCO site (conversion rate >95%). When the temperature is less than 110℃, the 1-NCO site remains, and the gelation is stored. The vacuum negative pressure removes the residual toluene diisocyanate monomer (boiling point 120℃). If the vacuum is not sufficient, the free toluene diisocyanate is more than 1% (VOC exceeds the standard). The reaction degree reaches the Arrhenius platform zone within 1-2h.

[0108] In some embodiments, the trifunctional chain extender is trimethylolpropane, the auxiliary agent is phosphoric acid, and the isocyanate is toluene diisocyanate. The trifunctionality forms a star-shaped branched structure, and linear structure is preferentially formed to avoid gelation. Phosphoric acid chelates metal ions, inhibits oxidation side reactions, and catalyzes esterification to digest carboxyl groups.

[0109] In some embodiments, the preparation of the second prepolymer includes:

[0110] S21, providing tackifying resin, antioxidant, thermoplastic elastomer, polybutadiene polyol, polyester polyol, stabilizer, defoaming agent, and diisocyanate;

[0111] S22, placing the tackifying resin, antioxidant, and thermoplastic elastomer in a reaction kettle, and fully dispersing and uniformizing to obtain a second mixture;

[0112] S23, cooling the second mixture to 130-160°C, adding polybutadiene polyol, polyester polyol, stabilizer, defoaming agent, mixing, and then adding diisocyanate, and reacting until the second theoretical isocyanate value is reached to obtain a second prepolymer. Specifically, the tackifying resin and the thermoplastic elastomer are both nonpolar or weakly polar substances, and they have good compatibility when they are melted at a high temperature of about 200°C, at which time the antioxidant can be uniformly dispersed to provide protection. Although the polybutadiene polyol is also nonpolar, it contains active hydroxyl groups, and the early addition of the polybutadiene polyol to the high-temperature environment can cause oxidative side reactions, so the temperature needs to be reduced to 130-160°C before the polybutadiene polyol is added.

[0113] In specific embodiments, the second mixture is cooled to 130°C, 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, or any value within the range of 130-160°C. 160°C is a critical point - higher than the melting point of the polyester polyol (60-90°C) to ensure that it is completely melted, and lower than the decomposition temperature of the polybutadiene.

[0114] It should be noted that the diisocyanate is added at an appropriate temperature after the polyol is added. At this time, the viscosity of the system is low, and the isocyanate can quickly diffuse to ensure that each isocyanate group finds a corresponding hydroxyl group. If all the materials are added at once as in the traditional process, the benzene rings in the thermoplastic elastomer can shield some of the reaction sites, leading to uneven crosslinking. In addition, the polyester polyol may precipitate microcrystals at a temperature below 130°C, causing local concentration to be uneven; and the 4-NCO sites of TDI can overreact at a temperature above 160°C, leading to branching and causing the viscosity to skyrocket.

[0115] In some embodiments, in step S22, the mixture is stirred at 200-220°C for 0.5-1h to ensure that it is fully dispersed and uniform. This temperature range is much higher than the softening point of the tackifying resin (100-120°C), and it is actually used to completely destroy the styrene microzones of the thermoplastic elastomer. However, the temperature must be controlled to be below 220°C, otherwise the isoprene chains will be degraded.

[0116] In some embodiments, in step S23, the mixture is first dehydrated under vacuum at 130-140°C for 1.5-2h, and then the temperature is reduced to 110-120°C and the diisocyanate is added. The polyester polyol is in a supercooled melt state at this temperature range, and vacuuming can remove water without inducing crystallization. If the temperature is below 130°C, the polyester will crystallize instantly, leading to uneven dispersion.

[0117] In some embodiments, the second theoretical isocyanate value is 1.9%±0.1%. Through calculation, it can be found that each prepolymer molecule carries 1.8 isocyanate groups, ensuring that long chains are formed rather than dense crosslinking when it is reacted with the first prepolymer later.

[0118] In some embodiments, in step S30, the reaction conditions include:

[0119] The temperature is increased to 140-150℃, the first prepolymer and the catalyst are added to the second prepolymer, and stirring and dispersion are performed under vacuum for 20-30 min. The activation energy of the biuret reaction and the urethane reaction is different. At this temperature, the isocyanate group mainly undergoes intermolecular condensation to form a biuret bond with better heat resistance, and the formation of a low-temperature hydrolyzable urethane bond is avoided.

[0120] Preparation Example

[0121] Preparation Example 1

[0122] The preparation example of the present application provides preparation of the first prepolymer, which includes:

[0123] S11, 15 g of trimethylolpropane, 125 g of polybutadiene polyol, 262.35 g of Ricon130 resin, 0.15 g of phosphoric acid, and 97.5 g of toluene diisocyanate are provided;

[0124] S12, 15 g of trimethylolpropane, 125 g of polybutadiene polyol, 262.35 g of Ricon130 resin, 0.15 g of phosphoric acid are placed in a reaction kettle, vacuum stirring and melting at 130℃ for 1.5 h to make them fully dispersed and uniform and to remove water to obtain a first mixture;

[0125] S13, the first mixture is cooled to 70℃, 97.5 g of toluene diisocyanate is added, and the reaction is carried out under nitrogen for 1.5 h, and then the temperature is increased to 110℃, and the stirring reaction is carried out under vacuum and negative pressure conditions for 1.5 h, until the theoretical isocyanate value is 4.0±0.1%, i.e. the reaction is stopped, and the first prepolymer is discharged and vacuum packaged and sealed for storage.

[0126] Embodiment

[0127] Embodiment 1

[0128] The embodiment of the present application provides a hot melt adhesive and a preparation method thereof, wherein the preparation method of the hot melt adhesive includes:

[0129] S10, 45 g of the first prepolymer prepared in Preparation Example 1 is taken;

[0130] S20, a second prepolymer is prepared;

[0131] S21, 200.0 g of tackifying resin (carbon nine petroleum resin), 1.50 g of antioxidant 1010, 0.50 g of defoaming agent BYK535, 65.00 g of polyolefin elastomer D1116, 55.00 g of polybutadiene polyol Poly R45V, 90.00 g polyester polyol 7330, 0.15 g phosphoric acid, 35.35 g diphenylmethane diisocyanate;

[0132] S22, heat-melt dispersion of carbon nine petroleum resin, antioxidant 1010, defoaming agent BYK535, polyolefin elastomer D1116 under the condition of not lower than 200℃ and not lower than 600mmHg vacuum for 0.5h to obtain a second mixture;

[0133] S23, cooling to 130-160℃, adding polybutadiene polyol Poly R45V, polyester polyol 7330, phosphoric acid, dehydrating under the condition of 140℃ and not higher than -98.0Kpa vacuum for 1.5h, cooling to 110-120℃, adding diphenylmethane diisocyanate and reacting until the theoretical isocyanate value is 1.9±0.1% to obtain a second prepolymer;

[0134] S30, heating to 140℃, adding 45g of the first prepolymer and 7.5g of catalyst DMDEE into the second prepolymer, stirring and dispersing under vacuum for 20min, defoaming to obtain the hot melt adhesive.

[0135] Example 2

[0136] The same as example 1, except that the tackifying resin added is methyl styrene monomer resin.

[0137] Example 3

[0138] The same as example 2, except that the type of polyester polyol added is 7360.

[0139] Example 4

[0140] The same as example 1, except that the polybutadiene polyol added is LBH-2000 with a hydroxyl value of 0.91mmol / g. LBH-2000.

[0141] Example 5

[0142] The same as example 1, except that the polybutadiene polyol added is LBH-2000 with a hydroxyl value of 0.83mmol / g. LBH-2000.

[0143] Example 6

[0144] The same as example 2, except that the polybutadiene polyol added is LBH-2000 with a hydroxyl value of 0.83mmol / g. LBH-2000.

[0145] Comparative Example 1

[0146] Other conditions are the same as in Example 1, except that no first prepolymer is added.

[0147] Comparative Example 2

[0148] Other conditions are the same as in Example 1, except that no first prepolymer is added and the thermoplastic elastomer used is D1124.

[0149] Comparative Example 3

[0150] Other conditions are the same as in Example 2, except that no first prepolymer is added.

[0151] Comparative Example 4

[0152] Other conditions are the same as in Example 2, except that no first prepolymer is added and the thermoplastic elastomer used is D1124.

[0153] Comparative Example 5

[0154] Other conditions are the same as in Example 3, except that no first prepolymer is added.

[0155] Performance Test

[0156] The hot melt adhesive obtained in the above examples and comparative examples is used for dispensing by a hot melt point dispenser at 170℃, and a PC-PC bonded piece is prepared for tensile shear strength test. The adhesive layer thickness is 0.5mm, the overlapping area is 25mm*25mm, and the piece is cured at 25±1℃ and 65±5% environment for tensile shear strength test.

[0157] The shear strength is tested according to GB / T7124-2008.

[0158] Shear strength I is the test result after 2min of dispensing;

[0159] Shear strength II is the test result after 20min of dispensing;

[0160] Shear strength III is the bonding strength after 7 days of curing at 25±1℃ environment;

[0161] Shear strength IV is the bonding strength after 7 days of curing at -60℃ environment;

[0162] Shear strength V is the bonding strength after 7 days of curing at 120℃ environment.

[0163] The test results are shown in Table 1.

[0164] Table 1 is the performance test of the hot melt adhesive composition

[0165] Shear strength I Shear strength II Shear strength III Shear strength IV Shear strength V Example 1 0.51 MPa 2.11 MPa 6.58 MPa 2.35 MPa 0.98 MPa Example 2 0.58 MPa 2.28 MPa 7.02 MPa 2.20 MPa 1.52 MPa Example 3 0.25 MPa 2.05 MPa 6.62 MPa 2.25 MPa 1.05 MPa Example 4 0.52 MPa 2.16 MPa 6.75 MPa 0.90 MPa 1.10 MPa Example 5 0.50 MPa 2.10 MPa 6.59 MPa 1.18 MPa 1.05 MPa Example 6 0.49 MPa 2.15 MPa 6.66 MPa 1.30 MPa 1.18 MPa Comparative Example 1 0.48 MPa 1.88 MPa 5.50 MPa 2.12 MPa 0.50 MPa Comparative Example 2 0.42 MPa 1.78 MPa 4.88 MPa 1.58 MPa 0.35 MPa Comparative Example 3 0.50 MPa 1.95 MPa 6.22 MPa 1.96 MPa 0.90 MPa Comparative Example 4 0.48 MPa 1.90 MPa 6.18 MPa 2.05 MPa 0.55 MPa Comparative Example 5 0.23 MPa 1.80 MPa 6.32 MPa 2.10 MPa 0.26 MPa

[0166] From the test results of Table 1, it can be seen that in the examples, except for Example 3, the hot melt adhesives all have high initial adhesion strength, which can reduce the product pressure maintaining time in application, or even eliminate the pressure maintaining, and improve the process efficiency, among which the performance of Example 2 is the best. In contrast to the comparative examples, without adding the first prepolymer, the temperature resistance cannot meet the index requirements of high-temperature bonding performance. It can also be concluded that the polybutadiene polyols used in the examples have better temperature resistance than the polybutadiene polyols used in the comparative examples. R45V is better than other polybutadiene polyols in low-temperature wet bonding.

[0167] The hot melt adhesive prepared in the embodiments of the present application is a reactive hot melt adhesive prepared by blending a base material with terminal isocyanate groups with other resins and thermoplastic elastomers. Since it contains terminal isocyanate groups, it can perform a moisture curing reaction with air moisture, generate active amino groups with water vapor, and further react to form polyurea structures, etc. Through physical and chemical crosslinking processes, its adhesion to materials becomes stronger and stronger, and it also has good heat resistance and low-temperature resistance. The hot melt adhesive provided in the present application has higher initial adhesion strength than existing polyurethane hot melt adhesives, reaching 0.5 MPa at 2 min and 2.0 MPa at 20 min, and has high thermal stability, solving the problem of frequent adjustment of dispensing parameters due to viscosity rise caused by long-time heating. It is suitable for sealing and bonding of various types of vehicle display screens and structural bonding, and is also suitable for bonding of low-polarity materials.

[0168] In the above embodiments, the description of each embodiment has its own focus, and the parts not described or recorded in detail in a certain embodiment can be referred to the related description of other embodiments.

[0169] The above-described embodiments are only used to illustrate the technical solutions of the embodiments of the present application, and not to limit them; although the embodiments of the present application have been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the embodiments of the present application.

Claims

1. A hot melt adhesive, characterized in that, The components include the following weight parts: Polybutadiene polyol 5-15 parts; Polyester polyol 15-30 parts; Tackifying resin 35-45 parts; Thermoplastic elastomer 10-15 parts; Diisocyanate 5-10 parts; First prepolymer 5-10 parts; Antioxidant 0.2-0.5 parts; Catalyst 0.5-2.0 parts; Up to 0.2 parts of defoaming agent; Up to 0.1 parts of stabilizer; The raw material for preparing the first prepolymer includes liquid polybutadiene resin.

2. The hot melt adhesive of claim 1 wherein, The number average molecular weight of the polybutadiene polyol is between 2000-3000, and the polybutadiene polyol has a glass transition temperature < -55℃.

3. The hot melt adhesive of claim 1 wherein, The number average molecular weight of the polyester polyol is between 2000-4000; And / or, the hydroxyl value of the polyester polyol is 30-60 mg KOH / g; And / or, the melting temperature of the polyester polyol is 60-90℃; And / or, the crystallinity of the polyester polyol is ≥ 40%.

4. The hot melt adhesive of claim 1 wherein, The softening point of the tackifying resin is between 100-120℃.

5. The hot melt adhesive of claim 1 wherein, The polybutadiene polyol is at least one of primary hydroxyl liquid polybutadiene, secondary hydroxyl liquid polybutadiene, hydrogenated primary hydroxyl liquid polybutadiene, and hydrogenated secondary hydroxyl liquid polybutadiene; And / or, the polyester polyol is a crystalline polyester polyol, which is obtained by polycondensation of aromatic diacid and linear aliphatic diol; And / or, the tackifying resin includes at least one of petroleum resin, rosin resin, terpene resin, methyl styrene resin, and modified resin thereof; And / or, the thermoplastic elastomer is styrene-isoprene-styrene; And / or, the diisocyanate includes at least one of diphenylmethane diisocyanate, toluene diisocyanate, p-phenylene diisocyanate, and isophorone diisocyanate; And / or, the antioxidant is at least one of antioxidant 1010, antioxidant 1076, antioxidant 164, and antioxidant 264; And / or, the defoaming agent is one of BYK-A530, BYK-A535, BYK-A550, BYK-A555, BYK-A560, and BYK-A595; And / or, the stabilizer is at least one of phosphoric acid or polyphosphoric acid; And / or, the catalyst is at least one of dimorpholinyl diethyl ether and triethylenediamine.

6. A method for producing a hot melt adhesive, characterized by, It includes: Preparation of a first prepolymer, the raw material for preparing the first prepolymer includes liquid polybutadiene resin; Preparation of a second prepolymer, the second prepolymer is an end-isocyanate polyurethane / polyester prepolymer; Adding the first prepolymer and catalyst to the second prepolymer to obtain the hot melt adhesive.

7. The production method according to claim 6, wherein The preparation of the first prepolymer includes: Providing polybutadiene polyol, tri-functional chain extender, liquid polybutadiene, auxiliary agent, and isocyanate; Mixing the tri-functional chain extender, the polybutadiene polyol, the liquid polybutadiene, and the auxiliary agent, and dehydrating under vacuum to obtain a first mixture; Cooling the first mixture to 60-80℃, and adding the isocyanate to the first mixture, and reacting to the first theoretical isocyanate value to obtain the first prepolymer.

8. The production method according to claim 7, wherein The dehydrating under vacuum includes: Stirring under vacuum at 120-140℃ for 1.5-2h; And / or, the reaction to the first theoretical isocyanate value, including: Reacting under nitrogen for 1-2h, then heating to 110-120℃, stirring under vacuum for 1-2h, and the first theoretical isocyanate value is 4.0±0.1%; And / or, the trihydroxy chain extender is trimethylolpropane, the auxiliary is phosphoric acid, and the isocyanate is toluene diisocyanate.

9. The production method according to claim 6, wherein The preparation of the second prepolymer includes: Providing tackifying resin, antioxidant, thermoplastic elastomer, polybutadiene polyol, polyester polyol, stabilizer, defoaming agent, and diisocyanate; Placing the tackifying resin, antioxidant, and thermoplastic elastomer in a reaction kettle, and fully dispersing and uniformly obtaining a second mixture; Cooling the second mixture to 130-160℃, adding the polybutadiene polyol, polyester polyol, stabilizer, defoaming agent, and then adding diisocyanate, and reacting to the second theoretical isocyanate value to obtain the second prepolymer.

10. The production method according to claim 9, wherein The placing of the tackifying resin, antioxidant, and thermoplastic elastomer in a reaction kettle, and fully dispersing and uniformly obtaining a second mixture, includes: Stirring at 200-220℃ for 0.5-1h to fully disperse and uniformly; And / or, cooling the second mixture to 130-160℃, adding the polybutadiene polyol, polyester polyol, stabilizer, defoaming agent, and then adding diisocyanate, includes: Firstly, dehydrating under vacuum at 130-140℃ for 1.5-2h, and then cooling to 110-120℃ and adding diisocyanate; And / or, the second theoretical isocyanate value is 1.9%±0.1%.

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