High performance thermal expansion cavity sealing material and method of making same

Abstract

This invention relates to a thermally expandable cavity sealing material and its preparation method. The material comprises a matrix of ethylene-vinyl acetate copolymer and rubber elastomer, combined with an AC foaming agent, a weakly basic organic compound, an inorganic metal oxide, and a crosslinking system. By creating a reactive environment between the weakly basic organic compound and the inorganic metal oxide under specific temperature conditions before the foaming agent decomposes, the subsequent decomposition behavior of the foaming agent is regulated, transforming the gas release process from a centralized to a phased process. Through the synergistic limitation of component ratios and process parameters, the foaming process is matched with the structure formation process, thereby improving the uniformity and stability of the cell structure. Under heating conditions, this material achieves a relatively stable volume expansion process, improving the adequacy of cavity filling and enhancing the material's structural retention capacity during use.

Description

Technical Field

[0001] This invention relates to the technical field of automotive sealing materials, and in particular to a high-performance thermal expansion cavity sealing material and its preparation method. Background Technology

[0002] With the development of lightweighting and structural integration in automobiles, the cavity structure in the vehicle body is becoming increasingly complex, with uneven cavity size distribution and diverse structural variations. This places higher demands on the fluidity, expansion capacity, and structural stability of sealing materials during the heating process. Thermally expandable sealing materials, which can expand and fill cavities during heating, are gradually becoming an important material type in the fields of vehicle body sealing, sound insulation, and protection.

[0003] In existing technologies, thermal expansion sealing materials are typically composed of thermoplastic resins and rubber as the matrix, combined with chemical foaming agents and cross-linking systems. During use, under certain temperature conditions, the foaming agent decomposes to produce gas, which drives the material to expand and fill the cavity. However, because the decomposition of the foaming agent usually occurs concentrated within a narrow temperature range, the gas release process is sudden and uneven. This can easily lead to large local stresses within the material in a short period of time, resulting in problems such as unstable cell structure, uneven cell size distribution, and local collapse.

[0004] Furthermore, due to the lack of effective matching between the foaming process and the formation of the material's internal structure, the material often fails to form sufficient supporting structure during the rapid gas release phase, leading to excessive expansion or structural damage during expansion. In subsequent stages, it becomes difficult to maintain a stable cell morphology, thus affecting the material's overall sealing performance and long-term reliability. This problem is particularly pronounced in complex cavity structures, easily resulting in insufficient filling or localized failure.

[0005] Therefore, how to achieve more controllable gas release behavior during the thermal expansion of materials, and how to achieve a reasonable match between the expansion process and the structure formation process, thereby improving the uniformity of cavity filling and structural stability, has become a key technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned problems existing in the prior art and provide a thermal expansion cavity sealing material and its preparation method, so that the material has a more stable volume change process during thermal expansion and improves the uniformity of cavity filling and structural stability.

[0007] To achieve the above objectives, a first aspect of the present invention provides a high-performance thermal expansion cavity sealing material, comprising the following components by weight: 40-60 parts of ethylene-vinyl acetate copolymer, The rubber elastomer comprises 10-30 parts, wherein the rubber elastomer is one or both of ethylene propylene diene monomer (EPDM) rubber and butyl rubber. 10-20 parts of AC foaming agent 0.5 to 5 parts of a weakly basic organic compound. Inorganic metal oxides 1-8 parts, Crosslinking agent 0.5–2.5 parts, Crosslinking aid 0.5-3 parts, Antioxidant 0.3–1.2 parts, Heat stabilizer 0.5–2.5 parts; The weakly basic organic compound is selected from one or two of imidazoles, fatty amines, or pyridines. The inorganic metal oxide is selected from one or two of zinc oxide, magnesium oxide, or calcium oxide.

[0008] As a further improvement of the present invention, the weight part M of the weakly basic organic compound B The AC foaming agent has a weight part M A The average particle size of the AC foaming agent is d. A The following relationship must be satisfied:

[0009] The essence of the above relationship is not simply limiting the ratio of weakly basic organic compounds to AC foaming agents, but rather taking into account the particle size factor of the foaming agent to jointly constrain the effective pre-activation strength of the foaming agent under the action of weakly basic organic compounds during the pre-mixing stage. Wherein, M... B / M A It reflects the intensity of the weak alkaline effect corresponding to a unit amount of foaming agent.

[0010] If only M is limited B / M A While this method can characterize the approximate ratio between weakly basic organic compounds and blowing agents, it is still insufficient to reflect the differences in reaction sensitivity of blowing agents with different particle sizes in actual systems. This is because changing the particle size of AC blowing agents alters the contactable interfaces on the particle surface, the uniformity of localized heating, and the degree to which they form a locally pre-activated environment with the weakly basic organic compounds. With smaller particle sizes, there are more particles per unit mass, resulting in more surface contact sites and a significantly enhanced effect of the weakly basic organic compounds on the blowing agent. With larger particle sizes, the total particle surface area decreases, the localized pre-activation effect weakens, and the system is more likely to revert to the traditional one-time concentrated decomposition mode. Therefore, considering only M... B / M A This can lead to a distortion in the judgment of the actual pre-activation degree, and the introduction of ln(d) AAfter that, the effect of particle size variation on pre-activation intensity can be factored into the same evaluation metric. The reason for using a logarithmic term instead of directly using d is... A This is because the effect of particle size on the surface behavior of foaming agents does not increase linearly. Changes in the smaller particle size range are more sensitive, while the marginal effect gradually weakens as the particle size increases further. The logarithmic function precisely reflects this actual law of being sensitive at first and then slowing down.

[0011] The lower limit of this relationship, 0.1, corresponds to the critical state of insufficient pre-activation. When (M B / M A )×ln(d A When the concentration is below 0.1%, either the amount of weakly basic organic compound is too low, or the foaming agent particle size is too small and excessively dispersed, resulting in unstable local action points, or the combination of particle size and dosage leads to a weak degree of activation during the premixing stage. In this case, the weakly basic organic compound is insufficient to substantially change the subsequent decomposition path of the AC foaming agent. When the temperature rises, the foaming agent still mainly undergoes traditional centralized and sudden decomposition, and the gas release rhythm is similar to that of ordinary systems. It is difficult to form a staged gas release process of first building the framework and then expanding the cells, ultimately resulting in large cells, an increase in locally interconnected pores, and an unstable expansion process.

[0012] The upper limit of this relation, 0.7, corresponds to the critical state of excessive pre-activation. When (M B / M A )×ln(d A A value above 0.7 indicates that the weakly basic organic compound has an excessively strong effect on the blowing agent, or that the activation of the blowing agent surface is overly concentrated under the current particle size conditions. This will lead to two adverse consequences. First, the AC blowing agent will enter the rapid decomposition zone earlier during subsequent heating, causing premature gas release. At this time, the matrix resin and crosslinking system have not yet established sufficient support, making it prone to local bubbling, blistering, and collapse. Second, excessive local activation will cause the decomposition reaction to become concentrated again, rather than forming the staged gas release sought in this scheme, thus disrupting the rhythm of first forming the initial framework and then further expansion. In other words, this upper limit corresponds to the boundary point where pre-activation shifts from effective control to over-catalysis. Once this boundary point is exceeded, although the system appears to foam faster on the surface, the cell stability, structural retention, and subsequent adhesion retention will actually decrease.

[0013] As a further improvement of the present invention, the inorganic metal oxide has a weight part M D The weight parts M of the weakly basic organic compound B And the crosslinking agent is M parts by weight. C It satisfies the following relationship: .

[0014] The above relationship addresses the question of whether the system can promptly fix the bubbles after the gas is released. Essentially, it defines the dynamic equilibrium relationship between inorganic metal oxides, crosslinking agents, and weakly basic organic compounds. Specifically, M... D The amount of inorganic metal oxide added does not simply enhance the filler, but rather participates in regulating the local reaction environment during premixing and subsequent heating, preventing the weakly basic organic compound from having an overly sharp effect on the foaming agent, and also affecting the thermal response and stability of the matrix surrounding the gas release area. C The amount of crosslinking agent added determines the system's ability to form a network support and fix the cell walls during foaming. M B This represents the activation intensity of the weakly basic organic compound on the decomposition pathway of the foaming agent. The reason for using M in the denominator is... B 2 Instead of M B This is because the effect of weakly basic organic compounds on the system is not linear. On the one hand, it affects the initial decomposition sensitivity of the AC blowing agent; on the other hand, it also affects the gas release rate distribution, making the gas release process more concentrated or more dispersed. Therefore, M B The increase of M not only means a stronger activation effect, but also that the intensity and rhythm of the post-activation gas release will be amplified. This effect manifests as an approximately quadratic strengthening trend in the system. In other words, as M increases... B Ascending, the system's response to M D and M C The compensation demand does not increase proportionally, but rather increases faster; therefore, M is adopted. B 2 It can more accurately reflect the nonlinear influence of weakly alkaline organic compounds on the overall foaming and shaping balance.

[0015] The lower limit of 0.2 in this relationship represents the imbalance boundary where the outgassing intensity is too high relative to the stabilizing capacity. When the value of the relationship is below 0.2, it indicates that the combined stabilizing effect of inorganic metal oxides and crosslinking agents on the system is insufficient to match the pre-activation intensity brought by the weakly basic organic compounds. The consequence is that although the blowing agent has already undergone a phased decomposition trend under the action of the weakly basic organic compounds, once the gas is released, the system lacks sufficiently rapid network fixation and local thermal stability support. The initial cell skeleton formed in the first stage is weak, and during the second stage of outgassing, it is easy to cause further cell merging, cell wall thinning, or even local rupture. In this case, the material will exhibit problems such as an active surface during the expansion process but a loose final structure, a decreased closed-cell rate, and significant shrinkage in the later stages. This lower limit does not simply emphasize that the crosslinking agent or inorganic oxide cannot be too little, but rather indicates that only when the overall stabilizing effect of the system reaches a certain proportion or higher than the weakly basic activation effect can the aforementioned phased outgassing truly transform into a favorable structural evolution, rather than evolving into outgassing followed by instability.

[0016] The upper limit of 3.0 in this relationship represents another imbalance boundary where the stabilizing ability is too high relative to the outgassing intensity. When the value of the relationship is higher than 3.0, it indicates that the constraint and shaping ability provided by the inorganic metal oxide and crosslinking agent are too strong, while the decomposition activation provided by the weakly basic organic compound is relatively insufficient. In this case, although the system is not prone to bubble collapse, another problem arises: the crosslinking network forms too early and too quickly, and the cells are fixed prematurely before they have completed effective expansion. The gas in the second stage cannot fully drive the cells to continue growing, ultimately leading to insufficient expansion ratio and inadequate cavity filling, especially in complex corners or large tolerance cavities where it is difficult to achieve sufficient occupancy. At the same time, excessive inorganic oxide constraint can also reduce the local matrix fluidity, which is not conducive to the uniform distribution of gas between cells and may cause the coexistence of local dense areas and local under-expanded areas. The upper limit is set to prevent the system from going from uncontrolled outgassing to another extreme, namely, excessive suppression of outgassing and limited foaming. Therefore, the technical effect corresponding to this upper limit is to control the time difference between gas release and cell fixation within an appropriate range, so that the material will neither collapse due to lack of support nor lose its expansion potential due to premature shaping.

[0017] As a further improvement of the present invention, the weight ratio of the EPDM rubber to the butyl rubber is 1:(0.3-1.5).

[0018] As a further improvement of the present invention, the weakly basic organic compound is one or two of 2-methylimidazole, 1-methylimidazole, triethylamine or pyridine.

[0019] As a further improvement of the present invention, the inorganic metal oxide is zinc oxide or magnesium oxide.

[0020] As a further improvement of the present invention, the average particle size of the AC foaming agent is 3 to 15 micrometers.

[0021] A second aspect of the present invention provides a method for preparing a thermal expansion cavity sealing material, comprising the following steps: S1: Add the ethylene-vinyl acetate copolymer and the rubber elastomer into the mixing equipment and mix them at 80-110℃ for 3-8 minutes; S2: Add a weakly alkaline organic compound and an inorganic metal oxide, and mix at 100-125°C for 3-8 minutes; S3: After cooling the system to 75-95℃, add AC foaming agent, crosslinking agent and crosslinking aid, mix for 2-5 minutes and then discharge to form the product.

[0022] A second aspect of the present invention provides a method for preparing the thermal expansion cavity sealing material as described above, comprising the following steps: S1: Add the ethylene-vinyl acetate copolymer and the rubber elastomer into the mixing equipment and mix them at 80-110℃ for 3-8 minutes; S2: Add a weakly alkaline organic compound and an inorganic metal oxide, and mix at 100-125°C for 3-8 minutes; S3: After cooling the system to 75-95℃, add AC foaming agent, crosslinking agent and crosslinking aid, mix for 2-5 minutes and then discharge to form; S4: The obtained material is heated at 140-180℃ to cause foaming and cross-linking.

[0023] As a further improvement of the present invention, the mixing temperature T in step S2, and the weight parts M of the inorganic metal oxide... D The weight parts M of the weakly basic organic compound B The following relationship must be satisfied: .

[0024] By establishing a correspondence between process conditions and system reaction intensity, the interaction state formed by weakly alkaline organic compounds and inorganic metal oxides in the premixing stage is kept within a controllable range, thereby ensuring that the change of decomposition path can be stably achieved in the subsequent foaming process.

[0025] In step S2, the weakly basic organic compound and inorganic metal oxide are first introduced into the system. At this point, the AC foaming agent has not yet been added or has not reached significant decomposition conditions. Therefore, the essence of this stage is not foaming, but rather establishing a precursor environment that can influence subsequent decomposition behavior. The formation of this environment is controlled by three factors: temperature T, the intensity of the weakly basic organic compound's action, and the moderating ability of the inorganic metal oxide to influence this action. Increased temperature enhances molecular motion and local reactivity, making it easier for the weakly basic organic compound to form an effective action area around the foaming agent particles. The inorganic metal oxide, on the one hand, buffers the local acid-base environment, and on the other hand, influences the distribution and stability of the weakly basic organic compound in the system through its surface properties, thereby changing its influence on the subsequent decomposition behavior of the foaming agent. Therefore, (M D / M B The value of (T-90) reflects the adjustment ratio of the inorganic metal oxide to the weak alkaline effect, while (T-90) / 30 reflects the degree of temperature increase relative to the initial activation range. The product of the two represents the overall effective pre-activation intensity of the system under the current process conditions.

[0026] When this relationship value is below 0.1, it indicates that the regulatory effect of inorganic metal oxides relative to weakly basic organic compounds in the system is insufficient, or the mixing temperature is too low, preventing the weakly basic organic compounds from forming a stable and uniform working environment in the system despite their addition. In this case, the influence of the weakly basic organic compounds on the foaming agent remains mainly local or weak. During subsequent heating, the foaming agent still mainly undergoes traditional concentrated decomposition, making it difficult to form a staged gas release process. Specifically, the gas release in the early stage of foaming is still relatively concentrated, the cell formation lacks layers, and local rapid expansion followed by collapse is prone to occur, making the expansion process unstable and the cavity filling effect uneven. This lower limit corresponds to the system not yet having truly established a pre-activated state capable of changing the decomposition path.

[0027] When this relationship value is higher than 2.5, it indicates that the interaction between inorganic metal oxides and temperature is too strong, making the environment for the weakly basic organic compounds in the premixing stage too active. At this time, although the foaming agent has not completely decomposed, its subsequent decomposition sensitivity has been significantly increased, and it may even rapidly enter the decomposition range in the early stage of heating, thus causing the gas release to occur prematurely and in a concentrated manner, which weakens the originally intended staged release characteristics. At the same time, the excessively strong effect of inorganic metal oxides will restrict the local fluidity of the matrix, making the system more prone to areas of excessive local constraint during the subsequent foaming process, resulting in limited or uneven cell expansion, ultimately manifested as a decrease in expansion ratio or insufficient local filling. This upper limit corresponds to the critical state where the pre-activation effect changes from regulating the decomposition path to prematurely triggering decomposition. Once this range is exceeded, the system will return to a state unfavorable to stable foaming.

[0028] Between the aforementioned upper and lower limits, the system exists in a relatively stable pre-activation range. Within this range, the weakly basic organic compounds, regulated by inorganic metal oxides, can distribute uniformly under appropriate temperature conditions, creating an environment that regulates the decomposition of the foaming agent without causing it to prematurely enter the rapid decomposition stage. Therefore, during subsequent heating, some decomposition sites of the foaming agent are preferentially activated, releasing the first-stage gas, while the remaining sites continue to decompose at higher temperatures, resulting in the release of the second-stage gas. Simultaneously, because the pre-mixing stage has already homogenized the internal environment of the system, the spatial distribution of gas release is more consistent, thus improving the coordination of cell formation and expansion.

[0029] Furthermore, this relationship indirectly ensures the time matching between the foaming process and the cross-linking process. When the pre-activation intensity is within the aforementioned range, the temperature range corresponding to the first stage of gas release usually overlaps with the initial stage of the cross-linking reaction, allowing the system to gradually build a network structure while forming initial cells. The second stage of gas release occurs after further cross-linking, at which point the material already possesses a certain structural support capacity, capable of withstanding subsequent gas expansion without significant collapse. This process of first forming a framework and then further expanding allows the cell structure to both fully expand and remain stable, thereby achieving a simultaneous improvement in both expansion effect and structural integrity.

[0030] A third aspect of the present invention provides a cavity structure in which the above-mentioned thermal expansion cavity sealing material is disposed.

[0031] Specifically, this method uses ethylene-vinyl acetate copolymer and rubber elastomer to form a continuous phase, introduces weakly basic organic compounds and inorganic metal oxides, and establishes a controlled pre-activation environment around the foaming agent through a pre-mixing process within a specific temperature range, before the foaming agent officially decomposes. As a result, the foaming agent no longer exhibits the centralized, sudden gas release characteristic of traditional systems during subsequent heating, but rather displays a controlled, phased release. It is this early intervention in foaming behavior that enables this method to simultaneously improve expansion and filling, structural stability, and mechanical retention by altering the formation mechanism of the foaming process.

[0032] Traditional thermal expansion cavity sealing materials generally face a difficult-to-resolve contradiction when heated: once the foaming agent reaches its decomposition temperature, it rapidly releases a large amount of gas, while the internal cross-linking network of the material has not yet been fully established. Although the gas can quickly drive volume expansion, it also causes rapid cell growth, thinning of cell walls, and an increase in locally interconnected pores. This leads to an increased expansion ratio but decreased structural strength, loosening of the bonding area, and a tendency to collapse or detach after thermal cycling.

[0033] In this scheme, the weakly basic organic compound is not simply added to the system as an additive, but rather acts on the surface of the foaming agent particles together with the inorganic metal oxide under pre-mixing temperature conditions, forming a localized reaction environment that affects its subsequent decomposition sensitivity. Since this temperature range is below the temperature required for significant decomposition of the foaming agent, this stage does not cause premature gas release, but it can alter the chemical environment on the surface of the foaming agent particles. Upon subsequent heating, some decomposition sites are activated first, releasing the first stage of gas, and an initial expansion skeleton is formed inside the material. Subsequently, as the temperature further increases, the remaining decomposition sites release the second stage of gas, and the subsequent gas continues to expand the pores under the constraint of the existing skeleton. Thus, the gas is no longer released all at once, but gradually released under the existing support capacity of the material, significantly mitigating the problems of sudden macropore formation and instantaneous bubble wall instability in traditional systems.

[0034] The direct result of this mechanism is that the internal pores of the material transform from the disordered enlargement seen in traditional systems to a gradual formation process of nucleation, expansion, and fixation. The amount of gas released in the first stage is relatively controlled, primarily serving to establish the initial pore framework and local volume support, allowing the cross-linking system to advance synchronously at this stage. The gas released in the second stage further expands the existing structure; while the pores continue to enlarge, they are no longer completely unsupported. In other words, the volume expansion process is broken down into two stages that cooperate with network formation, enabling the material to maintain good closed-cell ratio, cell wall integrity, and cohesive strength even at higher expansion levels. For automotive cavity sealing applications, this means that after heating, the material can not only more fully penetrate the cavity edges and dimensional fluctuation areas, but also maintain good structural support after expansion, preventing later shrinkage, fragmentation, or localized loss of seal due to excessive pore coarsening.

[0035] Secondly, the component parameter relationships set in this scheme are not simply limited by the formulation ratio, but rather incorporate the amount of weakly basic organic compound, the particle size of the foaming agent, the effect strength of the inorganic metal oxide, and the fixation ability of the crosslinking system into the same constraint system. In particular, by introducing the average particle size of the foaming agent into the parameter relationships, the specific surface area and surface reaction sensitivity of the foaming agent particles are effectively taken into consideration. For the same weight of weakly basic organic compound: if the foaming agent particles are too fine, there are too many contact sites on their surface, resulting in excessive pre-activation and causing subsequent decomposition to be moved forward, leading to localized excessively rapid foaming; if the particles are too coarse, the surface reaction is insufficient, the degree of pre-activation is inadequate, and it still approaches the traditional centralized gas release mode. Only when the amount of weakly basic organic compound and the particle size of the foaming agent both fall within a specific range can the degree of pre-activation both break the original single path and prevent the system from reacting excessively prematurely.

[0036] Furthermore, the coupling relationship between inorganic metal oxides, weakly basic organic compounds, and crosslinking agents also plays a crucial role. Inorganic metal oxides participate in regulating the local acid-base environment and thermal response behavior, while also influencing the speed and uniformity of network formation during the crosslinking process. When the amount added is too low, it insufficiently compensates for the pre-activation environment formed by the weakly basic organic compounds, making it difficult to effectively accelerate the decomposition of the foaming agent; when the amount added is too high, it makes the local reaction environment too strong, causing the system to prematurely enter a state unfavorable for uniform expansion. Simultaneously, if the amount of crosslinking agent added is mismatched with the aforementioned two factors, even if gas release is achieved in stages, if network establishment is too slow, it will still cause instability in the later stages of cell expansion; if network formation is too fast, it will restrict the second-stage expansion, resulting in insufficient volume increase. Therefore, controlling the amounts of inorganic metal oxides, weakly basic organic compounds, and crosslinking agents within a certain range through coupling constraints essentially matches the relative rhythm of the three processes. That is, the three sub-processes of pre-activation, gas release, and shaping must be synchronized and coordinated to obtain a result that is both fully filled and does not collapse the cells.

[0037] Furthermore, limiting the premixing temperature is a crucial trigger for the entire technical solution to be effective. At lower temperatures, although the weakly alkaline organic compounds and inorganic metal oxides are added to the system, they are insufficient to form a stable pre-activated environment around the foaming agent particles, resulting in a near-traditional one-time decomposition pattern. At higher temperatures, the foaming agent may undergo adverse changes during the mixing stage, reducing its subsequent expansion potential and compromising its storage and processing stability. Only within a specific temperature range, where effective interaction between the aforementioned components is established without premature decomposition of the foaming agent, will the subsequent heating process result in two gas release stages. Therefore, the material's effectiveness depends not only on the formulation itself but also on the combined effect of the components and processes in a specific time sequence. Consequently, this solution does not simply rely on increasing fillers, foaming agents, or strengthening the adhesive resin; instead, it first adjusts the decomposition path and then matches the crosslinking rate to ultimately achieve rhythmic control of the expansion behavior.

[0038] In summary, this solution, through the synergistic constraints of weakly alkaline organic compounds, inorganic metal oxides, foaming agent particle size, crosslinking system, and premixing temperature, alters the decomposition path and gas release rhythm of the foaming agent. This transforms the thermal expansion material from a traditional one-time expansion mode to a controlled, staged expansion mode, thereby simultaneously improving cavity filling performance, cell stability, and structural retention. The effectiveness of this technology is built upon a reconstruction of the foaming process mechanism, rather than simply superimposing or conventionally adjusting existing formulations.

[0039] The present invention, by adopting the above technical solution, has the following beneficial effects: (1) This scheme introduces weakly alkaline organic compounds and inorganic metal oxides within a specific temperature range to create a pre-activated environment around the foaming agent particles before their formal decomposition, thus transforming the gas release of the foaming agent from a traditional one-time concentrated burst into a controlled two-stage release. The first stage gas is released when the cross-linked network is initially formed, establishing the initial expansion skeleton; the second stage gas continues to expand the pores under the constraint of the existing skeleton. As a result, the gas release rhythm is matched with the material structure establishment process, fundamentally changing the contradictory relationship in thermal expansion sealing materials where sufficient expansion leads to a loose structure.

[0040] (2) This scheme incorporates the dosage of weakly basic organic compounds, the particle size of the foaming agent, the amount of inorganic metal oxides added, and the dosage of crosslinking agents into a coupled constraint system. The introduction of the foaming agent particle size allows for consideration of specific surface area and surface reaction sensitivity. This parameter relationship is not a simple limitation of the formulation ratio, but rather reflects the window conditions for controlling the decomposition path. When all parameters fall within a specific range, the degree of pre-activation can break the traditional one-time decomposition path without causing the system to react excessively prematurely. Only within this window can the aforementioned staged release effect be achieved.

[0041] (3) Due to the coordination between the degassing rhythm and cross-linking and shaping, this scheme achieves a higher expansion ratio while maintaining a more complete cell structure, a higher proportion of closed cells, and better cohesive strength. After heating, the material can more fully fill the cavity corners and dimensional fluctuation areas, and is less prone to local delamination, pulverization, or failure under long-term vibration, thermal cycling, and service environments. This effect stems from the reconstruction of the foaming formation mechanism, rather than being achieved by conventional means such as simply increasing the cross-linking density or increasing the amount of foaming agent. Detailed Implementation

[0042] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0043] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0044] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0045] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0046] The present invention will now be described in detail with reference to specific embodiments, which are intended to understand rather than limit the invention.

[0047] Unless otherwise specified, in the following examples, the ethylene-vinyl acetate copolymer used is ExxonMobil™ EVA 1005 manufactured by ExxonMobil. The EPDM rubber used is NORDEL™ IP 4520 manufactured by Dow Chemical Company; The butyl rubber used is Exxon™ Butyl 268 manufactured by ExxonMobil. AC foaming agent uses azodicarbonamide foaming agent produced by Jiangsu Suopu Chemical Co., Ltd. The zinc oxide used is industrial-grade zinc oxide produced by Zhuzhou Smelting Group; The dicumyl peroxide used is Trigonox® BC-FF manufactured by AkzoNobel. Triallyl isocyanurate was selected from TAIC products manufactured by Jiangsu Runfeng Synthetic Technology Co., Ltd. The antioxidant used is Irganox 1010 manufactured by BASF. The heat stabilizer used is industrial-grade calcium stearate.

[0048] Example 1 This embodiment discloses a high-performance thermal expansion cavity sealing material, the formulation of which is as follows: 50 parts of ethylene-vinyl acetate copolymer; 18 parts of EPDM rubber; 10 parts butyl rubber; 15 parts of AC foaming agent; 2.5 parts of 2-methylimidazole; 4 parts zinc oxide; 1.2 parts of dicumyl peroxide; 1.5 parts triallyl isocyanurate; Antioxidant 1010 0.8 parts; 1.2 parts heat stabilizer; The average particle size of AC foaming agent is 8 micrometers.

[0049] Its preparation method is as follows: S1: Add ethylene-vinyl acetate copolymer, ethylene propylene diene monomer (EPDM) rubber, and butyl rubber to a Banbury mixer and mix at 95°C with a rotor speed of 60 rpm for 5 minutes to fully plasticize the matrix resin and form a uniform continuous phase. Then, raise the temperature to 105°C and continue mixing for 2 minutes to eliminate local stress and improve the homogeneity of the system.

[0050] S2: While maintaining the system temperature at 112℃, add 2-methylimidazole and zinc oxide, and continue mixing for 5 minutes, controlling the rotor speed at 50 rpm. After this step, allow the system to cool naturally to 90℃.

[0051] S3: When the system temperature drops to 90℃, add AC foaming agent, dicumyl peroxide, and triallyl isocyanurate in sequence, along with antioxidant 1010 and calcium stearate. Mix for 3 minutes at a speed of 40 rpm to ensure uniform dispersion of all components. Press the mixed material into sheets using an open mill to obtain sheets with a thickness of 3 mm.

[0052] S4: Place the sheet in a mold and heat it at 165°C for 25 minutes to cause the material to foam and cross-link, thus obtaining the final thermal expansion sealing material.

[0053] Example 2 The difference between this embodiment and Embodiment 1 lies in the amount of each component used in the formulation, as follows: 42 parts of ethylene-vinyl acetate copolymer; 14 parts of EPDM rubber; 8 parts butyl rubber; 10 parts of AC foaming agent; 0.8 parts of 2-methylimidazole; 2 parts zinc oxide; 0.6 parts of dicumyl peroxide; 0.8 parts of triallyl isocyanurate; Antioxidant 1010 0.5 parts; 0.8 parts heat stabilizer.

[0054] The average particle size of AC foaming agent is 4 micrometers.

[0055] Example 3 The difference between this embodiment and Embodiment 1 lies in the amount of each component used in the formulation, as follows: 60 parts of ethylene-vinyl acetate copolymer; 25 parts of EPDM rubber; 15 parts butyl rubber; 20 parts of AC foaming agent; 5 parts of 2-methylimidazole; 8 parts zinc oxide; 2.5 parts of dicumyl peroxide; 3 parts of triallyl isocyanurate; Antioxidant 1010, 1.2 parts; 2.5 parts heat stabilizer.

[0056] The average particle size of AC foaming agent is 14 micrometers.

[0057] Comparative Example 1 The difference between this comparative example and Example 1 is that the formulation does not contain 2-methylimidazole, and 2-methylimidazole is not added in step S2 of the preparation method; the rest are the same.

[0058] Comparative Example 2 The difference between this comparative example and Example 1 is that the formulation does not contain zinc oxide, and zinc oxide is not added in step S2 of the preparation method; the rest are the same.

[0059] Comparative Example 3 The difference between this comparative example and Example 1 is that the pre-mixing step of the weakly basic organic compound and inorganic metal oxide is omitted; all components are added and mixed at once, while the remaining components and their amounts remain the same as in Example 1. The preparation method is as follows: S1: Add ethylene-vinyl acetate copolymer, ethylene propylene diene monomer (EPDM) rubber and butyl rubber to a mixer and mix at 95°C for 5 minutes with a rotor speed of 60 rpm to fully plasticize the matrix resin.

[0060] S2: Under the same mixing conditions, directly add 2-methylimidazole, zinc oxide, AC foaming agent, dicumyl peroxide, triallyl isocyanurate, antioxidant and heat stabilizer, and mix at 95°C for 4 minutes to disperse all components simultaneously.

[0061] S3: Press the mixed material into sheets to obtain sheets with a thickness of 3 mm.

[0062] S4: Heat the sheet at 165°C for 25 minutes to induce foaming and cross-linking reactions in the material.

[0063] Comparative Example 4 The difference between this comparative example and Example 1 lies in the amount of the formulation components, as follows: 50 parts of ethylene-vinyl acetate copolymer; 18 parts of EPDM rubber; 10 parts butyl rubber; 15 parts of AC foaming agent; 5.5 parts of 2-methylimidazole; 4 parts zinc oxide; 1.2 parts of dicumyl peroxide; 1.5 parts triallyl isocyanurate; Antioxidant 1010 0.8 parts; Heat stabilizer 1.2 parts.

[0064] Comparative Example 5 The difference between this comparative example and Example 1 lies in the amount of the formulation components, as follows: 50 parts of ethylene-vinyl acetate copolymer; 18 parts of EPDM rubber; 10 parts butyl rubber; 15 parts of AC foaming agent; 0.4 parts of 2-methylimidazole; 4 parts zinc oxide; 1.2 parts of dicumyl peroxide; 1.5 parts triallyl isocyanurate; Antioxidant 1010 0.8 parts; Heat stabilizer 1.2 parts.

[0065] Comparative Example 6 The difference between this comparative example and Example 1 is that the temperature in step S2 is controlled at 85°C.

[0066] Performance testing 1. Expansion Ratio Test: The sheets obtained in Examples 1-3 and Comparative Examples 1-6 were cut into 20 mm × 20 mm × 3 mm samples. The length, width, and thickness dimensions before foaming were recorded, and the initial volume was calculated. The samples were then placed flat in a forced-air drying oven and heated at 165°C for 25 min. After cooling to room temperature, the length, width, and thickness dimensions after foaming were measured, and the volume after foaming was calculated. The expansion ratio was calculated as the ratio of the volume after foaming to the volume before foaming. Each group underwent five parallel tests, and the average value was taken. The test results are shown in Table 1.

[0067] Table 1. Expansion Ratio Test Results

[0068] As shown in Table 1, Example 1 exhibits the highest expansion ratio. Examples 2 and 3 show slightly lower expansion levels than Example 1, but are still significantly higher than all comparative examples. This indicates that within the component relationships and process window defined in this scheme, the material has a more sufficient volume expansion capacity after heating, enabling it to better fill cavities.

[0069] 2. Staged Expansion Behavior Test: To verify the effect of this method on regulating the foaming rhythm, the samples were prepared at 20 mm × 20 mm × 3 mm and heated at 165℃ for 5 min, 10 min, 15 min, 20 min, and 25 min respectively. The volume at each time point was measured, and the expansion ratio relative to the initial volume was calculated. Each test was performed three times, and the average value was taken. This method can directly reflect the change in the volume growth rate of the material during the heating process, and can be used to determine whether there is a phenomenon of transitioning from a single rapid gas release to staged expansion. The test results are shown in Table 2.

[0070] Table 2. Results of expansion ratio detection at different time points

[0071] As shown in Table 2, the growth rate of Example 1 was relatively mild before 10 minutes, but continued to increase significantly between 10 and 20 minutes, indicating that the foaming was not completed all at once in the early stages, but rather went through a process of first establishing an initial expansion structure and then further expanding. Comparative Examples 1-6, on the other hand, mostly approached their final expansion volume within the first 10 to 15 minutes, with minimal subsequent growth, exhibiting a typical one-time rapid degassing pattern. This result directly supports the inventive point of this scheme: controlling the foaming path.

[0072] 3. Closed-cell ratio test: The foamed sample was cut into regular blocks, and its true density and apparent density were determined using the gas displacement method. The closed-cell ratio was then calculated based on these measurements. Three parallel samples were taken for each sample during the test, and the average value was recorded. A higher closed-cell ratio indicates more closed cells and more intact cell walls, which is more conducive to maintaining volume and mechanical strength. The test results are shown in Table 3.

[0073] Table 3 Results of closed-pore ratio test

[0074] Table 3 shows that the example group, especially Example 1, not only had a high expansion ratio but also a higher closed-cell ratio. This indicates that the proposed solution maintained good cell sealing and structural integrity while increasing volume. The comparative examples generally exhibited both insufficient expansion and low closed-cell ratio, indicating that a stable synergistic relationship between foaming and shaping was not established. 4. Peel Strength Test: A 2 mm thick PP sheet was used as the substrate. The sealant to be tested was attached to the surface of the substrate and heated at 165℃ for 25 min to allow it to foam and adhere to the substrate. After cooling for 24 h, a 25 mm wide peel sample was prepared and subjected to a 180° peel test on a universal testing machine at a tensile speed of 50 mm / min. The average peel force was recorded and converted into peel strength. Each test was performed 5 times, and the average value was taken. The test results are shown in Table 4.

[0075] Table 4 Peel strength test results

[0076] As shown in Table 4, Example 1 exhibits the highest expansion ratio and peel strength, followed by Example 3. Although Example 2 is near the lower limit of the parameter window, it is still superior to the comparative examples. This result indicates that this solution does not exhibit the common problems of higher expansion, looser structure, and poorer adhesion found in traditional thermal expansion systems. Instead, it achieves a simultaneous improvement in expansion and bonding strength under specific formulation and process conditions.

[0077] 5. Strength retention rate test after thermal cycling: The foamed sample bonded to the PP board was placed in a thermal cycling chamber, kept at -40℃ for 1 hour, then raised to 85℃ and kept for 1 hour, which was recorded as one cycle. A total of 50 cycles were performed. After the cycle, the sample was removed and placed at room temperature for 12 hours, and then the peel strength was measured according to the peel strength test method. The retention rate was calculated as the ratio of the peel strength after thermal cycling to the initial peel strength. The test results are shown in Table 5.

[0078] Table 5. Peel strength and retention rate after thermal cycling

[0079] As shown in Table 5, Examples 1-3 maintained a high level of interfacial bonding after thermal cycling, with Example 1 exhibiting the highest retention rate. This indicates that the bubble structure obtained by this scheme is more stable, with a more uniform internal stress distribution, which reduces crack propagation and interfacial delamination during temperature cycling. In the comparative examples, especially when the weak alkali component was excessive or insufficient, oxide synergy was lacking, or the key premixing process was not performed, the strength retention rate decreased significantly, demonstrating that the various key elements in this scheme do indeed work together to contribute to long-term stability.

[0080] 6. Compression Set Test: The foamed sample was cut into cylindrical specimens with a diameter of 29 mm and a thickness of 12.5 mm. It was compressed to 50% of its original thickness at room temperature, then kept at 70℃ for 22 h. After recovery for 30 min, the final thickness was measured and the compression set was calculated. Each test was performed three times, and the average value was taken. The lower this index, the better the skeletal support capacity of the foamed material, and the less likely it is to collapse during long-term service. The test results are shown in Table 6.

[0081] Table 6 Results of Compression Permanent Deformation Test

[0082] Table 6 further illustrates that the foamed structures formed in the example groups have greater resilience, with Example 1 showing the best performance. This is consistent with the aforementioned expansion ratio and closed-cell ratio results, meaning that the scheme forms a more complete and stable cell skeleton, rather than a loose structure obtained simply by instantaneous large-scale gas release.

[0083] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A high performance thermal expansion cavity sealing material, characterized by, It comprises the following components by weight: 40-60 parts of ethylene-vinyl acetate copolymer, The rubber elastomer comprises 10-30 parts, wherein the rubber elastomer is one or both of ethylene propylene diene monomer (EPDM) rubber and butyl rubber. 10-20 parts of AC foaming agent 0.5 to 5 parts of a weakly basic organic compound. Inorganic metal oxides 1-8 parts, Crosslinking agent 0.5-2.5 parts, Crosslinking aid 0.5-3 parts, Antioxidant 0.3–1.2 parts, Heat stabilizer 0.5–2.5 parts; The weakly basic organic compound is selected from one or two of imidazoles, fatty amines, or pyridines. The inorganic metal oxide is selected from one or two of zinc oxide, magnesium oxide, or calcium oxide.

2. The thermal expansion cavity sealing material according to claim 1, characterized in that, The weight parts M of the weakly basic organic compound B The AC foaming agent has a weight part M A The average particle size of the AC foaming agent is d. A The following relationship must be satisfied:

3. The thermal expansion cavity sealing material according to claim 1, characterized in that, The inorganic metal oxide in parts by weight M D The weight parts M of the weakly basic organic compound B And the crosslinking agent is M parts by weight. C It satisfies the following relationship: .

4. The thermal expansion cavity sealing material according to claim 1, characterized in that, The weight ratio of EPDM rubber to butyl rubber is 1:(0.3-1.5).

5. The thermal expansion cavity sealing material according to claim 1, characterized in that, The weakly basic organic compound is one or two of 2-methylimidazole, 1-methylimidazole, triethylamine, or pyridine.

6. The thermal expansion cavity sealing material according to claim 1, characterized in that, The inorganic metal oxide is zinc oxide or magnesium oxide.

7. The thermal expansion cavity sealing material according to claim 1, characterized in that, The average particle size of the AC foaming agent is 3 to 15 micrometers.

8. A method for preparing a thermal expansion cavity sealing material as described in any one of claims 1 to 7, characterized in that, Includes the following steps: S1: Add the ethylene-vinyl acetate copolymer and the rubber elastomer into the mixing equipment and mix them at 80-110℃ for 3-8 minutes; S2: Add a weakly alkaline organic compound and an inorganic metal oxide, and mix at 100-125°C for 3-8 minutes; S3: After cooling the system to 75-95℃, add AC foaming agent, crosslinking agent and crosslinking aid, mix for 2-5 minutes and then discharge to form; S4: The obtained material is heated at 140-180℃ to cause foaming and cross-linking.

9. The preparation method according to claim 8, characterized in that, The mixing temperature in step S2 is T (°C), and the weight parts M of the inorganic metal oxide are... D and the weight parts M of the weakly basic organic compound. B The following relationship must be satisfied: .

10. A cavity structure, characterized in that, The cavity structure is provided with the thermal expansion cavity sealing material according to any one of claims 1 to 7.

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