Long-acting storage and split charging method for low-temperature hot melt adhesive

Abstract

The invention provides a long-acting storage and split charging method for low-temperature hot melt adhesive, which comprises the following steps: S1, heating the low-temperature hot melt adhesive to a molten state, quantitatively filling and sealing in a primary container; s2, standing and cooling the sealed primary container; and S3, the cooled primary container is placed in a rigid outer protection tube, the rigid outer protection tube is filled with inert gas, then a drying agent is added, and then the rigid outer protection tube is subjected to airtight sealing. After the low-temperature hot melt adhesive subpackaged and stored by the method is stored for 6 months, the NCO content of the low-temperature hot melt adhesive is kept in a range of 95%-105% of an initial value, the viscosity change does not exceed + / -10% of the initial value, the crust thickness does not exceed 1 mm, the storage life of the low-temperature hot melt adhesive is prolonged by more than 30 times from 3-5 days of a traditional subpackaging mode, and the service life of the low-temperature hot melt adhesive is prolonged. The problems of waste, unreliable performance and the like caused by too short storage period of a small-dose low-temperature hot melt adhesive are solved.

Description

Technical Field

[0001] This application belongs to the field of adhesive packaging technology, specifically relating to a method for long-term storage and packaging of low-temperature hot melt adhesive. Background Technology

[0002] Polyurethane reactive hot melt adhesives, or PUR hot melt adhesives for short, are widely used in precision bonding fields such as electronics, automotive manufacturing, medical devices, and high-end packaging due to their excellent bonding strength, heat resistance, solvent resistance, and creep resistance. Unlike traditional EVA-type hot melt adhesives that cure through physical cooling, PUR adhesives undergo an irreversible cross-linking chemical reaction between the isocyanate groups at the ends of their molecular chains and moisture in the air after heating and application, thus achieving secondary curing and forming a robust polymer network. This characteristic gives PUR adhesives excellent durability, but also makes them extremely sensitive to moisture during storage.

[0003] Currently, industrially available PUR adhesives are primarily supplied in large-capacity (e.g., 20 kg / drum) sealed metal containers, suitable for centralized, continuous production lines. However, with the manufacturing industry moving towards greater flexibility and precision, and the increasing prevalence of decentralized applications such as after-sales maintenance, research and development, and small-batch production, the market demand for small-dose, ready-to-use PUR adhesive packaging is becoming increasingly urgent. To meet this demand, the industry typically attempts to repackage PUR adhesives into plastic tubes (such as PP tubes or PPS tubes) or aluminum foil bags.

[0004] However, existing repackaging technologies have significant drawbacks: First, the barrier properties of the plastic tubes themselves are limited, failing to effectively prevent the penetration of moisture and oxygen in the long term; second, simple heat sealing or screw cap sealing cannot achieve absolute airtightness, allowing ambient moisture to slowly penetrate the packaging during storage and transportation. This causes the repackaged PUR adhesive to pre-cur within a short period (usually only 3-5 days) due to moisture absorption, manifesting as skin formation on the adhesive surface, a sharp increase in viscosity, a decrease in isocyanate group content, and eventually complete failure. This not only results in expensive adhesive waste but also seriously affects the stability of production plans and the bonding reliability of the final product, limiting the wider application of PUR adhesives. Especially for highly sensitive substances like PUR adhesives, the amount of residual water and oxygen inside the packaging, even in very small repackaging volumes, is a critical factor determining the success or failure of long-term storage. Existing technologies lack a systematic solution to provide effective protection for highly reactive PUR adhesives from repackaging to final storage, while maintaining controllable costs.

[0005] Therefore, developing a technology that enables small-dose, ultra-long shelf life, and highly reliable packaging of PUR hot melt adhesive has become a key technical challenge that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the issue of cross-linking and curing of small-volume, low-temperature hot melt adhesives during long-term storage due to residual trace amounts of moisture and oxygen in the container, this application provides a method for long-term storage and packaging of low-temperature hot melt adhesives.

[0007] In a first aspect, this application provides a method for long-term storage and packaging of low-temperature hot melt adhesive, comprising the following steps: S1: After heating the low-temperature hot melt adhesive to a molten state, it is quantitatively filled and sealed in a primary container; S2: Allow the sealed primary container to stand and cool; S3: Place the cooled primary container into the rigid outer protective tube, fill the rigid outer protective tube with inert gas, add a desiccant, and then seal the rigid outer protective tube in an airtight manner.

[0008] First, the molten adhesive is poured into a primary container and sealed. After cooling to room temperature, a rigid outer protective seal is then applied. This prevents the high-temperature adhesive vapor from causing premature desiccant deactivation within the rigid outer protective tube. Cooling before sealing prevents negative pressure from forming within the rigid outer protective tube. If the hot adhesive were directly poured into the sealed aluminum tube, cooling and shrinkage would create negative pressure, potentially drawing in external moisture through tiny gaps. This step protects the desiccant's activity and eliminates potential risks, ensuring long-term storage.

[0009] Furthermore, the low-temperature hot melt adhesive is a polyurethane reactive hot melt adhesive.

[0010] Furthermore, the heating temperature is 100-120℃.

[0011] At this temperature, ensure that the low-temperature hot melt adhesive has uniform flowability and is free of lumps.

[0012] Furthermore, the primary container is a polypropylene tube or a polyphenylene sulfide tube.

[0013] Furthermore, the filling capacity of the primary container is 20-50 mL; preferably, the filling capacity of the primary container is 30 mL.

[0014] Furthermore, the filling speed is 8-12 mL / s; preferably, the filling speed is 10 mL / s.

[0015] The purpose of controlling the filling speed is to avoid foaming, as the oxygen in the bubbles can cause the product to form a skin.

[0016] Furthermore, the settling time is 1-2 hours.

[0017] Further, cool to 22-28℃.

[0018] Cooling to 22-28℃ ensures the stability of the low-temperature hot melt adhesive.

[0019] Static cooling is used to prevent negative pressure from forming inside the aluminum tube, which would draw in trace amounts of moisture from tiny gaps or the material itself.

[0020] Furthermore, the inert gas is nitrogen with a purity of not less than 99.99%.

[0021] Furthermore, the pressure of the inert gas is 0.05-0.10 MPa; the time is 2-15 seconds.

[0022] The injection of high-purity nitrogen is used to replace the air inside the aluminum tube and eliminate water vapor interference.

[0023] Furthermore, the desiccant is an irreversible desiccant that can chemically react with water.

[0024] Furthermore, the desiccant includes, but is not limited to, calcium oxide or anhydrous calcium sulfate.

[0025] Furthermore, the amount of the desiccant used is 1.8-5g.

[0026] Desiccants are used to adsorb residual moisture.

[0027] Before sealing, high-purity nitrogen is introduced to create an inert atmosphere, and a desiccant that reacts chemically with water is added. Nitrogen replacement removes most of the free oxygen and water vapor, and the reactive desiccant irreversibly chemically captures residual moisture and any subsequent trace amounts of moisture that may seep in, thus fundamentally eliminating the two major factors that cause PUR adhesive to crosslink and cure—oxygen and water vapor.

[0028] Furthermore, the rigid outer protective tube is a metal tube; preferably, the rigid outer protective tube is an aluminum tube.

[0029] Aluminum tubes, especially those with rolled-up caps, provide a perfect barrier against moisture and oxygen. As long as the seal is intact, the external environment cannot penetrate. The seal formed by the mechanical rolling of the aluminum tube is a result of the plastic deformation of the metal, resulting in extremely high and durable airtightness. It can easily pass the 0.2MPa airtightness test. The aluminum tube provides protection for the internal PP or PPS tube primary containers, resisting pressure and impact.

[0030] Furthermore, the internal dimensions of the rigid outer protective tube are adapted to the dimensions of the primary container.

[0031] Furthermore, the inner diameter of the rigid outer protective tube is 19-23 mm larger than the outer diameter of the primary container tube.

[0032] The inner diameter of the rigid outer protective tube is 19-23 mm larger than the outer diameter of the primary container tube, which provides sufficient volume for holding a sufficient amount of desiccant.

[0033] Furthermore, the length of the rigid outer protective tube is at least 5.5 mm longer than the length of the primary container.

[0034] The rigid outer protective tube provides a longer inert gas buffer path and a larger gas capacity, forming a stable atmosphere buffer zone. This better resists pressure changes caused by temperature fluctuations and dilutes any slowly seeping impurity gases, maintaining long-term stability of the internal dew point and oxygen content. It also facilitates automated gripping and capping operations and allows for future compatibility with longer primary containers.

[0035] The rigid outer protective tube seal, combined with high-purity inert gas replacement and reactive irreversible desiccant, constitutes a dual guarantee of passive isolation and active removal of low-temperature hot melt adhesive.

[0036] Furthermore, the dimensions of the primary container are: outer diameter of the tube body 25.4-25.8 mm, length 128.2-133.0 mm.

[0037] Furthermore, the dimensions of the rigid outer protective tube are: length 138.5-141.5mm, inner diameter 45-47mm.

[0038] Furthermore, the outer wall of the primary container is provided with at least one radial protrusion; the maximum diameter of the outer edge of the radial protrusion is 0.5-1.5 mm smaller than the inner diameter of the rigid outer protective tube.

[0039] Furthermore, the radial protrusion is an annular flange or two symmetrically arranged protrusions.

[0040] Furthermore, the rigid outer protective tube is airtightly sealed by a mechanical roll-on seal.

[0041] Furthermore, the sealing cap used for mechanical crimp sealing has a concave structure that is recessed towards the inside of the rigid outer protective tube. The depth of the concave structure is consistent with the length difference between the rigid outer protective tube and the primary container. When mechanical crimp sealing is performed, the sealing cap is fastened to the rigid outer protective tube, and the bottom of the concave structure contacts the end of the primary container, applying axial pressure to the primary container; thereby preventing the primary container from axially shifting within the rigid outer protective tube after airtight sealing.

[0042] The outer diameter of the radial protrusion is 0.5-1.5 mm smaller than the inner diameter of the rigid outer protective tube. Combined with the airtight seal of the sealing cap, it applies axial pressure to the primary container. The primary container (PP / PPS tube) is inside the rigid outer protective tube (aluminum tube) and cannot shake or move axially, thus avoiding the loosening of the tube cap, failure of the seal, or stress inside the colloid caused by repeated collisions.

[0043] Furthermore, after 6 months of storage, the low-temperature hot melt adhesive packaged and stored using the aforementioned long-term storage and packaging method maintains an NCO content within the range of 95% to 105% of the initial value, a viscosity change of no more than ±10% of the initial value, and a skin thickness of no more than 1 mm.

[0044] Furthermore, the long-term storage and packaging method for the low-temperature hot melt adhesive further includes step S4 after step S3: placing the airtight, rigid outer protective tube into an outer packaging tray with at least one dividing groove; the size of the dividing groove is adapted to the size of the rigid outer protective tube.

[0045] Furthermore, the diameter of the partition groove is 47-48 mm and the depth is 141-143 mm; it is used to accommodate and fix the rigid outer protective tube.

[0046] Secondly, this application provides a low-temperature hot melt adhesive storage unit, which is prepared by the long-term storage and packaging method of the low-temperature hot melt adhesive described in the first aspect.

[0047] Furthermore, the low-temperature hot melt adhesive storage unit includes: A primary sealed container and a rigid outer protective tube are arranged from the inside out; The primary sealed container is encapsulated with low-temperature hot melt adhesive. The rigid outer protective tube is filled with inert gas and contains a desiccant, and its two ends are airtight.

[0048] Furthermore, the internal dimensions of the rigid outer protective tube are adapted to the dimensions of the primary container; the inner diameter of the rigid outer protective tube is 19-23 mm larger than the outer diameter of the primary container tube; and the length of the rigid outer protective tube is at least 5.5 mm longer than the length of the primary container. Furthermore, the dimensions of the primary container are: outer diameter of the tube body 25.4-25.8 mm, length 128.2-133.0 mm.

[0049] Furthermore, the dimensions of the rigid outer protective tube are: length 138.5-141.5mm, inner diameter 45-47mm.

[0050] Furthermore, the outer wall of the primary container is provided with at least one radial protrusion; the maximum diameter of the outer edge of the radial protrusion is 0.5-1.5 mm smaller than the inner diameter of the rigid outer protective tube.

[0051] The airtight sealing method at both ends of the rigid outer protective tube is mechanical crimp sealing; the sealing cap used for mechanical crimp sealing has a concave structure that is recessed inward towards the rigid outer protective tube. The depth of the concave structure is consistent with the difference between the length of the rigid outer protective tube and the length of the primary container. When mechanical crimp sealing is performed, the sealing cap is fastened to the rigid outer protective tube, the bottom of the concave structure contacts the end of the primary container, and applies axial pressure to the primary container.

[0052] Furthermore, the primary container is a polypropylene tube or a polyphenylene sulfide tube.

[0053] Furthermore, the filling capacity of the primary container is 20-50 mL; preferably, the filling capacity of the primary container is 30 mL.

[0054] Furthermore, the rigid outer protective tube is an aluminum tube.

[0055] Furthermore, the inert gas is nitrogen with a purity of not less than 99.99%.

[0056] Furthermore, the desiccant is an irreversible desiccant that can chemically react with water.

[0057] Furthermore, the desiccant is calcium oxide or anhydrous calcium sulfate.

[0058] Furthermore, the amount of desiccant used is 1.8-3g; preferably, the amount of desiccant used is 2g.

[0059] Furthermore, the dimensions of the rigid outer protective tube are: length 138.5-141.5mm, inner diameter 45-47mm.

[0060] Furthermore, after 6 months of storage, the NCO content of the low-temperature hot melt adhesive in the storage unit remains within the range of 95% to 105% of the initial value, the viscosity change does not exceed ±10% of the initial value, and the skin thickness does not exceed 1 mm.

[0061] Thirdly, this application provides an outer packaging tray for accommodating the low-temperature hot melt adhesive storage unit described in the second aspect, the outer packaging tray having at least one partition groove whose size is adapted to the size of the rigid outer protective tube.

[0062] Furthermore, the diameter of the partition groove is 47-48 mm and the depth is 141-143 mm; it is used to accommodate and fix the rigid outer protective tube.

[0063] Fourthly, this application provides a long-term storage system for low-temperature hot melt adhesive, including the low-temperature hot melt adhesive storage unit described in the second aspect and the outer packaging tray described in the fourth aspect.

[0064] It should be noted that the principle of the long-term storage and packaging method or the low-temperature hot melt adhesive storage unit provided in this application is universal. By adjusting the type of inert gas (such as nitrogen or argon) and the type of desiccant (such as dehydration or deoxygenation), this system can be widely used for the long-term storage of other sensitive substances that require strict isolation from moisture and oxygen, providing a reliable technical platform for the miniaturization and commercialization of high-value chemicals.

[0065] Compared with the prior art, this application includes the following beneficial technical effects: This application creates a long-term stable, ultra-low humidity inert microenvironment for PUR hot melt adhesives, which are extremely sensitive to moisture, by constructing a multi-layered synergistic protection system consisting of a rigid outer protective tube, a high-purity inert atmosphere, a reactive desiccant, and an airtight seal. PUR hot melt adhesives packaged and stored using this method maintain their key performance indicator—NCO content—within 95%-105% of their initial value after 6 months of storage, with viscosity changes not exceeding ±10%, and only trace amounts of surface skin less than 1 mm thick appearing. This represents a more than 30-fold increase in storage life compared to the traditional 3-5 days of packaging methods. It solves the problems of waste and unreliable performance caused by short storage periods for small-dose PUR hot melt adhesives, fundamentally removing obstacles to their widespread application in decentralized, flexible high-end manufacturing and maintenance scenarios.

[0066] The long-term storage and packaging method for low-temperature hot melt adhesives provided in this application not only extends the storage period of PUR hot melt adhesives, but more importantly, ensures the stability of the core performance of the adhesive throughout the entire storage period. The strict control of NCO content and viscosity means that the adhesive used at the end of the storage period has a curing speed, fluidity, and final bonding strength that are basically consistent with those at the time of manufacture. This provides a reliable guarantee for fields with extremely high requirements for process consistency, such as precision electronic assembly and high-end repair, and avoids batch quality risks caused by adhesive performance degradation.

[0067] This application achieves the fixation of internal components by using a sealing cap with a concave structure that extends inward toward the rigid outer protective tube. The maximum diameter of the radially protruding outer edge of the primary container is 0.5-1.5 mm smaller than the inner diameter of the rigid outer protective tube, and the axial pressure applied to the primary container by the sealing cap. This effectively prevents the cap from loosening or the colloid from shaking or shifting during transportation. In addition, the matching outer packaging tray divider provides precise positioning and cushioning for the rigid outer protective tube, forming a multi-layered physical protection from the inside out, further ensuring transportation safety.

[0068] The long-term storage and packaging method for low-temperature hot melt adhesive provided in this application includes clearly defined process parameters such as filling speed, temperature, pressure, time, and precise dimensional matching design, such as the dimensions of aluminum tubes and PP / PPS tubes, and outer packaging trays and aluminum tubes. These parameters provide a solid foundation for fully automated production, significantly improving product consistency and yield, and ensuring that the quality of each product meets the requirements for long-term storage.

[0069] This application utilizes a systematic combination of rigid sealed containers, a protective atmosphere, and active stabilizers (such as desiccants) to create a long-lasting and stable storage microenvironment for low-temperature hot melt adhesives, demonstrating high versatility. By simply changing the type of protective atmosphere (e.g., replacing nitrogen with argon) or the type of active stabilizer (e.g., replacing desiccant with an oxygen scavenger), this technology platform can be immediately applied to small-size, long-lasting packaging of other high-value chemicals sensitive to oxygen or moisture, such as anaerobic adhesives, high-grade synthetic lubricants, certain pharmaceutical intermediates, and photocurable prepolymers. This provides ample room for the transformation of technological achievements and the expansion of application fields.

[0070] In summary, this application provides a systematic and highly reliable solution for the long-term storage of low-temperature hot melt adhesives. It has achieved groundbreaking and beneficial effects in multiple dimensions, including storage life, performance stability, physical reliability, production efficiency, and technical versatility, and has significant industrial application value and market prospects. Attached Figure Description

[0071] The present application will be described in further detail below with reference to the accompanying drawings and preferred embodiments. However, those skilled in the art will understand that these drawings are drawn only for the purpose of explaining the preferred embodiments and therefore should not be construed as limiting the scope of this disclosure. Furthermore, unless specifically indicated, the drawings are only schematic representations of the composition or structure of the described objects and may contain exaggerated depictions, and the drawings are not necessarily drawn to scale.

[0072] Figure 1 This is a flowchart of a long-term storage and packaging method for low-temperature hot melt adhesive.

[0073] Figure 2 The images show the PP pipe before and after the flat-bottomed aluminum tube is inserted, and the aluminum tube after the airtight seal. Among them, (a) is the image of the PP pipe before the flat-bottomed aluminum tube is inserted; (b) is the image of the aluminum tube after the airtight seal. Detailed Implementation

[0074] The present invention will be further illustrated below with examples, but the implementation of this application is not limited thereto. The following embodiments should not be construed as limiting the scope of protection of this application. If those skilled in the art make some non-essential improvements and adjustments to this application based on the above content, they shall still fall within the scope of protection of this application.

[0075] Chemicals and reagents PUR hot melt adhesive: PUR3742, sourced from Huabai (Xinxing) Technology Co., Ltd.

[0076] 075-22 series desiccant: Source: Huabai (Xinxing) Technology Co., Ltd.

[0077] 065-50 series desiccant: Source: Huabai (Xinxing) Technology Co., Ltd.

[0078] 2819 series desiccant: Source: Huabai (Xinxing) Technology Co., Ltd.

[0079] Unless otherwise specified, all other reagents used in the embodiments of this application are from conventional commercially available products.

[0080] Test method: NCO content detection Instruments and equipment: 1000mL volumetric flask, 250mL conical flask, iodine flask, 5L pipette, acid burette, electric furnace, electronic balance.

[0081] Operating steps: Take samples from two iodine flasks (flask A and flask B) for parallel titration, and then take one iodine flask (flask C) for blank titration. First, dry the iodine flasks used for sampling at 120℃ (they must be completely dry). Accurately weigh 2-3g of sample (if the theoretical content of isocyanate groups is high, the sample amount can be reduced accordingly, but the sample amount should not be less than 1g). Then add the sample to flasks A and B respectively (note that the sample should not stick to the flask wall during sampling).

[0082] Add 10 mL of di-n-butylamine-toluene solution (or 20 mL if the NCO content is greater than 10%) to the sample (bottle A and bottle B), shake well to dissolve the sample, and let stand for 15–20 minutes. Alternatively, dissolve quickly by heating with an electric furnace, but do not heat to boiling; allow the NCO and dibutylamine to react completely. Add the di-n-butylamine-toluene solution directly to the blank iodine flask (bottle C), then add 30–50 mL of isopropanol. Then (bottles A, B, and C) add 4–5 drops of bromocresol green indicator and shake well. Before titration, rinse the burette three times with standard hydrochloric acid solution.

[0083] Add hydrochloric acid solution (note that there should be no air bubbles in the burette and no droplets on the burette wall), and titrate with standard hydrochloric acid solution until the solution turns yellow (and does not fade within 15 seconds) as the endpoint.

[0084] After each titration in bottles A, B, and C, the volume of hydrochloric acid standard solution consumed must be recorded.

[0085] calculate: Bottle A: NCO% = (V′ - V) A )×C×0.042 / mA ×100% Bottle B: NCO% = (V′ - V) B )×C×0.042 / m B ×100% Average NCO% = (NCO% of bottle A + NCO% of bottle B) / 2 illustrate: V′: Volume (mL) of hydrochloric acid standard solution consumed in the blank experiment. V A Volume (mL) of hydrochloric acid standard solution consumed by sample A V B Volume (mL) of hydrochloric acid standard solution consumed by sample B C: Concentration of the hydrochloric acid standard solution (mol / L) m A Mass of sample A (g) m B Mass of sample B (g) Viscosity testing Instruments and equipment: Bollerfeld high-temperature viscometer, dropper.

[0086] The test was conducted according to ASTM D3236, with test conditions of 140°C, 27# rotor, and 100 RPM. Example 1 This embodiment provides a method for long-term storage and packaging of low-temperature hot melt adhesive, such as... Figure 1 As shown, the specific steps include: S1: Heat the low-temperature PUR hot melt adhesive to 110℃ until the PUR is in a molten state. Then, fill the PP tube with an outer diameter of 25.6mm and a length of 129.2mm at a filling capacity of 30mL per tube and a filling speed of 10mL / s. Immediately seal the PP tube opening.

[0087] S2: Let the sealed PP pipe stand for 2 hours to cool to 25℃.

[0088] S3: Place the cooled PP tube into a flat-bottomed aluminum tube with an inner diameter of 46mm and a length of 140mm. Fill the aluminum tube with high-purity nitrogen (purity ≥99.99%) to displace the air inside and eliminate moisture interference. Then, add CaO desiccant at a dosage of 2g / tube to absorb residual moisture. Finally, quickly crimp and seal both ends of the aluminum tube. (The following section describes the process for sealing the aluminum tube without inserting the PP tube into the flat-bottomed aluminum tube.) Figure 1 As shown.

[0089] The airtightness of the aluminum tube must be tested to ensure that there is no leakage under a pressure of 0.2 MPa for 5 minutes.

[0090] After the aluminum tube is sealed in an airtight manner, place it into the cardboard divider slot. The single slot dimensions are: diameter 47.5mm and depth 142mm, which are adapted to the size of the aluminum tube to ensure that the aluminum tube is not squeezed, and then pack it into a cardboard box.

[0091] This application uses a different desiccant based on Example 1, and the parameters are shown in Table 1. The remaining parameters are the same as those in Example 1.

[0092] Table 1

[0093] This application tested the skinning condition, NCO content, and viscosity of the PP pipe nozzle and tail of Examples 1-5 at 1 month, 2 months, 3 months, 4 months, 5 months, and 6 months, respectively. The results are shown in Table 2.

[0094] When the nozzle of the encapsulated PUR hot melt adhesive has no skin or only a slight skin; the NCO content remains within ±5% of the initial value; and the viscosity deviates from the initial value by ≤10%, the encapsulated PUR hot melt adhesive is judged to have stable performance and meet the requirements.

[0095] Table 2

[0096] As shown in Table 2, the performance of PUR hot melt adhesive can be maintained within 3 months in all examples; the performance of PUR hot melt adhesive using 2819 series desiccant can be maintained up to 5 months, and the performance of PUR hot melt adhesive using anhydrous calcium sulfate in Example 2 and using 075-22 series desiccant in Example 3 can be maintained up to 6 months.

[0097] This application uses PPS tubes for research based on Example 2. The parameters are shown in Table 3. The remaining parameters are the same as those in Example 2.

[0098] Table 3

[0099] In this application, the crusting condition, NCO content, and viscosity of each PPS nozzle and tail section were tested in January, March, April, May, and June for Examples 6-10, respectively. The results are shown in Table 4.

[0100] Table 4

[0101] As shown in Table 4, the performance of PUR hot melt adhesive, which uses anhydrous calcium sulfate in Example 7 and 075-22 series desiccant in Example 8, can be maintained for up to 6 months.

[0102] This application uses a small-nozzle aluminum tube with a length of 225 mm and an inner diameter of 47 mm as a basis for the study in Example 2. The parameters are shown in Table 5. The other parameters are the same as in Example 2.

[0103] Table 5

[0104] In this application, the skinning condition, NCO content, and viscosity of the PP pipe nozzle and tail of each embodiment were tested at 1 month, 2 months, 3 months, 4 months, 5 months, and 6 months, respectively. The results are shown in Table 6.

[0105] Table 6

[0106] As shown in Table 6, using a small-nozzle aluminum tube with a length of 225 mm and an inner diameter of 47 mm as a rigid outer protective tube, the performance of PUR hot melt adhesive in Examples 11-15 can be maintained for 3 months; the performance of PUR hot melt adhesive using 2819 series desiccant can be maintained for up to 5 months, and the performance of PUR hot melt adhesive using anhydrous calcium sulfate in Example 12 and 075-22 series desiccant in Example 13 can be maintained for up to 6 months. This trend is consistent with the use of a flat-bottomed aluminum tube with an inner diameter of 46 mm and a length of 140 mm as a rigid outer protective tube, indicating that the rigid outer protective tube provides a longer inert gas buffer path and a larger gas capacity, forming a stable atmosphere buffer zone, resisting pressure changes caused by temperature fluctuations, and diluting impurity gases that may slowly infiltrate, maintaining the long-term stability of internal dew point and oxygen content.

[0107] Comparative Example 1 Compared with Example 1, no desiccant was added in this comparative example. In step S3, high-purity nitrogen (purity ≥99.99%) was introduced to replace the air in the aluminum tube to eliminate moisture interference. Then, a vacuum was drawn, and then the two ends of the aluminum tube were quickly rolled and sealed.

[0108] Comparative Example 2 Compared with Example 1, this comparative example performs steps S1-S2, that is, only PP tubes are used to encapsulate PUR hot melt adhesive.

[0109] Based on Example 1, this application uses an aluminum foil bag to compare with an aluminum tube. In step S3, the cooled PP tube is placed into a 230mm×100mm aluminum foil bag, and high-purity nitrogen (purity ≥99.99%) is introduced into the aluminum tube to replace the air inside the aluminum tube and eliminate water vapor interference. Then, a vacuum is drawn and then quickly sealed. The parameters are shown in Table 7. The remaining steps and parameters are the same as in steps S1 and S2.

[0110] Table 7

[0111] At 5 days, the skin formation, NCO content, and viscosity of the PP pipe nozzles and tails of each comparative sample were tested, and the results are shown in Table 8.

[0112] Table 8

[0113] As shown in Table 8, PUR hot melt adhesive encapsulated only in PP tubes and encapsulated in PP tubes with aluminum foil bags as outer protection developed severe skin crusting at the nozzle and tail within 5 days, indicating that the aluminum foil bags could not effectively block the penetration of water vapor and oxygen.

[0114] Comparative Example 2: Skin crust formation at the mouth and tail after 5 days of storage and repackaging. Figure 2 As shown, Figure 2 This indicates that using only PP tubes to encapsulate PUR hot melt adhesive resulted in severe skin formation at the nozzle and tail within 5 days.

[0115] In the specific embodiments of this application, slight skinning refers to a continuous and uniform cured skin layer formed on the surface of the colloid, with a maximum thickness of less than 0.5 mm. Under normal use conditions (i.e., unscrewing the cap and applying the colloid directly), this skin layer can be easily broken through by pressure without forming hard lumps or particles that hinder the normal extrusion of the colloid. Furthermore, the internal state of the colloid that flows out after breaking through is normal and does not affect the final bonding performance. No skinning refers to a smooth and glossy colloid surface with no visible cured film. Severe skinning refers to a thick and hard cured skin layer formed on the surface of the colloid, with a thickness exceeding 1 mm, or in the form of lumps or granules.

[0116] The present application has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present application. The descriptions of the embodiments above are only for the purpose of helping to understand the present disclosure and its core ideas. It should be noted that those skilled in the art can make several improvements and modifications to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A long-term storage and dispensing method of low-temperature hot melt adhesive, characterized in that, The method comprises the following steps: S1: heating the low-temperature hot melt adhesive to a molten state, then quantitatively filling and sealing in a primary container; S2: placing and cooling the sealed primary container; S3: placing the cooled primary container into a rigid outer protective tube, filling inert gas into the rigid outer protective tube, then adding a drying agent, and then airtight sealing the rigid outer protective tube.

2. The long-term storage and dispensing method of the low-temperature hot melt adhesive according to claim 1, characterized in that, The low-temperature hot melt adhesive is a polyurethane reactive hot melt adhesive; the heating temperature is 100-120℃; The primary container is a polypropylene tube or a polyphenylene sulfide tube; the filling capacity of the primary container is 20-50mL; the filling speed is 8-12mL / s; The standing time is 1-2 hours; the cooling temperature is 22-28℃; The inert gas is nitrogen with a purity of not less than 99.99%; the inert gas filling pressure is 0.05-0.10MPa; the time is 2-15 seconds; The drying agent is an irreversible drying agent capable of chemically reacting with water; the drying agent comprises calcium oxide or anhydrous calcium sulfate; The rigid outer protective tube is a metal tube.

3. The long-term storage and dispensing method of the low-temperature hot melt adhesive according to claim 1, characterized in that, The rigid The inner size of the rigid outer protective tube is matched with the size of the primary container; the inner diameter of the rigid outer protective tube is 19-23mm larger than the outer diameter of the primary container tube body; the length of the rigid outer protective tube is at least 5.5mm longer than the length of the primary container.

4. The long-term storage and dispensing method of the low-temperature hot melt adhesive according to claim 3, wherein, The size of the primary container is: the outer diameter of the tube body is 25.4-25.8mm, and the length is 128.2-133.0mm; the size of the rigid outer protective tube is: the length is 138.5-141.5mm, and the inner diameter is 45-47mm.

5. The long-term storage and dispensing method of the low-temperature hot melt adhesive according to claim 1, wherein, At least one radial protrusion is arranged on the outer wall of the primary container; the maximum diameter of the outer edge of the radial protrusion is 0.5-1.5mm smaller than the inner diameter of the rigid outer protective tube.

6. The long-term storage and dispensing method of the low-temperature hot melt adhesive according to claim 1, wherein, The airtight sealing mode of the rigid outer protective tube is mechanical roll-sealing; the sealing cover used for mechanical roll-sealing has a concave structure recessed towards the inner direction of the rigid outer protective tube, the depth of the concave structure is consistent with the length difference between the rigid outer protective tube and the primary container, when the mechanical roll-sealing is performed, the sealing cover is buckled on the rigid outer protective tube, the bottom of the concave structure is in contact with the end of the primary container, and the axial pressure is applied to the primary container.

7. The long-term storage and dispensing method of the low-temperature hot melt adhesive according to claim 1, wherein, The long-term storage and sub-packaging method of the low-temperature hot melt adhesive further comprises the following step S4 after step S3: placing the airtight sealed rigid outer protective tube into an outer packaging tray provided with at least one separation groove. The size of the separation groove is matched with the size of the rigid outer protective tube; the diameter of the separation groove is 47-48mm, and the depth is 141-143mm.

8. A low-temperature hot melt adhesive storage unit prepared by the long-term storage and sub-packaging method of the low-temperature hot melt adhesive according to any one of claims 1-7.

9. An overwrap tray for housing the cryogenic hot melt adhesive storage unit of claim 7, wherein, The outer packaging tray is provided with at least one separation groove; The size of the separation groove is matched with the size of the rigid outer protective tube; the diameter of the separation groove is 47-48mm, and the depth is 141-143mm.

10. A long-term storage system of low-temperature hot melt adhesive, comprising the low-temperature hot melt adhesive storage unit according to claim 8 and the outer packaging tray according to claim 9.

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