A foaming carton sealing hot melt adhesive and its preparation method

Abstract

The present invention belongs to the technical field of hot melt adhesives, and particularly relates to a foaming hot melt adhesive for sealing a box and a preparation method thereof. The present invention comprises the following raw materials in parts by weight: 10-15 parts of PVB resin, 15-20 parts of EVA resin, 5-10 parts of EVA-g-MA resin, 30-50 parts of tackifying resin, 15-25 parts of Fischer-Tropsch wax, 0.3-1 parts of antioxidant, and 1-3 parts of active silica powder. In order to further reduce the cost of use without affecting the bonding performance of the hot melt adhesive, a foaming hot melt adhesive is proposed, which significantly increases its foaming rate by adding PVB resin to the EVA hot melt adhesive system. At the same time, the overall bonding force is adjusted by compounding a certain amount of EVA-g-MA resin, so that the sealing hot melt adhesive of the present invention does not affect the bonding force on the product to be bonded, and can also greatly reduce its usage, thereby achieving the purpose of reducing the cost of the hot melt adhesive.

Description

Technical Field

[0001] The invention belongs to the technical field of hot melt adhesives, and in particular relates to a foaming box sealing hot melt adhesive and a preparation method thereof. Background Art

[0002] EVA hot-melt adhesive is a solvent-free, water-free, 100% solid, fusible polymer adhesive. It is solid at room temperature but becomes a flowable, viscous liquid upon heating. When melted, it becomes a light brown, translucent or white liquid. Its main component is a resin copolymerized under high pressure with ethylene and vinyl acetate, supplemented with tackifiers, viscosity modifiers, and antioxidants. EVA hot-melt adhesive offers strong adhesion, affordability, low pollution levels, and fast curing, making it widely used in industries such as packaging, woodworking, printing, medical, electronics, footwear, and textiles. It can be used for sealing cartons, applying labels, producing sanitary disposable medical supplies, and bonding electronic components and wood products. EVA hot-melt adhesive also offers excellent flexibility, high and low temperature resistance, and environmental friendliness, meeting green packaging and environmental standards.

[0003] EVA hot melt adhesive as a traditional carton sealing hot melt adhesive has the following disadvantages:

[0004] 1. The low temperature resistance of EVA hot melt adhesive is relatively poor;

[0005] 2. EVA hot melt adhesive has the problem of drawing during use, which seriously affects the neatness and beauty of the appearance of the sealing product;

[0006] 3. The cost of using EVA sealing glue is relatively high. Summary of the Invention

[0007] The purpose of the present invention is to provide a foaming hot melt adhesive for sealing carton and a preparation method thereof to address the comprehensive problems of the existing EVA carton sealing adhesive in the prior art, such as high cost, poor low temperature resistance, and adhesive stringing that affects the appearance.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A foaming hot melt adhesive for sealing a box comprises the following raw materials in parts by weight: 10-15 parts of PVB resin, 15-20 parts of EVA resin, 5-10 parts of EVA-g-MA resin, 30-50 parts of tackifying resin, 15-25 parts of Fischer-Tropsch wax, 0.3-1 part of antioxidant, and 1-3 parts of active silicon micropowder.

[0010] In the technical solution of the present invention, in order to further reduce the use cost without affecting the bonding performance of the hot melt adhesive, a foaming hot melt adhesive for sealing boxes is proposed. By adding PVB resin to the EVA hot melt adhesive system, its foaming rate is significantly increased. At the same time, by compounding a certain amount of EVA-g-MA resin to adjust the overall bonding strength, the hot melt adhesive for sealing boxes of the present invention does not affect the bonding strength on the products to be bonded, and can also greatly reduce its usage, thereby achieving the purpose of reducing the cost of the hot melt adhesive.

[0011] In the technical solution of the present invention, a small amount of branching (acetal between molecules) is formed in the PVB resin itself during the synthesis process, so that a small amount of PVB molecules cannot move freely when the PVB resin is melted. Therefore, when air is blown in, bubbles of various pore sizes are more likely to form. The addition of active silica powder and the PVB resin can produce a heterogeneous nucleation effect, thereby increasing the bubble density. The synergistic effect of the locked branches in the PVB and the heterogeneous nucleation of the active silica powder can significantly improve the foaming ratio.

[0012] In the technical solution of the present invention, the hydroxyl groups of the PVB resin and the side chain carboxyl groups in the EVA-g-MA resin can form strong hydrogen bonds. The EVA-g-MA resin is maleic anhydride grafted EVA, and the strong polar bonds of the strong hydrogen bonds can increase the thickness of the liquid film at the interface between the foams, making the formed foam less likely to dissipate, and thus having a good foam stabilizing effect. Furthermore, the PVB resin side chains used in the hot melt adhesive of the present invention contain highly polar hydroxyl groups, and the carboxyl groups in the EVA-g-MA resin can form strong hydrogen bonds with the surface of the bonding substrate, thereby increasing the bonding force with the substrate surface, which can effectively offset the technical defect of reduced bonding force caused by the reduced contact area between the adhesive and the substrate surface due to foaming.

[0013] In the technical solution of this invention, because PVB and EVA molecules are not completely miscible, there is a slight microscopic phase separation between the two. As a result, during the hot melt adhesive cooling process, the PVB molecules solidify preferentially from the system, allowing the adhesive strands to quickly separate from the hot melt adhesive liquid, thus enhancing the hot melt adhesive's breakage resistance. When using this hot melt adhesive, the stringing phenomenon that seriously affects the appearance of the box will not occur.

[0014] As a preferred embodiment of the present invention, the butyral content of the PVB resin is 70%-90%, and the viscosity of the PVB resin in a 5% methanol solution is in the range of 100-150 mPa.s.

[0015] In order to achieve the foaming purpose of hot melt adhesive, a large number of foaming resins were tested and it was found that PVB resin has the characteristics of high temperature solubility, its side chain has a strong polar hydroxyl group, and has a good bonding effect on various paper fiber substrates. PVB resin itself has a foam stabilizing effect and intermolecular branching can increase the formation of foams of various pore sizes.

[0016] The hot melt adhesive of this invention features a PVB resin with a moderate butyral content, exhibiting excellent low-temperature toughness. This synergistic effect, combined with a small amount of active silica powder, effectively counteracts internal silver streaks produced by low-temperature impacts, thereby enhancing the hot melt adhesive's low-temperature resistance. Furthermore, the small amount of crosslinking in the PVB resin's molecular chains effectively limits the movement of low-molecular-weight segments in the hot melt adhesive system at high temperatures, thereby enhancing the system's high-temperature resistance.

[0017] As a preferred embodiment of the present invention, the melt index of the EVA-g-MA resin at 190° C. is in the range of 100-500 g / 10 min; the vinyl acetate content is in the range of 19%-33%; and the grafting rate is in the range of 1%-3%.

[0018] In the EVA hot melt adhesive system of the present invention, when the melt mass flow rate of the EVA-g-MA resin is 100-500 g / 10 min, the fluidity is good, which is conducive to the penetration and bonding of the box sealing hot melt adhesive.

[0019] EVA with a VA content of 19-33% has good compatibility with petroleum resin and rosin, which is beneficial to the fluidity of the hot melt adhesive product. The grafting rate range is 1%-3%. Within this grafting rate range, it has good compatibility with PVB resin and has little effect on the high-temperature aging effect of the entire system.

[0020] If the ratio of PVB resin to EVA-g-MA resin is too large (over 3:1), the prepared hot melt adhesive will have a turbid appearance and the fluidity of the entire system will be poor. When the ratio of PVB:EVA is lower than 1.5:1, the compatibility of the entire system will improve, the hot melt adhesive will become very clear and transparent, and the wire breaking effect of the hot melt adhesive will become worse. In addition, the price of EVA-g-MA is relatively high, and excessive use will increase the cost of the hot melt adhesive. Therefore, as a more preferred technical solution of the present invention, the mass ratio between the PVB resin and the EVA-g-MA resin is (3-1.5):1.

[0021] As a preferred embodiment of the present invention, the EVA resin has a melt index of 50-200 g / 10 min at 190°C, and a vinyl acetate content of 19-33%. In the EVA hot melt adhesive system of the present invention, selecting an EVA resin within this range can better control the overall viscosity and compatibility of the system.

[0022] As a preferred embodiment of the present invention, the tackifying resin comprises 20-30 parts of a C5 / C9 copolymerized petroleum resin and 10-20 parts of a rosin pentaerythritol ester. The C5 / C9 copolymerized petroleum resin has a softening point of 90-110°C, while the rosin pentaerythritol ester resin also has a softening point of 90-110°C. The C5 / C9 copolymerized petroleum resin, also known as a C5 / C9 composite petroleum resin, combines the excellent properties of both C5 and C9 petroleum resins, offering superior overall performance. It has a higher iodine value than C9 petroleum resin, excellent solubility, and compatibility with both polar and non-polar polymers.

[0023] As a preferred embodiment of the present invention, the softening point temperature range of the Fischer-Tropsch wax is 80-120°C.

[0024] As a preferred embodiment of the present invention, the particle size of the active silica powder ranges from 1 to 3 μm. The active silica powder primarily enhances heterogeneous nucleation in the hot melt adhesive system of the present invention, thereby increasing the number of long bubble points in the hot melt adhesive and further improving the foaming rate. Furthermore, a small amount of silica powder can effectively disrupt the regularity of polymer crystallization, thereby reducing the low-temperature brittleness of the product.

[0025] As a preferred embodiment of the present invention, the antioxidant includes antioxidant 1010 and antioxidant 168. Antioxidant 1010 is the primary antioxidant, and 168 is the secondary antioxidant. In the hot melt adhesive system of the present invention, the antioxidant can be antioxidant 1010, or a combination of antioxidant 1010 and antioxidant 168.

[0026] In another aspect, the present invention provides a method for preparing a foaming hot melt adhesive for sealing a box, comprising the following steps:

[0027] Step 1: Add the raw materials described in claim 1 to a reactor in order, mix, heat and melt to obtain a molten mixture liquid, keep it at 130° C. to 150° C. and evacuate; specifically, the melting temperature of the reactor is 190° C., the stirring rate of the reactor is 1000 to 1200 r / h, and the vacuum pressure is -0.05 MPa to -0.08 MPa;

[0028] Specifically, the order of adding the raw materials is: first add Fischer-Tropsch wax and rosin pentaerythritol ester, then add antioxidant, PVB, EVA, EVA-g-MA after melting, and finally add C5 / C9 petroleum resin;

[0029] Step 2: Filter the molten mixture liquid in step 1, and then extrude and granulate it underwater to form hot melt adhesive particles.

[0030] Specifically, the molten mixture liquid is filtered through a double-layer filter bag with a mesh size of 200 to 400, and then discharged into a single-screw extruder for underwater granulation. The screw speed is 90 r / h to 100 r / h, the pelletizing speed is 1300 r / h to 1500 r / h, the dehydrator speed is 600 r / h to 700 r / h, the cooling water temperature is 5 to 10° C., and the screw and die head insulation temperature is 100 to 130° C.

[0031] Preferably, a water-soluble release agent is added to the cooling water, and the water-soluble release agent includes: modified water-soluble paraffin wax and modified water-soluble silicone oil.

[0032] Preferably, the amount of the water-soluble release agent is 2‰ to 5‰ of the cooling water.

[0033] The hot melt adhesive prepared by the technical solution of the present invention is compounded with PVB resin, EVA resin and EVA-g-MA resin. By further optimizing the compounding ratio, the hot melt adhesive system has foaming properties, which effectively saves the amount of hot melt adhesive during use. By compounding a certain amount of EVA-g-MA resin to adjust the overall bonding strength, the box sealing hot melt adhesive of the present invention does not affect the bonding strength on the products to be bonded and can also greatly reduce its usage.

[0034] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0035] 1. The technical solution of the present invention provides a foaming hot melt adhesive for sealing boxes. PVB resin, EVA resin, and EVA-g-MA resin are compounded. By further optimizing the compounding ratio, the hot melt adhesive system has foaming properties, effectively saving the amount of hot melt adhesive during use. By compounding a certain amount of EVA-g-MA resin to adjust the overall bonding strength, the hot melt adhesive of the present invention does not affect the bonding strength of the products to be bonded, and can also greatly reduce its usage, thereby achieving the purpose of reducing the cost of the hot melt adhesive. Compared with the hot melt adhesive of the prior art, the foaming hot melt adhesive of the present invention can seal more than twice the number of boxes at the same content.

[0036] 2. In the technical solution of the present invention, in the foaming hot melt adhesive system, the addition of active silica powder and PVB resin can produce a heterogeneous nucleation effect, thereby increasing the cell density. The side chains in PVB play an important role in locking the cells and stabilizing the foam, which significantly improves the foaming ratio.

[0037] 3. In the technical solution of this invention, because PVB resin and EVA resin are not completely miscible, there is a slight microscopic phase separation between the two. As a result, during the cooling process of the hot melt adhesive, the PVB resin solidifies first and quickly separates from the hot melt adhesive liquid, enhancing the hot melt adhesive's wire breaking performance. When using this hot melt adhesive, the appearance of the box can be ensured to be clean and beautiful. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0039] Example 1

[0040] This embodiment provides a foaming hot melt adhesive for sealing boxes, comprising the following raw materials in parts by weight:

[0041] 8 parts of PVB resin (butyral content is 85%), 20 parts of EVA resin, 10 parts of EVA-g-MA resin (including 28% vinyl acetate and 2.5% maleic anhydride grafting rate), 20 parts of Fischer-Tropsch wax, 0.5 parts of antioxidant 1010, 2.5 parts of active silica powder; 25 parts of C5 / C9 copolymer petroleum resin and 15 parts of rosin pentaerythritol ester.

[0042] The foaming hot melt adhesive for sealing is prepared as follows:

[0043] Step 1: Set the temperature of the reactor to 190° C. When the temperature of the reactor rises to 100° C., add Fischer-Tropsch wax and rosin pentaerythritol ester; control the speed of the reactor to about 1000-1200 r / h, and stir for 40-60 minutes until completely melted;

[0044] Step 2: adding antioxidant, PVB resin, EVA resin and EVA-g-MA resin into the reactor in sequence, stirring at a speed of 800-1000 r / h, and stirring and mixing for 2-2.5 hours until completely melted;

[0045] Step 3: Add C5 / C9 copolymerized petroleum resin to the reactor in step 2 and stir for 30 to 40 minutes until it is completely melted to obtain a uniformly mixed liquid. After keeping the temperature at 130 to 150° C., evacuate the mixture for 30 to 40 minutes at a vacuum pressure of -0.05 to -0.08 MPa.

[0046] Step 4: The mixture liquid of step 3 is filtered through a double-layer filter bag with a mesh size of 200 to 400, and then discharged into a single screw extruder for underwater granulation (screw speed 90 to 100 r / h, pelletizing speed 1300 to 1500 r / h, dehydrator speed 600 to 700 r / h, cooling water 5 to 10°C, and screw and die head insulation temperature 100 to 130°C).

[0047] Example 2

[0048] This embodiment provides a foaming hot melt adhesive for sealing a box, comprising the following raw materials in parts by weight: (The types of raw materials are the same as those in Example 1, the only difference being the proportions)

[0049] 10 parts of PVB resin, 20 parts of EVA resin, 10 parts of EVA-g-MA resin, 20 parts of Fischer-Tropsch wax, 0.5 parts of antioxidant 1010, 2.5 parts of active silica powder; 25 parts of C5 / C9 copolymer petroleum resin and 15 parts of rosin pentaerythritol ester.

[0050] Please refer to Example 1 for the specific preparation steps.

[0051] Example 3

[0052] This embodiment provides a foaming hot melt adhesive for sealing boxes, comprising the following raw materials in parts by weight: (The types of raw materials are the same as those in Example 1, the only difference being the proportions;)

[0053] 12.5 parts of PVB resin, 20 parts of EVA resin, 10 parts of EVA-g-MA resin, 20 parts of Fischer-Tropsch wax, 0.5 parts of antioxidant 1010, 2.5 parts of active silica powder; 25 parts of C5 / C9 copolymer petroleum resin and 15 parts of rosin pentaerythritol ester.

[0054] Please refer to Example 1 for the specific preparation steps.

[0055] Example 4

[0056] This embodiment provides a foaming hot melt adhesive for sealing a box, comprising the following raw materials in parts by weight: (The types of raw materials are the same as those in Example 1, the only difference being the proportions)

[0057] 15 parts of PVB resin, 20 parts of EVA resin, 10 parts of EVA-g-MA resin, 20 parts of Fischer-Tropsch wax, 0.5 parts of antioxidant 1010, 2.5 parts of active silica powder; 25 parts of C5 / C9 copolymer petroleum resin and 15 parts of rosin pentaerythritol ester.

[0058] Please refer to Example 1 for the specific preparation steps.

[0059] Example 5

[0060] This embodiment provides a foaming hot melt adhesive for sealing a box, comprising the following raw materials in parts by weight: (The types of raw materials are the same as those in Example 1, the only difference being the proportions)

[0061] 20 parts of PVB resin, 20 parts of EVA resin, 10 parts of EVA-g-MA resin, 20 parts of Fischer-Tropsch wax, 0.5 parts of antioxidant 1010, 2.5 parts of active silica powder; 25 parts of C5 / C9 copolymer petroleum resin and 15 parts of rosin pentaerythritol ester.

[0062] Please refer to Example 1 for the specific preparation steps.

[0063] Examples 1 to 5 mainly change the weight of PVB and compare the performance of the final hot melt adhesive.

[0064] The raw material contents of the hot melt adhesives of Examples 1 to 5 are summarized in Table 1:

[0065] Table 1 is a summary of the raw material contents of the hot melt adhesives of Examples 1-5

[0066]

[0067] 1. The hot melt adhesives of Examples 1-5 were tested for foaming rate:

[0068] The specific test method is as follows: using a FoamMelt200 foaming hot melt adhesive machine produced by Nordson Corporation of the United States, air or nitrogen is introduced to make the hot melt adhesive of the present invention become a colloid filled with small bubbles in the hot melt adhesive machine. The foaming time is 5 minutes, and then the test is carried out according to the test method.

[0069] Foaming rate test method: Heat the unfoamed hot melt adhesive to 170°C, weigh 100g with a measuring cylinder, and measure the volume V1. At the same time, foam the hot melt adhesive and let it stand for 5 minutes. When the foam stabilizes, weigh 100g with a measuring cylinder and measure the system V2. Foaming rate = (V2-V1) / V1*100%.

[0070] Wire breaking performance test method: add 100g of hot melt adhesive into a constant temperature tank (the tank is kept at 170℃), use a glass rod to pick up the liquid, the liquid is 40cm above the tank mouth, and measure the length of the wire (from the glass rod to the end of the wire) after the first drop of glue falls.

[0071] Test method for low-temperature and high-temperature resistance: Cartons are sealed on a beer production line equipped with a FoamMe1t200 foaming hot melt adhesive machine from Nordson Corporation of the United States. After sealing, the finished products are placed in a -18°C cold storage for 24 hours, and then placed in a high-temperature box at 60°C for insulation for 24 hours. The beer boxes are then torn open to observe the area of broken material.

[0072] Adhesion test method: The boxes are sealed on a beer production line equipped with a FoamMe1t 200 foaming hot melt adhesive machine from Nordson Corporation of the United States. After sealing, the finished products are kept at 25°C for 24 hours, and the tension is tested by pulling the side cover of the beer box with a tensile testing machine.

[0073] Glue transparency test: Use a glass rod to pick up the glue and visually inspect its transparency.

[0074] The hot melt adhesive foaming rate data of Examples 1-5 obtained through testing are shown in Table 2 below:

[0075] Table 2 is the hot melt adhesive foaming rate data of Examples 1-5

[0076] Example 1 Example 2 Example 3 Example 4 Example 5 Foaming rate (%) 26％ 47％ 75％ 112％ 103％

[0077] 2. Viscosity tests were performed on the hot melt adhesives of Examples 1-5 respectively:

[0078] The test method was carried out according to the method in GB / T 2794. The hot melt adhesive viscosity data obtained in Examples 1-5 are shown in Table 3 below:

[0079] Table 3 is the hot melt adhesive viscosity data of Examples 1-5

[0080]

[0081] 3. Wire breaking performance test, specific test method: test results are shown in Table 4:

[0082] Table 4 shows the performance data of the hot melt adhesive broken wires in Examples 1-5.

[0083]

[0084] 4. Low temperature and high temperature resistance: Specific test methods, test data table 5:

[0085] Table 5 shows the high and low temperature resistance data of the hot melt adhesives of Examples 1-5.

[0086]

[0087]

[0088] 5. Adhesion performance test: Specific test method, test data table 6:

[0089] Table 6 is the hot melt adhesive bonding test data of Examples 1-5

[0090]

[0091] Testing of various properties of the hot melt adhesive samples prepared in Examples 1-5 above revealed that as the amount of PVB used increased, the hot melt adhesive's foaming rate and viscosity gradually increased. This is primarily due to the branched structure in the PVB, which stabilizes the movement of the PVB molecular chains, stabilizing and locking the bubbles, and promoting heterogeneous nucleation and foam generation. In Examples 1-4, increasing the PVB content significantly improved the hot melt adhesive's filament breaking performance. This is primarily due to the increasing amount of PVB, which gradually deteriorates the compatibility of the system. As the hot melt adhesive cools, the PVB branched structure solidifies, causing microscopic phase separation in the hot melt adhesive system and breaking the hot melt adhesive filaments.

[0092] After the hot melt adhesive was used to seal the cartons in Examples 1-4, its high-temperature and low-temperature resistance gradually improved. This was mainly due to the addition of an appropriate amount of PVB. The hydroxyl groups in the PVB could form hydrogen bonds with the paper, enhancing the bonding effect. However, in Example 5, a large area of peeling occurred. This was mainly because the excessive addition of PVB caused a sharp change in the compatibility of the entire system, resulting in a significant increase in the viscosity of the hot melt adhesive, poor fluidity, and inability to penetrate the pores of the carton during sealing. As can be seen from Table 6, the foaming rate of the hot melt adhesive samples in Examples 1-4 increased, the amount of hot melt adhesive used decreased, but the bond strength with the carton increased. This is mainly because the increased PVB content and the increase in the number of hydrogen bonds caused the increase in bond strength, which effectively offset the decrease in bonding caused by the reduction in contact area.

[0093] Example 6

[0094] In order to study the interaction between active silica powder and PVB resin, the following hot melt adhesive samples, Example 6-1 to Example 6-5, were prepared by varying the weight fraction of active silica powder. The specific raw material contents are summarized in Table 7:

[0095] Table 7 is a summary of raw materials for Example 6-1 to Example 6-5

[0096]

[0097] The foaming rate of the hot melt adhesive samples was tested; the test results are summarized in Table 8:

[0098] Table 8 is the foaming performance table of the hot melt adhesive samples of Example 6-1 to Example 6-5

[0099] Example 6-1 Example 6-2 Example 6-3 Example 6-4 Example 6-5 Foaming rate (%) 85％ 98％ 103％ 112％ 110％

[0100] The present invention also conducted a low temperature resistance test on the hot melt adhesive samples of the above embodiment. The specific test method is shown in Table 9:

[0101] Table 9 is a table showing the low temperature resistance of the hot melt adhesive samples of Examples 6-1 to 6-5.

[0102]

[0103] From the data in Table 8, it can be seen that the addition of silica powder has a certain auxiliary effect on improving the foaming rate of the hot melt adhesive. When the silica powder is added to a certain amount, its effect on the foaming rate tends to be stable because the marginal effect of heterogeneous nucleation in the system is decreasing. At the same time, with the increase of silica powder content, its low-temperature adhesion also increases to a certain extent. However, when it increases to 4%, its low-temperature resistance decreases. This is mainly because as the silica powder content increases, the silica powder partially agglomerates, causing microscopic phase separation, reducing the fluidity of the adhesive, increasing the low-temperature brittleness of the hot melt adhesive, and thus worsening the adhesion.

[0104] Example 7

[0105] To adjust the overall adhesion of the system, a certain amount of EVA-g-MA resin was compounded. Furthermore, the present invention further investigated the regulatory effect of the EVA-g-MA resin and its ratio to PVB resin on the adhesive properties of the hot melt adhesive system. To compare the optimal compounding ratio, hot melt adhesives containing different amounts of EVA-g-MA resin were tested for adhesion, post-sealing peel strength, and wire breakage. The specific test results are shown below:

[0106] Specifically, the following hot melt adhesive samples Example 7-1 to Example 7-5 were prepared;

[0107] Table 10 is the ingredient list of the hot melt adhesive samples of Examples 7-1 to 7-5

[0108]

[0109] Examples 7-1 to 7-6 provide hot melt adhesive samples containing different ratios of PVB resin and EVA-g-MA resin to investigate their effects on the hot melt adhesive system. The following performance tests were performed on the hot melt adhesive samples of Examples 7-1 to 7-6:

[0110] Table 11 is a summary of the properties of the hot melt adhesive samples of Examples 7-1 to 7-5

[0111]

[0112] Table 11 shows that when the ratio of PVB:EVA-g-MA is greater than 3:1, the compatibility of the entire hot melt adhesive system is poor, the viscosity of the hot melt adhesive is relatively high, the fluidity of the hot melt adhesive is poor, and the curing speed is very fast. The hot melt adhesive does not have time to penetrate into the interior of the corrugated paper to form an effective physical bond, resulting in poor bonding strength. When PVB:EVA-g-MA=3-1.5:1, the compatibility of the hot melt adhesive changes significantly, from slightly turbid and translucent to transparent. This is mainly because EVA-g-MA plays a solubilizing role in the system, which gradually improves the compatibility of the system. When the PVB:EVA-g-MA ratio reaches 1.875:1, the length of the hot melt adhesive string is only 15 cm. This liquid is similar to a Bingham fluid, and its string has good retraction properties, so that when 2-3 drops are dropped with a glass rod, the string is basically invisible. When the amount of EVA-g-MA continues to increase, the compatibility of the system becomes very good, and the hot melt adhesive's filament breaking property becomes worse. When PVB:EVA-g-MA=1.25:1, its tensile strength value decreases instead. This is mainly because after the amount of EVA-g-MA is greatly increased, the viscosity increases, the hot melt adhesive's fluidity deteriorates, and its physical anchoring bonding effect deteriorates.

[0113] Example 8

[0114] This embodiment provides a foaming hot melt adhesive for sealing boxes, comprising the following raw materials in parts by weight:

[0115] 15 parts of PVB resin (butyral content is 70%), 20 parts of EVA resin, 10 parts of EVA-g-MA resin (including 33% vinyl acetate and 2.5% maleic anhydride grafting rate), 20 parts of Fischer-Tropsch wax, 0.5 parts of antioxidant 1010, 2 parts of active silica powder; 25 parts of C5 / C9 copolymer petroleum resin and 15 parts of rosin pentaerythritol ester.

[0116] The raw material ratios of this embodiment are consistent with those of embodiment 7-5, with the only difference being the change in the butyral content of the PVB resin and the vinyl acetate content and grafting rate of the EVA-g-MA resin.

[0117] Example 9

[0118] This embodiment provides a foaming hot melt adhesive for sealing boxes, comprising the following raw materials in parts by weight:

[0119] 15 parts of PVB resin (butyral content is 90%), 20 parts of EVA resin, 10 parts of EVA-g-MA resin (including 33% vinyl acetate and 2.5% maleic anhydride grafting rate), 20 parts of Fischer-Tropsch wax, 0.5 parts of antioxidant 1010, 2 parts of active silica powder; 25 parts of C5 / C9 copolymer petroleum resin and 15 parts of rosin pentaerythritol ester.

[0120] Example 10

[0121] This embodiment provides a foaming hot melt adhesive for sealing boxes, comprising the following raw materials in parts by weight:

[0122] 15 parts of PVB resin (butyral content is 80%), 20 parts of EVA resin, 10 parts of EVA-g-MA resin (including 33% vinyl acetate and 1.0% maleic anhydride grafting rate), 20 parts of Fischer-Tropsch wax, 0.5 parts of antioxidant 1010, 2 parts of active silica powder; 25 parts of C5 / C9 copolymer petroleum resin and 15 parts of rosin pentaerythritol ester.

[0123] Example 11

[0124] This embodiment provides a foaming hot melt adhesive for sealing boxes, comprising the following raw materials in parts by weight:

[0125] 15 parts of PVB resin (butyral content is 80%), 20 parts of EVA resin, 10 parts of EVA-g-MA resin (including 33% vinyl acetate and 3.0% maleic anhydride grafting rate), 20 parts of Fischer-Tropsch wax, 0.5 parts of antioxidant 1010, 2 parts of active silica powder; 25 parts of C5 / C9 copolymer petroleum resin and 15 parts of rosin pentaerythritol ester.

[0126] Example 12

[0127] This embodiment provides a foaming hot melt adhesive for sealing boxes, comprising the following raw materials in parts by weight:

[0128] 15 parts of PVB resin (butyral content is 80%), 20 parts of EVA resin, 10 parts of EVA-g-MA resin (including 19% vinyl acetate and 1.0% maleic anhydride grafting rate), 20 parts of Fischer-Tropsch wax, 0.5 parts of antioxidant 1010, 2 parts of active silica powder; 25 parts of C5 / C9 copolymer petroleum resin and 15 parts of rosin pentaerythritol ester.

[0129] Example 13

[0130] This embodiment provides a foaming hot melt adhesive for sealing boxes, comprising the following raw materials in parts by weight:

[0131] 15 parts of PVB resin (butyral content is 80%), 20 parts of EVA resin, 10 parts of EVA-g-MA resin (including 19% vinyl acetate and 3.0% maleic anhydride grafting rate), 20 parts of Fischer-Tropsch wax, 0.5 parts of antioxidant 1010, 2 parts of active silica powder; 25 parts of C5 / C9 copolymer petroleum resin and 15 parts of rosin pentaerythritol ester.

[0132] Among them, the ingredient lists of Examples 8 to 12 are summarized in Table 12:

[0133] Table 12 is a summary of the ingredient list of Examples 8 to 12

[0134]

[0135] The hot melt adhesive samples of Examples 8-12 were tested for foaming rate and adhesive properties. The specific test results are shown in Table 13:

[0136] Table 13 shows the foaming rate and bonding performance test data of the hot melt adhesive samples of Examples 8-12

[0137]

[0138] The data in Table 13 show that, comparing Examples 8 and 9, increasing the butyral group content increases the viscosity of the hot melt adhesive, while simultaneously increasing its expansion ratio and decreasing its tensile test value. This is primarily because, as the acetal group content increases, the acetal groups in the PVB molecules rapidly increase, creating more branched structures. This increases the viscosity of the hot melt adhesive, improves foam stabilization during the foaming process, and increases the expansion ratio. Increasing the acetal content reduces the number of hydroxyl groups in the PVB, resulting in fewer hydrogen bonds and, consequently, lower tensile strength. Comparing Examples 10 and 11, it can be seen that within the 1-3% grafting ratio, increasing the grafting ratio and decreasing the viscosity leads to greater tensile strength when the hot melt adhesive is bonded to a carton. This is primarily because a higher grafting ratio increases the proportion of carboxyl groups in the MA, thereby forming more hydrogen bonds with the paper surface and, consequently, better adhesion. A comprehensive comparison of Examples 10, 11, 12, and 13 reveals that a VA content within the 19-28% range has minimal effect on the adhesive strength, expansion ratio, and viscosity of the hot melt adhesive. Therefore, the acetal content of PVB and the MA grafting rate in EVA-g-MA given in the patent of this invention have an impact on each other. To achieve ideal sealing performance, these two key parameters need to be comprehensively considered.

[0139] Comparative Example 1

[0140] This comparative example provides a hot melt adhesive, comprising the following raw materials in parts by weight:

[0141] Referring to the raw material ratio of Example 7-5, other ingredients remain unchanged, and only the PVB resin is replaced with SIS (styrene-butadiene rubber, S segment <20%).

[0142] Comparative Example 2

[0143] This comparative example provides a hot melt adhesive, comprising the following raw materials in parts by weight:

[0144] The raw material ratio of reference example 7-5 remains unchanged, and only the PVB resin is replaced with POE (melt index: 30-50 (190° C.).

[0145] Comparative Example 3

[0146] This comparative example provides a hot melt adhesive, comprising the following raw materials in parts by weight:

[0147] Referring to the raw material ratio of Example 7-5, other things remain unchanged, only the EVA-g-MA resin is replaced by EVA-Cl (chlorinated EVA, chlorination value: 18-24%, VA content 19-33%).

[0148] Table 14 is a list of hot melt adhesive samples for comparative examples 1-3.

[0149]

[0150] The hot melt adhesive samples of Comparative Examples 1-3 were subjected to the following performance tests. The test results are shown in Table 15 below:

[0151] Table 15 shows the performance data of hot melt adhesive samples

[0152]

[0153] The comparative examples above show that the foaming rate of the SIS (S segment <20%) hot melt adhesive used in Comparative Example 1 is significantly lower than that of the hot melt adhesive using PVB resin. Furthermore, its viscosity is relatively high, its peel strength is relatively weak, and its stringing is abnormally severe. This is primarily because the addition of SIS (styrene-isoprene-styrene (SIS) block copolymer) prolongs the open time of the hot melt adhesive, requiring longer curing time. Consequently, SIS cannot nucleate during the foaming process, which also causes more stringing. Comparative Example 2 uses POE, which has relatively good foaming and string breaking performance, but poor peel strength. This is primarily because POE, a non-polar polymer, cannot form polar or hydrogen bonds with the paper surface, resulting in reduced peel strength. Comparative Example 3 uses chlorinated EVA, which is much less polar than EVA-MA, resulting in a poorer solubilization effect, increased viscosity, and a lack of chlorine atoms to form hydrogen bonds with the substrate, thus reducing the adhesive's adhesion.

[0154] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A foaming hot melt adhesive for sealing a box, characterized in that: The invention comprises the following raw materials in parts by weight: 10-15 parts of PVB resin, 15-20 parts of EVA resin, 5-10 parts of EVA-g-MA resin, 30-50 parts of tackifying resin, 15-25 parts of Fischer-Tropsch wax, 0.3-1 parts of antioxidant, and 1-3 parts of active silica powder; The butyral content of the PVB resin is 70%-90%; The vinyl acetate content in the EVA-g-MA resin is in the range of 19%-33%, and the grafting rate is in the range of 1%-3%; The mass ratio between the PVB resin and the EVA-g-MA resin is (3-1.5):

1.

2. The foaming hot melt adhesive for sealing a box according to claim 1, characterized in that: The viscosity of the PVB resin in a 5% methanol solution ranges from 100 to 150 mPa.s.

3. The foaming hot melt adhesive for sealing a box according to claim 2, characterized in that: The melt index of the EVA-g-MA resin at 190° C. ranges from 100 to 500 g / 10 min.

4. The foaming hot melt adhesive for sealing a box according to claim 1, characterized in that: The melt index of the EVA resin at 190° C. is in the range of 50-200 g / 10 min. The vinyl acetate content in the EVA resin is in the range of 19-33%.

5. The foaming hot melt adhesive for sealing a box according to claim 1, characterized in that: The tackifying resin comprises 20-30 parts of C5 / C9 copolymerized petroleum resin and 10-20 parts of rosin pentaerythritol ester; the softening point temperature range of the C5 / C9 copolymerized petroleum resin is 90-110°C, and the softening point temperature range of the rosin pentaerythritol ester resin is 90-110°C.

6. The foaming hot melt adhesive for sealing a box according to claim 1, characterized in that: The softening point temperature range of the Fischer-Tropsch wax is 80-120°C.

7. The foaming hot melt adhesive for sealing a box according to claim 1, characterized in that: The particle size of the active silicon powder is in the range of 1-3 μm.

8. The foaming hot melt adhesive for sealing a box according to claim 1, characterized in that: The antioxidants include antioxidant 1010 and antioxidant 168.

9. A method for preparing the foaming hot melt adhesive for sealing box according to any one of claims 1 to 8, characterized in that: The steps include: Step 1, adding the raw materials described in claim 1 to a reactor in order, mixing, heating and melting to obtain a molten mixture liquid, keeping the temperature at 130° C. to 150° C. and evacuating the mixture; the order of adding the raw materials is as follows: first adding Fischer-Tropsch wax and rosin pentaerythritol ester, then adding antioxidant, PVB, EVA, EVA-g-MA after melting, and finally adding C5 / C9 copolymer petroleum resin; Step 2: Filter the molten mixture liquid in step 1, and then extrude and granulate it underwater to form hot melt adhesive particles, wherein the molten mixture liquid is filtered through a double-layer filter bag with a mesh size of 200 to 400, and then discharged into a single-screw extruder for extrusion and underwater granulation, wherein the screw speed is 90 r / h to 100 r / h, the pelletizing speed is 1300 r / h to 1500 r / h, the dehydrator speed is 600 r / h to 700 r / h, the cooling water temperature is 5 to 10°C, and the screw and die head insulation temperature is 100 to 130°C.

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