Solvent-free adhesive for flexible package printing and preparation method thereof

Abstract

The invention relates to the technical field of solvent-free adhesives, and particularly discloses a solvent-free adhesive for flexible package printing and a preparation method of the solvent-free adhesive. The invention relates to a solvent-free adhesive for flexible package printing. The solvent-free adhesive is prepared from the following raw materials in parts by weight: 45-55 parts of biopolyester; 25-30 parts of a plasticizer; 2-3 parts of an antioxidant; 1-1.5 parts of a mildew preventive; 0.2 to 0.3 part of a leveling agent; 5-10% of a filler; 0.5-5 parts of a natural extract; 4-6 parts of mica powder; 5 to 10 parts of polyethylene glycol; 2-5 parts of PE wax; the preparation method comprises the following steps: melting the biopolyester, adding the plasticizer, the filler, the natural extract, the mica powder, the polyethylene glycol and the PE wax, uniformly mixing, adding the antioxidant, the mildew preventive and the flatting agent, and uniformly mixing. The solvent-free adhesive for flexible package printing can exert remarkable and excellent stability when being applied in a cooking environment.

Description

Technical Field

[0001] This application relates to the technical field of solvent-free adhesives. More specifically, it relates to a solvent-free adhesive for flexible packaging printing and its preparation method. Background Art

[0002] In recent years, the requirements for sustainable development and environmental protection have become increasingly strong globally, driving the green development transformation of various industries. In the field of packaging materials, especially in high-end packaging applied to the medical and food industries, traditional solvent-based glues have been gradually phased out due to environmental pollution and health risks. Instead, new solvent-free glues have emerged. These products, with a smaller environmental footprint and higher hygiene standards, have become an important symbol of industry upgrading.

[0003] Solvent-free adhesives contain no organic solvents, have zero VOC emissions, and are harmless to the environment and human health. They are particularly suitable for food packaging because they do not cause problems such as the migration of volatile organic compounds (VOCs) and aromatic amines, ensuring the safety of food. Solvent-free adhesives for flexible packaging printing are mainly used in the lamination process in flexible packaging printing to bond different materials together. Their core advantages lie in environmental protection, energy conservation, and high efficiency. At the same time, polyester solvent-free adhesives have excellent bonding strength, can firmly bond various materials such as plastics, papers, metals, etc., ensuring the sealing and integrity of the packaging. They also have good chemical resistance and durability, can maintain stable performance in various environments, and are suitable for a variety of packaging requirements. Therefore, they have broad application prospects in flexible packaging printing.

[0004] Regarding the above related technologies, the inventor believes that although polyester solvent-free adhesives maintain excellent bonding performance at extremely low temperatures and can also meet the application requirements in high-temperature environments, when applied in food packaging composite films, they often inevitably need to be subjected to cooking. In this application scenario, the colloidal structure of the solvent-free adhesive is prone to significant structural damage, resulting in a significant reduction in bonding stability and even bonding failure.

[0005] Therefore, there is an urgent need to propose a solution to solve the above technical problems. Summary of the Invention

[0006] In order to improve the stability of the solvent-free adhesive in the cooking environment, this application provides a solvent-free adhesive for flexible packaging printing and its preparation method.

[0007] In the first aspect, this application provides a solvent-free adhesive for flexible packaging printing, adopting the following technical solution: A solvent-free adhesive for flexible packaging printing is made from raw materials comprising the following parts by weight: 45 - 55 parts of bio-polyester; 25 - 30 parts of plasticizer; 2 - 3 parts of antioxidant; 1 - 1.5 parts of mildew preventive; 0.2 - 0.3 parts of leveling agent; 5 - 10% of filler; 0.5 - 5 parts of natural extract; 4 - 6 parts of mica powder; 5 - 10 parts of polyethylene glycol; 2 - 5 parts of PE wax.

[0008] By adopting the above technical solutions, bio - polyester is a kind of polyester material that can be degraded by the action of natural microorganisms (such as bacteria, fungi, etc.). Usually, renewable resources such as starch, wood, vegetable oil, etc. are used as raw materials, and these raw materials come from nature. Using bio - polyester as the main raw material of the solvent - free adhesive for flexible packaging printing can not only effectively reduce the dependence on traditional petroleum resources but also have better environmental benefits. Mica powder has a layered silicate structure. During its application, the polymer will enter between the mica powder lamellae, and the mica powder dispersed in the polymer matrix also has good gas - liquid barrier properties, which can significantly improve the retort resistance of the solvent - free adhesive for flexible packaging printing; polyethylene glycol can significantly improve the thermal stability of the solvent - free adhesive, effectively prevent the decomposition of materials at high temperatures, and during the high - temperature retorting process, it can keep the solvent - free adhesive after application in better structural stability; PE wax has low volatility and will not volatilize or migrate during the high - temperature retorting process, so it can stably play its own role during the application process and improve the stability of the solvent - free adhesive during retorting; at the same time, when mica powder, polyethylene glycol, and PE wax are used in combination, they can be evenly dispersed in the polymer system of bio - polyester through mutual cooperation and form a maze structure that can effectively block gas and liquid through adhesion between each other. And this structure can stably exist at high temperatures, which can thus play an excellent protective role for bio - polyester, enabling the finally obtained solvent - free adhesive for flexible packaging printing to exhibit significantly excellent stability when applied in a retorting environment.

[0009] Preferably, the weight ratio of the mica powder, polyethylene glycol, and PE wax is 5:7:4.

[0010] By adopting the above technical solutions, when the mica powder, polyethylene glycol, and PE wax with the above weight ratio are used in combination, the structural system formed by their combination in bio - polyester is relatively uniform, and it shows good compatibility with the polymer system of bio - polyester, resulting in lower adverse effects caused by retorting, and thus obtaining a solvent - free adhesive for flexible packaging printing with better application quality in a retorting environment.

[0011] Preferably, the mica powder is composed of silicate lamellar structures with a thickness of 0.8 - 1.2 nm, a lamellar spacing of 0.9 - 2.1 nm, and a particle size of 100 - 150 μm.

[0012] By adopting the above technical solution, after the mica powder of the above specifications is applied, it can be fully dispersed in the polymer of the biodegradable polyester, and the biodegradable polyester between its own lamellae can be stably present. Moreover, after being combined with polyethylene glycol and PE wax, it can form a relatively tight and effective protection for the biodegradable polyester, and thus a solvent-free adhesive for soft packaging printing with excellent retort resistance can be obtained.

[0013] Preferably, the average molecular weight of the polyethylene glycol is 6000 - 8000.

[0014] By adopting the above technical solution, the viscosity of polyethylene glycol will first increase with the increase of the molecular weight. Polyethylene glycol with too low molecular weight has weak adhesion performance, while too high molecular weight will lead to enhanced intermolecular interaction and it is difficult to play the corresponding effect; and the structure formed by the polyethylene glycol of the above molecular weight in combination with mica powder and PE wax can show better compatibility with the biodegradable polyester, and thus the corresponding effects exerted by the compounding of mica powder, polyethylene glycol and PE wax are better.

[0015] Preferably, the melt viscosity of the PE wax is 40 - 60 cps at 140 °C.

[0016] By adopting the above technical solution, the PE wax has a molecular lubricating effect. During the application process of the PE wax of the above specifications, it can fully act between the polymer molecules of the biodegradable polyester and coordinate with mica powder and polyethylene glycol to exert excellent corresponding effects, and thus a solvent-free adhesive for soft packaging printing with better application quality in the retort environment can be obtained.

[0017] Preferably, 3 - 6 parts by weight of a functional additive are further added to the raw materials. The functional additive is composed of modified silica and modified polytetrafluoroethylene fiber, and the weight ratio of modified silica to modified polytetrafluoroethylene fiber is 1:(1.4 - 1.8); The modified silica is prepared through the following steps: Take the silica raw material and disperse it in the N-methylpyrrolidone solvent, then add γ-aminopropyltriethoxysilane. After the stirring reaction is completed, it is washed and dried to obtain the modified silica; The modified polytetrafluoroethylene fiber is prepared through the following steps: Take the polytetrafluoroethylene fiber raw material and immerse it in the ethanol solution containing rare earth element compounds. After the surface treatment is completed, it is taken out and dried to obtain the modified polytetrafluoroethylene fiber; The rare earth element compound is composed of lanthanum nitrate and cerium nitrate.

[0018] By adopting the above technical solutions, after the silica is surface-treated with γ-aminopropyltriethoxysilane, the obtained modified silica can be more uniformly dispersed in the solvent-free adhesive, and exhibits excellent binding properties with the polymer molecules therein, effectively blocking the penetration of water vapor inside the adhesive film and bringing about an improvement in the retort resistance performance; after the polytetrafluoroethylene fiber is surface-treated with rare earth elements, the obtained modified polytetrafluoroethylene fiber can exhibit better interfacial binding properties with the polymer molecules, and through the network structure formed by itself, plays a role in supporting and protecting the structure of the biodegradable polyester, thereby being able to improve the stability of the solvent-free adhesive when applied in a retort environment; when the modified silica and the modified polytetrafluoroethylene fiber are used as functional additives, they are compounded with each other, and can play an excellent synergistic effect. When the solvent-free adhesive for soft packaging printing obtained is applied in a retort environment, it can exhibit better stability. At the same time, the dot-network system formed by the cooperation of the modified silica and the modified polytetrafluoroethylene fiber in the solvent-free adhesive can form excellent complementarity with the structural system formed by the compounding of mica powder, polyethylene glycol, and PE wax in the solvent-free adhesive, and the synergistic cooperation between them also significantly improves the retort resistance performance of the solvent-free adhesive for soft packaging printing.

[0019] Preferably, the weight ratio of the modified silica to the modified polytetrafluoroethylene fiber is 1:1.6.

[0020] By adopting the above technical solutions, when the modified silica and the modified polytetrafluoroethylene fiber in the above weight ratio are used as functional additives, their mutual cooperation can exert a relatively excellent and remarkable application effect, and thus a solvent-free adhesive for soft packaging printing with better quality can be obtained.

[0021] Preferably, the filler is a composition of one or more of calcium carbonate, talcum powder, white carbon black, clay, titanium dioxide, and barium sulfate.

[0022] By adopting the above technical solutions, the use of the filler can play a role in reducing the shrinkage rate, increasing the gap filling property, and reducing the cost, and the above types of fillers are all applicable to the solvent-free adhesive for soft packaging printing and can stably exert their own excellent characteristic functions.

[0023] Preferably, the natural extract is a composition of one or more of rosin resin, terpene resin, and petroleum resin.

[0024] By adopting the above technical solutions, the above types of natural extracts can enhance the adhesion of the solvent-free adhesive, making the bonding part more firm; can also improve the fluidity of the solvent-free adhesive, making it easier to apply on the surface of the object to be bonded; at the same time, can also improve the bonding effect of the solvent-free adhesive to a certain extent in a high-temperature environment; and thus a solvent-free adhesive for soft packaging printing with excellent application quality can be obtained after application.

[0025] In a second aspect, the present application provides a method for preparing a solvent-free adhesive for flexible packaging printing, adopting the following technical solution: A method for preparing a solvent-free adhesive for flexible packaging printing includes the following steps: (1) Prepare raw materials including biodegradable polyester, plasticizer, antioxidant, mildew preventive, leveling agent, filler, natural extract, mica powder, polyethylene glycol, and PE wax according to the ratio; (2) Melt the biodegradable polyester in step (1), then add the plasticizer, filler, natural extract, mica powder, polyethylene glycol, and PE wax and mix them evenly, and then add the antioxidant, mildew preventive, and leveling agent and mix them evenly to obtain a solvent-free adhesive for flexible packaging printing.

[0026] By adopting the above technical solution, the above preparation method is simple in operation, and the raw materials are added and used step by step, which is convenient for quality control during the process, and can ensure that the raw materials can cooperate fully with each other, thereby exerting excellent effects, ensuring the obtained solvent-free adhesive for flexible packaging printing has excellent and stable quality, and the whole is also suitable for large-scale industrial production.

[0027] In summary, the present application has the following beneficial effects: 1. By the compound use of mica powder, polyethylene glycol, and PE wax in the present application, an effective gas-liquid barrier coordination structure can be formed in the polymer system of biodegradable polyester, and this structure can stably exist at high temperatures, thereby playing an excellent protective role on the biodegradable polyester, so that the finally obtained solvent-free adhesive for flexible packaging printing can exhibit remarkable stability when applied in a cooking environment; 2. The present application adds and uses a functional additive composed of modified silica and modified polytetrafluoroethylene fibers, which can effectively block the penetration of water vapor inside the adhesive film, and play a role in supporting and protecting the structure of the biodegradable polyester, and form an excellent complement with the structure system formed by the compound of mica powder, polyethylene glycol, and PE wax in the solvent-free adhesive, thereby significantly improving the retort resistance of the solvent-free adhesive for flexible packaging printing. Specific Embodiments

[0028] The present application will be further described in detail below with reference to preparation examples, examples, and comparative examples.

[0029] The raw materials used in the preparation examples, examples, and comparative examples of the present application are all commercially available except as otherwise specified.

[0030] The biodegradable polyester is purchased from Total PLA LX575 in Thailand; The plasticizer is a plasticizer derived from vegetable oil and is purchased from Adeka ADK CIZER O-180A environmentally friendly plasticizer; The antioxidant is purchased from BASF antioxidant B215; The mildew preventive is purchased as Troy Tory MICROPEL 5DIDP antibacterial and mildew preventive; The leveling agent is purchased as BYK-330 leveling agent from BYK; The filler is calcium carbonate, and the light calcium carbonate purchased from Demao Mineral Products Processing Co., Ltd. in Lingshou County has a specification of 1500 mesh; The natural extract is terpene resin, and the terpene resin purchased as Jinlin brand terpene resin T100; The silica raw material is purchased as Evonik untreated precipitated silica SIPERANT 22S; The polytetrafluoroethylene fiber raw material is purchased from Xiamen Bairun Fluorine Materials Technology Co., Ltd., and the model is BR-SF-4D.

[0031] Preparation examples of raw materials and / or intermediates Preparation example 1 A modified silica is obtained by the following steps: Take the silica raw material and disperse it in 5 times the volume of N-methylpyrrolidone solvent, then add γ-aminopropyltriethoxysilane, and after stirring and reacting at 100 r / min for 5 h, wash and dry to obtain the modified silica.

[0032] Note: The weight ratio of the above silica raw material to γ-aminopropyltriethoxysilane is 95:5.

[0033] Preparation example 2 A modified polytetrafluoroethylene fiber is obtained by the following steps: Take the polytetrafluoroethylene fiber raw material and immerse it in 10 times the volume of ethanol solution containing rare earth element compounds. After surface treatment at 35 °C for 1 h, take it out and dry it at 120 °C for 4 h to obtain the modified polytetrafluoroethylene fiber.

[0034] Note: The above rare earth element compounds are composed of lanthanum nitrate and cerium nitrate in a weight ratio of 12:15, and the concentration of the ethanol solution containing rare earth element compounds is 0.2%. Examples

[0035] Example 1 A solvent-free adhesive for soft packaging printing, the components required for its preparation and their corresponding weights are shown in Table 1, and it is obtained by the following steps: (1) Prepare raw materials including bio-polyester, plasticizer, antioxidant, mildew preventive, leveling agent, filler, natural extract, mica powder, polyethylene glycol and PE wax according to the ratio; (2)Melt the biodegradable polyester in step (1), then add a plasticizer, a filler, a natural extract, mica powder, polyethylene glycol, and PE wax and mix them evenly. Then add an antioxidant, a mildew preventive, and a leveling agent and mix them evenly to obtain a solvent-free adhesive for soft packaging printing.

[0036] Note: The mica powder is composed of silicate sheet structures with a thickness of 1 nm, a layer spacing of 1.5 nm, and a particle size of 125 μm. The average molecular weight of the polyethylene glycol is 7000. The melt viscosity of the PE wax is 50 cps at 140 °C.

[0037] Example 2-3 A solvent-free adhesive for soft packaging printing, which is different from that in Example 1 in that the components required for its preparation and their corresponding weights are shown in Table 1.

[0038] Table 1 Components required for the preparation of Examples 1-3 and their weight parts (kg / part) Component Example 1 Example 2 Example 3 Bio-polyester 50 45 55 Plasticizer 27.5 25 30 Antioxidant 2.5 2 3 Mildew-proof agent 1.25 1 1.5 Leveling agent 0.25 0.2 0.3 Filler 7.5 5 10 Natural extract 2.75 0.5 5 Mica powder 5 4 6 Polyethylene glycol 7.5 5 10 PE wax 3.5 2 5 Example 4 A solvent-free adhesive for soft packaging printing, which is different from that in Example 1 in that the total amount of mica powder, polyethylene glycol, and PE wax remains unchanged, and the weight part ratio among the three is adjusted to 5:7:4.

[0039] Example 5 A solvent-free adhesive for soft packaging printing, which is different from that in Example 1 in that the mica powder is composed of silicate sheet structures with a thickness of 0.8 nm, a layer spacing of 0.9 nm, and a particle size of 100 μm.

[0040] Example 6 A solvent-free adhesive for soft packaging printing, which is different from that in Example 1 in that the mica powder is composed of silicate sheet structures with a thickness of 1.2 nm, a layer spacing of 2.1 nm, and a particle size of 150 μm.

[0041] Example 7 A solvent-free adhesive for soft packaging printing, which is different from that in Example 1 in that the average molecular weight of the polyethylene glycol is 6000.

[0042] Example 8 A solvent-free adhesive for soft packaging printing, which is different from that in Example 1 in that the average molecular weight of the polyethylene glycol is 8000.

[0043] Example 9 A solvent-free adhesive for soft packaging printing, which is different from that in Example 1 in that the melt viscosity of the PE wax is 40 cps at 140 °C.

[0044] Example 10 A solvent-free adhesive for soft packaging printing, which is different from that of Example 1 in that the melting viscosity of the PE wax is 60 cps at 140 °C.

[0045] Example 11 A solvent-free adhesive for soft packaging printing, which is different from that of Example 1 in that 4.5 parts by weight of a functional additive is further added to the raw materials. The functional additive is composed of modified silica and modified polytetrafluoroethylene fibers in a weight ratio of 1:1.6, and the modified silica is obtained from Preparation Example 1, and the modified polytetrafluoroethylene fibers are obtained from Preparation Example 2. The functional additive is added together with mica powder, polyethylene glycol and PE wax during use.

[0046] Example 12 A solvent-free adhesive for soft packaging printing, which is different from that of Example 11 in that the added weight of the functional additive is 3 parts.

[0047] Example 13 A solvent-free adhesive for soft packaging printing, which is different from that of Example 11 in that the added weight of the functional additive is 6 parts.

[0048] Example 14 A solvent-free adhesive for soft packaging printing, which is different from that of Example 11 in that the functional additive is composed of modified silica and modified polytetrafluoroethylene fibers in a weight ratio of 1:1.4.

[0049] Example 15 A solvent-free adhesive for soft packaging printing, which is different from that of Example 11 in that the functional additive is composed of modified silica and modified polytetrafluoroethylene fibers in a weight ratio of 1:1.8.

[0050] Example 16 A solvent-free adhesive for soft packaging printing, which is different from that of Example 11 in that unmodified silica is not used in the raw materials.

[0051] Example 17 A solvent-free adhesive for soft packaging printing, which is different from that of Example 11 in that unmodified polytetrafluoroethylene fibers are not used in the raw materials.

[0052] Example 18 A solvent-free adhesive for soft packaging printing, which is different from that of Example 11 in that the modified silica is replaced with silica raw materials in equal mass.

[0053] Example 19 A solvent-free adhesive for soft packaging printing, which is different from that of Example 11 in that the modified polytetrafluoroethylene fibers are replaced with polytetrafluoroethylene fiber raw materials in equal mass.

[0054] Comparative Example Comparative Example 1 A solvent-free adhesive for flexible packaging printing, which is different from Example 1 in that mica powder and PE wax are not used in the raw materials.

[0055] Comparative Example 2 A solvent-free adhesive for flexible packaging printing, which is different from Example 1 in that polyethylene glycol and PE wax are not used in the raw materials.

[0056] Comparative Example 3 A solvent-free adhesive for flexible packaging printing, which is different from Example 1 in that mica powder and polyethylene glycol are not used in the raw materials.

[0057] Comparative Example 4 A solvent-free adhesive for flexible packaging printing, which is different from Example 1 in that mica powder is not used in the raw materials.

[0058] Comparative Example 5 A solvent-free adhesive for flexible packaging printing, which is different from Example 1 in that polyethylene glycol is not used in the raw materials.

[0059] Comparative Example 6 A solvent-free adhesive for flexible packaging printing, which is different from Example 1 in that PE wax is not used in the raw materials.

[0060] Comparative Example 7 A solvent-free adhesive for flexible packaging printing, which is different from Example 1 in that mica powder, polyethylene glycol and PE wax are not used in the raw materials.

[0061] Comparative Example 8 A solvent-free adhesive for flexible packaging printing, which is different from Example 11 in that mica powder, polyethylene glycol and PE wax are not used in the raw materials.

[0062] Performance Detection Test Test Samples: The solvent-free adhesives for flexible packaging printing obtained in Examples 1-19 were used as Test Samples 1-19, and the solvent-free adhesives for flexible packaging printing obtained in Comparative Examples 1-8 were used as Control Samples 1-8.

[0063] Test Method: The peel test is another commonly used method to evaluate the bonding strength of polyurethane adhesives. This test simulates the peel force situation in actual applications and measures the peel strength of the solvent-free adhesive. The principle is as follows: The solvent-free adhesive is applied between two specimens of the same size and bonded together. Under the action of the peel force, the maximum force value when the specimens are separated is measured, and the peel strength is calculated according to the specimen size. During the process, it is carried out according to the standard test method GB / T 2790-1995 "Test Method for 180° Peel Strength of Adhesives", and specimens are prepared and the peel test is carried out.

[0064] Take a solvent-free adhesive sample for soft packaging printing, test it according to the above method, and record the obtained peel strength as A; then place the measurement specimen prepared from the same solvent-free adhesive sample for soft packaging printing according to the above test on a high-temperature cooking test bench, cook it at a temperature of 121 °C, a relative humidity of 100%, and a steam pressure of 205 kPa for 4 h, then dry it and continue the peel test, and record the obtained peel strength as B; finally, calculate the peel strength loss rate of the solvent-free adhesive for soft packaging printing, and the peel strength loss rate = (A - B) / A. The smaller the peel strength loss rate, the better the retort resistance of the solvent-free adhesive for soft packaging printing.

[0065] After successively completing the above tests on test samples 1-19 and control samples 1-8, record the corresponding results in Table 2.

[0066] Table 2 Test results of test samples 1-19 and control samples 1-8 Combined with Example 1 and Comparative Examples 1-7 and combined with Table 2, it can be seen that by the compound use of mica powder, polyethylene glycol and PE wax, the retort resistance of the solvent-free adhesive for soft packaging printing can be significantly improved; and if any one of mica powder, polyethylene glycol and PE wax is used alone or any two are used in combination, although it can bring a reduction in the peel strength loss rate during the above test, the effect is limited, and the combination of any two can only bring a simple superposition of effects; thus, it can be seen that only when the three raw materials are used together can a significant improvement effect of 1 + 1 > 2 be brought, and then the obtained solvent-free adhesive for soft packaging printing can exhibit significantly excellent stability when applied in a cooking environment. Combined with Examples 2-4 and combined with Table 2, it can be seen that when the weight ratio of mica powder, polyethylene glycol and PE wax is 5:7:4, the corresponding effect brought by its application is better, and the solvent-free adhesive for soft packaging printing has better application quality in a cooking environment.

[0067] Combined with Example 1 and Examples 5-10 and combined with Table 2, it can be seen that mica powder is composed of silicate sheet structures with a thickness of 0.8 - 1.2 nm, the interlayer spacing is 0.9 - 2.1 nm, and the particle size is 100 - 150 μm; the average molecular weight of polyethylene glycol is 6000 - 8000; the melt viscosity of PE wax is 40 - 60 cps at 140 °C; when the raw materials of the above specifications are used, the solvent-free adhesive for soft packaging printing with better application quality in a cooking environment can be obtained.

[0068] Combined with Example 1 and Examples 11 - 15 and Table 2, it can be seen that by adding and using a functional additive composed of modified silica and modified polytetrafluoroethylene fibers, the retort resistance of the solvent-free adhesive for flexible packaging printing can be further improved. Further combined with Examples 16 - 17 and Table 2, it can be seen that if modified silica or modified polytetrafluoroethylene fibers are used alone, although it can bring an improvement in retort resistance and reduce the peel strength loss rate obtained from the above tests, the corresponding effects are extremely limited, and the sum of the improvement effects brought by each used alone is far less excellent than the combined use of the two. Thus, it can be seen that excellent synergistic effects can be exerted between modified silica and modified polytetrafluoroethylene fibers. Further combined with Examples 18 - 19 and Table 2, it can be seen that if modified silica is replaced with silica raw material in equal mass, or modified polytetrafluoroethylene fibers are replaced with polytetrafluoroethylene fiber raw material in equal mass, it will lead to an obvious loss in the retort resistance of the solvent-free adhesive for flexible packaging printing, indicating that the combination between modified silica and modified polytetrafluoroethylene fibers is irreplaceable.

[0069] This specific embodiment is only an interpretation of the present application, and it is not a limitation of the present application. Those skilled in the art can make modifications without creative contributions to this embodiment according to needs after reading this specification, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A solvent-free adhesive for flexible packaging printing, characterized in that, It is made from raw materials comprising the following parts by weight: Bio-polyester: 45 - 55 parts; Plasticizer: 25 - 30 parts; Antioxidant: 2 - 3 parts; Mildew-proof agent: 1 - 1.5 parts; Leveling agent: 0.2 - 0.3 parts; Filler: 5 - 10%; Natural extract: 0.5 - 5 parts; Mica powder: 4 - 6 parts; Polyethylene glycol: 5 - 10 parts; PE wax: 2 - 5 parts.

2. The solvent-free adhesive for flexible packaging printing according to claim 1, wherein: The weight ratio of the mica powder, polyethylene glycol and PE wax is 5:7:

4.

3. The solventless adhesive for soft package printing according to claim 1, characterized in that: The mica powder is composed of silicate lamellar structures with a thickness of 0.8 - 1.2 nm, a lamellar spacing of 0.9 - 2.1 nm, and a particle size of 100 - 150 μm.

4. The solvent-free adhesive for flexible packaging printing according to claim 1, wherein: The average molecular weight of the polyethylene glycol is 6000 - 8000.

5. The solvent-free adhesive for soft-packaging printing according to claim 1, wherein: The melt viscosity of the PE wax is 40 - 60 cps at 140 °C.

6. The solvent-free adhesive for soft packaging printing according to claim 1, wherein: A functional aid with a weight of 3 - 6 parts is also added to the raw materials. The functional aid is composed of modified silica and modified polytetrafluoroethylene fibers, and the weight ratio of the modified silica to the modified polytetrafluoroethylene fibers is 1:(1.4 - 1.8); The modified silica is obtained through the following steps: Take silica raw materials and disperse them in an N-methylpyrrolidone solvent, then add γ-aminopropyltriethoxysilane. After the stirring reaction ends, wash and dry to obtain the modified silica; The modified polytetrafluoroethylene fibers are obtained through the following steps: Take polytetrafluoroethylene fiber raw materials and immerse them in an ethanol solution containing rare earth element compounds. After completing the surface treatment, take them out and dry to obtain the modified polytetrafluoroethylene fibers; The rare earth element compounds are composed of lanthanum nitrate and cerium nitrate.

7. The solvent-free adhesive for soft-packaging printing according to claim 6, characterized in that: The weight ratio of the modified silica to the modified polytetrafluoroethylene fibers is 1:1.

6.

8. The solvent-free adhesive for soft-packaging printing according to claim 1, wherein: The filler is a composition of one or more of calcium carbonate, talc powder, white carbon black, kaolin, titanium dioxide and barium sulfate.

9. The solvent-free adhesive for soft-packaging printing according to claim 1, wherein: The natural extract is a composition of one or more of rosin resin, terpene resin and petroleum resin.

10. The preparation method of the solvent-free adhesive for flexible packaging printing according to claim 1, characterized in that: It includes the following steps: (1) Prepare raw materials including bio-polyester, plasticizer, antioxidant, mildew-proof agent, leveling agent, filler, natural extract, mica powder, polyethylene glycol and PE wax according to the ratio; (2) Melt the bio-polyester in step (1), then add the plasticizer, filler, natural extract, mica powder, polyethylene glycol and PE wax and mix them evenly, and then add the antioxidant, mildew-proof agent and leveling agent and mix them evenly to obtain a solvent-free adhesive for soft packaging printing.

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