Aromatic primary amine-free two-component composite adhesive for food packaging

Abstract

The invention belongs to the technical field of food packaging materials, and particularly relates to a two-component composite adhesive for food packaging without aromatic primary amine. The raw materials of the adhesive comprise an adhesive A and an adhesive B which are prepared independently and mixed during use, the adhesive A comprises polyether polyol, castor oil, diphenylmethane diisocyanate and hexamethylene diisocyanate, the adhesive B comprises polyester polyol, bisphenol A type polyether polyol, dipropylene glycol and epoxy resin, the NCO value of the adhesive A is 13.5 + / -0.5, the NCO value of the adhesive B is 13.5 + / -0.5, and the NCO value of the adhesive B is 13.5 + / -0.5. And the viscosity of the glue B at 25 DEG C is 800 to 1200 mPa.S. The beneficial effects of the invention at least comprise the following two points. First, when the adhesive is applied to the food packaging composite material, the basic physical and chemical properties are qualified, and the adhesive also has the outstanding advantage of no aromatic primary amine. And secondly, the preparation method and the use method of the adhesive are relatively simple and efficient, and the material cost is relatively low.

Description

Technical Field

[0001] This application belongs to the field of food packaging materials technology, and in particular relates to a two-component composite adhesive for food packaging that does not contain aromatic primary amines. Background Technology

[0002] Commonly used two-component composite adhesives in the food packaging industry mainly consist of a base agent and a curing agent, which is the meaning of the term "two-component" mentioned above. Generally, the main component of the base agent can be isocyanate, while the curing agent mainly includes polyols and curing resins.

[0003] On the other hand, one of the typical representatives of the above-mentioned isocyanates is diphenylmethane diisocyanate (MDI), which, when used in combination with polyether polyols and epoxy resins, can produce aromatic polyurethane adhesives.

[0004] The main advantages of the above-mentioned aromatic polyurethane adhesives in the food packaging field are: high bonding strength, good flexibility, outstanding folding resistance, excellent chemical resistance, and adaptability to different production process conditions.

[0005] For example, Chinese invention patent application CN109054723A, published on December 21, 2018, discloses a solvent-free adhesive resistant to boiling. Its raw material composition includes an isocyanate component and a curing agent. The former includes isocyanate, polyether polyol, and castor oil, while the latter includes epoxy resin, alkanolamine, polyether polyol, and castor oil.

[0006] The solvent-free adhesive in this patent application is the aforementioned two-component composite adhesive. Its main advantage is that the interpenetrating network formed between the polyurethane molecular chains and the epoxy resin molecular chains improves the adhesive's resistance to boiling.

[0007] However, in practical use, this solvent-free adhesive still has at least the following shortcomings in practicality and safety, specifically:

[0008] Due to aging, hydrolysis, and incomplete reactions, this solvent-free adhesive releases relatively more aromatic primary amines during use. These compounds may be harmful to the human body or even carcinogenic.

[0009] The main reason for this is that the residual, unreacted isocyanate groups in aromatic polyurethanes are prone to decomposition reactions, further generating aromatic primary amines. Summary of the Invention

[0010] This application provides a two-component composite adhesive for food packaging that does not contain aromatic primary amines. The technical problem to be solved is: how to make aromatic polyurethane adhesives, when used in the food packaging field, have the outstanding advantage of not containing aromatic primary amines while ensuring basic performance.

[0011] The technical solution adopted by this application to solve the above problems is: a two-component composite adhesive for food packaging that does not contain aromatic primary amines. The raw material composition includes A glue and B glue, which are prepared independently and mixed during use. The A glue includes polyether polyol, castor oil, diphenylmethane diisocyanate, and hexamethylene diisocyanate. The B glue includes polyester polyol, bisphenol A type polyether polyol, dipropylene glycol, and epoxy resin. The NCO value of the A glue is 13.5±0.5, and the viscosity of the B glue at 25°C is 800-1200 mPa·s.

[0012] A further preferred technical solution is that the NCO value of the A adhesive is adjusted by hexamethylene diisocyanate, and the viscosity of the B adhesive is adjusted by the bisphenol A type polyether polyol.

[0013] A further preferred technical solution is that the preparation method of the A-type adhesive includes the following steps in sequence:

[0014] S1. First, add the polyether polyol and castor oil to the dry reaction vessel, then heat to 110-120℃, then evacuate, and finally keep under vacuum for 1-2 hours.

[0015] S2. The reactor is kept under vacuum and cooled to 65-70°C. Then the diphenylmethane diisocyanate is added, and finally the temperature is raised to 80-85°C. The reaction is carried out for 2-3 hours.

[0016] S3. Add the hexamethylene diisocyanate to the reactor in batches, measuring the NCO value after each addition, until the NCO value is 13.5±0.5;

[0017] S4. The reactor is cooled to 40-45°C, and finally the discharge is opened to obtain the A-type adhesive.

[0018] A further preferred technical solution is that the preparation method of the B-type adhesive includes the following steps in sequence:

[0019] T1. First, add the polyester polyol, dipropylene glycol, and epoxy resin to the reactor, then heat to 110-115℃ and keep warm.

[0020] T2. The reactor is first evacuated, and then stirred for 1-2 hours;

[0021] T3. Add the bisphenol A type polyether polyol to the reactor in batches, stirring for 0.5 h after each addition, and then measure the viscosity until the viscosity at 25°C is 800-1200 mPa·s.

[0022] T4. The reactor is cooled down, and finally the discharge is opened to obtain the B-type adhesive.

[0023] A further preferred technical solution is that the A-type adhesive comprises the following components by weight:

[0024] 28-48 parts of polyether polyol

[0025] 8-15 parts castor oil

[0026] 5-25 parts of diphenylmethane diisocyanate

[0027] 30-52 parts of hexamethylene diisocyanate;

[0028] The B-type adhesive comprises the following components by weight:

[0029] 60-70 parts of polyester polyol

[0030] 12-18 parts of bisphenol A type polyether polyol

[0031] 2-15 parts of dipropylene glycol

[0032] 10-15 parts epoxy resin.

[0033] A further preferred technical solution is that the B-type adhesive also includes a UV stabilizer and an antioxidant.

[0034] A further preferred technical solution is that the method of using the adhesive includes the following steps in sequence:

[0035] P1. Mixing: Mix A and B glue in a weight ratio of 100:(50-55) and mix thoroughly.

[0036] P2. Coating: Applying a coating to any one of the following materials: aluminum foil, metallized film, PP, PE, and PET, to form a coating layer. The coating amount is 2.2-2.8 g / m². 2 ;

[0037] P3. Pressing: Press aluminum foil, aluminized film, PP, PE, and PET onto the coating to obtain a composite material;

[0038] P4. Curing: The composite material is heated for 2-4 hours to obtain the food packaging composite material. When the number of aluminum foil layers in the food packaging composite material is 1 or 2, the curing temperature is 70-75℃ and the curing time is 4 hours. When the number of aluminum foil layers is 0, the curing temperature is 60-75℃ and the curing time is 2-4 hours.

[0039] A further preferred technical solution is that the ultraviolet stabilizer is a benzophenone-based ultraviolet absorber, and its weight is 0.3-0.5% of the total weight of the B-type raw material.

[0040] A further preferred technical solution is that the antioxidant is a heat-resistant hindered phenolic antioxidant.

[0041] A further preferred technical solution is that the A glue and / or B glue also include a coupling agent.

[0042] In this application, the "free of aromatic primary amines" characteristic of the two-component composite adhesive refers to the following: according to the national standard GB 4806.15-2024, the total amount of aromatic primary amine migration is ≤0.01 mg / kg, which meets the requirement of "not detectable" and can be considered as "free of aromatic primary amines". Specifically, the detection method refers to GB 31604.52.

[0043] Furthermore, this two-component composite adhesive is used inside the food packaging composite material as an adhesive between the single-layer film materials of the aforementioned composite material. The single-layer film material refers to any one of the aforementioned aluminum foil, metallized film, PP, PE, and PET. Generally, the food packaging composite material comprises 2-3 layers of the aforementioned single-layer film material.

[0044] The main reasons why this two-component composite adhesive has the advantage of being "free of aromatic primary amines" are as follows:

[0045] First, the formulations of adhesives A and B are optimized to ensure that all isocyanate groups in the formulation react fully, reducing the presence of free isocyanate groups. Specifically, the ratio of polyol to isocyanate is adjusted, meaning the NCO value of adhesive A corresponds to the number of isocyanate groups, and the viscosity of adhesive B corresponds to the number of hydroxyl groups.

[0046] When the NCO value of adhesive A is 13.5±0.5 and the viscosity of adhesive B at 25℃ is 800-1200 mPa·s, the maximum reaction ratio of isocyanate groups is reached, meaning the number of free isocyanate groups is minimized. Generally, bound isocyanate groups only react to form aromatic primary amines under conditions such as ultraviolet light and humidity; the former corresponds to aging, and the latter to hydrolysis. Free isocyanate groups, however, can readily generate aromatic primary amines, and this is even more readily, frequently, and abundantly under the aforementioned conditions of ultraviolet light and humidity.

[0047] Secondly, in the above-mentioned method of using this adhesive, the "P4, curing" step is different from the existing common drying step, the former has a higher temperature and a longer holding time.

[0048] The curing step is similar to the drying step described above in that it can improve the crosslinking degree and reaction completeness of the adhesive. The difference is that the curing step in this application can also fully and appropriately remove trace amounts of moisture from the adhesive, reduce the probability and extent of the isocyanate groups undergoing the above-mentioned hydrolysis reaction, and greatly reduce the risk of hydrolysis and the generation of aromatic primary amines.

[0049] Third, the ultraviolet stabilizer and antioxidants mentioned above in this application can comprehensively improve the weather resistance of the adhesive, making the aging reaction and hydrolysis reaction relatively difficult to occur.

[0050] Importantly, the UV stabilizers and antioxidants mentioned above are all heat-resistant to ensure that the "P4, curing" steps will not cause the UV stabilizers and antioxidants to become less effective or ineffective.

[0051] More importantly, the heating environment of 70-75℃ or 60-75℃ in the "P4, Curing" step can make the UV stabilizer and antioxidant disperse more quickly and evenly in the adhesive material system, ultimately improving the overall performance.

[0052] Fourth, the aforementioned diphenylmethane diisocyanate is a relatively traditional aromatic isocyanate, but the aforementioned hexamethylene diisocyanate is a more stable aliphatic isocyanate. The latter partially replaces the former. The latter does not generate aromatic primary amines after hydrolysis, which can significantly reduce the risk of generating aromatic primary amines, and will not significantly reduce the basic physicochemical properties of the adhesive.

[0053] The beneficial effects of this application include at least the following two points.

[0054] First, when this adhesive is used on food packaging composite materials, its basic physicochemical properties are qualified, and it also has the outstanding advantage of not containing aromatic primary amines.

[0055] Secondly, the preparation and application methods of this adhesive are relatively simple and efficient, and the material cost is relatively low. Attached Figure Description

[0056] Figure 1 This is the cover of the test report for the food packaging composite material in Example 1 of this application.

[0057] Figure 2 This is one-third of the above test report.

[0058] Figure 3 This is page 2 / 3 of the aforementioned test report.

[0059] Figure 4 This is page 3 / 3 of the aforementioned test report. Detailed Implementation

[0060] The following description is merely a preferred embodiment of this application and is not intended to limit the scope of this application.

[0061] Example 1

[0062] A two-component composite adhesive for food packaging that does not contain aromatic primary amines, comprising separately prepared A-adhesive and B-adhesive, which are mixed during use.

[0063] Specifically, the raw material composition of Glue A includes the following components by weight:

[0064] 35.5 parts of polyether polyol

[0065] 10.5 parts castor oil

[0066] 9 parts of diphenylmethane diisocyanate

[0067] 45 parts of hexamethylene diisocyanate.

[0068] The aforementioned "part" corresponds to 50g. Specifically, the aforementioned polyether polyol is polyether 210, which is a polyether polyol with an average molecular weight of approximately 210 g / mol. The aforementioned diphenylmethane diisocyanate is specifically MDI-50, meaning that its composition contains approximately 50% pure 4,4'-MDI, with the remainder consisting of other isomers such as 2,4'-MDI and a small amount of 2,2'-MDI. This mixture provides better processing performance than pure 4,4'-MDI while maintaining high reactivity.

[0069] The coupling agent mentioned above is KH-560, and the hexamethylene diisocyanate mentioned above is specifically HT100 (Wanhua), which is a trimer based on hexamethylene diisocyanate (HDI), and has good weather resistance and mechanical properties.

[0070] Specifically, the raw material composition of Glue B includes the following components by weight:

[0071] 65 parts of polyester polyol

[0072] 14 parts of bisphenol A type polyether polyol

[0073] 3 parts of dipropylene glycol

[0074] 14.4 parts epoxy resin

[0075] 2.9 parts of KH-560 coupling agent

[0076] 0.50 parts of benzophenone-based ultraviolet absorber

[0077] 0.20 parts of hindered phenolic antioxidant.

[0078] The aforementioned "1 part" also corresponds to 50g, and the aforementioned bisphenol A type polyether polyol is specifically bisphenol A polyether (2208 Nanjing), with a molecular weight of 400. The aforementioned epoxy resin includes liquid bisphenol A type epoxy resin and solid bisphenol A type epoxy resin, the latter being in sheet form.

[0079] The preparation method of the above-mentioned A-type adhesive includes the following steps in sequence:

[0080] S1. First, add the polyether polyol and castor oil to the dry reaction vessel, then heat to 115°C, then evacuate to 1-50 kPa, and finally keep under vacuum for 2 hours.

[0081] S2. The reactor is kept under vacuum and cooled to 65°C. Then the diphenylmethane diisocyanate and coupling agent are added. Finally, the temperature is raised to 82°C and the reaction is carried out for 3 hours.

[0082] S3. Add the hexamethylene diisocyanate to the reactor in batches, measuring the NCO value after each addition, until the NCO value is 13.5±0.5;

[0083] S4. The reactor is cooled to 45°C, and finally the discharge is opened to obtain the A-type adhesive.

[0084] Specifically, the hexamethylene diisocyanate was added in batches of 5 parts per batch. After the 9th batch, the NCO value met the requirements. Therefore, the final amount of hexamethylene diisocyanate added was determined to be 9 batches, or 45 parts. Among them, the NCO content of MDI-50 was 34%, the NCO content of HT100 (Wanhua) was 23%, and the final NCO content of glue A was approximately 13.41%, i.e., the NCO value was 13.41.

[0085] The preparation method of the above-mentioned B-type adhesive includes the following steps in sequence:

[0086] T1. First, add the polyester polyol, dipropylene glycol, epoxy resin, and the above-mentioned KH-560 coupling agent to the reactor, then heat to 115°C and keep warm.

[0087] T2. The reactor is first evacuated to 1-50 kPa, and then stirred for 2 hours;

[0088] T3. Add the bisphenol A type polyether polyol to the reactor in batches, stirring for 0.5 h after each addition, and then measure the viscosity until the viscosity at 25°C is 800-1200 mPa·s.

[0089] T4. The reactor is cooled down, and finally the discharge is opened. If necessary, the material is filtered out to obtain the B-type adhesive.

[0090] Specifically, the bisphenol A type polyether polyol was added in batches of 2 parts per batch. After the 7th batch was added, the viscosity of the sampled material at 25°C was 1130 mPa·S, which met the requirements. Therefore, the final addition amount of the bisphenol A type polyether polyol was set at 7 batches, or 14 parts.

[0091] The method of using this adhesive includes the following steps in sequence.

[0092] P1. Mixing: Take 10 catties of A glue and 5.5 catties of B glue, and mix them thoroughly.

[0093] P2. Coating: Apply a coating to the aluminum foil to form a coating layer. The coating amount is 2.5 g / m². 2 ;

[0094] P3. Pressing: Pressing a PE film onto the coating to obtain a composite material;

[0095] P4. Curing: The composite material is heated for 4 hours at a temperature of 75°C to obtain the final food packaging composite material.

[0096] Example 2

[0097] A two-component composite adhesive for food packaging that does not contain aromatic primary amines, comprising separately prepared A-adhesive and B-adhesive, which are mixed during use.

[0098] Specifically, the raw material composition of Glue A includes the following components by weight:

[0099] 30 parts of polyether polyol

[0100] 9 parts castor oil

[0101] 20 parts of diphenylmethane diisocyanate

[0102] 40 parts of hexamethylene diisocyanate;

[0103] One part of coupling agent.

[0104] The aforementioned "part" corresponds to 50g. Specifically, the aforementioned polyether polyol is polyether 210, which is a polyether polyol with an average molecular weight of approximately 210 g / mol. The aforementioned diphenylmethane diisocyanate is specifically MDI-50, meaning that its composition contains approximately 50% pure 4,4'-MDI, with the remainder consisting of other isomers such as 2,4'-MDI and a small amount of 2,2'-MDI. This mixture provides better processing performance than pure 4,4'-MDI while maintaining high reactivity.

[0105] The coupling agent mentioned above is KH-560, and the hexamethylene diisocyanate mentioned above is specifically HT100 (Wanhua), which is a trimer based on hexamethylene diisocyanate (HDI), and has good weather resistance and mechanical properties.

[0106] Specifically, the raw material composition of Glue B includes the following components by weight:

[0107] 60.2 parts of polyester polyol

[0108] 12 parts of bisphenol A type polyether polyol

[0109] 11.9 parts of dipropylene glycol

[0110] 13.4 parts epoxy resin

[0111] Two parts of KH-560 coupling agent

[0112] 0.40 parts of benzophenone-based ultraviolet absorber

[0113] 0.10 parts of hindered phenolic antioxidant.

[0114] The aforementioned "1 part" also corresponds to 50g, and the aforementioned bisphenol A type polyether polyol is specifically bisphenol A polyether (2208 Nanjing), with a molecular weight of 400. The aforementioned epoxy resin includes liquid bisphenol A type epoxy resin and solid bisphenol A type epoxy resin, the latter being in sheet form.

[0115] The preparation method of the above-mentioned A-type adhesive includes the following steps in sequence:

[0116] S1. First, add the polyether polyol and castor oil to the dry reaction vessel, then heat to 115°C, then evacuate to 1-50 kPa, and finally keep under vacuum for 1 hour.

[0117] S2. The reactor is kept under vacuum and cooled to 65°C. Then the diphenylmethane diisocyanate and coupling agent are added. Finally, the temperature is raised to 85°C and the reaction is carried out for 3 hours.

[0118] S3. Add the hexamethylene diisocyanate to the reactor in batches, measuring the NCO value after each addition, until the NCO value is 13.5±0.5;

[0119] S4. The reactor is cooled to 45°C, and finally the discharge is opened to obtain the A-type adhesive.

[0120] Specifically, the hexamethylene diisocyanate was added in batches of 5 parts per batch. After the 8th batch, the NCO value met the requirements. Therefore, the final amount of hexamethylene diisocyanate added was determined to be 8 batches, or 40 parts. Among them, the NCO content of MDI-50 was 32%, the NCO content of HT100 (Wanhua) was 23%, and the final NCO content of glue A was approximately 13.60%, i.e., the NCO value was 13.60.

[0121] The preparation method of the above-mentioned B-type adhesive includes the following steps in sequence:

[0122] T1. First, add the polyester polyol, dipropylene glycol, epoxy resin, and the above-mentioned KH-560 coupling agent to the reactor, then heat to 115°C and keep warm.

[0123] T2. The reactor is first evacuated to 1-50 kPa, and then stirred for 1 hour.

[0124] T3. Add the bisphenol A type polyether polyol to the reactor in batches, stirring for 0.5 h after each addition, and then measure the viscosity until the viscosity at 25°C is 800-1200 mPa·s.

[0125] T4. The reactor is cooled down, and finally the discharge is opened. If necessary, the material is filtered out to obtain the B-type adhesive.

[0126] Specifically, the bisphenol A type polyether polyol was added in batches of 2 parts per batch. After the 6th batch was added, the viscosity of the sampled material at 25°C was 960 mPa·s, which met the requirements. Therefore, the final addition amount of the bisphenol A type polyether polyol was set at 6 batches, or 12 parts.

[0127] The method of using this adhesive includes the following steps in sequence.

[0128] P1. Mixing: Take 10 catties of A glue and 5 catties of B glue, and mix them thoroughly.

[0129] P2. Coating: Apply a coating to the aluminum foil to form a coating layer. The coating amount is 2.5 g / m². 2 ;

[0130] P3. Pressing: Pressing a PP film onto the coating to obtain a composite material;

[0131] P4. Curing: The composite material is heated for 4 hours at a temperature of 72°C to obtain the final food packaging composite material.

[0132] Example 3

[0133] A two-component composite adhesive for food packaging that does not contain aromatic primary amines, comprising separately prepared A-adhesive and B-adhesive, which are mixed during use.

[0134] Specifically, the raw material composition of Glue A includes the following components by weight:

[0135] 29.2 parts of polyether polyol

[0136] Castor oil 8.8 parts

[0137] 10 parts of diphenylmethane diisocyanate

[0138] 50 parts of hexamethylene diisocyanate;

[0139] Two parts of coupling agent.

[0140] The aforementioned "part" corresponds to 50g. Specifically, the aforementioned polyether polyol is polyether 210, which is a polyether polyol with an average molecular weight of approximately 210 g / mol. The aforementioned diphenylmethane diisocyanate is specifically MDI-50, meaning that its composition contains approximately 50% pure 4,4'-MDI, with the remainder consisting of other isomers such as 2,4'-MDI and a small amount of 2,2'-MDI. This mixture provides better processing performance than pure 4,4'-MDI while maintaining high reactivity.

[0141] The coupling agent mentioned above is KH-560, and the hexamethylene diisocyanate mentioned above is specifically HT100 (Wanhua), which is a trimer based on hexamethylene diisocyanate (HDI), and has good weather resistance and mechanical properties.

[0142] Specifically, the raw material composition of Glue B includes the following components by weight:

[0143] 64 parts of polyester polyol

[0144] 14 parts of bisphenol A type polyether polyol

[0145] 3.1 parts of dipropylene glycol

[0146] 14.5 parts epoxy resin

[0147] 4 parts of KH-560 coupling agent

[0148] 0.30 parts of benzophenone-based ultraviolet absorber

[0149] 0.10 parts of hindered phenolic antioxidant.

[0150] The aforementioned "1 part" also corresponds to 50g, and the aforementioned bisphenol A type polyether polyol is specifically bisphenol A polyether (2208 Nanjing), with a molecular weight of 400. The aforementioned epoxy resin includes liquid bisphenol A type epoxy resin and solid bisphenol A type epoxy resin, the latter being in sheet form.

[0151] The preparation method of the above-mentioned A-type adhesive includes the following steps in sequence:

[0152] S1. First, add the polyether polyol and castor oil to the dry reaction vessel, then heat to 115°C, then evacuate to 1-50 kPa, and finally keep under vacuum for 2 hours.

[0153] S2. The reactor is kept under vacuum and cooled to 65°C. Then the diphenylmethane diisocyanate and coupling agent are added. Finally, the temperature is raised to 80°C and the reaction is carried out for 3 hours.

[0154] S3. Add the hexamethylene diisocyanate to the reactor in batches, measuring the NCO value after each addition, until the NCO value is 13.5±0.5;

[0155] S4. The reactor is cooled to 45°C, and finally the discharge is opened to obtain the A-type adhesive.

[0156] Specifically, the hexamethylene diisocyanate was added in batches of 5 parts per batch. After the 10th batch, the NCO value met the requirements. Therefore, the final amount of hexamethylene diisocyanate added was set at 10 batches, or 50 parts. Among them, the NCO content of MDI-50 was 34%, the NCO content of HT100 (Wanhua) was 23%, and the final NCO content of glue A was approximately 13.90%, i.e., the NCO value was 13.90.

[0157] The preparation method of the above-mentioned B-type adhesive includes the following steps in sequence:

[0158] T1. First, add the polyester polyol, dipropylene glycol, epoxy resin, and the above-mentioned KH-560 coupling agent to the reactor, then heat to 115°C and keep warm.

[0159] T2. The reactor is first evacuated to 1-50 kPa, and then stirred for 1 hour.

[0160] T3. Add the bisphenol A type polyether polyol to the reactor in batches, stirring for 0.5 h after each addition, and then measure the viscosity until the viscosity at 25°C is 800-1200 mPa·s.

[0161] T4. The reactor is cooled down, and finally the discharge is opened. If necessary, the material is filtered out to obtain the B-type adhesive.

[0162] Specifically, the bisphenol A type polyether polyol was added in batches of 2 parts per batch. After the 7th batch was added, the viscosity of the sampled material at 25°C was 1020 mPa·s, which met the requirements. Therefore, the final addition amount of the bisphenol A type polyether polyol was set at 7 batches, or 14 parts.

[0163] The method of using this adhesive includes the following steps in sequence.

[0164] P1. Mixing: Take 10 catties of A glue and 5 catties of B glue, and mix them thoroughly.

[0165] P2. Coating: Apply a coating to the aluminum foil to form a coating layer. The coating amount is 2.5 g / m². 2 ;

[0166] P3. Pressing: Pressing a PP film onto the coating to obtain a composite material;

[0167] P4. Curing: The composite material is heated for 4 hours at a temperature of 72°C to obtain the final food packaging composite material.

[0168] Example 4

[0169] A two-component composite adhesive for food packaging that does not contain aromatic primary amines, comprising separately prepared A-adhesive and B-adhesive, which are mixed during use.

[0170] Specifically, the raw material composition of Glue A includes the following components by weight:

[0171] 47 parts of polyether polyol

[0172] 14.1 parts castor oil

[0173] 5.9 parts of diphenylmethane diisocyanate

[0174] 30 parts of hexamethylene diisocyanate;

[0175] 3 parts coupling agent.

[0176] The aforementioned "part" corresponds to 50g. Specifically, the aforementioned polyether polyol is polyether 210, which is a polyether polyol with an average molecular weight of approximately 210 g / mol. The aforementioned diphenylmethane diisocyanate is specifically MDI-50, meaning that its composition contains approximately 50% pure 4,4'-MDI, with the remainder consisting of other isomers such as 2,4'-MDI and a small amount of 2,2'-MDI. This mixture provides better processing performance than pure 4,4'-MDI while maintaining high reactivity.

[0177] The coupling agent mentioned above is KH-560, and the hexamethylene diisocyanate mentioned above is specifically HT100 (Wanhua), which is a trimer based on hexamethylene diisocyanate (HDI), and has good weather resistance and mechanical properties.

[0178] Specifically, the raw material composition of Glue B includes the following components by weight:

[0179] Polyester polyol 64.5 parts

[0180] 16 parts of bisphenol A type polyether polyol

[0181] 3.8 parts of dipropylene glycol

[0182] 14 parts epoxy resin

[0183] 1 part of KH-560 coupling agent

[0184] 0.5 parts of benzophenone-based ultraviolet absorber

[0185] 0.20 parts of hindered phenolic antioxidant.

[0186] The aforementioned "1 part" also corresponds to 50g, and the aforementioned bisphenol A type polyether polyol is specifically bisphenol A polyether (2208 Nanjing), with a molecular weight of 400. The aforementioned epoxy resin includes liquid bisphenol A type epoxy resin and solid bisphenol A type epoxy resin, the latter being in sheet form.

[0187] The preparation method of the above-mentioned A-type adhesive includes the following steps in sequence:

[0188] S1. First, add the polyether polyol and castor oil to the dry reaction vessel, then heat to 110°C, then evacuate to 1-50 kPa, and finally keep under vacuum for 2 hours.

[0189] S2. The reactor is kept under vacuum and cooled to 68°C. Then the diphenylmethane diisocyanate and coupling agent are added. Finally, the temperature is raised to 84°C and the reaction is carried out for 3 hours.

[0190] S3. Add the hexamethylene diisocyanate to the reactor in batches, measuring the NCO value after each addition, until the NCO value is 13.5±0.5;

[0191] S4. The reactor is cooled to 40°C, and finally the discharge is opened to obtain the A-type adhesive.

[0192] Specifically, the hexamethylene diisocyanate was added in batches of 5 parts per batch. After the 6th batch, the NCO value met the requirements. Therefore, the final amount of hexamethylene diisocyanate added was determined to be 6 batches, or 30 parts. Among them, the NCO content of MDI-50 was 34%, the NCO content of HT100 (Wanhua) was 23%, and the final NCO content of A glue was approximately 13.60%, i.e., the NCO value was 13.60.

[0193] The preparation method of the above-mentioned B-type adhesive includes the following steps in sequence:

[0194] T1. First, add the polyester polyol, dipropylene glycol, epoxy resin, and the above-mentioned KH-560 coupling agent to the reactor, then heat to 110°C and keep warm.

[0195] T2. The reactor is first evacuated to 1-50 kPa, and then stirred for 2 hours;

[0196] T3. Add the bisphenol A type polyether polyol to the reactor in batches, stirring for 0.5 h after each addition, and then measure the viscosity until the viscosity at 25°C is 800-1200 mPa·s.

[0197] T4. The reactor is cooled down, and finally the discharge is opened. If necessary, the material is filtered out to obtain the B-type adhesive.

[0198] Specifically, the bisphenol A type polyether polyol was added in batches of 2 parts per batch. After the 8th batch was added, the viscosity of the sampled material at 25°C was 1180 mPa·S, which met the requirements. Therefore, the final addition amount of the bisphenol A type polyether polyol was set at 8 batches, or 16 parts.

[0199] The method of using this adhesive includes the following steps in sequence.

[0200] P1. Mixing: Take 10 catties of A glue and 5.5 catties of B glue, and mix them thoroughly.

[0201] P2. Coating: Apply a coating to the PP to form a coating layer, with a coating amount of 2.5 g / m². 2 ;

[0202] P3. Pressing: Pressing a PE film onto the coating to obtain a composite material;

[0203] P4. Curing: The composite material is heated for 2 hours at a temperature of 60°C to obtain the final food packaging composite material.

[0204] Comparative Example 1

[0205] The food packaging composite material in this comparative example differs from that in Example 1 in only one aspect, namely, in terms of raw material composition, preparation method, and application method.

[0206] In this comparative example, the NCO value of glue A is approximately 15.2, which exceeds the range of 13.5 ± 0.5 mentioned above.

[0207] Comparative Example 2

[0208] The food packaging composite material in this comparative example differs from that in Example 1 in only one aspect, namely, in terms of raw material composition, preparation method, and application method.

[0209] In this comparative example, the "P4, curing" step is replaced with a common drying step, in which the composite material passes through the drying channel relatively quickly, the drying temperature is 30-40℃, and the residence time of any part of the composite material in the drying channel is ≤15s.

[0210] Comparative Example 3

[0211] The food packaging composite material in this comparative example differs from that in Example 1 in only one aspect, namely, in terms of raw material composition, preparation method, and application method.

[0212] In this comparative example, the UV stabilizer and antioxidant for glue B are benzotriazole UV stabilizers and thioester antioxidants, respectively, which have relatively poor thermal stability.

[0213] Comparative Example 4

[0214] The food packaging composite material in this comparative example differs from that in Example 1 in only two aspects, namely, the raw material composition, preparation method, and application method.

[0215] In this comparative example, the NCO value of glue A is approximately 15.2, which exceeds the range of 13.5 ± 0.5 mentioned above.

[0216] In this comparative example, the "P4, curing" step is replaced with a common drying step, in which the composite material passes through the drying channel relatively quickly, the drying temperature is 30-40℃, and the residence time of any part of the composite material in the drying channel is ≤15s.

[0217] Comparative Example 5

[0218] The food packaging composite material in this comparative example differs from that in Example 1 in only two aspects, namely, the raw material composition, preparation method, and application method.

[0219] In this comparative example, the NCO value of glue A is approximately 15.2, which exceeds the range of 13.5 ± 0.5 mentioned above.

[0220] In this comparative example, the UV stabilizer and antioxidant for glue B are benzotriazole UV stabilizers and thioester antioxidants, respectively, which have relatively poor thermal stability.

[0221] Comparative Example 6

[0222] The food packaging composite material in this comparative example differs from that in Example 1 in only two aspects, namely, the raw material composition, preparation method, and application method.

[0223] In this comparative example, the "P4, curing" step is replaced with a common drying step, in which the composite material passes through the drying channel relatively quickly, the drying temperature is 30-40℃, and the residence time of any part of the composite material in the drying channel is ≤15s.

[0224] In this comparative example, the UV stabilizer and antioxidant for glue B are benzotriazole UV stabilizers and thioester antioxidants, respectively, which have relatively poor thermal stability.

[0225] Comparative Example 7

[0226] The food packaging composite material in this comparative example differs from that in Example 1 in only three aspects, namely, the raw material composition, preparation method, and application method.

[0227] In this comparative example, the NCO value of glue A is approximately 15.2, which exceeds the range of 13.5 ± 0.5 mentioned above.

[0228] In this comparative example, the "P4, curing" step is replaced with a common drying step, in which the composite material passes through the drying channel relatively quickly, the drying temperature is 30-40℃, and the residence time of any part of the composite material in the drying channel is ≤15s.

[0229] In this comparative example, the UV stabilizer and antioxidant for glue B are benzotriazole UV stabilizers and thioester antioxidants, respectively, which have relatively poor thermal stability.

[0230] Peel strength test

[0231] In the above 4 embodiments and 7 comparative examples, 5 sheets of food packaging composite material were taken from each example. The length and width of each sheet were 20cm×5cm. The applicant's engineers made a subjective judgment based on their work experience. If the layering and peeling was relatively difficult, it was deemed qualified; otherwise, it was deemed unqualified.

[0232] If any one of the above five documents is unqualified, the final result will be "unqualified"; otherwise, if all of them are qualified, the result will be "qualified".

[0233] Total migration test of aromatic primary amines

[0234] According to the national standard GB 4806.15-2024, if the total migration value of aromatic primary amines is ≤0.01mg / kg, it is considered qualified; otherwise, it is unqualified. The test method refers to GB 31604.52.

[0235] In Example 1, 50 samples were sent for testing, and the test report is attached. Figure 1 , 2 3, 4. If any one of the samples fails, it is recorded as "unqualified". For self-inspection of Examples 2-4 and Comparative Examples 1-7, 5 samples are taken for each example. If any one of the samples fails, it is recorded as "unqualified".

[0236] Performance test results

[0237]

[0238] Results Analysis

[0239] First, as can be seen from the "peel strength test results", the adhesives in the four embodiments and seven comparative examples of this application all have sufficient bonding strength, and the corresponding food packaging composite materials all have sufficient structural strength.

[0240] Secondly, the food packaging composite materials in Examples 1-7 all failed the "total migration test results of aromatic primary amines", which proves the necessity of the above-mentioned three restrictions on "NCO value", "P4 and curing" steps, and "ultraviolet light stabilizers and antioxidants".

[0241] Third, as can be seen from Comparative Examples 1-3, among the above three limiting factors, the "NCO value" has the greatest impact on the final detection of aromatic primary amines, because Comparative Example 1 had the largest number of non-compliant samples.

[0242] Fourth, as can be seen from Comparative Examples 4-7, when at least two of the above three restrictions are not met, there is no clear pattern to the degree of non-compliance of the "total migration test result of aromatic primary amines". This may be related to the synergistic effect between the various restrictions.

[0243] The embodiments of this application have been described in detail above with reference to the accompanying drawings. However, this application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various modifications can be made without departing from the spirit of this application. These are non-inventive modifications and are protected by patent law as long as they are within the scope of the claims of this application.

Claims

1. A two-component composite adhesive for food packaging that does not contain aromatic primary amines, characterized in that: The raw material composition includes separately prepared and mixed A and B adhesives for use. The A adhesive includes polyether polyol, castor oil, diphenylmethane diisocyanate, and hexamethylene diisocyanate. The B adhesive includes polyester polyol, bisphenol A type polyether polyol, dipropylene glycol, and epoxy resin. The NCO value of the A adhesive is 13.5±0.5, and the viscosity of the B adhesive at 25°C is 800-1200 mPa·s.

2. The two-component composite adhesive for food packaging that does not contain aromatic primary amines according to claim 1, characterized in that: The NCO value of the A-type adhesive is adjusted using hexamethylene diisocyanate, and the viscosity of the B-type adhesive is adjusted using bisphenol A polyether polyol.

3. The two-component composite adhesive for food packaging that does not contain aromatic primary amines according to claim 1, characterized in that... The preparation method of the A-type adhesive includes the following steps in sequence: S1. First, add the polyether polyol and castor oil to the dry reaction vessel, then heat to 110-120℃, then evacuate, and finally keep under vacuum for 1-2 hours. S2. The reactor is kept under vacuum and cooled to 65-70°C. Then the diphenylmethane diisocyanate is added, and finally the temperature is raised to 80-85°C. The reaction is carried out for 2-3 hours. S3. Add the hexamethylene diisocyanate to the reactor in batches, measuring the NCO value after each addition, until the NCO value is 13.5±0.5; S4. The reactor is cooled to 40-45°C, and finally the discharge is opened to obtain the A-type adhesive.

4. The two-component composite adhesive for food packaging that does not contain aromatic primary amines according to claim 1, characterized in that... The preparation method of the B-type adhesive includes the following steps in sequence: T1. First, add the polyester polyol, dipropylene glycol, and epoxy resin to the reactor, then heat to 110-115℃ and keep warm. T2. The reactor is first evacuated, and then stirred for 1-2 hours; T3. Add the bisphenol A type polyether polyol to the reactor in batches, stirring for 0.5 h after each addition, and then measure the viscosity until the viscosity at 25°C is 800-1200 mPa·s. T4. The reactor is cooled down, and finally the discharge is opened to obtain the B-type adhesive.

5. The two-component composite adhesive for food packaging that does not contain aromatic primary amines according to claim 1, characterized in that... The A-type adhesive comprises the following components by weight: 28-48 parts of polyether polyol 8-15 parts castor oil 5-25 parts of diphenylmethane diisocyanate 30-52 parts of hexamethylene diisocyanate; The B-type adhesive comprises the following components by weight: 60-70 parts of polyester polyol 12-18 parts of bisphenol A type polyether polyol 2-15 parts of dipropylene glycol 10-15 parts epoxy resin.

6. The two-component composite adhesive for food packaging that does not contain aromatic primary amines according to claim 1, characterized in that: The B-type adhesive also includes a UV stabilizer and an antioxidant.

7. The two-component composite adhesive for food packaging that does not contain aromatic primary amines according to claim 6, characterized in that... The method of using the adhesive includes the following steps in sequence. P1. Mixing: Mix A and B glue in a weight ratio of 100:(50-55) and mix thoroughly. P2. Coating: Applying a coating to any one of the following materials: aluminum foil, metallized film, PP, PE, and PET, to form a coating layer. The coating amount is 2.2-2.8 g / m². 2 ; P3. Pressing: Press aluminum foil, aluminized film, PP, PE, and PET onto the coating to obtain a composite material; P4. Curing: The composite material is heated for 2-4 hours to obtain the food packaging composite material. When the number of aluminum foil layers in the food packaging composite material is 1 or 2, the curing temperature is 70-75℃ and the curing time is 4 hours. When the number of aluminum foil layers is 0, the curing temperature is 60-75℃ and the curing time is 2-4 hours.

8. The two-component composite adhesive for food packaging that does not contain aromatic primary amines according to claim 6, characterized in that: The ultraviolet stabilizer is a benzophenone-based ultraviolet absorber, and its weight is 0.3-0.5% of the total weight of the B-type raw material.

9. A two-component composite adhesive for food packaging that does not contain aromatic primary amines, as described in claim 6, characterized in that: The antioxidant is a heat-resistant hindered phenolic antioxidant.

10. The two-component composite adhesive for food packaging that does not contain aromatic primary amines according to claim 1, characterized in that: The A and / or B adhesives also include a coupling agent.

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