Aliphatic solvent-free polyurethane adhesive resistant to medium cooking

Abstract

The invention discloses an aliphatic solvent-free polyurethane adhesive resistant to medium cooking, and belongs to the technical field of adhesives, the polyurethane adhesive has the advantages of good thermal stability, strong adhesive ability, no volatile organic compound, no primary aromatic amine and medium resistance; the component A comprises an NCO compound containing adamantane, a rigid cage-shaped structure of adamantane gives a steric hindrance effect to reduce medium permeation and improve heat resistance at the same time, and a ureide bond obtained through a reaction of amino and isocyanate has good stability; through chemical modification, at least one of an epoxy group and a siloxane structure is introduced into at least one of a component A and a component B, so that not only can the bonding capacity be improved, but also the crosslinking density is improved, the compactness of a system is enhanced, and the medium resistance is further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of adhesives, and in particular relates to an aliphatic solvent-free polyurethane adhesive resistant to medium boiling. Background Art

[0002] With the rapid development of the food packaging industry, the safety and reliability of packaging materials are increasingly valued. In the field of liquid condiment packaging, the widespread use of strong solvent seasoning substances such as ethyl maltol has put forward higher requirements for adhesives used in packaging material lamination. Adhesives must not only ensure a firm bond between substrates, but also have excellent media resistance and meet the safety requirements of food contact materials.

[0003] Polyurethane adhesives can be divided into two categories: solvent-based and solvent-free. Traditional solvent-based polyurethane adhesives rely on organic solvents to reduce the viscosity of the system, but the emission of volatile organic compounds (VOCs) not only violates EU REACH, China's "Technical Specifications for Low Volatile Organic Content Coatings" and other regulations, but residual solvents may also contaminate end products through migration, causing food safety hazards. Therefore, solvent-free polyurethane adhesives have gradually become the mainstream of the market.

[0004] At present, the solvent-free polyurethane adhesives used for food packaging are mainly divided into the following categories: aromatic isocyanate (NCO) systems represented by TDI or MDI have excellent mechanical properties and fast curing speed, but aromatic isocyanates will release carcinogenic primary aromatic amines (PAAs) under high temperature or hydrolysis conditions. Although the end-capping technology can partially solve this problem, it is still difficult to completely avoid it in practical applications; alicyclic isocyanate systems represented by IPDI avoid the aromatic amine problem, but the medium resistance is still insufficient and the cost is high; modified systems designed with fluorine-containing modifications or high cross-linking degrees can improve the medium resistance to a certain extent, but often bring problems such as reduced processing performance or increased costs. Therefore, it is urgent to develop a new type of solvent-free two-component polyurethane adhesive that avoids the use of aromatic isocyanates while constructing a medium-resistant bonding interface. Summary of the invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the present invention provides a solvent-free polyurethane adhesive that does not contain aromatic isocyanate. Component A includes an NCO compound containing adamantane. The rigid cage structure of adamantane provides a steric hindrance effect to reduce medium penetration while improving heat resistance. The ureide bond obtained by reacting an amino group with an isocyanate has good stability. By chemical modification, an epoxy group and a siloxane structure are introduced into at least one of components A and B, which not only improves the bonding ability, but also improves the crosslinking density, enhances the compactness of the system, and further improves the medium resistance.

[0006] The technical solution for achieving the purpose of the present invention is as follows:

[0007] A medium cooking resistant aliphatic solvent-free polyurethane adhesive comprises a component A and a component B, wherein the component A is a polyurethane prepolymer terminated with isocyanate formed by the reaction of an NCO compound and a polyol A; the component B is a polyol B; the NCO compound comprises an aliphatic NCO compound not containing adamantane and an NCO compound containing adamantane; the NCO compound containing adamantane is obtained by the reaction of diaminoadamantane and an aliphatic NCO compound; the NCO compound containing adamantane has a molecular structure of the following formula I:

[0008] In Formula I, R1 and R2 are aliphatic compounds, including but not limited to straight-chain, branched-chain, and cyclic hydrocarbons;

[0009] The polyol A and the polyol B both contain common polyols, and at least one of the polyol A and the polyol B includes a special polyol; the special polyol has one or more of the following molecular structures of formula II:

[0010]

[0011] In formula II, R1, R2, R3, R4, R5 and R6 are alkyl compounds.

[0012] Preferably, the molar ratio of NCO to OH in component A and component B is 1.1-2; the special polyol is 0.5-30wt% of the total mass of polyols A and B; the mass ratio of the aliphatic NCO compound not containing adamantane to the NCO compound containing adamantane is (1-30):(70-99).

[0013] Preferably, the aliphatic NCO compound not containing adamantane is one or more of hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate and cyclohexane dimethylene diisocyanate.

[0014] Preferably, the common polyol is one or more of polyether polyol, polyester polyol, small molecule alcohol and vegetable oil modified polyol; the minimum functionality of the polyether polyol and polyester polyol is 2; the hydroxyl value of the polyether polyol is 50-500, and the hydroxyl value of the polyester polyol is 50-200.

[0015] Preferably, the special polyol is obtained by reacting triethanolamine or diethanolamine with 3-halopropyltrialkoxysilane or epihalohydrin; the 3-halopropyltrialkoxysilane is one or more of 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 3-bromopropyltrimethoxysilane and 3-bromopropyltriethoxysilane; the epihalohydrin is at least one of epichlorohydrin or epibromohydrin.

[0016] Preferably, the preparation method of the adamantane-containing NCO compound is as follows:

[0017] Weigh an aliphatic NCO compound and place it in a dry reactor and heat it to 50-60° C. Then dissolve diaminoadamantane in a polar aprotic solvent and add it dropwise into the reactor. Under an inert atmosphere, react for 12-16 hours to obtain an adamantane-containing NCO compound.

[0018] Preferably, the preparation method of component A is as follows:

[0019] Place the prepared polyol A in a reactor and dry it under vacuum. Then add the NCO compound and react for 2 to 3 hours. Then heat to 80 to 95°C and continue to react for 4 to 5 hours. Remove the solvent under vacuum at 50 to 70°C, take samples to measure the NCO value, discharge the material if it is qualified, and fill with nitrogen for protection to obtain component A.

[0020] Preferably, the preparation method of the B component is as follows: placing the prepared polyol B in a reaction kettle and drying it under vacuum, cooling it to 40-60° C., stirring and mixing it evenly, sampling and measuring OH, discharging the material if it is qualified, and filling it with nitrogen for protection to obtain the B component.

[0021] The present invention also protects the use of the above-mentioned medium cooking-resistant aliphatic solvent-free polyurethane adhesive in composite films of structures such as PET / AL / RCPP, PET / AL / NY / RCPP, and NY / RCPP.

[0022] Beneficial Effects

[0023] The invention has the following beneficial effects: the polyurethane adhesive of the invention has the advantages of good thermal stability, strong bonding ability, no volatile organic matter, no primary aromatic amine and medium resistance; an NCO compound containing adamantane is used as component A, the rigid cage structure of adamantane provides a steric hindrance effect to reduce medium penetration while improving heat resistance, and the ureide bond obtained by reacting an amino group with an isocyanate has good stability; an epoxy group and a siloxane structure are introduced into at least one component of A and B, and compared with direct doping, more reaction sites are provided through chemical reactions while converting supramolecular effects into chemical bonds, which not only improves the bonding ability, but also improves the crosslinking density and enhances the compactness of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The diagram shows the synthesis and structure of NCO compounds containing adamantane. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] In the examples, the experimental methods used are conventional methods unless otherwise specified, and the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0027] The raw materials and equipment used in the embodiments and comparative examples are described as follows:

[0028] Adamantane: Hunan Huibaishi Biotechnology;

[0029] Diethanolamine: Echo reagent;

[0030] Triethanolamine: Aiko's reagent;

[0031] Isophorone diisocyanate: Guangdong Wengjiang Chemical Reagent;

[0032] 3-Chloropropyltriethoxysilane: Ico reagent;

[0033] Epichlorohydrin: Aiko's reagent;

[0034] Polycaprolactone diol: average molecular weight 1000, Guangdong Wengjiang Chemical Reagent;

[0035] Polytetrahydrofuran 1: average molecular weight 1000, Guangdong Wengjiang Chemical Reagent;

[0036] Polytetrahydrofuran 2: average molecular weight 2000, Guangdong Wengjiang Chemical Reagent;

[0037] Diaminoadamantane (homemade)

[0038] At room temperature, adamantane reacts with bromine under the catalysis of iron to obtain dibromoadamantane, which is then reacted in diphenyl ether with urea and trifluoroacetic acid at 140-180°C for 1.5 hours to obtain diaminoadamantane.

[0039] Special polyol 1 (self-made)

[0040] 1 mol of diethanolamine and 1 mol of anhydrous DMSO solvent were added into a reactor, mixed evenly, and then nitrogen was introduced to replace the air in the reactor. 0.1 mol of catalyst potassium iodide and 1 mol of 3-chloropropyltriethoxysilane were added, and the temperature was raised to 80°C under stirring. The reaction was stirred overnight. After the reaction was completed, the reaction was naturally cooled to room temperature, the solvent was removed by rotary evaporation, and the reaction was washed with anhydrous ether to obtain special polyol 1.

[0041] Special polyol 2 (self-made)

[0042] 1 mol of diethanolamine, 1 mol of epichlorohydrin, 1.2 mol of triethylamine and 1000 mL of tetrahydrofuran were added into a 2000 mL reactor and stirred at 40°C for 10 h. After the reaction, the reaction solution was concentrated, the generated solid was filtered out, and the filtrate was concentrated to obtain special polyol 2.

[0043] Special polyol 3 (self-made)

[0044] 1 mol of triethanolamine, 1 mol of epichlorohydrin, 1.2 mol of triethylamine and 1000 mL of tetrahydrofuran were added into a 2000 mL reactor and stirred at 50°C for 18 h. After the reaction, the reaction solution was concentrated, the generated solid was filtered out, and the filtrate was concentrated to obtain special polyol 3.

[0045] NCO compounds containing adamantane

[0046] 42 mol of isophorone diisocyanate was weighed and placed in a dry reactor and heated to 60° C. Then 20 mol of diaminoadamantane was dissolved in DMF and added dropwise to the reactor. After reacting for 16 h under an argon atmosphere, an adamantane-containing NCO compound was obtained.

[0047] A Component 1

[0048] 6.8 kg of polytetrahydrofuran 2, 2.7 kg of polycaprolactone diol and 0.5 kg of special polyol 1 were placed in a reaction kettle and dried under vacuum. Then, 12 kg of isophorone diisocyanate and 1.2 kg of adamantane-containing NCO compound were added therein and reacted for 2 hours. The temperature was raised to 80°C and the reaction was continued for 5 hours. The solvent was removed under vacuum at 70°C. The NCO value was measured by sampling and was 16.8%. The qualified material was discharged and nitrogen was filled for protection to obtain component A 1.

[0049] A Component 2

[0050] 7.1 kg of polytetrahydrofuran 2 and 2.9 kg of polycaprolactone diol were placed in a reaction kettle and dried under vacuum. Then, 12 kg of isophorone diisocyanate and 1.2 kg of adamantane-containing NCO compound were added therein and reacted for 2 hours. The temperature was raised to 80°C and the reaction was continued for 5 hours. The solvent was removed under vacuum at 70°C. The NCO value of the sample was measured to be 17.6%. The qualified material was discharged and nitrogen was filled for protection to obtain component A 2.

[0051] A Component 3

[0052] 6.8 kg of polytetrahydrofuran 2, 2.7 kg of polycaprolactone diol and 0.5 kg of special polyol 1 were placed in a reaction kettle and dried under vacuum. Then 13.2 kg of isophorone diisocyanate was added and reacted for 2 hours. The temperature was raised to 80°C and the reaction was continued for 5 hours. The solvent was removed under vacuum at 70°C. The NCO value was measured at 18.3% by sampling. The qualified product was discharged and nitrogen was filled for protection to obtain component A 3.

[0053] B Component 1

[0054] 12.9 kg of polytetrahydrofuran 1, 19.6 kg of polycaprolactone diol and 0.5 kg of special polyol 1 were placed in a reaction kettle, dried under vacuum, stirred and mixed evenly, cooled to 40° C., discharged, and filled with nitrogen for protection to obtain component B 1.

[0055] B Component 2

[0056] 12.9 kg of polytetrahydrofuran 1, 19.6 kg of polycaprolactone diol and 0.5 kg of special polyol 2 were placed in a reaction kettle, dried under vacuum, stirred and mixed evenly, cooled to 40° C., discharged, and filled with nitrogen for protection to obtain component B 2.

[0057] B Component 3

[0058] 12.9 kg of polytetrahydrofuran 1, 19.6 kg of polycaprolactone diol and 0.5 kg of special polyol 3 were placed in a reaction kettle, dried under vacuum, stirred and mixed evenly, cooled to 40° C., discharged, and filled with nitrogen for protection to obtain component B 3.

[0059] B Component 4

[0060] 13.2 kg of polytetrahydrofuran 1 and 19.8 kg of polycaprolactone diol were placed in a reaction kettle and dried under vacuum, stirred and mixed evenly, cooled to 40° C., discharged, and filled with nitrogen for protection, to obtain B component 4.

[0061] B Component 5

[0062] 12.9 kg of polytetrahydrofuran 1, 19.6 kg of polycaprolactone diol, 0.35 kg of 3-aminopropyltriethoxysilane and 0.15 kg of diethanolamine were placed in a reaction kettle and dried under vacuum, then stirred and mixed evenly, cooled to 40° C., discharged, and filled with nitrogen for protection to obtain component B 5.

[0063] Example 1

[0064] Component A 1 and component B 1 were mixed at a mass ratio of 10:14.2 to obtain a polyurethane adhesive 1 having an NCO:OH molar ratio of 1.41:1.

[0065] Example 2

[0066] Component A 1 and component B 2 were mixed in a mass ratio of 10:14.2 to obtain a polyurethane adhesive 2 having an NCO:OH molar ratio of 1.36:1.

[0067] Example 3

[0068] The A component 1 and the B component 3 were mixed in a mass ratio of 10:14.2 to obtain a polyurethane adhesive 3 having an NCO:OH molar ratio of 1.36:1.

[0069] Example 4

[0070] Component A 2 and component B 1 were mixed at a mass ratio of 10:14.2 to obtain a polyurethane adhesive 4 having an NCO:OH molar ratio of 1.45:1.

[0071] Example 5

[0072] Component A 2 and component B 2 were mixed in a mass ratio of 10:14.2 to obtain a polyurethane adhesive 5 having an NCO:OH molar ratio of 1.39:1.

[0073] Example 6

[0074] Component A 2 and component B 3 were mixed in a mass ratio of 10:14.2 to obtain a polyurethane adhesive 6 having an NCO:OH molar ratio of 1.39:1.

[0075] Comparative Example 1

[0076] The A component 2 and the B component 4 were mixed in a mass ratio of 10:14.2 to obtain a polyurethane adhesive 7 having an NCO:OH molar ratio of 1.50:1.

[0077] Comparative Example 2

[0078] Component A 3 and component B 1 were mixed at a mass ratio of 10:14.2 to obtain a polyurethane adhesive 8 having an NCO:OH molar ratio of 1.55:1.

[0079] Comparative Example 3

[0080] Component A 1 and component B 5 were mixed in a mass ratio of 10:14.2 to obtain a polyurethane adhesive 9 having an NCO:OH molar ratio of 1.36.

[0081] The following is the test method of the performance parameters involved in the present invention:

[0082] Peel strength: The solvent-free two-component polyurethane adhesive prepared in the examples and comparative examples was subjected to a peeling test at 3.5 g / m 2 The three-layer structure PET / AL / RCPP was compounded with a certain amount of glue, and the T-peel strength was tested after aging in a 45°C oven for 72 hours. 12cm*12cm bags were made and filled with food containing ethyl maltol and a solution of 0.5% ethyl maltol aqueous solution and refined vegetable oil. After being steamed at 121°C for 40 minutes, the peel strength test was carried out, and the detection was carried out according to the GB / T2791-1995 method.

[0083] Aromatic amine migration test: SGS third-party test.

[0084] Table 1 Performance test of Examples 1 to 6 and Comparative Examples 1 to 3

[0085]

[0086]

[0087] It can be seen from the data of the embodiments and comparative examples in Table 1 that the polyurethane adhesive of the present invention not only has good initial bonding strength, but also has a peel strength that does not decrease but increases after being boiled with a medium solution; wherein the strength before boiling and the increased strength after boiling of embodiment 3 are both the highest, because the A component and the B component in embodiment 3 contain not only siloxane and epoxy groups but also trivalent hydroxyl groups and quaternary ammonium salt cations, the trivalent hydroxyl groups increase the crosslinking density before boiling, after boiling, the siloxane is hydrolyzed into silanol groups to increase the bonding strength between interfaces, the mutual reaction between silanol groups further enhances the crosslinking density of the adhesive, and reduces the influence of ethyl maltol, and during high temperature boiling, the epoxy groups can not only react with the hydroxyl groups in the hydrolyzed polyurethane, but also capture ethyl maltol. From the data of Comparative Example 1, it can be seen that the peel strength of the polyurethane adhesive without siloxane and epoxy groups before cooking is relatively low, and it also decreases significantly after cooking; from the data of Comparative Example 2, it can be seen that although the peel strength before cooking without adamantane structure is relatively high, the peel strength decreases after cooking, and its heat resistance is relatively poor; from the data of Comparative Example 3, it can be seen that when the silane coupling agent is directly doped, the peel strength is not as good as that of Examples 1 to 6. This is because when the silane coupling agent reacts with isocyanate, although a siloxane structure is provided, it is equivalent to terminating the reaction between the isocyanate structure and the polyol.

[0088] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific implementation methods described. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A medium-cooking-resistant aliphatic solvent-free polyurethane adhesive, comprising component A and component B, characterized in that: The component A is a polyurethane prepolymer terminated with isocyanate formed by the reaction of an NCO compound and a polyol A; the component B is a polyol B; the NCO compound includes an aliphatic NCO compound not containing adamantane and an NCO compound containing adamantane; the NCO compound containing adamantane is obtained by the reaction of diaminoadamantane and an aliphatic NCO compound; the NCO compound containing adamantane has a molecular structure of the following formula I: Formula I; wherein R1 and R2 are aliphatic compounds, including but not limited to straight-chain, branched-chain, and cyclic hydrocarbons; The polyol A and the polyol B both contain common polyols, and at least one of the polyol A and the polyol B contains special polyols; the special polyol has one or more of the molecular structures of the following formula II: Formula II; wherein R1, R2, R3, R4, R5, and R6 are alkyl compounds.

2. The medium-cooking-resistant aliphatic solvent-free polyurethane adhesive according to claim 1, characterized in that: The molar ratio of NCO to OH in the A component and the B component is 1.1 to 2; the special polyol is 0.5 to 30 wt% of the total mass of the polyols A and B; the mass ratio of the aliphatic NCO compound not containing adamantane to the NCO compound containing adamantane is (1 to 50): (50 to 99).

3. The medium-cooking-resistant aliphatic solvent-free polyurethane adhesive according to claim 1, characterized in that: The aliphatic NCO compound not containing adamantane is one or more of hexamethylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane diisocyanate and cyclohexane dimethylene diisocyanate.

4. The medium-cooking-resistant aliphatic solvent-free polyurethane adhesive according to claim 1, characterized in that: The common polyol is one or more of polyether polyol, polyester polyol, small molecule alcohol and vegetable oil modified polyol; the minimum functionality of the polyether polyol and polyester polyol is 2; the hydroxyl value of the polyether polyol is 50-500, and the hydroxyl value of the polyester polyol is 50-200.

5. The medium-cooking-resistant aliphatic solvent-free polyurethane adhesive according to claim 1, characterized in that: The special polyol is obtained by reacting triethanolamine or diethanolamine with 3-halopropyltrialkoxysilane or epihalohydrin; the 3-halopropyltrialkoxysilane is one or more of 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 3-bromopropyltrimethoxysilane and 3-bromopropyltriethoxysilane; the epihalohydrin is at least one of epichlorohydrin or epibromohydrin.

6. The medium-cooking-resistant aliphatic solvent-free polyurethane adhesive according to claim 1, characterized in that: The preparation method of the adamantane-containing NCO compound is as follows: Weigh an aliphatic NCO compound and place it in a dry reactor and heat it to 50-60° C. Then dissolve diaminoadamantane in a polar aprotic solvent and add it dropwise into the reactor. Under an inert atmosphere, react for 12-16 hours to obtain an adamantane-containing NCO compound.

7. The medium-cooking-resistant aliphatic solvent-free polyurethane adhesive according to claim 1, characterized in that: The preparation method of the A component is as follows: Place the prepared polyol A in a reactor and dry it under vacuum. Then add the NCO compound and react for 2 to 3 hours. Then heat to 80 to 95°C and continue to react for 4 to 5 hours. Remove the solvent under vacuum at 50 to 70°C, take samples to measure the NCO value, discharge the material if it is qualified, and fill with nitrogen for protection to obtain component A.

8. The medium-cooking resistant aliphatic solvent-free polyurethane adhesive according to claim 1, characterized in that: The preparation method of the B component is as follows: placing the prepared polyol B in a reaction kettle and drying it under vacuum, cooling it to 40-60° C., stirring and mixing it evenly, sampling and testing OH, discharging the material if it is qualified, and filling it with nitrogen for protection to obtain the B component.

9. Use of the medium cooking resistant aliphatic solvent-free polyurethane adhesive as claimed in any one of claims 1 to 8 in compounding films of structures such as PET / AL / RCPP, PET / AL / NY / RCPP, and NY / RCPP.

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