Benzene-free ketone-free polyurethane adhesive for intaglio printing and preparation method thereof
Patent Information
- Application Number
- CN202511780388.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-28
- Publication Date
- 2026-03-06
Smart Images
Figure CN121609867A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of polymer materials technology, and in particular to a benzene-free and ketone-free polyurethane adhesive for gravure printing and its preparation method. Background Technology
[0002] Polyurethane used as a binder in inks is primarily applied in gravure printing inks. Its main functions are dispersing pigments and binding the substrate, ensuring uniform pigment dispersion within the ink and firm adhesion to the substrate during printing. Polyurethane inks exhibit good color development, gloss, resistance to boiling, and gravure cleaning properties, making them suitable for printing on various substrates such as OPP, PET, and NY. Applications include packaging material printing, publication printing, and advertising material production. Product types mainly include solvent-based inks, water-based inks, and UV-curable inks. Currently, solvent-based inks still hold a significant market share.
[0003] Traditional solvent-based polyurethane adhesives typically use solvents such as toluene, xylene, and methyl ethyl ketone (MEK). These solvents are highly toxic and volatile, posing serious risks to the health of production workers and the environment.
[0004] With increasingly stringent environmental regulations, the market demand for green printing materials is becoming more urgent. While environmentally friendly alternatives such as water-based inks and UV inks have emerged, solvent-based inks still possess irreplaceable advantages in terms of overall performance (such as drying speed, substrate wettability, and printability) and cost. Therefore, developing polyurethane adhesives with performance comparable to traditional products but free of benzene and ketone solvents has become an important development direction for the industry.
[0005] While there have been attempts at developing benzene-free and ketone-free inks in the prior art, they often suffer from the following drawbacks: uneven adhesion to different substrates, making it difficult to meet the diverse needs of composite packaging; large batch-to-batch performance fluctuations of the adhesive, or poor storage stability, affecting the consistency of printing quality; and poor performance in terms of retort resistance, gloss, or drying speed. Summary of the Invention
[0006] This invention provides a benzene- and ketone-free polyurethane adhesive for gravure printing and its preparation method, which can solve the above-mentioned defects of existing polyurethane adhesives for solvent-based inks.
[0007] To solve the above-mentioned technical problems, the present invention provides a benzene-free and ketone-free polyurethane adhesive for gravure printing, which is prepared from the following raw materials in the indicated mass percentages: Isocyanate 15-25%; Polycaprolactone-polycarbonate modified polyester polyol 25-40%; The molecular structure regulator, at 1–5%, is composed of a diamine chain extender and a monoamine end-capping agent in a molar ratio of amino functional groups of 1:0.1–0.5. Catalyst 0.01–0.5%; The balance is free of benzene and ketone solvents, totaling 100%. The preparation method of the polycaprolactone-polycarbonate modified polyester polyol is as follows: (a) Preparation of polyester polyol: Under nitrogen protection, at least one of the following dicarboxylic acid, isophthalic acid, hydrogenated dimer acid, and sebacic acid is esterified and dehydrated at 130-150°C for 1-3 hours, and then the temperature is raised to 200-250°C and transesterification is carried out in the presence of a catalyst for 4-8 hours to obtain polyester polyol; b) Composite modification: The polyester polyol obtained in step a) is mixed with polycarbonate diol at a mass ratio of 1:0.5-1.5, and caprolactone monomer at a mass ratio of 1:0.5-1.5 with the polyester polyol is added. The mixture is reacted at 140-190℃ for 2-6 hours under nitrogen protection to obtain the polycaprolactone-polycarbonate modified polyester polyol.
[0008] In a preferred embodiment of the present invention, the catalyst is at least one of an organobismuth catalyst or an organotin catalyst.
[0009] In a preferred embodiment of the present invention, the polyester polyol has an acid value of less than 1, a hydroxyl value of 60-120 mgKOH / g, and a number-average molecular weight of 1000-2000. The polycarbonate diol is a polycarbonate-1,6-hexanediol ester with a number average molecular weight of 1000-2000.
[0010] In a preferred embodiment of the present invention, the diamine chain extender is isophorone diamine; and the monoamine end-capping agent is diethylamine or n-butylamine.
[0011] In a preferred embodiment of the present invention, the isocyanate component is an alicyclic diisocyanate, including at least one of isophorone diisocyanate or hydrogenated diphenylmethane diisocyanate.
[0012] In a preferred embodiment of the present invention, the benzene-free and ketone-free solvent is at least one of n-propyl acetate, ethyl acetate, and propylene glycol methyl ether.
[0013] To address the aforementioned technical problems, this invention provides a method for preparing a polyurethane adhesive, comprising the following steps: (1) Prepolymerization: Under inert gas protection, the polycaprolactone-polycarbonate modified polyester polyol is dehydrated, then mixed with 50-70% of the total mass of benzene-free and ketone-free solvent, the isocyanate component is added, and the temperature is raised to 70-90℃ and reacted at a constant temperature for 3-5 hours to obtain an isocyanate-terminated prepolymer solution. (2) Chain extension and end capping: Cool the obtained prepolymer solution to 10-40℃, mix the remaining benzene-free and ketone-free solvent with the molecular structure regulator thoroughly and uniformly, and slowly add it dropwise to the prepolymer solution to achieve chain extension and viscosity increase. After the dropwise addition is completed, continue to keep the reaction at 10-40℃ for 2-6 hours. (3) Curing and discharge: After the reaction is completed, the system is heated to 40-50°C and kept warm for 1-2 hours. Then the temperature is lowered to below 40°C, filtered, discharged, and packaged.
[0014] In a preferred embodiment of the present invention, in step (1), the dehydration conditions are: temperature 60-80°C, time 0.5-1 hour, and vacuum degree -0.095--0.098 MPa.
[0015] In a preferred embodiment of the present invention, in step (2), the dripping process is completed within 0.5 to 1.5 hours.
[0016] To solve the above-mentioned technical problems, the present invention provides a gravure printing ink, which contains 10 to 40% of the above-mentioned polyurethane binder by weight of the ink.
[0017] The beneficial effects of this invention are as follows: This invention provides a benzene-free and ketone-free polyurethane adhesive for gravure printing and its preparation method. By using a specific mass ratio of polycaprolactone-polycarbonate modified polyester polyol and utilizing a molecular structure regulator that combines monoamine and diamine, a high-performance benzene-free and ketone-free polyurethane adhesive is successfully prepared. This adhesive simultaneously possesses universal high adhesion, high batch stability, and excellent storage stability on various substrates such as OPP, PET, and NY. Thus, while ensuring environmental friendliness, it significantly improves the overall applicability and quality reliability of the product in the high-end gravure printing field. Attached Figure Description
[0018] Figure 1 This is a schematic diagram of the process flow for preparing a benzene-free and ketone-free polyurethane adhesive for gravure printing according to the present invention. Detailed Implementation
[0019] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.
[0020] Example 1 (a) Preparation of polyester polyol: In a 2L four-necked flask equipped with a stirrer, thermometer, fractionating column, and nitrogen inlet tube, 450g of adipic acid, 400g of 1,4-butanediol, and 100g of neopentyl glycol were added. Nitrogen gas was introduced for protection, and the temperature was slowly raised to 140°C to initiate the esterification and dehydration reaction, maintaining this temperature for 2 hours. Subsequently, the temperature was gradually increased to 230°C over 3 hours, and 0.5g of tetrabutyl titanate catalyst was added for transesterification reaction over 6 hours. The reaction was stopped when the acid value of the reactants dropped to 0.9 mgKOH / g and the hydroxyl value reached 95 mgKOH / g, yielding a polyester polyol (A1) with a number average molecular weight of approximately 1200.
[0021] (b) Composite Modification: In another 1L reactor, 400g of the polyester polyol (A1) prepared above, 300g of polycarbonate-1,6-hexanediol ester with a number average molecular weight of 1500, and 300g of caprolactone monomer were added. Under nitrogen protection, the mixture was heated to 170°C and reacted for 4 hours. After the reaction was completed, polycaprolactone-polycarbonate modified polyester polyol (B1) was obtained, and its hydroxyl value was measured to be 75 mgKOH / g.
[0022] Example 2 This embodiment discloses a benzene- and ketone-free polyurethane adhesive for gravure printing, which is prepared from the following raw materials in the indicated mass percentages: Isophorone diisocyanate (IPDI) 22%; Example 1 prepared 35% of polycaprolactone-polycarbonate modified polyester polyol (B1); Molecular structure regulator: 2.5% (composed of isophorone diamine and diethylamine in a molar ratio of amino functional groups of 1:0.3) Organic bismuth catalyst 0.08%; 40.42% n-propyl acetate, a benzene-free and ketone-free solvent.
[0023] The specific steps for preparing this polyurethane adhesive are as follows: (1) Prepolymerization: In a four-necked flask equipped with a stirrer, thermometer, condenser and nitrogen inlet tube, the formulated amount of polycaprolactone-polycarbonate modified polyester polyol (B1) was added and dehydrated at 75°C and -0.097MPa vacuum for 40 minutes. Then, 60% of the total solvent mass of n-propyl acetate and the formulated amount of IPDI were added and reacted at 82°C for 4 hours to obtain an isocyanate-terminated prepolymer solution.
[0024] (2) Chain extension and end-capping: The obtained prepolymer solution was cooled to 25°C. Isophorone diamine and diethylamine were dissolved in the remaining 40% n-propyl acetate to prepare a mixed solution. Under stirring, the mixed solution was slowly added dropwise to the above 25°C prepolymer solution over 1 hour, and the reaction temperature was controlled to never exceed 35°C by using a cold water bath. After the addition was complete, the reaction was continued at 30°C for 1 hour.
[0025] (3) Curing and Discharging: After the reaction is completed, the system is cooled to 45°C and kept at this temperature for 0.8 hours. Then, the temperature is further cooled to 35°C, filtered with a 400-mesh filter cloth, discharged and packaged to obtain a slightly yellow transparent viscous liquid, which is the benzene-free and ketone-free type polyurethane adhesive (or binder) for gravure printing.
[0026] Example 3 The raw material ratio is as follows: Hydrogenated diphenylmethane diisocyanate (H12MDI) 18%; Polycaprolactone-polycarbonate modified polyester polyol: 38% (its polyester polyol portion is prepared by mixing adipic acid and sebacic acid in a mass ratio of 8:2, with 1,6-hexanediol, and then with polycarbonate diol in a mass ratio of 1:1, and adding an equal mass of caprolactone for composite modification) The molecular structure regulator 3% is composed of isophorone diamine and n-butylamine in a molar ratio of amino functional groups of 1:0.4. Organotin catalyst 0.05%; The solvent is free of benzene and ketones, with a content of 40.95%, and is obtained by mixing ethyl acetate and propylene glycol methyl ether in a mass ratio of 2:1. The preparation steps are the same as in Example 2. The dehydration conditions are 65℃, -0.096MPa, and 50 minutes; the prepolymerization temperature is 85℃ and the reaction time is 3.5 hours; the chain extension and end-capping reactions are carried out at 30℃, with a dropping time of 0.5 hours and a holding time of 3 hours; the ripening temperature is 40℃ and the time is 1 hour.
[0027] Comparative Example 1 The difference from Example 2 is that the polyester polyol modified with polycaprolactone-polycarbonate is not used. Instead, the unmodified polyester polyol (A1) prepared in step (a) of Example 1 is used in an amount of 35%, while the other components and processes remain unchanged.
[0028] Comparative Example 2 The difference from Example 2 is that no monoamine end-capping agent (diethylamine) is added to the molecular structure regulator; only an equimolar amount of diamine chain extender (isophorone diamine) is used, while the other components and processes remain unchanged.
[0029] Performance testing The polyurethane adhesives prepared in Examples 2-3 and Comparative Examples 1-2 were tested as follows, and the test results are shown in Table 1 below.
[0030] Physicochemical properties: Solid content and viscosity (25℃) were determined according to national standards.
[0031] Adhesion: The obtained adhesive was formulated into inks with the same pigments and additives, with the amount of adhesive added accounting for 30% of the total weight of the ink. The inks were coated onto OPP, PET, and NY films using a bar coater. After drying at 80°C, the inks were tested using a cross-cut adhesion tester and 3M tape.
[0032] Storage stability: The adhesive was placed in a 50°C oven for 14 days to accelerate storage, and then stored at room temperature for 6 months. The appearance was observed and the viscosity change rate was measured.
[0033] Resistant to boiling: The PET film printed with ink was boiled at 121°C for 40 minutes, and the adhesion was tested after cooling.
[0034] Table 1 According to the test results shown in Table 1, the products of Examples 2 and 3 exhibited excellent adhesion on various substrates, good storage stability, and good resistance to boiling. Comparative Example 1, lacking composite modification, showed poor adhesion to OPP and NY. Comparative Example 2, lacking monoamine end-capping, resulted in excessive cross-linking and gelation, rendering it unusable. This demonstrates that the synergistic effect of the specific composite polyol and molecular structure regulator in this invention is key to achieving comprehensive high performance.
[0035] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.
Claims
1. A polyurethane adhesive for use in a benzene- and ketone-free gravure printing, characterized by comprising: Prepared from the following raw materials in the following mass percentages: Isocyanate 15-25%; Poly-caprolactone-polycarbonate modified polyester polyol 25-40%; Molecular structure regulator 1-5%, consisting of a di-amine chain extender and a mono-amine end-capping agent in a molar ratio of amino functional groups of 1:0.1-0.5; Catalyst 0.01-0.5%; The balance is a benzene-free and ketone-free solvent, the total amount being 100%; The poly-caprolactone-polycarbonate modified polyester polyol is prepared by: (a) Preparation of polyester polyol: under nitrogen protection, esterification and dehydration of at least one di-acid selected from adipic acid, isophthalic acid, hydrogenated dimer acid, and sebacic acid, and at least one di-alcohol selected from 1,4-butanediol, 1,6-hexanediol, neopentyl glycol, methyl pentanediol, ethyl butyl propylene glycol, and cyclohexane dimethyl alcohol, at 130-150°C for 1-3 hours, then heated to 200-250°C, and ester exchange reaction is carried out in the presence of a catalyst for 4-8 hours to obtain polyester polyol; b) Compound modification: mixing the polyester polyol obtained in step a) with polycarbonate di-alcohol in a mass ratio of 1:0.5-1.5, adding caprolactone monomer in a mass ratio of 1:0.5-1.5 to the polyester polyol, and reacting at 140-190°C for 2-6 hours under nitrogen protection to obtain the poly-caprolactone-polycarbonate modified polyester polyol.
2. The polyurethane adhesive according to claim 1, characterized in that, The catalyst is at least one of an organic bismuth catalyst or an organic tin catalyst.
3. The polyurethane adhesive according to claim 1, characterized in that, The acid value of the polyester polyol is less than 1, the hydroxyl value is 60-120 mgKOH / g, and the number average molecular weight is 1000-2000. The polycarbonate di-alcohol is poly-caprolactone-1,6-hexanediol ester with a number average molecular weight of 1000-2000.
4. The polyurethane adhesive of claim 1, wherein, The di-amine chain extender is isophorone diamine, and the mono-amine end-capping agent is diethylamine or n-butylamine.
5. The polyurethane adhesive of claim 1, wherein, The isocyanate component is a cycloaliphatic di-isocyanate, including at least one of isophorone di-isocyanate or hydrogenated diphenyl methane di-isocyanate.
6. The polyurethane adhesive of claim 1, wherein, The benzene-free and ketone-free solvent is at least one of n-propyl acetate, ethyl acetate, and propylene glycol methyl ether.
7. A process for the preparation of a polyurethane adhesive according to any one of claims 1 to 6, characterized in that, The method comprises the following steps: (1) Pre-polymerization: under inert gas protection, the poly-caprolactone-polycarbonate modified polyester polyol is dehydrated, then mixed with a benzene-free and ketone-free solvent accounting for 50-70% of the total mass of the benzene-free and ketone-free solvent, and the isocyanate component is added, and the temperature is raised to 70-90°C for constant temperature reaction for 3-5 hours to obtain an isocyanate-terminated pre-polymer solution; (2) Chain extension and end capping: the obtained pre-polymer solution is cooled to 10-40°C, the remaining benzene-free and ketone-free solvent and the molecular structure regulator are fully mixed and uniformly mixed, then slowly added to the pre-polymer solution to achieve chain extension and tackification, and after the addition is completed, the reaction is continued at 10-40°C for 2-6 hours; (3) Curing and discharging: after the reaction is completed, the system is heated to 40-50°C and aged for 1-2 hours, then continuously cooled to below 40°C, filtered and discharged, and packaged.
8. The method of claim 7, wherein, In step (1), the dehydration is carried out at a temperature of 60-80°C for 0.5-1 hour under a vacuum of -0.095 to -0.098 MPa.
9. The method of claim 7, wherein, In step (2), the dropwise addition is carried out over a period of 0.5-1.5 hours.
10. A gravure printing ink, characterized by 10-40% of the polyurethane adhesive according to any one of claims 1-6, based on the total weight of the ink.