Polyurethane ink resin as well as preparation method and application thereof

Abstract

The invention discloses polyurethane ink resin as well as a preparation method and application thereof, and belongs to the technical field of polyurethane ink resin. The polyurethane ink resin disclosed by the invention is prepared by reacting the following raw materials and a solvent in percentage by weight: 22 to 28 weight percent of polymer polyol, 2 to 6 weight percent of polyisocyanate, 0.5 to 3 weight percent of amine chain extender, 0.1 to 3 weight percent of end-capping reagent and 65 to 75 weight percent of solvent, the proportion of the isopropanol in the solvent is 5 to 10 weight percent, and the proportion of the ethyl acetate in the solvent is 95 to 90 weight percent. The invention also discloses a preparation method of the polyurethane ink resin and application of the polyurethane ink resin in preparation of solvent type gravure composite ink. The printing ink prepared from the polyurethane printing ink resin has the characteristics of low raw ink viscosity, excellent high-speed transferability, high covering power, rapid redissolution, good plate cleaning property and the like, is particularly suitable for high-machine-speed printing scenes, and also has an unexpected effect of improving the adhesion of the printing ink.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane ink resins, and in particular relates to a polyurethane ink resin and a preparation method and application thereof. Background Art

[0002] In the field of gravure printing, polyurethane inks have always occupied a core position in ink research and development due to their excellent substrate adhesion, outstanding pigment wetting and dispersion, and outstanding high-temperature cooking resistance. With the continuous enhancement of global environmental awareness, the solvent system of polyurethane solvent-based inks has also changed from a benzophenone system to an ester-alcohol system based on esters and alcohols. This transformation not only meets the environmental protection requirements of VOCs emission reduction, but also provides a new technical path for optimizing ink performance.

[0003] In recent years, high-solid, low-viscosity inks have attracted the attention of researchers for their environmental and economic benefits. Compared with traditional solvent-based inks, high-solid, low-viscosity inks have higher solid content and lower solvent release ratios. For example, the solvent dilution ratio of ordinary white ink is about 80%, while the dilution ratio of high-solid, low-viscosity white ink is only about 50%. This type of ink reduces the use of organic solvents, thereby reducing solvent volatilization and loss, and is more environmentally friendly and economical. High-solid, low-viscosity inks are often used in high-speed shallow printing scenarios, with a small amount of ink and a very fast printing speed, usually above 300 meters / minute. Therefore, the ink is required to have the characteristics of low viscosity, good transferability, good covering power, fast re-dissolution speed, and good plate cleaning.

[0004] However, the existing technical system faces a significant technical bottleneck: in order to ensure high hiding performance, the current high-solid low-viscosity ink generally increases the pigment ratio. This makes the original ink viscosity of the high-solid low-viscosity ink prepared by the urethane ink resin high, resulting in poor transfer performance, insufficient hiding power, and slow re-dissolution during high-speed printing, which easily leads to printing defects. Although the performance of high-solid low-viscosity ink can be optimized by adjusting the ink formula, the effect of this improvement is not significant.

[0005] Therefore, developing a high-performance polyurethane ink resin designed specifically for high-solid, low-viscosity white ink has become a key way to solve this problem. Summary of the invention

[0006] One of the purposes of the present invention is to provide a polyurethane ink resin, which adjusts the solubility of the solvent system for polymer segments by increasing the proportion of ethyl acetate in the system to more than 90% and controlling the isopropanol content to less than 10%, reduces the molecular weight of polyurethane, and increases the drying speed. The prepared ink has the characteristics of low base ink viscosity, excellent high-speed transferability, high hiding power, rapid re-dissolution and good plate cleaning, and is particularly suitable for high-speed printing scenarios. The increase of ester components in the solvent system not only increases the speed of ink solvent volatilization and ink layer drying, but also has an unexpected effect of improving ink adhesion.

[0007] A second object of the present invention is to provide a method for preparing the polyurethane ink resin.

[0008] A third object of the present invention is to provide an application of polyurethane ink resin.

[0009] To achieve the above purpose, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention discloses a polyurethane ink resin, which is prepared by reacting raw materials and solvents in the following proportions: 22-28wt% polymer polyol, 2-6wt% polyisocyanate, 0.5-3wt% amine chain extender, 0.1-3wt% end capping agent, and 65-75wt% solvent; the proportion of isopropanol in the solvent is 5-10wt%, and the proportion of ethyl acetate is 95-90wt%.

[0010] In some embodiments of the present invention, the polymer polyol is selected from polyester polyols; preferably, the functionality of the polymer polyol is 2, and the number average molecular weight is 1000-5000, preferably 2000-4000.

[0011] In some embodiments of the present invention, the polyester polyol is a hydroxyl-terminated polyester polyol produced by polycondensation of a diol and a dibasic acid; Preferably, the diol is selected from at least one of ethylene glycol, diethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, methyl propanediol, 1,3-butylene glycol, 1,4-butylene glycol, neopentyl glycol, 1,6-hexanediol, 3-methyl-1,5-pentanediol, and 1,4-cyclohexyl glycol, more preferably neopentyl glycol; Preferably, the dibasic acid is adipic acid.

[0012] In some embodiments of the present invention, the polyisocyanate is selected from at least one of toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, cyclohexane dimethylene diisocyanate, trimethyl-1,6-hexamethylene diisocyanate, and methylcyclohexyl diisocyanate, and is preferably isophorone diisocyanate.

[0013] In some embodiments of the present invention, the amine chain extender is selected from at least one of isophoronediamine, ethylenediamine, propylenediamine, 1,6-hexanediamine, 1,4-butanediamine, and neopentyldiamine; preferably isophoronediamine.

[0014] In some embodiments of the present invention, the end-capping agent is selected from at least one of ethylamine, propylamine, butylamine, diethylamine, di-n-butylamine, diethanolamine, n-octylamine, and isooctylamine; preferably di-n-butylamine.

[0015] In some embodiments of the present invention, the solid content of the polyurethane ink resin is 25% to 35%, preferably 28% to 32%; or / and viscosity is 200 to 700 mPa.s, preferably 300 to 600 mPa.s; or / and the number average molecular weight is 10,000 to 40,000, preferably 10,000 to 30,000.

[0016] In a second aspect, the present invention discloses a method for preparing the above-mentioned polyurethane ink resin, comprising the following steps: S1. Prepolymerization: Put the polymer polyol, polyisocyanate, catalyst and part of the solvent into a container, perform prepolymerization under protective gas and heating conditions, and then cool to room temperature to obtain a prepolymer solution; preferably, the prepolymerization is completed at 70 to 110° C. for 4 to 6 hours; S2. The amine chain extender, the end-capping agent and the remaining solvent are placed in another container and mixed evenly to obtain a chain extender solution; then the prepolymer solution obtained in step S1 is added dropwise to the chain extender solution, and isophorone diisocyanate is added until the viscosity of the reaction system is 280-320 Pa.s, and then the temperature is raised to react to generate a polyurethane ink resin; preferably, the temperature is raised to 45-55°C and the reaction is carried out for 30-120 minutes.

[0017] The catalyst described in the present invention is a prior art, and a catalyst commonly used in the art can be used, including: at least one of dimethyltin diacetate, dibutyltin dibutyrate, dibutyltin di(2-ethylhexanoate), dibutyltin dilaurate, dioctyltin dilaurate, zinc dioctoate (II), zirconium acetylacetonate, 2,2,6,6-tetramethyl-3,5-heptanedione zirconium, bismuth neodecanoate and bismuth 2-ethylhexanoate; preferably bismuth neodecanoate. The amount of the catalyst added can be the conventional amount used in the art.

[0018] In some embodiments of the present invention, in the prepolymerization reaction of step S1, the solvent used is ethyl acetate, and the amount used is 35-40% of the total amount of ethyl acetate.

[0019] In a third aspect, the present invention discloses the use of the above-mentioned polyurethane ink resin in the preparation of solvent-based gravure composite ink.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The present invention is scientifically designed and ingeniously conceived. By optimizing the solvent ratio, the proportion of ethyl acetate in the system is increased to more than 90% and the isopropanol content is controlled to be less than 10%, the solvent system's solubility for polymer chain segments is adjusted, and the molecular weight and impact resistance of polyurethane are effectively reduced. The present invention limits the growth of polyurethane molecular chains, significantly reduces the molecular weight, and accelerates the curing process of the ink layer. The prepared ink has the characteristics of low original ink viscosity, excellent high-speed transferability, high hiding power, rapid re-dissolution and good plate cleaning, and is particularly suitable for high-speed printing scenarios. The increase of ester components in the solvent system not only increases the speed of ink solvent volatilization and ink layer drying, but also has an unexpected effect of improving ink adhesion. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are 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 this application.

[0022] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0023] The raw materials used in the embodiments and comparative examples are as follows: Polyester polyol A, obtained by the reaction of adipic acid and neopentyl glycol, with a number average molecular weight of 2000; Bismuth neodecanoate catalyst: BICAT8118; Ethyl acetate: EA; Isopropyl alcohol: IPA; Isophorone diamine: IPDA; Di-n-butylamine: DBA.

[0024] Example 1 This embodiment discloses a method for preparing the polyurethane ink resin of the present invention, and the specific steps are as follows: S1. Prepolymerization 100 g of polyester polyol A, 20.5 g of IPDI, 0.08 g of catalyst BICAT8118 and 10 g of solvent EA were put into a flask, reacted at 75° C. for 5 hours, cooled to 50° C., and then 100 g of solvent EA was added, stirred and cooled to room temperature to obtain a prepolymer solution; S2. Aggregation In another flask, 5.0 g of amine chain extender IPDA, 3.0 g of end-capping agent di-n-butylamine, 175 g of solvent EA and 15 g of solvent IPA were added and stirred to obtain a chain extender solution; then, the prepolymer solution prepared in step S1 was slowly added dropwise to the chain extender solution under stirring at room temperature, and after the addition was completed, 1.0-4.0 g of IPDI was added according to the initial viscosity and stirring was continued until the viscosity reached about 300 mPa.s, and then the temperature was raised to 50°C and kept warm for 1.0 hour to obtain a polyurethane resin, which was recorded as Eg1.

[0025] Example 2 This embodiment discloses a method for preparing the polyurethane ink resin of the present invention, and the specific steps are as follows: S1. Prepolymerization 100 g of polyester polyol A, 20.5 g of IPDI, 0.08 g of catalyst BICAT8118 and 10 g of solvent EA were put into a flask, reacted at 75° C. for 5 hours, cooled to 50° C., and then 100 g of solvent EA was added, stirred and cooled to room temperature to obtain a prepolymer solution; S2. Aggregation In another flask, add 5.0g of amine chain extender IPDA, 3.0g of end-capping agent di-n-butylamine, 169g of solvent EA and 21g of solvent IPA, and stir to obtain a chain extender solution; then, under stirring at room temperature, slowly drop the prepolymer solution prepared in step S1 into the chain extender solution, after the dropwise addition is completed, add 1.0-4.0g of IPDI according to the initial viscosity and continue stirring until the viscosity reaches about 300mPa.s, then raise the temperature to 50°C and keep warm for 1.0 hour to obtain a polyurethane resin, recorded as Eg2.

[0026] Example 3 This embodiment discloses a method for preparing the polyurethane ink resin of the present invention, and the specific steps are as follows: S1. Prepolymerization 100 g of polyester polyol A, 20.5 g of IPDI, 0.08 g of catalyst BICAT8118 and 10 g of solvent EA were put into a flask, reacted at 75° C. for 5 hours, cooled to 50° C., and then 100 g of solvent EA was added, stirred and cooled to room temperature to obtain a prepolymer solution; S2. Aggregation In another flask, add 5.0g of amine chain extender IPDA, 3.0g of end-capping agent di-n-butylamine, 160g of solvent EA and 30g of solvent IPA, and stir well to obtain a chain extender solution; then, under stirring at room temperature, slowly drop the prepolymer solution prepared in step S1 into the chain extender solution, after the dropwise addition is completed, add 1.0-4.0g of IPDI according to the initial viscosity and continue stirring until the viscosity reaches about 300mPa.s, then raise the temperature to 50°C and keep warm for 1.0 hour to obtain a polyurethane resin, recorded as Eg3.

[0027] Comparative Example 1 S1. Prepolymerization, same as in Example 1 100 g of polyester polyol A, 20.5 g of IPDI, 0.08 g of catalyst BICAT8118 and 10 g of solvent EA were put into a flask, reacted at 75° C. for 5 hours, cooled to 50° C., and then 100 g of solvent EA was added, stirred and cooled to room temperature to obtain a prepolymer solution; S2. Aggregation In another flask, add 6.0g of amine chain extender IPDA and 2.0g of end-capping agent di-n-butylamine, 130g of solvent EA and 60g of solvent IPA, stir well to obtain a chain extender solution, then slowly drop the prepolymer solution prepared in step S1 into the chain extender solution under stirring at room temperature, after the dropwise addition is completed, add 1.0-4.0g of IPDI according to the initial viscosity and continue stirring until the viscosity reaches about 300mPa.s, then heat to 50°C and keep warm for 1.0 hour to obtain a polyurethane resin, recorded as C1.

[0028] Comparative Example 2 S1. Prepolymerization, same as in Example 1 100 g of polyester polyol A, 20.5 g of IPDI, 0.08 g of catalyst BICAT8118 and 10 g of solvent EA were put into a flask, reacted at 75° C. for 5 hours, cooled to 50° C., and then 100 g of solvent EA was added, stirred and cooled to room temperature to obtain a prepolymer solution; S2. Aggregation In another flask, add 6.0g of amine chain extender IPDA and 2.0g of end-capping agent di-n-butylamine, 100g of solvent EA and 90g of solvent IPA, stir well to obtain a chain extender solution, then slowly drop the above prepolymer solution into the chain extender solution under stirring at room temperature, after the dropwise addition is completed, add 1.0-4.0g of IPDI according to the initial viscosity and continue stirring until the viscosity reaches about 300mPa.s, then raise the temperature to 50°C and keep warm for 1.0 hour to obtain a polyurethane resin, recorded as C2.

[0029] Test Example 1 The polyurethane resins obtained in Examples 1-3 and Comparative Examples 1-2 were tested, and the results are shown in the following table: Table 1 Properties of polyurethane resins obtained in Examples 1-3 and Comparative Examples 1-2

[0030] The number average molecular weight in Table 1 was measured by GPC.

[0031] Table 1 compares the physical properties of polyurethane resins under different solvent systems. The experimental design maintains the solid content of the five groups of resin samples at 30%, and the viscosity is stabilized at around 300 mPa·s through process control. In terms of solvent ratio, Examples Eg1-Eg3 use a system with an isopropanol content of <10% and ethyl acetate >90%, while Comparative Examples C1 and C2 use a system with isopropanol >20% and ethyl acetate <80%. The results of determining the number average molecular weight by the APC method show that under similar viscosity conditions, compared with the control sample with a high isopropanol content, the low isopropanol system (Eg1-Eg3) has a weakened ability to dissolve and reduce the viscosity of the solvent, resulting in hindered molecular chain growth, and the number average molecular weight of the final product shows a significant downward trend.

[0032] Test Example 2 The polyurethane resin obtained in the examples and comparative examples was prepared into ink: according to the formula in Table 2, each raw material was put into a 200 ml glass bottle, and then an equal mass of 1 mm diameter glass beads was added. After sealing, the bottle was ground with an oscillator for 2 to 3 hours to obtain a polyurethane ink for gravure printing.

[0033] Table 2 Ester soluble polyurethane gravure ink formula

[0034] The inks prepared in this test example were subjected to performance tests.

[0035] (1) Ink viscosity test Test method: Use four cups test, record the ink flow time, and test 3 times to get the average value.

[0036] (2) Ink re-dissolution and plate cleaning test Test method: Use a gravure ink proofing machine to proof the ink, rinse the plate with ethyl acetate solvent, observe the ink dissolution speed and the cleanliness of the plate, and evaluate the ink solubility and plate cleanliness. The faster the ink dissolves and the more ink is dissolved, the better the solubility and the higher the score; the cleaner the plate of the proofing machine and the higher the cleanliness, the higher the score. Evaluation criteria: 1-5 points, 5 points is the best.

[0037] The test method is as follows: rinse with 50ml ethyl acetate / 100cm² plate surface. Use a stopwatch to accurately time, use the grid analysis method (divide the plate into 1cm² grids) to quantify the residual area, and use a standard colorimetric card to compare the cleanliness.

[0038] Table 3 Ink resolubility scoring criteria

[0039] Table 4 Layout cleanliness rating criteria (based on residual color depth)

[0040] (3) Ink hiding and transfer test method: Use a gravure ink proofing machine to proof the ink, place the proofed sample on black cardboard to compare and observe the transfer effect. The more complete the transfer and the less missed prints, the better the transfer effect. Place the sample on the small hole inside the integrating sphere spectrophotometer to test the hiding power. The higher the data, the stronger the hiding power. Evaluation criteria: 1-5 points, 5 points is the best.

[0041] The test uses a standard light box (D65 light source), an observation distance of 30cm, an observation angle of 45°, and requires simultaneous evaluation of solid color blocks and 50% flat screen areas. Each indicator must meet the corresponding grade requirements to be assessed. Abnormal phenomena such as ink layer adhesion and drawing will be automatically downgraded. The specific scoring criteria are as follows: Table 5 Ink hiding and transfer rating criteria

[0042] (4) Ink adhesion test Test method: Use tape to stick and tear the samples on PET and OPP film, observe the proportion of ink sticking off, and evaluate the ink adhesion. The less ink sticking off, the better the ink adhesion, and the higher the score. Evaluation criteria: 1-5 points, 5 points is the best.

[0043] The specific test method is as follows: Use standard tape (such as 3M tape) to stick it on the ink surface with constant pressure, let it stand for 5 seconds, then quickly tear it vertically. Repeat the test 3 times at the same position and take the worst result as the score.

[0044] Visually inspect the sample at a distance of 30 cm under natural light. If the shedding ratio is between the two scores (e.g. 12%), the lower score shall be used.

[0045] Special case handling: If the substrate (PET / OPP) is damaged due to tearing and the ink falls off, it needs to be recorded and retested. If the tape has residual ink or the surface of the substrate is contaminated and affects the judgment, the test is considered invalid. The following is a scoring standard table for the ink adhesion test, which is based on the quantitative evaluation of the degree of ink falling off after the tape is torn: Table 6 Ink Adhesion Scoring Standard

[0046] The test results are listed in Table 7.

[0047] Table 7 Impact resistance test results of gravure polyurethane white ink

[0048] The performance in the above table is obtained by testing under the same test conditions.

[0049] According to the comparative analysis of the experimental data in the above table, it can be seen that the white ink performance of the five groups of resin systems shows significant differences: although the resin bulk viscosity of C1, C2 and Eg1-Eg3 is similar, the original ink prepared by the Eg1-Eg3 system exhibits better rheological properties: its original ink viscosity is 28.5-33.4 seconds, while C1 and C2 are 45.8 and 52.6 seconds respectively; its viscosity is reduced by about 27~46%, showing better processing applicability.

[0050] When diluted to the working ink state, the process advantages of the Eg1-Eg3 system are further highlighted: the working ink viscosity is stable in the range of 11.6-12.0 seconds, 2-3 seconds lower than the C1 and C2 systems. This feature is directly converted into performance improvement in the printing process: the transfer performance score of Eg1-Eg3 is 4.5-5, and the hiding performance score is 5, while the transfer performance scores of the C1 and C2 systems are 3 and 4, and the hiding performance scores are 3 and 4. It is worth noting that due to the smaller molecular weight of the Eg1-Eg3 resin, its ink resolubility and cleanliness performance are also better, which effectively ensures the stability of continuous printing.

[0051] In addition, the applicant surprisingly found that in terms of substrate adaptability, the Eg1-Eg3 system showed a breakthrough: the adhesion score of its ink on OPP and PET substrates was 4.5-5, while the scores of C1 and C2 were 3 and 4. Eg1-Eg3 has an unexpected effect of improving ink adhesion.

[0052] In general, compared with resins C1 and C2 with conventional alcohol-ester solvent ratios, the inks formulated with resins Eg1 to Eg3 with adjusted alcohol-ester ratios exhibit lower viscosity, better transfer and hiding properties, better redissolution and plate cleaning properties, and stronger substrate adhesion, and are particularly suitable for the application of high-solid content, low-viscosity inks in shallow-web and high-speed printing.

[0053] Finally, it should be noted that the above embodiments are only preferred embodiments of the present invention to illustrate the technical solution of the present invention, but not to limit it, and certainly not to limit the patent scope of the present invention. Any changes or modifications that are made to the main design concept and spirit of the present invention without any substantial meaning, and the technical problems they solve are still consistent with the present invention, should be included in the protection scope of the present invention; in addition, the direct or indirect application of the technical solution of the present invention in other related technical fields is also included in the patent protection scope of the present invention.

Claims

1. A polyurethane ink resin, characterized in that: The invention is prepared by reacting raw materials and solvents in the following proportions: 22-28 wt% of polymer polyol, 2-6 wt% of polyisocyanate, 0.5-3 wt% of amine chain extender, 0.1-3 wt% of end-capping agent, and 65-75 wt% of solvent; the proportion of isopropanol in the solvent is 5-10 wt%, and the proportion of ethyl acetate is 95-90 wt%.

2. The polyurethane ink resin according to claim 1, characterized in that: The polymer polyol is selected from polyester polyols.

3. The high-performance polyurethane ink resin for high-solid and low-viscosity white ink according to claim 1, characterized in that: The polyester polyol is a hydroxyl-terminated polyester polyol generated by polycondensation of diol and dibasic acid.

4. The polyurethane ink resin according to claim 1, characterized in that: The polyisocyanate is selected from at least one of toluene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate, 1,4-cyclohexane diisocyanate, cyclohexane dimethylene diisocyanate, trimethyl-1,6-hexamethylene diisocyanate, and methylcyclohexyl diisocyanate.

5. The polyurethane ink resin according to claim 1, characterized in that: The amine chain extender is selected from at least one of isophoronediamine, ethylenediamine, propylenediamine, 1,6-hexanediamine, 1,4-butanediamine, and neopentyldiamine.

6. The polyurethane ink resin according to claim 1, characterized in that: The end-capping agent is selected from at least one of ethylamine, propylamine, butylamine, diethylamine, di-n-butylamine, diethanolamine, n-octylamine and isooctylamine.

7. The polyurethane ink resin according to any one of claims 1 to 6, characterized in that: The solid content of the polyurethane ink resin is 25% to 35%; or / and viscosity is 200-700mPa.s; Or / and the number average molecular weight is 10,000 to 40,000.

8. The method for preparing the polyurethane ink resin according to any one of claims 1 to 7, characterized in that: The steps include: S1. Prepolymerization: Put polymer polyol, polyisocyanate, catalyst and part of ethyl acetate into a container, react at 70-110°C for 4-6h under protective gas conditions, cool to 45-55°C, add part of ethyl acetate, stir evenly, and then cool to room temperature to obtain a prepolymer solution; S2. Polymerization: The amine chain extender, the end-capping agent and the remaining solvent are placed in another container and mixed evenly to obtain a chain extender solution; the prepolymer solution obtained in step S1 is then added dropwise to the chain extender solution, and isophorone diisocyanate is added until the viscosity of the reaction system is 280-320 Pa.s, and then the temperature is raised to 45-55°C for reaction for 30-120 minutes to generate a polyurethane ink resin.

9. The preparation method according to claim 8, characterized in that: In the prepolymerization reaction of step S1, the amount of ethyl acetate added for the first time is 2-5% of the total amount of ethyl acetate, and the amount of ethyl acetate added after cooling to 45-55° C. is 30-35% of the total amount of ethyl acetate.

10. The use of the polyurethane ink resin according to any one of claims 1 to 7, characterized in that: The application is application in preparing solvent-based gravure composite ink.

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