A polyurethane binder for aqueous alcohol gravure printing inks and a process for its preparation

Abstract

This invention discloses a polyurethane adhesive for water-soluble alcohol-based gravure printing inks and its preparation method. The polyurethane adhesive comprises the following raw materials in parts by weight: 60-85 parts polyester diol, 3-9 parts sulfonate polyether diol, 10-30 parts diisocyanate, 2-8 parts amine chain extender, 0.01-0.1 parts catalyst, 80-120 parts alcohol diluent, and 80-120 parts deionized water. The polyurethane adhesive for water-soluble alcohol-based gravure printing inks and its preparation method proposed in this invention are soluble in a mixed solvent of alcohol and water. When used in inks, it effectively overcomes the problems of slow drying speed and low production efficiency of existing water-based inks.

Description

Technical Field

[0001] This invention belongs to the field of printing ink technology, and particularly relates to a polyurethane adhesive for alcohol-water soluble gravure printing ink and its preparation method. Background Technology

[0002] In recent years, water-based inks, which are emerging in the gravure printing market, use water as a solvent, reducing pollution from volatile organic compounds and making them environmentally friendly. However, water has a high latent heat of volatilization and a slow drying speed, which cannot meet the high-speed printing requirements of gravure printing machines. Adding alcohol to water-based inks can partially improve the drying speed, reaching a machine speed of 150-180 meters per minute. However, compared to the 300-350 meters per minute of solvent-based gravure printing inks, the printing speed is still relatively low, resulting in low production efficiency and a lack of market competitiveness for the products.

[0003] Alcohol-based water-soluble polyurethane adhesives solve this problem. These adhesives can be dissolved in a mixture of ethanol and water, resulting in inks that dry quickly, print at high speeds, have low odor, and emit low VOCs, significantly improving the workshop environment. Furthermore, the low volatility of water gives these inks the advantage of low flammability, reducing the risk of fire caused by static electricity and flammable solvents, thus greatly enhancing their safety. Summary of the Invention

[0004] Based on the above-mentioned technical problems, the present invention proposes a polyurethane adhesive for alcohol-water soluble gravure printing ink and its preparation method. The polyurethane adhesive is soluble in a mixed solvent of alcohol and water. When used in ink, it can effectively overcome the problems of slow drying speed and low production efficiency of existing water-based inks.

[0005] The present invention proposes a polyurethane adhesive for water-soluble alcohol-based gravure printing ink, comprising the following raw materials in parts by weight: 60-85 parts polyester diol, 3-9 parts sulfonate polyether diol, 10-30 parts diisocyanate, 2-8 parts amine chain extender, 0.01-0.1 parts catalyst, 80-120 parts alcohol diluent, and 80-120 parts deionized water; wherein the polyester diol is polypropylene adipate with a molecular weight of 500-4000.

[0006] In this invention, by selecting sulfonate polyether diols as polyol monomers, water-soluble groups of sulfonate are introduced into the main chain structure of polyurethane molecules, thereby improving the water solubility of the obtained polyurethane. However, since the presence of water-soluble groups alone will reduce the alcohol solubility of polyurethane, by selecting polypropylene adipate with a molecular weight of 500-4000 as polyol monomers, alcohol-soluble groups of polypropylene adipate can be further introduced into the main chain structure of polyurethane molecules, thereby significantly improving the alcohol solubility of the obtained polyurethane. In this invention, by combining the above two reasonable selections of polyol monomers, a polyurethane that is both soluble in alcohol solvents and has good hydrophilicity is obtained, ultimately showing effective solubility in alcohol-water mixed solvents.

[0007] Preferably, the polyester diol is at least one of poly(1,2-propanediol adipate) with a molecular weight of 1,000, 2,000 or 3,000.

[0008] In this invention, when the polyester diol is specifically poly(1,2-propanediol adipate) with a molecular weight of 1000, 2000 or 3000, in addition to further improving the alcohol-water solubility of the obtained polyurethane adhesive, the ester group has strong polarity, strong ability to form hydrogen bonds, and large intermolecular forces. Therefore, the obtained polyurethane adhesive also has advantages such as good pigment dispersion, large cohesive energy, strong adhesion, high wear resistance, and good heat resistance.

[0009] Preferably, the sulfonate polyether diol is a Sulfadiol GS-7Q type polyether diol.

[0010] In this invention, the Sulfadiol GS-7Q type polyether diol contains both hydrophilic groups of sulfonate and ether bonds that can promote the solubility of polyurethane alcohols. Therefore, the selective addition of GS-7Q can further improve the alcohol water solubility of the resulting polyurethane adhesive.

[0011] Preferably, the mass ratio of the polyester diol to the sulfonate-type polyether diol is 9-16:1.

[0012] In this invention, the alcohol-water solubility of the polyurethane adhesive is not achieved by a single water-soluble or alcohol-soluble monomer, but rather by the compounding of sulfonate polyether diol and polypropylene adipate in a specific ratio, which allows the polyurethane as a whole to precisely meet the solubility characteristics of alcohol-water solubility. Therefore, this invention limits the mass ratio of the polyester diol and the sulfonate polyether diol to 9-16:1, which further optimizes the alcohol-water solubility of the polyurethane adhesive.

[0013] Preferably, the diisocyanate is at least one selected from isophorone diisocyanate, toluene diisocyanate, dicyclohexylmethane diisocyanate, diphenylmethane-4,4'-diisocyanate, 1,6-hexane diisocyanate, or tetramethylphenyldimethyl diisocyanate.

[0014] In this invention, the specific selection of diisocyanate can result in better yellowing resistance, water resistance, and heat resistance of the polyurethane adhesive.

[0015] Preferably, the amine chain extender is at least one of ethylenediamine, isophorone diamine, hexamethylenediamine, or diethylenetriamine.

[0016] In this invention, amine chain extenders, as post-chain extenders, improve the molecular weight, thermal stability, and water resistance of the resulting polyurethane to a certain extent.

[0017] Preferably, the catalyst is at least one of organic bismuth, tetrabutyl titanate, stannous octoate, or stannous chloride; and the alcohol solvent is at least one of isopropanol, ethanol, or n-propanol.

[0018] In this invention, alcohol solvents are used as diluents, which have the advantages of being easy to handle, safe and environmentally friendly, and recyclable.

[0019] This invention also proposes a method for preparing a polyurethane adhesive for alcohol-water-soluble gravure printing ink, comprising the following steps:

[0020] S1. Polyester diol, sulfonate-type polyether diol, diisocyanate and catalyst are mixed and subjected to a prepolymerization reaction to obtain NCO-terminated polyurethane prepolymer.

[0021] S2. The NCO-terminated polyurethane prepolymer is added to a solution composed of an amine chain extender, an alcohol diluent, and deionized water to carry out a chain extension reaction, thereby obtaining the polyurethane adhesive for water-soluble gravure printing ink.

[0022] In this invention, a polyurethane prepolymer that is soluble in alcohol solvents and has good hydrophilicity is synthesized by selecting polyester diol, sulfonate-type polyether diol, and diisocyanate as raw materials. Then, an amine chain extender is added for post-chain extension. This process ensures that the resulting polyurethane has an ordered structure and a controllable reaction. Furthermore, the resulting polyurethane adhesive is used in the production of alcohol-based water-based inks, resulting in inks with low odor, low VOC emissions, non-flammability, fast drying speed, good adhesion to PET, OPP, and other plastic substrates, high composite strength, and vibrant colors and strong layering in the printed products.

[0023] Preferably, in step S1, the temperature of the prepolymerization reaction is 80-90℃ and the time is 2-6h; in step S2, the temperature of the chain extension reaction is 30-50℃ and the time is 2-4h.

[0024] Preferably, the NCO content of the NCO-terminated polyurethane prepolymer is 1.4-2.2%.

[0025] In this invention, the NCO content in the NCO-terminated polyurethane prepolymer is limited to confirm whether the prepared reaction product is qualified.

[0026] Preferably, the polyurethane adhesive for the alcohol-water soluble gravure printing ink has a rotational viscosity of 500-1500 mPa·s at 25°C and a solid content of 34-36%.

[0027] In this invention, by limiting the viscosity and solid content of the polyurethane adhesive, an emulsion with relatively uniform viscosity, particle size and distribution is ensured. At the same time, it is beneficial to the dispersion and flow of the polyurethane adhesive. When used in ink, it helps the ink to dry, thereby shortening the drying time.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] The polyurethane adhesive of this invention incorporates sulfonate polyether diols, whose sulfonate groups possess strong hydrophilicity. Furthermore, through the rational selection of polyester polyols, the resulting polyurethane adhesive achieves excellent alcohol-water solubility. This characteristic allows the polyurethane adhesive to be used to produce inks using a mixture of alcohol and water. The use of this alcohol-water mixture in the resulting ink reduces VOC emissions and meets the requirements of high-speed gravure printing, thus solving the problems of slow speed, low production efficiency, and poor drying in ordinary gravure polyurethane water-based ink printing machines. Detailed Implementation

[0030] The present invention will now be described in detail through specific embodiments. However, these embodiments are clearly provided for illustrative purposes and are not intended to limit the scope of the present invention.

[0031] Example 1

[0032] A polyurethane adhesive for alcohol-water soluble gravure printing ink is prepared by the following method:

[0033] (1) NCO-terminated polyurethane prepolymer:

[0034] raw material Quality Poly(1,2-propylene adipate) (Mn = 2000) 79.2 Sulfadiol GS-7Q (Sulfonate polyether diol) 4.0 Isophorone diisocyanate (IPDI) 16.79 Organic bismuth catalysts 0.01

[0035] According to the above formula, poly(1,2-propylene adipate) (Mn=2000), sulfonate polyether diol Sulfadiol GS-7Q, isophorone diisocyanate IPDI and organic bismuth catalyst were mixed and reacted at 90°C for 3 hours. The NCO% was determined by di-n-butylamine titration to obtain an NCO-terminated polyurethane prepolymer with an NCO% of 2.15.

[0036] (2) Polyurethane adhesive:

[0037] raw material Quality NCO-terminated polyurethane prepolymer of step (1) 33.2 ethanol 32.5 Deionized water 32.5 Isophorone diamine IPDA 1.8

[0038] According to the above formula, isophorone diamine (IPDA), ethanol and deionized water are mixed to form a mixed solution. Under stirring, the NCO-terminated polyurethane prepolymer from step (1) is added to the mixed solution within 25 minutes. After reacting at 40°C for 3 hours, a transparent and stable polyurethane adhesive is obtained with a viscosity of 510 mPa·s and a solid content of 35.1%.

[0039] Example 2

[0040] A polyurethane adhesive for alcohol-water soluble gravure printing ink is prepared by the following method:

[0041] (1) NCO-terminated polyurethane prepolymer:

[0042] raw material Quality Poly(1,2-propylene adipate) (Mn = 1000) 65.8 Sulfadiol GS-7Q (Sulfonate polyether diol) 7.7 Dicyclohexylmethane diisocyanate (HMDI) 26.47 Tetrabutyl titanate 0.03

[0043] According to the above formula, poly(1,2-propylene adipate) (Mn=1000), sulfonate polyether diol Sulfadiol GS-7Q, dicyclohexylmethane diisocyanate HMDI and tetrabutyl titanate were mixed and reacted at 80°C for 4 hours. The NCO% was determined by di-n-butylamine titration to obtain an NCO%-terminated polyurethane prepolymer with an NCO% of 1.43.

[0044] (2) Polyurethane adhesive:

[0045] raw material Quality NCO-terminated polyurethane prepolymer of step (1) 33.8 Isopropanol 32.5 Deionized water 32.5 Isophorone diamine IPDA 1.2

[0046] According to the above formula, isophorone diamine (IPDA), isopropanol and deionized water are mixed to form a mixed solution. Under stirring, the NCO-terminated polyurethane prepolymer from step (1) is added to the mixed solution within 20 minutes. After reacting at 50°C for 2 hours, a transparent and stable polyurethane adhesive is obtained with a viscosity of 1490 mPa·s and a solid content of 35.9%.

[0047] Example 3

[0048] A polyurethane adhesive for alcohol-water soluble gravure printing ink is prepared by the following method:

[0049] (1) NCO-terminated polyurethane prepolymer:

[0050] raw material Quality Poly(1,2-propylene adipate) (Mn = 3000) 80.2 Sulfadiol GS-7Q (Sulfonate polyether diol) 6.0 Isophorone diisocyanate (IPDI) 13.78 stannous chloride 0.02

[0051] According to the above formula, poly(1,2-propylene adipate) (Mn=3000), sulfonate polyether diol Sulfadiol GS-7Q, isophorone diisocyanate IPDI and stannous chloride were mixed and reacted at 90°C for 3 hours. The NCO% was determined by di-n-butylamine titration to obtain an NCO%-terminated polyurethane prepolymer with an NCO% of 1.74.

[0052] (2) Polyurethane adhesive:

[0053]

[0054]

[0055] According to the above formula, isophorone diamine (IPDA), n-propanol and deionized water are mixed to form a mixed solution. Under stirring, the NCO-terminated polyurethane prepolymer from step (1) is added to the mixed solution within 30 minutes. After reacting at 40°C for 3 hours, a transparent and stable polyurethane adhesive is obtained with a viscosity of 1090 mPa·s and a solid content of 35.4%.

[0056] Comparative Example 1

[0057] A polyurethane adhesive, which is prepared by the following method:

[0058] (1) NCO-terminated polyurethane prepolymer:

[0059] raw material Quality Poly(3-methyl-1,5-pentanediol adipate) (Mn = 2000) 79.2 Sulfadiol GS-7Q (Sulfonate polyether diol) 4.0 Isophorone diisocyanate (IPDI) 16.79 Organic bismuth catalysts 0.01

[0060] According to the above formula, poly(3-methyl-1,5-pentanediol adipate) (Mn=2000), sulfonate polyether diol Sulfadiol GS-7Q, isophorone diisocyanate IPDI and organic bismuth catalyst were mixed and reacted at 90℃ for 3 hours. The NCO% was determined by di-n-butylamine titration to obtain an NCO-terminated polyurethane prepolymer with an NCO% of 2.03.

[0061] (2) Polyurethane adhesive:

[0062]

[0063]

[0064] According to the above formula, isophorone diamine (IPDA), ethanol and deionized water are mixed to form a mixed solution. Under stirring, the NCO-terminated polyurethane prepolymer from step (1) above is added to the mixed solution within 25 minutes. After reacting at 40°C for 3 hours, a turbid and opaque solution is obtained. After standing for two hours, the solution separates into layers.

[0065] Comparative Example 2

[0066] A polyurethane adhesive, which is prepared by the following method:

[0067] (1) NCO-terminated polyurethane prepolymer:

[0068] raw material Quality Poly(1,2-propylene adipate) (Mn = 2000) 79.2 2,2-Dimethylolpropionic acid (DMPA) 4.0 Isophorone diisocyanate (IPDI) 16.79 Organic bismuth catalysts 0.01 Triethylamine 2.5

[0069] According to the above formula, poly(1,2-propylene adipate) (Mn=2000), 2,2-dimethylolpropionic acid (DMPA), isophorone diisocyanate (IPDI), and organic bismuth catalyst were mixed and reacted at 90°C for 3 hours. The NCO% was determined by di-n-butylamine titration to obtain a polyurethane prepolymer with an NCO% of 2.09. After cooling the polyurethane prepolymer to 25°C, triethylamine was added, and the mixture was stirred for 15 minutes to obtain a fully neutralized NCO-terminated polyurethane prepolymer.

[0070] (2) Polyurethane adhesive:

[0071] raw material Quality NCO-terminated polyurethane prepolymer of step (1) 33.2 ethanol 32.5 Deionized water 32.5 Isophorone diamine IPDA 1.8

[0072] According to the above formula, isophorone diamine (IPDA), ethanol and deionized water are mixed to form a mixed solution. Under stirring, the NCO-terminated polyurethane prepolymer from step (1) above is added to the mixed solution within 25 minutes. After reacting at 40°C for 3 hours, a turbid and opaque solution is obtained. After standing for two hours, the solution separates into layers.

[0073] The polyurethane adhesives obtained in Examples 1-3 were used to prepare printing inks according to the formulations described in Table 1 below, i.e., the raw materials of the following formulations were filled into a container with a volume of 250 cm³. 3 In a sealed plastic bottle, mix quickly for 2-3 hours to obtain a printing ink composition.

[0074] Table 1 Working formulations for printing ink compositions

[0075]

[0076]

[0077] The above printing ink composition was subjected to the following performance tests, and the test results are shown in Table 2 below:

[0078] (1) Ink initial drying test method:

[0079] Apply the ink composition to a 50u fineness gauge with a scraper, blow it with a hairdryer on a low cool setting for 5 seconds, and then quickly press the ink surface of the fineness gauge at 0-15u, 16-35u, and 36-50u respectively with the thumb for 1-2 seconds, and observe the ink residue on the thumb surface.

[0080] Evaluation criteria: O: No ink residue on the thumb surface of 0-15u, 16-35u, and 36-50u; △: No ink residue on the thumb surface of 0-15u, no ink residue on the thumb surface of 16-35u, and ink residue on the thumb surface of 36-50u; ×: Ink residue on the thumb surface of 0-15u or ink residue on the thumb surface of 16-35u.

[0081] (2) Ink adhesion fastness test method:

[0082] Apply the ink composition to a surface-treated plastic film using a wire rod, achieving a solid content thickness of 2-3 μm. After drying with a hairdryer, apply 3M tape to the coated surface and quickly peel the tape off at a right angle to the coating surface, observing the condition of the coated surface.

[0083] Evaluation criteria: O: Ink residue ≥ 90%; △: Ink residue 50-90%; ×: Ink residue < 50%.

[0084] (3) Ink viscosity testing method:

[0085] Temperature the ink composition to room temperature (approximately 25°C). Pour the sample ink into a No. 3 Zahn cup until the ink is level with the edge of the Zahn cup. Use a glass rod to remove air bubbles. The viscosity of the ink is the time required for the sample to flow from the beginning until the flow stops and the first drop appears. Refer to the ink viscosity test method GB / T13217.4-91 for details.

[0086] (4) Ink fineness inspection method:

[0087] For specific details, please refer to the ink fineness test method GB / T13217.3-91.

[0088] (5) Test method for the composite strength of ink-printed products:

[0089] Apply the ink composition to a surface-treated polyester film (PET) using a filament applicator to achieve a solid content thickness of 2-3 μm; after drying with a hairdryer, apply a two-component polyurethane adhesive using the filament applicator, with an adhesive application rate of 2-2.5 g / m². 3(The two-component polyurethane adhesive used is Asahikawa Chemical's XCUA-5070A / XCUA-5070B, with a ratio of 100:7), and then it is laminated with a surface-treated CPP film and cured at 50°C for 48 hours; the composite film is made into a 15mm wide sample, and the T-peel strength is measured using a universal electronic tensile tester, which is used as the composite strength; the larger the value, the higher the composite strength.

[0090] (6) Ink anti-blocking test method:

[0091] Apply the ink composition to a surface-treated polyester film (PET) using a wire rod to achieve a solid content thickness of 2-3 μm, and thoroughly dry with a blower. Align the coated and uncoated sides and apply an ink at 50°C at a rate of 2.0 kgf / cm². 2 After applying the load for 2 hours, peel off the material and observe its surface condition, referring to the ink anti-blocking test method GB / T13217.8-91.

[0092] Evaluation criteria: O: No adhesion during peeling; △: Adhesion during peeling; ×: Ink transfer occurs.

[0093] (7) Ink resolubility test method:

[0094] The ink composition was coated onto a glass plate to achieve a solid content thickness of 2-3 μm. After being stored at room temperature (approximately 25°C) for 30 seconds, it was immersed in a mixed solvent of ethanol and water at a weight ratio of 1:1, and the resolubility of the ink film was observed.

[0095] Evaluation criteria: O: Coating redissolved; ×: Coating not dissolved and remaining on the glass plate.

[0096] (8) Ink stability test method:

[0097] After storing the prepared ink composition at room temperature (approximately 25°C) for 30 days, observe the ink layering and sedimentation.

[0098] Evaluation criteria: O: No layering or sedimentation in the ink; △: No layering in the ink, with a small amount of sedimentation; ×: Layering in the ink, or with a large amount of sedimentation.

[0099] Table 2. Test results of the ink compositions obtained in the examples and comparative examples.

[0100]

[0101]

[0102] The composite strength test results are shown in Table 3:

[0103] Table 3 shows the composite strength test results of the ink compositions obtained in the examples and comparative examples.

[0104]

[0105] As can be seen from the comparative examples, neither of them could obtain a transparent and stable polyurethane solution when using poly(3-methyl-1,5-pentanediol adipate) as the polyester diol in Comparative Example 1 nor when using 2,2-dimethylolpropionic acid as the hydrophilic chain extender in Comparative Example 2. Only when poly(1,2-propylene adipate) and sulfonate polyether diol were used as the diols in the examples could a transparent and stable polyurethane solution be obtained, and the polyurethane adhesive used to make alcohol-water soluble inks showed better performance. At the same time, compared with Examples 1 and 2, although sulfonate polyether diol and poly(propylene adipate) were used as the diols, the ratio of the two did not meet the 9-16:1 requirement. In Example 3, the ratio of the two met the 9-16:1 requirement, and the resulting polyurethane adhesive used to make alcohol-water soluble inks obviously had better performance.

[0106] Therefore, it can be seen that the ink formulated with the alcohol-water soluble polyurethane adhesive obtained by the present invention dries quickly, has good adhesion to PET, PE and OPP plastic substrates, and has high composite strength, making it suitable for high-speed gravure printing.

[0107] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A polyurethane adhesive for alcohol-water soluble gravure printing ink, characterized in that, The raw materials include the following parts by weight: 60-85 parts polyester diol, 3-9 parts sulfonate polyether diol, 10-30 parts diisocyanate, 2-8 parts amine chain extender, 0.01-0.1 parts catalyst, 80-120 parts alcohol diluent, and 80-120 parts deionized water. The polyester diol is at least one of poly(1,2-propanediol adipate) with a molecular weight of 1000, 2000 or 3000; the sulfonate polyether diol is Sulfadiol GS-7Q type polyether diol; the mass ratio of the polyester diol to the sulfonate polyether diol is 9-16:

1.

2. The polyurethane adhesive for water-soluble alcohol-based gravure printing ink according to claim 1, characterized in that, The diisocyanate is at least one selected from isophorone diisocyanate, toluene diisocyanate, dicyclohexylmethane diisocyanate, diphenylmethane-4,4'-diisocyanate, 1,6-hexane diisocyanate, or tetramethylphenyldimethyl diisocyanate.

3. The polyurethane adhesive for alcohol-water-soluble gravure printing ink according to claim 1 or 2, characterized in that, The amine chain extender is at least one of ethylenediamine, isophorone diamine, hexamethylenediamine, or diethylenetriamine.

4. The polyurethane adhesive for alcohol-water-soluble gravure printing ink according to claim 1 or 2, characterized in that, The catalyst is at least one of organic bismuth, tetrabutyl titanate, stannous octoate, or stannous chloride; the alcohol diluent is at least one of isopropanol, ethanol, or n-propanol.

5. A method for preparing a polyurethane adhesive for an alcohol-water-soluble gravure printing ink according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Polyester diol, sulfonate-type polyether diol, diisocyanate and catalyst are mixed and subjected to a prepolymerization reaction to obtain NCO-terminated polyurethane prepolymer. S2. The NCO-terminated polyurethane prepolymer is added to a solution composed of an amine chain extender, an alcohol diluent, and deionized water to carry out a chain extension reaction, thereby obtaining the polyurethane adhesive for water-soluble gravure printing ink.

6. The method for preparing the polyurethane adhesive for alcohol-water-soluble gravure printing ink according to claim 5, characterized in that, In step S1, the temperature of the prepolymerization reaction is 80-90℃ and the time is 2-6h; in step S2, the temperature of the chain extension reaction is 30-50℃ and the time is 2-4h.

7. The method for preparing the polyurethane adhesive for alcohol-water-soluble gravure printing ink according to claim 5 or 6, characterized in that, The NCO content of the NCO-terminated polyurethane prepolymer is 1.4-2.2%.

8. The method for preparing the polyurethane adhesive for alcohol-water-soluble gravure printing ink according to claim 5 or 6, characterized in that, The polyurethane adhesive for the alcohol-water soluble gravure printing ink has a rotational viscosity of 500-1500 mPa·s at 25°C and a solid content of 34-36%.

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