A high heat-resistant inkjet printing ink and its application

Abstract

This application provides a highly heat-resistant inkjet printing ink. The ink comprises, by total weight, 5-30% epoxy acrylic resin, 4-26% isocyanate, 2-35% modified acrylate, 10-85% acrylate monomer, and 3-18% photoinitiator. This application optimizes the dosage of each component in the system, specifically specifying the weight ratio of epoxy acrylic resin: caprolactone-modified acrylate: monofunctional acrylate monomer: multifunctional acrylate monomer. While ensuring low viscosity and suitable surface tension, this ink also improves the flexibility of the ink layer after UV and thermal curing. When used as a solder mask layer on a circuit board, the ink layer meets the reflow performance, adhesion, and tin resistance requirements of the solder mask circuit board.

Description

Technical Field

[0001] The present invention relates to the technical field of inkjet printing inks, and in particular to a high-heat-resistant inkjet printing ink and applications thereof. Background Art

[0002] Inkjet printing technology has begun replacing traditional, highly polluting and energy-intensive printing methods in many industries. The inks used also avoid the environmental impact of traditional solvent-based inks. As a digital printing technology, UV inkjet printing offers advantages such as ease of operation, non-impact transfer, and low substrate requirements. Its application in the circuit board industry has been extensively researched, with solder mask printing being a key application. Compared to traditional solder mask printing methods, solder mask printing is gaining increasing attention due to its advantages such as time and labor savings and shortened production processes. However, current solder mask printing technology still has numerous drawbacks, including: 1. High ink viscosity, resulting in poor ink flow; 2. Low surface tension, the primary driver of jet necking, resulting in low printing accuracy; 3. High ink layer brittleness and susceptibility to cracking; 4. Ink layers prepared using a free-radical UV curing + thermal curing method have poor heat resistance, failing to meet the reflow resistance requirements for circuit boards; and 5. Poor adhesion of the ink layer to the substrate.

[0003] Chinese patents CN108359312A, CN114539845B, and CN116004056A all disclose solder mask inkjet UV inks and their preparation methods. However, in actual testing, solder mask prepared using a free radical UV curing + thermal curing method, because the system is primarily composed of conventional UV monomers, has a high crosslink density, large shrinkage, and insufficient toughness, failing to meet the high heat resistance requirements of the circuit board industry. Summary of the Invention

[0004] In order to solve the above technical problems, the present invention first provides a high heat-resistant inkjet printing ink; based on the total weight of the components, the components of the ink include: 5-30% epoxy acrylic resin, 4-26% isocyanate, 2-35% modified acrylate, 10-85% acrylate monomer, and 3-18% photoinitiator.

[0005] Furthermore, based on the total weight of the components, the components of the ink include: 5-25% epoxy acrylic resin, 8-20% isocyanate, 3-30% modified acrylate, 10-80% acrylate monomer, and 3-15% photoinitiator.

[0006] Furthermore, the epoxy acrylic resin includes but is not limited to at least one of bisphenol A epoxy acrylic resin, bisphenol F epoxy acrylic resin, novolac epoxy acrylic resin, epoxy acrylate resin, and modified epoxy acrylate resin.

[0007] Furthermore, the epoxy acrylic resin is a modified epoxy acrylate resin, and the modified group is selected from at least one of a glycidyl group, an acryl group, an amide group, and a C3-C6 alkylene group.

[0008] Furthermore, the epoxy equivalent of the epoxy acrylic resin is 100-1500, preferably 100-1200, and more preferably 100-900.

[0009] Preferably, the modified epoxy acrylate resin is a glycidyl- and acryloyl-co-modified epoxy acrylate resin, such as Shin-Nakamura Chemical EA-1010N.

[0010] Furthermore, the modified acrylate is at least one of caprolactone-modified acrylate, polyurethane acrylate, polyester acrylate, and epoxy soybean oil-modified acrylate.

[0011] Preferably, the modified acrylate is caprolactone-modified acrylate.

[0012] Furthermore, the caprolactone-modified acrylate has the following structure:

[0013]

[0014] Where n≥1.

[0015] Furthermore, in the caprolactone-modified acrylate, 1≤n≤5, preferably 1≤n≤3.

[0016] In a preferred embodiment, in the caprolactone-modified acrylate, 1≤n≤2.

[0017] Furthermore, the acrylate monomer includes a monofunctional acrylate monomer and / or a multifunctional acrylate monomer; the multifunctional monomer refers to an acrylate monomer with a functionality ≥ 2, and can be selected from at least one of a difunctional acrylate monomer, a trifunctional acrylate monomer, a tetrafunctional acrylate monomer, and a pentafunctional acrylate monomer.

[0018] Furthermore, the weight ratio of the epoxy acrylic resin: caprolactone-modified acrylate: monofunctional acrylic ester monomer: multifunctional acrylic ester monomer is (5-20): (5-25): (15-45): (10-30); preferably (8-15): (5-20): (20-44): (15-25). In the prior art, epoxy resins used in inkjet printing have high viscosity and are brittle and prone to cracking after curing. This application uses epoxy acrylic resins with shorter soft chains to enhance the flexibility of the ink layer. However, the use of epoxy acrylic resins alone cannot solve the cracking problem of the ink when using both UV curing and thermal curing methods, nor can it achieve the reflow soldering protection performance of the ink layer for the subsequent circuit board. On this basis, the present application adds caprolactone-modified acrylate to the system. Caprolactone can significantly improve the toughness of the ink layer under the UV curing system. More importantly, the caprolactone-modified UV monomer still has a high degree of freedom of hydroxyl groups even after UV curing, and can fully react with blocked isocyanates at high temperatures, giving the solder mask ink layer higher toughness, which can perfectly relieve the internal thermal stress caused by high temperature during the reflow soldering process of the present application's solder mask ink layer, and at the same time can also improve the reaction degree of epoxy acrylate, giving the system higher bonding strength. It is worth noting that the ink of the present application is The ink used for inkjet printing also needs to pay special attention to the viscosity and surface tension of the ink to improve the smoothness and precision line width of the printing. In addition, the UV curing process of this application is a comprehensive reaction of epoxy acrylic resin, caprolactone-modified acrylate, monofunctional acrylate monomer and multifunctional acrylate monomer. Only when the weight ratio of each component is strictly controlled to 5-20:5-25:15-45:10-30, can the solder mask ink layer have sufficient bonding force while also having sufficient toughness and adhesion, solve the problems of anti-reflow soldering and anti-tinning performance, and reduce the viscosity of the inkjet ink and increase the surface tension.

[0019] Furthermore, the monofunctional acrylate monomer includes but is not limited to at least one of acryloylmorpholine (ACMO), cyclotrimethylolpropane formal acrylate (CTFA), isobornyl acrylate (IBOA), dicyclopentenyl acrylate (DCPA), trimethylcyclohexyl acrylate (TMCHA), tetrahydrofuran acrylate (THFA), 4-hydroxybutyl acrylate (4-HBA), ethoxylated nonylphenol acrylate, tetrahydrofurfural acrylate, methoxypolyethylene glycol monomethacrylate, allyl methacrylate, and isooctyl acrylate.

[0020] Preferably, the monofunctional acrylate monomer includes at least one of acryloylmorpholine, cyclotrimethylolpropane formal acrylate, isobornyl acrylate, dicyclopentenyl acrylate, trimethylcyclohexyl acrylate, tetrahydrofuran acrylate, and 4-hydroxybutyl acrylate.

[0021] In one embodiment, the monofunctional acrylate monomer includes acryloylmorpholine, cyclotrimethylolpropane formal acrylate, isobornyl acrylate and trimethylcyclohexyl acrylate, with a weight ratio of (3-8): (10-15): (3.5-7): (15-25), preferably 5:13:5.2:20.

[0022] In one embodiment, the monofunctional acrylate monomer includes acryloylmorpholine, isobornyl acrylate and trimethylcyclohexyl acrylate in a weight ratio of (5-10): (13-18): (15-25), preferably 8:15:20.

[0023] In one embodiment, the monofunctional acrylate monomer includes cyclotrimethylolpropane formal acrylate, dicyclopentenyl acrylate, and tetrahydrofuran acrylate, and the weight ratio is (13-20): (7.5-12.5): (10-16), preferably 15:9.2:12.

[0024] In one embodiment, the monofunctional acrylate monomer includes cyclotrimethylolpropane formal acrylate, dicyclopentenyl acrylate and trimethylcyclohexyl acrylate in a weight ratio of (3-8): (5.2-9.5): (15-23), preferably 5:7.2:18.

[0025] In one embodiment, the monofunctional acrylate monomer includes acryloylmorpholine, isobornyl acrylate and 4-hydroxybutyl acrylate in a weight ratio of (8-13): (7-14): (13-18), preferably 11:10:15.

[0026] Furthermore, the bifunctional acrylate monomer is selected from at least one of 1,6-hexanediol diacrylate (HDDA), 1,3-butanediol dimethacrylate, dipropylene glycol diacrylate (DPGDA), cyclohexanedimethanol diacrylate, polyethylene glycol (200) dimethacrylate, polyethylene glycol (400) dimethacrylate, polyethylene glycol (200) diacrylate (PEG (200) DA), and polyethylene glycol (400) diacrylate.

[0027] Furthermore, the bifunctional acrylate monomer includes at least one of 1,6-hexanediol diacrylate, dipropylene glycol diacrylate, and polyethylene glycol (200) diacrylate.

[0028] In one embodiment, the bifunctional acrylate monomer is 1,6-hexanediol diacrylate or dipropylene glycol diacrylate.

[0029] In one embodiment, the bifunctional acrylate monomer includes 1,6-hexanediol diacrylate and dipropylene glycol diacrylate in a weight ratio of (8-12):(3-9), preferably 10:5.

[0030] In one embodiment, the bifunctional acrylate monomer includes 1,6-hexanediol diacrylate, dipropylene glycol diacrylate and polyethylene glycol (200) diacrylate, and the weight ratio of the three is (9-16): (1-5): (3-8), preferably 12:3:5.

[0031] Furthermore, the trifunctional acrylate monomer is selected from triethoxylated trimethylolpropane triacrylate and / or pentaerythritol triacrylate.

[0032] Furthermore, the total amount of the trifunctional acrylate monomer should not exceed 6% of the total weight of the ink components, preferably not more than 5%, and more preferably not more than 3%. When the trifunctional acrylate monomer content is too high, the intermolecular forces and bonding forces within the system increase significantly, leading to an increase in the viscosity of the ink, which is not conducive to the inkjet printing process. Furthermore, excessive cohesion in the system reduces the adhesion strength of the solder mask ink layer to the substrate. Furthermore, during thermal curing and high-temperature reflow soldering, the network skeleton structure in the system cannot withstand the damage caused by thermal stress, resulting in reflow soldering performance failure. Therefore, it is necessary to stipulate that the trifunctional acrylate monomer content should not exceed 5% of the total components.

[0033] Furthermore, the isocyanate is a blocked isocyanate.

[0034] Furthermore, the blocked isocyanate is selected from aliphatic blocked isocyanates and / or alicyclic blocked isocyanates. Aliphatic or alicyclic blocked isocyanates have better heat resistance and can be used in inkjet printing inks under curing conditions that combine UV curing and thermal curing, thereby improving the reflow resistance of the solder mask ink layer.

[0035] Furthermore, the deblocking temperature of the blocked isocyanate is 80-180° C., and the blocked isocyanate may be selected from at least one of Covestro BL3575, BL3475, and Lanxess BI 7951 / BI 7950.

[0036] Furthermore, the photoinitiator includes but is not limited to methyl benzoylbenzoate, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), bis(2,6-dimethylbenzoyl)-2,4,4-trimethylpentylphosphine oxide, 4-methylphenylthiobenzophenone (BMS), 2-methyl-1-[4-methylthiophenyl]-2-morpholinyl-1-propanone, 1-hydroxy-cyclohexyl-phenyl ketone, 2,2-dimethyl One or more of oxy-1,2-diphenylethan-1-one, 2-hydroxy-2-methyl-1-phenyl-1-propanone, isopropylthioanthraquinone (mixture of 2 and 4 isomers), 4-dimethylamino-benzoic acid ethyl ester, 4-dimethylamino-benzoic acid (2-ethyl) ester, tribromomethylphenyl sulfone, 4-chlorobenzophenone, 4-methylbenzophenone, and 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one.

[0037] In a preferred embodiment, the photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide.

[0038] Furthermore, the components of the high heat-resistant inkjet printing ink may also include leveling agents, defoaming agents, wetting agents, dispersants (such as BYK-333, BYK-361N, etc.), surfactants and other additives, pigments (BASF's Pigment Blue 15:4, Pigment Yellow 180, etc.), etc. The present invention is not strictly limited to this and can be adaptively adjusted according to actual needs.

[0039] Furthermore, the content of the auxiliary agent and the pigment in the components does not exceed 6% of the total weight of the components.

[0040] Furthermore, the high heat-resistant inkjet printing ink has a viscosity of 10-30 cps at 25° C. and a surface tension of 28-34 mN / m.

[0041] Secondly, the present application also provides the application of the high heat-resistant inkjet printing ink in the solder mask layer of a circuit board.

[0042] Furthermore, the high heat-resistant inkjet printing ink is cured by a UV curing + thermal curing mode.

[0043] Beneficial effects

[0044] 1. This application optimizes the dosage of each component in the system, especially the weight ratio of epoxy acrylic resin: caprolactone-modified acrylate: monofunctional acrylate monomer: multifunctional acrylate monomer. On the basis of ensuring that the ink has a low viscosity and appropriate surface tension, it also improves the flexibility of the ink layer after UV curing and thermal curing. When the ink layer is used as a solder mask layer of a circuit board, it also improves the reflow performance, adhesion and tin resistance.

[0045] 2. This application uses caprolactone-modified acrylate with a specific degree of polymerization to further control the viscosity of the system and improve the solder resistance of the ink layer, alleviating thermal stress during high-temperature curing and reflow soldering;

[0046] 3. This application uses specific types and amounts of acrylate monomers to undergo a cross-linking reaction with the epoxy acrylic resin, modified acrylate, isocyanate, etc. in the system under UV light, further balancing the cohesion of the ink layer and its adhesion to the substrate, and improving its viscosity;

[0047] 4. This application optimizes the ink components and utilizes the synergy between the components to enable the ink to meet the curing mode of free radical UV curing + thermal curing, thereby improving the heat resistance of the ink layer. DETAILED DESCRIPTION

[0048] Example

[0049] The following Examples 1-5 and Comparative Examples 1-3 all provide a highly heat-resistant inkjet ink. The specific component formula is shown in Table 1 below. The caprolactone-modified acrylate was purchased from Juren Chemical, and the TPO was purchased from Tianjin Jiuri JRCure-1108. The additive was a leveling agent (BYK-361N), added at 0.2% of the total ink volume. The pigment was BASF Pigment Blue 15:4, added at 0.8% of the total ink volume.

[0050] Table 1

[0051]

[0052]

[0053] Performance testing method:

[0054] The high heat-resistant inkjet printing ink of each embodiment and comparative example was spray-printed onto a copper-clad laminate, and irradiated with a UV lamp until cured. The following experiments were performed on the cured inkjet printing film layer:

[0055] 1. Adhesion performance: refer to the standard "GB / T13217.7-2009";

[0056] 2. Reflow performance: refer to standard IPC-SM-840,3.7.3.

[0057] Performance test results:

[0058] The test results are shown in Table 2, where "OK" means the test passed and "NG" means the test failed.

[0059] Table 2

[0060]

[0061] Analyzing the above results, we can see that:

[0062] Comparative Example 1 and Comparative Example 1: In Comparative Example 1, epoxy acrylic resin is not used, and the amount of isocyanate and caprolactone modified acrylate is increased, but the adhesion of the film layer is poor, and the resistance to tin precipitation and reflow soldering is not good.

[0063] Comparative Example 2 and Comparative Example 3: In Comparative Example 3, the amount of caprolactone-modified acrylate is reduced, and the amount of pentaerythritol triacrylate is increased. However, the viscosity of the ink is high, the adhesion of the film layer after curing is reduced, and the tin precipitation resistance and reflow soldering resistance are not passed, which may be because the cohesion and internal stress of the system are too high.

[0064] Comparative Example 3 and Comparative Example 2: Comparative Example 2 does not use lactone-modified acrylate, but increases the content of 4-hydroxybutyl acrylate; however, the viscosity of the prepared ink is very low and the reflow soldering performance is poor.

[0065] In summary, only when the relative amounts of the system components are appropriate can an ink with low viscosity and appropriate surface tension be prepared. The film layer of the ink after UV light and heat curing has strong adhesion, high flexibility and excellent heat resistance.

Claims

1. A high heat-resistant inkjet printing ink, characterized in that: The ink comprises, by total weight of the components, 5-30% epoxy acrylic resin, 4-26% isocyanate, 2-35% modified acrylate, 10-85% acrylate monomer, and 3-18% photoinitiator; The epoxy acrylic resin includes at least one of bisphenol A epoxy acrylic resin, bisphenol F epoxy acrylic resin, novolac epoxy acrylic resin, epoxy acrylate resin, and modified epoxy acrylate resin; The modified acrylate is caprolactone-modified acrylate, and the caprolactone-modified acrylate has the following structure: Among them, 1≤n≤5; The acrylate monomers include monofunctional acrylate monomers and multifunctional acrylate monomers; The weight ratio of the epoxy acrylic resin: caprolactone modified acrylate: monofunctional acrylate monomer: multifunctional acrylate monomer is (5-20): (5-25): (15-45): (10-30).

2. The inkjet printing ink according to claim 1, characterized in that The epoxy acrylic resin is a modified epoxy acrylate resin, and the modified group is selected from at least one of a glycidyl group, an acryl group, an amide group, and a C3-C6 alkylene group.

3. The inkjet printing ink according to claim 2, characterized in that: The modified epoxy acrylate resin is an epoxy acrylate resin co-modified with a glycidyl group and an acryl group.

4. The inkjet printing ink according to claim 1, characterized in that The weight ratio of the epoxy acrylic resin: caprolactone modified acrylate: monofunctional acrylate monomer: multifunctional acrylate monomer is (8-15): (5-20): (20-44): (15-25).

5. The inkjet printing ink according to any one of claims 1 to 4, characterized in that: The high heat-resistant inkjet printing ink has a viscosity of 10-30 cps at 25° C. and a surface tension of 28-34 mN / m.

6. Use of the inkjet printing ink according to any one of claims 1 to 5 in the solder mask layer of a circuit board.

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