Abstract: This paper addresses the issue of easy damage to the surface of optical glass displays during the manufacturing and preparation process. We have developed and prepared an ultra-resistant UV glass protective ink specifically designed for use with cutting fluids. The study investigates the effects of varying ratios of photoinitiators, UV resin formulations, active diluent monomer compositions, and different adhesion promoters on the ink’s surface drying time, adhesion strength, resistance to cutting fluids, and alkali-removal performance. The ultra-resistant UV protective ink developed in this study exhibits rapid curing speed, moderate hardness (2H), excellent adhesion to glass substrates, an alkali-removal time of 60 seconds, and outstanding resistance to cutting fluids—specifically, a resistance duration of 1.2 hours.

Keywords: UV glass protective ink; ultra-resistant cutting fluid; photopolymerization; optical glass display

Chinese Library Classification: TQ637

Document Identification Code: A

I. Preface

Over the past decade or so, as consumer electronics—particularly touch-screen mobile phones—have become increasingly prevalent, the demand for glass screens has risen accordingly. Optical glass, from its raw sheet form to a screen of a predetermined size, undergoes a series of processing steps—including positioning, cutting, engraving, drilling, and edge finishing—which can potentially cause scratches on the glass surface, leading to low yield rates and higher costs. Therefore, it is essential to treat the glass surface to enhance its performance. Glass protective inks exhibit excellent adhesion and masking properties, outstanding scratch resistance, and are easily removed by alkaline solutions after processing, effectively addressing the challenges associated with glass fabrication. Glass protective inks are primarily categorized into thermosetting and UV-curable types. Among these, UV-curable glass protective inks have become the mainstream solution due to their simple processing, high efficiency, and environmental friendliness. Differentiation in mobile phone design is a key strategy that many manufacturers employ to gain a competitive edge. As the screen is the most direct interface through which we interact with a mobile phone, it plays a decisive role in shaping the overall user experience. The trend toward more complex and larger glass screens has extended the time required for glass processing. Consequently, the corresponding glass protective inks must possess exceptional resistance to cutting fluids to ensure the reliability of the manufacturing process.

Currently, most UV glass protective ink products available on the market fail to meet customers’ requirements, which demand that these glass protective inks possess excellent adhesion and masking properties, outstanding scratch resistance, and superior resistance to cutting fluids. Therefore, the purpose of this study is to develop an ultra-resistant-to-cutting-fluid UV glass protective ink that exhibits good adhesion and masking performance, exceptional scratch resistance, and superior resistance to cutting fluids. Furthermore, this study investigates the effects of different photoinitiators, reactive diluent monomers, oligomers, and adhesion promoters on the performance of this protective ink.

II. Main Raw Materials and Testing Instruments

1. Main raw materials and testing instruments

(1) Main raw materials

UV Resins: Polyester acrylate resin B-51, polyester acrylate resin B-505, modified polyester acrylate resin B-531, modified epoxy acrylate resin B-186, and phosphate ester acrylate monomer B-02 (all of the above resins are sourced from Guangdong Boxing New Materials Technology Co., Ltd.).

Photoinitiators: 1-Hydroxycyclohexyl phenyl ketone 184, 2,4,6-trimethylbenzoyl-diphenyl phosphine oxide TPO, and 2,4-diethylthioxanthone DETX (all of the above photoinitiators are sourced from Tianjin Jiuri New Materials Co., Ltd.);

UV monomers: tetrahydrofuran acrylate THFA and dipentaerythritol hexaacrylate DPHA (both monomers supplied by Sartomer), N,N-dimethylacrylamide DMAA (supplied by Kao Corporation, Japan);

Additives: Silane coupling agents γ-aminopropyltriethoxysilane KH550, γ-glycidoxypropyltrimethoxysilane KH560, and γ-(methacryloyloxy)propyltrimethoxysilane KH570 (all of the above silane coupling agents are supplied by Jiangxi Chenguang New Materials Co., Ltd.); filler: 3000-mesh talc powder (Guilin Talc Technology Development Co., Ltd.), pigment: phthalocyanine blue (Yixing Yuxing Pigment Factory), defoaming agent (BASF Chemie, Germany); commercially available cutting fluid HC3310 (Guangzhou Kaidi Petrochemical Co., Ltd.); sodium hydroxide (AR grade, Guangzhou Chemical Reagent Factory).

(2) Test Instruments

UV mercury lamp RW-UVA 3-2-3-bx (Shenzhen Runwo Electromechanical Co., Ltd.); high-speed disperser (Shanghai Modern Environmental Co., Ltd.); three-roll mill (Changzhou Longxin Chemical Machinery Co., Ltd.).

2. Preparation of Ink Samples

This ink is prepared by uniformly mixing, at specific proportions, a UV main resin, an active diluent, a photoinitiator, pigments, an adhesion promoter—silane coupling agent—, an antifoaming agent, and a filler—talc powder—followed by high-speed dispersion and grinding using a three-roll mill. The specific procedure is as follows:

Under room temperature conditions, thoroughly mix the UV resin, reactive diluent, photoinitiator, pigment, silane coupling agent, and defoaming agent until the photoinitiator is completely dissolved. Then, add the filler talc powder and disperse it using a high-speed disperser at 1000 rpm for 10 minutes to obtain a preliminarily homogeneous ink mixture. Next, grind the mixture three times using a three-roll mill to produce the finished ink product described in this experiment.

3. Preparation of Glass Substrates and Performance Testing

(1) Preparation of test glass plates

Thoroughly stir the finely ground finished ink, let it stand for 10 minutes, and take an appropriate amount to apply onto a 200-mesh screen-printing mesh. Screen-print the ink onto a pre-treated, clean mobile phone glass surface. Allow it to sit for a short while until all bubbles have completely disappeared. Place the screen-printed glass plate onto the conveyor belt of a UV mercury lamp curing machine and cure it under ultraviolet light (irradiation dose: 1500 mJ/cm²) to obtain the glass plate coated with the protective ink ready for testing.

(2) Performance Testing Methods

Surface-drying performance: After the ink coating on a glass plate has been cured by UV mercury lamp irradiation, the degree of surface dryness of the ink is assessed using the fingertip touch method to determine the curing status of the ink.

Hardness Test: Measured using a pencil hardness tester, in accordance with the national standard GB/T 6739-2006.

Adhesion Test: The grid test method, conducted in accordance with the national standard GB/T 9286-1988;

Cutting Fluid Resistance Test: Take 8% concentration cutting fluid HC3310 and place it in a beaker. Heat it to 50℃ using a constant-temperature heating jacket. At 50℃, immerse the glass substrate to be tested into the cutting fluid and start timing. Every 0.5 hours, remove the substrate for adhesion testing and record its resistance performance to the cutting fluid—in other words, the longer the resistance time, the better the protective ink performance of the glass, and the more favorable it is for the processing of optical glass displays.

Film-removal performance testing: The film-removal method involves using a strong alkaline solution. Specifically, a 5% sodium hydroxide aqueous solution is prepared in a beaker, heated to 70°C using a constant-temperature heating jacket, and maintained at this temperature. The glass panel to be tested is then immersed in the sodium hydroxide solution, and timing begins immediately. The glass panel is gently shaken continuously throughout the process. Timing stops once the ink coating has completely detached from the glass surface. The time recorded at this point—the duration required for film removal—is measured in seconds. Typically, on the market, the alkaline film-removal time requirement for glass protective inks is that, at temperatures between 60°C and 70°C, the alkaline removal time should fall within the range of 60 to 180 seconds to meet the standard requirements.

III. Results and Discussion

A typical UV-curable ink consists of basic components such as UV resin, reactive diluent monomers, photoinitiators, fillers, pigments, and additives. UV-curable glass protective ink is a functional temporary protective ink that requires the ink to exhibit the following performance characteristics:

1. UV-curable protective ink exhibits excellent screen-printing compatibility.

2. The film formed by this ink after UV curing has a dry surface, exhibits excellent adhesion to glass substrates, and possesses moderate hardness to ensure scratch resistance during the production process. It also demonstrates good resistance to cutting and machining, does not develop bubbles or edge chipping during processing, and can be easily stripped off after glass processing is complete.

Therefore, the main resin used in this study is polyester acrylate B-51, whose structure includes hydrophilic groups and flexible long carbon chains, giving it outstanding characteristics such as excellent flexibility, rapid curing rate, low volatility, and minimal irritation. B-51 exhibits good adhesion to glass substrates and can withstand commonly used cutting fluids with a pH of 9–10; it can also be stripped using strong alkaline solutions. For these reasons, B-51 was selected as the primary resin for the glass protective ink formulation in this study. To enhance the ink’s resistance to cutting fluids, one of three different types of auxiliary resins—B-186, B-531, or B-505—was added to the formulation. B-186 is a modified epoxy acrylate containing IBOA monomer, characterized by a fast curing rate, excellent adhesion to glass substrates, resistance to boiling water, high-temperature stability, and superior chemical resistance. B-531 is a di-functional polyester acrylate that displays exceptional adhesion to substrates such as metal, PET, matte OPP film, and glass; it also boasts excellent flexibility, impact resistance, and resistance to yellowing. B-505 is a modified polyester acrylate with strong adhesion to metal, glass, and plastic substrates. The adhesion promoter added to the formulation is B-02, an acrylic monomer based on phosphate esters. B-02 exhibits excellent adhesion-promoting effects on both glass and metal substrates; however, due to its relatively high acid value, excessive addition may compromise the ink’s resistance to cutting fluids. Therefore, an optimal dosage of 1–2% is recommended. To clearly identify the influence of each component on the ink system and determine the final optimal formulation, all components in the formulation are expressed as weight percentages. The specific formulation ratios and performance test results are shown in Table 1. In the performance tests listed in the table, hardness tests, adhesion tests, cutting-fluid resistance tests, and strong-alkali stripping tests were conducted only after the ink formulation had fully dried.

Table 1: UV Glass Protective Inks with Different Formulations and Their Performance Test Results

Continued from the previous table

1. The Influence of Photoinitiators on the Surface Drying Performance of Inks

Photoinitiators are an essential component in UV-curable ink systems. Under irradiation by a light source, they undergo a transition from the ground state to the excited state, generating active free radicals that initiate free-radical or cationic polymerization reactions involving reactive double bonds. Different photoinitiators exhibit varying sensitivities to different wavelengths of ultraviolet light and differ in their polymerization efficiency. Photoinitiator 184 is popular among users due to its outstanding photoinitiation performance and other well-balanced overall properties. TPO boasts high initiation efficiency and is particularly suitable for colored systems; however, it is relatively more expensive. DETX is generally not used alone but rather in combination with other photoinitiators to enhance light absorption efficiency, thereby accelerating the curing speed, or it can be combined with hydrogen-donor additives to further boost the photoinitiator's initiation efficiency. As shown in Table 1, in experimental groups E1 through E5, under the condition that all other components and their concentrations remain unchanged, neither photoinitiator 184 nor TPO used individually could achieve surface drying of the ink coating. However, when either 184 or TPO was supplemented with a certain amount of DETX, a satisfactory surface-drying effect was achieved. Considering both the economic viability and effectiveness of the formulation, we adopted a photoinitiator combination featuring 184 as the primary component, complemented by TPO and DETX.

2. The Effect of Active Diluent Ratios on Ink Hardness and Surface Drying Performance

Active diluents, also known as monomers, play a crucial role in photopolymerizable ink systems by adjusting the viscosity of the ink. Since they participate directly in the reaction system, they do not produce the high levels of VOC emissions typically associated with solvent-based inks. Active diluents significantly influence the performance of ink systems: monofunctional active diluents exhibit strong diluting power, relatively slow curing speed, low volumetric shrinkage, and excellent adhesion; multifunctional active diluents, on the other hand, have higher cross-linking density and faster reaction rates, making them particularly suitable for enhancing the curing speed and surface hardness of the ink. In Table 1, E5 through E8 utilize a combination of the monofunctional monomer THFA and the multifunctional monomer DPHA. When the amount of THFA is relatively high, the resulting ink exhibits lower hardness. As the proportion of DPHA increases to 10%, the ink hardness rises to 2H, meeting the production process’s requirement for scratch resistance. Further increasing the DPHA content does not lead to a significant improvement in surface hardness, which remains at 2H. Moreover, excessive use of the multifunctional active diluent in E7 begins to degrade the ink’s adhesion properties, and the increased cross-linking density ultimately prolongs the alkali stripping time of the finished ink product. Therefore, in this study, we selected a DPHA content of 10% as the base formulation level.

3. The impact of auxiliary resins on ink adhesion

When using polyester acrylate B-51 alone as the glass protective ink, its resistance to cutting fluids can meet general application requirements. However, in applications with more stringent requirements, further enhancement of the cutting-fluid resistance is necessary. As shown in Table 1, samples E9–E11 were prepared by combining modified epoxy acrylate B-186, modified polyester acrylate B-531, and modified polyester acrylate B-505 with polyester acrylate B-51, respectively. A silane coupling agent KH-550 was used as an adhesion promoter. Sample E6, which used only polyester acrylate B-51, served as a control. The results indicate that incorporating any of these three resins as auxiliary resins into the formulation can significantly improve the cutting-fluid resistance of the glass protective ink. Moreover, the adhesion performance and alkali stripping performance both meet the required standards. In particular, when resin B-505 was used as the auxiliary resin, the ink exhibited the best cutting-fluid resistance, reaching up to 0.6 hours. Therefore, this study adopts a combination of B-51 and B-505 as the main resins for the glass protective ink.

4. The Effect of Adhesion Promoters on the Resistance of Inks to Cutting Fluids

With the main formulation of the glass-protecting ink already established, we tested the effects of different adhesion promoters on the ink’s resistance to cutting fluids. As shown in Table 1, E11–E14 used various types of silane coupling agents along with B-02 as the adhesion promoter. The results indicate that when the silane coupling agent KH-550 is employed as the adhesion promoter, the glass-protecting ink exhibits the best resistance to cutting fluids, reaching a duration of 1.2 hours—a level that meets the stringent demands of the market. Moreover, the cutting-fluid resistance of the glass-protecting ink using silane coupling agents as adhesion promoters is consistently superior to that achieved with the phosphate ester-based acrylate adhesion promoter B-02. This may be attributed to the fact that the substrate is glass, whose primary component is SiO2. Silane coupling agents can form chemical bonds with the small amount of hydroxyl groups present on the glass surface, thereby further enhancing the adhesion between the ink and the glass substrate. At the same time, the Si-O-Si bonds formed by these coupling agents can be cleaved under strong alkaline conditions, making the glass-protecting ink easily removable by alkaline solutions—a feature that aligns perfectly with market requirements for alkali-releasable performance. Furthermore, when KH-550 is used as the adhesion promoter, the ink demonstrates the best resistance to cutting fluids. This may be explained by the fact that, compared to other silane coupling agents, the amino group in amino-silane coupling agents can rapidly undergo a Michael addition reaction with the acrylate double bonds, thus significantly increasing the adhesive strength between the ink and the glass substrate and ultimately improving the ink’s resistance to cutting fluids.

IV. Summary and Outlook

This paper addresses the issue of easy damage to the surface of optical glass displays during the cutting and fabrication process. We have developed and prepared an ultra-resistant UV glass protective ink specifically designed for use with cutting fluids. The study investigates the effects of varying ratios of photoinitiators, UV resin formulations, active diluent monomers, and different adhesion promoters on the ink’s surface drying time, adhesion strength, resistance to cutting fluids, and alkali-removal performance. The results show that the optimal ink formulation—comprising 35 wt% of main resin B-51, 15 wt% of B-505, 10 wt% of the active diluent monomer THFA, 10 wt% of DPHA, 3 wt% of photoinitiator 184, 1.5 wt% of TPO, 0.5 wt% of DETX, 0.5 wt% of defoaming additive, 0.5 wt% of phthalocyanine blue dye, and 23 wt% of 300-mesh talc filler, along with 1 wt% of adhesion promoter KH-550—exhibits rapid surface drying, moderate hardness (2H), excellent adhesion, and an alkali-removal time of 60 seconds, meeting market requirements. Moreover, this ink demonstrates outstanding resistance to cutting fluids, with a resistance duration of 1.2 hours, fully satisfying the stringent demands placed on glass protective inks during the processing and cutting of optical glass displays, thereby promoting the development of display manufacturing in the electronics industry.

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