UV (ultraviolet) shadowless glue for laminating PP (polypropylene) plastic IMD (in-mold decoration) injection molding membrane and preparation method thereof

Abstract

The invention discloses UV (ultraviolet) shadowless glue suitable for laminating a PP (polypropylene) plastic IMD (in-mold decoration) injection molding membrane and a preparation method of the UV shadowless glue. The UV shadowless glue is prepared from functional monomers such as epoxy acrylate, urethane acrylate, trimethylolpropane triacrylate, tripropylene glycol diacrylate and the like, a photoinitiator 1173, an onium salt cationic photoinitiator, a hydroxybenzene triazine ultraviolet absorbent, a low-alkalinity compound light stabilizer, a silane coupling agent, fumed silica, a curing agent, a curing agent, a curing agent, a curing agent, a curing agent and a solvent. The preparation method comprises the following steps: premixing the monomers, dispersing the stabilizer, compounding the main agent, adding the auxiliaries and the like. The glue adopts a free radical-cation synergistic photo-initiation system to realize rapid surface drying and deep curing, and the ultraviolet aging resistance of the glue is improved by adding a weather-resistant stable component. The obtained UV shadowless glue has the advantages of stable construction viscosity, high peel strength, matched thermal expansion coefficient and excellent water, engine oil, ethanol, gasoline and other medium resistance, and is especially suitable for high-reliability lamination application of PP membranes under IMD injection molding conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, in particular to a UV shadowless adhesive for laminating PP plastic IMD injection molding films and a preparation method thereof. Background Art

[0002] Shadowless adhesive, also known as UV adhesive, photosensitive adhesive, or UV-curing adhesive, is an adhesive that relies on ultraviolet (UV) radiation to complete its curing reaction. UV photoinitiators absorb UV light to generate free radicals or cations, which trigger monomer polymerization and cross-linking reactions, achieving a rapid transition from liquid to solid. This type of adhesive offers advantages such as fast curing, high transparency, and resistance to yellowing and whitening. It is widely used in the bonding and packaging of glass products, electrical and electronic products, the automotive industry, optoelectronics, medical supplies, and other fields.

[0003] However, existing UV adhesives still have many limitations. For example, traditional epoxy resin adhesives and unsaturated resin UV adhesives have low strength, poor bonding performance, and high curing energy requirements (300mj / cm 2 The curing process releases toxic gases and often requires high temperatures, which compromises operational safety and energy conservation and emission reduction. Furthermore, these adhesives generally suffer from low elongation and poor weather resistance, making them difficult to adapt to complex operating environments and offering limited shock absorption at the bonding interface.

[0004] In recent years, IMD (In-Mold Decoration) technology has become increasingly popular in the decorative and functional applications of plastic products. Common plastic materials include ABS, PC, PMMA, etc. However, PP (polypropylene) plastic presents significant difficulties in IMD injection molding applications due to its large shrinkage rate and low surface energy. On the one hand, the shrinkage of PP plastic can easily cause the diaphragm to burst due to thermal expansion and contraction during the injection molding process; on the other hand, its low surface energy makes it difficult to form an effective bond with the diaphragm. Therefore, existing technologies generally only use PP for IML (In-Mold Labeling) blow molding processes and are not suitable for IMD injection molding.

[0005] Currently, the common method for laminating PP plastic parts with films is to print first and then attach them. However, this method is not only inefficient and time-consuming, but also suffers from unstable adhesion quality, with the film prone to falling off after a period of use. Furthermore, existing UV adhesives for IMD films are not designed specifically for the characteristics of PP materials. They fail to meet the process requirements for laminating PP plastic IMD films in terms of coating drying, heat and weather resistance, bond strength, refractive index, and high-temperature injection stability.

[0006] Therefore, there is an urgent need to develop a UV shadowless adhesive specifically for laminating PP plastic IMD injection molding films to solve the bonding problem of PP plastic in IMD injection molding applications in the existing technology. Summary of the Invention

[0007] In view of the above-mentioned shortcomings of the prior art, the purpose of the present invention is to provide a UV shadowless adhesive for laminating PP plastic IMD injection molding diaphragms and a preparation method thereof, so as to solve the problem that PP plastic is difficult to apply to IMD injection molding in the prior art, as well as the problem of diaphragm bonding of PP plastic in IMD injection molding applications.

[0008] A UV shadowless adhesive suitable for laminating PP plastic IMD injection molding films, the UV shadowless adhesive comprising the following components by mass percentage:

[0009] Epoxy acrylate: 30% to 38%, providing high cross-linking density, enhancing hardness and chemical resistance after curing;

[0010] Polyurethane acrylate: 15% to 20%, which gives the glue flexibility and impact toughness, and adapts to the stress changes caused by thermal shrinkage of PP;

[0011] Trimethylolpropane triacrylate (TMPTA): 20% to 30%, a multifunctional monomer that enhances crosslinking density and mechanical strength;

[0012] Tripropylene glycol diacrylate (HDDA): 10% to 20%, to adjust the viscosity and curing rate of the glue and balance the flexibility of the laminated film;

[0013] Photoinitiator 1173: 3% to 5%, using a highly efficient free radical initiator to accelerate surface curing;

[0014] Onium salt cationic photoinitiator: 0.5% to 2%, synergistic deep curing, reducing curing shrinkage;

[0015] Hydroxyphenyltriazine UV absorber: 0.5% to 1.5%, to improve weather resistance;

[0016] Low alkalinity composite light stabilizer: 0.5% to 2%, improves weather resistance;

[0017] Silane coupling agent: 0.5% to 1.5%, enhances adhesion;

[0018] Fumed silica: 0.3% to 1%, thixotropic thickening to prevent sagging;

[0019] Defoaming agent: 0.3% to 1%, eliminates bubbles and improves the uniformity of the adhesive layer.

[0020] Among them, photoinitiator 1173 and onium salt cationic photoinitiator form a dual-mechanism initiation system, improving surface and deep-layer curing efficiency; hydroxyphenyltriazine ultraviolet absorber (hydroxyphenyltriazine UVA) and low-alkalinity composite light stabilizer (low-alkalinity composite HALS) jointly improve light aging resistance, ensuring the long-term use of IMD film outdoors or in strong light environments.

[0021] This formula is designed to simultaneously meet the performance requirements of the IMD injection molding process, such as high adhesion, heat shock resistance, low-energy rapid curing, and excellent weather resistance, especially to solve the problems caused by the low surface energy and large thermal deformation of PP materials.

[0022] Further preferably, the UV shadowless adhesive is composed of the following components by mass percentage:

[0023] Epoxy acrylate: 34%,

[0024] Polyurethane acrylate: 17%,

[0025] Trimethylolpropane triacrylate: 25%,

[0026] Tripropylene glycol diacrylate: 15%,

[0027] Photoinitiator 1173: 4%,

[0028] Onium salt cationic photoinitiator: 1%,

[0029] Hydroxyphenyltriazine UV absorber: 0.8%,

[0030] Low alkalinity composite light stabilizer: 1.2%,

[0031] Silane coupling agent: 1%,

[0032] Fumed silica: 0.5%,

[0033] Defoaming agent: 0.5%.

[0034] This formulation provides a preferred implementation formula, derived from a combination of formulas proven to be the most effective in experimental testing. By optimizing the ratio, it balances the IMD diaphragm's flexibility (polyurethane acrylate), hardness (epoxy acrylate), fast curing, and adhesion properties; achieving the optimal application viscosity and curing speed during the coating process; and ensuring that stress concentration during subsequent injection molding does not cause diaphragm cracking or delamination.

[0035] Furthermore, the UV shadowless adhesive has the following performance indicators:

[0036] a. Viscosity is (55±5) s (25℃, Ford Cup No. 4), suitable for 300-400 LPI anilox roll coating; ensure uniform coating in high speed 300-400 LPI anilox roll, neither sagging nor plate clogging;

[0037] Wherein the "s" in "viscosity is (55±5) s (25℃, Ford Cup No. 4)" means: the time (in seconds) taken for the glue to completely flow out of the Ford Cup No. 4, which is the standard representation of the efflux time method for measuring viscosity. It means that when measured at 25℃ using Ford Cup No. 4, the glue should completely flow out of the cup within 50-60 seconds. This time reflects the dynamic flowability of the glue, which is not the absolute viscosity in units of Pa·s or cP, but the operational viscosity of the UV mask glue indirectly represented by the standard efflux time.

[0038] b. The light energy required for UV curing is not less than 100 mj / cm 2 , and the effective wavelength range is 200-400 nm; meet the needs of rapid and deep curing, and improve production efficiency;

[0039] This performance indicator refers to the minimum ultraviolet energy required for the UV mask glue to achieve complete curing, with the unit being millijoules per square centimeter (mJ / cm 2 ). It represents the radiation intensity required for the material to change from a liquid state to a stable solid state. The UV irradiance meter is used to measure the irradiance intensity and energy output of the UV lamp, and the irradiation time is adjusted so that the total energy is ≥100 mJ / cm 2 , and the glue layer is completely cured (no sticky hand, no surface drying, and peelable test). Low energy requirement means that it is suitable for most commercial UV light sources, reduces energy consumption and improves curing efficiency, and is suitable for high-speed production lines.

[0040] c. Linear expansion coefficient of the glue layer after curing is 9.05±1×10 -5 / K; match the thermal expansion properties of the film, avoid peeling and cracking;

[0041] By measuring the linear expansion coefficient of the cured layer after curing the UV mask glue, the value is close to the thermal expansion coefficient of the PP film (usually 8-10×10 -5 / K), which can effectively prevent the cracking or peeling of the bonding interface caused by thermal stress mismatch, and is suitable for high-temperature cycle applications of injection molding.

[0042] d. 180° peel strength is not less than 0.3 N / mm; ensure long-term firm bonding;

[0043] This performance index represents the force required to peel the bonded film in the opposite direction at 180°, with units of Newton per millimeter (N / mm), measuring the bonding strength. The test method is to bond the PP substrate with the film and cure, use a peel tester to peel at an angle of 180° and record the force value. ≥0.3 N / mm is usually the industry's minimum requirement for IMD injection molding film structure, and the product of the present application exceeds this value, ensuring that the film does not fall off due to shrinkage or stress after injection molding, suitable for complex curved surfaces and structural parts.

[0044] e. No abnormal phenomena at -30°C to 80°C temperature cycle; UV shadowless glue is resistant to cold and hot impact, ensuring stability in complex industrial environments.

[0045] This performance index refers to whether the structure undergoes abnormal changes such as peeling, cracking, and blistering under repeated high and low temperature alternating environmental stress. Test method: the bonded sample after curing of the UV shadowless glue is first frozen in a cold and hot cycle oven at -30°C for 2-4 hours; then transferred to 80°C for heating for 2-4 hours; complete one cycle, a total of 3-5 rounds; check the appearance of the bonding interface and the glue layer. There are two stages of high temperature injection and cooling molding during the IMD injection molding process, and the glue layer must withstand cold and hot impact; this test can simulate the actual use and processing process to verify the reliability of the glue in extreme environments.

[0046] f. No abnormalities in water, 10W / 30 engine oil, anhydrous ethanol, and 93# gasoline immersion tests.

[0047] This performance index belongs to the category of chemical resistance, aiming to evaluate the structural stability and bonding strength of the UV shadowless glue after long-term contact with various typical industrial liquid media, verifying its adaptability in actual application environments. Mainly includes the following indicators:

[0048] Water resistance test

[0049] Test conditions: after placing the IMD film sample after lamination at room temperature (23°C ± 2°C) for 24 hours; immerse in 20°C ± 2°C pure water for 4 hours; take out and dry naturally, observe the glue layer state and bonding interface.

[0050] Performance judgment standard: no blistering, peeling, swelling, whitening or loose bonding phenomenon in the glue layer; the surface is still smooth and transparent, and the bonding strength has not decreased significantly.

[0051] Technical significance: verify the hydrolysis resistance of the UV glue in humid, high humidity, and cleaning conditions, suitable for household appliances, medical or humid environment structural bonding.

[0052] Engine oil resistance test

[0053] Test conditions: After the laminated IMD diaphragm sample is placed at room temperature for 24 hours, it is immersed in 10W / 30 engine lubricating oil at 20℃±2℃ for 12 hours. The sample is removed and wiped dry, and the changes in the adhesive layer and the adhesion status are observed.

[0054] Performance judgment criteria: The colloid has no softening, swelling, or oil leakage; the adhesive film has no warping, falling off, or decreased bonding strength.

[0055] Technical significance: Simulates the oil resistance of motorcycles, motor housings and other parts in oily environments to ensure that there is no delamination or penetration failure during long-term operation.

[0056] Ethanol resistance test

[0057] Test conditions: After laminating the IMD film sample, let it stand at room temperature for 24 hours. Then soak it in anhydrous ethanol at 20℃±2℃ for 4 hours. After drying, evaluate the transparency, adhesion, and deformation of the adhesive layer.

[0058] Performance judgment criteria: The adhesive layer is not sticky, does not whiten, and does not fall off; the bonding interface is complete and has strong resistance to solvent corrosion.

[0059] Technical significance: It meets the requirements of medical and electrical housing surface disinfection, alcohol wiping and other environments to ensure that the adhesive layer is stable and not corroded.

[0060] Gasoline resistance test

[0061] Test conditions: Immerse the laminated IMD diaphragm sample in 93# gasoline for 60 minutes (20±2°C); let it dry naturally and observe the bonding condition between the surface and the structure.

[0062] Performance judgment criteria: The adhesive layer has no swelling, softening, cracking or delamination; the appearance has no gloss loss or peeling.

[0063] Technical significance: Directly verify the gasoline resistance of the product in fuel exposure or gas stations, and peripheral components of the power system. It is suitable for components in the fuel tank area of ​​automobiles and motorcycles.

[0064] This type of chemical medium tolerance test simulates the actual working conditions of the PP film and UV adhesive laminate structure in typical usage scenarios such as outdoor environments, mechanical operation, chemical cleaning, and solvent contact. It can fully reflect the cross-linking stability, anti-penetration ability and adhesion durability of the adhesive layer, and is an essential verification item for industrial-grade adhesive materials.

[0065] Furthermore, the epoxy acrylate is a high-functionality prepolymer with a bisphenol A structure; and the polyurethane acrylate has a flexible segment in the molecular chain.

[0066] Epoxy acrylate, with its bisphenol A structure, offers increased hardness and chemical stability. Polyurethane acrylate, with its flexible chain segments, enhances low-temperature flexibility and stress-relieving properties, making it particularly suitable for materials prone to shrinkage, such as PP. The combination of these two materials enhances the adhesive interface's resistance to stress cracking, improving the injection molding stability and service life of the IMD diaphragm.

[0067] The present invention provides a method for preparing the UV shadowless adhesive, comprising the following steps:

[0068] S1. Compound monomer: Mix trimethylolpropane triacrylate and tripropylene glycol diacrylate in proportion, stir at 400±30 rpm for 300 seconds, and set aside;

[0069] S2. Compound stabilizer: Mix the hydroxyphenyltriazine UV absorber and the low-alkalinity composite light stabilizer in proportion, stir at 200±30 rpm for 180 seconds, and set aside;

[0070] S3, prepolymer mixing: epoxy acrylate, polyurethane acrylate and the compound monomer of step S1 are added into a reaction kettle according to a proportion, and stirred at 400±30 rpm for 600-800 seconds at 40-60°C until uniformly mixed;

[0071] S4, adding auxiliary agents: adding photoinitiator 1173, onium salt cationic photoinitiator, silane coupling agent, fumed silica, defoaming agent and the compounded stabilizer of step S2 to the prepolymer of step S3 in sequence, and stirring continuously for 30 to 60 minutes until fully dispersed;

[0072] S5. Purification and filtration: Remove impurities through a 200-400 mesh filter or centrifuge to obtain UV shadowless adhesive.

[0073] The preparation method is precisely defined by the five-step process from S1 to S5. S1 to S2 are the uniform compounding of the early monomers and stabilizers to provide mixing uniformity for subsequent reactions; S3 is the combination of the resin and the main monomer and stirring under appropriate temperature conditions to avoid premature curing; S4 is the key auxiliary agent addition step to ensure the integrity of the light-curing system; S5 ensures consistent quality control of the final glue.

[0074] Furthermore, the method includes UV curing verification in step S6: a small amount of UV shadowless adhesive prepared in step S5 is coated on the surface of the substrate and irradiated with a 365nm ultraviolet lamp to evaluate its curing rate and hardness; wherein the UV irradiation time is controlled between 0.05 and 1.2 seconds.

[0075] The curing speed and hardness of the prepared adhesive are tested using 365nm UV light; the curing time window (0.05-1.2 seconds) matches the production cycle and curing efficiency. This ensures that the process meets the IMD production rhythm, provides a test basis for batch glue consistency and end-use performance, and also provides verifiability and testing standardization value.

[0076] The present invention provides a UV shadowless adhesive for laminating PP plastic IMD injection molding films and a preparation method thereof, which overcomes many technical bottlenecks in the application of existing UV glues in PP materials and has the following significant technical advantages and beneficial effects:

[0077] 1) Significantly improve the bonding performance of PP materials

[0078] The present invention uses epoxy acrylate and polyurethane acrylate in combination, thereby ensuring cross-linking hardness and structural stability while enhancing the flexible adaptability and stress buffering capacity of the glue to the PP substrate, effectively improving its bonding firmness and finished product consistency during the IMD injection molding process.

[0079] 2) Optimize UV ​​curing efficiency and energy consumption control

[0080] The glue adopts a dual mechanism synergistic initiation system formed by 1173 and onium salt photoinitiator, which can achieve rapid curing of the surface and deep layer under low UV light energy conditions. The energy required for curing is lower than that of traditional UV glue (≤100mj / cm 2 ), which improves the curing rate and reduces energy consumption, meeting the beat requirements of large-scale high-speed IMD injection molding process.

[0081] 3) Enhance environmental adaptability and long-term stability

[0082] Compared with the existing technology, the UV shadowless adhesive formula of the present invention specifically introduces modified components such as photoinitiator 1173, onium salt cationic photoinitiator, hydroxyphenyltriazine ultraviolet absorber, low-alkalinity composite light stabilizer and an appropriate amount of fumed silica. These improvements show significant effects in improving temperature resistance and weather resistance.

[0083] Among them, photoinitiator 1173 is a highly efficient free radical initiator that can quickly initiate polymerization reactions under lower light energy. It is combined with an onium salt cationic photoinitiator to construct a free radical-cationic dual initiation system, which can not only achieve rapid surface curing, but also effectively promote uniform curing of the deep adhesive layer, thereby enhancing the cross-linking density and improving the overall thermal stability and colloidal structure integrity.

[0084] Hydroxyphenyltriazine ultraviolet absorbers (UVA) have excellent absorption range coverage and can effectively shield UV radiation in the range of 200-400nm, preventing the adhesive layer from yellowing, chain breakage and photolysis failure under long-term ultraviolet exposure; while low-alkalinity composite light stabilizers (HALS) can achieve continuous protection of the polymer main chain by capturing degradation intermediates in the form of free radicals, significantly improving the UV aging stability and outdoor weather resistance of UV shadowless adhesives.

[0085] In addition, the introduction of fumed silica not only acts as a thixotropy regulator to improve coating stability, but also forms a fine inorganic filler network structure after the adhesive layer is cured, thereby enhancing heat creep resistance, further inhibiting thermal expansion deformation, and improving the dimensional stability and interface bonding strength of the material under high and low temperature alternating working conditions.

[0086] Taking into account the synergistic effect of the above components, the UV shadowless adhesive provided by the present invention can maintain structural stability under temperature cycles from -30°C to 80°C and long-term UV exposure conditions without cracking, bubbling or degumming, which is significantly superior to the UV adhesive colloids in the prior art that do not adopt the above-mentioned stabilization system.

[0087] 4) Good fluidity and construction adaptability

[0088] The colloid viscosity is controlled at 55±5 seconds (25℃, coating -4 cups), which is suitable for the high-precision coating process of 300-400LPI high-line count anilox roller. It has excellent fluidity and thixotropy, which can avoid problems such as sagging, bubbles or dot clogging, ensuring the uniformity of glue coating and coating quality.

[0089] 5) Excellent media resistance and mechanical strength

[0090] After curing, the adhesive layer not only has high peel strength (≥0.3N / mm), but can also withstand thermal cycling shocks from -30℃ to 80℃, and can withstand long-term immersion in media such as pure water, engine oil, ethanol, gasoline, etc. without abnormalities, meeting the stringent usage requirements in complex industrial environments.

[0091] 6) The process is clear, and the preparation is simple and easy to control

[0092] The preparation method proposed in the present invention can realize industrial-scale production through standardized ingredients, temperature-controlled stirring, and the sequential addition and purification of auxiliary agents. It has high formula stability, good product consistency, and is easy to implement quality control and process standardization.

[0093] In summary, the present invention not only achieves a technological breakthrough in the field of IMD injection molding film lamination of PP plastics, but also has significant improvements in bonding strength, construction adaptability, environmentally friendly curing, aging resistance, etc., and has good promotion and application value and industrialization prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0094] The contents and symbols of the drawings in this specification are briefly described as follows:

[0095] Figure 1 This is a radar chart of the comprehensive scores of Example 1, Example 2, and Example 3 under six key performance indicators. DETAILED DESCRIPTION

[0096] The present invention will be further described below with reference to some non-limiting embodiments of the present invention. However, it should be understood that these descriptions are merely illustrative and are not intended to limit the scope of the present invention. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessary confusion of the present invention.

[0097] Example 1: Preparation and performance testing of low cross-linking ratio glue

[0098] This embodiment provides a UV shadowless adhesive suitable for laminating PP plastic IMD injection molding films, and its component ratio and preparation process are as follows:

[0099] 1. The formula composition (by mass percentage) is shown in Table 1-1.

[0100] Table 1-1 Components of UV shadowless adhesive in percentage by mass in Example 1

[0101] Component name Content (wt%) Epoxy acrylate 30％ polyurethane acrylate 20％ Trimethylolpropane triacrylate (TMPTA) 20％ Tripropylene glycol diacrylate (HDDA) 10％ Photoinitiator 1173 5％ Onium salt cationic photoinitiators 2％ Hydroxyphenyltriazine UV absorbers 1.5％ Low Alkalinity Composite Light Stabilizer (HALS) 2％ Silane coupling agent KH-550 1.5％ Fumed silica 1％ Defoaming agent UV-225 1％

[0102] 2. Preparation process: The steps for preparing the UV shadowless adhesive are as follows:

[0103] Step S1: Premixing of compound monomers

[0104] Trimethylolpropane triacrylate (TMPTA) and tripropylene glycol diacrylate (HDDA) were added to a stainless steel reaction vessel in proportion, and stirred at room temperature (25°C ± 2°C) at a stirring speed of 400 ± 30 rpm for 300 seconds to form a uniform and transparent composite monomer A.

[0105] Step S2: Stabilizer premixing

[0106] The hydroxyphenyltriazine ultraviolet absorber (UVA) and the low-alkalinity composite HALS light stabilizer (HALS) were weighed in proportion and mixed, and stirred at 200±30 rpm in a glass container for 180 seconds to form a uniform stabilizer mixture B.

[0107] Step S3: Mixing the main resin with the compound monomer

[0108] Put epoxy acrylate and polyurethane acrylate into the main stirring tank, start the stirrer, and add the compound monomer A obtained in step S1;

[0109] The stirring speed was controlled at 400±30 rpm, the temperature was raised to 40-50°C, and the stirring time was controlled at 600-800 seconds to ensure the homogeneity of the system but not to initiate the prepolymerization reaction.

[0110] Step S4: Add additives in sequence

[0111] While maintaining stirring, add the following additives in sequence. Continue stirring for 30 to 60 seconds after adding each additive to fully disperse it:

[0112] Photoinitiator 1173;

[0113] Onium salt cationic photoinitiators;

[0114] Silane coupling agent KH-550;

[0115] Fumed silica (slowly dispersed and added);

[0116] Defoaming agent UV-225;

[0117] Stabilizer mixture B.

[0118] After all components are added, continue stirring for 30 to 60 minutes until the system is fully dispersed and there are no agglomerated particles or precipitates when observed with the naked eye.

[0119] Step S5: Purification and Filtration

[0120] Use a 300-mesh stainless steel filter to physically filter the mixed liquid to remove impurities and unreacted agglomerates; if necessary, perform a vacuum degassing treatment (-0.09 MPa, 5 minutes); or use a high-speed centrifugation at 2000 rpm (3 minutes) to remove fine impurities; ultimately, a transparent, uniform, and bubble-free UV shadowless adhesive product is obtained.

[0121] Step S6: Curing Verification

[0122] A small amount of the prepared glue solution was sampled and applied to the surface of the plasma-treated PP film. A UV curing lamp with a wavelength of 365 nm (intensity of 100 mW / cm 2 ) irradiate for 0.6 to 1.2 seconds, observe its surface drying and complete curing; the surface of the cured adhesive layer is smooth, uniform, without pinholes, bubbles, or sagging, and is suitable for 300 to 400 LPI anilox roller process.

[0123] 3. Test results

[0124] The following is a detailed description of the performance test results of the UV shadowless adhesive prepared in Example 1. The test items cover key indicators such as rheological properties, curing properties, bonding strength, thermal stability and chemical resistance. All of them are performed using standardized test methods and are given in Tables 1-2 and in an explanatory form.

[0125] Table 1-2 Summary and description of test results of Example 1

[0126]

[0127]

[0128] 4. Summary and analysis:

[0129] Rheological properties: precise viscosity control, good coating adaptability, suitable for film material process of fine pattern anilox printing;

[0130] UV curing performance: The dual-initiator system ensures rapid curing of the surface and deep layers, with surface curing time of 0.6 to 1.2 seconds for complete drying.

[0131] Adhesion ability: It exhibits excellent initial adhesion and peel strength for PP / film composite structures, meeting IMD process requirements;

[0132] Thermodynamic properties: The thermal expansion coefficient is well matched with PP, and it will not delaminate or crack even after repeated high and low temperature impacts;

[0133] Chemical resistance: No obvious abnormalities after immersion in a variety of typical media (pure water, engine oil, ethanol, gasoline), with high reliability.

[0134] The glue formula of this embodiment has high softness and good workability; however, the bonding strength is slightly lower and the curing time is slightly longer, which is suitable for ordinary-grade IMD requirements.

[0135] Example 2: Highly cross-linked and high curing rate glue

[0136] 1. The formula composition (by mass percentage) is shown in Table 2-1.

[0137] Table 2-1 Components of UV shadowless adhesive in Example 2 by mass percentage

[0138] Component name Content (wt%) Epoxy acrylate (bisphenol A type structure) 38％ Polyurethane acrylate (containing soft segments) 15％ Trimethylolpropane triacrylate (TMPTA) 30％ Tripropylene glycol diacrylate (HDDA) 20％ Photoinitiator 1173 3％ Onium salt cationic photoinitiators 0.5％ Hydroxyphenyltriazine UV absorbers 0.5％ Low Alkalinity Composite Light Stabilizer (HALS) 0.5％ Silane coupling agent KH-550 0.5％ Fumed silica 0.3％ Defoaming agent UV-225 0.3％

[0139] 2. Preparation process

[0140] The preparation steps of the UV shadowless adhesive described in this embodiment are as follows:

[0141] Step S1: Add TMPTA and HDDA into a stirred tank and stir at 400±30 rpm for 300 seconds to form a composite monomer A;

[0142] Step S2: mixing the hydroxyphenyltriazine ultraviolet absorber and the HALS light stabilizer in proportion, and stirring at 200±30 rpm for 180 seconds to form a composite stabilizer B;

[0143] Step S3: putting epoxy acrylate and polyurethane acrylate into a stirring tank, adding compound monomer A, controlling the temperature at 40-50° C., and stirring for 600-800 seconds;

[0144] Step S4: adding photoinitiator 1173, onium salt cationic photoinitiator, KH-550, fumed silica, defoamer and compound stabilizer B in sequence, and continuing stirring for 30 to 60 minutes;

[0145] Step S5: Filter the glue solution through a 300-mesh filter and degas at -0.09 MPa for 5 minutes or centrifuge at 2000 rpm for 3 minutes;

[0146] Step S6: The sample is dropped onto the PP film and irradiated with a 365nm ultraviolet light source for 0.05 to 0.1 seconds. The film is completely cured and has a smooth surface without bubbles.

[0147] 3. Test results are shown in Table 2-2.

[0148] Table 2-2 Summary and description of test results of Example 2

[0149]

[0150] 4. Summary and analysis:

[0151] Rheological properties: The viscosity of this embodiment is controlled at about 52 seconds (25°C, coating -4 cups), which is lower than that of Example 1. It has faster fluidity and self-spreading properties and is suitable for high-speed coating applications, especially for automated spray and roller coating systems.

[0152] UV curing performance: Using a higher ratio of TMPTA and HDDA, combined with a dual initiation system (free radical + cation), the UV curing time is shortened to within 0.05 to 0.1 seconds. The curing efficiency is the fastest among the three groups, suitable for high-speed continuous IMD injection molding cycles;

[0153] Adhesion ability: After curing, the peel strength of the adhesive layer reaches 0.35N / mm, which is significantly higher than the IMD film bonding process requirement of 0.3N / mm. It has excellent adhesion and is suitable for laminating decorative film parts with high structural strength requirements.

[0154] Thermodynamic properties: The linear thermal expansion coefficient of the adhesive layer is 9.07×10 -5 / K, can better match the thermal deformation characteristics of PP film, and is not prone to debonding or bubbling under repeated injection molding temperature difference shock;

[0155] Chemical resistance: After immersion tests in typical industrial media such as pure water, 10W / 30 engine oil, anhydrous ethanol and 93# gasoline, the adhesive layer showed no softening, no peeling, and no decrease in bonding strength, demonstrating good chemical stability. It is suitable for complex oily environments such as motorcycle housings and electrical seals.

[0156] The glue formula of this embodiment has the fastest curing speed and good structural rigidity; however, the viscosity is low and the construction stability is slightly poor; the flexibility is insufficient and may be limited in scenarios with severe thermal expansion and contraction.

[0157] 1.1 Example 3: Preparation and performance testing of the optimal ratio of UV shadowless adhesive

[0158] This embodiment adopts the optimal ratio formula, which has the best balance between peel strength, thermal matching, construction performance and environmental adaptability.

[0159] 1. The formula composition (by mass percentage) is shown in Table 3-1.

[0160] Table 3-1 Components of UV shadowless adhesive in Example 3 by mass percentage

[0161] Component name Content (wt%) Epoxy acrylate (bisphenol A type) 34％ Polyurethane acrylate (containing soft segments) 17％ Trimethylolpropane triacrylate (TMPTA) 25％ Tripropylene glycol diacrylate (HDDA) 15％ Photoinitiator 1173 4％ Onium salt cationic photoinitiators 1％ Hydroxyphenyltriazine UV absorbers 0.8％ Low Alkalinity Composite Light Stabilizer (HALS) 1.2％ Silane coupling agent KH-550 1％ Fumed silica 0.5％ Defoaming agent UV-225 0.5％

[0162] 2. Preparation process

[0163] The preparation steps were carried out in full accordance with the standard procedures from S1 to S6 in Example 1.

[0164] 3. Test results are shown in Table 3-2.

[0165] Table 3-2 Summary and description of test results of Example 3

[0166]

[0167]

[0168] 4. Summary and analysis:

[0169] Rheological properties: The viscosity of this embodiment is controlled at 55 seconds (25°C, coating -4 cups), which is in the center of the recommended application window. It has the strongest coating adaptability and is suitable for 300-400LPI anilox roller fine pattern printing process. It also has good uniformity and anti-sagging performance.

[0170] UV curing performance: The rational design of the free radical and cationic synergistic photoinitiator system, combined with a moderate ratio of bifunctional / trifunctional monomers, allows the adhesive layer to be completely dry within 0.08 to 0.2 seconds, achieving both high efficiency and curing depth, meeting the pre-curing requirements of high-speed IMD films.

[0171] Adhesion ability: The peel strength is as high as 0.38N / mm, the highest among the three groups of examples, significantly higher than the conventional PP film bonding process standard of ≥0.3N / mm. It is suitable for complex bonding scenarios such as multi-layer film stacking and curved surface composites with high requirements for structural stability.

[0172] Thermodynamic properties: The linear thermal expansion coefficient of the adhesive layer is 9.05×10 -5 / K, precisely matches the thermal deformation characteristics of the PP substrate, and is less likely to cause interfacial stress mismatch during injection molding cooling shrinkage or high and low temperature cycling environments, ensuring long-term stability of the composite layer;

[0173] Chemical resistance: Immersion tests in typical media such as pure water, 10W / 30 motor oil, anhydrous ethanol and 93# gasoline showed stability, without softening, blistering, peeling or loss of adhesion, demonstrating excellent chemical resistance. It is suitable for complex working environments such as automobiles, motorcycles, and electrical appliances.

[0174] This formula is the most preferred solution of the present invention, achieving a good balance between hardness, flexibility, photocuring efficiency and environmental adaptability. It is suitable for high-reliability occasions such as outdoor components, automotive instruments, motorcycle panels, etc., and has mass production and process stability.

[0175] Comparative analysis of embodiments:

[0176] Table 4 Comparison of test results of Example 1, Example 2 and Example 3

[0177]

[0178] As shown in Table 4, the following is a comparative analysis of the test items of Example 1, Example 2, and Example 3:

[0179] 1. Comparison of formula structure and flexibility

[0180] Example 1 emphasizes flexibility and workability, has the lowest epoxy acrylate content (30%) and the highest polyurethane content (20%), and is suitable for occasions with high flexibility requirements.

[0181] Example 2 emphasizes curing speed and strength, with epoxy acrylate reaching 38% and trifunctional monomer TMPTA as high as 30%, which may easily lead to excessive rigidity and poor flexibility.

[0182] The third embodiment is between the two, taking into account both hardness and flexibility, ensuring that there is no film bursting or cracking, and is suitable for high-reliability occasions.

[0183] 2. Comparison of curing efficiency and energy consumption

[0184] The second embodiment has the fastest curing time, which takes only 0.05 to 0.1 seconds to complete, and is suitable for high-speed production on the assembly line.

[0185] The curing time of Example 3 is 0.08 to 0.2 seconds, and the efficiency is only slightly lower than that of Example 2, but the curing uniformity and the applicable layer thickness range are wider;

[0186] The first embodiment cures slowly and is suitable for scenarios with loose process requirements.

[0187] 3. Adhesion performance comparison

[0188] In terms of peel strength, Example Three is the highest (0.38 N / mm) and is more stable, especially suitable for PP and PET composite long-term service applications;

[0189] Example Two (0.35 N / mm) and Example One (0.32 N / mm) are also higher than the industry standard, but slightly inferior to Example Three.

[0190] 4. Environmental adaptability

[0191] All examples passed high and low temperature, water, oil, alcohol, gasoline tests; Example Three maintained the best form in medium resistance and high and low temperature cycles, without discoloration and delamination, and was the best among the three.

[0192] According to the objective technical data of the test results of Example One, Example Two and Example Three, combined with typical industrial material evaluation standards, a semi-quantitative scoring method is used to construct, as shown in Table 5, the test results of Example One, Example Two and Example Three are assigned to each test item according to the source and scoring logic of the project dimension in the summary and explanation, and the assigned table of test items is obtained, as shown in Table 6. These scores are based on the quantitative data (such as peel strength, viscosity) + qualitative results (such as “no abnormalities”) for engineering material scoring logic conversion, generating a comparative visualization radar chart (such as Figure 1

[0193] Table 5 Radar chart performance score index table

[0194]

[0195] Note: This table explains in detail the scoring source and logical basis of each performance dimension, explains the corresponding experimental data or material performance indicators behind the score, and ensures that the score has traceability and engineering rationality.

[0196] Table 6 Example performance dimension quantitative scoring table

[0197] index Example 1 Example 2 Example 3 Viscosity construction 8 7 9 UV curing speed 6 10 9 Peel strength 7 8 10 Thermal expansion matching 9 8 10 Coating suitability 8 7 10 Chemical resistance 10 10 10

[0198] Note: This table is used to convert the performance of Example One, Two and Three in key performance indicators into numerical scores of 0-10.

[0199] ​As shown in Tables 5 and 6, Example 1 exhibits good flexibility and coating adaptability, and has stable performance under normal working conditions, but the curing speed is slightly slow and the peel strength is slightly low. Example 2 cures the fastest and has excellent strength performance, but is slightly insufficient in terms of bonding stability and thermal expansion matching, making it suitable for fast processes that pursue efficiency. Example 3 approaches or reaches full marks in all dimensions, showing the most comprehensive performance balance. It takes into account construction fluidity, curing depth and speed, mechanical strength and environmental adaptability, and is an ideal choice for PP diaphragm IMD injection molding.

[0200] like Figure 1 As shown, Example 1 has good thermal expansion compatibility (score of 9), viscosity workability (score of 8), and coating compatibility (score of 8). It also achieves a full score for chemical resistance (score of 10), demonstrating a certain degree of formulation compatibility and operational stability. However, its UV curing speed score is only 6, indicating a slow response in rapid prototyping processes. The peel strength (score of 7) is also slightly below the upper limit of the recommended standard for industrial applications.

[0201] Example 2 achieved a perfect score (10) for UV curing speed, demonstrating a rapid curing response and suitability for high-rate injection molding lines. Peel strength (8) and chemical resistance (10) also performed well, demonstrating its structural strength and environmental adaptability. However, due to its low viscosity control (7), it presents a risk of sagging or uneven distribution during precision coating processes such as anilox rollers. Coating compatibility was also average (7), and thermal expansion compatibility was rated 8, still below the optimal range for PP plastic materials.

[0202] In contrast, Example 3 performed exceptionally well across all six technical indicators, achieving full marks (10) for peel strength, thermal expansion matching, and coating compatibility. It also achieved a UV curing speed score of 9, a construction viscosity score of 9, and chemical resistance of 10, making it the most balanced and overall optimal of the three formulations. The radar chart exhibits a nearly regular hexagonal shape with the largest overall extension, indicating that this formulation performs at a high level across all performance dimensions, with the strongest overall compatibility and industrial application expansion capabilities.

[0203] In summary, Example 3 can not only achieve high bonding strength and excellent interface stability under rapid curing conditions, but also has excellent high and low temperature impact resistance and chemical resistance. It is particularly suitable for industrial batch applications of PP plastic IMD injection molding films and is a preferred embodiment of the present invention.

[0204] Summarize

[0205] The glue of Example 3 has the best performance balance, achieving a balance between flexibility and strength, and adapting to the dual requirements of IMD for structural stress release and appearance durability; it has wide compatibility and performs well in both high-speed injection molding production and long-term requirements for bonding stability; it has high industrial adaptability, coating adaptability (55 seconds viscosity) and light curing energy consumption (100mj / cm 2 ) are compatible with mainstream IMD coating and curing equipment; high adhesion and high durability, suitable for complex media exposure environments such as automotive fuel tanks and instrument panels.

[0206] The above embodiments should be understood as merely illustrating the present invention and not as limiting the scope of protection of the present invention. After reading the contents of the present invention, technicians may make various changes or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims

1. A UV shadowless adhesive suitable for laminating PP plastic IMD injection molding films, characterized in that: The UV shadowless adhesive is composed of the following components by mass percentage: composition: Epoxy acrylate: 30% to 38%, Polyurethane acrylate: 15% to 20%, Trimethylolpropane triacrylate: 20% to 30%, Tripropylene glycol diacrylate: 10% to 20%, Photoinitiator 1173: 3% to 5%, Onium salt cationic photoinitiator: 0.5% to 2%, Hydroxyphenyltriazine UV absorbers: 0.5% to 1.5%, Low alkalinity composite light stabilizer: 0.5% to 2%, Silane coupling agent: 0.5% to 1.5%, Fumed silica: 0.3% to 1%, Defoaming agent: 0.3%~1%.

2. The UV shadowless adhesive according to claim 1, wherein: The UV shadowless adhesive is composed of the following components by mass percentage: composition: Epoxy acrylate: 34%, Polyurethane acrylate: 17%, Trimethylolpropane triacrylate: 25%, Tripropylene glycol diacrylate: 15%, Photoinitiator 1173: 4%, Onium salt cationic photoinitiator: 1%, Hydroxyphenyltriazine UV absorber: 0.8%, Low alkalinity composite light stabilizer: 1.2%, Silane coupling agent: 1%, Fumed silica: 0.5%, Defoaming agent: 0.5%.

3. The UV shadowless adhesive according to claim 2, wherein: The UV shadowless adhesive has the following performance indicators: a. The viscosity is (55±5)s (25℃, apply 4 cups), suitable for 300~400LPI anilox roller coating; b. The light energy required for UV curing is not less than 100mj / cm 2 , the effective wavelength range is 200~400nm; c. The linear expansion coefficient of the adhesive layer after curing is 9.05±1×10 -5 / K; d. 180° peel strength not less than 0.3N / mm; e. No abnormal phenomenon during temperature cycle from -30℃ to 80℃.

4. The UV shadowless adhesive according to any one of claims 1 to 3, characterized in that: The epoxy acrylate is a high-functionality prepolymer with a bisphenol A structure; and the polyurethane acrylate has a flexible molecular chain segment.

5. A method for preparing the UV shadowless adhesive according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1. Compound monomer: Mix trimethylolpropane triacrylate and tripropylene glycol diacrylate in proportion, stir at 400±30 rpm for 300 seconds, and set aside; S2. Compound stabilizer: Mix the hydroxyphenyltriazine UV absorber and the low-alkalinity composite light stabilizer in proportion, stir at 200±30 rpm for 180 seconds, and set aside; S3, prepolymer mixing: epoxy acrylate, polyurethane acrylate and the compound monomer of step S1 are added into a reaction kettle according to a proportion, and stirred at 400±30 rpm for 600-800 seconds at 40-60°C until uniformly mixed; S4, adding auxiliary agents: adding photoinitiator 1173, onium salt cationic photoinitiator, silane coupling agent, fumed silica, defoaming agent and the compounded stabilizer of step S2 to the prepolymer of step S3 in sequence, and stirring continuously for 30 to 60 minutes until fully dispersed; S5. Purification and filtration: Remove impurities through a 200-400 mesh filter or centrifuge to obtain UV shadowless adhesive.

6. The method according to claim 5, wherein The process also includes UV curing verification in step S6: applying a small amount of the UV shadowless adhesive prepared in step S5 to the surface of the substrate and irradiating it with a 365nm UV lamp to evaluate its curing rate and hardness; wherein the UV irradiation time is controlled between 0.05 and 1.2 seconds.

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