A method for preparing a uv adhesive

Abstract

The application provides a preparation method of a UV adhesive, comprising the following steps: S1, mixing saturated dibasic acid, dibasic alcohol and a catalyst, and performing esterification reaction by subsection temperature rising to 220-230 DEG C, obtaining a prepolymer when the acid value is less than 10 mg KOH / g; S2, vacuumizing the prepolymer, reducing the acid value to less than 0.5 mg KOH / g, then adding unsaturated acid / anhydride to perform polycondensation reaction under the condition of 160-170 DEG C until the acid value is less than 3 mg KOH / g, obtaining an unsaturated polyester resin; S3, mixing the unsaturated polyester resin with acrylic monomer and a photoinitiator, obtaining the UV adhesive. The UV adhesive prepared by the preparation method has the advantages of low curing shrinkage and excellent mechanical properties, and can realize the effects of complete corner coverage, no easy warping and no residual glue.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, specifically, it relates to a method for preparing a UV adhesive. Background Technology

[0002] UV curing technology is an energy-saving and environmentally friendly technology. It saves energy, cures quickly (typically within seconds to tens of seconds), is beneficial for automated production lines, and is solvent-free, protecting the environment by not emitting toxic gases or carbon dioxide into the atmosphere, thus earning it the reputation of a "green technology." UV curing technology is a photoprocessing technique that uses ultraviolet light of a specific wavelength to rapidly polymerize liquid unsaturated monomers and prepolymers into a solid state. The UV curing reaction is essentially a light-induced polymerization and cross-linking reaction. However, the rapid reaction speed and significant shrinkage during UV curing can lead to incomplete application at edges and corners. Therefore, solving the problem of high shrinkage in current UV adhesives is of significant research importance and application value. Summary of the Invention

[0003] The purpose of this invention is to provide a method for preparing a UV adhesive, which results in a UV adhesive with advantages such as low curing shrinkage and excellent mechanical properties, and can achieve complete edge and corner coverage, resistance to peeling, and no adhesive residue.

[0004] According to one aspect of the present invention, a method for preparing a UV adhesive is provided, comprising the following steps: S1, mixing a saturated diacid, a diol, and a catalyst, and performing an esterification reaction by progressively heating the mixture to 220–230°C until the acid value of the resulting mixture is <10 mg KOH / g to obtain a prepolymer; S2, evacuating the prepolymer to reduce the acid value of the resulting mixture to <0.5 mg KOH / g, and then adding an unsaturated acid / anhydride to it and performing a polycondensation reaction at 160–170°C until the acid value of the resulting mixture is <3 mg KOH / g. KOH / g yields unsaturated polyester resin; S3, the unsaturated polyester resin is mixed with acrylic monomer and photoinitiator to obtain UV adhesive; wherein, the feeding ratio of saturated diacid, diol, and unsaturated acid / anhydride is determined according to the mass ratio of saturated diacid to diol to unsaturated acid / anhydride = 500~700: 250~400: 2~9; acrylic monomers include monofunctional acrylic monomers and polyfunctional acrylic monomers, and the mass ratio of monofunctional acrylic monomers to polyfunctional acrylic monomers is ≤800:100.

[0005] The method for preparing UV adhesives provided by this invention first involves esterifying a saturated diacid and a diol in a segmented heating process according to a specific feed ratio, ensuring that the acid value of the product at the reaction endpoint is <10 mg KOH / g. Then, by vacuuming, the acid value of the reaction system is reduced to <0.5 KOH / g, allowing water to escape from the reaction system and promoting the forward esterification reaction, thus ensuring a high molecular weight of the synthesized polymer. Further, an unsaturated acid / anhydride is introduced into the reaction system to introduce unsaturated double bonds, achieving an acid value of <3 mg KOH / g for the resulting unsaturated polyester resin. Then, acrylic monomers are introduced into the unsaturated polyester resin. By controlling the type and proportion of acrylic monomers, the UV adhesive after photocuring achieves low curing shrinkage and excellent mechanical properties.

[0006] Since the raw materials, their proportions, and the feeding method have a decisive influence on the molecular weight of polyester resin, this invention employs a segmented heating method to avoid the evaporation of diols during the esterification reaction, promoting the forward esterification reaction and ensuring that saturated diacids and diols are fully esterified in a specific ratio, thereby achieving the reaction endpoint of acid value <10mgKOH / g. On the other hand, by applying vacuum to bring the acid value of the reaction system to <0.5mgKOH / g, the temperature is lowered and a specific amount of unsaturated acid / anhydride is added to further ensure that the polycondensation reaction is fully completed in a specific ratio, thus obtaining an unsaturated polyester resin with a low acid value.

[0007] Therefore, the preparation method provided by this invention ensures the accuracy of raw material feeding and controls the reaction endpoints of each step by controlling the feeding of raw materials and reaction conditions. This allows the esterification and polycondensation reactions to proceed fully and controllably, resulting in an unsaturated polyester resin with an expected acid value of <3 mg KOH / g. This unsaturated polyester resin has a high molecular weight and low internal stress. Furthermore, it uses acrylic monomers, including polyfunctional and monofunctional acrylic monomers, to crosslink with the aforementioned unsaturated polyester resin. As a result, the UV adhesive possesses advantages such as low curing shrinkage and excellent mechanical properties, achieving complete edge coverage, resistance to peeling, and no residue. Moreover, the preparation method provided by this invention is simple to operate, low in cost, and suitable for industrial production.

[0008] Preferably, the saturated dicarboxylic acid includes at least one of isophthalic acid, succinic acid, adipic acid, and sebacic acid;

[0009] Preferably, the diol includes at least one of neopentyl glycol, ethylene glycol, diethylene glycol, and 1,6-hexanediol;

[0010] Preferably, the catalyst includes at least one of monobutyltin oxide and dibutyltin oxide.

[0011] Preferably, the mass ratio of saturated dicarboxylic acid, diol, and catalyst is 500–700: 250–400: 0.8–1.2.

[0012] Preferably, the photoinitiator includes at least one of 2-hydroxy-2-methyl-1-propanone, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyldiphenoxyphosphine, ethyl 2,4,6-trimethylbenzoylphenylphosphonate, and bis(1-(2,4-difluorophenyl)-3-pyrrolithyl)dicentectan.

[0013] Preferably, the specific operation of segmented heating includes the following steps: first, heating the reaction system to 155-165°C and holding it at that temperature for 30 minutes to 1 hour; then heating it to 175-185°C and holding it at that temperature for 30 minutes to 1 hour; subsequently heating it to 195-205°C and holding it at that temperature for 30 minutes to 1 hour; and finally heating it to 215-225°C and holding it at that temperature.

[0014] Preferably, the heating rate in the segmented heating process is 1–5 °C / 10 minutes. By controlling the heating rate during the esterification reaction, the esterification reaction can be carried out fully and controllably, avoiding excessively rapid heating that could cause unreacted alcohols to evaporate with water vapor outside the reaction system, leading to deviations in the formulation ratio and making it difficult for the esterification reaction to be fully completed.

[0015] Preferably, the unsaturated acid / anhydride includes unsaturated dicarboxylic acids / anhydrides.

[0016] Preferably, the unsaturated acid / anhydride includes an unsaturated monobasic acid and an unsaturated diabasic anhydride, with a mass ratio of unsaturated monobasic acid to unsaturated diabasic anhydride of <2.5:1. In the above scheme, unsaturated monobasic acid and unsaturated diabasic anhydride are introduced simultaneously during the polycondensation reaction, and their feed amounts are reasonably set. An appropriate amount of unsaturated monobasic acid can end-cap the polymer, giving the unsaturated polyester resin suitable cohesive strength, which can further improve the mechanical properties of the UV adhesive and reduce its curing shrinkage rate.

[0017] Preferably, the unsaturated dicarboxylic anhydride includes maleic anhydride. Maleic anhydride helps reduce water production and promotes the forward esterification reaction.

[0018] Preferably, the unsaturated monocarboxylic acid includes at least one of oleic acid, linoleic acid, and linolenic acid. These monocarboxylic acids are long-chain molecular acids, which can effectively toughen the polymer, improving the crack resistance and flexibility of the unsaturated polyester resin.

[0019] Preferably, during the S2 polycondensation reaction, triphenyl phosphite is also added, with a mass ratio of triphenyl phosphite to unsaturated acid / anhydride of 1–2:2–9. Triphenyl phosphite, as an antioxidant stabilizer, can stabilize and enhance the molecular structure of the polymer, preventing chain scission and cross-linking at high temperatures, thereby improving the mechanical properties, service life, and stability of the resulting UV adhesive. Therefore, this invention, by adding triphenyl phosphite and rationally setting its dosage, effectively promotes the forward polycondensation reaction and improves the mechanical properties of the resulting unsaturated polyester resin.

[0020] Preferably, the monofunctional acrylic monomers include at least one selected from n-butyl acrylate, isobornyl acrylate, tert-butyl acrylate, and lauryl acrylate; the polyfunctional acrylic monomers include at least one selected from diethylene glycol diacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, neopentyl glycol diacrylate, and pentaerythritol triacrylate. The monofunctional and polyfunctional acrylic monomers mentioned above can exert a synergistic effect, improving the mechanical properties and stability of the UV adhesive while ensuring a low curing shrinkage rate, and avoiding problems such as adhesive residue.

[0021] Preferably, the mass ratio of monofunctional acrylic monomer to polyfunctional acrylic monomer is 400–800:100–200. By controlling the ratio of monofunctional acrylic monomer to polyfunctional acrylic monomer within the above range, the curing shrinkage rate of the UV adhesive can be reduced while ensuring its mechanical properties.

[0022] According to another aspect of the present invention, a UV adhesive is provided, prepared by the above-described method for preparing UV adhesives. The UV adhesive provided by the present invention exhibits low curing shrinkage and excellent mechanical properties, achieving complete edge and corner coverage, resistance to peeling, and no adhesive residue. Detailed Implementation

[0023] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0024] Example 1

[0025] This embodiment provides a UV adhesive, the preparation method of which includes the following steps:

[0026] S1. 269g of diol (52g neopentyl glycol, 217g ethylene glycol), 587.676g of saturated dicarboxylic acid (540.2g adipic acid, 47.476g isophthalic acid), and 1.1g of monobutyltin oxide were added to a four-necked flask and mixed. Nitrogen gas was introduced and the temperature was increased in stages (first to 160℃ and held for 30min, then increased to 180℃ at a rate of 2℃ / 10min and held for 1h, then increased to 200℃ at a rate of 1℃ / 10min and held for 1h, and finally increased to 220℃ at a rate of 5℃ / 10min and held) to carry out the esterification reaction. The acid value was tested every hour until the acid value of the resulting mixture was <10mgKOH / g, thus obtaining the prepolymer.

[0027] S2. Add 1.1g of triphenyl phosphite to the prepolymer, evacuate to -0.098MPa, and test the acid value every hour until the acid value is <0.5mgKOH / g. Cool to 160℃, add 0.5g of triphenyl phosphite and 3.104g of unsaturated acid / anhydride (0.556g of oleic acid and 2.548g of maleic anhydride) to carry out polycondensation reaction, keep warm, and test the acid value every 30min until the acid value of the resulting mixture is <3mgKOH / g; to obtain unsaturated polyester resin;

[0028] S3. Add 720g of acrylic monomer and 3g of photoinitiator 2-hydroxy-2-methyl-1-propanone to unsaturated polyester resin, stir evenly, cool, and remove nitrogen gas to obtain a light yellow UV adhesive. The acrylic monomer consists of 600g of monofunctional acrylic monomer (450g butyl acrylate, 150g isobornyl acrylate) and 120g of polyfunctional acrylic monomer (100g pentaerythritol triacrylate, 20g 1,6-hexanediol diacrylate).

[0029] Example 2

[0030] This embodiment refers to Example 1 for preparing a UV adhesive. The difference between this embodiment and Example 1 is that the unsaturated acid / anhydride used in the preparation of the UV adhesive in this embodiment includes only 3.104g of maleic anhydride. Apart from the above difference, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0031] Example 3

[0032] This embodiment refers to Example 1 for preparing a UV adhesive. The difference between this embodiment and Example 1 is that in the preparation of the UV adhesive, the amount of oleic acid used is 2.29g and the amount of maleic anhydride is 0.814g. Apart from the above difference, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0033] Example 4

[0034] This embodiment refers to Example 1 for preparing a UV adhesive. The difference between this embodiment and Example 1 is that the acrylic monomer used in the preparation of the UV adhesive in this embodiment consists of 800g of monofunctional acrylic monomer and 100g of polyfunctional acrylic monomer. Apart from the above difference, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0035] Example 5

[0036] This embodiment refers to Example 1 for preparing a UV adhesive. The difference between this embodiment and Example 1 is that the acrylic monomer used in the preparation of the UV adhesive in this embodiment consists of 400g of monofunctional acrylic monomer and 200g of polyfunctional acrylic monomer. Apart from the above difference, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0037] Example 6

[0038] This embodiment refers to Example 1 for preparing a UV adhesive. The difference between this embodiment and Example 1 is that the acrylic monomer used in the preparation of the UV adhesive in this embodiment consists of 300g of monofunctional acrylic monomer and 200g of polyfunctional acrylic monomer. Apart from the above difference, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0039] Example 7

[0040] This embodiment refers to Example 1 for preparing a UV adhesive. The difference between this embodiment and Example 1 is that in the preparation of the UV adhesive in this embodiment, 500g of saturated dicarboxylic acid, 250g of diol, and 9g of unsaturated acid / anhydride are used. Apart from the above differences, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0041] Example 8

[0042] This embodiment refers to Example 1 for preparing a UV adhesive. The difference between this embodiment and Example 1 is that in the preparation of the UV adhesive in this embodiment, 700g of saturated dicarboxylic acid, 400g of diol, and 2g of unsaturated acid / anhydride are used. Apart from the above differences, the materials and process operations used in this embodiment are strictly consistent with those in Example 1.

[0043] Comparative Example 1

[0044] This comparative example provides a UV adhesive, the preparation method of which includes the following steps:

[0045] S1. 269g of diol (52g neopentyl glycol, 217g ethylene glycol), 587.676g of saturated dicarboxylic acid (540.2g adipic acid, 47.476g isophthalic acid), and 1.1g of monobutyltin oxide were added to a four-necked flask and mixed. Nitrogen gas was introduced and the temperature was increased in stages (first to 160℃ and held for 30min, then increased to 180℃ at a rate of 2℃ / 10min and held for 1h, then increased to 200℃ at a rate of 1℃ / 10min and held for 1h, and finally increased to 220℃ at a rate of 5℃ / 10min and held) to carry out the esterification reaction. The acid value was tested every hour until the acid value of the resulting mixture was <10mgKOH / g, thus obtaining the prepolymer.

[0046] S2. Add 1.1g of triphenyl phosphite to the prepolymer, evacuate to -0.098MPa, and test the acid value every hour until the acid value is 5mgKOH / g. Cool to 160℃, add 0.5g of triphenyl phosphite and 3.104g of unsaturated acid / anhydride (0.556g of oleic acid and 2.548g of maleic anhydride) to carry out polycondensation reaction, keep warm, and test the acid value every 30min until the acid value of the resulting mixture is 8mgKOH / g; obtain unsaturated polyester resin;

[0047] S3. Add 720g of acrylic monomer and 3g of photoinitiator 2-hydroxy-2-methyl-1-propanone to unsaturated polyester resin, stir evenly, cool, and remove nitrogen gas to obtain a light yellow UV adhesive. The acrylic monomer consists of 600g of monofunctional acrylic monomer (450g butyl acrylate, 150g isobornyl acrylate) and 120g of polyfunctional acrylic monomer (100g pentaerythritol triacrylate, 20g 1,6-hexanediol diacrylate).

[0048] Comparative Example 2

[0049] This comparative example prepares a UV adhesive according to Example 1. The difference between this comparative example and Example 1 is that in the preparation of the UV adhesive in this comparative example, the unsaturated acid / anhydride is mixed simultaneously with the saturated diacid and diol. Apart from the above difference, the materials and process operations used in this comparative example are strictly consistent with those in Example 1.

[0050] Comparative Example 3

[0051] This comparative example prepares a UV adhesive according to Example 1. The difference between this example and Example 1 is that the acrylic monomer is replaced with the same mass of styrene in the preparation of the UV adhesive. Apart from the above difference, the materials and process operations used in this comparative example are strictly consistent with those in Example 1.

[0052] Comparative Example 4

[0053] S1. Add 269g of diol (52g of neopentyl glycol, 217g of ethylene glycol), 587.676g of saturated diacid (540.2g of adipic acid, 47.476g of isophthalic acid), and 1.1g of monobutyltin oxide to a four-necked flask and mix. Purge with nitrogen and rapidly heat to 220℃ at a rate of 20℃ / 10min to carry out the esterification reaction. Take a sample every hour to test the acid value until the acid value of the resulting mixture is <10mgKOH / g, and the prepolymer is obtained.

[0054] S2. Add 1.1g of triphenyl phosphite to the prepolymer, evacuate to -0.098MPa, and take samples every hour to test the acid value. After 5 hours, the acid value of the resulting mixture is 3mgKOH / g. At this point, the acid value no longer decreases. Cool down to 160℃, add 0.5g of triphenyl phosphite and 3.104g of unsaturated acid / anhydride (0.556g of oleic acid and 2.548g of maleic anhydride) to carry out polycondensation reaction, keep warm, and take samples every 30 minutes to test the acid value until the acid value of the resulting mixture is 6mgKOH / g. At this point, the acid value no longer decreases, and the unsaturated polyester resin is obtained.

[0055] S3. Add 720g of acrylic monomer and 3g of photoinitiator 2-hydroxy-2-methyl-1-propanone to unsaturated polyester resin, stir evenly, cool, and remove nitrogen gas to obtain a light yellow UV adhesive. The acrylic monomer consists of 600g of monofunctional acrylic monomer (450g butyl acrylate, 150g isobornyl acrylate) and 120g of polyfunctional acrylic monomer (100g pentaerythritol triacrylate, 20g 1,6-hexanediol diacrylate).

[0056] Comparative Example 5

[0057] This comparative example prepares a UV adhesive according to Example 1. The difference between this comparative example and Example 1 is that in the preparation of the UV adhesive in this comparative example, 700g of saturated dicarboxylic acid, 400g of diol, and 1.5g of unsaturated acid / anhydride are used. Apart from the above differences, the materials and process operations used in this comparative example are strictly consistent with those in Example 1.

[0058] Comparative Example 6

[0059] This comparative example prepares a UV adhesive according to Example 1. The difference between this comparative example and Example 1 is that in the preparation of the UV adhesive in this comparative example, 500g of saturated dicarboxylic acid, 250g of diol, and 10g of unsaturated acid / anhydride are used. Apart from the above differences, the materials and process operations used in this comparative example are strictly consistent with those in Example 1.

[0060] Comparative Example 7

[0061] This comparative example prepares a UV adhesive according to Example 1. The difference between this comparative example and Example 1 is that the acrylic monomer used in the preparation of the UV adhesive in this comparative example consists of only 720g of monofunctional acrylic monomer. Apart from the above difference, the materials and process operations used in this comparative example are strictly consistent with those in Example 1.

[0062] Comparative Example 8

[0063] This comparative example prepares a UV adhesive according to Example 1. The difference between this comparative example and Example 1 is that the acrylic monomer used in the preparation of the UV adhesive in this comparative example consists of only 720g of multifunctional acrylic monomer. Apart from the above difference, the materials and process operations used in this comparative example are strictly consistent with those in Example 1.

[0064] Comparative Example 9

[0065] This comparative example prepares a UV adhesive according to Example 1. The difference between this comparative example and Example 1 is that the acrylic monomers used in the preparation of the UV adhesive in this comparative example consist of 900g of monofunctional acrylic monomers and 100g of polyfunctional acrylic monomers. Apart from the above difference, the materials and process operations used in this comparative example are strictly consistent with those in Example 1.

[0066] Test Example 1

[0067] 1. Participants

[0068] The UV adhesives prepared in Examples 1-8 and Comparative Examples 1-9 were used as test subjects in this test.

[0069] 2. Test Items

[0070] (1) Flexibility test: The test object was coated on a 10cm*2cm transparent soft plastic with a coating thickness of 2mm, and subjected to 250mJ / cm. 2 After irradiating with a UV lamp for 5 seconds, the product was left to stand for 20 minutes. Then, a bending test was performed to observe the number of bends when bubbles began to appear in the cured product. The more bends performed when bubbles began to appear, the better the flexibility of the test object.

[0071] (2) Edge shrinkage and curing shrinkage rate: The test object was coated on a 1cm*1cm glass surface with a coating thickness of 2mm, and subjected to 250mJ / cm 2 After irradiating with a UV lamp for 5 seconds, the sample was left to stand for 20 minutes. The size of the edge shrinkage was then measured using a two-dimensional measuring instrument. The curing shrinkage rate was calculated using the following formula: edge shrinkage amount / initial size of the test object.

[0072] (3) Residual adhesive: Remove the adhesive film and observe whether there is residual adhesive.

[0073] 3. Test Results

[0074] Table 1. Performance test results of Examples 1-8 and Comparative Examples 1-9

[0075]

[0076]

[0077] The test results are shown in Table 1. The performance test results of Example 1 and Comparative Example 1 were compared. Table 1 shows that, under the same conditions of other materials and operations for preparing the UV adhesive, the UV adhesive prepared in Example 1 had low curing shrinkage, excellent flexibility, and no residue. In contrast, Comparative Example 1 introduced unsaturated acid / anhydride for polycondensation when the acid value of the reaction system was 5 mg KOH / g. The resulting UV adhesive had significantly inferior flexibility and a significantly higher curing shrinkage than Example 1, and also produced residue. This indicates that, compared to Comparative Example 1, Example 1, by controlling the acid value of the reaction system, effectively controlled the endpoint of the polycondensation reaction, promoted its full progress, and thus ensured that the UV adhesive had suitable cohesion, reduced its shrinkage, and improved its mechanical properties.

[0078] The performance test results of Example 1 and Comparative Example 2 were compared. Table 1 shows that, under the same conditions of other materials and operations in preparing the UV adhesive, the UV adhesive prepared in Example 1 exhibited low curing shrinkage, excellent flexibility, and no residue. In contrast, Comparative Example 2, by simultaneously mixing unsaturated acid / anhydride with saturated diacid and diol during prepolymer preparation, resulted in gelation, terminating the synthesis of the UV adhesive. This indicates that, compared to Comparative Example 2, Example 1, by employing a stepwise addition of saturated diacid, diol, and unsaturated acid / anhydride, can promote the forward synthesis of the UV adhesive, thereby ensuring a higher yield.

[0079] The performance test results of Example 1 were compared with those of Comparative Examples 3, 7-8. Table 1 shows that, under the same conditions of other materials and operations for preparing the UV adhesive, the UV adhesive prepared in Example 1 had low curing shrinkage, excellent flexibility, and no residue. Comparative Example 3, by replacing the acrylic monomer with styrene, produced a UV adhesive with significantly inferior flexibility and a significantly higher curing shrinkage than Example 1. Comparative Example 7 used only monofunctional acrylic monomers, resulting in a UV adhesive with residue. Comparative Example 8 used only polyfunctional acrylic monomers, resulting in a UV adhesive with a higher curing shrinkage and inferior flexibility than Example 1. Comparative Example 9 used acrylic monomers with a mass ratio of monofunctional acrylic monomers to polyfunctional acrylic monomers > 800:100, resulting in a UV adhesive with residue. This demonstrates that, compared to Comparative Examples 3 and 7-9, Example 1, by using acrylic monomers as crosslinking monomers and controlling the composition and ratio of acrylic monomers, enables the acrylic monomers to copolymerize with the unsaturated double bonds on the unsaturated polyester molecular chain to form a crosslinked network structure, thereby reducing the shrinkage rate of the UV adhesive and improving its mechanical properties.

[0080] The performance test results of Example 1 and Comparative Example 4 were compared. Table 1 shows that, under the same conditions of other materials and operations for preparing the UV adhesive, the UV adhesive prepared in Example 1 had low curing shrinkage, excellent flexibility, and no residue. In contrast, Comparative Example 4 did not use a segmented heating method during the prepolymer preparation process, resulting in a UV adhesive with significantly inferior flexibility and a significantly higher curing shrinkage rate than Example 1, and the presence of residue. This is because the heating rate in Comparative Example 4 was too rapid, causing unreacted alcohol to evaporate with water vapor outside the reaction system, leading to a deviation in the formulation ratio. This made it difficult for the esterification reaction to be fully completed, thereby reducing the mechanical properties of the resulting UV adhesive and increasing its curing shrinkage rate.

[0081] The performance test results of Example 1 were compared with those of Comparative Examples 5-6. Table 1 shows that, under the same conditions of other materials and operations in preparing the UV adhesive, the UV adhesive prepared in Example 1 had low curing shrinkage, excellent flexibility, and no residue. In contrast, the unsaturated acid / anhydride amounts used in Comparative Examples 5-6 exceeded the range of saturated dicarboxylic acid:diol:unsaturated acid / anhydride mass = 500-700:250-400:2-9. As a result, the UV adhesive prepared in Comparative Example 5 showed residue, and the UV adhesive prepared in Comparative Example 6 had a higher curing shrinkage and inferior flexibility than that of Example 1. This indicates that, compared to Comparative Examples 5-6, Example 1, by rationally setting the amount of raw materials, allowed the esterification and polycondensation reactions to proceed fully and controllably, thereby improving the mechanical properties of the UV adhesive and reducing its curing shrinkage.

[0082] The performance test results of Example 1 were compared with those of Examples 2-3. Table 1 shows that, under the same conditions of other materials and operations in preparing the UV adhesive, Example 2 did not introduce an unsaturated monobasic acid into the unsaturated acid / anhydride mixture. Therefore, the resulting UV adhesive had slightly lower flexibility and a slightly higher curing shrinkage rate than Example 1. Example 3 used an unsaturated monobasic acid to unsaturated diacid anhydride mass ratio ≥2.5:1, resulting in residual adhesive in the UV adhesive. This indicates that, compared to Examples 2-3, Example 1, by simultaneously introducing an unsaturated monobasic acid and anhydride during the polycondensation reaction and appropriately setting their amounts, allows the unsaturated monobasic acid to end-cap the polymer, giving the unsaturated polyester resin suitable cohesive strength, thereby reducing the curing shrinkage rate of the UV adhesive and improving its mechanical properties.

[0083] The performance test results of Example 1 were compared with those of Examples 4-6. Table 1 shows that, under the same conditions of other materials and operations in preparing the UV adhesive, the mass ratio of monofunctional acrylic monomers to polyfunctional acrylic monomers used in Example 6 was <400-800:100-200. Consequently, the UV adhesive obtained in Example 6 exhibited inferior flexibility and a higher curing shrinkage rate compared to Examples 1 and 4-5. This indicates that, compared to Example 6, Examples 1 and 4-5, by using acrylic monomers composed of a specific ratio of monofunctional and polyfunctional acrylic monomers, allowed for a synergistic effect between the two monomers, thereby reducing the curing shrinkage rate and improving the mechanical properties of the UV adhesive.

[0084] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A method for preparing a UV adhesive, characterized in that, Includes the following steps: S1. A saturated dicarboxylic acid, a diol, and a catalyst are mixed and subjected to a staged heating reaction for esterification. The prepolymer is obtained when the acid value of the resulting mixture is <10 mg KOH / g. The staged heating operation includes the following steps: first, the reaction system is heated to 155-165°C and held for 30 minutes to 1 hour; then, the temperature is raised to 175-185°C and held for 30 minutes to 1 hour; then, the temperature is raised to 195-205°C and held for 30 minutes to 1 hour; finally, the temperature is raised to 215-225°C and held. S2. Vacuum the prepolymer to reduce the acid value of the resulting mixture to <0.5mg KOH / g, then add unsaturated acid / anhydride to it and carry out polycondensation reaction at 160-170°C until the acid value of the resulting mixture is <3mg KOH / g to obtain unsaturated polyester resin. S3. The unsaturated polyester resin is mixed with acrylic monomer and photoinitiator to obtain the UV adhesive. The feeding ratio of the saturated dicarboxylic acid, the dicarboxylic acid, and the unsaturated acid / anhydride is determined according to the following formula: mass of the saturated dicarboxylic acid: mass of the diol: mass of the unsaturated acid / anhydride = 500-700: 250-400: 2-9. The acrylic monomers include monofunctional acrylic monomers and polyfunctional acrylic monomers, wherein the mass ratio of the monofunctional acrylic monomers to the polyfunctional acrylic monomers is ≤800:

100.

2. The method for preparing the UV adhesive as described in claim 1, characterized in that, The segmented heating rate is 1–5 °C / 10 minutes.

3. The method for preparing the UV adhesive as described in claim 1, characterized in that, The unsaturated acid / anhydride includes unsaturated monocarboxylic acids and unsaturated dicarboxylic anhydrides, wherein the mass ratio of the unsaturated monocarboxylic acid to the unsaturated dicarboxylic anhydride is < 2.5:

1.

4. The method for preparing the UV adhesive as described in claim 3, characterized in that, The unsaturated dicarboxylic anhydride includes maleic anhydride.

5. The method for preparing the UV adhesive as described in claim 3, characterized in that, The unsaturated monocarboxylic acid includes at least one of oleic acid, linoleic acid, and linolenic acid.

6. The method for preparing the UV adhesive as described in claim 1, characterized in that, During the S2 polycondensation reaction, triphenyl phosphite is also added, and the mass ratio of triphenyl phosphite to the unsaturated acid / anhydride is 1-2:2-9.

7. The method for preparing the UV adhesive as described in claim 1, characterized in that, The monofunctional acrylic monomer includes at least one of n-butyl acrylate, isobornyl acrylate, tert-butyl acrylate, and lauryl acrylate; the polyfunctional acrylic monomer includes at least one of diethylene glycol diacrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, neopentyl glycol diacrylate, and pentaerythritol triacrylate.

8. The method for preparing the UV adhesive as described in claim 7, characterized in that, The mass ratio of the monofunctional acrylic monomer to the polyfunctional acrylic monomer is 400-800:100-200.

9. A UV adhesive, characterized in that, It is prepared by the method of preparing the UV adhesive as described in any one of claims 1 to 8.

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