Isocyanate curing agent for optical cement as well as preparation method and application of isocyanate curing agent

Abstract

The invention belongs to the technical field of isocyanate curing agents, and particularly relates to an isocyanate curing agent for optical cement as well as a preparation method and application of the isocyanate curing agent. The isocyanate curing agent is a product (NCO-terminated polyisocyanate prepolymer) which is prepared by reacting xylylene diisocyanate with polyhydric alcohol; the polyol at least comprises 2, 2-dimethylolbutanol and polyether polyol, the molecular weight of the polyether polyol is 200-4000, and the functionality of the polyether polyol is 2; the viscosity of the isocyanate curing agent at 25 DEG C is greater than or equal to 6000 mPa.s and less than or equal to 14000 mPa.s. The isocyanate curing agent based on xylylene diisocyanate is prepared, so that a product (such as an adhesive) of the isocyanate curing agent has good bonding force and elongation at break, and the isocyanate curing agent is suitable for use scenes of optical cement.

Description

Technical Field

[0001] This invention belongs to the field of isocyanate curing agent technology, and particularly relates to an isocyanate curing agent for optical adhesives, its preparation method and application. Background Technology

[0002] Optical adhesives are used in consumer electronics devices to bond electronic screen panels and covers. As electronic devices become increasingly foldable and wearable, their screens will be subjected to deformation stress more frequently. This requires optical adhesives to not only meet basic bonding performance requirements but also to absorb or dissipate strain energy.

[0003] XDI (diphenyl phthalate) has the characteristics of high refractive index and resistance to yellowing, which are very suitable for the application characteristics in the optical field and can be used as a raw material for optical adhesive curing agents; however, due to the low functionality of XDI, there are currently no mature products on the market.

[0004] For example, patent document CN105940030A discloses a method for preparing polyisocyanate based on XDI, and the resulting polyisocyanate product has good adhesive properties. However, the cured product is brittle and has low elongation. If it is bonded to a flexible substrate, it is prone to breakage under repeated bending or impact, which does not meet the requirements for optical adhesive bonding of flexible screens.

[0005] Therefore, developing isocyanate curing agents that meet the flexibility requirements of optical adhesive bonding is a direction worthy of further research. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes an isocyanate curing agent for optical adhesives, its preparation method, and its application. By blending 2,2-dimethylolol with a specific polyether diol in a suitable ratio, an isocyanate curing agent based on dimethyl phthalate can be prepared, enabling its products (such as adhesives) to exhibit good adhesion and elongation at break, making it suitable for applications in optical adhesives.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] In the first aspect, an isocyanate curing agent for optical adhesives is provided, the isocyanate curing agent being a product obtained by reacting dimethyl phthalate with a polyol (NCO-terminated polyisocyanate prepolymer).

[0009] The polyol contains at least 2,2-dimethylolbutanol (i.e., trimethylolpropane) and polyether polyols with a molecular weight of 200-4000 (e.g., 250, 300, 400, 500, 600, 800, 1000, 1200, 1500, 1800, 2000, 2200, 2400, 2500, 2800, 3000, 3200, 3400, 3500, 3800) and a functionality of 2.

[0010] The isocyanate curing agent has a viscosity at 25°C that is greater than or equal to 6000 mPa·s and less than or equal to 14000 mPa·s, for example, viscosities of 6500 mPa·s, 7000 mPa·s, 7500 mPa·s, 8000 mPa·s, 8500 mPa·s, 9000 mPa·s, 9500 mPa·s, 10000 mPa·s, 11000 mPa·s, 12000 mPa·s, and 13000 mPa·s.

[0011] In this document, the isocyanate curing agent is in liquid form and does not require dilution with an external solvent. According to the isocyanate curing agent provided by this invention, in some embodiments, the solid content of the isocyanate curing agent is 100 wt%.

[0012] In this document, the average number of isocyanate functional groups in the isocyanate curing agent is greater than or equal to 2.0 and less than or equal to 6.3. For example, the average number of isocyanate functional groups is 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, and 6.0.

[0013] In some embodiments, the polyether polyol is selected from one or more of polyethylene glycol, polypropylene glycol, and polytetrahydrofuran ether diol. For example, the polyether polyol may be polypropylene glycol or polytetrahydrofuran ether diol with a molecular weight of 400 to 2000.

[0014] The polyol may also include, for example, monohydric alcohols, dihydric alcohols, and trihydric alcohols with a molecular weight of 32-200. The amount of such small molecule alcohols added can be calculated as 0.012 times the total number of hydroxyl moles of 2,2-dihydroxymethylbutanol.

[0015] In some embodiments, the preparation of the isocyanate curing agent includes at least two "reaction stages" and two "separation stages". For example, the preparation process of the isocyanate curing agent is "reaction first, then separation, then reaction again, and then separation again".

[0016] In some embodiments, the reaction stage is the esterification reaction of phenylene diisocyanate with a polyol. The two reaction stages, in chronological order, can be referred to as "first-stage reaction" and "second-stage reaction." The first-stage reaction can be understood as the esterification reaction of phenylene diisocyanate with 2,2-dimethylolbutanol; the second-stage reaction can be understood as the esterification reaction of phenylene diisocyanate, phenylene diisocyanate derivatives, and polyether polyol.

[0017] In some embodiments, during the reaction phase, the ratio of the molar number of isocyanate groups of dimethyl phthalate to the molar number of hydroxyl groups of the polyol (i.e., the total molar number of hydroxyl groups of 2,2-dimethylolbutanol and polyether polyol) is R1, where 4.0 ≤ R1 ≤ 8.0.

[0018] In some embodiments, during the reaction stage, the molar ratio of hydroxyl groups of 2,2-dimethylolbutanol to that of the polyether polyol is R2, where 0.6 ≤ R2 ≤ 9.0. If there are two or more types of polyether polyols, the molar ratio of hydroxyl groups of the polyether polyol with the largest molecular weight to that of the polyether polyol with the smallest molecular weight is R3, where 0.2 ≤ R3 ≤ 3.0 (e.g., R3 is 0.25, 0.3, 0.4, 0.5, 0.6, 0.8, 1.0, 1.5, 2.0, 2.5, 2.6, 2.9), preferably 0.2 ≤ R3 ≤ 2.8.

[0019] In this invention, the separation stage can be understood as the process by which the obtained reaction solution is evaporated through a thin film or by extractive distillation to remove phenylene diisocyanate monomers from the reaction solution to a specific proportion. The two separation stages are, in chronological order, referred to as "first-stage separation" and "second-stage separation." That is, "first-stage separation" is performed on the obtained reaction solution after "first-stage reaction," and "second-stage separation" is performed on the obtained reaction solution after "second-stage reaction."

[0020] In a second aspect, a method for preparing the isocyanate curing agent as described above is provided, comprising the following steps:

[0021] (1) Phthalimide diisocyanate was contacted with 2,2-dimethylolbutanol to carry out a first-stage reaction to obtain a prepolymer reaction solution;

[0022] (2) The obtained prepolymer reaction liquid is subjected to a first-stage separation to obtain heavy component-I; the proportion of isocyanate monomer in the obtained heavy component-I is 10 to 30 wt% (e.g., 12 wt%, 15 wt%, 18 wt%, 20 wt%, 25 wt%, 29 wt%), preferably 10 to 28 wt%.

[0023] (3) Add polyether polyol to the obtained heavy component-I to carry out the second stage reaction to obtain polymer reaction solution;

[0024] (4) The obtained polymer reaction solution is subjected to a second-stage separation to obtain a heavy component-II; the proportion of isocyanate monomer in the obtained heavy component-II is 0.01 to 0.47 wt% (e.g., 0.02 wt%, 0.04 wt%, 0.05 wt%, 0.08 wt%, 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.46 wt%), preferably 0.05 to 0.45 wt%, which is the isocyanate curing agent.

[0025] According to the preparation method provided by the present invention, in some embodiments, the process conditions for the first stage reaction include: a reaction temperature of 50-90℃ (e.g., 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, 85℃), preferably 60-90℃, and a reaction time of 2-8h (e.g., 2.5h, 3.0h, 3.5h, 4.0h, 4.5h, 5.0h, 5.5h, 6.0h, 6.5h, 7.0h, 7.5h), preferably 2-7h.

[0026] In some implementations, the process conditions for the first-stage separation include: a separation temperature of 130-195°C (e.g., 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C), preferably 130-190°C; and a separation pressure of 10-105 Pa (e.g., 15 Pa, 20 Pa, 25 Pa, 30 Pa, 35 Pa, 40 Pa, 45 Pa, 50 Pa, 55 Pa, 60 Pa, 65 Pa, 70 Pa, 75 Pa, 80 Pa, 85 Pa, 90 Pa, 95 Pa, 100 Pa), preferably 10-100 Pa.

[0027] In the first stage of separation, phenyl dimethyl diisocyanate monomer is removed from the reaction solution to a final concentration of 10–30 wt%.

[0028] In some embodiments, the process conditions for the second-stage reaction include: a reaction temperature of 50-90°C (e.g., 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C), preferably 60-90°C, and a reaction time of 2-8 hours (e.g., 2.5 hours, 3.0 hours, 3.5 hours, 4.0 hours, 4.5 hours, 5.0 hours, 5.5 hours, 6.0 hours, 6.5 hours, 7.0 hours, 7.5 hours), preferably 2-7 hours.

[0029] In some embodiments, the process conditions for the second-stage separation include: a separation temperature of 130-195°C (e.g., 135°C, 140°C, 145°C, 150°C, 155°C, 160°C, 165°C, 170°C, 175°C, 180°C, 185°C, 190°C), preferably 130-190°C; and a separation pressure of 10-105 Pa (e.g., 15 Pa, 20 Pa, 25 Pa, 30 Pa, 35 Pa, 40 Pa, 45 Pa, 50 Pa, 55 Pa, 60 Pa, 65 Pa, 70 Pa, 75 Pa, 80 Pa, 85 Pa, 90 Pa, 95 Pa, 100 Pa), preferably 10-100 Pa.

[0030] In the second stage of separation, the phthalimide diisocyanate monomer is removed from the reaction solution to a concentration of 0.01–0.47 wt%.

[0031] According to the preparation method provided by the present invention, in some embodiments, in the first stage reaction, the ratio of the molar number of isocyanate groups of dimethyl phthalate to the total molar number of hydroxyl groups of 2,2-dimethylolbutanol and polyether polyol is R1, 4.0≤R1≤8.0 (for example, R1 is 4.1, 4.4, 4.5, 4.6, 4.8, 5.0, 5.2, 5.4, 5.5, 5.8, 6.0, 6.5, 7.0, 7.5, 7.8), preferably 4.2≤R1≤8.0.

[0032] In some embodiments, during the second-stage reaction, the molar ratio of hydroxyl groups of 2,2-dimethylolbutanol to polyether polyol is R2, where 0.6 ≤ R2 ≤ 9.0 (e.g., R2 is 0.65, 0.8, 0.9, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.1, 4.4, 4.5, 4.6, 4.8, 5.0, 5.2, 5.4, 5.5, 5.8, 6.0, 6.5, 7.0, 7.5, 7.8, 8.0, 8.5, 8.8), preferably 0.7 ≤ R2 ≤ 9.0. If there are two or more types of polyether polyols, the ratio of the number of molar hydroxyl groups of the polyether polyol with the largest molecular weight to the number of molar hydroxyl groups of the polyether polyol with the smallest molecular weight is R3, where 0.2≤R3≤3.0 (for example, R3 is 0.25, 0.3, 0.4, 0.5, 0.6, 0.8, 1.0, 1.5, 2.0, 2.5, 2.6, 2.9), preferably 0.2≤R3≤2.8.

[0033] In this invention, there are no special restrictions on the way the polyol is added. The components contained in the polyol can be mixed and then added, or different components can be added to the system in any order.

[0034] In a third aspect, the application of the isocyanate curing agent as described above or the isocyanate curing agent prepared by the method described above in optical adhesives is provided.

[0035] In this invention, the specific steps and process conditions for applying the isocyanate curing agent in optical adhesives can be conventional choices in the art, and will not be elaborated here.

[0036] In the isocyanate curing agent formulation provided by the present invention, 2,2-dimethylol alcohol is preferably combined with a polyether polyol of a specific molecular weight, and the ratio of the two is controlled within a suitable range. A certain amount of 2,2-dimethylol alcohol can improve the functionality of the system and ensure that the product has a certain shear strength. On this basis, by adjusting the content of polyether polyol within a suitable range, the elongation at break of the target product can be further improved.

[0037] The technical solution of this invention prepares an isocyanate curing agent based on dimethyl phthalate, which enables the products made from it (such as adhesives) to have good adhesion and elongation at break. When bonded to a flexible substrate, it is not easy to break under repeated bending or impact, which meets the requirements of optical adhesive bonding of flexible screens and is suitable for optical adhesive application scenarios. Detailed Implementation

[0038] To provide a detailed understanding of the technical features and content of this invention, preferred embodiments will be described in more detail below. While preferred embodiments are described in the examples, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply.

[0039] The present invention employs the following testing method:

[0040] (1) Viscosity test method: Dynamic mechanical viscosity was measured using a BrookField DV-IPrime viscometer with an S21 rotor at 25°C;

[0041] (2) Test method for the content of free unreacted isocyanate monomers: The test was conducted using the national standard GB / T18446-2009 and the Agilent GC-7890B gas chromatograph.

[0042] (3) Shear strength test method of the product: The prepared isocyanate curing agent is prepared according to the "adhesive preparation method". Then, according to JIS K 7110-1999, the obtained adhesive is applied to polyimide board-1 and bonded to polyimide board-2 (bonding area 25mm×12.5mm, bonding layer thickness 0.3mm). After curing at 25℃ for 1.5 hours, it is then cured at room temperature (18~28℃, 45~55%RH) for 6 days. After that, the tensile shear strength of the bonded board is determined by using a Sungoll SGL-8000 tensile testing machine at a tensile speed of 10mm / min.

[0043] (4) Test method for elongation at break of product: The prepared isocyanate curing agent is prepared according to the "Adhesive Preparation Method", and then the elongation at break of the obtained adhesive product is tested according to GB / T 1040.2-2006.

[0044] The adhesive formulation method is as follows: the isocyanate curing agent prepared in each example and comparative example is mixed with a mixed polyol, wherein the equivalent ratio (NCO / OH) of the isocyanate groups in the curing agent to the hydroxyl groups in the polyol is 1.065. The mixed polyol is ACR7502 (Tongde Chemical) and ACTCOL (Mitsui Chemicals) in a mass ratio of 3:2.

[0045] The main raw materials used in the following embodiments are as follows:

[0046] XDI (diphenyl phthalate): Wanhua Chemical, purity >99%;

[0047] 2,2-Dimethylolbutanol (trimethylolpropane, molecular weight 134): Aladdin reagent, purity >99%;

[0048] Polypropylene glycol-400: Kepler Biotechnology, purity >99%;

[0049] Polypropylene glycol-1000: Haian Petrochemical, purity >99%;

[0050] Polypropylene glycol-2000: Jiateng Chemical, purity >99%;

[0051] Polytetrahydrofuran ether diol-650: Dixin Chemical, purity >99%;

[0052] Acrylic polyol: ACR7502, Tongde Chemical, purity >99%;

[0053] Unless otherwise specified, all other raw materials and reagents are available through commercial channels.

[0054] The reaction and separation processes in the following examples and comparative examples were all carried out in an environment with sufficient dry nitrogen. The isocyanate curing agents obtained in the following examples had a solid content of 100 wt%.

[0055]

Example 1

[0056] The preparation process of the isocyanate curing agent is as follows:

[0057] (1) Weigh 500g of phenyl dimethyl diisocyanate and add it to a glass flask. Heat the flask to 55°C and add 29.01g of 2,2-dihydroxymethylbutanol. Keep stirring and control the reaction at 55°C for 6.0h to obtain the polyisocyanate prepolymer reaction solution.

[0058] (2) The polyisocyanate prepolymer reaction solution was passed through a thin-film evaporator with a separation temperature of 150℃ and a separation pressure of 20Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-I obtained after separation was 25wt%.

[0059] (3) Add 42.41g of polypropylene glycol-400 and 193.35g of polypropylene glycol-1000 to the obtained heavy component-I, keep stirring, and control the reaction at 55℃ for 6.0h to obtain polymer reaction solution;

[0060] (4) The polymer reaction solution is then passed through a thin-film evaporator with a separation temperature of 150°C and a separation pressure of 20Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-II obtained after separation is 0.35wt%, which is the isocyanate curing agent.

[0061]

Example 2

[0062] The preparation process of the isocyanate curing agent is as follows:

[0063] (1) Weigh 500g of phenyl dimethyl diisocyanate and add it to a glass flask. Heat the flask to 65°C and add 46.86g of 2,2-dihydroxymethylbutanol. Keep stirring and control the reaction at 65°C for 6.0h to obtain the polyisocyanate prepolymer reaction solution.

[0064] (2) The polyisocyanate prepolymer reaction solution was passed through a thin-film evaporator with a separation temperature of 180℃ and a separation pressure of 60Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-I obtained after separation was 20wt%.

[0065] (3) Add 32.93g of polypropylene glycol-400 and 17.46g of polypropylene glycol-1000 to the obtained heavy component-I, keep stirring, and control the reaction at 65℃ for 6.0h to obtain polymer reaction solution;

[0066] (4) The polymer reaction solution is then passed through a thin-film evaporator with a separation temperature of 180℃ and a separation pressure of 60Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-II obtained after separation is 0.38wt%, which is the isocyanate curing agent.

[0067]

Example 3

[0068] The preparation process of the isocyanate curing agent is as follows:

[0069] (1) Weigh 500g of phenyl dimethyl diisocyanate and add it to a glass flask. Heat the flask to 80°C and add 50.21g of 2,2-dihydroxymethylbutanol. Keep stirring and control the reaction at 80°C for 4.0h to obtain the polyisocyanate prepolymer reaction solution.

[0070] (2) The polyisocyanate prepolymer reaction solution was passed through a thin-film evaporator with a separation temperature of 160℃ and a separation pressure of 30Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-I obtained after separation was 17wt%.

[0071] (3) Add 15.97g of polypropylene glycol-400 and 22.45g of polypropylene glycol-1000 to the obtained heavy component-I, keep stirring, and control the reaction at 60℃ for 6.0h to obtain polymer reaction solution;

[0072] (4) The polymer reaction solution is then passed through a thin-film evaporator with a separation temperature of 160℃ and a separation pressure of 30Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-II obtained after separation is 0.33wt%, which is the isocyanate curing agent.

[0073]

Example 4

[0074] The preparation process of the isocyanate curing agent is as follows:

[0075] (1) Weigh 500g of phenyl dimethyl diisocyanate and add it to a glass flask. Heat the flask to 90°C and add 22.87g of 2,2-dihydroxymethylbutanol. Keep stirring and control the reaction at 90°C for 2.0h to obtain the polyisocyanate prepolymer reaction solution.

[0076] (2) The polyisocyanate prepolymer reaction solution was passed through a thin-film evaporator with a separation temperature of 130℃ and a separation pressure of 10Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-I obtained after separation was 22wt%.

[0077] (3) Add 42.41g of polypropylene glycol-400 and 523.92g of polypropylene glycol-2000 to the obtained heavy component-I, keep stirring, and control the reaction at 90℃ for 3.0h to obtain polymer reaction solution;

[0078] (4) The polymer reaction solution is then passed through a thin-film evaporator with a separation temperature of 163°C and a separation pressure of 30Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-II obtained after separation is 0.40wt%, which is the isocyanate curing agent.

[0079]

Example 5

[0080] The preparation process of the isocyanate curing agent is as follows:

[0081] (1) Weigh 500g of phenyl dimethyl diisocyanate and add it to a glass flask. Heat the flask to 55°C and add 26.94g of 2,2-dihydroxymethylbutanol. Keep stirring and react at 55°C for 3.0h to obtain the polyisocyanate prepolymer reaction solution.

[0082] (2) The polyisocyanate prepolymer reaction solution was passed through a thin-film evaporator with a separation temperature of 150℃ and a separation pressure of 20Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-I obtained after separation was 12wt%.

[0083] (3) Add 73.83g of polypropylene glycol-400 to the obtained heavy component-I, keep stirring, and control the reaction at 70℃ for 3.0h to obtain polymer reaction solution;

[0084] (4) The polymer reaction solution is then passed through a thin-film evaporator with a separation temperature of 150°C and a separation pressure of 45Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-II obtained after separation is 0.46wt%, which is the isocyanate curing agent.

[0085]

Example 6

[0086] The preparation process of the isocyanate curing agent is as follows:

[0087] (1) Weigh 500g of phenyl dimethyl diisocyanate and add it to a glass flask. Heat the flask to 70°C and add 26.49g of 2,2-dihydroxymethylbutanol. Keep stirring and control the reaction at 70°C for 5.2h to obtain the polyisocyanate prepolymer reaction solution.

[0088] (2) The polyisocyanate prepolymer reaction solution was passed through a thin-film evaporator with a separation temperature of 150℃ and a separation pressure of 30Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-I obtained after separation was 16wt%.

[0089] (3) Add 82.50g of polytetrahydrofuran ether diol-650 to the obtained heavy component-I, keep stirring, and control the reaction at 70℃ for 4.5h to obtain polymer reaction solution;

[0090] (4) The polymer reaction solution is then passed through a thin-film evaporator with a separation temperature of 165°C and a separation pressure of 60Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-II obtained after separation is 0.37wt%, which is the isocyanate curing agent.

[0091]

Example 7

[0092] The preparation process of the isocyanate curing agent is as follows:

[0093] (1) Weigh 500g of phenyl dimethyl diisocyanate and add it to a glass flask. Heat the flask to 80°C and add 19.88g of 2,2-dihydroxymethylbutanol. Keep stirring and control the reaction at 80°C for 5.0h to obtain the polyisocyanate prepolymer reaction solution.

[0094] (2) The polyisocyanate prepolymer reaction solution was passed through a thin-film evaporator with a separation temperature of 190℃ and a separation pressure of 100Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-I obtained after separation was 19wt%.

[0095] (3) Add 114.50g of polypropylene glycol-1000 to the obtained heavy component-I, keep stirring, and control the reaction at 80℃ for 7.0h to obtain polymer reaction solution;

[0096] (4) The polymer reaction solution is then passed through a thin-film evaporator with a separation temperature of 180℃ and a separation pressure of 70Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-II obtained after separation is 0.32wt%, which is the isocyanate curing agent.

[0097] Comparative Example 1

[0098] The preparation process of the isocyanate curing agent is as follows:

[0099] (1) Weigh 500g of phenyl dimethyl diisocyanate and add it to a glass flask. Heat the flask to 55°C and add 55.79g of 2,2-dihydroxymethylbutanol. Keep stirring and control the reaction at 55°C for 6.0h to obtain the polyisocyanate prepolymer reaction solution.

[0100] (2) The polyisocyanate prepolymer reaction liquid is passed through a thin-film evaporator with a separation temperature of 150℃ and a separation pressure of 20Pa to separate the unreacted isocyanate monomers and collect the heavy components. The proportion of isocyanate monomers in the obtained heavy components is 0.35wt%, which is the isocyanate curing agent.

[0101] Comparative Example 2

[0102] The preparation process of the isocyanate curing agent is as follows:

[0103] (1) Weigh 500g of phenyl dimethyl diisocyanate and add it to a glass flask. Heat the flask to 55°C and add 20.08g of 2,2-dihydroxymethylbutanol. Keep stirring and control the reaction at 55°C for 6.0h to obtain the polyisocyanate prepolymer reaction solution.

[0104] (2) The polyisocyanate prepolymer reaction solution was passed through a thin-film evaporator with a separation temperature of 150℃ and a separation pressure of 20Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-I obtained after separation was 25wt%.

[0105] (3) Add 56.63g of polypropylene glycol-400 and 257.59g of polypropylene glycol-1000 to the obtained heavy component-I, keep stirring, and control the reaction at 55℃ for 6.0h to obtain polymer reaction solution;

[0106] (4) The polymer reaction solution is then passed through a thin-film evaporator with a separation temperature of 150°C and a separation pressure of 20Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-II obtained after separation is 0.35wt%, which is the isocyanate curing agent.

[0107] Comparative Example 3

[0108] The preparation process of the isocyanate curing agent is as follows:

[0109] (1) Weigh 500g of phenyl dimethyl diisocyanate and add it to a glass flask. Heat the flask to 55°C and add 52.44g of 2,2-dihydroxymethylbutanol. Keep stirring and control the reaction at 55°C for 6.0h to obtain the polyisocyanate prepolymer reaction solution.

[0110] (2) The polyisocyanate prepolymer reaction solution was passed through a thin-film evaporator with a separation temperature of 150℃ and a separation pressure of 20Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-I obtained after separation was 25wt%.

[0111] (3) Add 5.31g of polypropylene glycol-400 and 24.14g of polypropylene glycol-1000 to the obtained heavy component-I, keep stirring, and control the reaction at 55℃ for 6.0h to obtain polymer reaction solution;

[0112] (4) The polymer reaction solution is then passed through a thin-film evaporator with a separation temperature of 150°C and a separation pressure of 20Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component-II obtained after separation is 0.35wt%, which is the isocyanate curing agent.

[0113] Comparative Example 4

[0114] The preparation process of the isocyanate curing agent is as follows:

[0115] (1) Weigh 500g of phenyl dimethyl diisocyanate and add it to a glass flask. Heat the flask to 55°C and add 55.79g of 2,2-dimethylolbutanol, 42.41g of polypropylene glycol-400 and 193.35g of polypropylene glycol-1000. Keep stirring and react at 55°C for 6.0h to obtain the polyisocyanate prepolymer reaction solution.

[0116] (2) The polyisocyanate prepolymer reaction liquid is passed through a thin-film evaporator with a separation temperature of 150°C and a separation pressure of 20Pa to separate the unreacted isocyanate monomers and collect the heavy components. The proportion of isocyanate monomers in the obtained heavy components is 0.34wt%, which is the isocyanate curing agent.

[0117] Comparative Example 5

[0118] The preparation process of the isocyanate curing agent is as follows:

[0119] (1) Weigh 500g of phenyl dimethyl diisocyanate and add it to a glass flask. Heat the flask to 55°C and add 42.41g of polypropylene glycol-400 and 193.35g of polypropylene glycol-1000. Keep stirring and control the reaction at 55°C for 6.0h to obtain the polyisocyanate prepolymer reaction solution.

[0120] (2) The polyisocyanate prepolymer reaction solution is passed through a thin-film evaporator with a separation temperature of 150°C and a separation pressure of 20Pa to remove the isocyanate monomer from the reaction solution. The proportion of isocyanate monomer in the heavy component obtained after separation is 0.35wt%, which is the isocyanate curing agent.

[0121] Table 1. Basic indicators and performance test results of each embodiment and comparative example.

[0122]

[0123]

[0124] In the isocyanate curing agent formulations of each embodiment, 2,2-dimethylol alcohol and polyether polyol of a specific molecular weight were selected and the ratio of the two was controlled within a suitable range to obtain an isocyanate curing agent based on dimethyl phthalate. This resulted in products (such as adhesives) with good adhesion and elongation at break. When bonded to a flexible substrate, the product is not easily broken under repeated bending or impact.

[0125] The curing agent formulation of Comparative Example 1 did not contain polyether polyol, resulting in a curing agent with high viscosity and low elongation at break. After being bonded to the flexible substrate, it was prone to breakage under repeated bending or impact, failing to meet the requirements for optical adhesive bonding of flexible screens.

[0126] In the curing agent formulations of Comparative Examples 2 and 3, the ratio of 2,2-dimethylolbutanol to polyether polyol was not controlled within a suitable range. As a result, the shear strength and elongation at break of the products made from the cured agents were not ideal and could not meet the requirements for use.

[0127] Although the curing agent formulation of Comparative Example 4 combines 2,2-dimethylol-butanol with polyether polyol, phthalimide diisocyanate is not polymerized stepwise with 2,2-dimethylol-butanol and polyether polyol, which results in a relatively low degree of polymerization of the obtained heavy components, thereby reducing the shear strength of the product.

[0128] In the curing agent formulation of Comparative Example 5, only polyether polyol was used without the addition of 2,2-dimethylolbutanol, which resulted in a low degree of crosslinking of the obtained heavy components, thus making the product lack basic shear strength.

[0129] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the spirit of the invention.

Claims

1. An isocyanate curing agent for optical adhesive, characterized by, The isocyanate curing agent is a product prepared by reacting a xylylene diisocyanate with a polyol; The polyol comprises at least 2,2-dimethylol butanol and a polyether polyol having a molecular weight of 200-4000 and a functionality of 2; The isocyanate curing agent has a viscosity of greater than or equal to 6000 mPa·s and less than or equal to 14000 mPa·s at 25℃.

2. The isocyanate curing agent according to claim 1, characterized in that, The isocyanate curing agent has a solid content of 100 wt%.

3. The isocyanate curing agent according to claim 1 or 2, characterized in that, The polyether polyol is selected from one or more of polyethylene glycol, polypropylene glycol and polytetrahydrofuran ether glycol.

4. The isocyanate curing agent according to any one of claims 1 to 3, characterized in that, The preparation of the isocyanate curing agent comprises at least two "reaction stages" and two "separation stages".

5. The isocyanate curing agent according to claim 4, characterized in that, The reaction stage is an urethane reaction process of the xylylene diisocyanate with the polyol.

6. The method for producing an isocyanate curing agent according to any one of claims 1 to 5, wherein The preparation method comprises the following steps: (1) contacting the xylylene diisocyanate with 2,2-dimethylol butanol to perform a first stage reaction to obtain a prepolymer reaction liquid; (2) performing a first stage separation on the obtained prepolymer reaction liquid to obtain a heavy component-I after separation; the proportion of isocyanate monomers in the obtained heavy component-I is 10-30 wt%, preferably 10-28 wt%; (3) adding a polyether polyol to the obtained heavy component-I to perform a second stage reaction to obtain a polymer reaction liquid; (4) performing a second stage separation on the obtained polymer reaction liquid to obtain a heavy component-II after separation; the proportion of isocyanate monomers in the obtained heavy component-II is 0.01-0.47 wt%, preferably 0.05-0.45 wt%, which is the isocyanate curing agent.

7. The preparation method according to claim 6, wherein the process conditions of the first stage reaction comprise: a reaction temperature of 50-90℃, preferably 60-90℃, and a reaction time of 2-8h, preferably 2-7h; the process conditions of the first stage separation comprise: a separation temperature of 130-195℃, preferably 130-190℃, and a separation pressure of 10-105Pa, preferably 10-100Pa; the process conditions of the second stage reaction comprise: a reaction temperature of 50-90℃, preferably 60-90℃, and a reaction time of 2-8h, preferably 2-7h; the process conditions of the second stage separation comprise: a separation temperature of 130-195℃, preferably 130-190℃, and a separation pressure of 10-105Pa, preferably 10-100Pa. In the first stage reaction, the ratio of the number of moles of isocyanate groups of the xylylene diisocyanate to the total number of moles of hydroxyl groups of the 2,2-dimethylol butanol and the polyether polyol is R1, and 4.0≤R1≤8.0, preferably 4.2≤R1≤8.

0.

8. The production method according to claim 6 or 7, characterized by, In the second stage reaction, the ratio of the number of moles of hydroxyl groups of the 2,2-dimethylol butanol to the number of moles of hydroxyl groups of the polyether polyol is R2, and 0.6≤R2≤9.0, preferably 0.7≤R2≤9.

0.

9. The production method according to any one of claims 6 to 8, characterized by, 10. Use of the isocyanate curing agent according to any one of claims 1-5 or the isocyanate curing agent prepared by the preparation method according to any one of claims 6-9 in an optical adhesive. ​

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