CN109627996B - High-light-transmittance optical transparent adhesive for attaching touch screen and synthetic method thereof - Google Patents

Abstract

The invention discloses a high-light-transmittance optical transparent adhesive for attaching a touch screen and a synthesis method thereof. The raw material formula of the high-light-transmittance optical transparent adhesive comprises, by weight, 30-50 parts of (methyl) acrylic acid alkyl ester, 25-40 parts of (methyl) acrylic acid hydroxyalkyl ester, 1-3 parts of N atom-containing polar monomer, 10-20 parts of cross-linking agent, 0.01-0.02 part of chain transfer agent and 0.5-1 part of thermal initiator. The high-light-transmittance optical transparent adhesive disclosed by the invention is in a pressure-sensitive state after being subjected to thermosetting, has moderate initial adhesion and excellent permanent adhesion, is not displaced and not easy to fall off after being attached, has the light transmittance of over 99.5%, the haze value of less than 0.1%, the refractive index close to the refractive index of glass of 1.49, and is environment-friendly in synthesis method.

Description

A kind of high light transmittance optical transparent adhesive for touch screen bonding and synthesis method thereof

technical field

The invention belongs to an optical adhesive, in particular to a high-transmittance optical transparent adhesive for laminating liquid crystal displays and a synthesis method thereof. The sensitive adhesive belongs to the field of electronic information technology.

Background technique

Most of the current smartphone and tablet markets use direct bonding technology to eliminate the gap between the LCM (liquid crystal module) and the touch screen glass or film. Most touch panel manufacturers are used to using optical tape OCA lamination technology with high production efficiency and uniform thickness when laminating glass. This has a great relationship with the nature of OCA. OCA is suitable for small lamination surfaces such as mobile phones and tablets The production efficiency is high, especially the heat-curing OCA, which can be cured by heating and made into a film, which is convenient and quick to use.

UV curing OCA requires ultraviolet light irradiation, but since the border part of the touch panel is printed with opaque ink, the ultraviolet rays cannot penetrate the ink to irradiate these places, resulting in uncured areas, which are not cured even if they are irradiated with a side light source. Complete curing cannot be ensured, which greatly increases equipment costs and reduces production efficiency.

At present, OCA mainly uses the United States, Japan and South Korea as its main suppliers, the United States is mainly based on 3M, Japan is mainly based on Sekisui, Nitto, Prince, Hitachi, and Riei, and South Korea is mainly LGH (a subsidiary of LG), But the high-performance products these companies have developed are largely kept secret.

Chinese invention patent application CN107057612A (2017.08.18) discloses a high light transmittance acrylic pressure-sensitive adhesive and a preparation method thereof. The acrylic pressure-sensitive adhesive is prepared from the following raw materials by weight: cohesive monomer 0-30 parts, 50-75 parts of viscous monomer, 1-10 parts of functional monomer, 5-10 parts of o-phenylphenoxyethyl acrylate, 0.3-0.8 parts of initiator, 100-150 parts of solvent, and 0.1 part of curing agent wt%～0.5wt%. The high light transmittance acrylate pressure-sensitive adhesive provided by the present invention has high permeability (light transmittance ≥ 93%), no adhesive residue phenomenon under normal use and treatment, and high peeling strength, and there is no glue residue during use. The phenomenon of debonding and adhesive layer and interface damage can solve the bonding problems in the fields of aerospace, electronic and electrical and optical devices such as LCD, PDP and OLED. However, the performance of the pressure-sensitive adhesive obtained by this technology needs to be improved. For example, its light transmittance is only 93%-96%, while the light transmittance of the OCA optical adhesive currently required by high-end equipment must be above 99%. This may be due to process problems and Lack of special monomers; secondly, the initial tack of the pressure-sensitive adhesive obtained by this technology is as high as No. 10 steel balls. The initial tack of international high-end OCA films is generally No. 6 steel balls. Excessive initial tack will seriously affect the film. The first use, which brings great inconvenience to the production of the electronic equipment industry, may be because the film is too soft, the ratio of soft and hard monomers is improper, and the molecular weight and cross-linking degree of the prepolymer are not enough, the molecular weight is too small, and the initial viscosity is relatively low. big. Thirdly, the sticky force of the pressure-sensitive adhesive obtained by this technology is too small, which is more than 72h, while the sticky force of the high-end adhesive film needs to be more than 240h, otherwise it is easy to fall off during use. Fourth, the prior art uses acrylic acid, a common functional monomer, which is highly acidic. When an optical adhesive containing this monomer is used to attach an optical device containing electrodes such as a touch screen, the electrodes will be corroded.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the problems existing in the prior art, and to provide a light transmittance of more than 99.5%, a haze value of less than 0.1%, a refractive index close to the glass refractive index of 1.49, a moderate initial viscosity, and excellent holding power. Environmentally friendly, high-transmittance optical transparent adhesive for touch screen lamination with thermal curing function and synthesis method thereof.

The optically transparent adhesive of the present invention is in the form of thermal curing, and the synthesized prepolymer is coated on the release film to form a BAB type sandwich structure, wherein B is the release film and A is the adhesive film. Then, after passing through a vacuum drying box, the adhesive film is thermally cured. When in use, the screen can be pasted by removing the release film, which is convenient to use.

1) Utilize the effect of hydrophilic hydroxyl group in hydroxyalkyl acrylate, and cooperate with large molecular weight cross-linking agent, so that only a small amount of water vapor in the film is evenly dispersed, and no cloud point will be formed, thereby increasing light transmittance and reducing haze again. , the high molecular weight cross-linking agent has a larger refractive index, which improves the light transmittance to a large extent (the high refractive index will be closer to the refractive index of the substrate, reducing light loss); the film obtained by the present invention, these items Important optical performance indicators are far better than the current domestic optical transparent glue.

2) Water vapor has a great influence on the light transmittance and haze of the film. When the light transmittance reaches more than 90%, a small amount of water vapor in the system is an important reason for affecting the light transmittance and haze of the system; After pre-dehydration treatment, most of the water vapor is removed, which greatly reduces the amount of water in the system that has a great impact on light transmittance and haze. After dehydration, the light transmittance of the film can be greatly improved. and reduce haze.

3) The sticking force and the initial sticking force are a pair of opposite properties. The smaller molecular weight and the degree of cross-linking make the film cohesive strength not enough, so the sticking force is too small; monomer, and the use of a large molecular weight cross-linking agent 1,1'-(1,3 benzenedicarbonyl)-bis-(2-methylaziridine) (bisamide), the N atom has a strong polarity, making The interaction between the molecular chains in the prepolymer is enhanced, and finally the film has a moderate molecular weight, a high degree of cross-linking, and an appropriate ratio of soft and hard monomers, so the initial viscosity is moderate and the adhesion is excellent.

The object of the present invention is achieved through the following technical solutions:

A high transmittance optical transparent adhesive for touch screen bonding: in parts by weight, the raw material formula includes 30-50 parts of alkyl (meth)acrylate, 25-40 parts of hydroxyalkyl (meth)acrylate , 1-3 parts of polar monomers containing N atom, 10-20 parts of crosslinking agent, 0.01-0.02 parts of chain transfer agent, 0.5-1 part of thermal initiator;

Described crosslinking agent is 1,1'-(1,3 benzenedicarbonyl)-bis-(2-methylaziridine);

The alkyl (meth)acrylate is methyl acrylate, ethyl acrylate, isopropyl acrylate, isoamyl acrylate, sec-butyl acrylate, n-butyl acrylate, isobornyl acrylate, 2-methyl acrylate Butyl acrylate, 4-methyl-2-pentyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, tert-butyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate , one or more of isobornyl methacrylate and butyl methacrylate;

Described hydroxyalkyl (meth)acrylate is hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate;

The N atom-containing polar monomer is N-alkyl (meth)acrylamide, N,N-dialkyl (meth)acrylamide or N-vinyl lactam;

All raw materials were dehydrated before use.

In order to further achieve the object of the present invention, preferably, the N-vinyl lactam is one or more of N-vinyl pyrrolidone and N-vinyl caprolactam;

Preferably, the chain transfer agent is dodecyl mercaptan.

Preferably, the thermal initiator is azobisisobutyronitrile.

Preferably, the raw material formulation further includes one or more of inorganic fillers, reactive or non-reactive plasticizers, heat stabilizers, defoaming agents, preservatives and diluents.

Preferably, the dehydration treatment refers to the dehydration of solid raw materials through a vacuum oven; the dehydration of liquid raw materials through oil bath vacuum dehydration and then molecular sieve dehydration. Molecular sieve dehydration is then carried out in a liquid state during heating.

Preferably, the dehydration in the vacuum oven is to place the solid substance in a vacuum oven at 50-80°C for 12-24 hours to remove water vapor before use; the vacuum dehydration in the oil bath is to control the temperature of the oil bath to be 0-10 higher than the boiling point temperature of the monomer. ℃, dehydration time 1-3h, cooling.

Preferably, the molecular sieve is a natural zeolite or a synthetic zeolite molecular sieve, and the models are 3A, 4A, 5A, 10Z, 13Z, Y or sodium mordenite molecular sieve.

The method for synthesizing a high-transmittance optical transparent adhesive for bonding a touch screen includes the following steps:

1) Carry out vacuum dehydration of the monomer and crosslinking agent in the raw material according to their respective boiling points. The temperature of the oil bath is 0-10°C higher than that of the monomer, and the dehydration time is 1-3h. Molecular sieves are dehydrated for 12-36h, and the molecular sieves are removed for later use. The solid substances are placed in a vacuum oven at 50-80°C for 12-24h to remove water vapor before use;

2) Add alkyl (meth)acrylate, hydroxyalkyl (meth)acrylate, N atom-containing polar monomer and chain transfer agent, add solvent, and heat up to 70-90°C;

3) in the heating process, the initiator is dissolved in the solvent and added;

4) After the dropwise addition of the initiator is completed, the temperature is raised to 70-90°C and the reaction is continued for 4-6h, then the temperature is lowered to 35-50°C, a mixture of a crosslinking agent and a solvent is added, the temperature is kept for 20-40min, and the temperature is lowered to obtain a liquid pressure sensitive glue;

5) Coat the liquid pressure-sensitive adhesive on the release film with a coating machine, pass through the drying tunnel, and then attach another layer of release film to form a BAB type OCA optically transparent adhesive.

Preferably, the solvent is ethyl acetate (EA), acetone or absolute ethanol.

In the raw materials of the present invention, the initiator is solid, and most of the remaining substances are liquid, but some monomers are solid at room temperature, and appear liquid after heating in the oil bath. High temperature will affect molecular sieves. What is more special is that the chain transfer agent dodecyl mercaptan (NDM) is liquid, and the amount used in the examples is very small (1-2 drops, 0.1 g in weight), and the purity is very high, and it is basically impossible to dehydrate further. Therefore, Vacuum dehydration in oil bath and molecular sieve dehydration can be avoided, and it can be placed in an oven before use.

Compared with the prior art, the present invention has the following advantages and beneficial effects:

1) Utilize the effect of hydrophilic hydroxyl group in hydroxyalkyl acrylate, and cooperate with large molecular weight cross-linking agent, so that only a small amount of water vapor in the film is evenly dispersed, and no cloud point will be formed, thereby increasing light transmittance and reducing haze again. , the high molecular weight crosslinking agent has a larger refractive index, which improves the light transmittance to a large extent (the high refractive index will be closer to the refractive index of the substrate, reducing light loss); the light transmittance of the film obtained by the present invention exceeds 99.5%, the haze value is lower than 0.1%, and the refractive index is close to the glass refractive index of 1.49. These important optical performance indicators are far better than the current domestic optical transparent adhesives.

2) Water vapor has a great influence on the light transmittance and haze of the film. When the light transmittance reaches more than 90%, a small amount of water vapor in the system is an important reason for affecting the light transmittance and haze of the system; After pre-dehydration treatment, most of the water vapor is removed, which greatly reduces the amount of water in the system that has a great impact on light transmittance and haze. After dehydration, the light transmittance of the film can be greatly improved. and reduce haze.

3) The sticking force and the initial sticking force are a pair of opposite properties. The smaller molecular weight and the degree of cross-linking make the film cohesive strength not enough, so the sticking force is too small; monomer, and the use of a large molecular weight cross-linking agent 1,1'-(1,3 benzenedicarbonyl)-bis-(2-methylaziridine) (bisamide), the N atom has a strong polarity, making The interaction between the molecular chains in the prepolymer is enhanced, and finally the film has a moderate molecular weight, a high degree of cross-linking, and an appropriate ratio of soft and hard monomers, so the initial viscosity is moderate and the adhesion is excellent.

4) Monomers and solvents used in the present invention The optical adhesive of the present invention is thermally cured, the equipment is simple, and it is convenient to use after being made into an adhesive film.

5) The adhesive film made by the present invention is a pressure-sensitive adhesive, with moderate initial tack, no displacement during lamination, and the lamination process is similar to the existing process, and no new equipment is required.

6) The adhesive film of the present invention can be further cured after the lamination process, which greatly enhances the bonding strength and ensures that it will not fall off.

7) The functional monomer acrylic acid is often used in the prior art in this field. This monomer is highly acidic. When an optical adhesive containing this monomer is used to attach an optical device containing electrodes such as a touch screen, the electrodes will be corroded. In the invention, the monomer containing polar N atom is used to replace acrylic acid as the functional monomer, which does not affect the mechanical properties of the adhesive film at all, and the prepared adhesive film does not corrode the electrode due to the acidic monomer, which is a good solution to the problem. Corrosion problem of raw materials in production in this field.

8) The prior art often uses peroxide as an initiator, and the peroxide is placed for a long time to cause serious yellow edges, which seriously affects the optical properties such as appearance, light transmittance and haze; the formula of the present invention does not use peroxide as an initiator. agent, can truly achieve ultra-high light transmittance and ultra-low haze.

Detailed ways

For better understanding of the present invention, the present invention will be further described below with reference to the examples, but the embodiments of the present invention are not limited to this.

In the present invention, BA is butyl acrylate, HEA is hydroxyethyl acrylate, IBOMA is isobornyl methacrylate, MMA is methyl methacrylate, MA is methyl acrylate, NVP is N-vinylpyrrolidone, and NVC is N - vinyl caprolactam, NDM is dodecyl mercaptan, EA is ethyl acetate, AIBN is azobisisobutyronitrile.

The optical adhesive prepolymer in the present invention is uniformly coated on the release film by a film applicator, and then covered with another layer of release film to form a BAB type adhesive film, wherein B refers to the release film, and A refers to the optical adhesive The film is then thermally cured in a vacuum drying oven. When in use, the release film can be peeled off for lamination.

The light transmittance was measured using a Lambda950 UV-Vis spectrophotometer with a film thickness of 50um. The refractive index was measured using an Abbe refractometer, and the haze was measured using a haze meter. The initial tack test uses an initial tack tester of model CZY-G, the holding force test uses a tack tester of model CZY-GS, and the 180° peel force test uses a universal tensile machine with a film width of 25mm.

Embodiment 1 (E1): raw material formula is shown in Table 1

Table 1 embodiment 1 raw material formula table

raw material BA HEA IBOMA NVP NDM EA AIBN acetone Bisamide anhydrous ethanol mass/g 20 20 5 1 0.1 70 0.4 4 8 10

Raw material pretreatment: butyl acrylate (BA), hydroxyethyl acrylate (HEA), isobornyl methacrylate (IBOMA), N-vinylpyrrolidone (NVP) and cross-linking agent bisamide were vacuum dehydrated for 1h before use , the temperature of the oil bath is the same as their respective boiling points, then the monomers (BA, HEA, IBOMA, NVP), the crosslinking agent bisamide and the solvent ethyl acetate (EA) are then subjected to 3A type molecular sieve adsorption and dehydration for 12h, dodecyl Thiol (NDM) and azobisisobutyronitrile AIBN were placed in a vacuum oven for 12h for use.

After pretreatment, BA, HEA, IBOMA, NVP and NDM were added to a 500ml four-necked flask according to the amount given in the formula, and then 55g EA was added. , and the oil bath was heated, and the temperature was gradually raised to 70 °C (the temperature displayed by the thermometer). During the heating process, dissolve AIBN in acetone, and then add the remaining EA to form an initiator solution with a concentration of about 0.021g/mL. Shake well and add it to the PTFE constant pressure dropping funnel. When the temperature in the flask reaches 70 °C, start The initiator solution was added dropwise, and the dropwise addition process of the initiator solution was about 1 h. After the end, remove the thermometer and the polytetrafluoroethylene constant pressure funnel, install a nitrogen protection device, the nitrogen flow rate is 20mL/s, and keep the oil bath at 70°C to continue the reaction for 6h. Then, the temperature in the flask was lowered to 35°C, and a solution mixed with bisamide and absolute ethanol was added dropwise. The dropwise addition was completed in about 20 minutes, the reaction was continued for 20 minutes, and the temperature was lowered to discharge.

Embodiment 2 (E2): raw material formula is shown in Table 2

Table 2 embodiment 2 formula table

raw material BA HPA MMA NMMA NDM EA AIBN acetone Bisamide anhydrous ethanol mass/g 20 20 5 1 0.1 70 0.4 4 8 10

Raw material pretreatment: BA, hydroxypropyl acrylate (HPA), methyl methacrylate (MMA), N-methylmethacrylamide (NMMA) and cross-linking agent bisamide were vacuum dehydrated for 2h before use, oil bath The temperature of the pot is 5 °C higher than their respective boiling points, and then BA, HPA, MMA, NMMA, bisamide, EA, acetone and absolute ethanol are subjected to 4A type molecular sieve adsorption and dehydration for 12h, dodecyl mercaptan (NDM) and azo Diisobutyronitrile AIBN was placed in a vacuum oven for 12h for use.

After pretreatment, BA, HPA, MMA, NMMA and NDM were added to a 500ml four-necked flask according to the amount given in the formula, and then 55g EA was added. , and the oil bath was heated, and the temperature was gradually raised to 80°C (the temperature displayed by the thermometer). During the heating process, dissolve AIBN in acetone, and then add the remaining EA to form an initiator solution with a concentration of about 0.021g/mL. Shake well and add it to the PTFE constant pressure dropping funnel. When the temperature in the flask reaches 80 °C, it starts. The initiator solution was added dropwise, and the dropwise addition process of the initiator solution was about 1.5h. After the end, remove the thermometer and the polytetrafluoroethylene constant pressure funnel, install a nitrogen protection device, the nitrogen flow rate is 20 mL/s, and keep the oil bath at 80 °C to continue the reaction for 5 h. Then, the temperature in the flask was lowered to 40°C, and a solution mixed with bisamide and absolute ethanol was added dropwise. The dropwise addition was completed in about 30 min, the reaction was continued for 30 min, and the temperature was lowered to discharge.

Embodiment 3 (E3): raw material formula is shown in Table 3

Table 3 embodiment 3 formula table

Raw material pretreatment: BA, hydroxyethyl methacrylate (HEMA), methyl acrylate (MA), N,N-dimethylmethacrylamide (N,N-DMMA) and crosslinker bisamide before use Vacuum dehydration was carried out for 3h, the temperature of the oil bath was 5°C higher than the respective boiling points, and then BA, HEMA, MA, N,N-DMMA, bisamide, EA, acetone and absolute ethanol were subjected to 5A type molecular sieve adsorption and dehydration for 36h, ten Dialkyl mercaptan (NDM) and azobisisobutyronitrile AIBN were placed in a vacuum oven for 24h for use.

Add BA, HEMA, MA, N,N-DMMA and NDM after pretreatment into a 500ml four-necked flask according to the amount given in the formula, and then add 55g EA. The experimental device is equipped with mechanical stirring with digital display function, condensation device and thermometer, rotating speed At 120 r/min, the oil bath was heated, and the temperature was gradually increased to 90 °C (the temperature displayed by the thermometer). During the heating process, dissolve AIBN in acetone, then add the remaining EA to form an initiator solution with a concentration of about 0.021g/mL, shake it up and add it to a constant pressure dropping funnel of PTFE, and start dropping when the temperature in the flask reaches 90°C. Add the initiator solution, and the dropwise addition process of the initiator solution is about 2h. After the end, remove the thermometer and the polytetrafluoroethylene constant pressure funnel, install a nitrogen protection device, the nitrogen flow rate is 20mL/s, and keep the oil bath at 90°C to continue the reaction for 4h. Then, the temperature in the flask was lowered to 45°C, and a solution mixed with bisamide and absolute ethanol was added dropwise. The dropwise addition was completed in about 40 min, the reaction was continued for 30 min, and the temperature was lowered to discharge.

Embodiment 4 (E4): raw material formula is shown in Table 4

Table 4 embodiment 4 formula table

raw material BA HPMA IBOMA NVC NDM EA AIBN acetone Bisamide anhydrous ethanol mass/g 20 20 5 1 0.1 70 0.4 4 8 10

Raw material pretreatment: BA, hydroxypropyl methacrylate (HPMA), isobornyl methacrylate (IBOMA), N-vinyl caprolactam (NVC) and cross-linking agent bisamide were vacuum dehydrated for 2h before use, oil bath The temperature of the pot is 10 °C higher than their respective boiling points, and then BA, HPMA, IBOMA, NVC, bisamide, EA, acetone and absolute ethanol are subjected to 10Z molecular sieve adsorption and dehydration for 24h, dodecyl mercaptan (NDM) and azo Diisobutyronitrile AIBN was placed in a vacuum oven for 24h for use.

After pretreatment, BA, HPMA, IBOMA, NVC and NDM were added to a 500ml four-necked flask according to the amount given in the formula, and then 55g EA was added. , and the oil bath was heated, and the temperature was gradually raised to 80°C (the temperature displayed by the thermometer). During the heating process, dissolve AIBN in acetone, then add the remaining EA to form an initiator solution with a concentration of about 0.021g/mL, shake it up and add it to a constant pressure dropping funnel, and start dropping when the temperature in the flask reaches 80°C. Add the initiator solution, and the dropwise addition process of the initiator solution is about 2h. After the end, remove the thermometer and the polytetrafluoroethylene constant pressure funnel, install a nitrogen protection device, the nitrogen flow rate is 20 mL/s, and keep the oil bath at 80 °C to continue the reaction for 5 h. Then, the temperature in the flask was lowered to 50°C, and a solution mixed with bisamide and absolute ethanol was added dropwise. The dropwise addition was completed in about 30 minutes, the reaction was continued for 40 minutes, and the temperature was lowered to discharge.

Comparative Example 1 (CE1): See Table 5 for the raw material formula

Table 5 Comparative example 1 raw material formula table

raw material BA MA NVP NDM EA AIBN acetone Bisamide anhydrous ethanol mass/g 40 5 1 0.1 70 0.4 4 8 10

Raw material pretreatment: BA, MA, NVP and cross-linking agent bisamide were dehydrated in vacuum for 3 hours before use, and the oil bath temperature was 10 °C higher than their respective boiling points, and then BA, MA, NVP, bisamide, EA, acetone and no Water ethanol is then subjected to 3A type molecular sieve adsorption and dehydration for 36 hours, and the amount of dodecyl mercaptan (NDM) is very small, which can be placed in a vacuum oven for 24 hours with azobisisobutyronitrile AIBN.

After pretreatment, BA, MA, NVP and NDM were added to a 500ml four-necked flask according to the amount given in the formula, and then 55g EA was added. The bath was heated, and the temperature was gradually increased to 70°C (the temperature indicated by the thermometer). During the heating process, dissolve AIBN in acetone, then add the remaining EA to form an initiator solution with a concentration of about 0.021g/mL, shake it up and add it to a PTFE constant pressure dropping funnel, and start dropping when the temperature in the flask reaches 70°C. Add the initiator solution, and the dropwise addition process of the initiator solution is about 1h. After the end, remove the thermometer and the polytetrafluoroethylene constant pressure funnel, install a nitrogen protection device, the nitrogen flow rate is 20mL/s, and keep the oil bath at 70°C to continue the reaction for 6h. Then, the temperature in the flask was lowered to 45°C, and a solution mixed with bisamide and absolute ethanol was added dropwise. The dropwise addition was completed in about 20 min, the reaction was continued for 30 min, and the temperature was lowered to discharge.

Comparative Example 2 (CE2): See Table 6 for the formulation of raw materials

Table 6 Comparative example 2 formula table

raw material BA HEA MA NMMA NDM EA AIBN acetone Bisamide anhydrous ethanol mass/g 20 20 5 1 0.1 70 0.4 4 8 10

The above raw materials are not pretreated.

Add BA, HEA, MA, NMMA and NDM in the formula table into a 500ml four-necked flask according to the amount given in the formula, and then add 55g EA. The experimental device is equipped with mechanical stirring with digital display function, condensation device and thermometer, and the rotation speed is 90r/min. , and the oil bath was heated, and the temperature was gradually raised to 80°C (the temperature displayed by the thermometer). During the heating process, dissolve AIBN in acetone, then add the remaining EA to form an initiator solution with a concentration of about 0.021g/mL, shake it up and add it to a constant pressure dropping funnel, and start dropping when the temperature in the flask reaches 80°C. Add the initiator solution, and the dropwise addition process of the initiator solution is about 1.5h. After the end, remove the thermometer and the polytetrafluoroethylene constant pressure funnel, install a nitrogen protection device, the nitrogen flow rate is 20 mL/s, and keep the oil bath at 80 °C to continue the reaction for 5 h. Then, the temperature in the flask was lowered to 30° C., and a solution mixed with bisamide and absolute ethanol was added dropwise. The dropwise addition was completed in about 30 min, the reaction was continued for 30 min, and the temperature was lowered to discharge.

Comparative Example 3 (CE3): See Table 7 for the raw material formula

Table 7 Comparative example 3 formula table

raw material BA HPA MMA NDM EA AIBN acetone Bisamide anhydrous ethanol mass/g 20 20 5 2d 70 0.4 4 8 10

Raw material pretreatment: BA, HPA, MMA and cross-linking agent bisamide were dehydrated in vacuum for 2 hours before use, and the oil bath temperature was 5 °C higher than their respective boiling points, and then BA, HPA, MMA, bisamide, EA, acetone and no Water ethanol was then subjected to 4A type molecular sieve adsorption and dehydration for 24 hours, and dodecyl mercaptan (NDM) and azobisisobutyronitrile AIBN were placed in a vacuum oven for 24 hours for use.

After pretreatment, BA, HPA, MMA and NDM were added to a 500ml four-necked flask according to the amount given in the formula, and then 55g EA was added. The bath was heated, and the temperature was gradually raised to 80°C (the temperature indicated by the thermometer). During the heating process, dissolve AIBN in acetone, then add the remaining EA to form an initiator solution with a concentration of about 0.021g/mL, shake it up and add it to a constant pressure dropping funnel, and start dropping when the temperature in the flask reaches 80°C. Add the initiator solution, and the dropwise addition process of the initiator solution is about 1.5h. After the end, remove the thermometer and the polytetrafluoroethylene constant pressure funnel, install a nitrogen protection device, the nitrogen flow rate is 20 mL/s, and keep the oil bath at 80 °C to continue the reaction for 5 h. Then, the temperature in the flask was lowered to 40°C, and a solution mixed with bisamide and absolute ethanol was added dropwise. The dropwise addition was completed in about 30 minutes, the reaction was continued for 20 minutes, and the temperature was lowered to discharge.

Comparative Example 4 (CE4): See Table 8 for the raw material formula

Table 8 Comparative Example 4 Recipe Table

raw material BA HEMA IBOMA NVP NDM EA AIBN acetone anhydrous ethanol mass/g 20 20 5 1 0.1 70 0.4 4 10

Raw material pretreatment: BA, HEMA, IBOMA, N,N-DMMA and cross-linking agent bisamide are dehydrated in vacuum for 3 hours before use, and the temperature of the oil bath is the same as their respective boiling points, and then BA, HEMA, IBOMA, NVP, EA, Acetone and absolute ethanol were then subjected to 5A molecular sieve adsorption and dehydration for 36 hours, and dodecyl mercaptan (NDM) and azobisisobutyronitrile AIBN were placed in a vacuum oven for 24 hours for use.

After pretreatment, BA, HEMA, IBOMA, NVP and NDM were added to a 500ml four-neck flask according to the amount given in the formula, and then 55g EA was added. , and the oil bath was heated, and the temperature was gradually raised to 90 °C (the temperature displayed by the thermometer). During the heating process, dissolve AIBN in acetone, then add the remaining EA to form an initiator solution with a concentration of about 0.021g/mL, shake it up and add it to a constant pressure dropping funnel of PTFE, and start dropping when the temperature in the flask reaches 90°C. Add the initiator solution, and the dropwise addition process of the initiator solution is about 2h. After the end, remove the thermometer and the polytetrafluoroethylene constant pressure funnel, install a nitrogen protection device, the nitrogen flow rate is 20mL/s, and keep the oil bath at 90°C to continue the reaction for 4h. Then, the temperature in the flask was lowered to 45°C, and a solution mixed with bisamide and absolute ethanol was added dropwise. The dropwise addition was completed in about 40 min, the reaction was continued for 20 min, and the temperature was lowered to discharge.

Testing the optical and mechanical properties of the film When testing the optical properties, the prepolymer was coated on the release film, thermally cured in a vacuum drying oven, and then transferred to the optical glass using a Lambda950 UV-Vis Spectrophotometer to measure the light transmittance The Abbe refractometer is used for the refractive index test, and the haze meter is used for the haze test. The film thickness after curing was 50 μm.

When testing the mechanical properties, the prepolymer was coated on the PET film, heat-cured at 80°C in a vacuum drying oven for 5 minutes, and the initial tack, tack and 180° peel force were tested. The initial tack test is performed according to GBT4852-2002 pressure-sensitive adhesive tape initial tack test method (rolling ball method). Test method for 180° peel strength of sensitive adhesive tapes.

The optical and mechanical properties test results are shown in Table 9:

Table 9 Optical properties test results of each film

project Light transmittance T% Haze H% Refractive index R E1 99.5 0 1.487 E2 99.6 0.1 1.488 E3 99.5 0 1.486 E4 99.5 0.1 1.488 CE1 97.3 0.5 1.480 CE2 95.6 0.8 1.478 CE3 99.5 0.1 1.488 CE4 99.6 0 1.486

It can be seen from the test results in Table 9 that the light transmittances of the optical films prepared by all the formulations of the examples are all above 99.5%, the haze values are all below 0.1%, and the refractive index is close to the refractive index of glass 1.49. Therefore, , the optical properties of the optical films produced by these formulations meet the current requirements of any industry. This is mainly because the pretreatment of the raw materials reduces the water vapor of the system to a very low level, and the only water vapor in the system when the hydroxyl-containing monomer is used is uniformly dispersed without forming a cloud point, which greatly improves the optical performance. The comparative examples 1 and 2 have low transmittance, relatively high haze and relatively low refractive index. From the observation and analysis of the formula, it is inferred that the comparative example 1 is due to the lack of hydroxyalkyl acrylate and the absence of hydroxyl groups in the system. A small amount of water vapor is uniformly dispersed, thus forming a cloud point, which reduces the light transmittance and increases the haze. In Comparative Example 2, since the raw material has not undergone pre-dehydration treatment, there is a lot of water vapor in the system, which has a great influence on the optical properties of the film.

From the test results of mechanical properties in Table 10, it can be seen that the initial adhesion of the adhesive films of all the examples is not large, and the value is moderate, which meets the needs of the industry, and this is also the ideal value of the initial adhesive force of the international high-end OCA optical adhesive film. This is mainly due to the moderate ratio of soft and hard monomers, the appropriate amount of polar monomers containing N atoms, and the use of bisamide crosslinking agents to make the polymer molecular weight and crosslinking degree moderate. In contrast, the initial tack of 3 and 4 is as high as 11 and 12, respectively, while the holding force is too small and the peel strength is insufficient. This is mainly due to the lack of polar monomers containing N atoms in the formula, and the interaction between molecular chains is too high. Weak, or lack of cross-linking agent, the prepolymer cross-linking degree is too low, the molecular weight is small, the cohesive strength is not enough, the initial tack is too large, the holding force is too small, and the peel strength is insufficient.

Table 10 Test results of mechanical properties of each sample

For those skilled in the art, under the principle of the present invention, the technical solutions described in the above embodiments can be modified, or some technical features thereof can be equivalently replaced. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (9)

1. A high light transmittance optical transparent adhesive for touch screen bonding is characterized in that: in parts by weight, its raw material formula comprises 30-50 parts of (meth) acrylic acid alkyl esters, 25-40 parts of (methyl) acrylates. ) hydroxyalkyl acrylate, 1-3 parts of polar monomers containing N atom, 10-20 parts of crosslinking agent, 0.01-0.02 parts of chain transfer agent and 0.5-1 part of thermal initiator; Described crosslinking agent is 1,1'-(1,3 benzenedicarbonyl)-bis-(2-methylaziridine); The alkyl (meth)acrylate is methyl acrylate, ethyl acrylate, isopropyl acrylate, isoamyl acrylate, sec-butyl acrylate, n-butyl acrylate, isobornyl acrylate, 2-methyl acrylate Butyl acrylate, 4-methyl-2-pentyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, tert-butyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate , one or more of isobornyl methacrylate and butyl methacrylate; Described hydroxyalkyl (meth)acrylate is hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate; The N atom-containing polar monomer is N-alkyl (meth)acrylamide, N,N-dialkyl (meth)acrylamide or N-vinyl lactam; All raw materials are subjected to dehydration treatment before use; the dehydration treatment refers to the dehydration of solid raw materials through a vacuum oven; the dehydration of liquid raw materials through oil bath vacuum dehydration and then molecular sieve dehydration. The vacuum oil bath is heated for dehydration, and then the molecular sieve dehydration is carried out in a liquid state during heating. 2. The high light transmittance optically transparent adhesive for bonding a touch screen according to claim 1, wherein the N-vinyl lactam is one of N-vinyl pyrrolidone and N-vinyl caprolactam or variety. 3 . The optically transparent adhesive with high light transmittance for bonding a touch screen according to claim 1 , wherein the chain transfer agent is dodecyl mercaptan. 4 . 4 . The high transmittance optically transparent adhesive for bonding a touch screen according to claim 1 , wherein the thermal initiator is azobisisobutyronitrile. 5 . 5. The optically transparent adhesive with high light transmittance for bonding a touch screen according to claim 1, wherein the raw material formula further comprises inorganic fillers, reactive or non-reactive plasticizers, thermal stabilizers, One or more of foaming agents, preservatives and diluents. 6. The high-transmittance optically transparent adhesive for bonding a touch screen according to claim 1, wherein the dehydration in the vacuum oven is to place the solid substance in a vacuum oven at 50-80°C for 12-24h to remove water vapor before use. ; In the oil bath vacuum dehydration, the temperature of the oil bath is controlled to be 0-10°C higher than the boiling point temperature of the monomer, the dehydration time is 1-3h, and the temperature is lowered. 7. The optically transparent adhesive with high light transmittance for bonding a touch screen according to claim 1, wherein the molecular sieve is a natural zeolite or a synthetic zeolite molecular sieve, and the models are 3A, 4A, 5A, 10Z, 13Z, Y Or sodium mordenite molecular sieve. 8. The method for synthesizing the high transmittance optical transparent adhesive for bonding a touch screen according to any one of claims 1-7, characterized in that it comprises the following steps: 1) Carry out vacuum dehydration of the monomer and crosslinking agent in the raw material according to their respective boiling points. The temperature of the oil bath is 0-10°C higher than that of the monomer, and the dehydration time is 1-3h. Molecular sieves are dehydrated for 12-36h, and the molecular sieves are removed for later use. The solid substances are placed in a vacuum oven at 50-80°C for 12-24h to remove water vapor before use; 2) Add alkyl (meth)acrylate, hydroxyalkyl (meth)acrylate, N atom-containing polar monomer and chain transfer agent, add solvent, and heat up to 70-90°C; 3) in the heating process, the initiator is dissolved in the solvent and added; 4) After the dropwise addition of the initiator is completed, the temperature is raised to 70-90°C and the reaction is continued for 4-6h, then the temperature is lowered to 35-50°C, a mixture of a crosslinking agent and a solvent is added, the temperature is kept for 20-40min, and the temperature is lowered to obtain a liquid pressure sensitive glue; 5) Coat the liquid pressure-sensitive adhesive on the release film with a coating machine, pass through the drying tunnel, and then attach another layer of release film to form a BAB type OCA optically transparent adhesive. 9 . The method for synthesizing high-transmittance optically transparent adhesive for bonding a touch screen according to claim 8 , wherein the solvent is ethyl acetate, acetone or anhydrous ethanol. 10 .