OCA optical pressure-sensitive adhesive with low volume shrinkage and preparation method thereof

Abstract

The invention relates to the technical field of adhesives, and discloses an OCA optical pressure-sensitive adhesive with low volume shrinkage and a preparation method thereof, the OCA optical pressure-sensitive adhesive comprises the following raw materials by mass: 80-100% of a copolymer and 0-20% of tackifying resin; the structural general formula of the copolymer is M1-b-(M2-ran-M3-ran-M4)-b-M5 or M1-b-(M2-ran-M4)-b-(M3-ran-M4)-b-M5, wherein M1, M2, M3, M4 and M5 are comonomers in the block copolymer, and the structural general formula of the copolymer is shown in the description. Wherein M1 and M5 are hard monomers, M2 is a soft monomer, M3 is isobornyl acrylate and / or isobornyl methacrylate, and M4 is one or more of methacrylic acid, acrylic acid, hydroxyethyl acrylate, hydroxypropyl acrylate and hydroxyethyl methacrylate. According to the invention, the isobornyl acrylate monomer with a large side group structure is added into the copolymer and is matched with the functional monomer containing hydroxyl or carboxyl to slow down the volume shrinkage in the curing process of the optical adhesive, the volume shrinkage rate of the pressure-sensitive adhesive prepared from the copolymer obtained by adjusting the proportion of the monomer formula can be greatly reduced, and the mechanical property is kept excellent.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and in particular to an OCA optical pressure-sensitive adhesive with low volume shrinkage and a preparation method thereof. Background Art

[0002] With the widespread application of optical devices in various fields, the performance requirements for optical adhesives are becoming increasingly higher. In existing technologies, optical adhesives often shrink in volume during the curing process, which may lead to a decrease in the optical performance of the device and even affect the long-term stability of the device.

[0003] Previous patents have proposed numerous methods and combinations for creating optical adhesives with low volume shrinkage. These approaches fall into two main categories: adding an expandable monomer to offset shrinkage during the curing process; and adding carbon nanowires, modified silica, and other additives to fill voids and reduce shrinkage.

[0004] CN103396741A discloses a zero-VOC photopolymerizable acrylate pressure-sensitive adhesive composition and preparation method. Using photopolymerization technology, a high-molecular-weight linear acrylic copolymer with an appropriate molecular weight distribution is selected. By controlling the ratio of soft and hard monomers, a continuous swelling dispersion method is used to produce an interpenetrating network structure of a polyacrylic acid matrix resin. The type and amount of functional monomers and inorganic fillers are then further regulated to form a photopolymerizable inorganic hybrid acrylate pressure-sensitive adhesive composition. The composition boasts stable performance, uniform dispersion, zero solvent, zero VOC, and is environmentally friendly. The resulting acrylate pressure-sensitive adhesive tape exhibits superior flexibility, initial tack, sustained tack, hardness, tensile strength, elongation, and volume shrinkage resistance to emulsion-based or water-dispersed acrylic pressure-sensitive adhesive films.

[0005] CN105585982A discloses an acrylate hot melt pressure-sensitive adhesive and a preparation method thereof. The acrylate hot melt pressure-sensitive adhesive comprises the following raw materials: 1 to 10 parts of a hard monomer, 70 to 95 parts of a soft monomer, 1 to 5 parts of a functional monomer, 1 to 5 parts of a polymerizable UV photoinitiator, 0.2 to 0.5 parts of a free radical polymerization initiator, and 0.01 to 0.1 parts of a molecular weight regulator. The acrylate hot melt pressure-sensitive adhesive has improved storage stability and weather resistance, a very small volume shrinkage during curing and cross-linking, high adhesion to the coated substrate, and is not prone to adhesive transfer. It can be widely used in food contact and medical fields. Although some progress has been made, there are still some challenges, such as slow curing speed, poor modulus and transmittance in optical adhesive properties, and other performance degradation. Summary of the Invention

[0006] In order to solve the problem of high volume shrinkage of pressure-sensitive adhesives, the present invention provides an OCA optical pressure-sensitive adhesive with low volume shrinkage. Isobornyl acrylate monomers with large side group structures are added to the copolymer, and functional monomers containing hydroxyl or carboxyl groups are combined to slow down the volume shrinkage of the optical adhesive during curing.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] An OCA optical pressure-sensitive adhesive with low volume shrinkage, comprising 80-100% of a copolymer and 0-20% of a tackifying resin in a mass ratio;

[0009] The general structural formula of the copolymer is M1-b-(M2-ran-M3-ran-M4)-b-M5 or M1-b-(M2-ran-M4)-b-(M3-ran-M4)-b-M5, wherein M1, M2, M3, M4, and M5 are comonomers in the block copolymer;

[0010] Among them, M1 and M5 are hard monomers, M2 is a soft monomer, M3 is isobornyl acrylate and / or isobornyl methacrylate, and M4 is one or more of methacrylic acid, acrylic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, and hydroxyethyl methacrylate.

[0011] The present invention selects four monomer types: hard monomers, soft monomers, isobornyl methacrylate, and functional monomers containing hydroxyl or carboxyl groups. Isobornyl methacrylate, due to its high side-aggregate molecular weight, can reduce inter-molecular stress during polymer curing. Hydroxyl or carboxyl functional monomers can form reversible hydrogen bonds with each other, synergistically mitigating volume shrinkage during the curing process of the optical adhesive. By adjusting the monomer ratios, the resulting copolymer can significantly reduce volume shrinkage while maintaining excellent mechanical properties.

[0012] The mass of the copolymer comonomer is 100%, wherein the total mass of M1 and M5 accounts for less than 20% of the comonomer, the mass of M2 accounts for 55-90%, the mass of M3 accounts for 5-40%, and the mass of M4 accounts for 2-5%.

[0013] Preferably, the total mass of M1 and M5 accounts for less than 15% of the total comonomer, and more preferably, the total mass of M1 and M5 accounts for less than 8% of the total comonomer. A low styrene content helps to achieve a low volume shrinkage after curing.

[0014] The hard monomer includes one or more of styrene, methyl acrylate, isobornyl acrylate, cyclohexyl acrylate, methyl methacrylate, acrylamide, acrylonitrile and vinyl acetate, and its glass transition temperature ranges from 60 to 150° C.;

[0015] The soft monomer includes one or more of isooctyl acrylate, isooctyl methacrylate, 2-propylheptyl acrylate, octyl acrylate, and octyl methacrylate, and the glass transition temperature thereof is less than -50°C.

[0016] The blocks formed by M1 and M5 each have a number average molecular weight of 0.2 to 15,000 g / mol; the blocks formed by M2, M3, and M4 have a total number average molecular weight of 96,000 to 296,000 g / mol; and the number average molecular weight of the copolymer is 100,000 to 300,000 g / mol.

[0017] The tackifying resin includes one or more of T-90, T-100, T-110, T-120, T-801, T-801L, 900L, 901L, TP2019 and 803L.

[0018] The present invention also provides a method for preparing the OCA optical pressure-sensitive adhesive with low volume shrinkage, comprising the steps of:

[0019] Step 1: Dissolve the RAFT agent in water, add the M1 monomer and mix, then add the first initiator and react for 1-3 hours to obtain a latex formed by the M1 homopolymer;

[0020] Step 2: Adding sodium hydroxide aqueous solution to the latex of step 1, then adding M2 monomer, water and a second initiator, and reacting for 2-5 hours in an oxygen-free environment to obtain an M1-b-M2 copolymer emulsion; then adding a mixed monomer of M3 monomer and M4, and reacting for 1-5 hours in an oxygen-free environment to obtain an M1-b-(M2-ran-M3-ran-M4) copolymer emulsion;

[0021] Step 3, adding M5 monomer to the emulsion of step 2, adding a second initiator, and reacting for 2-7 hours in an oxygen-free environment to obtain an M1-b-(M2-ran-M3-ran-M4)-b-M5 copolymer emulsion;

[0022] Step 4, mixing the copolymer emulsion with a demulsifier, washing and drying the precipitated product to obtain the copolymer;

[0023] Step 5: dissolving the copolymer and the tackifying resin in a dispersion medium, coating the mixture into a film in an inert gas environment, and drying the film to obtain the OCA optical pressure-sensitive adhesive.

[0024] Preferably, step 2 is replaced by: adding sodium hydroxide aqueous solution to the latex of step 1, then adding a mixed monomer of M2 and 1 / 10-1 of M4, water and a second initiator, and reacting for 2-5 hours in an anaerobic environment to obtain an M1-b-(M2-ran-M4) copolymer emulsion; then adding M3 and the remaining M4 mixed monomer, and reacting for 2-5 hours in an anaerobic environment to obtain an M1-b-(M2-ran-M4)-b-(M3-ran-M4) copolymer emulsion, and correspondingly obtaining an M1-b-(M2-ran-M4)-b-(M3-ran-M4)-b-M5 copolymer emulsion in step 5. The volume shrinkage of the optical adhesive added in batches is lower because the distribution of hydroxyethyl acrylate is more uniform, the hydrogen bond formation is also more uniform, and the volume shrinkage of the optical adhesive is lower.

[0025] The reaction temperature in step 1 is 40-90° C.; the reaction temperature in step 2 is 30-60° C.; the demulsification temperature in step 3 is 30-60° C., and the demulsification time is more than 0.1 h.

[0026] The chemical structural formula of the RAFT agent is: R-(Mn1-b-Nn2)-X; wherein R is an isopropyl group, an acetic acid group, a 2-cyanoacetic acid group or a 2-aminoacetic acid group; in Mn1, M is a methacrylic acid monomer or an acrylic acid monomer unit, n1 is the average polymerization degree of M, and n1 ranges from 10 to 30; in Nn2, N is a styrene monomer, a n-butyl acrylate monomer, a methyl acrylate, an isooctyl acrylate or a methyl methacrylate monomer unit, n2 is the average polymerization degree of N, and n2 ranges from 1 to 8; the X group is an alkyl dithioester group or an alkyl trithioester group, and the added mass of the RAFT agent is 0.2% to 1.0% of the total mass of all monomers;

[0027] In step 2, sodium hydroxide is added to adjust the pH to between 7 and 10.

[0028] The demulsifier includes any one or more of HCl solution, H2SO4 solution, HNO3 solution, HBr acetic acid, lactic acid, formic acid, and acetic acid; the added mass is 1 / 15-1 / 25 of the mass of the copolymer emulsion.

[0029] The dispersion medium includes any one or more of diethyl ether, methyl tert-butyl ether, tetrahydrofuran, methyl ethyl ketone, ethyl acetate and methyl propionate.

[0030] The first initiator includes any one or more of ammonium persulfate, potassium persulfate, hydrogen peroxide and hydrogen peroxide derivatives; the mass is 1 / 50-1 of the molar mass of the RAFT agent;

[0031] The second initiator includes any one or more of azobisisobutylimidazoline hydrochloride, azobisisobutylamidine hydrochloride, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, sodium persulfate / potassium persulfate redox initiator and sodium persulfate / ammonium persulfate redox initiator, and the mass is 1 / 50-1 of the molar mass of the RAFT agent.

[0032] The low volume shrinkage OCA optical pressure-sensitive adhesive of the present invention will promote the development of optical display technology and improve the preparation process of optical adhesive while maintaining the excellent performance of the optical adhesive.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) Based on the effect of large side-group monomers on reducing stress between copolymer segments and hydrogen bonding between functional monomers, as well as the regulation of monomer ratios and preparation processes, the optical adhesive prepared in the present invention not only maintains excellent performance but also has a significant improvement in volume shrinkage compared to traditional copolymers.

[0035] (2) The present invention further controls the volume shrinkage of the polymer by regulating the amount and ratio of the first and last monomers. The low styrene content is more conducive to obtaining a low volume shrinkage after curing. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The volume shrinkage diagram of the optical pressure-sensitive adhesive prepared in the examples and comparative examples.

[0037] Figure 2 The optical transmittance of the optical pressure-sensitive adhesives prepared in Examples and Comparative Examples.

[0038] Figure 3 Modulus data of optical pressure-sensitive adhesives prepared for Examples and Comparative Examples. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with embodiment. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Those skilled in the art will make modifications or equivalent substitutions based on understanding the technical solution of the present invention, without departing from the spirit and scope of the technical solution of the present invention, and all should be encompassed within the protection scope of the present invention.

[0040] The raw materials used in the following specific embodiments were purchased from the market, and the structural formula of the RAFT agent is:

[0041]

[0042] Example 1

[0043] The specific steps for preparing an optical pressure-sensitive adhesive having a copolymer of poly(styrene-b-(isooctyl acrylate-ran-isobornyl acrylate-ran-hydroxyethyl acrylate)-b-styrene) are as follows:

[0044] Step 1: dissolving 1 part by mass of a RAFT agent in 20 parts by mass of water, adding 3 parts by mass of a styrene monomer and mixing, then adding 5 parts by mass of an aqueous solution of potassium sulfate (solid content of 0.1%), and reacting at 70° C. for 1.5 hours to obtain a styrene latex;

[0045] Step 2: Add 2 parts by mass of an aqueous sodium hydroxide solution (solid content: 5%) to the latex of step 1, then add 60 parts by mass of isooctyl acrylate monomer, 30 parts by mass of water, and 5 parts by mass of azobisisobutylimidazoline hydrochloride (solid content: 0.1%), and react at 45° C. in an anaerobic environment for 2 hours to obtain a polystyrene copolymer emulsion; then add 35 parts by mass of a mixed monomer of isobornyl acrylate and 5 parts by mass of hydroxyethyl acrylate, and continue to react at 45° C. in an anaerobic environment for 3 hours to obtain a poly(styrene-b-(isooctyl acrylate-ran-isobornyl acrylate-ran-hydroxyethyl acrylate)) copolymer emulsion;

[0046] Step 3, then adding 3 parts by mass of styrene monomer and 5 parts by mass of azobisisobutylimidazoline hydrochloride (solid content 0.1%), reacting at 45° C. in an oxygen-free environment for 5 hours to obtain a (styrene-b-(isooctyl acrylate-ran-isobornyl acrylate-ran-hydroxyethyl acrylate)-b-styrene) copolymer emulsion;

[0047] Step 4, mixing the copolymer emulsion with 500 parts by mass of dilute hydrochloric acid (solid content 6%), washing and drying the precipitated product to obtain the copolymer;

[0048] Step 5: dissolving 95 parts by mass of the copolymer and 5 parts by mass of T-90 tackifier in tetrahydrofuran, coating the mixture into a film in an argon environment, and naturally drying the film to obtain the OCA optical pressure-sensitive adhesive.

[0049] The mechanical properties of the optical pressure-sensitive adhesive were tested using a universal materials testing machine (Zwick / Roll Z020). The optical adhesive was cut into dumbbell-shaped specimens using a standard cutting knife. The test method was based on GB 16421-1996, with a tensile rate of 30 mm / min. The test was repeated at least three times for each sample.

[0050] The stress relaxation recovery performance of the optical pressure-sensitive adhesive was tested by DMA (TAQ800). The above optical pressure-sensitive adhesive film was cut into strips with a width of 5 mm and a length of 25 mm. The OCA optical pressure-sensitive adhesive was tested by stretching it for 1 hour at a strain of 500%, and then maintaining it at a stress of 0 MPa for 1 hour. The recovery data was recorded, and the strain recovery rate was calculated.

[0051] The volume shrinkage test method of optical pressure-sensitive adhesive is to cut the above optical adhesive film into strips with a width of 5 mm and a length of 25 mm, place the optical adhesive in an oven at 100°C for 24 minutes, and then test its area. The volume shrinkage rate is the ratio of the difference between the initial optical adhesive area and the initial optical adhesive area.

[0052] The addition amount of isooctyl acrylate, isobornyl acrylate and hydroxyethyl acrylate in step 2 was adjusted, and the preparation process remained unchanged. The mechanical properties, rebound performance, volume shrinkage and transmittance of the obtained copolymer were compared. The specific raw material amounts and results are shown in Table 1. The volume shrinkage is shown in Table 1. Figure 1 , the optical transmittance is as follows Figure 2 , the modulus is Figure 3 shown.

[0053] Table 1 Properties of optical pressure-sensitive adhesives with different comonomer dosages

[0054]

[0055] Table 1 shows the mechanical properties, rebound performance, volume shrinkage, and transmittance data for Examples 1-5 and Comparative Examples 1-3. Samples 1-3 show that, with a constant weight percentage of hydroxyethyl acrylate, increasing the isobornyl acrylate content significantly reduces the volume shrinkage of the polymer from 10% to 1%, significantly improving the volume shrinkage. This is because the large side groups of isobornyl acrylate significantly reduce stress between the polymers, preventing significant stress release in the optical adhesive during the heat-curing process.

[0056] The modulus of the optical adhesive increased from 183kPa to 232kPa, which was not a significant increase and was within the acceptable range. This was mainly based on the microphase separation formed between the head and terminal styrenes, which constructed the overall structural network of the optical adhesive, so that the addition of isobornyl acrylate monomers did not cause a significant change in the modulus. The resilience of the optical adhesive was also improved, from 96% to 98%. This was because the chain entanglement between the polymer chains inside the optical adhesive became smaller, thereby improving the recovery performance of the optical adhesive. The transmittance of the optical adhesive did not change with the change in the composition of its monomers, mainly because the acrylic ester monomers have excellent optical transmittance.

[0057] From Comparative Examples 1-3, it can be seen that the addition of either isobornyl acrylate or hydroxyethyl acrylate alone cannot reduce the volume shrinkage of the colloid, but the synergistic effect of the two comonomers can effectively reduce the volume shrinkage of the optical adhesive.

[0058] Comparative Example 1

[0059] The difference between Comparative Example 1 and Example 1 is that the mass fractions of isooctyl acrylate and isobornyl acrylate in step 2 are different, namely 60 and 40 respectively, and hydroxyethyl acrylate is not contained. The other preparation steps are the same as those in Example 1. As shown in Table 1, the volume shrinkage is as follows: Figure 1 , the optical transmittance is as follows Figure 2 , the modulus is Figure 3 shown.

[0060] Comparative Example 2

[0061] The difference between Comparative Example 2 and Example 1 is that the mass fraction of isooctyl acrylate in step 2 is different, which is 100, and it does not contain isobornyl acrylate and hydroxyethyl acrylate. The other preparation steps are the same as those in Example 1. As shown in Table 1, the volume shrinkage is as follows: Figure 1 , the optical transmittance is as follows Figure 2 , the modulus is Figure 3 shown.

[0062] Comparative Example 3

[0063] The difference between Comparative Example 3 and Example 1 is that the mass fractions of isooctyl acrylate and hydroxyethyl acrylate in step 2 are different, namely 95 and 5 respectively, and it does not contain isobornyl acrylate. The other preparation steps are the same as those in Example 1. As shown in Table 1, the volume shrinkage is as follows: Figure 1 , the optical transmittance is as follows Figure 2 , the modulus is Figure 3 shown.

[0064] Examples 6-7

[0065] Preparation of an optical pressure-sensitive adhesive containing a copolymer of poly(styrene-b-(isooctyl acrylate-ran-isobornyl acrylate-ran-hydroxyethyl acrylate)-b-styrene). The difference between Examples 6 and 7 lies in the adjustment of the mass fraction of styrene. The other monomer amounts and procedures are the same as in Example 1. The main purpose is to investigate the effect of varying styrene amounts on the monomer volume shrinkage.

[0066] The addition amount of styrene in steps 1 and 3 was adjusted, and the preparation process remained unchanged. The mechanical properties, rebound performance, volume shrinkage and transmittance of the obtained copolymers were compared. The specific results are shown in Table 2. The volume shrinkage is shown in Table 2. Figure 1 , the optical transmittance is as follows Figure 2 , the modulus is Figure 3 In Table 2, Example 1 is Sample 1.

[0067] Table 2 Properties of optical pressure-sensitive adhesives prepared with different styrene dosages

[0068] Serial number Sample number Styrene mass parts Modulus / kPa Resilience / % Volume shrinkage / % Transmittance / % Example 1 1 3 232 98 2 99 Example 6 6 5 320 99 5 99 Example 7 7 7 411 99 8 99

[0069] Table 2 shows the mechanical properties, rebound performance, volume shrinkage, and transmittance data for Sample 1 and Examples 6-7 in Example 1. As the mass fraction of styrene increases, the volume shrinkage of the polymer decreases. This is because microphase separation forms between the styrenes. The increase in styrene enhances the degree of phase separation, making the network structure within the optical adhesive more compact, thereby increasing the volume shrinkage of the optical adhesive during the curing process. Furthermore, the modulus of the optical adhesive increases significantly with increasing mass fraction of styrene, also due to the tighter network structure of the optical adhesive.

[0070] Examples 8-9

[0071] The optical pressure-sensitive adhesive in which the copolymer is poly(styrene-b-(isooctyl acrylate-ran-isobornyl acrylate-ran-hydroxyethyl acrylate)-b-styrene) is prepared. The monomer amounts used in Examples 8-9 are the same as in Example 1, except that step 2 is different. The main purpose is to explore the effect of different monomer addition orders on the monomer volume shrinkage rate.

[0072] The second step comprises adding 2 parts by mass of a sodium hydroxide aqueous solution (solid content: 5%) to the latex of the first step, then adding 60 parts by mass of an isooctyl acrylate monomer and 3 parts by mass of a mixed monomer of hydroxyethyl acrylate, 30 parts by mass of water, and 5 parts by mass of azobisisobutylimidazoline hydrochloride (solid content: 0.1%), and reacting the mixture for 2 hours in an oxygen-free environment to obtain a polystyrene copolymer emulsion; then adding 35 parts by mass of an isobornyl acrylate and 2 parts by mass of a mixed monomer of hydroxyethyl acrylate, and reacting the mixture for 3 hours in an oxygen-free environment to obtain a poly(styrene-b-(isooctyl acrylate-ran-isobornyl acrylate-ran-hydroxyethyl acrylate)) copolymer emulsion;

[0073] The amount of hydroxyethyl acrylate added in step 2 was adjusted, and the other preparation processes remained unchanged. The mechanical properties, rebound performance, volume shrinkage and transmittance of the obtained optical pressure-sensitive adhesive were compared. The specific results are shown in Table 3. The volume shrinkage is as follows: Figure 1 , the optical transmittance is as follows Figure 2 , the modulus is Figure 3 As shown, Example 1 in Table 3 is Sample 1.

[0074] Table 3 Properties of optical pressure-sensitive adhesives prepared with different amounts of hydroxyethyl acrylate

[0075]

[0076] Table 3 shows the mechanical properties, rebound performance, volume shrinkage, and transmittance data for Sample 1 in Example 1 and Examples 8-9. It can be seen that the volume shrinkage is lower when the optical adhesive is added in batches. This is because the hydroxyethyl acrylate is more evenly distributed, leading to more uniform hydrogen bonding. Hydrogen bonding resists shrinkage caused by stress relaxation caused by heat in the optical pressure-sensitive adhesive.

[0077] The above embodiments are used to illustrate the present invention rather than to limit the present invention. Any modifications and changes made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. An OCA optical pressure-sensitive adhesive with low volume shrinkage, characterized in that: The raw material comprises 80-100% of a copolymer and 0-20% of a tackifying resin in a mass ratio; The general structural formula of the copolymer is M1-b-(M2-ran-M3-ran-M4)-b-M5 or M1-b-(M2-ran-M4)-b-(M3-ran-M4)-b-M5, wherein M1, M2, M3, M4, and M5 are comonomers in the block copolymer; Among them, M1 and M5 are hard monomers, M2 is a soft monomer, M3 is isobornyl acrylate and / or isobornyl methacrylate, and M4 is one or more of methacrylic acid, acrylic acid, hydroxyethyl acrylate, hydroxypropyl acrylate, and hydroxyethyl methacrylate.

2. The OCA optical pressure-sensitive adhesive with low volume shrinkage according to claim 1, characterized in that: The mass of the copolymer comonomer is 100%, wherein the total mass of M1 and M5 accounts for less than 20% of the comonomer, the mass of M2 accounts for 55-90%, the mass of M3 accounts for 5-40%, and the mass of M4 accounts for 2-5%.

3. The OCA optical pressure-sensitive adhesive with low volume shrinkage according to claim 1, characterized in that: The hard monomer includes one or more of styrene, methyl acrylate, isobornyl acrylate, cyclohexyl acrylate, methyl methacrylate, acrylamide, acrylonitrile and vinyl acetate, and its glass transition temperature ranges from 60 to 150° C.; The soft monomer includes one or more of isooctyl acrylate, isooctyl methacrylate, 2-propylheptyl acrylate, octyl acrylate, and octyl methacrylate, and the glass transition temperature thereof is less than -50°C.

4. The OCA optical pressure-sensitive adhesive with low volume shrinkage according to claim 1, characterized in that: The blocks formed by M1 and M5 each have a number average molecular weight of 0.2 to 15,000 g / mol; the blocks formed by M2, M3, and M4 have a total number average molecular weight of 96,000 to 296,000 g / mol; and the number average molecular weight of the copolymer is 100,000 to 300,000 g / mol.

5. The OCA optical pressure-sensitive adhesive with low volume shrinkage according to claim 1, characterized in that: The tackifying resin includes one or more of T-90, T-100, T-110, T-120, T-801, T-801L, 900L, 901L, TP2019 and 803L.

6. The method for preparing an OCA optical pressure-sensitive adhesive with low volume shrinkage according to any one of claims 1 to 5, characterized in that: Including steps: Step 1: Dissolve the RAFT agent in water, add the M1 monomer and mix, then add the first initiator and react for 1-3 hours to obtain a latex formed by the M1 homopolymer; Step 2: Adding sodium hydroxide aqueous solution to the latex of step 1, then adding M2 monomer, water and a second initiator, and reacting for 2-5 hours in an oxygen-free environment to obtain an M1-b-M2 copolymer emulsion; then adding a mixed monomer of M3 monomer and M4, and reacting for 1-5 hours in an oxygen-free environment to obtain an M1-b-(M2-ran-M3-ran-M4) copolymer emulsion; Step 3, adding M5 monomer to the emulsion of step 2, adding a second initiator, and reacting for 2-7 hours in an oxygen-free environment to obtain an M1-b-(M2-ran-M3-ran-M4)-b-M5 copolymer emulsion; Step 4, mixing the copolymer emulsion with a demulsifier, washing and drying the precipitated product to obtain the copolymer; Step 5: dissolving the copolymer and the tackifying resin in a dispersion medium, coating the mixture into a film in an inert gas environment, and drying the film to obtain the OCA optical pressure-sensitive adhesive.

7. The method for preparing the OCA optical pressure-sensitive adhesive with low volume shrinkage according to claim 6, characterized in that: Step 2 is replaced by: adding aqueous sodium hydroxide solution to the latex of step 1, then adding a mixed monomer of M2 and 1 / 10-1 of M4, water and a second initiator, and reacting for 2-5 hours in an anaerobic environment to obtain an M1-b-(M2-ran-M4) copolymer emulsion; then adding M3 and the remaining M4 mixed monomer, and reacting for 2-5 hours in an anaerobic environment to obtain an M1-b-(M2-ran-M4)-b-(M3-ran-M4) copolymer emulsion, and correspondingly obtaining an M1-b-(M2-ran-M4)-b-(M3-ran-M4)-b-M5 copolymer emulsion in step 5.

8. The method for preparing the OCA optical pressure-sensitive adhesive with low volume shrinkage according to claim 1, characterized in that: The reaction temperature in step 1 is 40-90° C.; the reaction temperature in step 2 is 30-60° C.; the demulsification temperature in step 3 is 30-60° C., and the demulsification time is more than 0.1 h.

9. The method for preparing the OCA optical pressure-sensitive adhesive with low volume shrinkage according to claim 1, characterized in that: The chemical structural formula of the RAFT agent is: R-(Mn1-b-Nn2)-X; wherein R is an isopropyl group, an acetic acid group, a 2-cyanoacetic acid group or a 2-aminoacetic acid group; in Mn1, M is a methacrylic acid monomer or an acrylic acid monomer unit, n1 is the average polymerization degree of M, and n1 ranges from 10 to 30; in Nn2, N is a styrene monomer, a n-butyl acrylate monomer, a methyl acrylate, an isooctyl acrylate or a methyl methacrylate monomer unit, n2 is the average polymerization degree of N, and n2 ranges from 1 to 8; the X group is an alkyl dithioester group or an alkyl trithioester group, and the added mass of the RAFT agent is 0.2% to 1.0% of the total mass of all monomers; The demulsifier includes any one or more of HCl solution, H2SO4 solution, HNO3 solution, HBr acetic acid, lactic acid, formic acid, and acetic acid; the added mass is 1 / 15-1 / 25 of the mass of the copolymer emulsion; The dispersion medium includes any one or more of diethyl ether, methyl tert-butyl ether, tetrahydrofuran, methyl ethyl ketone, ethyl acetate and methyl propionate.

10. The method for preparing the OCA optical pressure-sensitive adhesive with low volume shrinkage according to claim 1, characterized in that: The first initiator includes any one or more of ammonium persulfate, potassium persulfate, hydrogen peroxide and hydrogen peroxide derivatives; the mass is 1 / 50-1 of the molar mass of the RAFT agent; The second initiator includes any one or more of azobisisobutylimidazoline hydrochloride, azobisisobutylamidine hydrochloride, 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone, sodium persulfate / potassium persulfate redox initiator and sodium persulfate / ammonium persulfate redox initiator, and the mass is 1 / 50-1 of the molar mass of the RAFT agent.

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