CN115521754B

CN115521754B - Acrylic acid adhesive with low water absorption rate and preparation method thereof

Info

Publication number: CN115521754B
Application number: CN202211242278.0A
Authority: CN
Inventors: 刘斌; 黄成生
Original assignee: Colltech Dongguan Bonding Technology Co ltd
Current assignee: Guangdong Deju Technology Co.,Ltd.
Priority date: 2022-10-11
Filing date: 2022-10-11
Publication date: 2023-05-19
Anticipated expiration: 2042-10-11
Also published as: CN115521754A

Abstract

The invention provides an acrylic acid adhesive with low water absorption rate and a preparation method thereof, and the acrylic acid adhesive comprises the following raw materials: the polyurethane acrylate oligomer is prepared by firstly preparing low-molecular polyamide by polycondensation of unsaturated fatty acid dimer and diamine, then reacting the low-molecular polyamide with diisocyanate to generate isocyanate-terminated oligomer, and finally reacting the isocyanate-terminated oligomer with hydroxy acrylic ester compounds. The adhesive prepared from unsaturated fatty acid dimer, diamine, diisocyanate and hydroxy acrylic ester compounds and taking the polyurethane acrylic ester oligomer and polybutadiene polyurethane acrylic ester oligomer as main resins has good insulating property and low water absorption rate, and still has good insulating property under high-temperature and high-humidity environments.

Description

Acrylic acid adhesive with low water absorption rate and preparation method thereof

Technical Field

The invention belongs to the technical field of UV (ultraviolet) curing adhesives, and particularly relates to an acrylic adhesive with low water absorption rate and a preparation method thereof.

Background

Electronic components such as piezoresistors, thermistors, ceramic capacitors, chips and the like are important protection or functional elements in the industries such as electronics and electricians. The encapsulating adhesive or the pouring sealant is a layer of insulating protective adhesive covering the outside of the components and parts, and has the functions of dampproofing, waterproofing, shockproof, mechanical damage prevention, heat insulation, insulating protection and the like. The encapsulating glue is classified into epoxy glue, polyurethane glue, acrylate glue (UV curing) and silica gel according to the kind of the main resin. The main resin of the acrylic adhesive (UV curing) is epoxy (methyl) acrylate, polyurethane (methyl) acrylate or polyester (methyl) acrylate, the dosage of the acrylic adhesive can be 50-90% of that of the adhesive, and the acrylic adhesive is matched with proper reactive diluent, photoinitiator and filler, so that the adhesive has the advantages of quick curing and simple process.

As patent CN201910264777.1 discloses an ultraviolet curing adhesive, a preparation method and application thereof, 40-55 parts of light curing resin, 40-50 parts of acrylic ester active monomer, 3-10 parts of photoinitiator and 0.5-8 parts of carbon black; the light-cured resin is at least one of polyurethane acrylic ester, epoxy acrylic ester and polyester acrylic ester. Patent CN202111562394.6 discloses a UV light-curable composition with low moisture vapor transmission rate and a preparation method thereof, which is prepared from the following raw materials: 25-30 parts by weight of acrylate monomer; 70-75 parts by weight of polybutadiene modified polyurethane acrylate oligomer; 3-5 parts by weight of a photoinitiator; 3-5 parts by weight of a chain transfer agent; 6-10 parts by weight of hydrophobic fumed silica. The technology is UV-cured acrylic glue, and the UV-cured acrylic glue can play a good role in moisture resistance and insulation when being applied to the field of electronic packaging. However, with the rapid development and application of the electronic industry in recent years, resin pouring sealants used for electronic packaging are required to be used under severe environmental conditions and to work reliably for a long time, and in particular, resin pouring sealants are required to sufficiently meet the requirement of having higher insulation resistance under high-temperature and high-humidity environments, and the above-mentioned technologies are also improved in terms of insulation performance gradually for main resins, but the insulation performance under the high-temperature and high-humidity environments tested is still poor.

Therefore, developing a UV curing adhesive with lower water absorption and excellent insulating property under high-temperature high-humidity severe environment has important significance in expanding the application of the UV curing adhesive in the field of electronic packaging.

Disclosure of Invention

In order to solve the technical problems, the invention provides the acrylic acid adhesive with low water absorption and the preparation method thereof.

In order to achieve the above purpose, the following specific scheme is adopted:

an acrylic adhesive with low water absorption comprises the following raw materials: the polyurethane acrylate oligomer is prepared by firstly preparing low-molecular polyamide by polycondensation of unsaturated fatty acid dimer and diamine, then reacting the low-molecular polyamide with diisocyanate to generate isocyanate-terminated oligomer, and finally reacting the isocyanate-terminated oligomer with hydroxy acrylic ester compounds.

Further, the acrylic adhesive comprises the following raw materials in parts by weight: 30-40 parts of polybutadiene polyurethane acrylate oligomer, 10-20 parts of polyurethane acrylate oligomer, 30-50 parts of reactive diluent, 3-10 parts of photoinitiator and 2-5 parts of thixotropic agent, wherein the number average molecular weight of the low molecular polyamide oligomer is 500-2000, the mol ratio of unsaturated fatty acid dimer to diamine is 1:2.5-3.3, and the mol ratio of diamine, diisocyanate and hydroxyacrylate compound is 1:0.85-0.9:0.9-1.

The unsaturated fatty acid dimer is selected from one or a combination of two or more of linoleic acid dimer, tall oil acid dimer and eleostearic acid dimer. Preferably, the unsaturated fatty acid dimer is a linoleic acid dimer.

The diamine is selected from one or a combination of two or more of ethylenediamine, 1, 2-propylenediamine, tetramethylenediamine and 1, 5-diaminopentane. Preferably, the diamine is ethylenediamine.

The diisocyanate is aromatic diisocyanate and is selected from one or a combination of two or more of 3,3' -dimethyl diphenyl methane-4, 4' -diisocyanate, 4' -diphenyl methane diisocyanate, dimethylbiphenyl diisocyanate, 2, 6-toluene diisocyanate, 2, 4-toluene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate and 1, 3-diisocyanatotoluene.

Preferably, the diisocyanate is selected from one or a combination of two or more of 3,3' -dimethyl diphenyl methane-4, 4' -diisocyanate, 4' -diphenyl methane diisocyanate and dimethyl diphenyl diisocyanate.

The hydroxy acrylic ester compound is selected from one or more of acrylic acid-2-hydroxy ethyl ester, acrylic acid-2-hydroxy propyl ester, methacrylic acid-2-hydroxy ethyl ester, methacrylic acid-2-hydroxy propyl ester, methacrylic acid-2-hydroxy isopropyl ester, 6-hydroxy hexyl acrylic ester, 5-hydroxy amyl acrylic ester and 4-hydroxy butyl acrylic ester.

Preferably, the hydroxy acrylic ester compound is selected from one or a combination of two or more of 2-hydroxyethyl acrylate and 2-hydroxypropyl acrylate.

The preparation method of the polyurethane acrylate oligomer comprises the following steps:

1) Adding unsaturated fatty acid dimer and diamine into a reaction kettle under an inert atmosphere, stirring, heating, reacting at constant temperature, controlling pressure during the reaction, naturally cooling to room temperature after the reaction is finished, releasing pressure, and distilling under reduced pressure to obtain low-molecular polyamide;

2) Adding diisocyanate into an organic solvent under an inert atmosphere, uniformly mixing, cooling and keeping the temperature, dropwise adding the low-molecular polyamide diluent obtained in the step 1), carrying out constant-temperature reaction under the stirring condition, naturally recovering to room temperature after the reaction is finished, and carrying out column chromatography to obtain an isocyanate-terminated oligomer;

3) Under inert atmosphere, the hydroxy acrylic ester compound, the catalyst and the polymerization inhibitor are dissolved in an organic solvent, the temperature is raised, the diluent of the isocyanate end-capped oligomer obtained in the step 2) is dripped, the reaction is carried out at constant temperature, the reaction is stopped when the-NCO value is monitored to be zero, and the polyurethane acrylic ester oligomer is obtained through column chromatography.

The stirring speed in the heating stage is 500-800r/min, the heating is up to 180-200 ℃, the reaction time is 3-8h, the stirring speed in the constant temperature reaction stage is 300-500r/min, and the pressure is controlled to be 1.45-1.75MPa;

the organic solvent in the step 2) is selected from one or a combination of two or more of DMF, DMSO, acetonitrile, acetone, diethyl ether, chloroform, dichloromethane, benzene and xylene; the temperature is reduced to (-5 ℃) to minus 5 ℃, the solvent of the low molecular polyamide diluent is the same as the organic solvent, the concentration of the low molecular polyamide diluent is 8-15wt%, the low molecular polyamide solution is dropped in 0.5-2 hours, the stirring speed is 300-500r/min, the constant temperature reaction time is 1-3 hours, and the eluent for column chromatography is a mixture of benzene/ethyl acetate according to the volume ratio of 3:4-7;

step 3) the organic solvent is the same as the organic solvent of step 2); the catalyst is not particularly limited, and is commonly used in the art, and may be one or a combination of two or more selected from triethylamine, dibutyltin laurate and stannous octoate; the dosage of the catalyst is 0.05 to 0.08 weight percent of the sum of the weight of the isocyanate end-capped oligomer and the weight of the hydroxy acrylic ester compound; the polymerization inhibitor is selected from one or a combination of two or more of hydroquinone, p-methoxyphenol and 2, 6-di-tert-butyl p-cresol, the dosage of the polymerization inhibitor is 0.1-0.5wt% of hydroxy acrylic ester compound, the temperature is raised to 60-80 ℃, the concentration of the isocyanate end-capped oligomer diluent is 10-20wt%, the organic solvent is the same as the organic solvent in the step 2), the constant temperature reaction time is 1-3h after the dripping of the isocyanate end-capped oligomer diluent is 1-2h, and the eluent for column chromatography is a mixture of benzene/ethyl acetate according to the volume ratio of 1:1-2; the method for monitoring the-NCO value is not particularly limited and is commonly used in the art, including the di-n-butylamine method.

The polybutadiene polyurethane acrylate oligomer is a polybutadiene acrylate oligomer containing (methyl) acrylate groups, wherein the (methyl) acrylate groups are connected to two ends of polybutadiene through chain segments containing carbamate, the viscosity of the polybutadiene polyurethane acrylate oligomer is 500-2000poise (45 ℃), and the polybutadiene polyurethane acrylate oligomer is specifically selected from one or a combination of two or more of Caddy TE-2000 and DYMAX BR-641S, DYMAX-643. The molecular skeleton of polybutadiene is similar to that of common solid rubber, so that the polybutadiene polyurethane acrylate oligomer containing the polybutadiene chain segment in the molecular structure also has good hydrolysis resistance and electrical insulation performance.

The reactive diluent is selected from one or a combination of two or more of isobornyl methacrylate, dimethylacrylamide, isobornyl acrylate, tricyclodecane dimethanol diacrylate, butyl acrylate, tetrahydrofuran methyl acrylate and phenoxyethyl acrylate.

The photoinitiator comprises one or two of hydrogen abstraction type free radical photoinitiator and cleavage type free radical photoinitiator, is selected from one or two or more of xylene ketone initiator, benzoin initiator, alpha-hydroxy ketone initiator, alpha-amino ketone initiator and acyl phosphine oxide initiator, and the initiator can be selected from one or two or more of Pasteur DarocurBP, darocur1173, irgacure184, irgacure651, irgacure819, irgacure907 and Irgacure TPO.

The thixotropic agent is selected from one or a combination of two or more of fumed silica, organic bentonite, hydrogenated castor oil and polyamide wax.

The thixotropic agent is preferably fumed silica, the average particle size of primary particles of the fumed silica is 5-50nm, and the specific surface area is 100-300m ² /g。

The fumed silica is selected from one or a combination of more than two of winning wound R202, R974, wake H18, H15, kabott TS620, TS 720.

The acrylic adhesive raw material with low water absorption rate can also comprise 1-10 parts of auxiliary agents, the auxiliary agents are not particularly limited, and the auxiliary agents are commonly used in the field and comprise one or a combination of two or more of tackifier, defoamer and dispersing agent.

The tackifier is one or a combination of two or more of vinyl trimethoxy silane, vinyl triethoxy silane, gamma-methacryloxypropyl trimethoxy silane and gamma-glycidol ether oxypropyl trimethoxy silane.

The defoamer is selected from one or a combination of two or more of BYK 088 and BYK 080A, TEGO 3062.

The invention also provides a preparation method of the acrylic adhesive with low water absorption, which comprises the following steps:

and uniformly mixing the polybutadiene polyurethane acrylate oligomer, the reactive diluent and the photoinitiator at room temperature, adding the thixotropic agent, uniformly mixing again, optionally adding the auxiliary agent, uniformly mixing, and performing vacuum deaeration to obtain the acrylic adhesive with low water absorption.

The application of the acrylic adhesive with low water absorption rate is that the adhesive is dispensed on an electronic component by a dispensing machine and is subjected to irradiation curing under light.

The height of the dispensing is 1-5mm, the light wave band is 300-500nm, the irradiation time is 10-60s, and the irradiation energy is 2000-5000mJ/cm ² 。

Compared with the prior art, the invention has the beneficial effects that:

the adhesive prepared from unsaturated fatty acid dimer, diamine, diisocyanate and hydroxy acrylic ester compounds and taking the polyurethane acrylic ester oligomer and polybutadiene polyurethane acrylic ester oligomer as main resins has good insulating property and low water absorption rate, and still has good insulating property under high-temperature and high-humidity environments.

The preparation method is simple, green and environment-friendly, and is suitable for industrial production.

Drawings

FIG. 1 is a circuit board diagram used before the surface insulation resistance test package is performed in application example 1;

FIG. 2 is a circuit board diagram after application example 1 is subjected to a surface insulation resistance test;

fig. 3 is a graph showing the surface insulation resistance test of application example 1.

Detailed Description

The invention is further illustrated below in connection with specific examples, but is not limited to the disclosure. Unless otherwise specified, "parts" are parts by weight in the examples of the present invention. All reagents used are those commercially available in the art.

Linoleic acid dimer average molecular weight was 560 and tall oil dimer average molecular weight was 795, all purchased from tin-free city far chemicals limited;

	chain isomer content wt%	Monocyclic isomer content wt%	Bicyclic isomer content wt%
				Linoleic acid dimer	5	55	40
Tall oil acid dimer	15	70	15

Preparation of polyurethane acrylate oligomers

Preparation example 1

1) Under the nitrogen atmosphere, adding 1mol of linoleic acid dimer and 2.5mol of ethylenediamine into a reaction kettle, stirring and heating to 200 ℃ at 500r/min, keeping the temperature for reaction for 6 hours, controlling the pressure in the kettle to fluctuate at 1.65-1.75MPa during the reaction, naturally cooling to room temperature after the reaction is finished, releasing pressure, and distilling under reduced pressure to obtain low-molecular polyamide;

2) Adding 2.125mol of 3,3 '-dimethyl diphenylmethane-4, 4' -diisocyanate into a mixed solvent consisting of 300mL of LDMF and 250mL of diethyl ether under the nitrogen atmosphere, uniformly mixing, cooling to 0 ℃ and keeping the temperature, diluting the low molecular polyamide solution obtained in the step 1) by using the mixed solvent consisting of DMF and diethyl ether according to the volume ratio of 6:5 until the concentration is 10wt%, dripping the low molecular polyamide solution into a reaction kettle, carrying out constant temperature reaction for 2 hours at the rotating speed of 300r/min after 1.5 hours, naturally recovering to room temperature after the reaction is finished, and carrying out column chromatography separation by using an eluent prepared by mixing benzene/ethyl acetate according to the volume ratio of 3:7 to obtain isocyanate end-capped oligomer;

3) 2.25mol of acrylic acid-2-hydroxyethyl ester, 0.43g of triethylamine and 0.61g of 2, 6-di-tert-butyl-p-cresol are dissolved in a mixed solvent consisting of 300mL of LDMF and 250mL of diethyl ether under the nitrogen atmosphere, the temperature is raised to 70 ℃, the isocyanate-terminated oligomer obtained in the step 2) is diluted to 15wt% by using the mixed solvent consisting of DMF and diethyl ether according to the volume ratio of 6:5, the diluted solution is dripped into a reaction system for 50min, then the reaction is carried out at constant temperature for 2h, the di-n-butylamine method is used for measuring the-NCO value to be zero, the reaction is stopped, and the polyurethane acrylic ester oligomer is obtained by carrying out column chromatographic separation by using an eluent which is formed by mixing benzene/ethyl acetate according to the volume ratio of 1:1.

Preparation example 2

The remainder was the same as in preparation example 1, except that tall oil acid dimer was used in equimolar place of linoleic acid dimer.

Preparation example 3

The remainder was the same as in preparation example 1, except that ethylenediamine was replaced with 1, 5-diaminopentane in equimolar amounts.

Preparation example 4

The remainder was the same as in preparation example 1 except that ethylenediamine was used in an amount of 3.3mol.

Comparative preparation example 1

The remainder was the same as in preparation example 1, except that adipic acid was equimolar substituted for linoleic acid dimer.

Preparation of acrylic adhesive with low water absorption

Example 1

30 parts of Caddy TE-2000, 20 parts of preparation example 1 polyurethane acrylate oligomer, 30 parts of isobornyl acrylate, 10 parts of isobornyl methacrylate, 5 parts of dimethylacrylamide, 2 parts of Irgacure184, 1 part of Irgacure TPO and 3 parts of DarocurrBP are uniformly mixed at room temperature, 5 parts of cabot TS720 is added, the mixture is uniformly mixed again, 2 parts of gamma-methacryloxypropyl trimethoxy silane is added, and the mixture is uniformly mixed, and vacuum defoamation is carried out under the vacuum degree of 0.08MPa to obtain the acrylic adhesive with low water absorption.

Examples 2 to 4

The remainder was the same as in example 1, except that the urethane acrylate oligomer prepared in preparation example 1 was replaced with the urethane acrylate oligomers prepared in preparation examples 2 to 4, respectively.

Example 5

35 parts of DYMAX BR-641S, 15 parts of the polyurethane acrylate oligomer prepared in preparation example 1, 25 parts of isobornyl acrylate, 15 parts of isobornyl methacrylate, 5 parts of dimethylacrylamide, 2 parts of Irgacure184, 1 part of Irgacure TPO and 3 parts of DarocurrBP are uniformly mixed at room temperature, 5 parts of cabot TS720 is added, the mixture is uniformly mixed again, 2 parts of gamma-methacryloxypropyl trimethoxysilane is added, and the mixture is uniformly mixed, and vacuum defoamation is carried out under the vacuum degree of 0.08MPa to obtain the acrylic adhesive with low water absorption rate.

Example 6

The remainder was the same as in example 1 except that 40 parts of TEO-2000 was used and 10 parts of urethane acrylate oligomer was used in preparation example 1.

Comparative example 1

The remainder was the same as in example 1, except that the urethane acrylate oligomer prepared in comparative preparation example 1 was used instead of the urethane acrylate oligomer prepared in preparation example 1.

Application example 1

The adhesive prepared in the above example 1 was applied to an electronic device by using an Shinewa SEC-DP300 dispenser, the height of the adhesive line was 2mm and the line width was 3mm, and then the light intensity was 150mW/cm at 365nm ² And (3) irradiating for 20s under an ultraviolet lamp with a lamp distance of 20cm to finish curing.

Application examples 2 to 6, comparative application example 1

The rest was the same as in application example 1, except that the adhesives were prepared in accordance with examples 2 to 6 and comparative example 1, respectively.

The low water absorption acrylic adhesives prepared in examples 1 to 6 and comparative example 1 were subjected to the following performance tests, and the results are shown in table 1:

viscosity: a rotational viscometer was used, with a 14# rotor, at 25 ℃.

Thixotropic coefficient: the viscosity of the same rotor at 2rpm and 20rpm respectively was measured by a rotary viscometer, and the ratio of the two was the thixotropic coefficient.

The following performance tests were carried out on the adhesives prepared in application examples 1 to 6 and comparative application example 1, and the results are shown in Table 1: (example test data are numbered as corresponding application example numbers for simplicity)

Water absorption rate: the adhesive was cured to a test specimen of 76.2mm x 25.4mm x 3.2mm by reference to the standard ASTM D570-05 test method for water absorption of plastics, the water absorption after 24h immersion in water at 23 ℃ was tested, and the water absorption was calculated according to the formula in the standard.

Surface resistance: the test is carried out by referring to the standard GB/T1410-2006 test method for volume resistivity and surface resistivity of solid insulating materials.

Surface Insulation Resistance (SIR): the IPC-B-24 insulating test plate is encapsulated by an adhesive according to the standard IPC-TM-650, then is kept stand for 168 hours under the hot-air condition of 85 ℃ and 85% RH, and then a 50V bias voltage is applied to the sample, and the loading time is 60s and 10 min.

TABLE 1

As can be seen from Table 1, the polyurethane acrylate oligomer prepared from unsaturated fatty acid dimer, diamine, diisocyanate and hydroxy acrylate compound, and the adhesive prepared by compounding the polyurethane acrylate oligomer with polybutadiene polyurethane acrylate oligomer as main resin have good insulating property and low water absorption rate, and still have good insulating property under high-temperature and high-humidity environment.

The foregoing detailed description is directed to one of the possible embodiments of the present invention, which is not intended to limit the scope of the invention, but is to be accorded the full scope of all such equivalents and modifications so as not to depart from the scope of the invention.

Claims

1. The acrylic acid adhesive with low water absorption is characterized by comprising the following raw materials: the polyurethane acrylate oligomer is prepared by firstly preparing low-molecular polyamide by polycondensation of unsaturated fatty acid dimer and diamine, then reacting the low-molecular polyamide with diisocyanate to generate isocyanate-terminated oligomer, and finally reacting the isocyanate-terminated oligomer with hydroxy acrylic ester compounds.

2. The low-water-absorption acrylic adhesive according to claim 1, wherein the acrylic adhesive comprises the following raw materials in parts by weight: 30-40 parts of polybutadiene polyurethane acrylate oligomer, 10-20 parts of polyurethane acrylate oligomer, 30-50 parts of reactive diluent, 3-10 parts of photoinitiator and 2-5 parts of thixotropic agent, wherein the molar ratio of unsaturated fatty acid dimer to diamine is 1:2.5-3.3, wherein the molar ratio of diamine, diisocyanate and hydroxy acrylic acid ester compound is 1:0.85-0.9:0.9-1.

3. The low water absorption acrylic acid adhesive according to claim 1, wherein the unsaturated fatty acid dimer is one or a combination of two or more selected from the group consisting of linoleic acid dimer, tall oil acid dimer, and eleostearic acid dimer.

4. The low water absorption acrylic adhesive according to claim 3, wherein the unsaturated fatty acid dimer is linoleic acid dimer.

5. The low water absorption acrylic adhesive according to claim 1, wherein the diamine is one or a combination of two or more selected from ethylenediamine, 1, 2-propylenediamine, tetramethylenediamine and 1, 5-diaminopentane.

6. The low water absorption acrylic adhesive of claim 5, wherein the diamine is ethylenediamine.

7. The low water absorption acrylic adhesive according to claim 1, wherein the diisocyanate is an aromatic diisocyanate selected from one or a combination of two or more of 3,3' -dimethylbiphenyl methane-4, 4' -diisocyanate, 4' -diphenylmethane diisocyanate, dimethylbiphenyl diisocyanate, 2, 6-toluene diisocyanate, 2, 4-toluene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, 1, 3-diisocyanatotoluene; the hydroxy acrylic ester compound is selected from one or more of acrylic acid-2-hydroxy ethyl ester, acrylic acid-2-hydroxy propyl ester, methacrylic acid-2-hydroxy ethyl ester, methacrylic acid-2-hydroxy propyl ester, methacrylic acid-2-hydroxy isopropyl ester, 6-hydroxy hexyl acrylic ester, 5-hydroxy amyl acrylic ester and 4-hydroxy butyl acrylic ester.

8. The low water absorption acrylic adhesive according to claim 7, wherein the diisocyanate is selected from one or a combination of two or more of 3,3' -dimethyl diphenylmethane-4, 4' -diisocyanate, 4' -diphenylmethane diisocyanate, dimethylbiphenyl diisocyanate; the hydroxy acrylic ester compound is selected from one or a combination of two or more of acrylic acid-2-hydroxy ethyl ester and acrylic acid-2-hydroxy propyl ester.

9. The low water absorption acrylic adhesive of claim 1, wherein the preparation method of the urethane acrylate oligomer comprises the following steps:

10. The low water absorption acrylic adhesive according to claim 9, wherein in the step 1), the stirring speed is 500-800r/min in the heating stage, the temperature is raised to 180-200 ℃, the reaction time is 3-8h, the stirring speed is 300-500r/min in the constant temperature reaction stage, and the pressure is controlled to be 1.45-1.75MPa; the temperature is reduced to-5 ℃ to 5 ℃ in the step 2), and the eluent for column chromatography is a mixture of benzene/ethyl acetate according to the volume ratio of 3:4-7; the eluent for column chromatography in the step 3) is a mixture of benzene/ethyl acetate in a volume ratio of 1:1-2.

11. The low water absorption acrylic adhesive according to claim 1, wherein the polybutadiene urethane acrylate oligomer is a polybutadiene acrylate oligomer containing a (meth) acrylate group, the (meth) acrylate group is linked to both ends of the polybutadiene through a segment containing a urethane, and the polybutadiene urethane acrylate oligomer has a viscosity of 500 to 2000poise at 45 ℃.

12. The low water absorption acrylic acid adhesive of claim 1, wherein the polybutadiene urethane acrylate oligomer is selected from one or a combination of two or more of Cadda TE-2000 and DYMAX BR-641S, DYMAX-643.

13. The method for preparing the low water absorption acrylic adhesive according to any one of claims 1 to 12, comprising the steps of:

and uniformly mixing the polybutadiene polyurethane acrylate oligomer, the reactive diluent and the photoinitiator at room temperature, adding the thixotropic agent, uniformly mixing again, and performing vacuum defoamation to obtain the acrylic adhesive with low water absorption.