High-viscosity acrylate adhesive and preparation method thereof

Abstract

The invention relates to the technical field of adhesives, in particular to a high-viscosity acrylate adhesive and a preparation method thereof. According to the preparation method of the acrylate adhesive provided by the invention, a solution is low in viscosity and good in heat transfer at the initial stage of reaction, firstly, decomposition of an initiator is promoted by adopting high temperature to induce the reaction to be rapidly carried out, and a large number of active sites are generated; along with the reaction, the system viscosity is increased, heat transfer is difficult, the reaction temperature is reduced, the reaction rate is slowed down, excessive reaction heat is avoided, meanwhile, the decomposition rate of an initiator can be slowed down by reducing the temperature, and formation of long-chain molecules is facilitated. Through high / low temperature segmented temperature control, the reaction process is easy to control, the high molecular weight acrylate polymer is synthesized under the condition of high monomer concentration, and the prepared acrylate adhesive has good stripping force, initial adhesion force, adhesion force, permanent adhesion force and durability.

Description

Technical Field

[0001] The present invention relates to the technical field of adhesives, and in particular to a high-viscosity acrylic adhesive and a preparation method thereof. Background Art

[0002] Solvent-based acrylic pressure-sensitive adhesives are polymerized from acrylic monomers and other monomers with vinyl functional groups. The cooperation between different monomers results in products with balanced mechanical and optical properties, excellent bonding performance, UV aging resistance and designability. They are widely used in electronics, automobiles, medicine and other fields. The relative molecular mass of the polymer is one of the main factors affecting the performance of acrylic pressure-sensitive adhesives. The larger the relative molecular mass, the better its overall performance. Therefore, in order to obtain better pressure-sensitive adhesive properties, the molecular mass of the polymer must be increased, and the increase in molecular weight is reflected in the increase in its viscosity. The synthesis of solvent-based acrylic polymers belongs to free radical polymerization reactions. The initiator content has an important influence on the molecular weight of the product. Reducing the initiator content slows down the reaction rate and helps to increase the molecular weight of the product; however, under this condition, a higher initiation temperature is required, which is prone to produce local gelation and also leads to incomplete reaction. Another method to increase the molecular weight of acrylic polymers is the step-by-step feeding method, which involves the step-by-step feeding of monomers, solvents, and initiators. This method removes the heat of reaction by adding cold materials during the reaction. This method has high requirements for feeding control, and the continuous addition of materials makes the system unstable. It works better when the monomer concentration is low, but the product molecular weight is low. Solvent-based polymerization systems have solvent chain transfer, which reduces the molecular weight of the polymer, and reduces the viscosity and cohesion of the product. Therefore, increasing the monomer concentration is an important way to prepare high molecular weight products. However, as the polymerization reaction proceeds, the viscosity of the solution will increase. The increase in viscosity will make it difficult for the heat of the polymerization reaction to dissipate, further accelerating the reaction rate and triggering implosion.

[0003] Acrylate polymerization is a free radical reaction, which is related to the polymerization solvent, polymerization process, etc. Low monomer concentration and high initiator content are conducive to the formation of low molecular weight products, while increasing the monomer concentration can increase the molecular weight, but the polymerization speed is fast and the heat release is large. During the reaction, the pole-holding phenomenon is serious, and it is difficult to remove heat, which is prone to explosion polymerization. Reducing the initiator content makes it difficult for the reaction to occur and easily leads to incomplete reaction. Summary of the invention

[0004] The object of the present invention is to provide a high-viscosity acrylic adhesive and a preparation method thereof in view of the above-mentioned deficiencies in the prior art.

[0005] The first object of the present invention is to provide a preparation method of a high-viscosity acrylate adhesive. The acrylate adhesive is prepared by dissolving a soft monomer, a hard monomer, a functional monomer, and an initiator in an organic solvent, reacting at a first temperature T1 for 0.5 - 3 h, then cooling to a second temperature T2 and reacting for 4 - 10 h, and then adding a solvent for dilution to obtain a solvent-based acrylate adhesive product;

[0006] When the 10-hour half-life temperature T of the initiator is less than 100 °C, T1 is greater than T and less than 100 °C; T2 is less than T, and the difference between T and T2 is 0.5 - 15 °C.

[0007] When the 10-hour half-life temperature T of the initiator is greater than 100 °C, the range of T1 is 65 - 100 °C, and the difference between T1 and T2 is 20 - 40 °C.

[0008] Further, the reaction is carried out at the first temperature T1 for 1 - 2 h, and then cooled to the second temperature T2 and reacted for 5 - 8 h.

[0009] Further, the initiator is one or more of organic peroxide initiators and azo initiators.

[0010] Further, the initiator is a mixture of one or more of 2,2'-azobisisobutyronitrile, benzoyl peroxide, di-tert-butyl peroxide, and diisopropylbenzene peroxide.

[0011] Further, the mass content of the initiator is 0.01% - 2% of the total monomer mass.

[0012] Further, the mass content of the initiator is 0.03% - 1% or 0.05% - 0.5% of the total monomer mass.

[0013] Further, the solvent is selected from any one or a mixture of two of ethyl acetate and toluene, and the mass content is 10% - 80% of the total monomer mass, more preferably 30% - 60%, and even more preferably 35% - 50%.

[0014] Further, the soft monomer is one or a mixture of two of butyl acrylate and isooctyl acrylate; the mass content is 40% - 99% of the total monomer mass, more preferably 50% - 97%, and even more preferably 65% - 96%; the hard monomer is a mixture of one or more of methyl methacrylate, styrene, and benzyl acrylate; the mass content is 0.5% - 40% of the total monomer mass, more preferably 1% - 30%, and even more preferably 1.5% - 28%.

[0015] Further, the functional monomer is a monomer containing polar groups; the monomer containing polar groups includes one or more of nitrogen-containing heterocyclic monomers, hydroxyl monomers, carboxyl monomers, and amide group monomers.

[0016] Further, the functional monomer is one or more mixtures of 2-hydroxyethyl methacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 6-hydroxyhexyl methacrylate, methacrylic acid, N-vinylpyrrolidone, N-2-hydroxyethyl acrylamide; the mass content is 0.5%-30% of the total monomer mass, further preferably 1%-25%, and even more preferably 1.5%-20%.

[0017] Further, the dilution concentration of the added solvent is 6%-40%, further preferably 10%-35%, and even more preferably 12%-30%.

[0018] The second object of the present invention is to provide a high-viscosity acrylate adhesive prepared by the above preparation method.

[0019] The present invention provides a preparation method of an acrylate adhesive. In the initial stage of the reaction, the solution viscosity is low and the heat transfer is good. First, high temperature is used to promote the decomposition of the initiator to induce the reaction to proceed rapidly, generating a large number of active sites; as the reaction progresses, the system viscosity increases and the heat transfer becomes difficult. The reaction temperature is reduced to slow down the reaction rate, avoid excessive reaction heat, and at the same time reduce the temperature to slow down the decomposition rate of the initiator, which is beneficial to the formation of long-chain molecules. By controlling the temperature in high / low temperature segments, the reaction process is easy to control, high molecular weight acrylate polymers can be synthesized under high monomer concentration conditions, and at the same time, a wide molecular weight distribution of the acrylate adhesive can be achieved, improving its viscosity. The prepared acrylate adhesive has good peel strength, tack, adhesion, holding power and durability.

[0020] The present invention provides a preparation method of an acrylate adhesive, which is applicable to high-concentration raw material monomers, has a short total reaction time, and the prepared acrylate adhesive has a large molecular weight and high viscosity. Description of the Drawings

[0021] Figure 1 It is the infrared spectrogram of the polyacrylate polymers obtained in Examples 1-5;

[0022] Figure 2 It is the infrared spectrogram of the polyacrylate polymers obtained in Examples 6-9;

[0023] Figure 3 It is the ultraviolet-visible light transmittance of the polyacrylate polymers obtained in Examples 8 and 9;

[0024] Figure 4 It is the nuclear magnetic spectrum of the polyacrylate polymer products obtained in Examples 8 and 9. Detailed implementation manners

[0025] The following are specific embodiments of the present invention and, in combination with the accompanying drawings, further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments.

[0026] The embodiments are prepared by the following method:

[0027] (1) Add a solvent, a soft monomer, a hard monomer, a functional monomer, and an initiator into a four-necked reactor equipped with a stirrer, a thermometer, a gas guide tube, and a condenser;

[0028] (2) Heat up to a first temperature under stirring conditions and keep the reaction for a period of time;

[0029] Before the start of this process, the reaction has not occurred. The solution contains some impurities and dissolved oxygen, which play a role in retarding the initiation reaction of the initiator; and under these conditions, the fluidity and heat transfer of the solution are good, and it is not easy to occur a violent polymerization reaction caused by difficult heat removal.

[0030] (3) After the high-temperature reaction is completed, cool down to a second temperature for further reaction. After reaching the predetermined reaction time, stop adding and add a solvent to dilute to the required concentration.

[0031] The 10-hour half-life temperature of the initiator used in the embodiments is shown in Table 1:

[0032] Table 1

[0033]

[0034] Example 1

[0035] Ethyl acetate is used as the solvent, and the total mass ratio of the solvent to the monomers is 4.5:5.5 and both are 50 g. The monomers are composed of butyl acrylate, 2-hydroxyethyl acrylate, benzyl acrylate, and methyl methacrylate mixed in a mass ratio of 95:2:2:1. The initiator 2,2'-azobisisobutyronitrile is 0.1% of the total mass of the monomers. Under stirring conditions, purge with nitrogen for 10 min to remove oxygen. React at a reaction temperature of 75 °C for 0.5 h, cool down to 65 °C and react for 7.5 h, stop heating and add ethyl acetate to dilute to 20%, and the viscosity is 1240.5 mPa·s.

[0036] Example 2

[0037] Ethyl acetate and toluene mixture is used as the solvent, with the mass ratio of ethyl acetate / toluene being 1:1. The total mass ratio of the mixed solvent to the monomer is 1:1 and both are 50 g. The monomer is composed of butyl acrylate, 2-hydroxyethyl acrylate, benzyl acrylate, and methyl methacrylate mixed in a mass ratio of 95:2:2:1. The initiator di-tert-butyl peroxide is 0.1% of the total mass of the monomer. Nitrogen is purged for 10 min under stirring conditions to remove oxygen. The reaction is carried out at a reaction temperature of 95 °C for 1 h, then cooled to 72 °C and reacted for 7 h. Heating is stopped and diluted with the mixed solvent to 20%, with a viscosity of 1741.5 mPa·s.

[0038] Example 3

[0039] Ethyl acetate is used as the solvent, with the total mass ratio to the monomer being 1:1 and both being 50 g. The monomer is composed of butyl acrylate, 2-hydroxyethyl acrylate, benzyl acrylate, and methyl methacrylate mixed in a mass ratio of 95:2:2:1. The initiator benzoyl peroxide is 0.1% of the total mass of the monomer. Nitrogen is purged for 10 min under stirring conditions to remove oxygen. The reaction is carried out at a reaction temperature of 75 °C for 1 h, then cooled to 70 °C and reacted for 7 h. Heating is stopped and diluted with the solvent to 20%, with a viscosity of 17907.5 mPa·s.

[0040] Example 4

[0041] Toluene is used as the solvent, with the ratio to the monomer being 1:1 and both being 50 g. The monomer is composed of butyl acrylate, 2-hydroxyethyl acrylate, benzyl acrylate, and methyl methacrylate mixed in a mass ratio of 95:2:2:1. The initiator benzoyl peroxide is 0.1% of the total mass of the monomer. Nitrogen is purged for 10 min under stirring conditions to remove oxygen. The reaction is carried out at a reaction temperature of 80 °C for 1 h, then cooled to 66 °C and reacted for 7 h. Heating is stopped and diluted with toluene to 20%, with a viscosity of 22249.5 mPa·s.

[0042] Example 5

[0043] Ethyl acetate is used as the solvent, with the ratio to the monomer being 1:1 and both being 50 g. The monomer is composed of butyl acrylate, 2-hydroxyethyl acrylate, benzyl acrylate, and methyl methacrylate mixed in a mass ratio of 95:2:2:1. The initiator benzoyl peroxide is 0.1% of the total mass of the monomer. The monomer and the solvent are poured into a four-necked flask, and the initiator is added. Nitrogen is purged for 10 min under stirring conditions to remove oxygen. The reaction is carried out at a reaction temperature of 80 °C for 1 h, then cooled to 66 °C and reacted for 7 h. Heating is stopped and diluted with ethyl acetate to 20%, with a viscosity of 25939.5 mPa·s.

[0044] Example 6

[0045] Ethyl acetate was used as the solvent, and the total mass ratio of the solvent to the monomers was 4:6, with both being 50 g. The monomers were composed of butyl acrylate, hydroxybutyl acrylate, benzyl acrylate, and methyl methacrylate in a mass ratio of 69:11:18:2. The initiator 2,2'-azobisisobutyronitrile was 0.1% of the total mass of the monomers. Nitrogen was purged for 10 min under stirring conditions to remove oxygen. The reaction was carried out at a reaction temperature of 75 °C for 1 h, then cooled to 70 °C and reacted for 7 h. Heating was stopped and ethyl acetate was added to dilute to 20%, and the viscosity was 7532 mPa·s.

[0046] Example 7

[0047] Ethyl acetate was used as the solvent, and the total mass ratio of the solvent to the monomers was 4.5:5.5, with both being 50 g. The monomers were composed of butyl acrylate, hydroxybutyl acrylate, benzyl acrylate, and methyl methacrylate in a mass ratio of 74:2:18:6. The initiator 2,2'-azobisisobutyronitrile was 0.1% of the total mass of the monomers. Nitrogen was purged for 10 min under stirring conditions to remove oxygen. The reaction was carried out at a reaction temperature of 68 °C for 1 h, then cooled to 63 °C and reacted for 7 h. Heating was stopped and ethyl acetate was added to dilute to 20%, and the viscosity was 25150 mPa·s.

[0048] Example 8

[0049] Ethyl acetate was used as the solvent, and the total mass ratio of the solvent to the monomers was 3:5, with the total mass of the monomers being 50 g. The monomers were composed of butyl acrylate, hydroxybutyl acrylate, benzyl acrylate, and methyl methacrylate in a mass ratio of 74:2:18:6. The initiator 2,2'-azobisisobutyronitrile was 0.1% of the total mass of the monomers. Nitrogen was purged for 10 min under stirring conditions to remove oxygen. The reaction was carried out at a reaction temperature of 68 °C for 1 h, then cooled to 62 °C and reacted for 7 h. Heating was stopped and ethyl acetate was added to dilute to 20%, and the viscosity was 10251 mPa·s.

[0050] Example 9

[0051] Using ethyl acetate as the solvent, the total mass ratio of the solvent to the monomers was 4:5, with the total mass of the monomers being 50 g. The monomers were composed of butyl acrylate, hydroxybutyl acrylate, benzyl acrylate, and methyl methacrylate in a mass ratio of 74:2:18:6. The initiator 2,2'-azobisisobutyronitrile was 0.1% of the total mass of the monomers. Nitrogen was purged for 10 min under stirring conditions to remove oxygen. The reaction was carried out at a reaction temperature of 68 °C for 1 h, then cooled to 62 °C and reacted for 7 h. Heating was stopped and ethyl acetate was added to dilute to 20%, and the viscosity was 7371 mPa·s.

[0052] Comparative Example 1

[0053] The total mass ratio of the solvent to the monomer is 4.5:5.5 and both are 50 g. The monomer is composed of butyl acrylate, 2-hydroxyethyl acrylate, benzyl acrylate, and methyl methacrylate mixed in a mass ratio of 95:2:2:1. The initiator 2,2'-azobisisobutyronitrile is 0.1% of the total mass of the monomer. Nitrogen is purged for 10 min under stirring conditions to remove oxygen. The reaction is carried out at a reaction temperature of 75 °C for 8 h, heating is stopped and ethyl acetate is added to dilute to 20%, and the viscosity is 566.4 mPa·s.

[0054] Compared with Example 1, the reaction is carried out under the reaction temperature condition of 75 °C throughout the process, but its viscosity is much lower than that of the product prepared in Example 1.

[0055] Comparative Example 2

[0056] Using ethyl acetate as the solvent, the ratio to the monomer is 1:1 and both are 50 g. The monomer is composed of butyl acrylate, 2-hydroxyethyl acrylate, benzyl acrylate, and methyl methacrylate mixed in a mass ratio of 95:2:2:1. The initiator di-tert-butyl peroxide is 0.1% of the total mass of the monomer. Nitrogen is purged for 10 min under stirring conditions to remove oxygen. The reaction is carried out at a reaction temperature of 95 °C for 8 h, heating is stopped and ethyl acetate is added to dilute to 20%, and the viscosity is 345 mPa·s.

[0057] Compared with Example 2, the reaction is carried out under the reaction temperature condition of 95 °C throughout the process, but its viscosity is much lower than that of the product prepared in Example 2.

[0058] Comparative Example 3

[0059] Ethyl acetate is used as the solvent, and the total mass ratio to the monomer is 1:1 and both are 50 g. The monomer is composed of butyl acrylate, 2-hydroxyethyl acrylate, benzyl acrylate, and methyl methacrylate mixed in a mass ratio of 95:2:2:1. The initiator benzoyl peroxide is 0.1% of the total mass of the monomer. Nitrogen is purged for 10 min under stirring conditions to remove oxygen. The reaction is carried out at a reaction temperature of 75 °C for 8 h, heating is stopped and the solvent is added to dilute to 20%, and the viscosity is 1097.5 mPa·s.

[0060] Compared with Example 3, the reaction is carried out under the reaction temperature condition of 75 °C throughout the process, but its viscosity is much lower than that of the product prepared in Example 3.

[0061] Comparative Example 4

[0062] Toluene was used as the solvent, and the ratio of toluene to the monomer was 1:1, with both being 50 g. The monomer was composed of butyl acrylate, 2-hydroxyethyl acrylate, benzyl acrylate, and methyl methacrylate, mixed in a mass ratio of 95:2:2:1. The initiator benzoyl peroxide was 0.1% of the total mass of the monomer. Nitrogen was purged for 10 min under stirring conditions to remove oxygen. The reaction was carried out at a reaction temperature of 80 °C for 8 h, then heating was stopped and toluene was added to dilute to 20%, and the viscosity was 2412 mPa·s.

[0063] Compared with Example 4, the reaction was carried out under the reaction temperature condition of 80 °C throughout the process, but its viscosity was much lower than that of the product prepared in Example 4.

[0064] Figure 1 、 Figure 2 Infrared spectra of the polyacrylate polymers obtained in Examples 1-9: The infrared absorption peaks of -CH3, -CH2, -CH, and -COOH can be clearly seen, and the characteristic absorption peak of C=C does not appear, indicating that the sample does not contain unreacted double bond functional groups.

[0065] Figure 3 Ultraviolet-visible light transmittance of the polyacrylate polymers obtained in Examples 8 and 9: The transmittance reaches more than 96% in the visible light region.

[0066] Figure 4 Nuclear magnetic spectra of the polyacrylate polymer products obtained in Examples 8 and 9: Except for the solvent peak, the peaks of other functional groups are also relatively obvious.

[0067] For those not covered above, the prior art applies.

[0068] Although some specific embodiments of the present invention have been described in detail by way of examples, those skilled in the art should understand that the above examples are only for illustration and not for limiting the scope of the present invention. Those skilled in the technical field to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar ways to substitute, but will not deviate from the direction of the present invention or exceed the scope defined by the appended claims. Those skilled in the art should understand that any modifications, equivalent substitutions, improvements, etc. made based on the technical essence of the present invention to the above embodiments should be included in the protection scope of the present invention.

Claims

1. A method for preparing a high-viscosity acrylic adhesive, characterized in that: The acrylic adhesive is prepared by dissolving a soft monomer, a hard monomer, a functional monomer and an initiator in an organic solvent, reacting at a first temperature T1 for 0.5-3 hours, cooling to a second temperature T2 for 4-10 hours, and then adding a solvent for dilution to obtain a solvent-based acrylic adhesive product; When the 10h half-life temperature T of the initiator is less than 100°C, T1 is greater than T and less than 100°C; T2 is less than T, and the difference between T and T2 is 0.5-15°C; When the 10h half-life temperature T of the initiator is greater than 100°C, the range of T1 is 75-100°C, and the difference between T1 and T2 is 20-40°C.

2. The preparation method according to claim 1, characterized in that: The reaction was carried out at the first temperature T1 for 1-2 hours, and then the temperature was lowered to the second temperature T2 for 5-8 hours.

3. The preparation method according to claim 1, characterized in that: The initiator is one or more of an organic peroxide initiator and an azo initiator.

4. The preparation method according to claim 3, characterized in that: The initiator is a mixture of one or more of 2,2'-azobisisobutyronitrile, benzoyl peroxide, di-tert-butyl peroxide, and di-tert-butyl diisopropylbenzene peroxide.

5. The preparation method according to claim 1, characterized in that: The mass content of the initiator is 0.01%-2% of the total monomer mass.

6. The preparation method according to claim 5, characterized in that: The mass content of the initiator is 0.03%-1% or 0.05%-0.5% of the total monomer mass.

7. The preparation method according to claim 1, characterized in that: The solvent is selected from any one of ethyl acetate and toluene or a mixture of the two, and the mass content is 10%-80% of the total monomer mass, more preferably 30%-60%, and further preferably 35%-50%; The soft monomer is one or a mixture of butyl acrylate and isooctyl acrylate; the mass content is 40%-99% of the total monomer mass, more preferably 50%-97%, and more preferably 65%-96%; the hard monomer is one or a mixture of methyl methacrylate, styrene, and benzyl acrylate; the mass content is 0.5%-40% of the total monomer mass, more preferably 1%-30%, and more preferably 1.5%-28%.

8. The preparation method according to claim 1, characterized in that: The functional monomer is a monomer containing a polar group; the monomer containing a polar group includes one or more of a nitrogen-containing heterocyclic monomer, a hydroxyl monomer, a carboxyl monomer, and an amide monomer; Or, the functional monomer is a mixture of one or more of 2-hydroxyethyl methacrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl methacrylate, 6-hydroxyhexyl methacrylate, methacrylic acid, N-vinyl pyrrolidone, and N-2-hydroxyethyl acrylamide; the mass content is 0.5%-30% of the total monomer mass, more preferably 1%-25%, and even more preferably 1.5%-20%.

9. The preparation method according to claim 1, characterized in that: The dilution concentration of the added solvent is 6%-40%, more preferably 10%-35%, and further preferably 12%-30%.

10. A high-viscosity acrylic adhesive prepared by the preparation method according to any one of claims 1 to 9.

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