Acrylate adhesive, pressure-sensitive adhesive tape and preparation method thereof

Abstract

The invention relates to an acrylate adhesive, a pressure-sensitive adhesive tape and a preparation method of the acrylate adhesive. The acrylate adhesive comprises the following components in parts by mass: 100 parts of an acrylate composition; 5-15 parts of a solvent; 0.5 to 1.5 parts of a curing agent; 1.0 to 3.0 parts of a modified silane coupling agent; the modified silane coupling agent is a long-chain amino organic silicon coupling agent generated by modifying an amino silane coupling agent by using ester group-containing long-chain alkane, the main chain of the modified coupling agent is long-chain alkane, and an amino group (-NH2) on the chain is modified by long-chain alkyl ester to become a (-CONH-) group with lower activity; the composition still retains one amino active group and three methoxyl active groups, and alkalinity is weakened due to absence of active protons, so that yellowing resistance of the composition is improved.

Description

Technical Field

[0001] The invention relates to the technical field of adhesive tapes, and in particular to an acrylic adhesive, a pressure-sensitive adhesive tape and a preparation method thereof. Background Art

[0002] With the rapid development of the information age, polarizing films are increasingly used in LCDs and wearables. Polarizing films are generally composed of two layers of triacetate cellulose film (TAC) and a polyvinyl alcohol film (PVA) sandwiched in the middle. A pressure-sensitive adhesive is attached to the TAC film on one side for bonding the polarizing film to the glass panel.

[0003] TAC (Tri-cellulose Acetate) has the best optical transmittance compared to other materials and is currently widely used in automotive displays. However, TAC itself is hygroscopic. Under high humidity and heat conditions, the acrylic adhesive layer in contact with the TAC interface is easily affected by water vapor, resulting in the problem of TAC substrate-adhesive layer or adhesive layer-glass interface detachment after the traditional acrylic tape based on TAC material is attached to the glass interface, causing various problems such as bulging and warping. In addition, some acrylic adhesive layers turn yellow due to the influence of ultraviolet rays, moisture and oxygen, affecting the appearance and normal use of the product.

[0004] Currently, there are only a few companies that can produce optical-grade TAC materials on the market, resulting in high prices. During the processing of TAC-based tapes, die-cutting and other processing plants also have higher requirements on the lamination and reworking performance of the tape in order to reduce costs.

[0005] Therefore, it is necessary to design an acrylic pressure-sensitive tape that is resistant to high humidity and heat, resistant to yellowing and can be reworked to meet the downstream customers' demand for the use of TAC-based acrylic tape. Summary of the invention

[0006] The first technical problem to be solved by the present invention is to provide a yellowing-resistant acrylic adhesive in view of the above-mentioned prior art.

[0007] The second technical problem to be solved by the present invention is to provide a pressure-sensitive adhesive tape using the above-mentioned acrylic adhesive in view of the above-mentioned prior art.

[0008] The third technical problem to be solved by the present invention is to provide a method for preparing the pressure-sensitive adhesive tape according to the above-mentioned prior art.

[0009] The technical solution adopted by the present invention to solve the above-mentioned first technical problem is: an acrylic adhesive, comprising the following components and mass fractions:

[0010]

[0011] The modified silane coupling agent is a long-chain amino silicone coupling agent generated by modifying an aminosilane coupling agent with a long-chain alkane containing an ester group.

[0012] Preferably, the preparation method of the modified silane coupling agent is to mix a long-chain alkyl ester or a derivative thereof (i.e., a long-chain alkane containing an ester group), an aminoorganosilane coupling agent and isopropanol, and react them under a nitrogen atmosphere, wherein the mass ratio of the long-chain alkyl ester or a derivative thereof to the aminoorganosilane coupling agent is 1-3:1, and the amount of isopropanol added is such that the aminoorganosilane coupling agent and the long-chain alkyl ester or a derivative thereof can be evenly dispersed.

[0013] Preferably, the aminoorganosilane coupling agent is at least one of N-2(aminoethyl)-3-aminopropylmethyldimethoxysilane (KH-792), γ-aminopropyltriethoxysilane (KH-550) and N-phenyl-γ-aminopropyltrimethoxysilane (KH-590), and the long-chain alkyl ester or its derivative is at least one of isopropyl alkyl acid esters with a long-chain carbon number of 12 to 16.

[0014] Preferably, the acrylic acid ester composition comprises the following raw materials and their weight fractions:

[0015]

[0016] The preparation method of the acrylic ester composition is as follows: a high Tg monomer, butyl acrylate, hydroxyethyl acrylate and acrylic acid are mixed in proportion to form a mixed solution, an initiator is dispersed in a solvent according to the number of portions to form an initiator solution, the initiator solution is dripped into the mixed solution in multiple stages, and reacted at 70-160° C. under a nitrogen protection atmosphere, and in the last initiator dripping stage, vinyl acetate is added to the mixed solution according to the number of portions to react until the reaction solution is transparent and uniform and the viscosity is significantly increased, then the temperature is reduced to 30-40° C., and filtered while hot, and the obtained filtrate is the acrylic ester composition.

[0017] The main raw material of the acrylic ester composition uses a high Tg monomer to enhance the cohesion of the composition; secondly, hydroxyethyl acrylate and acrylic acid are used in the synthesis process. Hydroxyethyl acrylate will introduce a hydroxyl group (-OH) as a bridging point for subsequent reaction with the curing agent hexamethylene diisocyanate (HDI); acrylic acid will introduce a carboxyl group (-COOH) as a reaction site for subsequent reaction with a modified silane coupling agent; vinyl acetate will react with low molecular weight small molecule segments in the composition system.

[0018] Preferably, the addition of the initiator solution is divided into four stages. Based on 100 parts of the initiator solution, in the first stage, 20-40 parts of the initiator solution are added to the reaction mixture, and the mixture is reacted at a constant temperature of 70°C-90°C in a nitrogen atmosphere for 1-2 hours; in the second and third stages, under the above reaction conditions, 10-20 parts of the initiator solution are sequentially added dropwise into the reaction solution within 0.5-1 hour for reaction; in the fourth stage, the temperature is raised to 130°C-150°C, vinyl acetate monomer is added, and the remaining 40-60 parts of the initiator solution are added dropwise into the reaction solution within 0.5-1 hour, and the reaction is continued for 2-4 hours in a nitrogen atmosphere. After the reaction solution is transparent and uniform and the viscosity of the system is significantly increased, the temperature is lowered to 30-40°C to obtain the acrylic ester composition.

[0019] In the synthesis process of the acrylic ester composition provided by the present invention, the addition process and amount of the initiator azobisisobutyronitrile (AIBN) are controlled to prolong the synthesis reaction time and reduce the generation of low molecular weight segments; and vinyl acetate is used to react with the low molecular weight small molecule segments generated in the synthesis process to further reduce the proportion of low molecular weight segments. The synthesized composition is tested by GPC, and the number average molecular weight is 1600kDa, and the molecular weight distribution is 3.2 (number average molecular weight / weight average molecular weight).

[0020] Preferably, the high Tg monomer is at least one of methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, 2-hydroxypropyl methacrylate, and cyclohexyl methacrylate; the initiator is one of azobisisobutyronitrile, dibenzoyl peroxide, and isopropylbenzene hydroperoxide; and the solvent is at least one of methyl acetate, ethyl acetate, and toluene.

[0021] Preferably, the curing agent includes a multifunctional epoxy curing agent and / or a multifunctional isocyanate curing agent, the multifunctional epoxy curing agent is at least one of an aromatic epoxy diamine compound and an alicyclic epoxy diamine compound, and the multifunctional isocyanate curing agent is at least one of toluene diisocyanate, benzyl diisocyanate, hexamethylene diisocyanate, and diphenylmethane diisocyanate.

[0022] The technical solution adopted by the present invention to solve the above-mentioned second technical problem is: a pressure-sensitive adhesive tape, comprising a release layer, an adhesive layer and a substrate layer arranged in sequence, the substrate layer is made of TAC, and the adhesive layer is formed by evenly mixing the components of the above-mentioned acrylic adhesive and waiting for the solvent to evaporate.

[0023] The technical solution adopted by the present invention to solve the third technical problem is: a method for preparing the above-mentioned acrylic pressure-sensitive adhesive tape, characterized in that it comprises the following steps:

[0024] (1) placing a certain amount of an acrylic ester composition in a pre-mixed container, adding a corresponding amount of a solvent, stirring evenly, then adding a corresponding amount of a curing agent, stirring evenly, and finally adding a corresponding amount of a modified silane coupling agent, stirring evenly, to obtain the acrylic ester adhesive;

[0025] (2) coating an acrylic adhesive on the release layer, and forming an adhesive layer after the solvent evaporates, and attaching the adhesive layer to the substrate layer, thereby obtaining the acrylic pressure-sensitive adhesive tape.

[0026] Compared with the prior art, the advantages of the present invention are: the main chain of the modified silane coupling agent of the present invention is a long-chain alkane, and the amino group (-NH2) on the chain is modified by a long-chain alkyl ester to become an amide (-CONH-) group with slightly lower activity, while one amino active group and three methoxy active groups are still retained. Because there is no active proton, the alkalinity is weakened, thereby improving the yellowing resistance of the adhesive.

[0027] In other words, the present invention adds a silane coupling agent modified by an aminolysis reaction to an acrylic adhesive, so that after the adhesive is used to prepare a TAC-based tape and bonded to glass, the tape exhibits excellent adhesion, moisture and heat resistance, and yellowing resistance in a high temperature and high humidity environment, and after the prepared tape is peeled off from the glass interface and then bonded again, it still exhibits excellent bonding performance.

[0028] That is, the TAC-based acrylic tape has the characteristics of being resistant to high temperature and high humidity environment after being bonded to glass, not being easy to come off or turn yellow, and being able to be bonded a second time without affecting the performance. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below in conjunction with specific embodiments.

[0030] The acrylic pressure-sensitive tape comprises a release layer, an adhesive layer and a base layer which are arranged in sequence. The base layer is made of TAC, the adhesive layer is an OCA adhesive layer, the release layer is 70um thick, and the base layer is 80um thick.

[0031] The adhesive layer is formed by uniformly mixing various components of the acrylic adhesive and allowing the solvent to evaporate.

[0032] Acrylic adhesives include the following components and mass fractions:

[0033]

[0034] The modified silane coupling agent is a long-chain amino organic silicon coupling agent generated by modifying an amino silane coupling agent with a long-chain alkane containing an ester group. The modified silane coupling agent is an amino-group concealed organic silane coupling agent.

[0035] The solvent in the following examples and comparative examples is ethyl acetate, and the curing agent is HDI.

[0036] The preparation method of the modified silane coupling agent of the following embodiments and comparative examples is to mix a long-chain alkane containing an ester group (isopropyl myristate (also known as isopropyl myristate), an aminosilane coupling agent (γ-aminopropyltriethoxysilane (KH-550)) and isopropanol, and react in a nitrogen atmosphere for 4 hours, wherein the mass ratio of isopropyl myristate to KH-550 is 1.5:1, and the amount of isopropanol added is such that isopropyl myristate and KH-550 can be evenly dispersed.

[0037] The acrylic acid ester compositions of the following embodiments and comparative examples include the following raw materials and their weight fractions:

[0038]

[0039] The preparation method of the acrylic ester composition is as follows: methyl methacrylate, butyl acrylate, hydroxyethyl acrylate and acrylic acid are mixed in corresponding parts to form a mixed liquid, initiator AIBN is dispersed in solvent ethyl acetate in parts to form an initiator solution, the initiator solution is dripped into the reaction liquid in parts in stages under a nitrogen protection atmosphere, and in the last dripping stage of the initiator, vinyl acetate monomer is added in parts, the reaction temperature is controlled until the viscosity of the reaction liquid is significantly increased, the temperature is lowered to 30°C, and it is filtered while hot, and the obtained filtrate is the acrylic ester composition.

[0040] The addition of the initiator solution is divided into four reaction stages. Based on 100 parts of the initiator solution, in the first stage, 40 parts of the initiator solution are added to the mixed solution, and the mixture is reacted at a constant temperature of 80°C for 2 hours in a nitrogen atmosphere. From the second stage to the third stage, under the above reaction temperature conditions, 10 parts of the initiator solution are respectively added dropwise into the reaction solution within 0.5 hours, and each reacts for 1 hour. In the fourth stage, the temperature is raised to 140°C, vinyl acetate reaction monomer is added, and the remaining 40 parts of the initiator solution are added dropwise into the reaction solution within 0.5 hours, and the reaction is continued for 4 hours in a nitrogen atmosphere. After the reaction solution is transparent and uniform and the viscosity of the system is significantly increased, the temperature is lowered to 30°C to obtain the acrylic ester composition.

[0041] In this context, a significant increase in the viscosity of the reaction liquid system refers to the phenomenon that the reaction liquid climbs upward along the stirring paddle when the stirring paddle is stirring, i.e., a "climbing" phenomenon occurs.

[0042] The preparation method of the acrylic pressure-sensitive adhesive tape comprises the following steps:

[0043] (1) placing a certain amount of an acrylic ester composition in a pre-mixed container, adding a corresponding amount of a solvent, stirring evenly, then adding a corresponding amount of a curing agent, stirring evenly, and finally adding a corresponding amount of a modified silane coupling agent, stirring evenly, to obtain the acrylic ester adhesive;

[0044] (2) coating the release layer with an acrylic adhesive, leaving it to stand for 20 minutes, and then baking it in an oven at 80° C. for 3 minutes to evaporate the solvent and form an adhesive layer, and attaching the adhesive layer to the substrate layer to obtain the acrylic pressure-sensitive adhesive tape.

[0045] The pressure-sensitive adhesive tape of the present invention is suitable for use on an outer screen of a vehicle-mounted central control display.

[0046] The present invention is described below in conjunction with specific embodiments and comparative examples: the addition amount of each material and the test results of each embodiment and comparative example are shown in the following table.

[0047] The silane coupling agent in Comparative Example 7 is not modified by using a long-chain alkane containing an ester group, and is KH-550.

[0048]

[0049]

[0050] As shown in the table above, the present invention includes 9 embodiments and 7 comparative examples. The type and amount of substances added in each embodiment, as well as the adhesion, retention, initial adhesion, yellowing (b value) and high temperature and humidity resistance of the final tape are listed in the table. The adhesion test standard in the attached table is GB / T 2792-2014, the retention test standard is GB / T4851-2014, and the initial adhesion test standard is GB / T 4852-2002. The yellowing standard of the tape is determined by the size of the b value, and the testing equipment is a UV-visible spectrophotometer. According to the vehicle-mounted explosion-proof film tape, the b value ≤2 is a normal phenomenon, and the b value>2 is a yellowing phenomenon. The high temperature and humidity resistance test method of the tape is: after removing the release film, the tape is bonded to the glass surface, vacuum degassing by a degassing machine, placed in a high temperature and high humidity environment, and after 1000 hours of high temperature and high humidity impact, an optical microscope is used to observe the water vapor intrusion and detachment at the bonding site.

[0051] According to the results in the attached table, by comparing Examples 3, 6, 9 and Comparative Examples 3 to 5, it can be seen that the amount of curing agent (hexamethylene diisocyanate) added has a greater influence on the high-humidity and heat resistance of the tape. Properly increasing the amount of curing agent used will improve the high-humidity and heat resistance of the tape, but the amount of curing agent added should not be too much to prevent excessive bridging and affect the performance of the tape. By comparing Examples 1, 4, 7 or 2, 5, 8, it can be seen that the amount of curing agent (hexamethylene diisocyanate) added does not affect the yellowing degree (b value) of the tape. By comparing Examples 7 to 9 and Comparative Examples 1, 2, 6, 7, it can be seen that the coupling agent will affect the yellowing degree (b value) of the tape. This is because the amino group on the coupling agent easily reacts with oxygen to form an oxidation product, resulting in yellowing. As the amount of coupling agent added increases, the b value also increases. Since the amino coupling agent is modified to become an amino-based concealed coupling agent, its anti-yellowing ability is improved. Therefore, after high temperature and high humidity treatment, the tape has a slight yellowing (b value ≤ 1), while the comparative example 7 in which the coupling agent is not modified has a serious yellowing (b value > 2). By comparing Examples 7 to 9 with Comparative Examples 1 to 2, it can be seen that the addition of the modified silane coupling agent can improve the high humidity and heat resistance of the tape. This is because when the tape is bonded to the glass interface, the three ethoxy groups (-C2H5O) in the modified silane coupling agent will hydrolyze to form silanol groups (-Si-OH), and the silanol groups will undergo a dehydration condensation reaction with the silanol groups on the glass interface to form a stable siloxy bond (-Si-O-Si-); in addition, the primary amine (-CONH-) in the modified coupling agent will react with the carboxyl group (-COOH) on the molecular chain of the acrylic ester composition and be embedded in the molecular chain structure of the acrylic ester composition, thereby improving the bonding performance of the tape and the glass interface and improving the ability to resist high humidity and heat. By comparing Examples 4 to 6 and Comparative Example 6, it can be seen that the aminosilane coupling agent is more suitable for improving the high humidity and heat resistance of the adhesive tape of the present invention. Although the γ-methacryloxypropyltrimethoxysilane (KH-570) used in Comparative Example 6 does not have an amino group to cause yellowing, it is not good for improving the high humidity and heat resistance of the adhesive tape.

[0052] The high-heat-resistant, yellowing-resistant and reworkable acrylic pressure-sensitive adhesive tape provided by the present invention uses a high Tg monomer in the preparation of an acrylic composition, and by controlling the addition time of a curing agent, the composition has fewer low molecular weight segments, so that under high temperature and high humidity conditions, the low molecular weight segments will not decompose, resulting in a decrease in the interfacial adhesion of the adhesive layer; the high molecular weight segments are more, and the overall average molecular weight is larger, so that the cohesive strength and heat resistance of the composition itself are better, and due to the lower adhesion, there will be no residual glue after the glass tape is applied to the glass interface to be adhered, and the adhesive performance of the tape is still maintained, which has the advantage of being reworkable. In addition, the silane coupling agent used is modified, and the aminosilane coupling agent is modified by an aminolysis reaction of a long-chain alkyl ester, and the highly active, easily oxidized and yellowed amino group (-NH2) is converted into an amide (-CONH-) group with slightly lower activity while still maintaining the performance of the silane coupling agent.

[0053] The high-humidity and heat-resistant acrylic tape provided by the present invention exhibits excellent high-temperature and high-humidity resistance after being bonded to glass. After aging for 1000 hours at 60°C / 90%Rh and 85°C / 85%Rh, no edge bulging or detachment occurs.

[0054] The above is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. All equivalent changes and modifications made based on the content of the present invention are included in the patent scope of the present invention.

Claims

1. An acrylic adhesive, characterized in that: Includes the following components and mass fractions: The modified silane coupling agent is a long-chain amino silicone coupling agent generated by modifying an aminosilane coupling agent with a long-chain alkane containing an ester group.

2. The acrylic adhesive according to claim 1, characterized in that: The preparation method of the modified silane coupling agent is to mix a long-chain alkyl ester or a derivative thereof, an aminoorganosilane coupling agent and isopropanol, and react them under a nitrogen atmosphere, wherein the mass ratio of the long-chain alkyl ester or a derivative thereof to the aminoorganosilane coupling agent is 1-3:1, and the amount of the isopropanol added is such that the aminoorganosilane coupling agent and the long-chain alkyl ester or a derivative thereof can be evenly dispersed.

3. The acrylic adhesive according to claim 2, characterized in that: The aminoorganosilane coupling agent is at least one of N-2(aminoethyl)-3-aminopropylmethyldimethoxysilane and N-phenyl-γ-aminopropyltrimethoxysilane; The long-chain alkyl ester or its derivative is at least one of the isopropyl alkyl esters with a long-chain carbon number of 12 to 16.

4. The acrylic adhesive according to claim 1, characterized in that: The acrylic acid ester composition comprises the following raw materials and their weight fractions: The preparation method of the acrylic ester composition is as follows: a high Tg monomer, butyl acrylate, hydroxyethyl acrylate and acrylic acid are mixed in proportion to form a mixed solution, an initiator is dispersed in a solvent according to the number of portions to form an initiator solution, the initiator solution is dripped into the mixed solution in stages, and reacted at 70-160° C. under a nitrogen protection atmosphere, and in the final dripping stage of the initiator, vinyl acetate is added to the mixed solution according to the number of portions to react, and after the reaction solution becomes transparent and uniform and the viscosity is significantly increased, the temperature is lowered to 30-40° C., and filtered while hot, and the obtained filtrate is the acrylic ester composition.

5. The acrylic adhesive according to claim 4, characterized in that: The addition of the initiator solution is divided into four stages. Based on 100 parts of the initiator solution, in the first stage, 20-40 parts of the initiator solution are added to the reaction mixture, and the reaction is carried out at a constant temperature of 70-90° C. for 1-2 hours in a nitrogen atmosphere; in the second and third stages, 10-20 parts of the initiator solution are sequentially added dropwise into the reaction solution within 0.5-1 hour under the above reaction conditions to carry out the reaction; in the fourth stage, the temperature is raised to 130-150° C., vinyl acetate monomer is added, and the remaining 40-60 parts of the initiator solution are added dropwise into the reaction solution within 0.5-1 hour, and the reaction is continued for 2-4 hours in a nitrogen atmosphere. After the reaction solution is transparent and uniform and the viscosity of the system is significantly increased, the temperature is lowered to 30-40° C. to obtain the acrylic ester composition.

6. The acrylic adhesive according to claim 4, characterized in that: The high Tg monomer is at least one of methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, 2-hydroxypropyl methacrylate, and cyclohexyl methacrylate.

7. The acrylic adhesive according to claim 4, characterized in that: The initiator is one of azobisisobutyronitrile, dibenzoyl peroxide, and isopropylbenzene hydroperoxide; and the solvent is at least one of methyl acetate, ethyl acetate, and toluene.

8. The acrylic adhesive according to claim 4, characterized in that: The curing agent includes a multifunctional epoxy curing agent and / or a multifunctional isocyanate curing agent, the multifunctional epoxy curing agent is at least one of an aromatic epoxy diamine compound and an alicyclic epoxy diamine compound, and the multifunctional isocyanate curing agent is at least one of toluene diisocyanate, xylylene diisocyanate, hexamethylene diisocyanate, and diphenylmethane diisocyanate.

9. A pressure-sensitive adhesive tape comprising a release layer, an adhesive layer and a substrate layer arranged in sequence, wherein the substrate layer is made of TAC, and the adhesive layer is formed by uniformly mixing the components of the acrylic adhesive according to any one of claims 1 to 8 and evaporating the solvent.

10. A method for preparing the pressure-sensitive adhesive tape according to claim 9, characterized in that: The steps include: (1) placing a certain amount of an acrylic ester composition in a pre-mixed container, adding a corresponding amount of a solvent, stirring evenly, then adding a corresponding amount of a curing agent, stirring evenly, and finally adding a corresponding amount of a modified silane coupling agent, stirring evenly, to obtain the acrylic ester adhesive; (2) coating an acrylic adhesive on the release layer, and forming an adhesive layer after the solvent evaporates, and attaching the adhesive layer to the substrate layer, thereby obtaining the acrylic pressure-sensitive adhesive tape.

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