High-temperature-resistant peelable acrylic pressure-sensitive adhesive and preparation method thereof

Abstract

The invention belongs to the technical field of pressure-sensitive adhesives, and particularly relates to a high-temperature-resistant peelable acrylic pressure-sensitive adhesive and a preparation method thereof. The adhesive is composed of the following materials in parts by weight: 30-90 parts of a soft monomer; 1-5 parts of a hard monomer; 2-10 parts of a functional monomer; and 0.01 to 2 parts of an initiator. Through compounding of soft and hard monomers and introduction of functional monomers, cohesive force and adhesive force of an adhesive layer are balanced, and unification of peelability at a high temperature (greater than or equal to 120 DEG C) (peel strength is less than or equal to 1.0 N / cm) and normal-temperature strong viscosity is realized; the adhesive has no solvent residue design (the solvent recovery rate is greater than or equal to 95%), meets environmental protection requirements, has excellent weather resistance and is suitable for long-term outdoor use.

Description

Technical Field

[0002] This invention belongs to the field of pressure-sensitive adhesive technology. More specifically, it relates to a high-temperature resistant, peelable acrylic pressure-sensitive adhesive and its preparation method. Background Technology

[0003] Vehicle stickers, bus body stickers, and adhesive materials used in high-temperature areas (such as engine compartment exterior trim) commonly face the problem of residual adhesive peeling.

[0004] CN112457442A discloses an aqueous plywood latex comprising 20-30% hard monomers, 20-30% soft monomers, 0.5-1.5% functional monomers, 0.5-1.5% emulsifiers, 0.05-0.5% oxidants, 0.05-0.5% reducing agents, 0.01-0.1% defoamers, 0.01-0.1% mildew inhibitors, and 40-60% softened water. Hard monomers refer to monomers with higher homopolymer glass transition temperatures, including methyl methacrylate, styrene, and acrylonitrile. Soft monomers refer to monomers with lower homopolymer glass transition temperatures, including butyl acrylate, isooctyl acrylate, vinyl tert-carbonate, and ethyl acrylate. Functional monomers refer to monomers providing specific functional groups, including acrylic acid, methacrylic acid, acrylamide, N-hydroxymethylacrylamide, isobornyl methacrylate, and itaconic acid. This invention utilizes a core-shell copolymerization method, employing butyl acrylate and styrene as the main monomers, and introduces functional monomers to carry out a polymerization reaction, to produce a two-component plywood latex with moderate hardness and high water resistance. In terms of performance, it can replace DA-905, and the cost can be greatly reduced.

[0005] CN111892679A discloses an acrylic pressure-sensitive adhesive for foam, its preparation process, and its application. The pressure-sensitive adhesive comprises the following components by weight percentage: 15%–30% isooctyl acrylate, 15%–30% butyl acrylate, 1%–6% acrylic acid, 1%–15% ethyl acrylate, 0.2%–2% hydroxypropyl acrylate, 0.5%–5% methyl methacrylate, 0.2%–2% glycidyl methacrylate, 0.5%–2% isobornyl methacrylate, 0.5%–2% initiator, and the remainder being solvent. This invention utilizes a stepwise polymerization method with a combination of soft monomers, hard monomers, and functional monomers. The resulting acrylic pressure-sensitive adhesive, after crosslinking, exhibits excellent adhesion to foam substrates without the need for additional resin additions, achieving the desired performance. The foam tape prepared using this invention has a long holding time and a warp resistance exceeding one month.

[0006] The pressure-sensitive adhesives mentioned above are not suitable for car stickers. Traditional PVC car stickers increase the cohesive strength of the adhesive layer by adding cross-linking agents, and can achieve residue-free peeling after use at lower temperatures (30°C and below). However, the peeling force will be greatly reduced, and there is a risk of easy detachment. In actual application environments, the actual temperature of a car body can reach over 50°C when it is outdoors in summer. Under such high-temperature environments, even with the addition of cross-linking agents, residue-free peeling cannot be achieved after long-term use. Manual cleaning is required, which can cause mechanical damage or chemical corrosion to the surface of the object to which the sticker is applied (such as car paint and metal parts), resulting in significant economic losses and environmental pollution. Summary of the Invention

[0007] The technical problem this invention aims to solve is to overcome the defects and shortcomings of existing vehicle stickers, such as residue when peeled off in high-temperature areas, and to provide a high-temperature resistant peelable acrylic pressure-sensitive adhesive and its preparation method. The pressure-sensitive adhesive provided by this invention can still be removed after long-term use in high-temperature (≥60℃) environments without leaving residue, and also exhibits excellent adhesion performance at room temperature.

[0008] The purpose of this invention is to provide a high-temperature resistant, peelable acrylic pressure-sensitive adhesive.

[0009] Another object of the present invention is to provide a method for preparing a high-temperature resistant peelable acrylic pressure-sensitive adhesive.

[0010] The above-mentioned objective of this invention is achieved through the following technical solution: An acrylic pressure-sensitive adhesive composition, by weight, comprises the following materials: 30-90 parts of soft monomer; 1-10 parts of hard monomer; 2-10 parts of functional monomer; Initiator: 0.01 to 2 parts.

[0011] Preferably, the soft monomer is butyl acrylate and isooctyl acrylate; the hard monomer is methyl methacrylate and vinyl acetate; the functional monomer is acrylic acid, glycidyl methacrylate, and ethoxyethoxyethyl acrylate; and the initiator is azobisisobutyronitrile. More preferably, the butyl acrylate is 70-75 parts; the isooctyl acrylate is 10-15 parts; the methyl methacrylate is 3-4 parts; the vinyl acetate is 6-7 parts; the acrylic acid is 3-5 parts; the glycidyl methacrylate is 0.5-1.5 parts; and the ethoxyethoxyethyl acrylate is 0.2-1 part.

[0012] Preferably, the functional monomer comprises a polar group modified monomer, wherein the polar group is a hydroxyl, epoxy, or carboxyl group.

[0013] Preferably, the glass transition temperature is -80℃ to -20℃, and the solid content is 40% to 60%.

[0014] The preparation method of the pressure-sensitive adhesive composition described above includes the following steps: (1) Mix some soft monomers, some hard monomers and some functional monomers to form a premixed liquid. Stir to form a homogeneous solution, heat to a certain temperature, add some initiator to initiate polymerization, control the temperature to a certain temperature and keep it at a certain temperature for a certain time to obtain a prepolymer solution. (2) Adjust the temperature of the prepolymer solution to a certain temperature, add a mixture of hard monomer, initiator and solvent to the prepolymer solution, and then add the remaining soft monomer, remaining functional monomer, initiator and solvent mixture to the premixed solution. After adding, keep warm for a certain time. (3) Then add some initiator, the remaining hard monomer and some solvent, and continue to keep warm; (4) Finally, the remaining initiator and solvent are added in stages, and the temperature is maintained. After the temperature maintenance is completed, the temperature is lowered to room temperature to obtain acrylic pressure-sensitive adhesive.

[0015] Preferably, in step (1), the soft monomers account for 30-90% of the total soft monomers; the hard monomers account for 10-80% of the total hard monomers; more preferably, the hard monomers account for 15-20% of the total hard monomers; the functional monomers account for 0-100% of the functional monomers; more preferably, the functional monomers account for 20-90% of the functional monomers; and even more preferably, the functional monomers account for 40-60% of the functional monomers.

[0016] Preferably, in step (1), the temperature is 60~80℃.

[0017] Preferably, in step (2), a portion of the hard monomers accounts for 10-80% of the total hard monomers, more preferably 15-20%; the temperature is 70-90℃.

[0018] Preferably, in steps (1)-(4), the heat preservation time is 1~2h.

[0019] A pressure-sensitive adhesive for vehicle stickers, characterized in that it is prepared by coating and drying the above-described composition, and has a peel strength ≥2.5 N / cm at room temperature and ≤1.0 N / cm at ≥60℃.

[0020] The present invention has the following beneficial effects: This invention balances the cohesive and adhesive forces of the adhesive layer by combining soft and hard monomers and introducing functional monomers, achieving a balance between peelability (peel strength ≤1.0N / cm) at high temperatures (≥120℃) and strong adhesion at room temperature.

[0021] This invention employs a segmented heating polymerization process to control molecular weight distribution, thereby avoiding excessive softening or embrittlement of the adhesive layer at high temperatures and improving temperature resistance stability.

[0022] This invention uses a segmented design of the synthesis process to give the polymer a wide molecular weight distribution. The low molecular weight fraction produced by the second stage of dripping mainly consists of soft monomers, which provide the pressure-sensitive adhesive with high initial tack and high peel strength. The high molecular weight fraction produced by the primer and the first stage of dripping contains hard monomers, which can effectively improve the cohesive force of the pressure-sensitive adhesive without losing its tack.

[0023] This invention increases the number of uniformly dispersed self-crosslinking points in the polymer by adding GMA, which can effectively replace or reduce the addition of traditional crosslinking agents. In traditional solutions, metal salt crosslinking agents may result in uneven crosslinking and excessively dense local crosslinking, which may lead to sacrificing viscosity in order to achieve appropriate cohesion.

[0024] This invention features a solvent-free design (solvent recovery rate ≥95%), which meets environmental protection requirements, and the adhesive layer has excellent weather resistance, making it suitable for long-term outdoor use. Detailed Implementation

[0025] The present invention will be further illustrated below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in this technical field.

[0026] The acrylate soft monomers are selected from n-butyl acrylate (abbreviated as n-BA, CAS NO.: 141-32-2) and isooctyl acrylate (abbreviated as 2-EHA, CAS NO.: 29590-42-9); providing initial tack and flexibility.

[0027] Hard monomers, selected from vinyl acetate (VAC, CAS NO.: 108-05-4) and methyl methacrylate (MMA, CAS NO.: 80-62-6), enhance the cohesiveness and temperature resistance of the adhesive layer.

[0028] Functional monomers, glycidyl methacrylate (GMA, CAS NO.: 106-91-2) and acrylic acid (AA, CAS NO: 79-10-7); introduce polar groups to improve adhesion and water resistance.

[0029] Initiator, 0.1%~1%, selected from azobisisobutyronitrile (AIBN, CAS NO.: 78-67-1), used for free radical polymerization reactions; Solvent, 30%~70%, selected from ethyl acetate (abbreviated EtOAc, CAS NO.: 141-78-6), toluene (abbreviated TL, CAS NO.: 108-88-3), etc., to adjust the viscosity of the adhesive for easy coating.

[0030] In the preparation methods of the acrylate pressure-sensitive adhesive compositions in the examples and comparative examples, the soft monomer is a mixture of BA and 2EHA; the hard monomer is a mixture of MMA and vinyl acetate; the functional monomer is a mixture of AA, GMA and EOEOEA; and the solvent is a mixture of ethyl acetate and toluene.

[0031] Unless otherwise specified, all reagents and materials used in the following examples are commercially available.

[0032] Example 1 An acrylic pressure-sensitive adhesive composition, by weight, comprises the following materials: Soft monomers: BA (butyl acrylate) 70 parts; 2-EHA (isooctyl acrylate) 15 parts; Hard monomers: MMA (methyl methacrylate) 3.5 parts; (vinyl acetate) 6.5 parts; Functional monomers: AA (acrylic acid) 3 parts; GMA (glycidyl methacrylate) 1.2 parts; EOEOEA (ethoxyethoxyethyl acrylate) 0.8 parts; Initiator: 0.5 parts of AIBN (azobisisobutyronitrile); Solvents: 60 parts ethyl acetate (EtOAc), 40 parts toluene (TL).

[0033] A method for preparing an acrylic pressure-sensitive adhesive composition includes the following steps: (1) Mix 42.5 parts of soft monomer, 1.75 parts of hard monomer and 2.5 parts of functional monomer, heat to 75°C, add 0.1 parts of initiator, stir and keep warm for 1 hour after initiation to obtain prepolymer solution; (2) Adjust the temperature of the prepolymer solution to 80°C, add 1.75 parts of hard monomer, 0.1 parts of initiator and 25 parts of solvent mixture to the prepolymer solution dropwise, and then add the remaining soft monomer, the remaining functional monomer, 0.1 parts of initiator and 25 parts of solvent mixture to the prepolymer solution dropwise. The dropwise addition is completed in 1 hour, and the solution is kept warm for 1 hour. (3) Continue to add 0.1 parts of initiator, 6.5 parts of hard monomer and 25 parts of solvent, and keep warm for 1.5 hours; (4) Add 0.1 parts of initiator and the remaining solvent, keep warm for 1.5 h; cool to room temperature to obtain an acrylic pressure-sensitive adhesive with a solid content of 51%, a viscosity of 8800 mPa·S, and a Tg of -58℃.

[0034] Performance testing: Peel strength at room temperature: 6.2 N / cm; hot peel at 120℃, no adhesive residue on the substrate surface after peeling.

[0035] Example 2 An acrylic pressure-sensitive adhesive composition, by weight, comprises the following materials: Soft monomers: BA (butyl acrylate) 72 parts; 2-EHA (isooctyl acrylate) 13 parts; Hard monomers: MMA (methyl methacrylate) 3.5 parts; VAC (vinyl acetate) 6.5 parts; Functional monomers: AA (acrylic acid) 3.6 parts; GMA (glycidyl methacrylate) 1 part; EOEOEA (ethoxyethoxyethyl acrylate) 0.4 parts; Initiator: 0.62 parts of AIBN (azobisisobutyronitrile); Solvents: 70 parts ethyl acetate (EtOAc), 30 parts toluene (TL).

[0036] An acrylic pressure-sensitive adhesive composition includes the following steps: (1) Mix 42.5 parts of soft monomer, 1.75 parts of hard monomer and 2.5 parts of functional monomer, heat to 75°C, add 0.12 parts of initiator, stir and keep warm for 1 hour after initiation to obtain prepolymer solution; (2) Adjust the temperature of the prepolymer solution to 80°C, add 1.75 parts of hard monomer, 0.1 parts of initiator and 25 parts of solvent mixture to the prepolymer solution dropwise, and then add the remaining soft monomer, the remaining functional monomer, 0.1 parts of initiator and 25 parts of solvent mixture to the prepolymer solution dropwise. The dropwise addition is completed in 1 hour, and the solution is kept warm for 1 hour. (3) Continue to add 0.15% initiator, 6.5 parts hard monomer and 25 parts solvent, and keep warm for 1.5h; (4) Add 0.15% initiator and the remaining solvent, keep warm for 1.5h; cool to room temperature to obtain an acrylic pressure-sensitive adhesive with a solid content of 51%, a viscosity of 8996 mPa·S, and a Tg of -56℃.

[0037] Performance testing: Peel strength at room temperature: 6.8 N / cm; hot peel at 120℃, no adhesive residue on the substrate surface after peeling.

[0038] Example 3 An acrylic pressure-sensitive adhesive composition, by weight, comprises the following materials: Soft monomers: BA (butyl acrylate) 74 parts; 2-EHA (isooctyl acrylate) 11 parts; Hard monomers: MMA (methyl methacrylate) 3.5 parts; VAC (vinyl acetate) 6.5 parts; Functional monomers: AA (acrylic acid) 4.2 parts; GMA (glycidyl methacrylate) 0.6 parts; EOEOEA (ethoxyethoxyethyl acrylate) 0.2 parts; Initiator: 0.74 parts of AIBN (azobisisobutyronitrile); Solvents: 80 parts ethyl acetate (EtOAc), 20 parts toluene (TL).

[0039] An acrylic pressure-sensitive adhesive composition includes the following steps: (1) Mix 42.5 parts of soft monomer, 1.75 parts of hard monomer and 2.5 parts of functional monomer, heat to 75°C, add 0.14 parts of initiator, stir and keep warm for 1 hour after initiation to obtain prepolymer solution; (2) Adjust the temperature of the prepolymer solution to 80°C, add 1.75 parts of hard monomer, 0.1 parts of initiator and 25 parts of solvent mixture to the prepolymer solution, and then add the remaining soft monomer, the remaining functional monomer, 0.1 parts of initiator and 25 parts of solvent mixture to the polymerization solution. The addition is completed in 1 hour, and the solution is kept warm for 1 hour. (3) Continue to add 0.2 parts of initiator, 6.5 parts of hard monomer and 25 parts of solvent, and keep warm for 1.5 hours; (4) Add 0.2 parts of initiator and the remaining solvent, keep warm for 1.5h; cool to room temperature to obtain an acrylic pressure-sensitive adhesive with a solid content of 51%, a viscosity of 9000 mPa·S, and a Tg of -54℃.

[0040] Performance testing: Peel strength at room temperature: 7.5 N / cm; hot peel at 120℃, no adhesive residue on the substrate surface after peeling.

[0041] Comparative Example 1 Except for the differences, Comparative Example 1 is basically the same as Example 2. The difference is that Comparative Example 1 does not contain hard monomers.

[0042] Comparative Example 2 Except for the differences, Comparative Example 2 is basically the same as Example 2, except that an equal amount of BA is used to replace GMA.

[0043] Comparative Example 3 Except for the differences, Comparative Example 3 is basically the same as Example 2, except that the dropwise addition step is omitted, and all the polymer is added at once. An acrylic pressure-sensitive adhesive composition includes the following steps: (1) Mix the soft monomer, 1.75 parts of hard monomer and functional monomer, heat to 75°C, add 0.12 parts of initiator, stir and keep warm for 1 hour after initiation; (2) Continue to add 0.25 parts of initiator, 6.5 parts of hard monomer and solvent, and keep warm for 1.5 hours; (3) Add 0.25 parts of initiator, keep warm for 1.5h; cool to room temperature to obtain acrylic pressure-sensitive adhesive.

[0044] The performance of Examples 1-3 and Comparative Examples 1-3 was tested, and the specific test results are shown in Tables 1-4. The specific test methods are as follows: After the pressure-sensitive adhesive is prepared, it can be applied using a comma-shaped scraper, with a coating weight of 30g. Dry it in a 90℃ oven for 3 minutes to complete the initial curing. Take samples and test them using the following methods: Initial tack: Test method refers to FINAT 9 20-minute peel strength: The test method is the same as FINAT1. The material is adhered to a steel plate, and the peel strength at 180° is tested after 20 minutes. Peel strength at 70℃×30 days: The test method is the same as that for peel strength at 70℃×30 days. The material is adhered to a steel plate, placed in a 70℃ oven for 30 days, stabilized at room temperature for 2 days, and then the peel strength at 180° is tested. Adhesion holding: The test method refers to GB / T4851-2014. The material is adhered to a steel plate at a temperature of 80℃ and a load of 800g. The maximum test duration is 168 hours.

[0045] Table 1

[0046] Table 2

[0047] Table 3

[0048] Table 4

[0049] As shown in Tables 1-4, compared with Example 2, Example 1 had an increased amount of functional monomers and a decreased amount of soft monomers, resulting in a slight decrease in initial tack, but no residual adhesive delamination was observed in the limit test, indicating better performance. Compared with Example 2, Example 3 had a decreased amount of functional monomers and an increased amount of soft monomers, resulting in a significant increase in initial tack, but a slight decrease in long-term adhesive strength and some residual adhesive delamination, indicating a significant deviation in overall performance. Compared with Example 2, Comparative Example 1 did not add hard monomers, resulting in insufficient adhesive cohesion and a slight increase in initial tack, but a slight decrease in long-term adhesive strength. Compared with Example 2, Comparative Example 2 did not add GMA, resulting in significant residual adhesive delamination and extremely poor overall performance. Compared with Example 2, Comparative Example 3 did not use a semi-continuous method but a one-pot method, resulting in a significantly more uniform molecular weight distribution and a slight decrease in initial tack.

[0050] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. An acrylic pressure-sensitive adhesive composition, characterized in that, It consists of the following materials in parts by weight. 30-90 parts of soft monomer; 1-10 parts of hard monomer; 2-10 parts of functional monomer; Initiator: 0.01 to 2 parts.

2. The acrylic pressure-sensitive adhesive composition according to claim 1, characterized in that, The soft monomers are butyl acrylate and isooctyl acrylate; the hard monomers are methyl methacrylate and vinyl acetate; the functional monomers are acrylic acid, glycidyl methacrylate and ethoxyethoxyethyl acrylate; and the initiator is azobisisobutyronitrile.

3. The pressure-sensitive adhesive polymer according to claim 1, characterized in that, The functional monomer includes a polar group-modified monomer, wherein the polar group is a hydroxyl, epoxy, or carboxyl group.

4. The pressure-sensitive adhesive composition according to claim 1, characterized in that, The glass transition temperature is -80℃ to -20℃, and the solid content is 40% to 60%.

5. The method for preparing the pressure-sensitive adhesive composition according to any one of claims 1-4, characterized in that, Includes the following steps: (1) Mix some soft monomers, some hard monomers and some functional monomers to form a premixed liquid. Stir to form a homogeneous solution, heat to a certain temperature, add some initiator to initiate polymerization, control the temperature to a certain temperature, keep the temperature for a certain time, and obtain a prepolymer solution. (2) Adjust the temperature of the prepolymer solution to a certain temperature, add a mixture of hard monomer, initiator and solvent to the prepolymer solution, and then add the remaining soft monomer, remaining functional monomer, initiator and solvent mixture to the premixed solution. After adding, keep warm for a certain time. (3) Then add some initiator, the remaining hard monomer and some solvent, and continue to keep warm; (4) Finally, the remaining initiator and solvent are added in stages, and the temperature is maintained. After the temperature maintenance is completed, the temperature is lowered to room temperature to obtain acrylic pressure-sensitive adhesive.

6. The method for preparing the pressure-sensitive adhesive composition according to claim 5, characterized in that: In step (1), the soft monomers account for 20-90% of the total soft monomers; the hard monomers account for 10-80% of the total hard monomers; and the functional monomers account for 0-100% of the functional monomers.

7. The method for preparing the pressure-sensitive adhesive composition according to claim 5, characterized in that: In step (1), the temperature is 60~85℃.

8. The method for preparing the pressure-sensitive adhesive composition according to claim 5, characterized in that: In step (2), a portion of the hard monomers is 10-80% of the total hard monomers; the temperature is 70-90°C.

9. The method for preparing the pressure-sensitive adhesive composition according to claim 5, characterized in that: In steps (1)-(4), the heat preservation time is 1~2h.

10. A pressure-sensitive adhesive for vehicle stickers, characterized in that, The product is prepared by coating and drying the composition according to any one of claims 1 to 4. At room temperature, the peel strength is ≥2.5 N / cm, and at ≥60°C, the peel strength is ≤1.0 N / cm.

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