Preparation process and device of high-stability water-based acrylic pressure-sensitive adhesive emulsion and adhesive

Abstract

The invention discloses a high-stability water-based acrylic pressure-sensitive adhesive emulsion preparation process and device and an adhesive. The process comprises the following steps: A, preparing a pre-emulsion and an initiator solution; b, adding a proper amount of an emulsifier, a buffering agent and deionized water into a reactor to serve as first system liquid, stirring and heating to 88-90 DEG C, and then adding a proper amount of an initiator and deionized water; c, the pre-emulsion is dropwise added, the time t0 when the emulsion starts to be dropwise added is determined through timing, the initiator solution starts to be dropwise added at the time t1, the pre-emulsion and the initiator solution are dropwise added within the time T1 from the time when the pre-emulsion and the initiator solution start to be dropwise added, heat preservation is conducted at 85-88 DEG C during the dropwise adding period, heat preservation is conducted for the time T2 after dropwise adding is completed, and the time t1 is not earlier than the time t0; and D, cooling to below 50 DEG C, and adjusting the pH value to obtain the emulsion. Through collaborative design of manufacturability including segmented control, improvement of emulsion storage, high temperature and high humidity, freeze-thaw cycle stability, production stability and the like is realized.

Description

Technical Field

[0001] This invention belongs to the field of adhesive technology, specifically relating to a high-stability waterborne acrylic pressure-sensitive adhesive latex preparation process, apparatus, and adhesive, which is particularly suitable for applications such as packaging, automotive interiors, and electronic tags that have high requirements for storage environment and operating temperature range. Background Technology

[0002] Waterborne acrylic pressure-sensitive adhesives are widely used in labels, tapes, protective films, and other fields due to their environmental friendliness, non-toxicity, and safety. They are typically prepared by emulsion polymerization, a process that involves dispersing acrylate monomers (such as butyl acrylate and 2-ethylhexyl acrylate) and functional monomers (such as acrylic acid and hydroxyethyl methacrylate) in an aqueous phase using an emulsifier, followed by free radical polymerization under the action of an initiator.

[0003] However, traditional emulsion polymerization processes face numerous challenges in terms of production stability and batch stability:

[0004] Temperature control is difficult, and gelation is severe: During polymerization, especially in the later stages of the reaction, as the monomer conversion rate increases, the viscosity of the system increases, which can easily lead to local overheating or uneven mixing, resulting in a large amount of gel. This gel not only affects the product's appearance and coating performance but also adheres to the reactor walls and agitators, causing a decrease in heat transfer efficiency, further exacerbating the risk of runaway reaction, and even requiring frequent shutdowns for cleaning, seriously affecting the stability of continuous production.

[0005] Large performance fluctuations between batches: Due to insufficient precision in controlling key process parameters (such as temperature profiles, feeding methods and rates, pH control, etc.), there are differences in molecular weight and distribution, latex particle size, and monomer residue between different batches of products. This ultimately results in poor batch stability of the pressure-sensitive adhesive's holding power, initial tack, 180° peel strength, and other properties.

[0006] Inaccurate reaction control: In traditional semi-continuous dripping processes, the dripping rate usually changes during polymerization. If the dripping rate and temperature are not properly matched, it can easily lead to a state of "monomer starvation" or "monomer excess". The former results in a slow reaction rate and low production efficiency, while the latter can easily cause explosive polymerization and gel formation.

[0007] The production process is cumbersome and prone to errors: Traditional emulsion polymerization processes involve many materials and steps, and many materials require a long time to dissolve. The preparation time between steps is short, resulting in high production pressure.

[0008] Therefore, in order to address the above-mentioned technical problems, it is necessary to provide a process, apparatus, and adhesive for preparing a highly stable waterborne acrylic pressure-sensitive adhesive latex. Summary of the Invention

[0009] The purpose of this invention is to provide a process, apparatus, and adhesive for preparing a highly stable water-based acrylic pressure-sensitive adhesive latex.

[0010] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:

[0011] The preparation process of a high-stability waterborne acrylic pressure-sensitive adhesive emulsion includes the following steps:

[0012] A. Prepare the pre-emulsion and initiator solution;

[0013] B. After adding an appropriate amount of emulsifier, buffer and deionized water to the reactor as the first system liquid, stir and heat to 88-90℃, then add an appropriate amount of initiator and deionized water.

[0014] C. Add the pre-emulsion and time it to determine the start time of the emulsion addition as t0. Start adding the initiator solution at t1. The pre-emulsion and initiator solution are added within the time T1, starting from their respective start times. Keep the temperature at 85-88℃ during the addition and keep it at the temperature for T2 after the addition is completed. The time t1 is not earlier than the time t0.

[0015] D. Cool the temperature to below 50℃ and adjust the pH to obtain the emulsion.

[0016] In one or more embodiments of the present invention, in step D, after adjusting the pH, an antifoaming agent and / or a bactericide are added, wherein the antifoaming agent is selected from: silicone-based antifoaming agents or non-silicone-based antifoaming agents; the bactericide is selected from: Kathon-based agents. Preferably, the amount of antifoaming agent is 0.1-0.5 wt% of the total weight of the monomers. The amount of bactericide is 0.1-0.5 wt% of the total weight of the monomers. Preferably, the silicone-based antifoaming agent is selected from: polydimethylsiloxane, fluorosiloxane, ethylene glycol siloxane, and silicone oil. Preferably, the non-silicone-based antifoaming agent is selected from: fatty amides, metallic soaps, fatty alcohols, and fatty acid esters. More preferably, the non-silicone-based antifoaming agent is selected from: Mobilad C402.

[0017] In one or more embodiments of the present invention, the pre-emulsion comprises, by weight: 450-550 parts of soft monomer, 15-100 parts of hard monomer, 0.5-5 parts of emulsifier, 0.3-6 parts of initiator, 300-500 parts of deionized water, and an appropriate amount of pH adjuster to adjust the pH value to 7-9.

[0018] And / or the pre-emulsion also includes 3-5 parts of complex functional monomers;

[0019] And / or the pre-emulsion also includes 0.5-2 parts of buffer.

[0020] In one or more embodiments of the present invention, the soft monomer is selected from: butyl acrylate, isooctyl acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl acrylate, isononyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, hexyl (meth)acrylate, n-nonyl (meth)acrylate, isoamyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, isooctadecyl (meth)acrylate, and 2-methylbutyl (meth)acrylate.

[0021] In one or more embodiments of the present invention, the hard monomer is selected from: methyl methacrylate, methacrylic acid, methyl acrylate, acrylamide, dimethacrylamide, isobornyl (meth)acrylate, N-vinylpyrrolidone, and acrylic acid.

[0022] In one or more embodiments of the present invention, the composite functional monomer is selected from: hydroxypropyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, acrylamide, N-hydroxymethylacrylamide, maleic anhydride, and glycidyl methacrylate.

[0023] In one or more embodiments of the present invention, the emulsifier is selected from: sodium allyl sulfonate, fatty alcohol polyoxyethylene ether; and / or

[0024] The initiator is selected from: ammonium persulfate; and / or

[0025] pH adjusters are selected from: ammonia, sodium bicarbonate; and / or

[0026] The buffer is selected from: sodium bicarbonate, ammonium bicarbonate, and sodium acetate.

[0027] In one or more embodiments of the present invention, in step C, time t1 is at least 20 minutes later than time t0.

[0028] In one or more embodiments of the present invention, the heat preservation time T2 is 0.5-2h.

[0029] In one or more embodiments of the present invention, the emulsifier is sodium allyl sulfonate in a mass ratio of 1:2-4 to fatty alcohol polyoxyethylene ether. Preferably, the emulsifier is sodium allyl sulfonate in a mass ratio of 1:2.5 to fatty alcohol polyoxyethylene ether.

[0030] In one or more embodiments of the present invention, the composite functional monomer is isononyl acrylate and hydroxypropyl methacrylate in a mass ratio of 2-4:1. Preferably, the composite functional monomer is isononyl acrylate and hydroxypropyl methacrylate in a mass ratio of 3:1.

[0031] In one or more embodiments of the present invention, the soft monomer is a mixture of butyl acrylate and isooctyl acrylate in a mass ratio of 5:3; the hard monomer is methyl methacrylate.

[0032] In one or more embodiments of the present invention, the concentration of the initiator aqueous solution is 5 wt%; 30% of the total amount of initiator is added in step B, and the remaining 70% is added to the initiator solution.

[0033] In one or more embodiments of the present invention, the solid content of the pre-emulsion is 45-50 wt%.

[0034] In one or more embodiments of the present invention, an apparatus is used to implement a process.

[0035] In one or more embodiments of the present invention, the adhesive is prepared by a process.

[0036] The pressure-sensitive adhesive latex of this invention has a solid content of 48-52 wt%, a viscosity of less than 200 mPa·s, and a PDI of latex particles ≤ 0.10. The latex meets the following requirements: storage stability ≥ 12 months, high temperature and high humidity (60℃ / 90%RH) stability ≥ 500 h, and freeze-thaw cycle (-20℃ / 25℃) ≥ 10 times without demulsification.

[0037] Compared with existing technologies, the high-stability waterborne acrylic pressure-sensitive adhesive emulsion preparation process, apparatus, and adhesive of this invention solves the problems of insufficient storage, high temperature and humidity, and freeze-thaw cycle stability of existing waterborne acrylic pressure-sensitive adhesives through the synergistic design of composite functional monomer system, compound emulsifier, and segmented control process. The obtained emulsion has a storage stability of ≥12 months, a high temperature and humidity (60℃ / 90%RH) stability of ≥500h, and no emulsion breakage after ≥10 freeze-thaw cycles. Simultaneously, the 180° peel strength is ≥8.5N / 25mm, the initial tack is ≥11# ball, and the holding power is ≥96h, making it suitable for packaging, automotive interiors, electronic tags, and other fields. Through the synergistic design of the process, including segmented control, especially through the synergistic design of composite functional monomer system, compound emulsifier, and segmented control process, improvements are achieved in emulsion storage, high temperature and humidity, freeze-thaw cycle stability, and production stability. Detailed Implementation

[0038] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments disclosed herein. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0039] This invention provides a process for preparing waterborne acrylic pressure-sensitive adhesive latex with synergistic improvement in multi-dimensional stability (storage, high temperature and humidity, freeze-thaw cycle) and excellent adhesive performance.

[0040] Unless otherwise specified, the following embodiments are included, but not limited to:

[0041] The defoamer is Mobilad C402; the bactericide is Kathon-isothiazolinone; the emulsifier is fatty alcohol polyoxyethylene ether; the initiator is ammonium persulfate; and the buffer is sodium acetate.

[0042] The monomers, initiators, and solvents used in the various embodiments and comparative examples are abbreviated as follows:

[0043]

[0044] Example 1

[0045] In this embodiment, the aqueous acrylic pressure-sensitive adhesive latex is prepared as follows:

[0046] a. Take 490 parts butyl acrylate, 30 parts acrylic acid, 60 parts methyl methacrylate, 5 parts emulsifier, and 200 parts deionized water and add them to the pre-emulsification tank. Stir at high speed for more than 30 minutes to form a stable pre-emulsion. Take 2 parts initiator and 5 parts deionized water and add them to the initiator tank to form an initiator solution.

[0047] b. Take 200 parts of deionized water, 1 part of emulsifier, and 1 part of buffer and add them to the bottom of the reactor. Turn on stirring and heating.

[0048] c. Heat to 88-90℃, dissolve 2 parts of initiator in 10 parts of deionized water and add to the reactor, then start adding the pre-emulsion dropwise.

[0049] d. After the temperature drops to 85-88℃ and the pre-emulsion is added dropwise for 30 minutes, start adding the initiator solution.

[0050] e. Maintain the temperature at 85-88℃, add the pre-emulsion dropwise for a total of 4 hours; add the initiator dropwise for a total of 4 hours (ending 30 minutes later than the pre-emulsion), and keep warm for 1 hour after the dropwise addition is completed.

[0051] f. When the temperature drops below 50℃, add ammonia to adjust the pH, add 0.1wt% bactericide and 0.1wt% defoamer (based on the total weight of monomers), filter and package.

[0052] Comparative Example 1

[0053] The only difference between this comparative example and Example 1 is that:

[0054] Step d is changed to "the temperature drops to 85-88℃, and the pre-emulsion and initiator solution are added dropwise simultaneously".

[0055] Step e is changed to "Maintain the temperature at 85-88℃, add the pre-emulsion and initiator solution dropwise for 90 minutes, then cool down to 75℃, add 1 part tert-butyl hydroperoxide and 1 part sodium formaldehyde sulfoxylate, and keep warm for 20 minutes".

[0056] Comparative Example 2

[0057] The only difference between this comparative example and Example 1 is that the amount of initiator in step a is changed to 3 parts, and the amount of initiator in step c is changed to 1 part.

[0058] Comparative Example 3

[0059] The only difference between this comparative example and Example 1 is that:

[0060] Step d is changed to "the temperature drops to 85-88℃, and the pre-emulsion and initiator solution are added dropwise simultaneously".

[0061] Step e is changed to "Maintain the temperature at 85-88℃, add the pre-emulsion and initiator solution dropwise for 90 minutes, then cool down to 75℃, add 1 part tert-butyl hydroperoxide and 1 part sodium formaldehyde sulfoxylate, and keep warm for 20 minutes".

[0062] Comparative Example 4

[0063] The only difference between this comparative example and Example 1 is that the amount of initiator in step a is changed to 3 parts, and the amount of initiator in step c is changed to 1 part.

[0064] Example 2

[0065] In this embodiment, the aqueous acrylic pressure-sensitive adhesive latex is prepared as follows:

[0066] a. Take 260 parts butyl acrylate, 240 parts isooctyl acrylate, 10 parts methacrylic acid, 60 parts methyl methacrylate, 5 parts emulsifier, and 200 parts deionized water and add them to the pre-emulsion kettle. Stir at high speed for more than 30 minutes to form a stable pre-emulsion. Take 2 parts initiator and 5 parts deionized water and add them to the initiator tank to form an initiator solution.

[0067] b. Take 180 parts of deionized water, 1 part of emulsifier, and 1 part of buffer and add them to the bottom of the reactor. Turn on stirring and heating.

[0068] c. Heat to 88-90℃, dissolve 2 parts of initiator in 10 parts of deionized water and add to the reactor, then start adding the pre-emulsion dropwise.

[0069] d. After the temperature drops to 85-88℃ and the pre-emulsion is added dropwise for 30 minutes, start adding the initiator solution.

[0070] e. Maintain the temperature at 85-88℃, add the pre-emulsion dropwise for a total of 4 hours; add the initiator dropwise for a total of 4 hours (ending 30 minutes later than the pre-emulsion), and keep warm for 1 hour after the dropwise addition is completed.

[0071] f. When the temperature drops below 50℃, add ammonia to adjust the pH, add 0.1wt% bactericide and 0.3wt% defoamer (based on the total weight of monomers), filter and package.

[0072] Furthermore, a balance between stability and adhesion performance can be achieved through the synergistic design of "multifunctional monomers regulating molecular structure + compound emulsifiers optimizing interface performance".

[0073] Example 11

[0074] The only difference between this embodiment and Embodiment 1 is that it also includes a composite functional monomer: 3 parts isononyl acrylate and 1 part hydroxypropyl methacrylate.

[0075] Example 12

[0076] The only difference between this embodiment and Embodiment 11 is that the composite functional monomer is replaced with 4 parts of isononyl acrylate and 1 part of hydroxypropyl methacrylate.

[0077] Example 13

[0078] The only difference between this embodiment and Embodiment 11 is that the composite functional monomer is replaced with 2 parts of isononyl acrylate and 1 part of hydroxypropyl methacrylate.

[0079] Example 14

[0080] The only difference between this embodiment and Example 11 is that the emulsifier is replaced with a mixture of 2 parts sodium allyl sulfonate and 5 parts fatty alcohol polyoxyethylene ether, wherein 5 parts of the mixture are added to the pre-emulsion and 2 parts are added to the bottom of the reactor.

[0081] Example 15

[0082] The only difference between this embodiment and Example 11 is that the emulsifier is replaced with a mixture of 2 parts sodium allyl sulfonate and 4 parts fatty alcohol polyoxyethylene ether, wherein 5 parts of the mixture are added to the pre-emulsion and 1 part is added to the bottom of the reactor.

[0083] Example 16

[0084] The only difference between this embodiment and Example 11 is that the emulsifier is replaced with a mixture of 1 part sodium allyl sulfonate and 4 parts fatty alcohol polyoxyethylene ether, wherein 3.5 parts of the mixture are added to the pre-emulsion and 1 part is added to the bottom of the reactor.

[0085] The following performance tests were performed on the waterborne acrylic pressure-sensitive adhesives prepared in each embodiment and Comparative Examples 1-4:

[0086]

[0087] Among them, the 180° peel strength test was conducted according to the GB 2792-1998 test method for 180° peel strength of pressure-sensitive adhesive tape.

[0088] This invention employs an alternating dripping method of pre-emulsion and initiator solution: the pre-emulsion is added first, followed by the initiator solution after a 30-minute delay, extending the total dripping time to 4 hours, with the initiator solution being added 30 minutes later than the pre-emulsion. After the dripping is complete, the solution is allowed to mature at a controlled temperature; no further cleanup is required.

[0089] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from the spirit or essential characteristics of this disclosure. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this disclosure.

[0090] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A process for preparing a highly stable waterborne acrylic pressure-sensitive adhesive latex, comprising the following steps: A. Prepare the pre-emulsion and initiator solution; B. After adding an appropriate amount of emulsifier, buffer and deionized water to the reactor as the first system liquid, stir and heat to 88-90℃, then add an appropriate amount of initiator and deionized water. C. Add the pre-emulsion and time it to determine the start time of the emulsion addition as t0. Start adding the initiator solution at t1. The pre-emulsion and initiator solution are added within the time T1, starting from the time they start adding. Keep the temperature at 85-88℃ during the addition and keep the temperature at T2 after the addition is completed. The time t1 is not earlier than the time t0. D. Cool the temperature to below 50℃ and adjust the pH with a pH adjuster to obtain the emulsion.

2. The process according to claim 1, characterized in that, In step D, after adjusting the pH, an antifoaming agent and / or a bactericide are added, wherein the antifoaming agent is selected from: silicone-based antifoaming agents or non-silicone-based antifoaming agents; and the bactericide is selected from: Kathon-based agents.

3. The process according to claim 1, characterized in that, The pre-emulsion comprises, by weight: 450-550 parts soft monomer, 15-100 parts hard monomer, 0.5-5 parts emulsifier, 0.3-6 parts initiator, 300-500 parts deionized water, and an appropriate amount of pH adjuster to adjust the pH value to 7-9. And / or, the preemulsion also includes 3-5 parts of a complex functional monomer; And / or, the preemulsion may also include 0.5-2 parts of buffer.

4. The process according to claim 3, characterized in that, The soft monomer is selected from: butyl acrylate, isooctyl acrylate, 2-ethylhexyl (meth)acrylate, n-octyl (meth)acrylate, isooctyl (meth)acrylate, isononyl acrylate, isononyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, hexyl (meth)acrylate, n-nonyl (meth)acrylate, isoamyl (meth)acrylate, n-decyl (meth)acrylate, isodecyl (meth)acrylate, dodecyl (meth)acrylate, isooctadecyl (meth)acrylate, and 2-methylbutyl (meth)acrylate.

5. The process according to claim 3, characterized in that, The hard monomer is selected from: acrylic acid, methyl methacrylate, methacrylic acid, methyl acrylate, acrylamide, dimethacrylamide, isobornyl methacrylate, and N-vinylpyrrolidone.

6. The process according to claim 3, characterized in that, The composite functional monomers are selected from: hydroxypropyl methacrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, acrylamide, N-hydroxymethylacrylamide, maleic anhydride, and glycidyl methacrylate.

7. The process according to claim 3, characterized in that, The emulsifier is selected from: sodium allyl sulfonate, fatty alcohol polyoxyethylene ether; and / or The initiator is selected from: ammonium persulfate; and / or The pH adjuster is selected from: ammonia, sodium bicarbonate; and / or The buffer is selected from: sodium bicarbonate, ammonium bicarbonate, and sodium acetate.

8. The process according to claim 1, characterized in that, In step C, time t1 is at least 20 minutes later than time t0.

9. An apparatus for performing the process according to any one of claims 1-8.

10. An adhesive prepared by the process according to any one of claims 1-8.

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