Low odor / low blush structural instant adhesive and method of making same

Abstract

The present application provides a low odor / low whitening structure instant adhesive and a preparation method thereof. The low odor / low whitening structure instant adhesive comprises 70-90 wt% of cyano acrylate, 3-20 wt% of acrylic acid copolymer, 1-13 wt% of fumed silica, 0.2-2 wt% of plasticizer, 0.1-1 wt% of carbon black and 0-0.05 wt% of additive in terms of mass fraction. The present application selects ultra-high purity monomers in the environment of low polymerization inhibitor, which can significantly shorten the polymerization induction period, so that the monomer can be instantaneously initiated and completely cured after contacting the surface of the substrate, thereby minimizing the release of volatile monomers into the environment, further reducing the gaseous monomer that causes respiratory tract / mucosa irritation from the source, and inhibiting the polymerization of volatile monomers in the air to form white powder.

Description

Technical Field

[0001] This invention relates to the field of instant adhesive technology, specifically to a low-odor / low-whitening instant adhesive and its preparation method. Background Technology

[0002] Cyanoacrylate adhesives (CAs) are a unique type of single-component, solvent-free, instant-curing adhesive. Their core curing mechanism stems from their unique molecular structure: the α-carbon atom is simultaneously connected to both a strongly electron-withdrawing cyano group (-CN) and an ester group (-COOR). This structure produces a significant inductive effect, resulting in the α-carbon atom exhibiting high electrophilicity. Trace amounts of anions (such as hydroxide ions) present in the environment or on the substrate surface... Initiated by substances such as water, alcohols, or amines, or by weakly alkaline substances, this molecule can undergo anionic polymerization instantaneously. This reaction has an extremely high chain growth rate, allowing the adhesive to form a strong polymer network within seconds to tens of seconds, achieving highly efficient bonding. Therefore, this type of adhesive is often called "instant adhesive."

[0003] Although cyanoacrylate adhesives are widely used in many fields such as medical, electronics, model making, and routine repair due to their ease of use, rapid curing, and high bond strength, their inherent material properties also bring significant limitations. The main disadvantages include:

[0004] (1) The cured polymer network has high rigidity but insufficient toughness. It fails by cracking under peeling force and impact load, and is brittle.

[0005] (2) The glass transition temperature is relatively low, and the operating temperature is usually no more than 80~100℃. It is easy to soften or decompose at high temperatures.

[0006] (3) Long-term exposure to a humid and hot environment will reduce the bonding strength, especially under acidic or alkaline conditions, it is prone to hydrolytic degradation and has poor water resistance;

[0007] (4) Because the volatiles of low molecular weight ester monomers are irritating to the skin and mucous membranes (such as eyes and respiratory tract), and the volatile monomers rapidly polymerize when they come into contact with moisture in the air near the bonding area, forming a white powdery polymer residue that is visible to the naked eye, i.e., the "whitening" phenomenon, which affects the appearance and function of precision parts.

[0008] Among the cyanoacrylate family, ethyl cyanoacrylate dominates the market due to its superior overall performance. However, precisely because of its relatively low molecular weight and high volatility, the ethyl acrylate monomer is more prone to volatilization during the curing process, resulting in particularly prominent irritation and whitening problems. This severely restricts its further promotion and market share increase in applications requiring higher environmental friendliness, aesthetics, and user comfort.

[0009] To address the whitening and irritation issues of ethyl cyanoacrylate, existing technologies primarily employ the following two strategies for improvement:

[0010] (1) Use cyanoacrylate monomers with larger molecular weight and significantly reduced volatility to replace ethyl ester. For example, patent CN112826976A discloses a technical solution for preparing low whitening adhesives using n-octyl cyanoacrylate as the main component. The low volatility of high molecular weight monomers effectively reduces the formation of whitening products.

[0011] (2) Introducing specific additives into the ethyl cyanoacrylate system to inhibit volatilization or accelerate surface curing. For example, patent CN101967354A improves the curing of ethyl acrylate plastics and reduces whitening by adding calixarene as an accelerator. Patent CN 115362230A prepares a low-irritation, low-whitening adhesive by using β-alkoxyalkyl aminoacrylate.

[0012] Current technologies primarily reduce whitening by adding accelerators or replacing them with cyanoacrylates of higher molecular weight. However, introducing other accelerators may introduce unknown biological safety concerns, and completely replacing them with cyanoacrylate alkoxy compounds would increase costs, limiting their further development.

[0013] Therefore, developing a novel adhesive formulation that can effectively overcome the inherent irritation and whitening defects of ethyl cyanoacrylate while retaining its core advantages of rapid curing, strong adhesion, and low cost to the maximum extent has become a key technical challenge that urgently needs to be addressed in this field. Summary of the Invention

[0014] To address the shortcomings of existing technologies, this invention provides a low-odor / low-whitening instant adhesive and its preparation method. By increasing the reaction rate of cyanoacrylate, the volatilization of monomers in the adhesive during the bonding process is reduced, thereby reducing the irritating odor and whitening phenomenon of cyanoacrylate adhesives during use, thus solving the problems mentioned in the background art.

[0015] To achieve the above objectives, the present invention provides the following technical solution:

[0016] According to a first aspect of the present invention, a low-odor / low-whitening structural instant adhesive is provided, comprising, by mass fraction, 70-90 wt% cyanoacrylate, 3-20 wt% acrylic copolymer, 1-13 wt% fumed silica, 0.2-2 wt% plasticizer, 0.1-1 wt% carbon black and 0-0.05 wt% additives, wherein the sum of the mass fractions of all components is 100 wt%.

[0017] Preferably, the low-odor / low-whitening structural instant adhesive comprises, by mass fraction, 75-85 wt% cyanoacrylate, 8-14 wt% acrylic copolymer, 5-10 wt% fumed silica, 0.5-1 wt% plasticizer, 0.3-0.5 wt% carbon black, and 0.005-0.01 wt% additives, with the sum of the mass fractions of all components being 100 wt%.

[0018] Preferably, the cyanoacrylate is selected from at least one of ethyl cyanoacrylate, methoxyethyl cyanoacrylate, n-butyl cyanoacrylate, and n-octyl cyanoacrylate.

[0019] More preferably, the cyanoacrylate is selected from a composition of ethyl cyanoacrylate and n-butyl cyanoacrylate, and in the low-odor / low-whitening structure instant adhesive, the mass fraction of ethyl cyanoacrylate is 52~59wt% and the mass fraction of n-butyl cyanoacrylate is 18~28wt%.

[0020] The composition selected from ethyl cyanoacrylate and n-butyl cyanoacrylate does not impair the polymerization activity, while maintaining the instantaneous drying characteristic of the curing speed. Combined with the acrylic copolymer, its fine particles act as physical crosslinking points in the curing network, which helps to improve the final bond strength.

[0021] Preferably, the anionic polymerization inhibitor content in the ethyl cyanoacrylate is less than 20 ppm, and the anionic polymerization inhibitor content in both methoxyethyl cyanoacrylate and n-butyl cyanoacrylate is less than 40 ppm.

[0022] More preferably, the content of anionic polymerization inhibitor in ethyl cyanoacrylate is less than 16 ppm, and the content of anionic polymerization inhibitor in n-butyl cyanoacrylate is less than 25 ppm.

[0023] Preferably, the acrylic copolymer is selected from at least one of methyl methacrylate, ethylene-methyl acrylate copolymer, and styrene-methyl acrylate copolymer.

[0024] More preferably, the acrylic copolymer is a composition of polymethyl methacrylate and styrene-methyl acrylate copolymer, wherein in the low-odor / low-whitening structure instant adhesive, the mass fraction of polymethyl methacrylate is 6.4~11.2wt% and the mass fraction of styrene-methyl acrylate copolymer is 1.6~2.8wt%.

[0025] Preferably, the acrylic copolymer has a particle size greater than 300 mesh.

[0026] More preferably, the acrylic copolymer has a particle size greater than 500 mesh.

[0027] Preferably, the fumed silica is hydrophobically modified silica, and the pH of the hydrophobically modified silica is 5-7.

[0028] More preferably, the pH of the hydrophobic modified silica is 5.5 to 6.5.

[0029] This application selects hydrophobically modified silica with a pH of 5.5 to 6.5 as a thixotropic agent. Its hydrophobic properties effectively inhibit moisture from entering the environment and causing thixotropy, while providing excellent anti-sagging and storage stability.

[0030] Preferably, the plasticizer is selected from at least one of tributyl citrate, acetylated tributyl citrate, and trioctyl citrate.

[0031] Preferably, the pH of the carbon black is 5 to 7.5.

[0032] Preferably, the pH of the carbon black is 6-7.

[0033] Preferably, the additive includes anionic polymerization inhibitors and free radical polymerization inhibitors, wherein the anionic polymerization inhibitor is selected from at least one of p-toluenesulfonic acid, phosphoric acid, fluoroboric acid, boron trifluoride ether, and SO2 gas;

[0034] The free radical polymerization inhibitor is selected from at least one of p-phenol, p-hydroxyanisole, and p-tert-butylcatechol.

[0035] More preferably, the anionic polymerization inhibitor is selected from boron trifluoride ethyl ether, and the free radical polymerization inhibitor is selected from p-hydroxyanisole.

[0036] According to a second aspect of the present invention, a method for preparing a low-odor / low-whitening structural instant adhesive is provided, comprising the following steps:

[0037] Step 1: Mix cyanoacrylate, fumed silica, plasticizer, carbon black and additives in a sealed reaction vessel at room temperature;

[0038] Step 2: Add the acrylic copolymer while stirring, introduce nitrogen gas and seal, then stir evenly using a disc stirrer.

[0039] This invention provides a low-odor / low-whitening instant adhesive and its preparation method. It has the following beneficial effects:

[0040] (1) The present solution provides a low-odor / low-whitening structured instant adhesive. By selecting ultra-high purity monomers in an environment with low polymerization inhibitors, the polymerization induction period can be significantly shortened, so that the monomers can be instantly initiated and completely cured after contacting the substrate surface, minimizing the release of volatile monomers into the environment. In turn, it reduces the gaseous monomers that cause respiratory / mucous membrane irritation from the source and inhibits the polymerization of volatile monomers in the air to form white powder.

[0041] (2) The present solution provides a low-odor / low-whitening structured instant adhesive, which introduces nano-sized carbon black particles to adjust the color of the adhesive, effectively covering the whitening phenomenon at the edges of cyanoacrylate during the curing process. At the same time, the carbon black selected from pH 5~7.5 can ensure that its acidity and alkalinity will not interfere with the anionic polymerization reaction of cyanoacrylate or cause instability of the system.

[0042] (3) The present solution provides a low-odor / low-whitening structured instant adhesive, which provides prepolymer network nodes through acrylic copolymer to accelerate local curing, and hydrophobic vapor phase silica balances thixotropic thickening to inhibit moisture-induced prepolymerization, thereby synergistically reducing monomer volatilization and the generation of whitening phenomenon.

[0043] (4) The present solution provides a low-odor / low-whitening instant adhesive. Through the combination of ultra-high purity monomer accelerated curing and nano carbon black physical masking, while maintaining the advantages of ethyl cyanoacrylate, it does not introduce exogenous additives with potential biosafety risks, and achieves low-odor and low-whitening instant adhesive without increasing costs. Detailed Implementation

[0044] To better illustrate the content of this invention, the following description is provided in conjunction with specific embodiments.

[0045] Example 1

[0046] A method for preparing a low-odor / low-whitening instant adhesive is as follows:

[0047] (1) Raw material weighing: 70 wt% of ethyl cyanoacrylate with an anionic polymerization inhibitor content of 18 ppm, 16.199 wt% of methyl methacrylate with an average particle size of 350 mesh, 13 wt% of hydrophobically modified silica with pH 6, 0.1 wt% of carbon black with pH 6, 0.7 wt% of tributyl limonene, and 0.001 wt% of a mixture of boron trifluoride ethyl ether and p-hydroxyanisole;

[0048] (2) Mix ethyl cyanoacrylate, hydrophobically modified silica, tributyl citric acid, carbon black, boron trifluoride ethyl ether and p-hydroxyanisole in a sealed reactor at room temperature;

[0049] (3) Add methyl methacrylate while stirring, then seal after passing nitrogen gas through, and stir evenly using a disc stirrer.

[0050] Example 2

[0051] The preparation method of this embodiment is the same as that of Example 1, except that in step (1), the mass fraction of ethyl cyanoacrylate is 82 wt%, the mass fraction of methyl methacrylate is 11.199 wt%, and the mass fraction of hydrophobic modified fumed silica is 6 wt%.

[0052] Example 3

[0053] The preparation method of this embodiment is the same as that of the previous embodiment, except that in step (1), the mass fraction of ethyl cyanoacrylate is 90 wt%, the mass fraction of methyl methacrylate is 6.199 wt%, and the mass fraction of hydrophobic modified fumed silica is 3 wt%.

[0054] Example 4

[0055] The preparation method of this embodiment is the same as that of Example 1, except that: the mass fraction of ethyl cyanoacrylate with an anionic polymerization inhibitor content of 18 ppm is 82 wt%, the mass fraction of methyl methacrylate with an average particle size of 350 mesh is 10.899 wt%, the mass fraction of hydrophobically modified silica with pH 6 is 6 wt%, the mass fraction of carbon black with pH 6 is 0.4 wt%, the mass fraction of tributyl limonene is 0.7 wt%, and the mass fraction of the mixture of boron trifluoride ethyl ether and p-hydroxyanisole is 0.001 wt%.

[0056] Example 5

[0057] The preparation method of this embodiment is the same as that of Example 1, except that: the mass fraction of ethyl cyanoacrylate with an anionic polymerization inhibitor content of 18 ppm is 82 wt%, the mass fraction of methyl methacrylate with an average particle size of 350 mesh is 10.399 wt%, the mass fraction of hydrophobically modified silica with pH 6 is 6 wt%, the mass fraction of carbon black with pH 6 is 0.8 wt%, the mass fraction of tributyl citric acid is 0.7 wt%, and the mass fraction of the mixture of boron trifluoride ethyl ether and p-hydroxyanisole is 0.001 wt%.

[0058] Example 6

[0059] The preparation method of this embodiment is the same as that of Example 1, except that: the mass fraction of ethyl cyanoacrylate with an anionic polymerization inhibitor content of 18 ppm is 82 wt%, the mass fraction of methyl methacrylate with an average particle size of 350 mesh is 10.892 wt%, the mass fraction of hydrophobically modified silica with pH 6 is 6 wt%, the mass fraction of carbon black with pH 6 is 0.4 wt%, the mass fraction of tributyl limonene is 0.7 wt%, and the mass fraction of the mixture of boron trifluoride ethyl ether and p-hydroxyanisole is 0.008 wt%.

[0060] Example 7

[0061] The preparation method of this embodiment is the same as that of Example 1, except that: the mass fraction of ethyl cyanoacrylate with an anionic polymerization inhibitor content of 18 ppm is 82 wt%, the mass fraction of methyl methacrylate with an average particle size of 350 mesh is 10.87 wt%, the mass fraction of hydrophobically modified silica with pH 6 is 6 wt%, the mass fraction of carbon black with pH 6 is 0.4 wt%, the mass fraction of tributyl citric acid is 0.7 wt%, and the mass fraction of the mixture of boron trifluoride ethyl ether and p-hydroxyanisole is 0.030 wt%.

[0062] Example 8

[0063] The preparation method of this embodiment is the same as that of Example 1, except that: the mass fraction of ethyl cyanoacrylate with an anionic polymerization inhibitor content of 15 ppm is 55 wt%, the mass fraction of n-butyl cyanoacrylate with an anionic polymerization inhibitor content of 20 ppm is 28 wt%, the mass fraction of polymethyl methacrylate with an average particle size of 550 mesh is 8.292 wt%, the mass fraction of styrene-methyl acrylate copolymer with an average particle size of 550 mesh is 1.6 wt%, the mass fraction of hydrophobically modified silica with pH 6 is 6 wt%, the mass fraction of carbon black with pH 6 is 0.4 wt%, the mass fraction of tributyl limonene is 0.7 wt%, and the mass fraction of the mixture of boron trifluoride ethyl ether and p-hydroxyanisole is 0.008 wt%.

[0064] Comparative Example 1

[0065] The comparative example was prepared using the same method as Example 1, except that the mass fraction of ethyl cyanoacrylate was 60 wt%, the mass fraction of methyl methacrylate was 23.199 wt%, and the mass fraction of hydrophobic modified silica was 16 wt%.

[0066] Comparative Example 2

[0067] The comparative example was prepared using the same method as Example 1, except that the mass fraction of ethyl cyanoacrylate was 95 wt%, the mass fraction of methyl methacrylate was 2.199 wt%, and the mass fraction of hydrophobic modified silica was 2 wt%.

[0068] Comparative Example 3

[0069] The comparative example was prepared using the same method as Example 1, except that: the mass fraction of ethyl cyanoacrylate was 82 wt%, the mass fraction of methyl methacrylate was 10.2 wt%, the mass fraction of hydrophobically modified silica was 6 wt%, the mass fraction of carbon black was 1 wt%, the mass fraction of tributyl citric acid was 0.7 wt%, and the mass fraction of the mixture of boron trifluoride ethyl ether and p-hydroxyanisole was 0.1 wt%.

[0070] The performance tests of the instant adhesives obtained in Examples 1 to 8 and Comparative Examples 1 to 3 of the present invention are shown in Table 1.

[0071] Irritation test: The sample is bonded with instant adhesive. Timing starts after the sample is bonded. If no irritating odor is detected within 5 seconds after bonding, it is considered to be extremely low irritation. If the odor dissipates within 5 to 10 seconds, it is considered to be very low irritation. If the odor dissipates within 10 to 15 seconds, it is considered to be low irritation. If the odor dissipates within 15 to 20 seconds, it is considered to be moderate irritation. If the odor dissipates for more than 20 seconds, it is considered to be high irritation.

[0072] Whitening degree test: Apply instant adhesive to a sealed transparent glass box and leave it at room temperature of 25°C and humidity of 65% for 10 hours. Observe the whitening degree of the glass box with and without instant adhesive. The whitening range diffusion distance is less than 1mm, which is considered almost no whitening. The whitening range diffusion distance is considered slight whitening. The whitening range diffusion distance is considered obvious whitening. The whitening range diffusion distance is >6mm, which is considered severe whitening.

[0073] Stability Test: The initial viscosity of the whitening adhesive was tested according to the method of HG / T 2492-2018. Then, the viscosity of the whitening adhesive after being kept at 70±2℃ for 120h was tested. The stability of the whitening adhesive was judged by the ratio of the viscosity after 120h to the initial viscosity. A viscosity ratio of 1.6~2 was considered as no thickening, a viscosity ratio of 2~3 was considered as no significant thickening, a viscosity ratio of 3~4.5 was considered as slight thickening, a viscosity ratio of 4.5~7 was considered as slight thickening, a viscosity ratio of 7~13 was considered as significant thickening, a viscosity ratio of 13~30 was considered as excessive thickening, and a viscosity ratio >30 was considered as gel-like.

[0074] Table 1

[0075]

[0076] A comparison of the data from Examples 1 to 3 in Table 1 shows that the purity of cyanoacrylate meets the standard. Excessive fumed silica content slightly reduces the heterogeneous curing rate, while insufficient fumed silica content leads to decreased storage stability. In addition, insufficient carbon black content results in a small amount of whitening residue.

[0077] Data from Examples 4 and 5 show that increasing the carbon black content significantly enhances the masking and whitening effect. However, excessive carbon black leads to dispersion difficulties and significantly reduces the shear strength of cyanoacrylate-structured instant adhesives.

[0078] Data from Examples 6 and 7 show that increasing the amount of additives can significantly improve the storage stability of adhesives. However, excessively high levels of polymerization inhibitors will reduce the reaction rate of cyanoacrylate monomers, resulting in decreased shear strength of the adhesives and increased whitening and irritation.

[0079] Example 8 represents the optimal combination, which, through the synergistic reduction of volatilization by dicyanoacrylate monomers, the enhancement of the network structure by ultrafine copolymer powder, and the combination of appropriate carbon black and fumed silica, can simultaneously reduce irritating odors and whitening phenomena.

[0080] Comparative data from Examples 1 to 3 show that the whitening phenomenon in ethyl cyanoacrylate-based adhesives can be adjusted by adding an appropriate amount of carbon black. However, excessive carbon black should be avoided as it can cause dispersion difficulties and affect bond strength. The irritation and bond strength of the adhesive can be controlled by the cyanoacrylate component and other additives. The faster the monomer reaction rate, the lower the irritation, the higher the shear strength, and the worse the stability of the adhesive. Comparisons show that the optimized cyanoacrylate structural adhesive possesses the best overall performance.

[0081] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A low-odor / low-whitening structural instant adhesive, characterized in that: By mass fraction, it includes 70-90 wt% cyanoacrylate, 3-20 wt% acrylic acid copolymer, 1-13 wt% fumed silica, 0.2-2 wt% plasticizer, 0.1-1 wt% carbon black, and 0-0.05 wt% additives, with the sum of the mass fractions of all components being 100 wt%. The cyanoacrylate is selected from at least one of ethyl cyanoacrylate, methoxyethyl cyanoacrylate, n-butyl cyanoacrylate, and n-octyl cyanoacrylate. The content of anionic polymerization inhibitor in the ethyl cyanoacrylate is less than 20 ppm; The content of anionic polymerization inhibitor in both methoxyethyl cyanoacrylate and n-butyl cyanoacrylate is less than 40 ppm. The acrylic copolymer has a particle size greater than 300 mesh; The fumed silica is hydrophobically modified silica, and the pH of the hydrophobically modified silica is 5-7; The pH of the carbon black is 5-7.5; The additives include anionic polymerization inhibitors and free radical polymerization inhibitors, wherein the anionic polymerization inhibitors are selected from boron trifluoride ethyl ether.

2. The low-odor / low-whitening structural instant adhesive according to claim 1, characterized in that: The acrylic copolymer is selected from at least one of methyl methacrylate, ethylene-methyl acrylate copolymer, and styrene-methyl acrylate copolymer.

3. The low-odor / low-whitening structural instant adhesive according to claim 1, characterized in that: The plasticizer is selected from at least one of tributyl citrate, acetylated tributyl citrate, and trioctyl citrate.

4. The low-odor / low-whitening structural instant adhesive according to claim 1, characterized in that: The free radical polymerization inhibitor is selected from at least one of p-phenol, p-hydroxyanisole, and p-tert-butylcatechol.

5. A method for preparing a low-odor / low-whitening instant adhesive according to any one of claims 1 to 4, characterized in that: Includes the following steps: Step 1: Mix cyanoacrylate, fumed silica, plasticizer, carbon black and additives in a sealed reaction vessel at room temperature; Step 2: Add the acrylic copolymer while stirring, introduce nitrogen gas and seal, then stir evenly using a disc stirrer.

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