TPO-free environment-friendly UV photocuring center glue and preparation method thereof

Abstract

The TPO-free environment-friendly UV photocuring center glue comprises the following components in percentage: a prepolymer, an active diluting monomer, a filler, a photoinitiator and an auxiliary agent, the prepolymer is an acrylate oligomer, and the acrylate oligomer comprises urethane acrylate, epoxy acrylate and epoxy resin; the active diluting monomer is an acrylate monomer; and the photoinitiators comprise a TPO-L photoinitiator, a BAPO photoinitiator and a TMO photoinitiator. The center glue disclosed by the invention does not contain solvent components and TPO, has the characteristics of short curing time, low volume shrinkage, good stability, good waterproofness, high temperature resistance, moisture resistance, weather resistance, low toxicity and low corrosion, and can not only meet the assembly quality requirement, but also meet the loudspeaker tone quality requirement; and the requirement of safe production is met, and stable bonding strength can be provided without damaging the surface effect of a bonded object. The device can also normally work in machines used in different temperature and humidity environments; the practicability is high.

Description

Technical Field

[0001] The invention relates to the technical field of UV adhesives, and in particular to a TPO-free environmentally friendly UV light-curing central adhesive for speakers and a preparation method thereof. Background Art

[0002] The center glue is a glue used to bond the diaphragm and voice coil of headphones, mobile phones, tablets, and laptop speakers. The stability of the adhesion between the diaphragm and the voice coil plays a key role in the sound quality and life of headphones, mobile phones, tablets, and laptop speakers; therefore, the role of the center glue used to bond the diaphragm and the voice coil is particularly important. At present, the center glue used for domestic speaker diaphragms and voice coils is mostly solvent-based adhesives. However, this type of solvent-based adhesive generally has problems such as inaccurate drying time, high volume shrinkage, unstable dry glue amount, easy yellowing of the colloid, and easy corrosion of the product structure by the solvent. These defects make it difficult for solvent-based adhesives to meet the needs of the current automated production line of speaker factories. Therefore, it is a general trend to replace solvent-based adhesives with UV light-curing adhesives that are solvent-free, fast curing, and controllable reaction, which are suitable for automated production lines.

[0003] However, the common UV light-curing center glue on the market has defects such as long curing time, unstable chemical properties, poor moisture and weather resistance, easy softening at high temperature or even loss of adhesion. These defects will cause the finished speakers made with this center glue to have deteriorated sound quality or even internal structural damage during subsequent testing and use. In addition, most UV light-curing center glues widely use TPO photoinitiators. The European Chemicals Agency (ETHA) has officially announced in 2023 that TPO, (2,4,6-trimethylbenzoyl) diphenylphosphine oxide, will be included in the 29th batch of Substances of Very High Concern (SVHC) candidate list because TPO contains reproductive toxicity and there is a risk of damaging the fertility of production and processing personnel. Summary of the invention

[0004] To this end, the purpose of the present invention is to provide a TPO-free environmentally friendly UV light-curing center glue for speakers and a preparation method thereof to solve the problems in the background technology.

[0005] To achieve the above purpose, the present invention mainly adopts the following technical solutions:

[0006] A TPO-free environment-friendly UV light-curing central adhesive comprises the following percentage components: 30-60% prepolymer; 20-60% active diluent monomer; 1-5% filler; 0.1-6% photoinitiator; 0-3% auxiliary agent; wherein the prepolymer is an acrylate oligomer, and the acrylate oligomer comprises polyurethane acrylate, epoxy acrylate, and epoxy resin with a carbon-carbon chain as the main chain; the active diluent monomer is an acrylate monomer; the filler is one or more of fumed silica, aluminum hydroxide powder, and titanium dioxide; the photoinitiator comprises 2,4,6-trimethylbenzoylphenylphosphonic acid ethyl ester (TPO-L photoinitiator), phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO photoinitiator) and 2,4,6-trimethylbenzoyl-di(p-tolyl)phosphine oxide (TMO photoinitiator).

[0007] Furthermore, the total addition amount of the three photoinitiators, TPO-L, BAPO and TMO, is about 5.5%.

[0008] Furthermore, the BAPO accounts for less than 10% of the total content of the photoinitiator, and the mass ratio of TPO-L to TMO is between 30:70 and 45:55.

[0009] Furthermore, the filler is small-particle fumed silica.

[0010] Furthermore, the auxiliary agent is a fluorescent brightener, a thixotropic agent and a defoaming agent.

[0011] Furthermore, the active diluent monomer is one or more of methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, propyl acrylate, hydroxypropyl acrylate, butyl acrylate, cyclohexyl acrylate, isooctyl acrylate, isodecyl acrylate, isobornyl acrylate, tetrahydrofurfuryl acrylate, methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, propyl methacrylate, hydroxypropyl methacrylate, butyl methacrylate, isobornyl methacrylate, tetrahydrofurfuryl methacrylate, and 3,3,5-trimethylcyclohexyl acrylate.

[0012] A method for preparing a TPO-free environmentally friendly UV light-curing central adhesive comprises the following steps:

[0013] Step 1, provide the following percentage components: prepolymer 30-60%; active diluent monomer 20-60%; filler 1-5%; photoinitiator 0.1-6%; auxiliary agent 0-3%; wherein the prepolymer is an acrylate oligomer, and the acrylate oligomer includes polyurethane acrylate, epoxy acrylate, and epoxy resin with a carbon-carbon chain as the main chain; the active diluent monomer is an acrylate monomer; the filler is one or more of fumed silica, aluminum hydroxide powder, and titanium dioxide; the photoinitiator includes 2,4,6-trimethylbenzoylphenylphosphonic acid ethyl ester (TPO-L photoinitiator), phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO photoinitiator) and 2,4,6-trimethylbenzoyl-di(p-tolyl)phosphine oxide (TMO photoinitiator).

[0014] Step 2: Dissolve 0.1-6% of the photoinitiator in 20-60% of the active diluent monomer, control the temperature to 20-30°C and stir to disperse evenly. After all the solids are dissolved, add 30-60% of the prepolymer, continue stirring at 30-40°C for 30 minutes, and finally slowly add the filler and additives in the formula amount in sequence, stir for 40-60 minutes until the mixture is evenly mixed to obtain the finished product.

[0015] Furthermore, in step 2, after adding the filler and the additive, the reactor needs to be evacuated to remove tiny bubbles in the glue solution.

[0016] Furthermore, the total addition amount of the three photoinitiators, TPO-L, BAPO and TMO, is about 5.5%.

[0017] Furthermore, the BAPO accounts for less than 10% of the total content of the photoinitiator, and the mass ratio of TPO-L to TMO is between 30:70 and 45:55.

[0018] Furthermore, the filler is small-particle fumed silica.

[0019] Furthermore, the auxiliary agent is a fluorescent brightener, a thixotropic agent and a defoaming agent.

[0020] Furthermore, the active diluent monomer is one or more of methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, propyl acrylate, hydroxypropyl acrylate, butyl acrylate, cyclohexyl acrylate, isooctyl acrylate, isodecyl acrylate, isobornyl acrylate, tetrahydrofurfuryl acrylate, methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, propyl methacrylate, hydroxypropyl methacrylate, butyl methacrylate, isobornyl methacrylate, tetrahydrofurfuryl methacrylate, and 3,3,5-trimethylcyclohexyl acrylate.

[0021] In summary, the TPO-free environmentally friendly UV light-curing center glue of the present invention has the characteristics of being free of solvent components, free of TPO, short curing time, low volume shrinkage, good stability, good waterproofness, high temperature resistance, moisture resistance, weather resistance, low toxicity, and low corrosion. It can meet the quality requirements of the sound membrane and voice coil combination of headphones, mobile phones, tablets, and laptop speakers, and at the same time meet the sound quality requirements of the speakers; and meet the requirements of safe production, and can provide stable bonding strength without destroying the surface effect of the adhered object. In addition, headphones, mobile phones, tablets, and laptops will be exposed to various temperature and humidity environments for a long time during transportation and use. In high temperature environments or high-intensity use, the equipment will also generate heat, causing the speakers to be in a relatively high temperature environment. The environmentally friendly UV light-curing center glue of the present invention will not soften at high temperatures, resulting in a significant decrease in bonding strength, and the speakers can work normally in machines used in different temperature and humidity environments; it is highly practical and has a strong promotional significance. DETAILED DESCRIPTION

[0022] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below.

[0023] The present invention provides a TPO-free environmentally friendly UV light-curing center adhesive, and particularly relates to an ultraviolet curing adhesive for bonding the diaphragm and voice coil of earphones, mobile phones, tablets, and laptop speakers. The TPO-free environmentally friendly UV light-curing center adhesive comprises: prepolymer, reactive diluent monomer, filler, photoinitiator, and auxiliary agent; the content of each component is (weight percentage): prepolymer 30-60%; reactive diluent monomer 20-60%; filler 1-5%; photoinitiator 0.1-6%; auxiliary agent 0-3%.

[0024] Wherein, the prepolymer is an acrylate oligomer. The acrylate oligomer includes polyurethane acrylate, epoxy acrylate, and epoxy resin with a carbon-carbon chain as the main chain. Specifically, the polyurethane acrylate can be: such as the model ETERCURE DR-U028FS and ETERCURE DR-U029-1 of Changxing Materials Industry Co., Ltd., and EBECRYL 4101 of Allnex Company of Germany. The epoxy acrylate is such as AG-70, AG-80, AFG-90H of Shanghai Huayi Company, and RJ313 of RYOJI Company of Japan. The epoxy resin refers to a polymer compound containing more than two epoxy groups in the structure. The high activity of the epoxy group makes the epoxy resin have a strong adhesion to materials with high surface activity, such as metal, glass, plastic, etc. At the same time, the addition of epoxy resin to the adhesive can also increase the cohesive strength, reduce the volume shrinkage rate and improve the mechanical properties. Polyurethane acrylate can enhance the impact resistance, weather resistance, water resistance and oil resistance of the adhesive.

[0025] The active diluent monomer is an acrylate monomer; the active diluent monomer is one or more of methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, propyl acrylate, hydroxypropyl acrylate, butyl acrylate, cyclohexyl acrylate, isooctyl acrylate, isodecyl acrylate, isobornyl acrylate, tetrahydrofurfuryl acrylate, methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, propyl methacrylate, hydroxypropyl methacrylate, butyl methacrylate, isobornyl methacrylate, tetrahydrofurfuryl methacrylate, and 3,3,5-trimethylcyclohexyl acrylate.

[0026] The filler is one or more of fumed silica, aluminum hydroxide powder, and titanium dioxide, and preferably fumed silica with a smaller particle size is used as the filler. The addition of the filler can improve the thixotropic properties of the adhesive and adjust the viscosity of the adhesive.

[0027] The photoinitiator is a cleavage-type photoinitiator, preferably a phosphorus-oxygen organic compound, more specifically a combination of 2,4,6-trimethylbenzoylphenylphosphonic acid ethyl ester (TPO-L photoinitiator), phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide (BAPO photoinitiator) and 2,4,6-trimethylbenzoyl-di (p-tolyl) phosphine oxide (TMO photoinitiator). The molecular structure of the TPO photoinitiator, i.e., (2,4,6-trimethylbenzoyl) diphenylphosphine oxide photoinitiator, contains two phenyl-phosphine chemical bonds, which affects reproductive health, while the structure of the TPO-L photoinitiator is similar to that of TPO, but one of the phenyl groups in the molecular structure is replaced by an ethoxy group, making it less toxic than TPO, but the disadvantage is that the initiation effect is worse than that of TPO. BAPO replaces a phenyl group with a 2,4,6-trimethylbenzoyl group, which is also less toxic than TPO, but has a higher initiation efficiency than TPO, but has a yellowing problem that cannot be ignored; TMO introduces a methyl group into each of the two original phenyl groups of TPO, turning it into a toluene group, which greatly reduces biological toxicity. At the same time, the initiation efficiency is slightly better than TPO, and the yellowing resistance is stronger. In addition, because BAPO and TMO have good light initiation effects, and polyurethane acrylate has a high light transmittance, the central glue has the advantage of fast curing speed.

[0028] The 2,4,6-trimethylbenzoylphenylphosphonic acid ethyl ester (TPO-L photoinitiator), phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide (BAPO photoinitiator) and 2,4,6-trimethylbenzoyl-di (p-tolyl) phosphine oxide (TMO photoinitiator) are used in a suitable proportion so that the adhesive does not need to worry about the photoinitiation effect, and can be resistant to yellowing and low in price. Further, the total addition amount of the three photoinitiators TPO-L, BAPO and TMO is about 5.5%, among which BAPO accounts for less than 10% of the total content of the photoinitiator, and when the mass ratio of TPO-L and TMO is between 30:70 and 45:55, a relatively low-cost TPO-free environmentally friendly UV light-curing center glue can be obtained, while having a relatively balanced yellowing resistance and initiation efficiency.

[0029] The auxiliary agents are fluorescent whitening agents, thixotropic agents and defoaming agents. Further, the fluorescent whitening agent is a domestic brand fluorescent whitening agent OB; the thixotropic agent is a Crayvallac ST of Arkema Company of France and BYK-410 of BYK Company of Germany; the defoaming agent is a polymer-based defoaming agent, preferably BYK-057 of BYK Company of Germany and Foamex 810 of Evonik Company of Germany.

[0030] The TPO-free environmentally friendly UV light-curing central adhesive of the present invention has the following beneficial effects:

[0031] 1. It has a faster curing speed and short curing time. When used as a center glue, it can be completely cured in 3-5 seconds under a light intensity of 1000mw / cm2, which can meet the needs of the automated production line of the speaker factory and further improve the speaker production efficiency. The volume shrinkage rate after curing is low, and the performance is more stable than other UV light-curing adhesives.

[0032] 2. Low volume shrinkage: The volume shrinkage of the fully cured core adhesive is less than 5.0%, and the volume of the adhesive is almost unchanged before and after curing, which will not affect the bonding effect of the speaker diaphragm and voice coil due to the shrinkage of the curing volume. The setting of the epoxy resin and the photoinitiator makes the adhesive have a high degree of cross-linking, thus having a low volume shrinkage, and having high cohesive strength and high temperature resistance.

[0033] 3. Excellent waterproof performance: After the core glue is fully cured, the water absorption rate is low, and the saturated water absorption rate is less than 1.0%. It will not fall off and no dissolution will occur after being completely immersed in pure water for 360 hours, which greatly enhances the waterproof performance of the product.

[0034] 4. Excellent resistance to high temperature, humidity and weather resistance. After the core adhesive is bonded to the speaker diaphragm and voice coil and cured, it has a high degree of cross-linking and high cohesive strength. After being tested at high temperature and high humidity of 85℃×85%RH×168h, the attenuation of the maximum force in the top force test is less than 10%. It can meet the production, transportation and use requirements under different temperature and humidity conditions.

[0035] 5. Advanced environmental performance. This core adhesive liquid does not use TPO photoinitiator, does not contain solvent components, does not contain heavy metal ions, and has low odor characteristics. It complies with the "GB 33372-2020 Limits of Volatile Organic Compounds in Adhesives" and the VOC limit requirements of the EU RoHS Directive (EU) 201 / 863, and complies with the "people-oriented" green chemistry principle of chemical production;

[0036] Tables 1 and 2 below are some experimental parameter tables for reference.

[0037]

[0038]

[0039] Table 1 Example and the ratio of the prepared UV light curing center glue

[0040]

[0041] Table 2 Performance test conditions and results of UV light curing center glue prepared in Example

[0042] Note: The objects tested for maximum top force in Table 2 are all PEEK-made magnetic diaphragms and enameled copper coils in the 3411 speaker model, and the amount of glue applied is 7mg-10mg.

[0043] In addition, the present invention also discloses a method for preparing a TPO-free environmentally friendly UV light-curing central adhesive, which is used to prepare the TPO-free environmentally friendly UV light-curing central adhesive, and the specific preparation steps are as follows:

[0044] Step 1: Material preparation: prepare the various component materials included in the above-mentioned TPO-free environmentally friendly UV light-curing central adhesive; the specific percentages and specific substances are not repeated here.

[0045] Step 2: Dissolve 0.1-6% of the photoinitiator in 20-60% of the active diluent monomer, control the temperature to 20-30°C and stir to disperse evenly. After all the solids are dissolved, add 30-60% of the prepolymer, continue stirring at 30-40°C for 30 minutes, and finally slowly add the filler and additives in the formula amount in sequence. Vacuum the reactor to remove tiny bubbles in the glue solution, and stir for 40-60 minutes until the mixture is evenly mixed to obtain the finished product.

[0046] In summary, the TPO-free environmentally friendly UV light-curing center glue of the present invention has the characteristics of being free of solvent components, free of TPO, short curing time, low volume shrinkage, good stability, good waterproofness, high temperature resistance, moisture resistance, weather resistance, low toxicity, and low corrosion. It can meet the quality requirements of the sound membrane and voice coil combination of headphones, mobile phones, tablets, and laptop speakers, and at the same time meet the sound quality requirements of the speakers; and meet the requirements of safe production, and can provide stable bonding strength without destroying the surface effect of the adhered object. In addition, headphones, mobile phones, tablets, and laptops will be exposed to various temperature and humidity environments for a long time during transportation and use. In high temperature environments or high-intensity use, the equipment will also generate heat, causing the speakers to be in a relatively high temperature environment. The environmentally friendly UV light-curing center glue of the present invention will not soften at high temperatures, resulting in a significant decrease in bonding strength, and the speakers can work normally in machines used in different temperature and humidity environments; it is highly practical and has a strong promotional significance.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A TPO-free environmentally friendly UV light-curing central adhesive, characterized by: The invention comprises the following components in percentage: 30-60% prepolymer; 20-60% active diluent monomer; 1-5% filler; 0.1-6% photoinitiator; and 0-3% auxiliary agent. The prepolymer is an acrylate oligomer, and the acrylate oligomer comprises polyurethane acrylate, epoxy acrylate, and epoxy resin with a carbon-carbon chain as the main chain; the active diluent monomer is an acrylate monomer; the filler is one or more of fumed silica, aluminum hydroxide powder, and titanium dioxide; the photoinitiator comprises 2,4,6-trimethylbenzoylphenylphosphonic acid ethyl ester (TPO-L photoinitiator), phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO photoinitiator), and 2,4,6-trimethylbenzoyl-di(p-tolyl)phosphine oxide (TMO photoinitiator).

2. The TPO-free environmentally friendly UV light-curing core adhesive as claimed in claim 1, characterized in that: The total addition amount of the three photoinitiators, TPO-L, BAPO and TMO, is about 5.5%.

3. The TPO-free environmentally friendly UV light-curing core adhesive as claimed in claim 2, characterized in that: The BAPO accounts for less than 10% of the total content of the photoinitiator, and the mass ratio of TPO-L to TMO is between 30:70 and 45:

55.

4. The TPO-free environmentally friendly UV light-curing core adhesive as claimed in claim 1, characterized in that: The filler is small-particle fumed silica.

5. The TPO-free environmentally friendly UV light-curing core adhesive as claimed in claim 1, characterized in that: The auxiliary agents are fluorescent whitening agent, thixotropic agent and defoaming agent.

6. The TPO-free environmentally friendly UV light-curing core adhesive as claimed in claim 1, characterized in that: The active diluent monomer is one or more of methyl acrylate, ethyl acrylate, hydroxyethyl acrylate, propyl acrylate, hydroxypropyl acrylate, butyl acrylate, cyclohexyl acrylate, isooctyl acrylate, isodecyl acrylate, isobornyl acrylate, tetrahydrofurfuryl acrylate, methyl methacrylate, ethyl methacrylate, hydroxyethyl methacrylate, propyl methacrylate, hydroxypropyl methacrylate, butyl methacrylate, isobornyl methacrylate, tetrahydrofurfuryl methacrylate, and 3,3,5-trimethylcyclohexyl acrylate.

7. A method for preparing a TPO-free environmentally friendly UV light-curing core adhesive, characterized in that: The steps include: Step 1: providing the components of the TPO-free environmentally friendly UV light-curing central adhesive as described in claims 1 to 6, Step 2: Dissolve 0.1-6% of the photoinitiator in 20-60% of the active diluent monomer, control the temperature to 20-30°C and stir to disperse evenly. After all the solids are dissolved, add 30-60% of the prepolymer, continue stirring at 30-40°C for 30 minutes, and finally slowly add the filler and additives in the formula amount in sequence, stir for 40-60 minutes until the mixture is evenly mixed to obtain the finished product.

8. The method for preparing the TPO-free environmentally friendly UV light-curing core adhesive according to claim 7, characterized in that: In step 2, after adding fillers and additives, the reactor needs to be evacuated to remove tiny bubbles in the glue solution.

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