Anti-crack acrylate adhesive for protective film and preparation method therefor

Abstract

The present invention relates to an anti-crack acrylate adhesive for a protective film. The anti-crack acrylate adhesive comprises an acrylic resin polymer, wherein the acrylic resin polymer is formed by carrying out emulsion polymerization on a monomer by means of a mixture containing an emulsifier, water, and an initiator, and the proportion of particles having a particle size of 330-500 nm in the entire particles of the acrylic resin polymer is 80% by volume or above. Compared with the prior art, an acrylate pressure-sensitive adhesive obtained in the present invention effectively solves the problem of cracking caused when the dry adhesive thickness is larger than 30 micrometers during application of the acrylate pressure-sensitive adhesive to a PE protective film, and the pressure-sensitive adhesive has relatively high initial adhesion, peeling force, and lasting adhesion, and meets the use requirements.

Description

Anti-cracking acrylic adhesive for protective film and preparation method thereof Technical Field

[0001] The invention relates to an acrylate adhesive, and in particular to an anti-cracking acrylate adhesive for a protective film and a preparation method thereof. Background Art

[0002] Acrylate pressure-sensitive adhesives (ASPAs) are a type of pressure-sensitive adhesive formed by copolymerizing various acrylate monomers or acrylic acid monomers with other vinyl-containing monomers. They are characterized by low cost, good transparency, and excellent aging resistance. They have promoted the development of various industries, including light industrial packaging, automotive manufacturing, machinery and building materials, health care, and daily life, providing packaging, fixation, protection, shielding, and visual reminders. In recent years, with the tightening of environmental protection policies and the increasing awareness of energy conservation and environmental protection, water-based acrylic emulsions have experienced rapid development. However, compared with solvent-based products, water-based emulsions have higher surface tension, making them more difficult to spread at low-surface-energy interfaces. They also have disadvantages such as high latent heat of evaporation and slow drying speeds.

[0003] Protective film (such as PE material) is a kind of material widely used to protect the surface of various high-gloss materials such as stainless steel plates, building profiles, home appliances, doors and windows, and glass products. Products with protective film attached can prevent their surfaces from being contaminated by rain, dust, grease, etc. during manufacturing, transportation, secondary processing, storage and use, thereby ensuring product quality and performance. Substrates such as PE have a low melting point and are not resistant to high temperatures, so the drying temperature is relatively low during the drying process after applying the adhesive emulsion. The adhesive protective film products used on the surface of frosted building profiles place very high demands on the performance of the adhesive itself. The products are required to have high initial adhesion, peeling strength and cohesion, that is, "stickable, sticky, tearable, and no adhesive residue" in order to achieve good adhesion to the frosted surface.

[0004] In order to achieve good adhesion, this type of protective film usually needs to have a thicker dry adhesive thickness (for example, >30μm). However, during the thick coating and drying process, due to the defects of the PE material itself, the drying temperature cannot be too high. At the same time, the latent heat of evaporation of water is large and the volatilization rate is slow. This leads to a large difference in the drying rate of the upper and lower layers during the drying process of the product, resulting in cracking of the film. This cracking phenomenon is more serious when used with a curing agent. This not only affects the appearance of the product, but also affects the product performance and causes residual glue. To address this problem, a high-solid content emulsion (>60%) can be prepared, but the technology of high-solid emulsion is still immature, and it is difficult to resolve the contradiction between solid content and viscosity. At the same time, the heat dissipation and stirring control during the production of high-solid emulsions are not good, and fine residues are easily generated, making the product unusable. The problem of cracking when thickly coated with acrylic adhesives for protective films has not been effectively solved.

[0005] Summary of the Invention

[0006] The purpose of the present invention is to solve the common problem of cracking of thick coating of acrylic adhesive for protective film, and to provide an anti-cracking acrylic adhesive for protective film and a preparation method thereof.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] An anti-cracking acrylic adhesive for a protective film contains an acrylic resin polymer, which is prepared by emulsion polymerization of monomers through a mixture containing an emulsifier, water, and an initiator.

[0009] The proportion of particles having a particle diameter of 330 to 500 nm in the entire particles of the acrylic resin polymer is 80% by volume or more.

[0010] Preferably, the proportion of particles having a particle size of 330 to 450 nm in the entire particles of the acrylic resin polymer is 80% by volume or more, more preferably 85% by volume or more, and even more preferably 90% by volume or more.

[0011] More preferably, the proportion of particles having a particle diameter of 340 to 400 nm in the entire particles of the acrylic resin polymer is 90% by volume or more, and even more preferably 95% by volume or more.

[0012] As a preferred technical solution of the present invention, the monomer comprises the following monomer raw material components: 60-95 parts of soft monomer, 3-15 parts of hard monomer, 1-5 parts of functional monomer,

[0013] The soft monomer is an acrylic soft monomer;

[0014] The hard monomer is one or more of styrene, methyl acrylate, and methyl methacrylate;

[0015] The functional monomers include one or more of acrylic acid, hydroxyethyl acrylate, and hydroxypropyl acrylate.

[0016] As a preferred technical solution of the present invention, the monomer comprises the following monomer raw material components: 75-92 parts of soft monomer, 5-10 parts of hard monomer, 2-4 parts of functional monomer,

[0017] And / or, the soft monomer is an acrylic ester monomer with a Tg range of -70°C to -20°C, including one or more of ethyl acrylate, butyl acrylate, isooctyl acrylate, and 2-ethylhexyl acrylate;

[0018] Further preferably, the soft monomer is an acrylic ester monomer with a Tg range of -70°C to -45°C, including one or more of butyl acrylate and isooctyl acrylate;

[0019] and / or, the hard monomer is one or more of styrene and methyl methacrylate;

[0020] And / or, the functional monomers are acrylic acid and hydroxyethyl acrylate. For example, in a specific embodiment, the weight ratio of acrylic acid to hydroxyethyl acrylate is 1:2.

[0021] As a preferred technical solution of the present invention, the emulsifier is a fatty alcohol ether sulfate anionic emulsifier or an alkyl polyoxyethylene ether sulfate anionic emulsifier. Based on the total weight of the monomer, the amount of the emulsifier is 0.3%-1.5%, preferably, the amount of the emulsifier is 0.4%-1.2%, and further preferably, the amount of the emulsifier is 0.45%-0.7%.

[0022] More preferably, the fatty alcohol ether sulfate anionic emulsifier may be sodium alkyl polyoxyethylene ether sulfate. In a specific embodiment, for example, LPS-630 anionic emulsifier produced by Lianhong may be used.

[0023] In a specific embodiment, the alkyl polyoxyethylene ether sulfate anionic emulsifier can be BASF's Disponil FES series emulsifier, such as Disponil FES 32, Disponil FES 147, Disponil FES 61, Disponil FES 77, etc.

[0024] Emulsifier is one of the key factors affecting the latex particles of emulsion polymers. The site of emulsion polymerization is micelles. Emulsifiers and monomers mix to form micelles. When the emulsifier is high, more micelles are formed, increasing the site of polymerization and reducing the polymer particle size. When the emulsifier is low, fewer micelles are formed and the polymer particle size increases. However, too little emulsifier is not conducive to the progress of emulsion polymerization and affects the performance of the emulsion. The present invention selects anionic emulsifiers such as fatty alcohol ether sulfates or alkyl polyoxyethylene ether sulfates to synthesize large-particle emulsions and meet the mechanical properties of the emulsion.

[0025] As a preferred technical solution of the present invention, the acrylic ester adhesive further comprises a post-stage auxiliary agent, based on the total weight of the acrylic resin polymer,

[0026] The post-stage auxiliary agent includes: 0.05% to 0.3% of a wetting agent;

[0027] and / or, 0.05%-0.15% defoaming agent;

[0028] and / or, 5%-15% of a film-forming aid.

[0029] Wetting agents can further improve the surface properties of adhesives, helping them to be better used in PE-based protective films; defoaming agents can reduce the generation of bubbles during the adhesive preparation process, helping to improve the quality of the emulsion; the introduction of film-forming aids reduces the film-forming temperature of the film, which can increase the flexibility of the molecular chain segments, thereby improving the film-forming properties of the emulsion and alleviating the cracking problem to a certain extent.

[0030] As a preferred technical solution of the present invention, the wetting agent includes one or more of alkyl polyoxyethylene ether and sodium dioctyl sulfosuccinate;

[0031] And / or, the defoaming agent includes one or more of mineral oil and organosilicon-modified defoaming agents, for example, BASF Foamaster 8034A defoaming agent and BASF defoaming agent FOAMSTAR A10.

[0032] And / or, the film-forming aid includes one or more of alcohol ester dodecahydrate and alcohol ester hexadecene.

[0033] As a preferred technical solution of the present invention, the monomer further contains an internal plasticizing monomer, and the internal plasticizing monomer includes one or more of dibutyl maleate, butyl maleate, isobutyl maleate, methyl maleate, and ethyl maleate. Preferably, the amount of the internal plasticizing monomer added is 5wt%-10wt%, more preferably 6wt%-9wt%, relative to the total weight of the monomer.

[0034] Dibutyl maleate, butyl maleate, isobutyl maleate, methyl maleate, ethyl maleate, etc. contain maleic acid groups with double bond structures, which can undergo conjugation reactions to make the polymer have better stability; at the same time, they contain ester groups, which can dry and cure quickly in adhesives, giving the polymer good flexibility, which is helpful in reducing cracks in the adhesive curing process.

[0035] When the adhesive of the present invention is used, it is used in combination with a curing agent. The added amount of the curing agent is 0.1% to 0.15% relative to the total weight of the adhesive. The curing agent is one or more of nitrogen pyridines, polyurethanes, and carbodiimides, preferably nitrogen pyridine curing agents.

[0036] A method for preparing an anti-cracking acrylic adhesive for a protective film comprises the following steps:

[0037] (1) Prepare the raw materials according to the recipe;

[0038] (2) Preparing a pre-emulsion: Mix water, an emulsifier, and the monomer raw material, stir evenly, and obtain a pre-emulsion. Take 2% to 5% of the total mass of the pre-emulsion as the seed emulsion;

[0039] (3) Prepare the reactor bottom liquid: add water to the reactor with stirring, heat it to the reaction temperature, add the initiator, and after 2 to 3 minutes, add the seed emulsion polymerization;

[0040] (4) After the seed emulsion polymerization reaction is completed, the remaining pre-emulsion and initiator are added dropwise at the same time. The addition is completed within 3-4 hours, and the product is obtained after post-treatment.

[0041] As a preferred technical solution of the present invention, the reaction temperature in step (3) is 81-84° C., and the seed emulsion polymerization time is 25-35 min.

[0042] The present invention adopts a seed emulsion preparation process, and the emulsion particle size can be controlled by controlling the selection amount of the seed emulsion. The emulsion particle size changes with the change of the seed amount, generally within the range of 2%-5% of the total mass of the pre-emulsion liquid. The smaller the seed amount, the larger the emulsion particle size; the more the seed amount, the smaller the emulsion particle size. The particle size and distribution of the emulsion can be effectively controlled by seeding.

[0043] As a preferred technical solution of the present invention, the post-treatment in step (4) includes: keeping warm for 25-35 minutes and adding initiator, continuing to keep warm for 1-2 hours, and keeping warm at 84±1°C; when the temperature is lowered to <45°C, adjusting the pH to 8-9;

[0044] and / or, adding a defoaming agent; and / or, adding a wetting agent; and / or, adding a film-forming aid.

[0045] As a preferred technical solution of the present invention, the initiator includes one or more of ammonium persulfate, sodium persulfate, and potassium persulfate, preferably ammonium sulfate. Based on the total weight of the acrylic resin polymer, the amount of the initiator added in step (3) is 0.1%-0.2%, and the amount of the initiator added in step (4) is 0.08%-0.1%; the amount of the initiator added in post-treatment is 0.02%-0.05%.

[0046] Compared with the prior art, the present invention has the following innovations:

[0047] 1. The present invention addresses the problem of cracking in thick coats of acrylic adhesive for protective films. The invention discovered that cracking in thick coats of adhesive is significantly related to the size of the latex particles. Specifically, a large-particle emulsion can improve the difference in drying rates between the surface and underlying emulsions during the drying process. This helps form a larger pore structure during film drying, releasing internal stress, reducing internal stress accumulation in the film, and lowering the risk of cracking. Therefore, the present invention synthesizes and prepares an emulsion with an average particle size of 330-500 nm based on a formula design by adjusting the type and amount of emulsifier and the polymerization process. This effectively solves the widespread cracking problem in thick coats of PE protective films.

[0048] 2. Improve the cracking problem of adhesives by introducing plasticizing monomers. The introduction of internal plasticizing monomers improves the flexibility of polymer chains and increases the mobility and fusion of molecular chains during the drying and cross-linking process, which is conducive to the formation of a complete and uniform film layer. Combined with the range control of emulsion particle size, it can better solve the problem of cracking in thick adhesive coatings.

[0049] 3. By adding a certain amount of film-forming aids and other post-stage additives in the later stage, the application performance of the product can be further improved. For example, the introduction of film-forming aids reduces the film-forming temperature of the film, increases the flexibility of the molecular chain segments, thereby improving the film-forming properties of the emulsion and helping to reduce cracking.

[0050] 4. The adhesive of the present invention uses PE as the base material, and the dry film thickness is greater than 30μm. Even at 42μm, the film has no cracks or cracks. When 0.125% of the curing agent is added, the dry film thickness is 30μm, the initial rolling ball adhesion is 25-30#, the 180° peel strength after 24 hours is 550-650gf / 25mm, and there is no residual adhesive after aging for 48 hours at 60℃ and 90% humidity. The sustained adhesion is 168 hours without slippage.

[0051] 5. This adhesive balances the initial adhesion and peeling strength of the product while maintaining good cohesion. It has excellent initial adhesion while maintaining high cohesion and high peeling strength, which is very suitable for use in building profiles and other aspects. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 is a photo of the cracking of the pressure-sensitive adhesive film when it is thickly coated;

[0053] Figure 2 is a photo of slight cracking of the pressure-sensitive adhesive film when thickly coated;

[0054] Figure 3 is a photo of the film remaining intact when the pressure-sensitive adhesive is thickly coated. DETAILED DESCRIPTION

[0055] During the development of acrylic pressure-sensitive adhesive products, cracking often occurs when thick coatings are applied to the adhesive film. This is especially true when applied to PE protective films, where the cracking problem is more severe (see Figure 1).

[0056] After extensive and in-depth research, the inventors speculate that the cause of the film cracking may be: during the film curing and drying process, there is a large difference in the curing rate between the upper and lower layers of the film. The surface of the film dries and cures too quickly, while the interior is still moist. This unevenness causes internal stress in the film, thereby causing cracking. In addition, when combined with the PE material film substrate, the PE film has low surface tension and poor compatibility, which exacerbates the cracking problem.

[0057] To address this issue, the inventors first attempted to add certain functional components. A certain amount of film-forming aid was added to the prepared masterbatch at a later stage. The introduction of the film-forming aid lowered the film-forming temperature of the adhesive film, increasing the flexibility of the molecular segments and improving the film-forming properties of the emulsion, which to some extent resolved the cracking issue. However, this improvement approach is relatively costly, requiring the subsequent addition of a large amount of film-forming aid (more than 10% relative to the total weight of the masterbatch to be effective). In addition to increasing costs, the introduction of the film-forming aid is not environmentally friendly and has an adverse effect on other properties of the adhesive, such as peel strength, holding strength, and initial tack. Therefore, introducing the film-forming aid separately at a later stage is not a suitable approach.

[0058] The inventors discovered through accidental experiments that some samples with the same formulation exhibited no cracking or crazing when applied thickly. After further research and analysis, the inventors discovered that larger emulsion particles can help alleviate cracking during the film drying process. When the prepared emulsion particle size is above 330 nm, cracking is reduced or eliminated when the adhesive is applied thickly.

[0059] The inventors determined that large-particle emulsions can improve the difference in drying rates between the surface and bottom layers of the emulsion during the drying process, and further speculated that the possible mechanism is that, on the one hand, large-particle emulsion particles help form a larger pore structure during the film drying process, which helps to release internal stress, reduce the internal stress accumulation of the film, and reduce the risk of cracking; on the other hand, large-particle emulsion particles can form a larger film pore structure, which helps to improve the flexibility and toughness of the film, enabling it to better adapt to stress changes during the drying process and reduce the risk of cracking. However, if the emulsion particle size is too large, it will have an adverse effect on the stability of the emulsion, and oversized latex particles are more difficult to prepare in practice, generally exceeding 500nm, and there is a relatively large risk of failure. Therefore, the emulsion particle size suitable for the acrylic adhesive of the present invention is controlled to be 330-500nm, preferably 330-450nm, and more preferably 340-380nm. Emulsions within this range can avoid the problem of cracking when thickly coated.

[0060] The inventors further discovered that the cracking problem can be addressed to some extent by introducing specialized functional monomers. For example, when designing the resin formulation, functional monomers with internal plasticizing properties, such as maleic acid esters such as dibutyl maleate, can improve the flexibility of the polymer chain segments. This increases the mobility and fusion of the molecular segments during the drying and crosslinking process, facilitating the formation of a complete, uniform film. While these monomers are relatively expensive, increasing product costs, combined with controlled emulsion particle size, they can effectively address the cracking problem in thick adhesive coatings.

[0061] On this basis, the present invention was completed.

[0062] The technical solution of the present invention includes:

[0063] The invention discloses an anti-cracking acrylic adhesive for a protective film, which contains an acrylic resin polymer. The acrylic resin polymer is prepared by emulsion polymerization of monomers using an emulsifier, water and an initiator. The particle size of the prepared resin polymer is controlled to be 330 to 500 nm, preferably 330 to 450 nm, and more preferably 340 to 400 nm.

[0064] In a specific embodiment, the monomers include: 60-95 parts of soft monomers, 3-15 parts of hard monomers, and 1-5 parts of functional monomers. As a preferred technical solution, the monomers include: 75-92 parts of soft monomers, 5-10 parts of hard monomers, and 2-4 parts of functional monomers.

[0065] Wherein, the soft monomer is an acrylic ester soft monomer, including one or more of ethyl acrylate, butyl acrylate, isooctyl acrylate, and 2-ethylhexyl acrylate; further preferably, the soft monomer is one or more of butyl acrylate and isooctyl acrylate;

[0066] The hard monomer is one or more of styrene, methyl acrylate, and methyl methacrylate. Preferably, the hard monomer is one or more of styrene and methyl methacrylate;

[0067] The functional monomers include one or more of acrylic acid, hydroxyethyl acrylate, and hydroxypropyl acrylate. Preferably, the functional monomers are acrylic acid and hydroxyethyl acrylate. For example, in a specific embodiment, the weight ratio of acrylic acid to hydroxyethyl acrylate is 1:2.

[0068] As a preferred technical solution of the present invention, the emulsifier is a fatty alcohol ether sulfate anionic emulsifier or an alkyl polyoxyethylene ether sulfate anionic emulsifier. Based on the total weight of the monomer, the amount of the emulsifier is 0.3%-1.5%, preferably, the amount of the emulsifier is 0.4%-1.2%, and further preferably, the amount of the emulsifier is 0.45%-0.7%.

[0069] The fatty alcohol ether sulfate anionic emulsifier may be sodium alkyl polyoxyethylene ether sulfate. In a specific embodiment, for example, LPS-630 anionic emulsifier produced by Lianhong may be used.

[0070] In a specific embodiment, the alkyl polyoxyethylene ether sulfate anionic emulsifier can be BASF's Disponil FES series emulsifier, such as Disponil FES 32, Disponil FES 147, Disponil FES 61, Disponil FES 77, etc.

[0071] The specific preparation method comprises the following steps:

[0072] (1) Prepare the raw materials according to the recipe;

[0073] (2) Preparing a pre-emulsion: Mix water, an emulsifier, and the monomer raw material, stir evenly, and obtain a pre-emulsion. Take 2% to 5% of the total mass of the pre-emulsion as the seed emulsion;

[0074] (3) Prepare the reactor bottom liquid: add water to the reactor with stirring, heat it to the reaction temperature of 81-84 ° C, add the initiator, add the seed emulsion polymerization for 25-35 minutes after 2-3 minutes;

[0075] (4) After the seed emulsion polymerization reaction is completed, the remaining pre-emulsion and initiator are added dropwise at the same time. The addition is completed within 3-4 hours. The mixture is kept warm for 25-35 minutes and the initiator is added. The mixture is kept warm for 1-2 hours at 84±1°C. When the temperature is lowered to <45°C, the pH is adjusted to 8-9.

[0076] As a preferred technical solution of the present invention, the initiator includes one or more of ammonium persulfate, sodium persulfate, and potassium persulfate, preferably ammonium sulfate.

[0077] Based on the total weight of the acrylic resin polymer, the amount of the initiator added in step (3) is 0.1%-0.2%, and the amount of the initiator added in step (4) is 0.08%-0.1%; the amount of the initiator added in the post-treatment is 0.02%-0.05%.

[0078] The present invention controls the emulsion particle size by controlling the amount of emulsifier added and the amount of seed emulsion taken. On the one hand, the emulsifier is one of the key factors affecting the latex particles of the emulsion polymer. The site of emulsion polymerization is micelles, and the emulsifier and monomer mix to form micelles. When the emulsifier is high, more micelles are formed, which increases the polymerization site and reduces the polymer particle size. When the emulsifier is low, fewer micelles are formed and the polymer particle size increases. However, too little emulsifier is not conducive to the progress of emulsion polymerization and affects the performance of the emulsion.

[0079] On the other hand, the emulsion particle size can be controlled by controlling the amount of seed emulsion selected. The emulsion particle size changes with the change of seed amount, generally within the range of 2%-5% of the total mass of the pre-emulsion. The less seed amount is taken, the larger the emulsion particle size is; the more seed amount is taken, the smaller the emulsion particle size is.

[0080] On the other hand, the present invention provides an improved technical solution, wherein the monomer further contains an internal plasticizing monomer, wherein the internal plasticizing monomer includes dibutyl maleate, butyl maleate, isobutyl maleate, methyl maleate, and ethyl maleate. Preferably, the amount of the internal plasticizing monomer added is 5wt%-10wt%, more preferably 6wt%-9wt%, relative to the total weight of the monomer.

[0081] Dibutyl maleate, butyl maleate, isobutyl maleate, methyl maleate, ethyl maleate, etc. contain maleic acid groups with double bond structures, which can undergo conjugation reactions to make the polymer have better stability; at the same time, they contain ester groups, which can dry and cure quickly in adhesives, giving the polymer good flexibility, which is helpful in reducing cracks in the adhesive curing process.

[0082] Finally, as a further improved technical solution, the acrylic adhesive further comprises a post-stage auxiliary agent, which comprises, based on the total weight of the acrylic resin polymer, 0.05% to 0.3% of a wetting agent; and / or 0.05% to 0.15% of a defoaming agent; and / or 5% to 15% of a film-forming auxiliary agent.

[0083] The wetting agent includes one or more of alkyl polyoxyethylene ether and sodium dioctyl sulfosuccinate; and / or the defoaming agent includes one or more of mineral oil and silicone modified defoaming agent, for example, BASF Foamaster 8034A defoamer and BASF defoamer FOAMSTAR A10; and / or the film-forming aid includes one or more of alcohol ester dodecahydrate and alcohol ester hexadecene.

[0084] Wetting agents can further improve the surface properties of adhesives, helping them to be better used in PE-based protective films;

[0085] Defoaming agents can reduce the generation of bubbles during the adhesive production process and help improve the quality of the emulsion;

[0086] The introduction of film-forming aids reduces the film-forming temperature of the film, increases the flexibility of the molecular chain segments, thereby improving the film-forming properties of the emulsion and alleviating the cracking problem to a certain extent.

[0087] The present invention is described in detail below through specific experiments.

[0088] Experiments 1 to 10

[0089] The formula of the main raw materials is shown in Table 1. The emulsifier in Table 1 is LPS-630 anionic emulsifier produced by Levima.

[0090] Taking Experiment 1 as an example, the typical preparation method is as follows:

[0091] (1) Preparation of pre-emulsion: 25 g of water and 1 g of LPS-630 anionic emulsifier were stirred and mixed uniformly, and then 4 g of methyl methacrylate, 4 g of styrene, 55 g of isooctyl acrylate, 20 g of butyl acrylate, 1 g of acrylic acid, and 2 g of hydroxyethyl acrylate were added. The mixture was emulsified for 30 min to obtain a pre-emulsion. About 5 wt% of the pre-emulsion was taken out as a seed emulsion.

[0092] (2) Reactor bottom liquid: 40 g of water was added to a reactor equipped with a stirrer, a condenser, and a thermometer. The temperature was raised to 84°C. Ammonium persulfate initiator (0.1 g of initiator was dissolved in 5 g of water) was added. After 2 to 3 minutes, the seed emulsion was added and the polymerization was carried out for 30 minutes. The temperature was controlled at 82 ± 1°C.

[0093] (3) Addition and insulation: After 30 minutes of seed emulsion polymerization, the remaining pre-emulsion and ammonium persulfate initiator (0.08 g of initiator dissolved in 5 g of water) were added dropwise simultaneously. The injection was completed in 210 minutes, and the temperature was controlled at 82 ± 1 °C. After the injection was completed, the temperature was kept at 30 minutes, and 0.02 g of ammonium persulfate initiator was added. The temperature was continued to be kept at 84 ± 1 °C for 90 minutes.

[0094] (4) Post-stage adjustment: When the temperature is less than 45°C, 1.5 g of ammonia water and 5 g of water are added dropwise to adjust the pH to 8-9 to obtain the product.

[0095] Table 1 (unit: g)

[0096] Experiments 1 to 10 obtained samples 1 to 10 respectively.

[0097] To the emulsion of sample 1, 5%, 8% and 10% of the total mass of the emulsion as the film-forming aid alcohol ester XII were added respectively to prepare samples 11, 12 and 13; to the emulsion of sample 3, 5% of the total mass of the emulsion as the film-forming aid alcohol ester XII was added to prepare sample 14.

[0098] Samples 1 to 14 were tested.

[0099] Particle size test: The particle size of the emulsion was tested using a Malvern particle size tester.

[0100] The specific method of the sample cracking test is as follows: add 0.125% nitrogen pyridine curing agent to the emulsion, mechanically stir for 20 minutes, then use an 80-micron wire rod to coat the emulsion on the PET substrate, place it on a composite board in a constant temperature drying oven at 90°C for drying (a composite board preheated to 90°C is placed in the oven in advance), and measure different dry adhesive thicknesses and film surface cracking.

[0101] The specific test results are shown in Table 2.

[0102] Table 2

[0103] As shown in Table 2, the particle diameter of latex particles is less (for example less than 300nm), and cracking phenomenon will occur when the dry glue thickness is >30 microns, and the less cracking of particle diameter is more serious (with reference to sample 1, sample 2, accompanying drawing 1). When the particle diameter of latex particles is greater than 300nm, crackle reduces, and only has slight cracking phenomenon (with reference to sample 3, accompanying drawing 2). When the particle diameter of latex particles is greater than 330nm, the film surface effect of adhesive film is significantly improved (with reference to sample 4), and the larger the particle diameter, the more obvious the improvement effect is. When the particle diameter is greater than 340nm, cracking phenomenon will not still occur when the dry glue thickness is >42 microns (with reference to sample 5~sample 8, accompanying drawing 3). But excessive particle diameter will cause emulsion storage stability, mechanical stability performance to decline. For example, in sample 8, when particle diameter is 498nm, difficulty increases during emulsion preparation, and emulsion is easy to demulsify, and the amount of slag discharge increases, and the emulsion storage stability, mechanical stability performance etc. prepared are all not as good as the emulsion of small particle size.

[0104] Experiments have also shown that the introduction of functional monomers with internal plasticizing effects (such as dibutyl maleate) can improve the film surface effect and make the film anti-cracking. For example, the emulsion particle size of Sample 9 is less than 300nm, but compared with Sample 1, the cracking phenomenon is slowed down after the introduction of some dibutyl maleate. Compared with Sample 3, the cracking phenomenon of Sample 10 disappears after the introduction of some dibutyl maleate, and even when the dry film thickness reaches 42±1μm, it remains crack-free. This is because the introduction of functional monomers with internal plasticizing effects improves the flexibility of the polymer chain segments, increases the movement and fusion of the molecular segments during the drying and cross-linking process, and is conducive to the formation of a complete and uniform film layer.

[0105] In addition, it can be seen from Samples 11 to 14 that the film-forming properties of the product can be improved by adding a certain amount of film-forming aid in the later stage, so that the film has the effect of thick coating without cracking, but the amount of film-forming aid added needs to be large to play a role (such as Sample 13), and the introduction of film-forming aid leads to a decrease in the peeling force, initial adhesion and holding force of the film, and also leads to a decrease in the high temperature and high humidity resistance of the film.

[0106] The present invention further provides the following application examples.

[0107] Example 1

[0108] The protective film is made of a thick coating of anti-cracking acrylic adhesive. The formula is shown in Table 3. The specific preparation method is as follows:

[0109] (1) Preparation of pre-emulsion: 26 g of water and 0.5 g of LPS-630 anionic emulsifier were stirred and mixed uniformly, and then 4 g of methyl methacrylate, 4 g of styrene, 55 g of isooctyl acrylate, 25 g of butyl acrylate, 1 g of acrylic acid, and 2 g of hydroxyethyl acrylate were added. The mixture was emulsified for 30 min to obtain a pre-emulsion. About 5 wt% of the pre-emulsion was taken out as a seed emulsion.

[0110] (2) Reactor bottom liquid: 40 g of water was added to a reactor equipped with a stirrer, a condenser, and a thermometer. The temperature was raised to 84°C. Ammonium persulfate initiator (0.15 g of initiator was dissolved in 5 g of water) was added. After 2 to 3 minutes, the seed emulsion was added and the polymerization was carried out for 30 minutes. The temperature was controlled at 82 ± 1°C.

[0111] (3) Addition and insulation: After 30 minutes of seed emulsion polymerization, the remaining pre-emulsion and ammonium persulfate initiator (0.12 g of initiator dissolved in 5 g of water) were added dropwise simultaneously. The injection was completed in 210 minutes, and the temperature was controlled at 82 ± 1 °C. After the injection was completed, the temperature was kept at 30 minutes, and 0.03 g of ammonium persulfate initiator was added. The temperature was continued to be kept at 84 ± 1 °C for 90 minutes.

[0112] (4) Post-stage adjustment: When the temperature is less than 45°C, 1.5 g of ammonia water is added dropwise to adjust the pH to 8-9 to obtain the product.

[0113] Example 2

[0114] The protective film is made of a thick coating of anti-cracking acrylic adhesive. The formula is shown in Table 3. The specific preparation method is as follows:

[0115] (1) Preparation of a pre-emulsion: 30 g of water and 0.6 g of Disponil FES 32 anionic emulsifier were stirred and mixed uniformly. Then, 7 g of methyl methacrylate, 3 g of styrene, 52 g of isooctyl acrylate, 40 g of butyl acrylate, 1 g of acrylic acid, and 2 g of hydroxyethyl acrylate were added. The mixture was emulsified for 30 min to obtain a pre-emulsion. Approximately 4 wt% of the pre-emulsion was taken out as a seed emulsion.

[0116] (2) Reactor bottom liquid: 48 g of water was added to a reactor equipped with a stirrer, a condenser, and a thermometer. The temperature was raised to 84°C. Ammonium persulfate initiator (0.15 g of initiator was dissolved in 5 g of water) was added. After 2 to 3 minutes, the seed emulsion was added and the polymerization was carried out for 30 minutes. The temperature was controlled at 82 ± 1°C.

[0117] (3) Addition and insulation: After 30 minutes of seed emulsion polymerization, the remaining pre-emulsion and ammonium persulfate initiator (0.12 g of initiator dissolved in 5 g of water) were added dropwise simultaneously. The injection was completed in 210 minutes, and the temperature was controlled at 82 ± 1 °C. After the injection was completed, the temperature was kept at 30 minutes, and 0.03 g of ammonium persulfate initiator was added. The temperature was continued to be kept at 84 ± 1 °C for 90 minutes.

[0118] (4) Post-stage adjustment: When the temperature is less than 45°C, 1.5 g of ammonia water is added dropwise to adjust the pH to 8-9 to obtain the product.

[0119] Example 3

[0120] The protective film is made of a thick coating of anti-cracking acrylic adhesive. The formula is shown in Table 3. The specific preparation method is as follows:

[0121] (1) Preparation of a pre-emulsion: 20 g of water and 0.4 g of Disponil FES 147 anionic emulsifier were stirred and mixed uniformly. Then, 4 g of methyl methacrylate, 1 g of styrene, 45 g of isooctyl acrylate, 30 g of butyl acrylate, 1 g of acrylic acid, and 2 g of hydroxyethyl acrylate were added. The mixture was emulsified for 30 min to obtain a pre-emulsion. Approximately 3.5 wt% of the pre-emulsion was taken out as a seed emulsion.

[0122] (2) Reactor bottom liquid: 40 g of water was added to a reactor equipped with a stirrer, a condenser, and a thermometer. The temperature was raised to 84°C. Ammonium persulfate initiator (0.15 g of initiator was dissolved in 5 g of water) was added. After 2 to 3 minutes, the seed emulsion was added and the polymerization was carried out for 30 minutes. The temperature was controlled at 82 ± 1°C.

[0123] (3) Addition and insulation: After 30 minutes of seed emulsion polymerization, the remaining pre-emulsion and ammonium persulfate initiator (0.12 g of initiator dissolved in 5 g of water) were added dropwise simultaneously. The injection was completed in 210 minutes, and the temperature was controlled at 82 ± 1 °C. After the injection was completed, the temperature was kept at 30 minutes, and 0.03 g of ammonium persulfate initiator was added. The temperature was continued to be kept at 84 ± 1 °C for 90 minutes.

[0124] (4) Post-stage adjustment: When the temperature is less than 45°C, 1.5 g of ammonia water is added dropwise to adjust the pH to 8-9, and 0.2 g of defoamer Foamaster 8034A and 0.5 g of wetting agent sodium dioctyl sulfosuccinate are added to obtain the product.

[0125] Example 4

[0126] The protective film is made of a thick coating of anti-cracking acrylic adhesive. The formula is shown in Table 3. The specific preparation method is as follows:

[0127] (1) Preparation of pre-emulsion: 25 g of water and 0.4 g of LPS-630 anionic emulsifier were stirred and mixed uniformly, and then 5 g of methyl methacrylate, 4 g of styrene, 55 g of isooctyl acrylate, 25 g of butyl acrylate, 1 g of acrylic acid, 2 g of hydroxyethyl acrylate, and 6 g of dibutyl maleate were added. The mixture was emulsified for 30 min to obtain a pre-emulsion. About 3 wt% of the pre-emulsion was taken out as a seed emulsion.

[0128] (2) Reactor bottom liquid: 48 g of water was added to a reactor equipped with a stirrer, a condenser, and a thermometer. The temperature was raised to 84°C. Ammonium persulfate initiator (0.15 g of initiator was dissolved in 5 g of water) was added. After 2 to 3 minutes, the seed emulsion was added and the polymerization was carried out for 30 minutes. The temperature was controlled at 82 ± 1°C.

[0129] (3) Addition and insulation: After 30 minutes of seed emulsion polymerization, the remaining pre-emulsion and ammonium persulfate initiator (0.12 g of initiator dissolved in 5 g of water) were added dropwise simultaneously. The injection was completed in 210 minutes, and the temperature was controlled at 82 ± 1 °C. After the injection was completed, the temperature was kept at 30 minutes, and 0.03 g of ammonium persulfate initiator was added. The temperature was continued to be kept at 84 ± 1 °C for 90 minutes.

[0130] (4) Post-stage adjustment: When the temperature is less than 45°C, 1.5 g of ammonia water is added dropwise to adjust the pH to 8-9, and 0.2 g of defoamer Foamaster 8034A and 0.5 g of wetting agent sodium dioctyl sulfosuccinate are added to obtain the product.

[0131] Table 3 (unit: g)

[0132] The products obtained in Examples 1 to 4 were tested using the following test methods:

[0133] The solid content of the emulsion is tested according to 4.3 of GB / T 20623-2006.

[0134] The viscosity test was performed using a Brookfield LV at 25°C, 2#, and 60 rpm.

[0135] The particle size was tested using a Malvern particle size tester.

[0136] The products of Examples 1 to 4 were subjected to anti-cracking tests and corresponding film physical property evaluations, and the test methods are as follows.

[0137] Cracking test: Add 0.125% curing agent to the acrylic emulsion and mechanically stir for 20 minutes. Then, use an 80-micron wire rod to coat the emulsion on a PET substrate and place it on a composite board in a 90°C constant temperature drying oven for drying (a composite board preheated to 90°C is placed in the oven in advance). Measure the dry adhesive thickness and film surface cracking.

[0138] Preparation of PE film: According to the above method, the emulsion was coated on a 60-μm PE film material and cured for 24 hours at a temperature of 23±1°C and a humidity of 50%±5.

[0139] Film physical property evaluation method:

[0140] Initial adhesion test: refer to GB / T4852-2002 and use an initial adhesion tester for testing;

[0141] 180° peel strength: Refer to GB / T2792-2014, tested using a universal testing machine;

[0142] Adhesion test: refer to GB4851-2014;

[0143] High temperature and high humidity test: Prepare the sample of the cured film according to the method of GB / T2792-1998, place the prepared film in a constant temperature and humidity chamber at a temperature of 60℃ and a humidity of 90% for 48 hours, take it out after 48 hours, and then place it under standard conditions for 2 hours. Observe whether there is any residual glue or steel plate contamination after tearing it off.

[0144] The test results are shown in Table 4.

[0145] Table 4

[0146] The above description of the embodiments is intended to facilitate understanding and use of the invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these embodiments and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above-described embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention, without departing from the scope of the present invention, should be within the scope of protection of the present invention.

Claims

1. An anti-cracking acrylic adhesive for a protective film, comprising an acrylic resin polymer, wherein the acrylic resin polymer is prepared by emulsion polymerization of a monomer with a mixture containing an emulsifier, water and an initiator, It is characterized in that The proportion of particles having a particle size of 330 to 500 nm in the entire particles of the acrylic resin polymer is 80% by volume or more; In parts by weight, the monomers include: 60-95 parts of soft monomers, 3-15 parts of hard monomers, and 1-5 parts of functional monomers; The soft monomer is an acrylic soft monomer with a Tg range of -70°C to -20°C; The hard monomer is one or more of styrene, methyl acrylate, and methyl methacrylate; The functional monomers include one or more of acrylic acid, hydroxyethyl acrylate, and hydroxypropyl acrylate.

2. The anti-cracking acrylic adhesive for a protective film according to claim 1, characterized in that: The monomers include: 75-92 parts of soft monomers, 5-10 parts of hard monomers, and 2-4 parts of functional monomers.

3. The anti-cracking acrylic adhesive for a protective film according to claim 2, characterized in that: The soft monomer includes one or more of ethyl acrylate, butyl acrylate, isooctyl acrylate, and 2-ethylhexyl acrylate; And / or, the hard monomer is one or more of styrene and methyl methacrylate; And / or, the functional monomers are acrylic acid and hydroxyethyl acrylate.

4. The anti-cracking acrylic adhesive for a protective film according to claim 1, characterized in that: The emulsifier is an anionic emulsifier of fatty alcohol ether sulfate or an anionic emulsifier of alkyl polyoxyethylene ether sulfate. The amount of the emulsifier is 0.3%-1.5% based on the total weight of the monomers.

5. The anti-cracking acrylic adhesive for a protective film according to claim 1, characterized in that: The acrylic ester adhesive further comprises a post-stage auxiliary agent, based on the total weight of the acrylic resin polymer, The latter stage auxiliary agent comprises: 0.05% to 0.3% of a wetting agent; and / or, 0.05%-0.15% of a defoaming agent.

6. The anti-cracking acrylic adhesive for a protective film according to claim 5, characterized in that: The wetting agent includes one or more of alkyl polyoxyethylene ether and sodium dioctyl sulfosuccinate; And / or, the defoaming agent includes one or more of mineral oil and organosilicon-modified defoaming agent.

7. The anti-cracking acrylic adhesive for protective film according to any one of claims 1 to 6, characterized in that: The monomer also contains an internal plasticizing functional monomer, The internal plasticizing functional monomer includes one or more of dibutyl maleate, butyl maleate, isobutyl maleate, methyl maleate, and ethyl maleate; The amount of the internal plasticizing functional monomer added is 5wt%-10wt% relative to the total weight of the monomers.

8. The method for preparing the anti-cracking acrylic adhesive for a protective film according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) Prepare the raw materials according to the formula; (2) preparing a pre-emulsion: mixing water, an emulsifier, and the monomer, stirring them evenly to obtain a pre-emulsion, and taking 2% to 5% of the total mass of the pre-emulsion as a seed emulsion; (3) Prepare the bottom liquid of the reactor: add water to the reactor with stirring, heat it to the reaction temperature, add the initiator, and after 2 to 3 minutes, add the seed emulsion polymerization; (4) After the seed emulsion polymerization reaction is completed, the remaining pre-emulsion liquid and initiator are added dropwise at the same time. The addition takes 3-4 hours to complete, and the product is obtained after post-treatment.

9. The method for preparing a crack-proof acrylic adhesive for a protective film according to claim 8, characterized in that: In step (3), the reaction temperature is 81-84° C. and the seed emulsion polymerization time is 25-35 min.

10. The method for preparing the anti-cracking acrylic adhesive for a protective film according to claim 8, characterized in that: The post-processing in step (4) includes: Keep warm for 25-35 minutes and add initiator, continue to keep warm for 1-2 hours, keep warm at 84±1℃; when the temperature drops to <45℃, adjust the pH to 8-9; and / or, adding a defoaming agent; and / or, adding a wetting agent.

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