Aqueous pressure sensitive adhesive composition and process for its preparation

Abstract

The present invention provides an aqueous pressure-sensitive adhesive composition and a method for producing the same, the aqueous pressure-sensitive adhesive composition comprising (A) a (meth)acrylate copolymer emulsion and (B) a dispersant. The dispersant has an acid value of 15 to 35 mg KOH / g. The aqueous pressure-sensitive adhesive composition of the present invention has excellent properties such as water whitening resistance, high transparency, and less air bubbles during lamination, and is suitable for use in low surface energy materials such as polyvinyl chloride.

Description

Technical Field

[0001] This invention relates to a water-based pressure-sensitive adhesive composition and its preparation method; more specifically, this invention relates to a water-based acrylic pressure-sensitive adhesive composition. The water-based pressure-sensitive adhesive composition of this invention possesses properties such as water resistance to whitening, high transparency, and minimal air bubble formation during lamination, thus solving the problems encountered in the application of pressure-sensitive adhesives on PVC and other films, and preparing a water-based acrylic pressure-sensitive adhesive that is resistant to plasticizers, water-resistant to whitening, highly transparent, and has excellent adhesion to the substrate. Background Technology

[0002] Pressure-sensitive adhesive (PSA) is a semi-solid material that can adhere to materials under relatively low pressure. It is used in industries such as product labels, printing, cold lamination films, household appliances, and vehicle wraps, such as advertising stickers. PSA can be classified according to its form as solvent-based, emulsion-based, and hot melt-based, and according to its composition as acrylic polymers, rubber, polysiloxane resins, and ethylene vinyl acetate (EVA) resins. Among them, acrylic polymer PSA is often used as an adhesive for optical films, transparent polyvinyl chloride (PVC) cold lamination films, or protective films due to its excellent light transmittance and high resistance to oxidation or yellowing.

[0003] Acrylic PSAs are currently dominated by solvent-based PSAs. However, in addition to requiring high mechanical properties, solvent-based PSAs also need to prevent small-molecule plasticizers from precipitating from the surface and significantly reducing the performance of the adhesive layer. Furthermore, because solvent-based PSAs release residual solvents into the air after use, there are issues with volatile organic compounds (VOCs) and carbon emissions. In contrast, aqueous PSA compositions use water as a dispersion medium, which is environmentally friendly and does not emit VOCs, and therefore has attracted much attention.

[0004] One of the required properties of waterborne PSA compositions is mechanical stability, specifically dispersion stability under mechanical shear forces. Insufficient mechanical stability in waterborne PSA compositions can easily lead to agglomeration during processes such as stirring, conveying, or coating, affecting operation and product quality, such as poor bonding quality and water resistance.

[0005] Waterborne acrylic PSA typically possesses high surface energy and high polarity, thus enabling it to adhere well to materials with high surface energy. However, its adhesion to materials with low surface energy, such as PVC film, is relatively poor, easily leading to lamination defects in practical applications, such as bubbling, uneven film surface, slow air venting, and haziness. Furthermore, waterborne acrylic PSA is generally inferior to solvent-based PSA in terms of plasticizer resistance, water whitening resistance, and clarity.

[0006] To address the aforementioned technical issues, the industry currently needs a water-based acrylic PSA that possesses water resistance to whitening, high transparency, excellent air venting during use to minimize film defects (i.e., high adhesion), and is suitable for low surface energy materials such as PVC films. Summary of the Invention

[0007] In view of the above problems, one object of the present invention is to provide an aqueous pressure-sensitive adhesive composition comprising: (A) a (meth)acrylate copolymer emulsion; and

[0008] (B) Dispersant;

[0009] The dispersant has an acid value of 15 to 35 mg KOH / g.

[0010] Another object of the present invention is to provide a method for preparing an aqueous pressure-sensitive adhesive composition, comprising the following steps:

[0011] (1) Preparation of (A) (meth)acrylate copolymer emulsion; and

[0012] (2) Add dispersant (B) to (A) (meth)acrylate copolymer emulsion.

[0013] The water-based pressure-sensitive adhesive composition of this invention possesses excellent properties such as water resistance, high transparency, minimal bubble formation during bonding, and suitability for low surface energy materials such as polyvinyl chloride. Detailed Implementation

[0014] This invention will be described in conjunction with the following embodiments. Besides the following embodiments, this invention can be carried out in other ways without departing from its spirit; the scope of this invention should not be interpreted or limited solely based on the disclosure in the specification.

[0015] To facilitate understanding of the disclosures herein, several terms are defined below. The terminology used herein is for descriptive purposes only and is not intended to limit the invention. Unless otherwise expressly stated, the singular form is intended to include the plural form. Further understanding: When the terms "comprising," "having," or "including" are used in this specification, they indicate the presence of the stated feature, number, step, component, or combination thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, components, or combinations thereof.

[0016] All figures for expression content, proportion, physical characteristics, etc., used in this specification and the claims should be understood to be modified by the term "about" in all cases. Herein, the term "about" means the acceptable error of a particular value as determined by someone generally skilled in the art, depending in part on how the value is measured or determined.

[0017] In this invention, the pressure-sensitive adhesive composition may include a pressure-sensitive adhesive polymer (e.g., the (A2) (meth)acrylate copolymer of this invention). The term "pressure-sensitive adhesive polymer" may refer to a polymer prepared by mixing and polymerizing one or more different kinds of monomers and having pressure-sensitive adhesive properties.

[0018] Generally, if the adhesion of water-based PSA to the surface to be bonded (e.g., posters, car bodies, etc., but not limited to this) is poor, the amount of wetting agent can be increased to solve this problem; however, increasing the amount of wetting agent may lead to a decrease in the water-whitening resistance of the PSA, making it prone to whitening upon contact with water. Furthermore, a trade-off often needs to be made between adhesion and the air venting of the bonded surface; excessive adhesion may lead to excessively fast bonding speeds, resulting in insufficient air venting. The water-based pressure-sensitive adhesive composition provided by this invention comprises (A) a (meth)acrylate copolymer emulsion and (B) a dispersant. The inventors of this application have discovered that by further adding a dispersant with a specific acid value to the (meth)acrylate copolymer emulsion of this invention, the resulting water-based pressure-sensitive adhesive composition can have good wetting properties. Therefore, the amount of subsequent wetting agent can be reduced or eliminated, and the resulting water-based pressure-sensitive adhesive composition possesses good adhesion properties, water-whitening resistance, film smoothness, and fast air venting speed.

[0019] This invention improves the adhesion and air release properties of PVC protective films made from water-based pressure-sensitive adhesive compositions by using a dispersant with a specific acid value. When the acid value of the dispersant is greater than 15 mg KOH / g, it can increase wettability to improve adhesion. However, when the acid value of the dispersant is higher than 35 mg KOH / g, the excessive adhesion can easily lead to insufficient air release. In one embodiment of this invention, the dispersant (B) has an acid value of 15 to 35 mg KOH / g, or 16 to 34 mg KOH / g, 17 to 33 mg KOH / g, 18 to 32 mg KOH / g, 19 to 31 mg KOH / g, 20 to 30 mg KOH / g, 21 to 29 mg KOH / g, 22 to 28 mg KOH / g, 23 to 27 mg KOH / g, 24 to 26 mg KOH / g, 25 mg KOH / g, or within any of the above two extremes. In this invention, the acid value of the dispersant is calculated based on the effective components of the dispersant.

[0020] The acid value mentioned above can be determined by the following steps:

[0021] (1) First, weigh 1-3g of the sample into an Erlenmeyer flask, then add about 50ml of neutral toluene / ethanol solution (toluene: ethanol (95%) = 1:1, add phenolphthalein indicator, and then add 0.1mol / L KOH until slightly red), shake to dissolve the sample (or heat to dissolve);

[0022] (2) Titrate the solution obtained in step (1) with an ethanol solution containing 0.1 mol / L potassium hydroxide (KOH) until it turns slightly pink, and record the volume of titrant used; and

[0023] (3) The acid value (AV) can be calculated using the following formula:

[0024]

[0025] According to one embodiment of the present invention, the dispersant (B) has an acid value of 15-35 mg KOH / g, which results in a better degassing rate during the application of the protective film and effectively improves the adhesion to the surface of the object to be applied. The object to be applied refers to items whose surface requires a protective film, such as, but not limited to, posters, advertising panels, photographs, and vehicle advertisements. Furthermore, when the dispersant (B) is a pigment-specific dispersant, such as a polycarboxylate-based dispersant, it can effectively improve the wetting effect of the PSA on the pigment in the coating of the object to be applied, thereby improving the adhesion of the aqueous PSA composition of the present invention to the object when applied to materials such as PVC protective films. Commercially available products of the dispersant (B) include "SN-DISPERSANT 5040" (supplier: SAN NOPCO; sodium polycarboxylate-based dispersant).

[0026] In this invention, the solid content of the (A) (meth)acrylate copolymer emulsion, i.e., the total weight (grams) of solid content per 100 grams of emulsion, is not particularly limited. In one embodiment of this invention, each 100 grams of emulsion may contain 30 to 70 grams of (A) (meth)acrylate copolymer emulsion, for example, 35 grams, 40 grams, 45 grams, 50 grams, 52 grams, 53 grams, 54 grams, 55 grams, 60 grams, 65 grams, or 70 grams of solid content.

[0027] In one embodiment of the present invention, based on 100 parts by weight of the solid content of the (A) (meth)acrylate copolymer emulsion, the content of the (B) dispersant is 0.2 to 4 parts by weight, for example, 0.2 parts by weight, 0.5 parts by weight, 0.8 parts by weight, 1 part by weight, 1.5 parts by weight, 2 parts by weight, 2.5 parts by weight, or 3 parts by weight.

[0028] In this invention, the content (concentration) of a component or additive is calculated based on its effective ingredient (i.e., the actual amount of the component or additive added multiplied by the solid content %).

[0029] The (A) (meth)acrylate copolymer emulsion of the present invention has a relatively small particle size, thus improving the clarity of PSA. In one embodiment of the present invention, the particle size of the above-mentioned (A) (meth)acrylate copolymer emulsion can be about 60 nm to about 250 nm, about 70 nm to about 240 nm, about 80 nm to about 230 nm, about 90 nm to about 220 nm, about 100 nm to about 210 nm, about 110 nm to about 200 nm, about 120 nm to about 170 nm, about 130 nm to about 140 nm, or within any of the above two extremes. The emulsion particle size can be measured by methods well known in the art to which this invention pertains, such as: Dynamic Light Scattering (DLS), Focused Beam Reflectance Measurement (FBRM), and optical microscopy. In one embodiment of the present invention, Dynamic Light Scattering (DLS) is used to measure the particle size of the (A) (meth)acrylate copolymer emulsion.

[0030] In this invention, the (A) (meth)acrylate copolymer emulsion comprises (A1) emulsifier and (A2) (meth)acrylate copolymer. As the emulsifier concentration in the emulsion increases, the surface tension decreases. When a sufficient amount of emulsifier molecules covers the solution surface, the emulsifier begins to aggregate and form microcells; the emulsifier concentration at this point is the critical microcell concentration (CMC), and the solution exhibits minimum surface tension (the surface tension remains constant even with further addition of emulsifier). Therefore, the critical microcell concentration (CMC) can be obtained by measuring the change in surface tension with emulsifier concentration, typically measured in an aqueous solution at 25°C. The surface tension can be measured, for example, using a commercially available surface tension measuring device and the well-known Wilhelmy plate method. In this invention, (A1) the emulsifier is preferably a low surface energy emulsifier, the preferred critical microcell concentration is 1 ppm to 100 ppm, the preferred surface tension is 10 to 50 mN / m (equivalent to 10 to 50 dyne / cm), and more preferably 25 to 40 mN / m, thereby improving the wettability of PSA and reducing the amount of downstream wetting agent used.

[0031] According to one embodiment of the present invention, the (A1) emulsifier used in the (meth)acrylate copolymer emulsion is an anionic emulsifier having a low critical microcell concentration (CMC), which can be from 1 ppm to 100 ppm, 2 ppm to 80 ppm, 3 ppm to 60 ppm, 4 ppm to 40 ppm, 5 ppm to 20 ppm, or 6 ppm to 10 ppm or any of the above two extremes, preferably about 7 ppm (i.e., mg / kg); the anionic emulsifier can reduce the surface tension of the solution to 25 mN / m to 40 mN / m, 30 mN / m to 39 mN / m, 31 mN / m to 38 mN / m, 32 mN / m to 36 mN / m, or 33 mN / m to 34 mN / m or any of the above two extremes, preferably about 33 mN / m.

[0032] Examples of anionic emulsifiers include: alkyl sulfate anionic emulsifiers such as sodium dodecyl sulfate, ammonium dodecyl sulfate, and potassium dodecyl sulfate; polyoxyethylene alkyl ether sulfate anionic emulsifiers such as sodium polyoxyethylene dodecyl ether sulfate; polyoxyethylene alkylphenyl ether sulfate anionic emulsifiers such as ammonium polyoxyethylene dodecyl phenyl ether sulfate and sodium polyoxyethylene dodecyl phenyl ether sulfate; sulfonate anionic emulsifiers such as sodium dodecylbenzenesulfonate; and sulfosuccinic acid anionic emulsifiers such as disodium dodecyl sulfosuccinate and disodium polyoxyethylene sulfosuccinate. However, this is not an exclusive limitation.

[0033] In one embodiment of the present invention, the anionic emulsifier may be, for example, a commercially available product of Sasol under the trade name "NOVELUTION PA89N" (supplier: Sasol; fatty alcohol alkoxy ether sulfate type emulsifier; solid content of 85 wt%), with a CMC of approximately 7 ppm; or a product of Solvay under the trade name "NOVELUTION PA89N". The commercially available product "RS-610" (supplier: Solvay; alkyl alcohol polyoxyethylene ether ammonium phosphate emulsifier; solids content 100wt%) has a CMC of approximately 20ppm; or Solvay's trade name " The commercially available product “A-103” (supplier: Solvay; nonylphenol polyoxyethylene ether sulfate emulsifier, solid content 34wt%, CMC approximately 100ppm).

[0034] According to one embodiment of the present invention, the (A2) (meth)acrylate copolymer of the present invention has structural units derived from the following monomers:

[0035] (a2-1) can form monomers of homopolymers with glass transition temperatures <0°C.

[0036] According to one embodiment of the present invention, the (A2) (meth)acrylate copolymer may further comprise structural units derived from one or more monomers selected from the group consisting of:

[0037] (a2-2) Monomers that can form homopolymers with glass transition temperatures ≥0°C;

[0038] (a2-3) Hydrophilic monomers that have hydroxyl or carboxyl functional groups;

[0039] (a2-4) Hydrophobic monomers; and

[0040] (a2-5) crosslinking monomer.

[0041] As used herein, "(meth)acrylic acid" includes acrylic acid and methacrylic acid, and "(meth)acrylate" includes acrylate and methacrylate. As used herein, "copolymerization" means block copolymerization, random copolymerization, graft copolymerization, or alternating copolymerization, and "copolymer" means block copolymer, random copolymer, graft copolymer, or alternating copolymer.

[0042] In one embodiment of the present invention, the (A2) (meth)acrylate copolymer of the present invention comprises structural units derived from (a2-1) monomers capable of forming homopolymers having a glass transition temperature of <0°C (i.e., a glass transition temperature less than 0°C), and optionally comprises structural units of (a2-2) monomers capable of forming homopolymers having a glass transition temperature of ≥0°C (i.e., a glass transition temperature of 0°C or above).

[0043] As used herein, the terms "monomer capable of forming a homopolymer with a glass transition temperature <0°C" or "monomer capable of forming a homopolymer with a glass transition temperature ≥0°C" refer to monomers that can form homopolymers composed of the same monomers, and that homopolymers have a glass transition temperature <0°C (or ≥0°C). In this invention, a polymer containing monomers as structural units can refer to monomers that, through polymerization, form the polymer's backbone (e.g., main chain) or side chains.

[0044] The (a2-1) and (a2-2) monomers used in this invention may include, but are not limited to, alkyl (meth)acrylate monomers, methacrylamide monomers, or vinyl carboxylate monomers. The selection of the (a2-1) and (a2-2) monomers used in this invention is not particularly limited, but mainly depends on the glass transition temperature of the isomeric polymer formed by the monomers. For example, monomers with a glass transition temperature < 0°C of the isomeric polymer can be selected from the aforementioned alkyl (meth)acrylate monomers, methacrylamide monomers, or vinyl carboxylate monomers as (a2-1) monomers, or monomers with a glass transition temperature ≥ 0°C of the isomeric polymer can be selected as (a2-2) monomers. The aforementioned alkyl (meth)acrylate monomers may have an alkyl group containing 1 to 20 carbon atoms, 1 to 16 carbon atoms, 1 to 12 carbon atoms, 1 to 8 carbon atoms, or 1 to 4 carbon atoms, and the alkyl group may be branched-chain or straight-chain alkyl. Examples of the above-mentioned (meth)acrylate alkyl monomers include, but are not limited to: methyl acrylate; methyl methacrylate (MMA); 2-methoxyethyl acrylate; butyl acrylate (BA), such as n-butyl acrylate or isobutyl acrylate; propyl acrylate, such as n-propyl acrylate; pentyl acrylate; hexyl acrylate, such as n-hexyl acrylate; heptyl acrylate, such as n-heptyl acrylate; octyl acrylate, such as n-octyl acrylate; or nonyl acrylate, such as n-nonyl acrylate. Examples of the above-mentioned (meth)acrylamide monomers include, but are not limited to: (meth)acrylamide; N,N-dimethylacrylamide; or N-(dodecyl)acrylamide. Examples of the above-mentioned carboxylic acid vinyl ester monomers include, but are not limited to: vinyl acetate or neononanoate.

[0045] The glass transition temperature of the isomeric polymer of the aforementioned monomer (a2-1) can be, for example, less than 0°C, less than -5°C, less than -10°C, less than -15°C, or less than -20°C, with no particular limitation on the lower limit, and can be, for example, -150°C, -125°C, or -100°C. A suitable range of the glass transition temperature can be -100°C to -20°C, -80°C to -25°C, or -60°C to -30°C. In one embodiment of the present invention, the monomer system is selected from vinyl neodecanoate, ethyl acrylate, butyl acrylate, isooctyl acrylate, or isooctyl methacrylate, or combinations thereof. Monomer (a2-1) is the main monomer for preparing the (A2) (meth)acrylate copolymer of the present invention. Compared to monomer (a2-2), monomer (a2-1) imparts flexibility to the (meth)acrylate copolymer; therefore, monomer (a2-1) can be called a soft monomer, and monomer (a2-2) can be called a hard monomer. (a2-1) The monomer gives the resulting pressure-sensitive adhesive good wettability to the substrate.

[0046] The glass transition temperature of the isomeric polymer of the aforementioned (a2-2) monomer can be, for example, 0°C or above, or 5°C or above. There is no particular upper limit to its glass transition temperature, and it can be, for example, 300°C, 250°C, or 200°C. A suitable range for the glass transition temperature is 5°C to 200°C, 5°C to 160°C, or 5°C to 120°C. In one embodiment of the present invention, the monomer system is selected from vinyl nonanoate, vinyl acetate, methyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, or isobutyl methacrylate, or combinations thereof. The (a2-2) hard monomer can be used as needed to further improve the holding power and creep resistance of the (meth)acrylate copolymer. According to one embodiment of the present invention, the amount of (a2-2) hard monomer does not exceed 10% by weight of the total monomer weight to avoid a situation where the pressure-sensitive adhesive composition is too hard and brittle or has poor adhesion after film formation.

[0047] According to one embodiment of the present invention, the (A2) (meth)acrylate copolymer of the present invention may, as needed, include structural units derived from the (a2-3) hydrophilic monomers to increase the compatibility of the (A2) (meth)acrylate copolymer with water. However, if the content of the hydrophilic monomer is too high, it will affect the water-whitening resistance of the waterborne PSA composition. In the present invention, the (a2-3) hydrophilic monomers are monomers having hydrophilic groups such as hydroxyl or carboxyl functional groups. The above-mentioned hydrophilic monomers having hydroxyl groups may include, but are not limited to: hydroxyalkyl methacrylates, such as hydroxyethyl methacrylate, hydroxypropyl methacrylate, hydroxybutyl methacrylate, hydroxyhexyl methacrylate, and hydroxyoctyl methacrylate; or hydroxyalkyleneglycol(meth)acrylates, such as 2-hydroxyethyleneglycol(meth)acrylate, 2-hydroxypropyleneglycol(meth)acrylate, etc. Hydrophilic monomers with carboxyl groups may include, but are not limited to: acrylic acid (AA), methacrylic acid, 2-(acryloyloxy)acetic acid, 2-(methacryloyloxy)acetic acid, 3-(acryloyloxy)propanoic acid, 3-(methacryloyloxy)propanoic acid, 4-(acryloyloxy)butyric acid, 4-(methacryloyloxy)butyric acid, acrylic acid dimer, itconic acid, maleic acid, maleic anhydride, etc. In one embodiment of the present invention, the hydrophilic monomer is selected from acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxypropyl methacrylate, or glycidyl methacrylate (which forms a hydroxyl-containing compound during emulsion polymerization), or combinations thereof. Preferably, acrylic acid, methacrylic acid, 2-hydroxyethyl acrylate (HEA), 2-hydroxyethyl methacrylate, or 2-hydroxypropyl (meth)acrylate is used as the hydrophilic monomer, but the invention is not limited thereto. In one embodiment of the present invention, because a relatively low content of hydrophilic monomer can be used, the water-whitening resistance of the waterborne PSA composition can be further improved.

[0048] According to one embodiment of the present invention, to improve the water-whitening resistance of the aqueous PSA composition, the (A2) (meth)acrylate copolymer of the present invention may, as needed, include structural units derived from the (a2-4) hydrophobic monomers. The inventors of this application have discovered that by using a specific weight ratio (about 0.5 to 3) of the amount of (a2-3) hydrophilic monomer to the amount of (a2-4) hydrophobic monomer, the amount of hydrophilic monomer and emulsifier can be further reduced while maintaining the dispersibility of the aqueous PSA composition, thereby improving the water-whitening resistance of the aqueous PSA composition. According to one embodiment of the present invention, the weight ratio of the amount of (a2-3) hydrophilic monomer to the amount of (a2-4) hydrophobic monomer is 1 to 2.8 (e.g., 1, 1.2, 1.5, 2, 2.3, or 2.5).

[0049] The hydrophobic monomers described above (a2-4) may be monomers having hydrophobic groups such as alkyl, aryl, or alkenyl groups. For example, the monomers having a phenyl hydrophobic group may include, but are not limited to, styrene monomers, such as styrene or styrene substituted with C1-4 alkyl groups, wherein the C1-4 alkyl group may be methyl, ethyl, propyl, or butyl; specific examples include, but are not limited to, styrene, o-methyl styrene, m-methyl styrene, or p-methyl styrene. In one embodiment of the present invention, the hydrophobic monomer system is selected from styrene, isobornyl acrylate, isobornyl methacrylate, acrylonitrile, ethylene tert-carbonate, cyclohexyl acrylate, or cyclohexyl methacrylate, or combinations thereof.

[0050] The inventors of this application have discovered that, in this invention, crosslinking monomers (a2-5) can be added as needed. In this invention, the crosslinking monomer can be a monomer containing crosslinking functional groups that can polymerize with monomers contained in pressure-sensitive adhesive polymers (such as the aforementioned (meth)acrylate). There are no particular limitations on the crosslinking monomers used in this invention; for example, they can be known crosslinking monomers in the field of pressure-sensitive adhesives. The aforementioned (a2-5) crosslinking monomer can be a silane crosslinking agent, preferably a self-crosslinking agent with double bonds. The aforementioned crosslinking agent can undergo a crosslinking reaction with the (A2) (meth)acrylate copolymer of this invention (e.g., the carboxyl group thereon), thus improving the water-whitening resistance of the waterborne PSA composition.

[0051] In one embodiment of the present invention, the crosslinking monomer system is selected from vinyltrimethoxysilane, vinyltriethoxysilane, vinyltri(2-methoxyethoxy)silane, or vinyltriacetoxysilane, or combinations thereof. In a specific example of the present invention, the crosslinking monomer may be a silane coupling agent (vinyltriethoxysilane) of the commercially available product "Silquest A-171" (supplier: Momentive).

[0052] In one embodiment of the present invention, based on the total weight of monomers (a2-1) to (a2-5), the amount of monomer (a2-1) is 80 to 98% by weight (e.g., 80%, 82%, 84%, 86%, 88%, 90%, 92%, 94%, 96%, or 98% by weight). Monomer (a2-1) is an essential monomer for preparing the (A2) (meth)acrylate copolymer of the present invention, and monomer (a2-1) imparts flexibility to the (meth)acrylate copolymer. When the amount of monomer (a2-1) is ≥80% by weight, the pressure-sensitive adhesive has good wettability to the substrate, but when the amount of monomer (a2-1) is >98% by weight, the holding power and creep resistance are insufficient.

[0053] (a2-2) The hard monomer may be used as needed to further improve the holding power and creep resistance of the (meth)acrylate copolymer. According to an embodiment of the present invention, the amount of (a2-2) hard monomer is no more than 10% by weight of the total monomer to avoid the pressure-sensitive adhesive composition becoming hard and brittle or having poor adhesion after film formation. For example, the amount of said (a2-2) monomer may be 0 to 10% by weight (e.g., 0% by weight, 2% by weight, 4% by weight, 6% by weight, 8% by weight, or 10% by weight).

[0054] (a2-3) the hydrophilic monomer, (a2-4) the hydrophobic monomer, and (a2-5) the crosslinking monomer may also be used as needed. For example, the amount of the (a2-3) hydrophilic monomer is 0 to 20% by weight (e.g., 0% by weight, 1% by weight, 2% by weight, 5% by weight, 10% by weight, 15% by weight, or 20% by weight); the amount of the (a2-4) hydrophobic monomer is 0 to 20% by weight (e.g., 0% by weight, 5% by weight, 10% by weight, 15% by weight, or 20% by weight); and the amount of the (a2-5) crosslinking monomer is 0 to 5% by weight (e.g., 0% by weight, 1% by weight, 2% by weight, 3% by weight, 4% by weight, or 5% by weight).

[0055] In one embodiment of the present invention, the weight ratio of the amount of hydrophilic monomer (a2-3) to the amount of hydrophobic monomer (a2-4) is 1 to 3 (e.g., 1, 1.2, 1.5, 2, 2.5, or 3).

[0056] According to one embodiment of the present invention, without impairing the target effect, in addition to the components explained above, the aqueous PSA composition of the present invention may contain any known suitable additives, such as polymerization initiators, wetting agents, defoamers, tackifying resins, bactericides, thickeners, curing agents, UV light stabilizers, antioxidants, colorants, reinforcing agents, fillers, surfactants or plasticizers or combinations thereof.

[0057] The polymerization initiator described above can be a water-soluble polymerization initiator. Specific examples of polymerization initiators include, but are not limited to, ammonium or alkali metal persulfates (e.g., ammonium persulfate) or peroxides (e.g., hydrogen peroxide). Furthermore, the polymerization initiator can be used in conjunction with one or more reducing agents to carry out emulsion polymerization reactions at low temperatures.

[0058] Wetting agents can increase the coatability of aqueous PSA compositions. In this invention, the wetting agent can be used within a range of concentrations well known in the art. In one embodiment of this invention, the aqueous PSA composition may use a relatively low concentration of wetting agent or may not require additional wetting agent addition. As a wetting agent, dioctyl sodium sulfosuccinate (DOSS) compounds may be used, but are not limited thereto.

[0059] The aforementioned tackifying resin may be, for example, but not limited to: hydrocarbon resin or hydrogenated hydrocarbon resin, rosin resin or hydrogenated rosin resin, rosin ester resin or hydrogenated rosin ester resin, terpene resin or hydrogenated terpene resin, terpene phenol resin or hydrogenated terpene phenol resin, polymerized rosin resin or polymerized rosin ester resin, but not limited to these.

[0060] The aqueous PSA composition of this invention can be coated onto a substrate as a pressure-sensitive adhesive. A release film can be further applied to the side of the pressure-sensitive adhesive opposite to the substrate, and a protective film (such as a cold lamination film) can be provided. The substrates include olefin-based resin sheets (such as polyethylene film, polypropylene film, ethylene-propylene copolymer film, etc.), vinyl chloride-based resin sheets (such as polyvinyl chloride film, also known as PVC film), polyester film, and other plastic films; foamed substrates such as polyurethane foam and polyethylene foam; papers such as kraft paper, crepe paper, and Japanese paper; fabrics such as cotton cloth and synthetic fiber cloth; non-woven fabrics such as polyester non-woven fabric and vinylon non-woven fabric; and metal foils such as aluminum foil and copper foil. In one embodiment of the present invention, the aqueous PSA composition of the present invention is particularly suitable for low surface energy substrates (e.g., PVC film), and has good coating and adhesion to low surface energy substrates, as well as good water whitening resistance and plasticizer resistance. It can avoid the PSA from deteriorating adhesion due to the precipitation of plasticizers in PVC film. Thus, the present invention can further provide an improved PVC protective film or cold lamination film.

[0061] The protective film of this invention can be adhered to the surface of an object using pressure-sensitive adhesive to protect the object's surface. There are no particular limitations on the objects described. In one embodiment of this invention, the objects specifically refer to those with a pigment-containing coating on their surface, such as, but not limited to, posters, advertising panels, photographs, and vehicle advertisements. The protective film of this invention exhibits good adhesion, high transparency, and a suitable air venting rate when adhered to the surface of an object, thus minimizing the formation of air bubbles during adhesion.

[0062] The method for preparing the aqueous pressure-sensitive adhesive composition of the present invention comprises the following steps:

[0063] (1) Preparation of (A) (meth)acrylate copolymer emulsion; and

[0064] (2) Add (B) dispersant and other additives as needed to (A) (meth)acrylate copolymer emulsion.

[0065] The preparation of the (A) (meth)acrylate copolymer emulsion in step (1) above includes mixing and stirring the (A1) emulsifier and (a2-1) monomer and (a2-2) to (a2-5) monomers selected as needed, and carrying out an emulsion polymerization reaction in an aqueous solution to obtain the (A) (meth)acrylate copolymer emulsion.

[0066] Step (1) above can be carried out in the presence of a polymerization initiator, the type of which can be as described above. Furthermore, a neutralizing agent can be added in step (1) to carry out a neutralization reaction. Any neutralizing agent known in the art can be used. According to an embodiment of the present invention, usable neutralizing agents include, for example, but not limited to, dimethylethanolamine (DMEA) or ammonia.

[0067] The additives in step (2) above include, but are not limited to, defoamers, wetting agents, tackifying resins, or bactericides.

[0068] In one specific embodiment of the method of the present invention, the aqueous pressure-sensitive adhesive composition of the present invention can be obtained by the following preparation steps I and II, but is not limited thereto:

[0069] I. Preparation of (A) (meth)acrylate copolymer emulsion:

[0070] (1) Add deionized water and buffer solution to the reactor to obtain bottom liquid (I), and introduce nitrogen gas. Heat to a certain temperature with stirring and keep the temperature constant.

[0071] (2) Add deionized water, (A1) emulsifier and (a2-1) to (a2-5) monomers to a beaker and stir for 30 to 60 minutes to pre-emulsify it to obtain pre-emulsion (II).

[0072] (3) Take another beaker and dissolve the initiator in deionized water to obtain an initiator aqueous solution (III).

[0073] (4) Control the reactor temperature within the reaction temperature range (e.g., 70–88°C), and add the pre-emulsion (II) and initiator aqueous solution (III) dropwise into the reactor, controlling the injection time to be 2–6 hours. During the injection process, control the reaction temperature and injection speed within the set range, and coordinate with an appropriate stirring rate. After the pre-emulsion (II) and initiator aqueous solution (III) are added, hold the temperature for about 30–120 minutes, then cool it and add a neutralizing agent to obtain the small particle size (A) (meth)acrylate copolymer emulsion as described in this invention.

[0074] II. Preparation of water-based pressure-sensitive adhesive compositions

[0075] Take an appropriate amount of the above-mentioned (A) (meth)acrylate copolymer emulsion, add (B) dispersant, and add additives as needed, stir thoroughly and filter to obtain the water-based pressure-sensitive adhesive composition of the present invention. In a specific embodiment of the present invention, the obtained water-based pressure-sensitive adhesive composition has a solid content of 50-55% by weight, a pH value of 6.5-8.5, and a viscosity of 600-1200 cps.

[0076] Example

[0077] The following embodiments are provided to further illustrate the present invention and are not intended to limit the scope of the invention. Any modifications and alterations that can be easily made by those skilled in the art are included within the scope of the disclosure in this specification and the appended claims.

[0078] The raw materials used in each preparation example and embodiment are described below:

[0079] The monomer of MMA is methyl methacrylate;

[0080] The BA monomer is butyl acrylate;

[0081] The monomer AA is acrylic acid;

[0082] HEA monomer is 2-hydroxyethyl acrylate;

[0083] ST monomer is styrene;

[0084] The monomer for A-171 is vinyltriethoxysilane (trade name: Silquest A-171; supplier: Momentive); the APS initiator is ammonium persulfate.

[0085] Emulsifier:

[0086]

[0087] Dispersant:

[0088]

[0089] Preparation of (meth)acrylate copolymer emulsions

[0090] Preparation Example 1

[0091] (1) Prepare a reaction vessel equipped with a stirrer, a dropping funnel, a condenser and a thermometer. Add 48g of deionized water and 0.076g of sodium acetate buffer to the reaction vessel to obtain the bottom liquid (I). Then introduce nitrogen gas and heat it to 80-85℃ with stirring, and keep it at a constant temperature.

[0092] (2) Add 20.3g of deionized water, 1.48g of anionic emulsifier PA89N (85% solid content), 1.37g of methyl methacrylate (MMA), 94.085g of butyl acrylate (BA), 1.68g of acrylic acid (AA), 1.47g of hydroxyethyl acrylate (HEA), 1.37g of styrene (ST), and 0.025g of vinyltrimethoxysilane (A-171) to a beaker, stir for 30 to 60 minutes to pre-emulsify it, and obtain a pre-emulsion (II);

[0093] (3) In a separate beaker, dissolve 0.4407 g of the initiator ammonium persulfate (APS) in 9.2 g of deionized water to obtain an initiator aqueous solution (III); and

[0094] (4) Control the reactor temperature within the reaction range of 78-88℃, and add the pre-emulsion (II) and initiator aqueous solution (III) dropwise into the reactor, controlling the injection time to be 4-6 hours. During the injection process, control the reaction temperature and injection speed within the set range, and coordinate with an appropriate stirring rate. After the pre-emulsion (II) and initiator aqueous solution (III) are added, hold the temperature for about 90-120 minutes, then cool it and add 1.6g of neutralizing agent ammonia water to obtain the small particle size (A) (meth)acrylate copolymer emulsion E1 of the present invention, with an emulsion particle size of 153nm and a solid content of 53.1%.

[0095] Preparation Example 2

[0096] Same as in Preparation Example 1, except that the amount of anionic emulsifier PA89N (solid content 85%) added is changed to 2.94g, and the small particle size (A) (meth)acrylate copolymer emulsion E2 of the present invention can be obtained, with an emulsion particle size of 106nm and a solid content of 53.4%.

[0097] Preparation Example 3

[0098] Same as in Preparation Example 1, except that the amount of anionic emulsifier PA89N (solid content 85%) added is changed to 0.59g, and the small particle size (A) (meth)acrylate copolymer emulsion E3 of the present invention can be obtained, with an emulsion particle size of 185nm and a solid content of 52.9%.

[0099] Preparation Example 4

[0100] Same as Preparation Example 1, except that the anionic emulsifier is replaced with RS-610 (100% solid content) and the amount added is 1.3g, so as to obtain the small particle size (A) (meth)acrylate copolymer emulsion E4 of the present invention, with an emulsion particle size of 132nm and a solid content of 53.3%.

[0101] Preparation Example 5

[0102] Same as in Preparation Example 1, except that the anionic emulsifier was replaced with A-103 (34% solid content) and the amount added was 3.7g, thus obtaining (A) (meth)acrylate copolymer emulsion E5, with an emulsion particle size of 183nm and a solid content of 53.5%.

[0103] Preparation Example 6

[0104] Same as in Preparation Example 1, except that the amount of anionic emulsifier PA89N (solid content 85%) added was changed to 4.12g. As a result, the viscosity of the pre-emulsion (II) was too high, making it difficult to add dropwise and thus the preparation could not be completed smoothly. Therefore, the pressure-sensitive adhesive was not prepared in the future.

[0105] Preparation Example 7

[0106] Same as in Preparation Example 1, except that the amount of anionic emulsifier PA89N (solid content 85%) added was changed to 0.42g. As a result, the pre-emulsion (II) was prone to separation, and more flocculations were produced during the reaction, making it impossible to complete the preparation smoothly. Therefore, the pressure-sensitive adhesive was not prepared in the subsequent steps.

[0107] Table 1 lists the monomers and emulsifiers used in the preparation of (meth)acrylate copolymer emulsions E1 to E7 of Examples 1 to 7, their amounts, and the particle size of the emulsions. The method for measuring the particle size of the emulsions is described in detail below.

[0108] [Table 1]

[0109]

[0110] As shown in Table 1, compared to Preparation Examples 1-4, Preparation Example 5 used an anionic emulsifier A-103 with a higher CMC value. Because a higher CMC value requires a larger amount of emulsifier to achieve a good emulsification effect, Preparation Example 5 also used an anionic emulsifier with an effective component content (calculated from the actual amount of emulsifier added and its solid content) of approximately 1.26% by weight. However, the emulsion particle size of the (meth)acrylate copolymer emulsion E5 obtained in Preparation Example 5 was larger than that of E1, but still fell within the category of small-particle-size emulsions. Furthermore, in Preparation Example 6, the effective component content of the emulsifier was too high, resulting in excessively high viscosity of the pre-emulsion (II), making dropwise addition difficult. In Preparation Example 7, the effective component content of the emulsifier was too low, causing the pre-emulsion (II) to easily separate into layers, and during the reaction, more flocculation occurred, making successful preparation impossible.

[0111] Therefore, the aqueous pressure-sensitive adhesive composition was prepared using only the (meth)acrylate copolymer emulsions E1 to E5 obtained in Preparation Examples 1 to 5.

[0112] Preparation of Waterborne Pressure-Sensitive Adhesive Compositions

[0113] Example 1

[0114] Take 100g of (meth)acrylate copolymer emulsion E1, add 2.2g of dispersant SN 5040 (solid content 45.86%), stir thoroughly and filter to obtain an aqueous pressure-sensitive adhesive composition with a solid content of 50-55% by weight, a pH value of 6.5-8.5, and a viscosity of 600-1200 cps.

[0115] Example 2

[0116] Same as Example 1, except that the amount of dispersant SN 5040 (solid content 45.86%) added was changed to 3.3g.

[0117] Example 3

[0118] Same as Example 1, except that the amount of dispersant SN 5040 (solid content 45.86%) added was changed to 1.1g.

[0119] Example 4

[0120] Same as Example 1, except that (meth)acrylate copolymer emulsion E2 was used instead.

[0121] Example 5

[0122] Same as Example 1, except that (meth)acrylate copolymer emulsion E3 was used instead.

[0123] Example 6

[0124] Same as Example 1, except that (meth)acrylate copolymer emulsion E4 was used instead.

[0125] Example 7

[0126] Same as Example 1, except that (meth)acrylate copolymer emulsion E5 was used instead.

[0127] Example 8

[0128] Same as Example 1, except that the amount of dispersant SN 5040 (solid content 45.86%) added was changed to 5.5g.

[0129] Example 9

[0130] Same as Example 1, except that the amount of dispersant SN 5040 (solid content 45.86%) added was changed to 0.22g.

[0131] Example 10

[0132] Same as Example 1, except that the dispersant is changed to SN 5027 (solid content 18.21%), and the dosage is 5.5g.

[0133] Example 11

[0134] Same as Example 1, except that the dispersant was changed to 755W (solid content 41.24%), and the dosage was 2.42g.

[0135] Example 12

[0136] Same as Example 1, except that the dispersant was changed to 760W (solid content 35.56%), and the dosage was 2.81g.

[0137] Preparation of Pressure-Sensitive Adhesive Tape

[0138] Pressure-sensitive adhesive tape was prepared using the aqueous pressure-sensitive adhesive composition of the above embodiments as follows: First, a PVC film with a length of 20 cm, a width of 40 cm, and a thickness of 11-13 micrometers was prepared. The aqueous pressure-sensitive adhesive composition of Examples 1 to 12 was coated on one surface of the PVC film and dried at 100°C for 4 minutes to form a pressure-sensitive adhesive layer with a thickness of about 11-13 micrometers.

[0139] Sexual quality measurement methods

[0140] 1. Solid content

[0141] Weigh and record the weight of the empty aluminum dish. Then weigh 1-2g of the (meth)acrylate copolymer emulsion sample and place it in the aluminum dish. After it has leveled, place it on a heating plate and bake at 150℃ for 15 minutes. Finally, weigh the (baked sample + aluminum dish) and calculate its solid content.

[0142]

[0143] 2. Acid value (AV)

[0144] (1) First, weigh 1-3g of the sample into an Erlenmeyer flask, then add about 50ml of neutral toluene / ethanol solution (toluene: ethanol (95%) = 1:1, with phenolphthalein indicator added, and then add 0.1mol / L KOH until slightly red), shake to dissolve the sample (or heat to dissolve);

[0145] (2) Titrate the solution obtained in step (1) with an ethanol solution containing 0.1 mol / L potassium hydroxide (KOH) until it turns slightly pink, and record the volume of titrant used; and

[0146] (3). Calculate the acid value (AV) using the following formula:

[0147]

[0148] 3. Particle size

[0149] In this invention, the emulsion particle size was measured using a Horiba LA-950 instrument. First, the (meth)acrylate copolymer emulsions obtained in Preparation Examples 1-5 were diluted 400-800 times with pure water. Then, an appropriate amount of water was added to a quartz measuring cell. The refractive index of the sample was set to 1.47-1.48, the refractive index of the dispersion was set to 1.33 (pure water), and the blue light transmittance was adjusted to 68-72%. After measuring the background blank value, several drops of the diluted aqueous pressure-sensitive adhesive composition sample were added to the quartz measuring cell, and the particle size distribution was measured.

[0150] 4. Peel strength

[0151] Measurements were performed according to the PSTC-1 (International Standard for Peel Adhesion of Pressure Sensitive Tape) test method established by the American Tape Association.

[0152] 5. Initial tack (Loop Tack)

[0153] Measurements were performed according to the PSTC-16 Test Method A (International Standard for Loop Tack) established by the American Tape Association.

[0154] Surface tension

[0155] Measurements were performed according to ASTM D1331 (Standard Test Methods for Surface and Interfacial Tension of Solutions of Paints, Solvents, Solutions of Surface-Active Agents, and Related Materials), established by the American Society for Testing and Materials.

[0156] Evaluation Methods and Standards Explanation

[0157] 1. fit

[0158] Cut a 2-inch x 5-inch sample, use a roller to attach the aforementioned pressure-sensitive tape to a black advertising paper, place it horizontally and start timing. Observe the appearance of the bonding interface and the air release effect every half hour, and record the time required for the sample to be fully bonded (here, full bonding means that the proportion of air bubbles in the total area of ​​the bonding interface is less than 5%), and score according to the time required for full bonding.

[0159]

[0160] 2. Resistant to water whitening

[0161] Cut a sample strip approximately 1 inch x 6 inches in size and place it in pure water at 25°C. Immerse the rubber surface in the water and start timing. Observe the appearance of the rubber surface every half hour until the rubber surface becomes foggy. Record the immersion time and score according to the time required for the surface to become foggy.

[0162]

[0163] Table 2 lists the composition and property test results of the water-based pressure-sensitive adhesives in Examples 1 to 12.

[0164] Table 2

[0165]

[0166] *The numbers in parentheses indicate the total weight (in grams) of solid components per 100 grams of emulsion.

[0167] **The weight (in grams) of the active ingredient in the dispersant is indicated in parentheses.

[0168] As shown in Table 2, the pressure-sensitive adhesives used in Examples 1-7 employed dispersants with acid values ​​between 15 and 35 mg KOH / g, exhibiting both superior adhesion and water-whitening resistance. Compared to Examples 1, 10, and 11, with the same dispersant active ingredient content of 1.88 parts by weight (based on a solid content of 100 parts by weight for the (meth)acrylate copolymer emulsion), the use of dispersants with higher acid values, SN 5027 and 755W, resulted in excessively strong adhesion between the pressure-sensitive adhesive film and the substrate. Gas at the bonding area was difficult to expel, affecting the bonding effect. Furthermore, the high acid value of the dispersant also increased the hydrophilicity of the pressure-sensitive adhesive, leading to poor water-whitening resistance. Compared to Example 1, in Example 12, with the same dispersant effective ingredient content of 1.88 parts by weight (based on the solid content of (meth)acrylate copolymer emulsion of 100 parts by weight), when using a dispersant with a lower acid value of 760W, the pressure-sensitive adhesive has poor wettability on the surface of the object being bonded, resulting in a slower gas expulsion rate at the bonding area, which in turn affects the bonding performance.

[0169] The pressure-sensitive adhesives in Examples 8 and 9 had the same composition as those in Example 1, except for the different content of the dispersant active ingredient. The results showed that, under the concept of this invention, using a dispersant with an acid value between 15 and 35 mg KOH / g, and adjusting the amount of dispersant, achieved the good adhesion and water-whitening properties described in this invention. In Example 8, the dispersant active ingredient content exceeded 4 parts by weight (based on 100 parts by weight of the solid content of the (meth)acrylate copolymer emulsion). Although this resulted in good wettability on the surface of the adhered object, it increased the hydrophilicity of the pressure-sensitive adhesive, thus affecting water-whitening resistance. In Example 9, the dispersant active ingredient content was less than 0.2 parts by weight (based on 100 parts by weight of the solid content of the (meth)acrylate copolymer emulsion). The pressure-sensitive adhesive did not wet the surface of the adhered object well enough, resulting in slower gas expulsion at the bonding area, thus affecting adhesion.

Claims

1. A water-based pressure-sensitive adhesive composition comprising: (A) (meth)acrylate copolymer emulsion, and (B) Dispersant, The (A) (meth)acrylate copolymer emulsion contains (A1) emulsifier and (A2) (meth)acrylate copolymer. The emulsifier (A1) is an anionic emulsifier with a critical microcell concentration of 1 ppm to 100 ppm, and the content of emulsifier (A1) is 0.5 to 3 parts by weight, based on 100 parts by weight of the total monomers used to prepare the (A2) (meth)acrylate copolymer. The (A2) (meth)acrylate copolymer described therein has structural units derived from the following monomers: (a2-1) Monomers capable of forming homopolymers with glass transition temperatures <0°C, and structural units of monomers selected from one or more groups of the following: (a2-2) Monomers that can form homopolymers with glass transition temperatures ≥0℃; (a2-3) Hydrophilic monomers having hydroxyl or carboxyl functional groups; (a2-4) A hydrophobic monomer, said hydrophobic monomer being selected from styrene, isobornyl acrylate, isobornyl methacrylate, acrylonitrile, vinyl tert-carbonate, cyclohexyl acrylate, or cyclohexyl methacrylate, or combinations thereof, and (a2-5) Crosslinking monomer, wherein the crosslinking monomer is selected from silanes having double bonds; and in, Based on the total weight of monomers (a2-1) to (a2-5), the amount of monomer (a2-1) is 80 to 98% by weight. The dispersant (B) has an acid value of 15 to 35 mg KOH / g, and the content of the dispersant (B) is 0.2 to 4 parts by weight based on 100 parts by weight of the solid content of the (A) (meth)acrylate copolymer emulsion.

2. The aqueous pressure-sensitive adhesive composition according to claim 1, wherein the particle size of the (A) (meth)acrylate copolymer emulsion is 60 to 250 nm.

3. The aqueous pressure-sensitive adhesive composition according to claim 1, wherein the dispersant (B) is a polycarboxylate dispersant.

4. The water-based pressure-sensitive adhesive composition according to claim 1, wherein the anionic emulsifier comprises an alkyl sulfate type anionic emulsifier, a polyoxyethylene alkyl ether sulfate type anionic emulsifier, a polyoxyethylene alkyl phenyl ether sulfate type anionic emulsifier, a sulfonate type anionic emulsifier, or a sulfosuccinic acid type anionic emulsifier.

5. A method for preparing an aqueous pressure-sensitive adhesive composition according to any one of claims 1 to 4, comprising the following steps: (1) Preparation of (A) (meth)acrylate copolymer emulsion; and (2) Add dispersant (B) to (A) (meth)acrylate copolymer emulsion. The (A) (meth)acrylate copolymer emulsion contains (A1) emulsifier and (A2) (meth)acrylate copolymer. The emulsifier (A1) is an anionic emulsifier with a critical microcell concentration of 1 ppm to 100 ppm, and the content of emulsifier (A1) is 0.5 to 3 parts by weight, based on 100 parts by weight of the total monomers used to prepare the (A2) (meth)acrylate copolymer. The dispersant (B) has an acid value of 15 to 35 mg KOH / g, and the content of the dispersant (B) is 0.2 to 4 parts by weight based on 100 parts by weight of the solid content of the (A) (meth)acrylate copolymer emulsion.

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