Pressure-sensitive adhesive articles

Abstract

A pressure-sensitive adhesive article is provided, comprising: (a) a substrate (Sa); (b) a layer (Lb) in contact with the substrate (Sa) of a pressure-sensitive composition (Cb) comprising one or more acrylic polymers (POLb) having a Tg of 20° C. or less; and (c) a layer (Lc) in contact with layer (Lb) comprising (i) one or more acrylic polymers (POLc1) having a Tg of 20° C. or less, and (ii) one or more acrylic tackifier polymers having a Tg of −10° C. or more. A method of producing the pressure-sensitive adhesive article, and bonded articles produced by using the pressure-sensitive adhesive article are also provided.

Description

[Technical field]

[0001] Pressure sensitive adhesives (PSAs) containing acrylic polymers have many desirable characteristics. For example, they generally have better resistance to chemical reagents and UV light than PSAs made from many other materials. It is often desirable to provide an acrylic-based PSA that bonds well to a polyolefin target substrate. In the past, tackifier compounds have sometimes been added to PSAs to increase the tack adhesion (also called "tackiness" or "tack") of the PSA to the target substrate. However, the addition of tackifiers usually results in an undesirable decrease in the shear resistance of the PSA.

[0002] No. 9,765,241 describes a pressure-sensitive adhesive article comprising a substrate, a layer containing an acrylic polymer, and a layer containing an acrylic polymer that includes polymerized units of one or more high-aliphatic vinyl monomers.

[0003] It is desirable to provide a PSA that contains an acrylic polymer and exhibits both good tack adhesion and good shear resistance when bonded to a polyolefin target substrate.In addition, it is desirable to provide a PSA that includes a layer in which the top layer (i.e., the layer adjacent to the target substrate) contains a relatively high level of tackifier and the other layers contain a relatively low level of tackifier.It is currently believed that in such a multi-layer PSA, if the tackifier migrates from the top layer into the other layers, the tack adhesion to the target substrate decreases.Therefore, it is also desirable to provide a multi-layer PSA that resists the migration of tackifier from the top layer.

[0004] The following is a description of the present invention.

[0005] The first aspect of the present invention is (a) a substrate (Sa); (b) in contact with the substrate (Sa) a layer (Lb) of a pressure-sensitive composition (Cb) comprising one or more acrylic polymers (POLb) having a Tg of 20° C. or less; (c) a layer (Lc) in contact with layer (Lb), the weight of which is based on the weight of layer (Lc), (i) one or more acrylic polymers (POLc1) having a Tg of 20° C. or less, of which 60% to 99.5% is present; and (ii) 0.5% to 40% of one or more acrylic polymers (POLc2) having a number average molecular weight of 2,000 or more and a number average molecular weight of 35,000 or less and a Tg of -10°C or more, by weight based on the weight of (POLc2), (A) 50% to 99.9% of one or more unsubstituted alkyl esters of (meth)acrylic acid, where the alkyl group has 1 to 20 carbon atoms; (B) 0% to 50% acrylic acid, methacrylic acid, or a mixture thereof; (C) and a layer (Lc) comprising an acrylic polymer (POLc2) comprising 0% to 50% polymerized units of one or more additional vinyl monomers.

[0006] A second aspect of the present invention is a method of making a pressure-sensitive article of the first aspect, the method comprising: (A) forming a layer of an aqueous composition (Qb) containing dispersed particles of an acrylic polymer (POLb) on a first surface; (B) forming on the second surface a layer of an aqueous composition (Qc) containing (i) an acrylic polymer (POLc1) and (ii) dispersed particles containing an acrylic polymer (POLc2); (C) drying a layer of the aqueous composition (Qb) to form a layer (Lb); (D) drying the layer of aqueous composition (Qc) to form a layer (Lc).

[0007] A third aspect of the invention is a bonded article produced by the process of contacting a substrate (Sd) with the article of the first aspect, the substrate (Sd) being in contact with a layer (Lc). [Brief description of the drawings]

[0008] Below is a brief description of the drawings.

[0009] [Figure 1] 1 is a vertical cross-sectional view of a pressure-sensitive adhesive article of the invention, showing a substrate (Sa) (1), a layer (Lb) (2) of a composition (Cb) containing one or more acrylic polymers (POLb), and a layer (Lc) (3) of a composition (Cc) containing a polymer (POLc1) and a polymer (POLc2). FIG. 1 is not drawn to scale in any sense. For example, the horizontal dimensions of the pressure-sensitive adhesive article of the invention shown in FIG. 1 may be 1000 times or more larger than the vertical dimensions shown in FIG. 1. [Diagram 2] Figure 2 shows preferred applications in which the pressure-sensitive adhesive articles of the present invention can be used (also not drawn to scale): Figure 2 shows a layer (Lc) (3) in contact with an additional substrate (Sd) (4).

[0010] The following is a detailed description of the present invention.

[0011] As used herein, the following terms have the definitions specified, unless the context clearly indicates otherwise.

[0012] As used herein, dynamic mechanical analysis (DMA) refers to a 1 second -1 DMA refers to measurements made in the linear viscoelastic range of shear geometry at frequencies of 0.01 mm to 0.1 mm. DMA measures Elastic Modulus (G'), Loss Modulus (G''), and Tan Delta. Elastic Modulus is reported herein in units of kilopascals (kPa).

[0013] The glass transition temperature (Tg) of a material is determined by differential scanning calorimetry using the midpoint method and a temperature scan rate of 10° C. per minute according to test method ASTM D7426-08 (American Society of Testing and Materials, Conshohocken, Pa., USA).

[0014] As used herein, a "polymer" is a relatively large molecule composed of the reaction product of smaller chemical repeating units. Polymers may have structures that are linear, branched, star-shaped, looped, hyperbranched, crosslinked, or combinations thereof, and polymers may have a single type of repeating unit ("homopolymer") or they may have two or more types of repeating units ("copolymer"). Copolymers may have different types of repeating units arranged randomly, sequentially, in blocks, in other arrangements, or in any mixture or combination thereof. The size of a polymer is characterized by the number average molecular weight, Mn, or the weight average molecular weight, Mw, both of which are measured by size exclusion chromatography.

[0015] As used herein, "weight of polymer" means the dry weight of the polymer.

[0016] Molecules that can react with each other to form repeat units of a polymer are known herein as "monomers." The repeat units so formed are known herein as "polymerized units" of the monomer.

[0017] The vinyl monomer has the structure [ka] In the formula, R 1 , R 2 , R 3 , and R 4 Each of is independently hydrogen, a halogen, an aliphatic group (such as, for example, an alkyl group), a substituted aliphatic group, an aryl group, a substituted aryl group, another substituted or unsubstituted organic group, or any combination thereof.

[0018] The alkyl group can be linear, branched, cyclic, or any combination thereof.

[0019] Some suitable vinyl monomers include, for example, styrene, substituted styrenes, dienes, ethylene, other alkenes, dienes, ethylene derivatives, and mixtures thereof. Ethylene derivatives include, for example, unsubstituted or substituted versions of the following: ethenyl esters of substituted or unsubstituted alkanoic acids (including, for example, vinyl acetate and vinyl neodecanoate), acrylonitrile, (meth)acrylic acid, (meth)acrylates, (meth)acrylamides, vinyl chloride, halogenated alkenes, and mixtures thereof. As used herein, "(meth)acrylic" means acrylic or methacrylic, "(meth)acrylate" means acrylate or methacrylate, and "(meth)acrylamide" means acrylamide or methacrylamide. "Substituted" means having at least one attached chemical group, such as, for example, an alkyl group, an alkenyl group, a vinyl group, a hydroxyl group, a carboxylic acid group, other functional groups, and combinations thereof. In some embodiments, substituted monomers include, for example, monomers with two or more carbon-carbon double bonds, monomers with hydroxyl groups, monomers with other functional groups, and monomers with combinations of functional groups. (Meth)acrylates are substituted and unsubstituted esters or amides of (meth)acrylic acid.

[0020] As used herein, an acrylic monomer is a monomer selected from (meth)acrylic acid, aliphatic esters of (meth)acrylic acid, aliphatic esters of (meth)acrylic acid having one or more substituents on the aliphatic group, (meth)acrylamide, N-substituted (meth)acrylamide, and mixtures thereof.

[0021] As used herein, a vinyl aromatic monomer is a monomer selected from styrene, alpha-alkyl styrenes, other substituted styrenes, and mixtures thereof.

[0022] As used herein, an "acrylic" polymer is one in which 50% or more of the polymerized units are acrylic monomers and 70% or more of the polymerized units are either acrylic or vinyl aromatic monomers. Percentages are by weight based on the weight of the polymer.

[0023] As used herein, a chain transfer agent is a substance that acts during free radical vinyl polymerization to transfer a radical from a growing polymer chain to a non-radical molecule. The molecule that accepts the radical may itself be the chain transfer agent.

[0024] As used herein, a tackifier is an organic compound having a molecular weight of 500 to 50,000 and a glass transition temperature of -10°C or greater.

[0025] A pressure sensitive adhesive (PSA) is an adhesive that forms a bond with a substrate when pressure is applied to bring the adhesive and substrate into contact. The bond is formed without the addition of additional materials or heat. As used herein, a pressure sensitive adhesive article is an article in which a pressure sensitive adhesive is adhered to a first substrate and a surface of the PSA (the "available surface") is available for contacting a second substrate. The available surface of the PSA may or may not come into contact with a release material. A release material is a material that forms a weak bond with the PSA and can be easily removed to expose the available surface.

[0026] A composition is considered to be "aqueous" herein if it contains water in an amount of 25% or more by weight based on the weight of the composition.

[0027] Particles are said to be dispersed in a liquid medium herein when they are distributed throughout the liquid medium, and the dispersed particles may form an emulsion, latex, dispersion, slurry, or some other composition in which particles are dispersed in a liquid medium. If water forms 50% or more by weight of the liquid medium (disregarding the weight of the dispersed particles), the liquid medium is considered to be an aqueous medium herein.

[0028] When we say that an aqueous composition is dried herein, we mean that the composition is either dried under ambient conditions or dried by the application of heat, exposure to a moving gas (which may or may not be heated), or a combination thereof.

[0029] The ratios presented herein are characterized as follows. For example, when a ratio is said to be 3:1 or more, it can be 3:1, or 5:1, or 100:1, but not 2:1. This characterization can be described in general terms as follows. When a ratio is said to be X:1 or more herein, it means that the ratio is Y:1, where Y is X or more. In another example, when a ratio is said to be 15:1 or less, it can be 15:1, or 10:1, or 0.1:1, but not 20:1. In general, when a ratio is said to be W:1 or less herein, it means that the ratio is Z:1, where Z is W or less.

[0030] The present invention includes the use of a substrate, herein labeled substrate (Sa). The substrate (Sa) may be of any material. Preferred are paper, polymeric films and metal foils. Among polymeric films, preferred are polyester films. Among polymeric films, preferred are those that are treated on at least one side by corona discharge.

[0031] In contact with the substrate (Sa) is a layer of a composition, referred to herein as composition (Cb). Composition (Cb) contains one or more polymers, referred to herein as polymers (POLb). Polymer (POLb) has a Tg of 20° C. or less, preferably 10° C. or less. Preferably, polymer (POLb) has a Tg of −100° C. or more.

[0032] Preferably, composition (Cb) has little or no tackifier, i.e. the amount of tackifier in composition (Cb) is less than 10%, more preferably 3% or less, more preferably 1% or less, more preferably zero, by weight based on the dry weight of composition (Cb).

[0033] Preferably, the polymer (POLb) is an acrylic polymer. Preferably, the amount of polymerized units of acrylic monomers in the polymer (POLb) is 50% or more, more preferably 70% or more, more preferably 90% or more, more preferably 99% or more, by weight based on the weight of the polymer (POLb). Preferably, the polymer (POLb) has an Mw of 10,000 or more, more preferably 50,000 or more.

[0034] Preferably, the polymer (POLb) contains one or more polymerized units of n-butyl acrylate (n-BA), ethyl acrylate (EA), isooctyl acrylate (i-OA), or mixtures thereof. As used herein, "isooctyl" is an unsubstituted alkyl group containing exactly 8 carbon atoms in a branched configuration. The term "isooctyl" includes all branched isomers of 8 carbon alkyl groups, and all mixtures of such isomers, including, for example, 2-ethylhexyl, dimethyl-hexyl, methyl-heptyl, trimethyl-pentyl, and mixtures thereof. Preferably, the sum of the amount of polymerized units of n-BA, polymerized units of EA, and polymerized units of i-OA in the polymer (POLb) is 50% or more, more preferably 75% or more, more preferably 90% or more, by weight based on the weight of the polymer (POLb).

[0035] Preferably, all polymers in composition (Cb) having a Mw of 10,000 or greater are acrylic polymers.

[0036] Preferably, the amount of polymer (POLb) in composition (Cb) is, by weight based on the dry weight of composition (Cb), 80% or more, more preferably 90% or more, more preferably 95% or more.

[0037] Preferably, composition (Cb) has the properties of a PSA. Preferably, composition (Cb) has an elastic modulus (G') of 20 kPa or more over a temperature range including the range of 10°C to 40°C. Preferably, composition (Cb) has an elastic modulus (G') of 1000 kPa or less, more preferably 500 kPa or less, over a temperature range including the range of 10°C to 40°C.

[0038] Preferably, the composition (Cb) is in contact with the surface of the substrate (Sa) which is being treated by corona discharge.

[0039] Layer (Lc) of composition (Cc) is in contact with layer (Lb) of composition (Cb). Composition (Cc) contains one or more polymers (POLc1). The essential and preferred characteristics of polymer (POLc1) are the same as those explained above for polymer (POLb). Polymers (POLb) and (POLc1) may be the same or different from each other. Preferably, the amount of (POLc1) in composition (Cc) is 70% or more, more preferably 80% or more, more preferably 85% or more, by weight based on the weight of composition (Cc). Preferably, the amount of (POLc1) in composition (Cc) is 99.5% or less, more preferably 99% or less, more preferably 98% or less, more preferably 95% or less, more preferably 91% or less, by weight based on the weight of composition (Cc).

[0040] In addition, the composition (Cc) contains an acrylic polymer (POLc2). The acrylic polymer (POLc2) has a number average molecular weight (Mn) of 2,000 or more. The acrylic polymer (POLc2) has a Mn of 35,000 or less. The acrylic polymer (POLc2) has a Tg of -10°C or more, more preferably 0°C or more, more preferably 10°C or more. Preferably, the Tg of the acrylic polymer (POLc2) is higher than the Tg of the acrylic polymer (POLc1). Preferably, the difference between the Tg of the acrylic polymer (POLc2) and the Tg of the acrylic polymer (POLc1) is 10°C or more, more preferably 20°C or more, more preferably 50°C or more.

[0041] The acrylic polymer (POLc2) contains polymerized units of one or more acrylic monomers, herein labeled as monomer (MON-A). The monomer (MON-A) is an unsubstituted alkyl ester of (meth)acrylic acid. The number of carbon atoms in the alkyl ester group in the monomer (MON-A) is 1 or more, preferably 2 or more, more preferably 3 or more. The number of carbon atoms in the alkyl ester group in the monomer (MON-A) is 20 or less, more preferably 10 or less, more preferably 8 or less. The amount of polymerized units of the monomer (MON-A) in the acrylic polymer (POLc2) is 50% or more, more preferably 75% or more, more preferably 85% or more, more preferably 95% or more, more preferably 99% or more, by weight based on the weight of the acrylic polymer (POLc2). The amount of polymerized units of the monomer (MON-A) in the acrylic polymer (POLc2) is 99.9% or less, preferably 99.8% or less, more preferably 99.6% or less, by weight based on the weight of the acrylic polymer (POLc2).

[0042] The acrylic polymer (POLc2) optionally contains polymerized units of one or more acrylic monomers, herein labeled as monomer (MON-B). Monomer (MON-B) is selected from acrylic acid, methacrylic acid, and mixtures thereof. When present, the amount of polymerized units of monomer (MON-B) in the acrylic polymer (POLc2) is 0.1% or more, more preferably 0.2% or more, more preferably 0.4% or more, by weight based on the weight of the acrylic polymer (POLc2). The amount of polymerized units of monomer (MON-A) in the acrylic polymer (POLc2) is 50% or less, more preferably 25% or less, more preferably 15% or less, more preferably 5% or less, more preferably 1% or less, by weight based on the weight of the acrylic polymer (POLc2).

[0043] The acrylic polymer (POLc2) optionally contains polymerized units of one or more acrylic monomers, herein labeled as monomer (MON-C). Monomer (MON-C) is any vinyl monomer, except that monomer (MON-C) is different from both monomers (MON-A) and (MON-B). The amount of polymerized units of monomer (MON-A) in the acrylic polymer (POLc2) is 50% or less, more preferably 10% or less, more preferably 2% or less, by weight based on the weight of the acrylic polymer (POLc2). The amount of polymerized units of monomer (MON-A) in the acrylic polymer (POLc2) may be zero.

[0044] The acrylic polymer (POLc2) can be produced by any method. In a preferred method, the polymerization to form the acrylic polymer (POLc2) is carried out in the presence of one or more chain transfer agents. Preferably, the amount of chain transfer agent is 1% or more, more preferably 2% or more, more preferably 4% or more, by weight based on the total weight of the monomers used to form the acrylic polymer (POLc2). Preferably, the amount of chain transfer agent is 10% or less, more preferably 8% or less, more preferably 6% or less, by weight based on the total weight of the monomers used to form the acrylic polymer (POLc2). Preferred chain transfer agents have one or more attached -SH groups. Preferred chain transfer agents also have a linear chain of n adjacent carbon atoms, where n is 2 or more, more preferably 4 or more, more preferably 6 or more.

[0045] Preferably, the amount of acrylic polymer (POLc2) in composition (Cc) is 30% or less, more preferably 20% or less, more preferably 15% or less, by weight based on the weight of composition (Cc). Preferably, the amount of acrylic polymer (POLc2) in composition (Cc) is 0.5% or more, more preferably 1% or more, more preferably 2% or more, more preferably 5% or more, more preferably 9% or more, by weight based on the weight of composition (Cc).

[0046] Preferably, composition (Cc) has the properties of a PSA. Preferably, composition (Cc) has an elastic modulus (G') of 5 kPa or more, more preferably 10 kPa or more, more preferably 20 kPa or more, over a temperature range including the range of 10°C to 40°C. Preferably, composition (Cc) has an elastic modulus (G') of 1000 kPa or less, more preferably 500 kPa or less, over a temperature range including the range of 10°C to 40°C.

[0047] Preferably, composition (Cc) contains little or no tackifier that is not an acrylic polymer, i.e. preferably the amount of tackifier that is not an acrylic polymer in composition (Cc) is less than 10%, more preferably 3% or less, more preferably 1% or less, more preferably zero, by weight based on the dry weight of composition (Cc).

[0048] It is useful to consider the amount (SUMc), defined herein as the sum of the weight of polymer (POLc1) and the weight of polymer (POLc2). Preferably, the ratio of the amount (SUMc) to the total weight of composition (Cc) is greater than or equal to 0.6:1, more preferably greater than or equal to 0.8:1, more preferably greater than or equal to 0.9:1.

[0049] It is useful to characterize the total thickness (TOT), which is the sum of the thickness of layer (Lb) and the thickness of layer (Lc). Preferably, the total thickness (TOT) is 1 micrometer or more, more preferably 2 micrometers or more, more preferably 5 micrometers or more. Preferably, the total thickness (TOT) is 50 micrometers or less, more preferably 40 micrometers or less.

[0050] Layers (Lb) and (Lc) can be characterized by coating weight, which is the weight of dry material per unit area.Preferably, the ratio of the coating weight of layer (Lb) to the coating weight of layer (Lc) is 0.1:1 or more, more preferably 0.25:1 or more, more preferably 0.67:1 or more.Preferably, the ratio of the coating weight of layer (Lb) to the coating weight of layer (Lc) is 9:1 or less, more preferably 4:1 or less, more preferably 1.5:1 or less.

[0051] In some embodiments, the pressure-sensitive article of the present invention has a release liner in contact with layer (Lc). The release liner has a low energy density surface, such as a silicone coating, to which PSA usually does not adhere well. When present, the release liner protects layer (Lc) of the pressure-sensitive article of the present invention until it is desired to use the pressure-sensitive article of the present invention by adhering the pressure-sensitive article of the present invention to a desired substrate (i.e., substrate (Sd)). The release liner can be easily removed from the pressure-sensitive article of the present invention and then contacted with substrate (Sd).

[0052] The pressure-sensitive article of the present invention can be manufactured by any method. In a preferred method, each of the layers (Lb) and (Lc) is constructed by forming a layer of an aqueous composition and then drying the layer of the aqueous composition.

[0053] Preferably, the layer (Lb) is formed by first providing an aqueous composition (AQb) containing dispersed particles of an acrylic polymer (POLb). The aqueous composition (AQb) may contain additional compounds in addition to water and the acrylic polymer (POLb). A preferred method of making the aqueous composition (AQb) is to carry out an aqueous emulsion polymerization to form dispersed particles of the aqueous polymer (POLb) in the form of a polymer latex, which can then function as the aqueous composition (AQb). Preferably, the polymer particles dispersed in the aqueous composition (AQb) have a volume average diameter of 50 to 750 nanometers. Preferably, the amount of acrylic polymer (POLb) present in the aqueous composition (AQb) is 20% to 55% by weight based on the total weight of the aqueous composition (AQb).

[0054] Similarly, a preferred method of making layer (Lc) is to provide a suitable aqueous composition (AQc) which is applied to layer (Lb) and then dried. Preferably, the aqueous composition (AQc) contains dispersed polymer particles. In some embodiments, the dispersed polymer particles contain both acrylic polymer (POLc1) and acrylic polymer (POLc2). In a preferred embodiment, the aqueous composition (AQc) contains dispersed particles of acrylic polymer (POLc1) and also contains separate dispersed particles of acrylic polymer (POLc2).

[0055] The aqueous dispersion (AQc) can be prepared by any method. In a preferred method, an aqueous emulsion polymerization is carried out to produce a latex of particles of an acrylic polymer (POLc1) dispersed in an aqueous medium (herein labeled as (AQc1)). The necessary and preferred features of the aqueous composition (AQc1) are the same as those described above for the aqueous composition (AQb). In some embodiments, a separate aqueous composition (herein labeled as (AQc2)) is provided containing particles of a polymer (POLc2) dispersed in an aqueous medium, and the aqueous compositions (AQc1) and (AQc2) are mixed together to form the aqueous composition (AQc). In a preferred embodiment (an "in situ" embodiment), the acrylic polymer (POLc2) is formed by aqueous emulsion polymerization of one or more monomers in (AQc1). In an in situ embodiment, the formed polymer (POLc2) may be formed on the particles of the polymer (POLc1). In a preferred in situ embodiment, particles of polymer (POLc2) are formed that are separate from particles of polymer (POLc1). In an in situ embodiment, one or more optional additional components can be added to the result of forming polymer (POLc2) in the presence of polymer (POLc1), and the result is used as aqueous composition (AQc).

[0056] The pressure sensitive articles of the present invention can be manufactured by any method. Preferably, the articles are manufactured by (A) forming a layer of an aqueous composition (Qb) containing dispersed particles of an acrylic polymer (POLb) on a first surface; (B) forming on the second surface a layer of an aqueous composition (Qc) containing (i) an acrylic polymer (POLc1) and (ii) dispersed particles containing an acrylic polymer (POLc2); (C) drying the layer of aqueous composition (Qb) to form a layer (Lb); (D) drying the layer of aqueous composition (Qc) to form layer (Lc).

[0057] In some embodiments, both steps (A) and (B) are performed, and then steps (C) and (D) are performed simultaneously. In such embodiments, a layer (Lb1) of the aqueous composition (Cb1) is applied to the substrate (Sa) (first surface), and while the layer (Lb1) of the aqueous composition (Cb1) is still wet, a layer (Lc1) of the aqueous composition (Cc1) is applied on the layer (Lb1) of the aqueous composition (Cb1) (second surface), and then the entire ensemble is dried. Among such embodiments, it is preferred that steps (A) and (B) are performed simultaneously. That is, a multi-layer coating device is used that simultaneously applies the layer (Lb1) of the aqueous composition (Cb1) to the substrate (Sa) and also applies the layer (Lc1) of the aqueous composition (Cc1) on the layer (Lb1) of the aqueous composition (Cb1), and then the entire ensemble is dried. One suitable coating device is a slide coater. The slide coater forms a liquid composite with a layer (Lb1) of aqueous composition (Cb1) underneath a layer (Lc1) of aqueous composition (Ca), the slide coater applies a layer of the entire composite onto the substrate (Sa) in a manner that keeps these layers intact, brings layer (Lb1) into contact with the substrate (Sa) and leaves layer (Lc1) in contact with air, and then dries the entire article to remove water from the aqueous composition.

[0058] Also contemplated are embodiments in which the pressure-sensitive article is made by a transfer coating method, for example a method comprising making a coating layer (second surface) of composition (Cc) on a release liner, then making a coating layer (first surface) of composition (Cb) on a layer of composition (Cb), then contacting the layer of composition (Cb) with a substrate (Sa) (preferably under pressure), and then removing the release liner. In such embodiments, step (B) is performed before step (A).

[0059] It is contemplated that the pressure-sensitive adhesive article of the present invention is utilized by contacting it with an additional substrate (Sd) that is the target substrate. It is contemplated that pressure is applied to bring the composition (Cc) and the substrate (Sd) into intimate contact and then released. It is contemplated that the result is a bonded article in which the composition (Cc) is bonded to the substrate (Sd) while the pressure-sensitive adhesive article remains intact. The substrate (Sd) may be any substrate. Preferably, the substrate (Sd) is a polyolefin.

[0060] The present invention is not limited to any particular mechanism. It is believed that tack is caused by the interaction between the layer (Lc) of the pressure-sensitive adhesive article of the present invention and the surface of the substrate (Sd) (i.e., the target substrate). It is believed that the pressure-sensitive article of the present invention has acceptable tack because the acrylic polymer (POLc2) is believed to function as a tackifier in the layer (Lc) that contacts the substrate (Sd). It is believed that the acrylic polymer (POLc2) resists migration from the layer (Lc) to the layer (Lb), thereby maintaining a high concentration of the acrylic polymer (POLc2) in the layer (Lc) (that contacts the substrate (Sd)) and therefore the ability to exert a relatively high tack adhesion to the substrate (Sd).

[0061] In contrast to the present invention, it is believed that the comparative pressure-sensitive article can be made similar to the pressure-sensitive article of the present invention, except that in the comparative article, the acrylic polymer (POLc2) is replaced by a conventionally known tackifier that is not an acrylic polymer, such as, for example, a rosin ester. It is expected that the rosin ester will freely migrate from the top layer (similar to layer (Lc)) to other layers (similar to layer (Lb)). Therefore, the complete improvement in tack performance that can be expected is not achieved, since the concentration of rosin ester in the top layer is reduced due to migration.

[0062] The following are examples of the present invention. Unless otherwise stated, operations were carried out at room temperature (about 23° C.).

[0063] Preparation Example 1 (PE1). The procedure for making an acrylic polymer suitable as acrylic polymer (POLc2) was as follows: A 3 liter, 4-neck round bottom flask was charged with 610 grams of water and ammonium persulfate (APS) at a level of 1.5% by weight based on monomer. A monomer emulsion feed consisting of 280 grams of water, 100 grams of anionic sulfated surfactant, 1000 grams of monomer, and n-dodecyl mercaptan (n-DDM) (5% by weight based on monomer) was then added uniformly to the flask over a period of 3 hours while maintaining a polymerization temperature of 84° C. Concurrent with the monomer emulsion feed was added APS at a level of 0.5% by weight based on monomer in 45 grams of water. After monomer addition, the batch was held at 84° C. for 30 minutes, then cooled to 70° C., and 1 gram of 28% aqueous ammonia was added. The batch was further cooled to room temperature and then filtered to recover the polymer product.

[0064] The monomer composition was 99.5% by weight n-butyl methacrylate and 0.5% by weight methacrylic acid.

[0065] Pressure sensitive adhesive compositions were made as follows: All samples were lightly formulated with 0.3% to 0.5% (by weight, wet / wet) of a wetting agent, such as Surfynol™ 440 wetting agent ("440") from Air Products, and 0.3% to 0.5% (by weight, wet / wet) of Aerosol OT-75 from Solvay, based on the total emulsion, unless otherwise noted, to improve wetting for laboratory drawdowns. The viscosity was then adjusted to approximately 1000 mPa*s (1000 cps) (Brookfield, RVDV, 30 rpm, 63#) using an ACRYSOL™ family of thickeners from The Dow Chemical Company, Midland, Michigan.

[0066] A laboratory drawdown to form a multi-layer article as shown in FIG. 1 was made as follows: Layer (Lb) (2) was coated onto a first silicone-coated paper or film release liner and then dried at 80° C. for 5 minutes at a wet coating thickness of 2-50 micrometers. Separately, layer (Lc) (3) was coated onto a second release liner and also dried at 80° C. for 5 minutes at a wet coating thickness of 2-50 micrometers. The non-tackified layer (i.e., layer (Lb)) was then transferred onto a corona-treated polypropylene ("PP") film (60 micrometers thick) by laminating the PP film (substrate (Sa) (1)) with the adhesive-coated first release liner. The first release liner was then removed to expose the non-tackified adhesive layer (Lb). This layer (Lb) was then contacted with layer (Lc) (now coated onto a second release liner) to form a laminate. The second release liner was then removed, resulting in the multi-layer structure shown in FIG.

[0067] Loop Tack (PSTC Test Method 16) (Pressure Sensitive Tape Council, One Parkview Plaza, Suite 800, Oakbrook Terrace, IL 60101, USA) was performed as follows. The Loop Tack test measures the initial adhesion when the adhesive contacts the substrate (Sd) (4). The adhesive laminate was conditioned for at least one day in a controlled environment (72-74°F (22.2-23.3°C) and 50% relative humidity) before testing. A 1-inch wide strip was cut and folded back to form a loop and expose the adhesive surface. It was then mounted between the jaws of an Instron™ tensile tester and the lower jaw was lowered against the substrate at a rate of 12 inches / minute so that a 1-inch by 1-inch square area of ​​adhesive was in contact with the substrate (Sd) (4) for 1 second. The adhesive was then pulled apart and the peak force to pull the adhesive away from the substrate was recorded. The substrate (Sd) (4) was low density polyethylene.

[0068] The pressure-sensitive adhesive articles were also analyzed using secondary ion mass spectrometry (SIMS) analysis by gas cluster ion beam etching in depth profiling mode, which reveals the relative concentrations of specific functional groups and molecular fragments as a function of depth. For samples containing rosin ester, the functional group studied was rosin acid functional group, and for samples containing acrylic polymer PE1, the functional group studied was butyl alcohol.

[0069] The materials used in these examples were as follows: [Table 1]

[0070] The results of the loop tack test were as follows: "Tack" is the peak force as above, reported in Newtons (N). "Ex" means "Example". Example numbers ending in "C" are comparative. "Comp" means "Composition". "Coat-Wt" means "Coat Weight" and is reported in grams of dry coating per square meter (gsm). "Tackifier" means either a rosin ester tackifier (in the comparative examples) or an acrylic polymer (POLc2) in the examples. "% Tackifier" is the weight percent of tackifier based on the total dry weight of the tackified layer. [Table 2]

[0071] SIMS results for Example 3C: The concentration of RE1 was uniform throughout the depth. That is, the concentration of RE1 was constant as a function of the total depth of layers (Lc) and (Lb). This emphasizes that when the layers were fabricated, RE1 was only present in layer (Lc) and not in layer (Lb), but when the sample was analyzed, RE1 was uniformly diffused throughout layers (Lb) and (Lc).

[0072] SIMS results of Example 1: Layer (Lc) showed a relatively high concentration of PE1, with only a slight decrease in concentration as the position approached the interface with layer (Lb). In layer (Lb), the concentration of PE1 decreased more rapidly as the position moved away from the interface between layers (Lc) and (Lb) and toward the substrate (Sa). In short, the concentration of PE1 was significantly higher in layer (Lc) than in layer (Lb). Confining PE1 to layer (Lc) is expected to promote good tack resistance in the pressure-sensitive article of the present invention.

[0073] The SIMS results are consistent with the tack results. Comparing Comparative Example 4C with Comparative Example 3C, it is clear that when the tackifier is free to migrate throughout both layers (as shown by the SIMS data), the reduction in tackifier concentration in the top layer results in a relatively large loss of tack performance: from 9 Newtons to 6.9 Newtons (a 23% reduction in tack). In contrast, comparing Comparative Example 2C with Example 1, it is clear that when the tackifier migration is significantly inhibited, the loss in tack performance is also small: from 5.8 Newtons to 5.4 Newtons (only a 7% reduction in tack). That is, when the tackifier does not migrate from the top layer, the pressure-sensitive article's ability to exhibit relatively high tack adhesion is maintained.

Claims

1. 1. A pressure sensitive adhesive article comprising: (a) a substrate (Sa); (b) a layer (Lb) of a pressure-sensitive composition (Cb) in contact with said substrate (Sa) and comprising one or more acrylic polymers (POLb) comprising butyl (meth)acrylate; (c) a layer (Lc) in contact with said layer (Lb), the weight of which is based on the weight of said layer (Lc), (i) one or more acrylic polymers (POLc1) comprising 60% to 99.5% butyl (meth)acrylate; and (ii) 0.5% to 40% of one or more acrylic polymers (POLc2), having a number average molecular weight of 2,000 or more and a number average molecular weight of 35,000 or less and a Tg of -10°C or more, by weight based on the weight of (POLc2); (A) 50% to 99.9% of one or more unsubstituted alkyl esters of (meth)acrylic acid, where the alkyl group has 1 to 20 carbon atoms; (B) 0% to 50% acrylic acid, methacrylic acid, or mixtures thereof; (C) and a layer (Lc) comprising an acrylic polymer (POLc2) that comprises 0% to 50% polymerized units of one or more additional vinyl monomers.

2. A pressure-sensitive article as described in claim 1, wherein the acrylic polymer (POLb) and the acrylic polymer (POLc1) further contain (meth)acrylic acid.

3. 2. The pressure-sensitive article of claim 1, wherein the acrylic polymer (POLc2) comprises 80% to 99.9% polymerized units of one or more unsubstituted alkyl esters of (meth)acrylic acid, and 0% to 20% polymerized units of (meth)acrylic acid, by weight based on the weight of the acrylic polymer (POLc2).

4. 10. A method for producing the pressure-sensitive article of claim 1, the method comprising: (A) forming a layer of an aqueous composition (Qb) containing dispersed particles of the acrylic polymer (POLb) on a first surface; (B) forming on the second surface a layer of an aqueous composition (Qc) containing (i) the acrylic polymer (POLc1) and (ii) dispersed particles containing the acrylic polymer (POLc2); (C) drying the layer of the aqueous composition (Qb) to form the layer (Lb); (D) drying said layer of said aqueous composition (Qc) to form said layer (Lc).

5. 5. The method of claim 4, wherein the aqueous composition (Qb) is produced by a process comprising aqueous emulsion polymerization of one or more monomers to produce dispersed particles of said acrylic polymer (POLb).

6. A bonded article manufactured by the process of contacting a substrate (Sd) with the article of claim 1, wherein said substrate (Sd) is in contact with said layer (Lc).

7. 7. The bonded article according to claim 6, wherein the substrate (Sd) is a polyolefin.

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