WO2021108160A1

WO2021108160A1 - Hot melt pressure-sensitive adhesives and processes for making same

Info

Publication number: WO2021108160A1
Application number: PCT/US2020/060773
Authority: WO
Inventors: Ronald G. WHITE; Jennifer J. AUSTIN; Andrew V. STEPHENS
Original assignee: Exxonmobil Chemical Patents Inc.
Priority date: 2019-11-25
Filing date: 2020-11-16
Publication date: 2021-06-03

Abstract

Hot melt pressure-sensitive adhesives (HMPSA) and processes for making same. The HMPSA composition can include an adhesive mixture comprising about 10 wt% to about 45 wt% of styrenic block copolymer, about 1 wt% to about 50 wt% of poly-a-olefin, about 0 wt% to about 65 wt% of tackifier, and about 0 wt% to about 50 wt% of process oil, with weight percentages being based upon the total weight of the adhesive mixture. The adhesive mixture can further be dissolved in a solution comprising about 25 wt% to about 50 wt% of the mixture accompanied by appropriate removal of the excess solvent. The HMPSA can have improved peel, tack, and shear properties.

Description

HOT MELT PRESSURE-SENSITIVE ADHESIVES AND PROCESSES FOR MAKING SAME

PRIORITY

[0001] This application claims priority to and the benefit of U.S. Provisional Application No. 62/939,796, filed November 25, 2019, and European Patent Application No. 20152033.5 which was filed January 15, 2020, the disclosures of which are incorporated herein by reference in their entireties.

FIELD

[0002] Embodiments disclosed herein generally relate to hot melt pressure-sensitive adhesive compositions and their applications. In particular, the adhesive compositions provided herein comprise a block copolymer component, a tackifier component and a poly-a- olefin.

BACKGROUND

[0003] Pressure-sensitive adhesives (PSA) are used in a variety of tape and label applications. Such adhesives may be applied to, for example, paper, plastic films, metal, etc. to form the aforementioned tape or labels. These tapes and labels may be affixed to a wide variety of substrates and in many cases are removeable or repositionable. Hot melt pressure- sensitive adhesives (HMPSA) are known in the art and consist of tackified thermoplastic elastomers such as styrenic block copolymers together with tackifying resin(s) and generally some plasticizing oil, an antioxidant, and optionally fillers. Styrenic block copolymers containing polystyrene and polybutadiene blocks and/or polyisoprene blocks are particularly useful. These materials are generally available as pure triblocks, (sometimes referred to as SIS and SBS copolymers) and diblocks (sometimes referred to as SI and SB copolymers or SIB copolymers). These block copolymers typically contain some residual unsaturation which can lead to poor ultraviolet and/or thermal stability. Another type of block copolymer known as SEBS or SEPS is fully saturated, but HMPSA formulations containing such block-copolymers fail to exhibit the high peel, tack, and shear properties typically required for some HMPSA applications.

[0004] A need therefore exists for improved HMPSA formulations, in particular formulations utilizing SEBS, that exhibit high peel, tack, and shear properties. Such HMPSA formulations could be optimized for HMPSA tape and label applications.

SUMMARY

[0005] Hot melt pressure-sensitive adhesive compositions and processes for making same are provided. In various embodiments, the hot melt pressure-sensitive adhesive composition can include an adhesive mixture comprising: about 10 wt% to about 45 wt% of styrenic block copolymer; about 1 wt% to about 50 wt% of poly-a-olefin oil; about 0 wt% to about 65 wt% of tackifier; and about 0 wt% to about 50 wt% of process oil, wherein the weight percentages are based upon the total weight of the adhesive mixture. The adhesive mixture can further be dissolved in a solution comprising about 25 wt% to about 50 wt% of the mixture accompanied by appropriate removal of the excess solvent. The hot melt pressure-sensitive adhesive composition can have improved peel, tack, and shear properties.

[0006] In some embodiments, a process for making the hot melt pressure-sensitive adhesive composition can include combining (a) about 10 wt% to about 45 wt% of styrenic block copolymer, (b) about 1 wt% to about 50 wt% of poly-a-olefin oil, (c) about 0 wt% to about 65 wt% of tackifier, and (d) about 0 wt% to about 50 wt% of process oil to form an adhesive mixture, wherein the foregoing weight percentages are based on the total weight of the adhesive mixture. The process can further include dissolving the adhesive mixture in a solvent to form a solution comprising about 25 wt% to about 50 wt% of the mixture. This solution is then drawn down to form a film by appropriate removal of the solvent. Once the polymer film is completely dried, it can be tested for PSA tape and label applications.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0008] FIG. 1 is a graph depicting the loss factor versus temperature of two hot melt pressure- sensitive adhesives, according to one or more embodiments provided herein.

[0009] FIG. 2 is a graph depicting the storage modulus versus temperature of additional hot melt pressure-sensitive adhesives, according to one or more embodiments provided herein.

DETAILED DESCRIPTION

[0010] It is to be understood that the following disclosure describes several exemplary embodiments for implementing different features, structures, or functions of the invention. Exemplary embodiments of components, arrangements, and configurations are described below to simplify the present disclosure; however, these exemplary embodiments are provided merely as examples and are not intended to limit the scope of the invention. Additionally, the present disclosure can repeat reference numerals and/or letters in the various exemplary embodiments and across the Figures provided herein. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various exemplary embodiments and/or configurations discussed in the Figures. Moreover, the formation of a first feature over or on a second feature in the description that follows can include embodiments in which the first and second features are formed in direct contact and can also include embodiments in which additional features can be formed interposing the first and second features, such that the first and second features cannot be in direct contact. The exemplary embodiments presented below also can be combined in any combination of ways, i.e., any element from one exemplary embodiment can be used in any other exemplary embodiment, without departing from the scope of the disclosure. The figures are not necessarily to scale and certain features and certain views of the figures can be shown exaggerated in scale or in schematic for clarity and/or conciseness

[0011] Additionally, certain terms are used throughout the following description and claims to refer to particular components. As one skilled in the art will appreciate, various entities can refer to the same component by different names, and as such, the naming convention for the elements described herein is not intended to limit the scope of the invention, unless otherwise specifically defined herein. Further, the naming convention used herein is not intended to distinguish between components that differ in name but not function.

[0012] Furthermore, in the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to.”

[0013] The term “or” is intended to encompass both exclusive and inclusive cases, i.e., “A or B” is intended to be synonymous with “at least one of A and B,” unless otherwise expressly specified herein.

[0014] The indefinite articles “a” and “an” refer to both singular forms (i.e., “one”) and plural referents (i.e., one or more) unless the context clearly dictates otherwise. Thus, embodiments using “an a-olefin” include embodiments where one, two or more a-olefins are used, unless specified to the contrary or the context clearly indicates that only one a-olefin is used.

[0015] The term “wt%” means percentage by weight, “vol%” means percentage by volume, “mol%” means percentage by mole, “ppm” means parts per million, and “ppm wt” and “wppm” are used interchangeably and mean parts per million on a weight basis. All concentrations herein, unless otherwise stated, are expressed on the basis of the total amount of the composition in question.

[0016] The term "a-olefin" refers to any linear or branched compound of carbon and hydrogen having at least one double bond between the a and b carbon atoms. For purposes of this specification and the claims appended thereto, when a polymer or copolymer is referred to as including an a-olefin, e.g. , poly- a-olefin, the a-olefin present in such polymer or copolymer is the polymerized form of the a-olefin. For example, when a copolymer is said to have a "styrene" content of 10 wt% to 30 wt%, it is understood that the repeating unit/mer unit or simply unit in the copolymer is derived from styrene in the polymerization reaction and the derived units are present at 10 wt% to 30 wt%, based on a weight of the copolymer.

[0017] The term "polymer" refers to any two or more of the same or different repeating units/mer units or units. The term "homopolymer" refers to a polymer having units that are the same. The term "copolymer" refers to a polymer having two or more units that are different from each other, and includes terpolymers and the like. The term "terpolymer" refers to a polymer having three units that are different from each other. The term "different" as it refers to units indicates that the units differ from each other by at least one atom or are different isomerically. Likewise, the definition of polymer, as used herein, includes homopolymers, copolymers, and the like. Furthermore, the term “styrenic block copolymer” refers to any copolymer that includes units of styrene and mid-block.

[0018] The term “tackifier” refers to an agent added to an adhesive composition to allow the polymer of the composition to be more adhesive by improving wetting during the application of the composition. In addition, the term “plasticizer” refers to a substance that improves the fluidity of a material. Furthermore, the term “process oil” refers to petroleum derived oils and synthetic plasticizers. Also, the term “mixture” refers to a material comprising more than one component.

[0019] The term “peel” refers to the resistance to separating an adhesive from a substrate by measuring the force needed to break the bond between the adhesive and substrate surface after applying the adhesive. The term “tack” refers to the resistance to separating an adhesive from a substrate by measuring the force needed to break the bond between the adhesive and substrate surface after lightly contacting the adhesive to the substrate surface. The term “shear” refers to the resistance to separating an adhesive from a substrate by measuring the time needed to break the bond between the adhesive and the substrate surface when applying force to the adhesive parallel to the substrate surface. [0020] Nomenclature of elements and groups thereof used herein are pursuant to the Periodic Table used by the International Union of Pure and Applied Chemistry after 1988. An example of the Periodic Table is shown in the inner page of the front cover of Advanced Inorganic Chemistry, 6^th Edition, by F. Albert Cotton et al. (John Wiley & Sons, Inc., 1999).

[0021] A detailed description will now be provided. Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references to the “invention” may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims. Each of the inventions will now be described in greater detail below, including specific embodiments, versions and examples, but the inventions are not limited to these embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the inventions, when the information in this disclosure is combined with publicly available information and technology.

Hot Melt Pressure-Sensitive Adhesive Composition

[0022] It has been surprisingly and unexpectedly discovered that a hot melt pressure- sensitive adhesive (HMPSA) that includes an adhesive mixture comprising about 10 wt% to about 45 wt% of styrenic block copolymer (SBC), about 1 wt% to about 50 wt% of poly-a- olefin (PAO), about 10 wt% to about 65 wt% of tackifier, and about 10 wt% to about 50 wt% of process oil, based upon the total weight of the adhesive mixture, has significantly improved peel, tack, and shear properties. Prior to the use of a poly-a-olefin with styrenic block copolymer to produce hot melt pressure-sensitive adhesives in accordance with one or more embodiments provided herein, it was believed that such poly-a-olefin would have a neutral impact on peel, tack, and shear properties. Without wishing to be bound by theory, it is believed that the compatibility of the tackifier with the mid-block is improved by the addition of the poly-a-olefin because the peel, tack, and shear properties are greatly improved.

[0023] According to a preferred embodiment, the adhesive mixture of the HMPSA can include about 10 wt% to about 30 wt% of the SBC, about 10 wt% to about 30 wt% of the PAO, about 30 wt% to about 60 wt% of the tackifier, and about 10 wt% to about 30 wt% of the process oil.

[0024] In an even more preferred embodiment, the adhesive mixture of the HMPSA can include about 10 wt% to about 30 wt% of the SBC, about 10 wt% to about 30 wt% of the PAO, about 30 wt% to about 60 wt% of the tackifier, and about 10 wt% to about 30 wt% of the process oil.

[0025] The adhesive mixture of the HMPSA can be dissolved in a solution comprising about 25 wt% to about 50 wt% of the adhesive mixture and a solvent compatible with the adhesive mixture. The solvent is accompanied by appropriate removal of the excess solvent. The resulting solution can be disposed upon a substrate selected based on the end-use application of the HMPSA. In one or more embodiments, the substrate is a polymer film. Examples of suitable polymer films include but are not limited to polyimide, polyester, polyurethane, acrylonitrile butadiene styrene (ABS), and polyvinyl chloride (PVC) films.

[0026] According to various embodiments, the improved peel, tack, and sheer properties of the HMPSA can be as follows. First, the HMPSA can have a 180° peel shear strength in the range of about 500 to about 2,000 kg/25 mm. Further, the HMPSA can have a pressure- sensitive loop tack shear strength in the range of about 1,100 to about 2,400 kg/25 mm². The HMPSA can also have a shear adhesion failure temperature of about 40°C to about 85 °C and a static shear test duration of about 40 min to about 18,000 min. Peel properties can be measured according to PSTC-lOl(A). Tack properties can be measured according to PSTC- 16. Shear properties can be measured according to ASTM-D4498 and PSTC- 107(A).

[0027] The glass transition temperature (Tg) of the HMPSA with the addition of the poly-a- olefin is higher than expected. In one or more embodiments, the HMPSA can have a glass transition temperature (Tg) in the range of about -5°C to about 15°C as measured by OP-224. It can further have a viscosity at 160°C of about 2,000 cPs to about 110,000 cPs as measured by OP-202.

Styrenic Block Copolymer

[0028] The styrenic block copolymer (SBC) can have a styrene weight percentage of about 13% to about 30% and a diblock weight percentage of about 0.1% to about 29.0%. The SBC can also have a melt flow rate at 200°C of about 0.1 g/10 min to about 12.0 g/10 min, as measured by ASTM D-1248. The SBC can also have a specific gravity that ranges from about 0.89 to about 0.92. Suitable SBCs can be or can include at least one styrene isoprene styrene (SIS) block copolymer (e.g., Kraton™ D1161 available from Kraton Polymers, FFC), styrene ethylene butylene styrene (SEBS) diblock copolymer (e.g., Kraton™ G1657 available from Kraton Polymers, EEC), SEBS triblock copolymer (e.g., Kraton™ G1652 available from Kraton Polymers, LLC), and any combinations thereof. In preferred embodiments, the SBC is a SEBS copolymer. [0029] In an embodiment in which the HMPSA includes a solution comprising from about 15 wt% to about 30 wt% of the adhesive mixture and the solvent is toluene, the solution has a viscosity at 25°C of about 100 cPs to about 5000 cPs, as measured by BAM 922. Poly-q-Olefin Oil

[0030] The poly-a-olefin (PAO), which serves as a plasticizer in the HMPSA formulation, can include one or more Group IV base oils, as defined by the American Petroleum Institute (API Publication 1509; www.API.org). Group IV base oils are synthetic oils that include hydrocarbon oils, such as polymerized and interpolymerized olefins, for example, polypropylenes, polybutylenes, propylene-butylene copolymers, propylene-isobutylene copolymers, ethylene-olefin copolymers, ethylene-alphaolefin copolymers, propylene-olefin copolymers, propylene-alphaolefin copolymers, butylene-olefin copolymers, butylene- alphaolefin copolymers, and the like.

[0031] PAO base oils can be derived from linear Ci to C32 alpha olefins, and mixtures thereof. See U.S. Patents 4,956,122; 4,827,064; and 4,827,073. PAOs are relatively low molecular weight hydrogenated oligomers or polymers of alphaolefins which include, but are not limited to, C2 to C32 alphaolefins, preferrably Cx to C20 alphaolefins, such as 1-octene, 1-decene, 1-dodecene and the like. PAOs further include dimers of higher olefins in the range of C14 to Ci₈ that provide low viscosity oils with acceptably low volatility. Depending on the starting olefin(s) and the finished viscosity, PAOs contain predominantly trimers and tetramers of the starting olefins, with minor amounts of higher oligomers.

[0032] PAOs can be conveniently made by the polymerization of an alphaolefin in the presence of a polymerization catalyst such as a Lewis acid catalyst, e.g, BF3 or AICI3, or a Friedel-Crafts catalyst, e.g., aluminum trichloride, boron trifluoride or complexes of boron trifluoride with water, alcohols such as ethanol, propanol or butanol, and carboxylic acids or esters such as ethyl acetate or ethyl propionate. Suitable methods for making PAOs are disclosed in U.S. Patents 4,149,178 and 3,382,291, the relevant portions thereof being incorporated by reference herein in their entirety. Other descriptions of PAO synthesis can be found in the following U.S. Patents: 3,742,082; 3,769,363; 3,876,720; 4,239,930; 4,367,352; 4,413,156; 4,434,408; 4,910,355; 4,956,122; and 5,068,487. The dimers of C14 to Cis olefins are described in U.S. Patent 4,218,330.

[0033] Alternatively or additionally, the catalyst system can be or can include one or more non-metallocene Ziegler-Natta catalysts. Alternatively or additionally, the catalyst system can include a metal oxide supported on an inert material, e.g., chromium oxide supported on silica. Such catalyst systems and uses thereof in the process for making PAOs are disclosed in, e.g., U.S. Patent Nos. 4,827,073 (Wu); 4,827,064 (Wu); 4,967,032 (Ho et a ); 4,926,004 (Pelrine et al.); and 4,914,254 (Pelrine), the relevant portions thereof being incorporated by reference herein in their entirety.

[0034] The catalyst system can alternatively or additionally include one or more metallocene catalysts. Metallocene-catalyzed PAO (mPAO) can be a homopolymer made from a single alphaolefin feed or can be a copolymer made from two or more different alphaolefins, each by employing a suitable metallocene catalyst system. Suitable metallocene catalysts can be or can include one or more simple metallocenes, substituted metallocenes, or bridged metallocene catalysts activated or promoted by, for instance, methylaluminoxane (MAO) or a non coordinating anion, such as N,N-dimethylanilinium tetrakis(perfluorophenyl)borate or other equivalent non-coordinating anions. mPAO and methods for producing mPAO employing metallocene catalysis are described in WO 2007/011832 and U.S. patent application 2009/0036725, the relevant portions thereof being incorporated by reference herein in their entirety.

[0035] Homopolymer mPAO compositions can be made from single alphaolefins chosen from alphaolefins in the Ci to C30 range, preferably C2 to Ci₆, most preferably C3 to C14 or C3 to C12. The homopolymers can be isotactic, atactic, syndiotactic, or of any other appropriate tacticity. The tacticity can be tailored by the choices of polymerization catalyst, polymerization reaction conditions, hydrogenation conditions, or combinations thereof.

[0036] Copolymer mPAO compositions can be made from at least two alphaolefins of C2 to C30 range, and typically have monomers randomly distributed in the finished copolymers. It is preferred that the average carbon number is at least 4.1. Advantageously, ethylene and propylene, if present in the feed, can be present in the amount of less than 50 wt% individually or preferably less than 50 wt% combined. The copolymers can be isotactic, atactic, syndiotactic or of any other appropriate tacticity.

[0037] Copolymer mPAO compositions can also be made from mixed feed linear alpha olefins (LAOs) having from two to 26 different linear alphaolefins selected from C2 to C30 linear alphaolefins. Such mixed feed LAO can be obtained from an ethylene growth process using an aluminum catalyst or a metallocene catalyst. The growth olefins can be mostly Ce to Ci₈ LAO. LAOs from other processes can also be used.

[0038] Useful alphaolefins can be obtained from a conventional LAO production facility, from a refinery, from a chemical plant, and even from Fischer-Tropsch synthesis processes (as reported in U.S. Patent 5,382,739). Alphaolefins include propylene, 1-butene, 1-pentene, 1- hexene, 1-octene, other Ci to C_½ alphaolefins, C_½+ alphaolefins, LAOs, and the like. For example, when used alone, C₂ to Ci6 alphaolefins, more preferably linear alphaolefins, are suitable to make homopolymers. Other combinations of alphaolefin plus LAO, such as for example, C₄ and C₁₄-LAO, Ob- and C₁₆-LAO, Cs-, C₁₀-, C₁₂-LAO, or Cs- and C₁₄-LAO, Ob-, Cio-, C₁₄-LAO, C₄, and C₁₂-LAO, etc., are suitable to make copolymers.

[0039] A feed comprising a mixture of LAOs selected from C2 to C30 LAOs or a single LAO selected from C2 to Ci₆ LAO, can be contacted with an activated metallocene catalyst under oligomerization conditions to provide a liquid product suitable for use as a component in adhesive formulations. Copolymer compositions made from two or more alphaolefins of C2 to C30 range, with monomers randomly incorporated into the copolymer, can also be used as a component in adhesive formulations. Other suitable PAOs are described in, for example, U.S. Patent Application No. 2013/0005633.

[0040] In one or more preferred embodiments, the PAO can be derived from Cs to C₂₀ alpha olefins such as 1-octene, 1-decene, 1-dodecene. The PAO can have a number average molecular weight (Mn) in the range of about 200 g/mol to about 7,000 g/mol.

[0041] The PAO can further have a kinematic viscosity at 100°C of about 1 cSt to about 5,000 cSt, such as about 1 to about 3,000 cSt, about 2 to about 2,000 cSt, about 2 to about 1,000 cSt, about 2 to about 800 cSt, about 2 to about 600 cSt, about 2 to about 500 cSt, about 2 to about 400 cSt, about 2 to about 300 cSt, about 2 to about 200 cSt, or about 5 to about 100 cSt, as measured by ASTM D445. The exact viscosity of the PAO base stock can be controlled by, e.g., the type and amount of monomer used, polymerization temperature, polymerization residence time, catalyst used, concentration of catalyst used, distillation and separation conditions, and mixing multiple PAO base stocks with different viscosity.

[0042] The PAO can further have a pour point of -10°C or less (preferably -20°C or less, preferably -25°C or less, preferably -30°C or less, preferably -35°C or less, preferably -40°C or less, preferably -50°C or less). In one or more embodiments, the PAO can have a pour point of -15 to -70°C (preferably -25 to -60°C).

[0043] The PAO can further have a glass transition temperature (Tg) of -40°C or less (preferably -50°C or less, preferably -60°C or less, preferably -70°C or less, preferably -80°C or less). In one or more embodiments, the PAO has a Tg of -50 to -120°C (preferably -60 to -100°C, preferably -70 to -90°C).

[0044] The PAO can further have a flash point of 200°C or more (preferably 210°C or more, preferably 220°C or more, preferably 230°C or more), preferably between 240°C and 290°C. In one or more embodiments, the PAO has a specific gravity (15.6°C) of 0.86 or less (preferably 0.855 or less, preferably 0.85 or less, preferably 0.84 or less).

[0045] The PAO can further have a bromine number in a range from Nb(PAO)l to Nb(PAO)2, where Nb(PAO)l and Nb(PAO)2 can be, independently, 0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, as long as Nb(PAO)l < Nb(PAO)2. To reach such a low bromine number, the PAO can be subjected to hydrogenation where the PAO has been in contact with a H2 containing atmosphere in the presence of a hydrogenation catalyst, such as Co, Ni, Ru, Rh, Ir, Pt, and combinations thereof, such that at least a portion of the residual carbon-carbon double bonds present on the PAO molecules become saturated.

[0046] Examples of suitable commercial PAO’s useful for the HMPSA compositions described herein include but are not limited to SpectraSyn™ synthetic non-metallocene PAO, SpectraSyn Ultra™ series chromium oxide-based PAO, and SpectraSyn Elite™ series mPAO, all available from ExxonMobil Chemical Company.

Process Oil

[0047] Process oils useful as plasticizers are known in the art. Examples of suitable process oils include paraffinic or naphthenic oils, aliphatic naphthenic oils, white oils, mineral oils, polybutenes, phthalates, and the like. In one or more embodiments, the process oil can be or can include a phthalate such as disoundecyl phthalate (DIUP), diisononylphthalate (DINP), and dioctylphthalates (DOP). Further useful plasticizers include those described in WO 01/18109A1 and U.S. Publication No. 2004/0106723, which are incorporated by reference herein. Examples of suitable commercially available process oils include but are not limited to Primol™ 352, Krystol™ 550, Nyflex™ 222B, Parapol™ 950, and Parapol™ 1300. Primol™ 352 is a white oil available from ExxonMobil Chemical Company located of Houston, Texas. Krystol™ 550 is a white oil available from Petro-Canada Lubricants. Nyflex™ 222B is a solvent refined naphthenic oil available from Nynas AB of Stockholm, Sweden. Parapol™ 950 and Parapol™ 1300 are polybutene oils, also commercially available from ExxonMobil Chemical Company.

Tackifier

[0048] The tackifier can be used to provide tack to the adhesive and to modify its viscosity. The tackifier can have a number- average molecular weight (Mn) of about 200 g/mol to about 2500 g/mol, as measured according to ETM 300-83. [0049] In one or more embodiments, the tackifier can be or can include at least one resin derived from renewable resources such as rosin derivatives including wood rosin, tall oil, gum rosin, rosin esters, natural and synthetic terpenes, and derivatives thereof. In additional embodiments, the tackifier can be or can include at least one hydrocarbon tackifier resin such as aliphatic hydrocarbon resins, at least partially hydrogenated aliphatic hydrocarbon resins, aliphatic/aromatic hydrocarbon resins, at least partially hydrogenated aliphatic aromatic hydrocarbon resins, aromatic resins, at least partially hydrogenated aromatic hydrocarbon resins, cycloaliphatic hydrocarbon resins, at least partially hydrogenated cycloaliphatic resins, cycloaliphatic/aromatic hydrocarbon resins, at least partially hydrogenated hydrocarbon resins, polyterpene resins, terpene -phenol resins, rosin esters, rosin acids, grafted resins, and mixtures of two or more of the foregoing. Additional examples of suitable tackifiers are disclosed in U.S. Patent Application No. 2016/0177141, which is incorporated by reference herein in its entirety.

[0050] The tackifier can be characterized by its softening point and aromaticity. The softening point is the temperature, measured in degrees Celsius, at which a material will flow, as determined by ASTM E-28. Aromaticity can be determined by NMR spectroscopy and is measured in mol % of aromatic protons. Aromatic content in tackifiers can change the compatibility ranges for use with styrenic block copolymers (SBC). For example, styrene- isoprene-styrene (SIS) block copolymers are more readily tackified and compatible with C5 resins with little aromatic content (less than 5 wt%) whereas styrene-butadiene- styrene (SBS) block copolymers require considerable tackifying resins with more aromatic content (more than 5 wt%). Tackifying resins range from being a liquid at 37°C to having a ring and ball softening point of about 135°C. Solid tackifying resins with a softening point greater than about 100°C, more preferably with a softening point greater than about 130°C, are particularly useful to improve the cohesive strength of the HMPSA formulations provided herein. The preferred tackifying resin is predominantly aliphatic. However, tackifying resins with increasing aromatic character are also useful, particularly when a second tackifier or mutually compatible plasticizer is employed.

[0051] Examples of suitable commercially available tackifiers include but are not limited to Eastotac™ H series resins available from Eastman Chemical Company of Kingsport, Tenn.; Wingtack™ resins available from Goodyear Chemical of Akron, Ohio; Zonatac™ resins available from Arizona Chemical Company of Panama City, Fla., Escorez™ 5300 and 5400 series resins available from ExxonMobil Chemical Company, and Kristalex™ resins available from Eastman Chemical Company.

Solvent

[0052] The solvent can be any non-polymeric species capable of being removed from the HMPSA by heating to a temperature below the decomposition temperature of the SBC and/or reducing the pressure of the solvent/SBC mixture. In one or more embodiments, the solvent can be an aliphatic or aromatic hydrocarbon fluid. Examples of suitable, preferably inert, hydrocarbon fluids are readily volatile liquid hydrocarbons such as hydrocarbons containing from 1 to 30, preferably 3 to 20, carbon atoms. Preferred examples include propane, n-butane, isobutane, mixed butanes, n-pentane, isopentane, neopentane, n-hexane, cyclohexane, isohexane, octane, other saturated Ce to Cx hydrocarbons, toluene, benzene, ethylbenzene, chlorobenzene, xylene, desulphurized light virgin naphtha, and any other hydrocarbon solvent recognized by those skilled in the art to be suitable for the purposes of this invention. Particularly preferred solvents are toluene and n-hexene.

Processes for Making the Hot Melt Pres sure- sensitive Adhesive

[0053] The hot melt pressure-sensitive adhesive can be made by first combining the SBC, the PAO, the tackifier, if any, and the process oil, if any, to form an adhesive mixture. The resulting adhesive mixture can then be dissolved in a solvent to form a solution comprising about 25 wt% to about 50 wt% of the solid mixture. Examples of suitable solvents are described above. The components of the adhesive mixture can be mixed with the solvent using any suitable mixing method such as blending, compounding, or roller milling.

[0054] After the formation of the adhesive solution, a substrate can be coated with the adhesive solution using any suitable coating method such as bar coating, roll coating (e.g., gravure coating or 3 -roll coating, and offset gravure coating, or 5 -roll coating), spray coating, curtain coating, and brush coating. Example of suitable substrates are described above. EXAMPLES

[0055] The foregoing discussion can be further described with reference to the following non-limiting examples. Although the examples can be directed to specific embodiments, they are not to be viewed as limiting the invention in any specific respect.

[0056] Two HMPSA blends with PAO (Ex.l and Ex.2) and one comparative HMPSA blend with process oil (CEx.l) were produced. The PAO used in Ex.l was SpectraSyn™ 40, and the PAO used in Ex. 2 was SpectraSyn™ 100. The process oil used in CEx.l was Primol™ 352. The SBC used in Ex.1-2 and CEx.l was Kraton™ G1652, which is a SEBS copolymer. The tackifier used in Ex.1-2 and CEx.l was Escorez™ 5400.

[0057] Each blend was made by first massing out the desired formulation directly into a steel can. After all the components were added, 100 g of technical grade toluene was added to the can. The can was then sealed and placed on a roller mil for a minimum of 18 hours until all solid material had been dissolved. The resulting solution contained 50 wt% of the solid mixture.

[0058] Subsequently, a doctor bar was used to coat the solution onto a polyester film having a thickness of 1.5 to 2.5 mil. More specifically, the doctor bar was placed at one end of the film, and the solution was poured onto the film next to the bar. The bar was then drawn down the length of the film, spreading the adhesive as it was drawn down. Thereafter, the doctor bar was cleaned. The excess solution was cut off of the film and discarded. The coated film was then placed in an out of the way place to dry overnight or longer when necessary. After drying was complete, a cover of release paper was applied to the coated film for ease of handling. [0059] The weight percent (wt%) of each component and certain mechanical properties of the HMPSA blends in Ex.1-2 and CEx.l are shown in Tables 1 and 2 below.

[0060] Table 1: Formulations of Examples 1-2 and Comparative Example 1.

[0061] Table 2: Mechanical properties of Examples 1-2 and Comparative Example 1.

[0062] As shown above, the HMPSA blends having 20 wt% SBC, 55 wt% tackifier, and 25 wt% PAO surprisingly and unexpectedly exhibited significantly improved adhesive properties. Specifically, Ex.1 and Ex.1 surprisingly and unexpectedly had improved peel, tack, and shear properties of: a 180° peel SS of 1,674 g/25 mm in Ex.l and 1,746 g/25 mm in Ex.2; a pressure- sensitive tape loop tack SS of 1,954 g/25 mm² in Ex.l and 1,138 g/25 mm² in Ex.2, a SAFT of 80° C in Ex.l and 84° C in Ex.2, and a static shear test duration of 17,280 min in Ex.l and 6,035 min in Ex.2. Without intending to be limited by theory, it is believed that the use of PAO instead of process oil as the plasticizer in Ex. 1-2 provided better compatibility of the tackifier with the hydrogenated mid-block of the SEBS copolymer, resulting in higher peel, tack, and shear.

[0063] The loss factor of the HMPSA blends of Ex.1-2 and CEx.1 was analyzed by Modular Compact Rheometer on a 25 mm parallel plate system in accordance with OP-267 to produce the loss factor by plotting the modulus ratio versus temperature relationship shown in FIG. 1 and the storage modulus versus temperature relationship shown in FIG. 2. As shown in FIG. 1, the loss factor of the HMPSA blends with PSA oil was similar to that of the HMPSA blend with process oil, indicating a shift in the glass transition temperature. Turning to FIG. 2, the rubber plateau of the HMPSA blends with PSA oil extended to a higher temperature than that of the HMPSA blend with process oil, which may explain the higher SAFT and shear properties of the inventive blends.

[0064] A HMPSA blend with PAO (Ex.3), a HMPSA blend with PAO and process oil (Ex.4), and one comparative HMPSA blend with process oil (CEx.2) were produced in the same manner as described above for the production of Ex.1-2 and CEx.l. The PAO used in Ex.3-4 was SpectraSyn™ 100. The process oil used in Ex.4 and CEx.2 was Primol™ 352. The SBC used in Ex.3-4 and CEx.2 was Kraton G1657, which is a SEBS copolymer. The tackifier used in Ex.3-4 and CEx.2 was Escorez™ 5400. The formulations and certain mechanical properties of each HMPSA blend in Ex.3-4 and CEx.2 are shown in Tables 3 and 4 below. [0065] Table 3: Formulations of Examples 3-4 and Comparative Example 2.

[0066] Table 4: Mechanical properties of Examples 3-4 and Comparative Example 2.

[0067] As shown above, the hot melt PSA blend of Ex. 3 having 20 wt% SBC, 55 wt% tackifier, 12.5 wt. % PAO, and 12.5% process oil, surprisingly and unexpectedly had a 180° peel test SS of 1,262 g/25 mm, a pressure-sensitive tape loop tack SS of 2,137 g/25 mm², a SAFT of 52° C, and a static shear test duration of 358 min. The hot melt PSA blend of Ex. 4 having 20 wt% SBC, 55 wt% tackifier, 25 wt% PAO, and 0.0 wt% process oil surprisingly and unexpectedly had a 180° peel test shear strength of 1,528 g/25 mm, a pressure-sensitive tape loop tack shear strength of 1,912 g/25 mm², a SAFT of 61° C, and a static shear test duration of 536 min. The peel and shear properties of the HMPSA blends unexpectedly improved incrementally as the amount of PAO was increased from 12.5 wt% in Ex.3 to 25 wt% in Ex.4.

Listing of Embodiments

[0068] This disclosure may further include any one or more of the following non-limiting embodiments:

[0069] 1. A hot melt pressure-sensitive adhesive composition, comprising: an adhesive mixture comprising a. about 10 wt% to about 45 wt% of styrenic block copolymer (SBC); b. about 1 wt% to about 50 wt% of poly-a-olefin (PAO); c. about 0 wt% to about 65 wt% of tackifier; and d. about 0 wt% to about 50 wt% of process oil, wherein weight percentages are based on a total weight of the adhesive mixture.

[0070] 2. The adhesive composition according to embodiment 1, wherein the adhesive mixture comprises about 10 wt% to about 30 wt% of the SBC, about 10 wt% to about 30 wt% of the PAO, about 30 wt% to about 60 wt% of the tackifier, and about 10 wt% to about 30 wt% of the process oil.

[0071] 3. The adhesive composition according to embodiments 1 or 2, wherein the adhesive mixture comprises about 15 wt% to about 25 wt% of the SBC, about 15 wt% to about 25 wt% of the PAO, about 40 wt% to about 60 wt% of the tackifier, and about 15 wt% to about 25 wt% of the process oil.

[0072] 4. The adhesive composition according to any embodiment 1 to 3, wherein the adhesive mixture is dissolved in a solution comprising about 25 wt% to about 50 wt% of the adhesive mixture accompanied by removal of the excess solvents. [0073] 5. The adhesive composition according to any embodiment 1 to 4, wherein the adhesive composition has a 180° peel shear strength of about 500 kg/25 mm to about 2,000 kg/25 mm as measured by PSTC-lOl(A).

[0074] 6. The adhesive composition according to any embodiment 1 to 5, wherein the adhesive composition has a pres sure- sensitive loop tack shear strength of about 1,100 kg/25 mm² to about 2,400 kg/25 mm² as measured by PSTC-16.

[0075] 7. The adhesive composition according to any embodiment 1 to 6, wherein the adhesive composition has a shear adhesion failure temperature of about 40°C to about 85°C as measured by ASTM D-4498.

[0076] 8. The adhesive composition according to any embodiment 1 to 7, wherein the adhesive composition has a static shear test duration of about 40 min to about 18,000 min as measured by PSTC- 107(A).

[0077] 9. The adhesive composition according to any embodiment 1 to 8, wherein the adhesive composition has a glass transition temperature (Tg) of about -5°C to about 15°C as measured by OP-224.

[0078] 10. The adhesive composition according to any embodiment 1 to 9, wherein the adhesive composition has a viscosity at 160°C of about 2,000 cPs to about 110,000 cPs C as measured by OP-202.

[0079] 11. The adhesive composition according to any embodiment 1 to 10, wherein the styrenic block copolymer comprises a styrene weight percentage of about 13% to about 30% and a diblock weight percentage of about 0.1% to about 29.0%.

[0080] 12. The adhesive composition according to any embodiment 1 to 11, wherein the styrenic block copolymer has a melt flow rate at 200°C of about 0.1 g/10 min to about 12.0 g/10 min, as measured by ASTM D-1238.

[0081] 13. The adhesive composition according to any embodiment 1 to 12, wherein the styrenic block copolymer comprises a styrene isoprene styrene (SIS) block copolymer, a styrene ethylene butylene styrene (SEBS) diblock copolymer, a SEBS triblock copolymer, or any combination thereof.

[0082] 14. The adhesive composition according to any embodiment 1 to 13, wherein the

PAO has a kinematic viscosity at 100°C of about 1 cSt to about 5,000 cSt as measured by ASTM D-445.

[0083] 15. The adhesive composition according to any embodiment 1 to 14, wherein the

PAO has a number average molecular weight (Mn) of about 200 g/mol to about 7,000 g/mol. [0084] 16. The adhesive composition according to any embodiment 1 to 15, wherein the

PAO comprises a monomer having 8 to 20 carbon atoms.

[0085] 17. The adhesive composition according to any embodiment 1 to 16, wherein the tackifier has a glass transition temperature (Tg) of about 40° C to about 70° C and a molecular weight (Mw) of about 200 g/mol to about 1,500 g/mol.

[0086] 18. A process for making a hot melt pres sure- sensitive adhesive composition, comprising: combining a. about 10 wt% to about 45 wt% of styrenic block copolymer (SBC); b. about 1 wt% to about 50 wt% of poly-a-olefin (PAO); c. about 0 wt% to about 65 wt% of tackifier; and d. about 0 wt% to about 50 wt% of process oil to form an adhesive mixture, wherein weight percentages are based on a total weight of the adhesive mixture.

[0087] 19. The process according to embodiment 18, further comprising dissolving the adhesive mixture in a solvent to form a solution comprising about 25 wt% to about 50 wt% of the adhesive mixture.

[0088] 20. The process according to embodiment 18 or 19, further comprising coating a polymer film with the solution.

[0089] 21. The process according to embodiment 19 or 20, wherein the solution comprises from about 15 wt% to about 30 wt% of the solid mixture and the solvent is toluene, and wherein the solution has a viscosity at 25 °C of about 100 cPs to about 5000 cPs, as measured by BAM 922.

[0090] 22. The process according to any embodiment 18 to 21, wherein the adhesive composition has a 180° peel shear strength of about 500 kg/25 mm to about 2,000 kg/25 mm as measured by PSTC-lOl(A).

[0091] 23. The process according to any embodiment 18 to 22, wherein the adhesive composition has a pressure-sensitive loop tack shear strength of about 1,100 kg/25 mm² to about 2,400 kg/25 mm² as measured by PSTC-16.

[0092] 24. The process according to any embodiment 18 to 23, wherein the adhesive composition has a shear adhesion failure temperature of about 40°C to about 85 °C as measured by ASTM D-4498.

[0093] 25. The process according to any embodiment 18 to 24, wherein the adhesive composition has a static shear test duration of about 40 min to about 18,000 min as measured by PSTC-107(A).

[0094] Certain embodiments and features have been described using a set of numerical upper limits and a set of numerical lower limits. It should be appreciated that ranges including the combination of any two values, e.g. , the combination of any lower value with any upper value, the combination of any two lower values, and/or the combination of any two upper values are contemplated unless otherwise indicated. Certain lower limits, upper limits and ranges appear in one or more claims below. [0095] Unless otherwise indicated, all numerical values are "about" or "approximately" the indicated value, meaning the values take into account experimental error, machine tolerances and other variations that would be expected by a person having ordinary skill in the art. It should also be understood that the precise numerical values used in the specification and claims constitute specific embodiments. Efforts have been made to ensure the accuracy of the data in the examples. However, it should be understood that any measured data inherently contains a certain level of error due to the limitation of the technique and/or equipment used for making the measurement.

[0096] Moreover, various terms have been defined above. To the extent a term used in a claim is not defined above, it should be given the broadest definition persons in the pertinent art have given that term as reflected in at least one printed publication or issued patent. Furthermore, all patents, test procedures, and other documents cited in this application are fully incorporated by reference to the extent such disclosure is not inconsistent with this application and for all jurisdictions in which such incorporation is permitted.

[0097] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

CLAIMS: What is claimed is:

1. A hot melt pres sure- sensitive adhesive composition, comprising: an adhesive mixture comprising: about 10 wt% to about 45 wt% of one or more styrenic block copolymers (SBC); about 1 wt% to about 50 wt% of one or more poly-a-olefins (PAO); about 0 wt% to about 65 wt% of one or more tackifiers; and about 0 wt% to about 50 wt% of one or more process oils, wherein all weight percentages are based on a total weight of the adhesive mixture.

2. The adhesive composition of claim 1, wherein the adhesive mixture comprises about 10 wt% to about 30 wt% of the SBC, about 10 wt% to about 30 wt% of the PAO, about 30 wt% to about 60 wt% of the tackifier, and about 10 wt% to about 30 wt% of the process oil.

3. The adhesive composition of claim 1, wherein the adhesive mixture comprises about 15 wt% to about 25 wt% of the SBC, about 15 wt% to about 25 wt% of the PAO, about 40 wt% to about 60 wt% of the tackifier, and about 15 wt% to about 25 wt% of the process oil.

4. The adhesive composition of claim 1, wherein the adhesive mixture is dissolved in a solution comprising about 25 wt% to about 50 wt% of the adhesive mixture accompanied by removal of the excess solvents.

5. The adhesive composition of claim 1, wherein the adhesive composition has a 180° peel shear strength of about 500 kg/25 mm to about 2,000 kg/25 mm as measured by PSTC- 101(A).

6. The adhesive composition of claim 1, wherein the adhesive composition has a pres sure- sensitive loop tack shear strength of about 1,100 kg/25 mm² to about 2,400 kg/25 mm² as measured by PSTC-16.

7. The adhesive composition of claim 1, wherein the adhesive composition has a shear adhesion failure temperature of about 40°C to about 85°C as measured by ASTM D-4498.

8. The adhesive composition of claim 1, wherein the adhesive composition has a static shear test duration of about 40 min to about 18,000 min as measured by PSTC- 107(A).

9. The adhesive composition of claim 1, wherein the adhesive composition has a glass transition temperature (Tg) of about -5°C to about 15°C as measured by OP-224.

10. The adhesive composition of claim 1, wherein the adhesive composition has a viscosity at 160°C of about 2,000 cPs to about 110,000 cPs C as measured by OP-202.

11. The adhesive composition of claim 1, wherein the styrenic block copolymer comprises a styrene weight percentage of about 13% to about 30% and a diblock weight percentage of about 0.1% to about 29.0%.

12. The adhesive composition of claim 1, wherein the styrenic block copolymer has a melt flow rate at 200°C of about 0.1 g/10 min to about 12.0 g/10 min as measured by ASTM D-1238.

13. The adhesive composition of claim 1, wherein the styrenic block copolymer comprises a styrene isoprene styrene (SIS) block copolymer, a styrene ethylene butylene styrene (SEBS) diblock copolymer, a SEBS triblock copolymer, or any combination thereof.

14. The adhesive composition of claim 1, wherein the PAO has a kinematic viscosity at 100°C of about 1 cSt to about 5,000 cSt as measured by ASTM D-445.

15. The adhesive composition of claim 1, wherein the PAO has a number average molecular weight (Mn) of about 200 g/mol to about 7,000 g/mol.

16. The adhesive composition of claim 1, wherein the PAO comprises a monomer having 8 to 20 carbon atoms.

17. The adhesive composition of claim 1, wherein the tackifier has a glass transition temperature (Tg) of about 40° C to about 70° C and a weight average molecular weight (Mw) of about 200 g/mol to about 1,500 g/mol.

18. A process for making a hot melt pressure-sensitive adhesive composition, comprising: combining a. about 10 wt% to about 45 wt% of styrenic block copolymer (SBC); b. about 1 wt% to about 50 wt% of poly-a-olefin (PAO); c. about 10 wt% to about 65 wt% of tackifier; and d. about 10 wt% to about 50 wt% of process oil, to form an adhesive mixture, wherein weight percentages are based on a total weight of the adhesive mixture.

19. The process of claim 18, further comprising dissolving the adhesive mixture in a solvent to form a solution comprising about 25 wt% to about 50 wt% of the adhesive mixture.

20. The process of claim 19, further comprising coating a polymer film with the solution.

21. The process of claim 19, wherein the solution comprises about 15 wt% to about 30 wt% of the adhesive mixture and the solvent is toluene, and wherein the solution has a viscosity at 25°C of about 100 cPs to about 5000 cPs as measured by BAM 922.

22. The process of claim 19, wherein the adhesive composition has a 180° peel shear strength of about 500 kg/25 mm to about 2,000 kg/25 mm as measured by PSTC-lOl(A).

23. The process of claim 19, wherein the adhesive composition has a pressure-sensitive loop tack shear strength of about 1,100 kg/25 mm² to about 2,400 kg/25 mm² as measured by PSTC-16.

24. The process of claim 19, wherein the adhesive composition has a shear adhesion failure temperature of about 40°C to about 85°C as measured by ASTM D-4498.

25. The process of claim 19, wherein the adhesive composition has a static shear test duration of about 40 min, to about 18,000 min as measured by PSTC-107(A).