WO2015157019A1

WO2015157019A1 - Pressure sensitive adhesive coated articles suitable for bonding to rough surfaces

Info

Publication number: WO2015157019A1
Application number: PCT/US2015/023330
Authority: WO
Inventors: Arlin L. WEIKEL; Corinne E. LIPSCOMB; Jonathan E. JANOSKI; John W. Vanderzanden; Kevin M. Lewandowski
Original assignee: 3M Innovative Properties Company
Priority date: 2014-04-11
Filing date: 2015-03-30
Publication date: 2015-10-15
Also published as: TW201544331A

Abstract

Adhesive coated articles are described comprising a substrate comprising a first major surface and a second opposing major surface and a pressure sensitive adhesive layer disposed on the first major surface of the substrate. In one embodiment, the pressure sensitive adhesive layer is cleanly removable from paper, reusable, and has a shear to orange peel dry wall with a 250 g weight of at least 500 minutes. The pressure sensitive adhesive layer is preferably a multilayer adhesive. In another embodiment, an adhesive coated article is described comprising a substrate comprising a first major surface and a second opposing major surface and a multilayer pressure sensitive adhesive layer disposed on the first major surface of the substrate. The multilayer pressure sensitive adhesive comprises a first adhesive layer disposed on the first major surface of the substrate, and a second pressure sensitive adhesive skin layer disposed upon the first layer. At least the second skin layer is an acrylic multilayer adhesive comprising no greater than 1 wt-% of polymerized units derived from acid functional monomers. In some favored embodiments, the first adhesive layer is conformable.

Description

PRESSURE SENSITIVE ADHESIVE COATED ARTICLES

SUITABLE FOR BONDING TO ROUGH SURFACES Brief Description of the Drawings

FIGs. 1-5 depict various cross-sectional views of embodiments of multilayer adhesive coated articles. FIGs. 6-8 depict the tan delta, the ratio of the shear loss modulus (G") to the shear storage modulus (G'), as determined by dynamic mechanical analysis. Summary

In one embodiment, an adhesive coated article is described comprising a substrate comprising a first major surface and a second opposing major surface and a pressure sensitive adhesive layer disposed on the first major surface of the substrate. The pressure sensitive adhesive layer is cleanly removable from paper, reusable, and has a shear to orange peel dry wall with a 250 g weight of at least 500 minutes. The pressure sensitive adhesive layer is preferably a multilayer adhesive.

In another embodiment, an adhesive coated article is described comprising a substrate comprising a first major surface and a second opposing major surface and a multilayer pressure sensitive adhesive layer disposed on the first major surface of the substrate. The multilayer pressure sensitive adhesive comprises a first adhesive layer disposed on the first major surface of the substrate, and a second pressure sensitive adhesive skin layer disposed upon the first layer. At least the second skin layer is an acrylic multilayer adhesive comprising no greater than 1 wt-% of polymerized units derived from acid functional monomers. In some favored embodiments, the first adhesive layer is conformable.

In some embodiments, the first and second adhesive layers are acrylic adhesives comprising no greater than 1 wt-% of polymerized units derived from acid functional monomers. In some embodiments, the first adhesive layer is crosslinked with a crosslinking monomer comprising at least one C3 to C20 olefin group. The substrate is a release liner, a backing, or an (e.g. mounting) article such as a hook. A removable release liner is typically disposed upon the second pressure sensitive adhesive skin layer until use.

In another embodiment, a method of using an adhesive-coated article is described comprising providing an article as described herein and adhering the pressure sensitive adhesive to a surface. The multilayer pressure sensitive adhesive is particularly useful for adhering to rough surfaces, such as orange peel drywall.

Detailed Description

The present disclosure describes pressure sensitive adhesive ("PSA") coated articles. The storage modulus of a pressure sensitive adhesive at the application temperature, typically room temperature (25°C), is less than 3 x 10⁶ dynes/cm² at a frequency of 1 Hz. In some embodiments, the adhesive is a pressure sensitive adhesive at an application temperature that is greater than room temperature. For example, the application temperature may be 30, 35, 40, 45, 50, 55, or 65°C. In this embodiment, the storage modulus of the pressure sensitive adhesive at room temperature (25°C) is typically greater than 3 x 10⁶ dynes/cm² at a frequency of 1 Hz. In some embodiments, the storage modulus of the pressure sensitive adhesive at room temperature (25°C) is less than 2 x 10⁶ dynes/cm² or 1 x 10⁶ dynes/cm² at a frequency of 1 Hz.

"Syrup composition" refers to a solution of a solute polymer in one or more solvent monomers, the composition having a viscosity from 100 to 8,000 cPs at 25°C. The viscosity of the syrup is greater than the viscosity of the solvent monomer(s).

Herein, "(meth)acryloyl" is inclusive of (meth)acrylate and (meth)acrylamide.

Herein, "(meth) acrylic" includes both methacrylic and acrylic.

Herein, "(meth)acrylate" includes both methacrylate and acrylate.

The term "alkyl" includes straight-chained, branched, and cyclic alkyl groups and includes both unsubstituted and substituted alkyl groups. Unless otherwise indicated, the alkyl groups typically contain from 1 to 20 carbon atoms. Examples of "alkyl" as used herein include, but are not limited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl, isobutyl, t-butyl, isopropyl, n-octyl, 2-octyl, n-heptyl, ethylhexyl, cyclopentyl, cyclohexyl, cycloheptyl, adamantyl, and norbornyl, and the like. Unless otherwise noted, alkyl groups may be mono- or polyvalent.

The term heteroalkyl refers to an alkyl group, as just defined, having at least one catenary carbon atom (i.e. in-chain) replaced by a catenary heteroatom such as O, S, or N.

The term olefin group refers to an unsaturated aliphatic straight-chained, branched, or cyclic (i.e. unsubstitued) hydrocarbon group having one or more double bonds. Those containing one double bond are commonly called alkenyl groups. In some embodiments, the olefin group may further comprise substituents as will subsequently be described. The olefin group is typically monovalent.

"Renewable resource" refers to a natural resource that can be replenished within a 100 year time frame. The resource may be replenished naturally or via agricultural techniques. The renewable resource is typically a plant (i.e. any of various photosynthetic organisms that includes all land plants, inclusive of trees), organisms of Protista such as seaweed and algae, animals, and fish. They may be naturally occurring, hybrids, or genetically engineered organisms. Natural resources such as crude oil, coal, and peat which take longer than 100 years to form are not considered to be renewable resources.

When a group is present more than once in a formula described herein, each group is

"independently" selected unless specified otherwise.

The pressure sensitive adhesive coated articles comprise a pressure sensitive adhesive disposed on a substrate. The substrate may be a backing or a release liner. In favored embodiments, the adhesive is a multilayer adhesive comprising at least two layers, a first adhesive layer and a second PSA skin layer disposed on the first adhesive layer. In favored embodiments, the first adhesive layer is conformable. As far as the build-up of the multilayer PSA is concerned, the PSA film comprises at least the first adhesive layer and at an outermost (i.e. exposed) PSA skin layer. The present invention is however not limited to two layers. For example, the multilayer PSA may comprise three, four, five or even more superimposed layers. In such an embodiment, it is preferred that the additional layers are beneath the second PSA skin layer. The additional layers may be referred to as intermediate layer(s). In other words, the multilayer adhesive may further comprise at least one intermediate adhesive layer between the first adhesive layer and the second PSA skin layer or between the first adhesive layer and the backing.

With reference to FIG. 1 , one embodied adhesive coated article 100 includes a substrate 1 10, such as a backing, comprising a first major surface 11 1 and a second opposing major surface 1 12. A multilayer adhesive is disposed on the first major surface of the substrate. The multilayer adhesive comprises a first (e.g. conformable) adhesive layer 120 disposed on the first major surface of the substrate.

A second PSA skin layer 130 is disposed upon the first layer. During use the PSA skin layer 130 is adhered to a surface. Adhesive coated article 100 may be a single-faced tape further comprising a release liner (not shown) disposed on the exposed surface 131 of second PSA skin layer 130.

In another embodiment, the adhesive coated article 200 in an unsupported (i.e. lacking a backing) multilayer PSA film. With reference to FIG. 2, the multilayer PSA film comprises a first adhesive layer 220 and a second PSA skin layer 230 disposed upon the first (e.g. conformable) adhesive layer.

Unsupported adhesive films typically having a thickness of at least 200 microns. Unsupported adhesive films are typically manufactured and provided between a pair of release liners (not shown).

With reference to FIG. 3, another embodied adhesive coated article 300 includes a substrate 310, such as a backing, comprising a first major surface 31 1 and a second opposing major surface 312. A multilayer adhesive is disposed on both the first major surface and the second opposing surface of the substrate. The multilayer adhesive comprises a first (e.g. conformable) adhesive layer 320 is disposed on the first major surface of the substrate and a second PSA skin layer 330 is disposed upon the first layer 320. During use both PSA skin layers 330 are adhered to (e.g. different) surfaces. Adhesive coated article 300 may be a double-faced tape further comprising a pair of release liners (not shown) disposed on the exposed surfaces 331 and 332 of the PSA skin layers 330.

With reference to FIG. 4, another embodied adhesive coated article 400 includes a substrate 410, such as a backing, comprising a first major surface 41 1 and a second opposing major surface 412. A multilayer adhesive is disposed on the first major surface of the substrate. The multilayer adhesive comprises a first (e.g. conformable) adhesive layer 420 disposed on the first major surface of the substrate and a second PSA skin layer 430 is disposed upon the first layer. Adhesive coated article 400 further comprises another adhesive layer 450 disposed on the second opposing major surface 412 of substrate (e.g. backing) 410.

Adhesive layer 450 may be a single layer adhesive, such as a permanent grade, non-removable pressure sensitive adhesive. Various permanent grade non-removable PSAs are known such as tackified rubber-based adhesive and various acrylic adhesives, as described for example in US Re 24,406; US 4,181,752; US 4,303,485; US 4,429,384; and US 4,330,590.

With reference to FIG. 5, another embodied adhesive coated article 500 includes article 570, such as a hook. A multilayer adhesive is disposed on the back surface 571 of the (e.g. hook) article in order that the article can be (e.g. removably) mounted to a surface by the multilayer PSA. The multilayer PSA comprises a first (e.g. conformable) adhesive layer 520 is disposed on the first major surface of the substrate and a second PSA skin layer 530 disposed upon the first layer. Adhesive coated article 500 may optionally further comprises an additional (e.g. permanent) adhesive layer (not shown) disposed between first adhesive layer 520 and article 570. Adhesive coated article 500 may optionally further comprising a backing (not shown). When adhesive coated article 500 includes both an additional adhesive layer and backing; the adhesive coated article may be the same as FIG. 4 wherein adhesive layer 450 is bonded to an article.

In some favored embodiments, the multilayer adhesive is an acrylic PSA; i.e. both the first and second layers are each acrylic PSAs. In such embodiments, the adhesive comprises a (meth)acrylic polymer prepared from one or more monomers common to acrylic adhesives, such as a (meth)acrylic ester monomers (also referred to as (meth)acrylate acid ester monomers and alkyl(meth)acrylate monomers) optionally in combination with one or more other monomers such as acid- functional ethylenically unsaturated monomers, non-acid-functional polar monomers, and vinyl monomers. The monomers are polymerized by means of crosslinked (meth)acrylate linkages. When the adhesive is an acrylic pressure sensitive adhesive it is typically free of urethane linkages.

The (meth)acrylic polymer comprises one or more (meth)acrylate ester monomers derived from a (e.g. non-tertiary) alcohol containing from 1 to 14 carbon atoms and preferably an average of from 4 to 12 carbon atoms.

Examples of monomers include the esters of either acrylic acid or methacrylic acid with non- tertiary alcohols such as ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1 -pentanol, 2-pentanol, 3- pentanol, 2-methyl- 1 -butanol, 3 -methyl- 1-butanol, 1-hexanol, 2-hexanol, 2-methyl- 1 -pentanol, 3-methyl- 1 -pentanol, 2-ethyl- 1 -butanol, 3, 5,5-trimethyl- 1-hexanol, 3-heptanol, 1-octanol, 2-octanol,

isooctylalcohol, 2-ethyl- 1-hexanol, 1-decanol, 2-propylheptanol, 1-dodecanol, 1 -tridecanol, 1- tetradecanol, and the like. In some embodiments, a preferred (meth)acrylate ester monomer is the ester of (meth)acrylic acid with isooctyl alcohol.

In some favored embodiments, the monomer is the ester of (meth)acrylic acid with an alcohol derived from a renewable source. A suitable technique for determining whether a material is derived from a renewable resource is through ¹⁴C analysis according to ASTM D6866-10, as described in US2012/0288692. The application of ASTM D6866-10 to derive a "bio-based content" is built on the same concepts as radiocarbon dating, but without use of the age equations. The analysis is performed by deriving a ratio of the amount of organic radiocarbon (¹⁴C) in an unknown sample to that of a modern reference standard. The ratio is reported as a percentage with the units "pMC" (percent modern carbon). One suitable monomer derived from a renewable source is 2-octyl (meth)acrylate, as can be prepared by conventional techniques from 2-octanol and (meth)acryloyl derivatives such as esters, acids and acyl halides. The 2-octanol may be prepared by treatment of ricinoleic acid, derived from castor oil, (or ester or acyl halide thereof) with sodium hydroxide, followed by distillation from the co-product sebacic acid. Other (meth)acrylate ester monomers that can be renewable are those derived from ethanol and 2-methyl butanol.

In some embodiments, the (e.g. pressure sensitive) adhesive composition (e.g. (meth)acrylic polymer and/or free-radically polymerizable solvent monomer) comprises a bio-based content of at least 25, 30, 35, 40, 45, or 50 wt-% using ASTM D6866-10, method B. In other embodiments, the (e.g.

pressure sensitive) adhesive composition comprises a bio-based content of at least 55, 60, 65, 70, 75, or 80 wt-%. In yet other embodiments, the (e.g. pressure sensitive) adhesive composition comprises a bio- based content of at least 85, 90, 95, 96, 97, 99 or 99 wt-%.

The (e.g. pressure sensitive) adhesive (e.g. (meth)acrylic polymer and/or free-radically polymerizable solvent monomer) comprises one or more low Tg (meth)acrylate monomers, having a Tg no greater than 10°C when reacted to form a homopolymer. In some embodiments, the low T_g monomers have a Tg no greater than 0°C, no greater than -5°C, or no greater than - 10°C when reacted to form a homopolymer. The Tg of these homopolymers is often greater than or equal to -80°C, greater than or equal to -70°C, greater than or equal to -60°C, or greater than or equal to -50°C. The Tg of these homopolymers can be, for example, in the range of -80°C to 20°C, -70°C to 10°C, -60°C to 0°C, or -60°C to - 10°C.

The low Tg monomer may have the formula

H₂C=CR¹C(0)OR⁸ wherein R¹ is H or methyl and R⁸ is an alkyl with 1 to 22 carbons or a heteroalkyl with 2 to 20 carbons and 1 to 6 heteroatoms selected from oxygen or sulfur. The alkyl or heteroalkyl group can be linear, branched, cyclic, or a combination thereof.

Exemplary low Tg monomers include for example ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, t-butyl acrylate, n-pentyl acrylate, isoamyl acrylate, n-hexyl acrylate, 2- methylbutyl acrylate, 2-ethylhexyl acrylate, 4-methyl-2-pentyl acrylate, n-octyl acrylate, 2-octyl acrylate, isooctyl acrylate, isononyl acrylate, decyl acrylate, isodecyl acrylate, lauryl acrylate, isotridecyl acrylate, octadecyl acrylate, and dodecyl acrylate.

Low Tg heteroalkyl acrylate monomers include, but are not limited to, 2-methoxyethyl acrylate and 2-ethoxyethyl acrylate.

In some embodiments, the (e.g. pressure sensitive) adhesive (e.g. (meth)acrylic polymer and/or free radically polymerizable solvent monomer) comprises low Tg monomer(s) having an alkyl group with 6 to 20 carbon atoms. In some embodiments, the low Tg monomer has an alkyl group with 7 or 8 carbon atoms. Exemplary monomers include, but are not limited to, 2-ethylhexyl methacrylate, isooctyl methacrylate, n-octyl methacrylate, 2-octyl methacrylate, isodecyl methacrylate, and lauryl methacrylate. Likewise, some heteroalkyl methacrylates such as 2-ethoxy ethyl methacrylate can also be used.

In some embodiments, the (e.g. pressure sensitive) adhesive (e.g. (meth)acrylic polymer and/or free-radically polymerizable solvent monomer) comprises a high Tg monomer, having a Tg greater than 10 °C and typically of at least 15 °C, 20 °C or 25°C, and preferably at least 50°C. Suitable high Tg monomers include, for example, t-butyl acrylate, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, s-butyl methacrylate, t-butyl methacrylate, stearyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate, norbornyl (meth) acrylate, benzyl methacrylate, 3,3,5 trimethylcyclohexyl acrylate, cyclohexyl acrylate, N-octyl acrylamide, and propyl methacrylate or combinations.

In some embodiments, the (meth)acrylic polymer is a homopolymer. In other embodiments, the (meth)acrylic polymer is a copolymer. Unless specified otherwise, the term polymer refers to both a homopolymer and copolymer.

The Tg of the copolymer may be estimated by use of the Fox equation, based on the Tgs of the constituent monomers and the weight percent thereof.

The alkyl (meth)acrylate monomers are typically present in the (meth)acrylic polymer in an amount of at least 85, 86, 87, 88, 89, or 90 up to 95, 96, 97, 98, or 99 parts by weight, based on 100 parts by weight of the total monomer or polymerized units. When high Tg monomers are included in a pressure sensitive adhesive, the adhesive may include at least 5, 10, 15, 20, to 30 parts by weight of such high Tg monomer(s).

When the (e,g. pressure sensitive) adhesive composition is free of unpolymerized components, such as tackifier, silica, and glass bubbles, the parts by weight of the total monomer or polymerized units is approximately the same as the wt-% present in the total adhesive composition. However, when the (e.g. pressure sensitive) adhesive composition comprises such unpolymerized components, the (e.g.

pressure sensitive) adhesive composition can comprises substantially less alkyl(meth)acrylate

monomer(s) and crosslinking monomer. The (e.g. pressure sensitive) adhesive composition comprises at least 50 wt-% of polymerized units derived from alkyl (meth)acrylate monomers. In some embodiments, the pressure sensitive adhesive composition comprises at least 50, 55, 60, 65, 70, 75, 80, 85, or 90 wt-% of one or more low Tg monomers.

Acrylic pressure sensitive adhesives often comprise an acid functional monomer (a subset of high Tg monomers), where the acid functional group may be an acid per se, such as a carboxylic acid, or a portion may be salt thereof, such as an alkali metal carboxylate. Common acid functional monomers include, but are not limited to, those selected from ethylenically unsaturated carboxylic acids, ethylenically unsaturated sulfonic acids, ethylenically unsaturated phosphonic acids, and mixtures thereof. Examples of such compounds include those selected from acrylic acid, methacrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, maleic acid, oleic acid, β-carboxyethyl (meth)acrylate, 2- sulfoethyl methacrylate, styrene sulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, vinylphosphonic acid, and mixtures thereof.

It has been found that the inclusion of acid functional monomers can affect the peel adhesion by causing the peel adhesion to increase upon aging. Thus, a multilayer adhesive composition that is initially cleanly removable can become not cleanly removable upon aging. In favored embodiments, at least the second PSA skin layer and preferably also the first layer as well as the entire multilayer adhesive comprises little or no acid functional monomers. Thus, the second PSA skin layer alone or in

combination with the first layer or entire multilayer PSA comprises less than 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1 or 0 wt-% of polymerized units derived from acid- functional monomers such as acrylic acid.

Acrylic pressure sensitive adhesives can optionally comprise other monomers such as a non-acid- functional polar monomer. Representative examples of suitable polar monomers include but are not limited to 2-hydroxyethyl (meth)acrylate; N-vinylpyrrolidone; N-vinylcaprolactam; acrylamide; mono- or di-N-alkyl substituted acrylamide; t-butyl acrylamide; dimethylaminoethyl acrylamide; N-octyl acrylamide; poly(alkoxyalkyl) (meth)acrylates including 2-(2-ethoxyethoxy)ethyl (meth)acrylate, 2- ethoxyethyl (meth)acrylate, 2-methoxyethoxyethyl (meth)acrylate, 2-methoxyethyl methacrylate, polyethylene glycol mono(meth)acrylates; alkyl vinyl ethers, including vinyl methyl ether; and mixtures thereof. Preferred polar monomers include those selected from the group consisting of 2-hydroxyethyl (meth)acrylate and N-vinylpyrrolidinone. In some embodiments, non-acid- functional polar monomer may be present in amounts of 0 to 10 parts by weight, or 0.5 to 5 parts by weight, based on 100 parts by weight total monomer. However, in some embodiments, the multilayer pressure sensitive adhesive comprises less than 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1 or 0 wt-% of polymerized units derived from non-acid polar monomers.

Acrylic pressure sensitive adhesives can optionally comprise vinyl monomers including vinyl esters (e.g., vinyl acetate and vinyl propionate), styrene, substituted styrene (e.g., a-methyl styrene), vinyl halide, and mixtures thereof. However, in some embodiments, the multilayer pressure sensitive adhesive comprises less than 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.1 or 0 wt-% of polymerized units derived from vinyl monomers.

The first and second layers of the multilayer PSA are generally crosslinked with a crosslinking monomer. The crosslinking monomer is selected such that is does not form corrosive by-products and has good color stability. In some embodiments, the pressure sensitive adhesive is free of crosslinkers such as aziridine crosslinkers, chlorinated triazine crosslinkers, melamine crosslinkers.

The concentration of crosslinking monomer is typically at least 0.1, 0.2, 0.3, 0.4 or 0.5 wt-% and can range up to 10, 1 1, 12, 13, 14, or 15 wt-%. However, as the concentration of such crosslinking monomer increases, the peel adhesion (180° to stainless steel) can decrease. Thus, in typically embodiments, the concentration of such crosslinking monomer is no greater than 9, 8, 7, 6, or 5 wt-% and in some favored embodiments, no greater than 4, 3, 2, or 1 wt-%. When the same crosslmking monomer is utilized in the first and second adhesive layer the concentration of crosslmking monomer in the second adhesive skin layer is typically greater than that of the first (e.g. conformable) layer. For example, the weight ratio of crosslinker of the first adhesive layer to second adhesive skin layer may be at least 1 : 1.5 or 1 :2 or 1 :2.5 or 1 :3 ranging up to 1 : 10 or 1 :9 or 1 :8.

The (e.g. pressure sensitive) adhesive composition may comprise a single crosslmking monomer, or a combination of two or more crosslinking monomers. Further, the crosslmking monomer may comprise two or more isomers of the same general structure.

In some embodiments, both the first adhesive layer and second PSA skin layer of the multilayer PSA each comprise a multifunctional (meth)acrylate. Further, a multifunctional (meth)acrylate may be the sole crosslinking monomer of the first and second layer, as well as the multilayer PSA. In other embodiments, the second PSA skin layer of the multilayer PSA comprises a multifunctional

(meth)acrylate and the first layer comprises a crosslinking monomer comprising at least one C3-C20 olefin group. In yet another embodiment, both the first adhesive layer and second PSA skin layer of the multilayer PSA each comprise a crosslinking monomer comprising at least one C3-C20 olefin group.

Further, a crosslinking monomer comprising at least one C3-C20 olefin group may be the sole crosslinking monomer of the first and second layer, as well as the multilayer PSA.

In some embodiments, the crosslinking monomer is a multifunctional (meth)acrylate. Examples of useful the pressure sensitive adhesive comprises include, but are not limited to, di(meth)acrylates, tri(meth)acrylates, and tetra(meth)acrylates, such as 1 ,6-hexanediol di(meth)acrylate, poly(ethylene glycol) di(meth)acrylates, polybutadiene di(meth)acrylate, polyurethane di(meth)acrylates, and propoxylated glycerin tri(meth)acrylate, and mixtures thereof. Generally the multifunctional

(meth)acrylate is not part of the original monomer mixture, but added subsequently after the formation of the (meth)acrylic polymer.

In some embodiments, at least one adhesive layer or the multilayer PSA comprises predominantly

(greater than 50%, 60%, 70%, 80%, or 90% of the total crosslinks) or exclusively crosslinks from a crosslinking monomer that comprises one or more C3-C20 olefin groups. The lower reactivity of the C3- C20 olefin group, as compared to a (meth)acrylate group, can be amendable to achieving an optical amount of crosslinking, especially when the adhesive is cured by (e.g. UV) radiation. In this

embodiment, at least the first adhesive layer or the multilayer PSA may be free of multifunctional

(meth)acrylate crosslinkers such as tripropylene glycol diacrylate and 1,6-hexanediol diacrylate (HDDA) depicted as follows:

In one embodiment, the crosslinking monomer comprises a (meth)acrylate group and a C6-C20 olefin group. The olefin group comprises at least one hydrocarbon unsaturation. In some embodiments, the olefin group comprises substituents. The crosslinking monomer may have the formula

Rl is H or CH₃,

L is an optional linking group; and

R2 is a C6-C20 olefin group, the olefin group being optionally substituted.

The C6-C20 olefin group is an unsaturated aliphatic straight-chained, branched, or cyclic (e.g. unsubstituted) hydrocarbon group having one or more double bonds. Those containing one double bond are commonly called alkenyl groups.

For embodiments wherein the crosslinking monomer comprises a (e.g. divalent) linking group, the linking group (i.e. L) typically has a molecular weight no greater than 1000 g/mole and in some embodiments no greater than 500 g/mole, 400 g/mole, 300 g/mole, 200 g/mole, 100 g/mole, or 50 g/mole.

In one embodiment, L comprises or consists of alkylene (e.g. ethylene) oxide repeat units. Such crosslinking monomer can be derived from reacting an ethoxylated alcohol with acryloyl chloride, methylene chloride and triethylamine, or by direct esterfication with acrylic acid.

In some embodiments, the crosslinking monomer comprises a (meth)acrylate group and an optionally substituted C6-C20 olefin group comprising a terminal hydrocarbon unsaturation. In this embodiment the hydrocarbon unsaturation has the formula:

- R³C=CR⁴R⁵ wherein R⁴ and R⁵ are H and R³ is H or (e.g. C1-C4) alkyl. Undecenyl (meth)acrylate includes such terminal unsaturation.

In other embodiments, the crosslinking monomer comprises a (meth)acrylate group and an optionally substituted C6-C20 olefin group comprising at least one hydrocarbon unsaturation in the backbone of the optionally substituted C6-C20 olefin group. In this embodiment, the hydrocarbon unsaturation has the formula:

- R³C=CR⁴R⁵ wherein R⁴ and R⁵ are independently alkyl and R³ is H or (e.g. C1-C4) alkyl. In some embodiments, R⁴ and R⁵ are each methyl. In this embodiment, R⁴ or R⁵ is the terminal alkyl group of the C6-C₂0 olefin group. Citronellyl (meth)acrylate, geraniol (meth)acrylate and farnesol (meth)acrylate include a hydrocarbon unsaturation of this type.

Other crosslmking monomer comprising a (meth)acrylate group and an optionally substituted Ce- C₂₀ olefin group comprising a terminal hydrocarbon unsaturation are described in PCT/US 14/33712, filed April 1 1 , 2014, incorporated herein by reference. Illustrative crosslmking monomers include for example geraniol (meth)acrylate (e.g. 3,7-dimethylocta-2,6-dienyl] prop-2-enoate), farnesol (meth)acrylate (e.g. 3,7, 1 1 -trimethyldodeca-2,6, 10-trienyl] prop-2-enoate) and oleyl (meth)acrylate.

In other embodiments, the crosslmking monomer comprises at least two terminal groups selected from allyl, methallyl, or combinations thereof. An allyl group has the structural formula

H2C=CH-CH2-. It consists of a methylene bridge (-CH2-) attached to a vinyl group (-CH=CH2).

Similarly, a (meth)ally group is a substituent with the structural formula H2C=C(CH3)-CH2-.

The crosslmking monomers, especially those comprising at least two terminal groups selected from allyl, methallyl, or combinations thereof; are typically free of vinyl groups, such as vinyl esters or vinyl ethers. Vinyl, also known as ethenyl, is the functional group -CH=CH2, namely the ethylene molecule (H2C=CH2) minus one hydrogen atom.

In one embodiment, the crosslmking monomer comprises two (meth)allyl groups and a

(meth)acrylate group. A crosslmking monomer of this type is commercially available from Sartomer, under the trade designation "SR 523". However, in typical embodiments, the crosslmking monomer is free of (meth)acrylate groups.

The crosslinking monomer comprising at least two terminal groups selected from allyl,

(meth)allyl, or combinations thereof typically has the formula (H₂C=C(R³)CH₂)_xZ wherein R is hydrogen or methyl,

Z is a heteroatom or multivalent linking group, and

x ranges from 2 to 6.

In some embodiments, x is 2 or 3. In some embodiments, y is 5-20.

For embodiments wherein the crosslinking monomer comprises a multivalent linking group, the linking group Z typically has a molecular weight no greater than 1000 g/mole and in some embodiments no greater than 500 g/mole, 400 g/mole, 300 g/mole, 200 g/mole, 100 g/mole, or 50 g/mole.

With reference to U.S. provisional application serial no. 61/978217, filed April 1 1, 2014, incorporated herein by reference Z can be a heteratom, such as oxygen; as well as a wide variety of multivalent (di-, tri-, tetra- penta-, and hexa-) linking groups. Z can comprise alkylene, arylene, ester, ether, amide, urethane, urea, amine, carbonate, silane, cyanurate, and combinations thereof. In some embodiments, Z comprises only one of such multivalent linking groups. In other embodiments, Z comprises more than one of the same class of multivalent linking groups (e.g. diester, triether). In yet other embodiments, Z comprises combinations of different classes of multivalent linking groups such as an ester or ether and an alkylene or arylene group.

In some embodiments, Z is a reaction product of a multifunctional alcohol having 2 to 6 hydroxyl groups. In this embodiment, the crosslinking monomer typically has the formula

(H₂C=C(R³)(CH₂)0)_xL² wherein L² is a linear or branched (C1-C12) alkylene optionally comprising one or more substituents such as hydroxyl groups or alkoxy groups;

x ranges from 2 to 6; and

R³ is hydrogen or methyl.

In some embodiments, x is at least 2, such as in the case of butane diol (meth)ally ether. In other embodiments, x is at least 3 and L² is a residue of a multifunctional alcohol such as glycerol,

trimethylolpropane, trimethylolpropane ethoxylate, trimethylolpropane propoxylate, pentaerythritol, 1 ,2,4-butanetriol, 1 , 1 , 1 -tris(hydroxymethyl)ethane, fructose, glucose, l,3,5-tris(2- hydroxyethyl)isocyanurate, dipentaerythritol, and di(trimethylolpropane).

Representative examples of such crosslinking monomers include for example pentaerythritol allyl ether and trimethylolpropane diallyl ether (TMPDE), depicted as follows:

Various other crosslinking monomers comprising at least two (meth)allyl groups are

commercially available including for example allyl ether; triallyl amine; 1, 1 1- dodecadiene; ethylene glycol diallyl ether; diallyl adipate; diallyl sebacate; diallyl maleate; diallyl terephthalate; diallyl isophthalate; triallyl cyanurate; triallyl isocyanurate; 1,3-diallyl urea; diallyl carbonate; and

diallyl(dimethyl)silane.

The (meth)acrylic copolymers and pressure sensitive adhesive composition can be polymerized by various techniques including, but not limited to, solvent polymerization, dispersion polymerization, solventless bulk polymerization, and radiation polymerization, including processes using ultraviolet light, electron beam, and gamma radiation. The monomer mixture may comprise a polymerization initiator, especially a thermal initiator or a photoinitiator of a type and in an amount effective to polymerize the comonomers.

One preferred method of preparing (meth)acrylic polymers includes partially polymerizing monomers to produce a syrup composition comprising the solute (meth)acrylic polymer and

unpolymerized solvent monomer(s). The unpolymerized solvent monomer(s) typically comprises the same monomer as utilized to produce the solute (meth)acrylic polymer. If some of the monomers were consumed during the polymerization of the (meth)acrylic polymer, the unpolymerized solvent monomer(s) comprises at least some of the same monomer(s) as utilized to produce the solute

(meth)acrylic polymer. Further, the same monomer(s) or other monomer(s) can be added to the syrup once the (meth)acrylic polymer has been formed. Partial polymerization provides a coatable solution of the (meth)acrylic solute polymer in one or more free-radically polymerizable solvent monomers. The partially polymerized composition is then coated on a suitable substrate and further polymerized.

In some embodiments, the crosslinking monomer is added to the monomer(s) utilized to form the (meth)acrylic polymer. Alternatively or in addition thereto, the crosslinking monomer may be added to the syrup after the (meth)acrylic polymer has been formed. One of the (meth)allyl groups of the crosslinker and other (e.g. (meth)acrylate) monomers utilized to form the (meth)acrylic polymer polymerize forming an acrylic backbone with the pendent (meth)allyl group. Without intending to be bound by theory, it is surmised that at least a portion of the carbon-carbon double bonds of the (meth)allyl group crosslink with each other during radiation curing of the syrup. Other reaction mechanisms may also occur.

In this embodiment, the pressure sensitive adhesive composition can be characterized as comprising the reaction product of a free-radically polymerizable syrup comprising

i) a free-radically polymerizable solvent monomer; and

ii) a solute (meth)acrylic polymer comprising polymerized units derived from one or more alkyl (meth)acrylate monomers,

wherein the syrup comprises at least one crosslinking monomer (as previously described) or the

(meth)acrylic solute polymer comprises polymerized units derived from at least one crosslinking monomer (as previously described).

The syrup method provides advantages over solvent or solution polymerization methods; the syrup method yielding higher molecular weight materials. These higher molecular weights increase the amount of chain entanglements, thus increasing cohesive strength. Also, the distance between cross-links can be greater with high molecular syrup polymer, which allows for increased wet-out onto a surface.

Polymerization of the (meth)acrylate solvent monomers can be accomplished by exposing the syrup composition to energy in the presence of a photoinitiator. Energy activated initiators may be unnecessary where, for example, ionizing radiation is used to initiate polymerization. Typically, a photoinitiator can be employed in a concentration of at least 0.0001 part by weight, preferably at least 0.001 part by weight, and more preferably at least 0.005 part by weight, relative to 100 parts by weight of the syrup.

A preferred method of preparation of the syrup composition is photoinitiated free radical polymerization. Advantages of the photopolymerization method are that 1) heating the monomer solution is unnecessary and 2) photoinitiation is stopped completely when the activating light source is turned off. Polymerization to achieve a coatable viscosity may be conducted such that the conversion of monomers to polymer is up to about 30%. Polymerization can be terminated when the desired conversion and viscosity have been achieved by removing the light source and by bubbling air (oxygen) into the solution to quench propagating free radicals. The solute polymer(s) may be prepared conventionally in a non- monomeric solvent and advanced to high conversion (degree of polymerization). When solvent

(monomeric or non-monomeric) is used, the solvent may be removed (for example by vacuum distillation) either before or after formation of the syrup composition. While an acceptable method, this procedure involving a highly converted functional polymer is not preferred because an additional solvent removal step is required, another material may be required (a non-monomeric solvent), and dissolution of the high molecular weight, highly converted solute polymer in the monomer mixture may require a significant period of time.

The polymerization is preferably conducted in the absence of solvents such as ethyl acetate, toluene and tetrahydrofuran, which are non-reactive with the functional groups of the components of the syrup composition. Solvents influence the rate of incorporation of different monomers in the polymer chain and generally lead to lower molecular weights as the polymers gel or precipitate from solution. Thus, the (e.g. pressure sensitive) adhesive can be free of unpolymerizable organic solvent.

Useful photoinitiators include benzoin ethers such as benzoin methyl ether and benzoin isopropyl ether; substituted acetophenones such as 2,2-dimethoxy-2-phenylacetophenone photoinitiator, available the trade name IRGACURE 651 or ESACURE KB-1 photoinitiator (Sartomer Co., West Chester, PA), and dimethylhydroxyacetophenone; substituted a-ketols such as 2- methyl-2-hydroxy propiophenone; aromatic sulfonyl chlorides such as 2-naphthalene-sulfonyl chloride; and photoactive oximes such as 1- phenyl-l,2-propanedione-2-(0-ethoxy-carbonyl)oxime. Particularly preferred among these are the substituted acetophenones.

Preferred photoinitiators are photoactive compounds that undergo a Norrish I cleavage to generate free radicals that can initiate by addition to the acrylic double bonds. The photoinitiator can be added to the mixture to be coated after the polymer has been formed, i.e., photoinitiator can be added to the syrup composition. Such polymerizable photoinitiators are described, for example, in U.S. 5,902,836 and 5,506,279 (Gaddam et al.).

Such photoinitiators preferably are present in an amount of from 0.1 to 1.0 part by weight, relative to 100 parts by weight of the total syrup content. Accordingly, relatively thick coatings can be achieved when the extinction coefficient of the photoinitiator is low. The syrup composition and the photoinitiator may be irradiated with activating UV radiation to polymerize the monomer component(s). UV light sources can be of two types: 1) relatively low light intensity sources such as blacklights, which provide generally 10 mW/cm² or less (as measured in accordance with procedures approved by the United States National Institute of Standards and

Technology as, for example, with a UVTMAP UM 365 L-S radiometer manufactured by Electronic

Instrumentation & Technology, Inc., in Sterling, VA) over a wavelength range of 280 to 400 nanometers; and 2) relatively high light intensity sources such as medium pressure mercury lamps which provide intensities generally greater than 10 mW/cm², preferably 15 to 450 mW/cm². Where actinic radiation is used to fully or partially polymerize the syrup composition, high intensities and short exposure times are preferred. For example, an intensity of 600 mW/cm² and an exposure time of about 1 second may be used successfully. Intensities can range from 0.1 to 150 mW/cm², preferably from 0.5 to 100 mW/cm², and more preferably from 0.5 to 50 mW/cm².

The degree of conversion can be monitored during the irradiation by measuring the index of refraction of the polymerizing medium as previously described. Useful coating viscosities are achieved with conversions (i.e., the percentage of available monomer polymerized) in the range of up to 30%, preferably 2% to 20%, more preferably from 5% to 15%, and most preferably from 7% to 12%. The molecular weight (weight average) of the solute polymer(s) is typically at least 100,000; 250,000;

500,000 g/mole or greater.

When preparing (meth)acrylic polymers described herein, it is expedient for the photoinitiated polymerization reactions to proceed to virtual completion, i.e., depletion of the monomeric components, at temperatures less than 70°C (preferably at 50°C or less) with reaction times less than 24 hours, preferably less than 12 hours, and more preferably less than 6 hours. These temperature ranges and reaction rates obviate the need for free radical polymerization inhibitors, which are often added to acrylic systems to stabilize against undesired, premature polymerization and gelation. Furthermore, the addition of inhibitors adds extraneous material that will remain with the system and inhibit the desired polymerization of the syrup composition and formation of the crosslinked pressure-sensitive adhesives. Free radical polymerization inhibitors are often required at processing temperatures of 70°C and higher for reaction periods of more than 6 to 10 hours.

One favored method of preparing a pressure sensitive adhesive composition comprises a) providing a syrup comprising

i) a free-radically polymerizable solvent monomer; and

(meth)acrylic solute polymer comprises polymerized units derived from at least one crosslinking monomer (as previously described);

b) applying the syrup to a substrate; and c) irradiating the applied syrup thereby crosslinking the adhesive composition.

The pressure sensitive adhesives may optionally contain one or more conventional additives. Preferred additives include tackifiers, plasticizers, dyes, antioxidants, UV stabilizers, and (e.g. inorganic) fillers such as (e.g. fumed) silica and glass bubbles.

The multilayer adhesive typically comprises fumed silica (e.g. 221 of FIG. 2). Fumed silica, also known as pyrogenic silica, is made from flame pyrolysis of silicon tetrachloride or from quartz sand vaporized in a 3000°C electric arc. Fumed silica consists of microscopic droplets of amorphous silica fused into (e.g. branched) three-dimensional primary particles that aggregate into larger particles. Since the aggregates do not typically break down, the average particle size of fumed silica is the average particle size of the aggregates. Fumed silica is commercially available from various global producers including Evonik, under the trade designation "Aerosil"; Cabot under the trade designation "Cab-O-Sil", and Wacker Chemie-Dow Corning. The BET surface area of suitable fumed silica is typically at least 50 m²/g, or 75 m²/g, or 100 m²/g. In some embodiments, the BET surface area of the fumed silica is no greater than 400 m²/g, or 350 m²/g, or 300 m²/g, or 275 m²/g, or 250 m²/g. The fumed silica aggregates preferably comprise silica having a primary particle size no greater than 20 nm or 15 nm. The aggregate particle size is substantially larger than the primary particle size and is typically at least 100 nm or greater.

The concentration of (e.g. fumed) silica can vary. In some embodiments, the second PSA skin layer comprises at least 5, 6, 7, 8, 9, or 10 wt-% of (e.g. fumed) silica and typically no greater than 20, 19, 18, 17, 16, or 15 wt-% of (e.g. fumed) silica. The first layer of the multilayer adhesive may comprise less silica than the skin layer. In some embodiments, the first layer comprises at least 0.5, 1. 0, 1.1, 1.2, 1.3, 1.4, or 1.5 wt-% of (e.g. fumed) silica and in some embodiments no greater than 5, 4, 3, or 2 wt-%.

The adhesive typically comprises glass bubbles (e.g. 226 of FIG. 2). Suitable glass bubbles generally have a density ranging from about 0.125 to about 0.35 g/cc. In some embodiments, the glass bubbles have a density less than 0.30, 0.25, or 0.20 g/cc. Glass bubbles generally have a distribution of particles sizes. In typical embodiments, 90% of the glass bubbles have a particle size (by volume) of at least 75 microns and no greater than 1 15 microns. In some embodiments, 90% of the glass bubbles have a particle size (by volume) of at least 80, 85, 90, or 95 microns. In some embodiments, the glass bubbles have a crush strength of at least 250 psi and no greater than 1000, 750, or 500 psi. Glass bubbles are commercially available from various sources including 3M, St. Paul, MN.

The concentration of glass bubbles can vary. In some embodiments, the first adhesive layer of the multilayer adhesive comprises at least 1, 2, 3, 4 or 5 wt-% of glass bubbles and typically no greater than 20, 15, or 10 wt-% of glass bubbles. The second skin layer of the multilayer adhesive may comprise less glass bubbles than the first conformable layer. In some embodiments, the second skin layer is free of glass bubbles.

The inclusion of glass bubbles can reduce the density of the adhesive. Another way of reducing the density of the adhesive is by incorporation of air or other gasses into the adhesive composition. In this embodiment, 226 can represent a bubble created by gas rather than a glass bubble. In some embodiments, adhesive may contain both glass bubbles and bubbles created by gas For example the (e.g. syrup) adhesive composition can be transferred to a frother as described for examples in U.S. Patent No. 4,415,615; incorporated herein by reference. While feeding nitrogen gas into the frother, the frothed syrup can be delivered to the nip of a roll coater between a pair of transparent, (e,g, biaxially-oriented polyethylene terephthalate) films. A silicone or fluorochemical surfactant is included in the froathed syrup. Various surfactants are known including copolymer surfactants described in U. S. Patent No. 6,852,781.

The multilayer pressure sensitive adhesive may optionally contain one or more conventional additives such as tackifiers, plasticizers, dyes, antioxidants, UV stabilizers.

In some embodiments no tackifier is used. When tackifiers are used, the concentration can range from 5 or 10 wt-% to 40, 45, 50, 55, or 60 wt-% of the (e.g. cured) adhesive composition.

Various types of tackifiers include phenol modified terpenes and rosin esters such as glycerol esters of rosin and pentaerythritol esters of rosin that are available under the trade designations "Nuroz", "Nutac" (Newport Industries), "Permalyn", "Staybelite", "Foral" (Eastman). Also available are hydrocarbon resin tackifiers that typically come from C5 and C9 monomers by products of naphtha cracking and are available under the trade names "Piccotac", "Eastotac", "Regalrez", "Regalite"

(Eastman), "Arkon" (Arakawa), "Norsolene", "Wingtack" (Cray Valley), "Nevtack", LX (Neville Chemical Co.), "Hikotac", "Hikorez" (Kolon Chemical), "Novares" (Rutgers Nev.), "Quintone"(Zeon), "Escorez" (Exxonmobile Chemical), "Nures", and "H-Rez" (Newport Industries). Of these, glycerol esters of rosin and pentaerythritol esters of rosin, such as available under the trade designations "Nuroz", "Nutac", and "Foral" are considered biobased materials.

Depending on the kinds and amount of components, the pressure sensitive adhesive can be formulated to have a wide variety of properties for various end uses.

In one favored embodiment, the adhesive composition and thickness is chosen to provide a synergistic combination of properties. In this embodiment, the adhesive can be characterized as having any one or combination of attributes including being conformable, cleanly removable, reusable, reactivatible, and exhibiting good adhesion to rough surfaces.

Thus, in some embodiments, at least the first adhesive layer is conformable. The conformability of an adhesive composition can be characterized using various techniques such as dynamic mechanical analysis (as determined by the test method described in the examples) that can be utilized to determine that shear loss modulus (G"), the shear storage modulus (G'), and tan delta, defined as the ratio of the shear loss modulus (G") to the shear storage modulus (G'). As used herein "conformable" refers to the first adhesive exhibiting a tan delta of at least 0.4 or greater at 25°C and 1 hertz. In some embodiments, the first adhesive has tan delta of at least 0.45, 0.50, 0.55, 0.65, or 0.70 at 25°C and 1 hertz. The tan delta at 25°C and 1 hertz of the first adhesive is typically no greater than 0.80 or 1.0. In some embodiments, the tan delta of the first adhesive is no greater than 1.0 at 1 hertz and temperatures of 40°C, 60°C, 80°C, 100°C and 120°C. In some embodiments, the first adhesive has tan delta of at least 0.4 or greater at 1 hertz and temperatures of 40°C, 60°C, 80°C, 100°C and 120°C.

The second skin adhesive is typically stiffer, i.e. less conformable that the first adhesive. Thus, the second skin adhesive has tan delta less than the first adhesive at 25°C by at least 0.5, 1.0, 1.5, 2.0, 2.5 or 3.0. Further, the second skin adhesive typically has a tan delta of less than 0.4 at 25°C and typically at least 0.2. In some embodiments, the tan delta of the second skin adhesive is less than 0.4 or 0.35 at temperatures of 40°C, 60°C, 80°C, 100°C and 120°C. In some embodiments, the second skin adhesive has a tan delta ranging from about 0.1 to 0.2 of at least 0.4 at 80°C, 100°C and 120°C.

The second skin adhesive typically has a higher crosslinking density than the first conformable adhesive layer, such as can be accomplished by use of a different crosslinker and/or a higher

concentration of crosslinker.

The first adhesive layer is typically substantially thicker than the second skin layer. Since the bulk of the multilayer adhesive is the first adhesive layer, the multilayer adhesive conforms to rough surfaces in a similar manner as the first adhesive layer, yet cab adhere more aggressively by inclusion of the second skin layer.

The multilayer PSA and adhesive coated articles can exhibit good adhesion to both smooth and rough surfaces. Various rough surfaces are known including for example, standard drywall, textured drywall, such as "knock down" and "orange peel"; cinder block, rough (e.g. Brazilian) tile and textured cement. Smooth surfaces, such as stainless steel, glass, and polypropylene have an average surface roughness (Ra) as can be measured by optical inferometry of less than 100 nanometer; whereas rough surfaces have an average surface roughness greater than 1 micron (1000 nanometers), 5 microns, or 10 microns.

Surfaces with a roughness in excess of 5 or 10 microns can be measured with stylus profilometry. Standard (untextured) drywall has an average surface roughness (Ra), of about 10-20 microns and a maximum peak height (Rt using Veeco's Vison software) of 150 to 200 microns. Orange peel and knockdown drywall have an average surface roughness (Ra) greater than 20, 25, 30, 35, 40, or 45 microns and a maximum peak height (Rt) greater than 200, 250, 300, 350, or 400 microns. Orange peel drywall can have an average surface roughness (Ra) of about 50-75 microns and a maximum peak height (Rt) of 450-650 microns. Knock down drywall can have an average surface roughness (Ra) greater than 75, 80, or 85 microns, such as ranging from 90- 120 microns and a maximum peak height (Rt) of 650-850 microns. In typical embodiments, Ra is no greater than 200, 175, or 150 microns and Rt is no greater than 1500, 1250, or 1000 microns. Cinder block and Brazilian tile typically have a similar average surface roughness (Ra) as orange peel drywall.

Although many conformable adhesives exhibit good initial adhesion to a rough surface, the multilayer PSA and articles described herein can exhibit a shear (with a mass of 250g) to orange peel dry wall of at least 500 minutes. In some embodiments, the multilayer PSA and articles exhibits a shear (with a mass of 250g) to orange peel dry wall of at least 1000, 5000, 10000, 15000, or 20000 minutes. The multilayer PSA and adhesive coated articles are cleanly removable from paper. By "cleanly removable from paper" it is meant that the paper does not tear and the paper does not have any staining or adhesive residue after removal of the adhesive from the paper when tested (according to Test Method 1 set forth in the examples). The 90° peel values to paper (according to Test Method 1 set forth in the examples) is typically at least 25 and no greater than 200 or 175 N/dm. In some embodiments, the 90° peel value to paper no greater than 50, 45, or 40 N/dm. The inclusion of the skin layer prevents excessive penetration of the conformable first layer into the paper which in tear can result in the paper tearing and not being cleaning removable.

The multilayer PSA and adhesive coated articles are reusable. By reuseable it is meant that multilayer PSA and/or article can repeatedly be removed and readhered at least 1, 2, 3, 4, or 5 times. In some embodiments, the adhesive coated backing or article can be readhered to paper at least 5, 10, 15, or 20 times while maintaining at least 80%, 85%, or 90% of the initial peel adhesion (according to the "Reusability" test further described in the examples).

Further, in some embodiments, the adhesive is reactivatible, i.e. contaminants can be removed by cleaning the adhesive layer(s) with soap and water, such as by the test methods described in WO 96/31564; incorporated herein by reference.

The multilayer adhesive can be applied to a substrate by various methods as described in the art. See for example U.S. Patent No. 4,818,610 and WO 201 1/09438.

The adhesives of the present invention may be coated upon a variety of flexible and inflexible backing materials using conventional coating techniques to produce adhesive-coated materials. Flexible substrates are defined herein as any material which is conventionally utilized as a tape backing or may be of any other flexible material. Examples include, but are not limited to plastic films such as

polypropylene, polyethylene, polyvinyl chloride, polyester (polyethylene terephthalate), polycarbonate, polymethylmethacrylate (PMMA), cellulose acetate, cellulose triacetate, and ethyl cellulose. Foam backings may be used. In some embodiments, the backing is comprised of a bio-based material such as polylactic acid (PLA).

Backings may also be prepared of fabric such as woven fabric formed of threads of synthetic or natural materials such as cotton, nylon, rayon, glass, ceramic materials, and the like or nonwoven fabric such as air laid webs of natural or synthetic fibers or blends of these. The backing may also be formed of metal, metalized polymer films, or ceramic sheet materials may take the form of any article

conventionally known to be utilized with pressure-sensitive adhesive compositions such as labels, tapes, signs, covers, marking indicia, and the like.

Backings can be made from plastics (e.g., polypropylene, including biaxially oriented polypropylene, vinyl, polyethylene, polyester such as polyethylene terephthalate), nonwovens (e.g., papers, cloths, nonwoven scrims), metal foils, foams (e.g., polyacrylic, polyethylene, polyurethane, neoprene), and the like. Foams are commercially available from various suppliers such as 3M Co., Voltek, Sekisui, and others. The foam may be formed as a coextruded sheet with the adhesive on one or both sides of the foam, or the adhesive may be laminated to it. When the adhesive is laminated to a foam, it may be desirable to treat the surface to improve the adhesion of the adhesive to the foam or to any of the other types of backings Such treatments are typically selected based on the nature of the materials of the adhesive and of the foam or backing and include primers and surface modifications (e.g., corona treatment, surface abrasion). Suitable primers include for example those described in EP 372756, US 5534391, US 6893731, WO2011/068754, and WO201 1/38448.

In some embodiments, the backing material is a transparent film having a transmission of visible light of at least 90 percent. The transparent film may further comprise a graphic. In this embodiment, the adhesive may also be transparent.

The above-described compositions can be coated on a substrate using conventional coating techniques modified as appropriate to the particular substrate. For example, these compositions can be applied to a variety of solid substrates by methods such as roller coating, flow coating, dip coating, spin coating, spray coating knife coating, and die coating. The composition may also be coated from the melt. These various methods of coating allow the compositions to be placed on the substrate at variable thicknesses thus allowing a wider range of use of the compositions. Coating thicknesses may vary as previously described. The syrup composition may be of any desirable concentration for subsequent coating, but is typically 5 to 20 wt-% polymer solids in monomer. The desired concentration may be achieved by further dilution of the coating composition, or by partial drying. Coating thicknesses of the cured coating may vary from about 25 (about 1 mil) to 1500 microns (60 mil). In typical embodiments, the coating thickness of the first layer ranges from about 20 to 40 mils; whereas the coating thickness of the second PSA skin ranges from about 1 to 5mils. When the multilayer PSA or article is intended to be bonded to a rough surface, the thickness of the adhesive layer typically ranges from the average roughness (Ra) to slightly greater than the maximum peak height (Rt).

The adhesive can also be provided in the form of a pressure-sensitive adhesive transfer tape in which at least one layer of the adhesive is disposed on a release liner for application to a permanent substrate at a later time. The adhesive can also be provided as a single coated or double coated tape in which the adhesive is disposed on a permanent backing.

For a single-sided tape, the side of the backing surface opposite that where the adhesive is disposed is typically coated with a suitable release material. Release materials are known and include materials such as, for example, silicone, polyethylene, polycarbamate, polyacrylics, and the like. For double coated tapes, another layer of adhesive is disposed on the backing surface opposite that where the adhesive of the invention is disposed. The other layer of adhesive can be different from the adhesive of the invention, e.g., a conventional acrylic PSA, or it can be the same adhesive as the invention, with the same or a different formulation. Double coated tapes are typically carried on a release liner. Additional tape constructions include those described in U.S. Pat. No. 5,602,221 (Bennett et al.), incorporated herein by reference. Objects and advantages of this invention are further illustrated by the following examples. The particular materials and amounts, as well as other conditions and details, recited in these examples should not be used to unduly limit this invention.

Components Utilized in the Examples

Preparatory Example 1 : Preparation of Citronellyl Acrylate (CiA)

A mixture of β-citronellol (300.00 g, 1.92 mol, Aldrich), hexane (1500 mL), and triethylamine (212.49 g, 2.10 mol, Aldrich) was cooled in an ice bath. Acryloyl chloride (190.08 g, 2.10 mol) was added drop-wise over 5 hours. The mixture was stirred for 17 hours at room temperature, then filtered. The solution was concentrated under vacuum and washed with water. The solvent was removed under vacuum to give a crude oil that was purified by vacuum distillation. A colorless oil (citronellyl acrylate) was collected at 70-75°C @ 0.30 mmHg (282.83 g).

Test Method 1 : 90° Angle Peel Adhesion Test on Paper Surfaces

Cut out a 1 in (2.54cm) wide and >3 in (7.62 cm) length specimen in the machine direction from the test sample. Remove the liner from one side of the adhesive and place it on an aluminum panel (2" x 5" (5.08 cm X 12.7 cm)). Remove liner from other side of adhesive and place it on a strip of copy paper* (1 inch (2.54cm) wide and >5 inches (7.62 cm)) using light finger pressure. Roll once in each direction with the standard FINAT test roller 4.5 lb (2 kg) at a speed of approx. at 12"/min. [305 mm]/min.). After applying the strips to the test panels, allow the panels samples to dwell at constant temperature and humidity (25^°C/50% RH) room for 10 minutes before using an Instron tester. Fix the test panel and strip into the horizontal support. Set the machine at 305 mm per minute jaw separation rate. Test results were measured in gram force per inch and converted to Newtons per dm. The peel values are the average of three 90° angle peel measurements.

*The copy paper utilized is available from Boise™ under the trade designation "X-9" (92 brightness, 24 lb. (90 gsm/12M), 500 sheets, 8.5 X 1 1 (216 mm X279 mm)).

Reusability was determined by repeating this test method using the same adhesive sample with a fresh piece of paper each time wherein each reuse is considered a cycle.

All the examples tested were cleanly removable from the copy paper unless specified otherwise, meaning that the paper did not tear and also did not have any staining or reside after removal of the adhesive.

Test Method 2: Static Shear Test on Dry Wall

Preparation of Drvwall for Testing

The substrates employed were standard smooth drvwall obtained from Home Depot (Woodbury, MN). Knock-down and orange-peel drywall was prepared by IUPAT (International Union of Painters and Allied Trades, 3205 Country Drive, Little Canada, MN, USA). Drywall was primed using paint roller with Sherwin-Williams Pro-Mar 200. Surfaces were dried for a minimum of 4 hours at ambient conditions before applying next coat of paint. White paint (Valspar Signature, Hi-def Advanced Color, Eggshell Interior, #221399, Ultra White / Base A) was applied to primed drywall using a new paint roller and allowed to dry at ambient conditions until tackless before applying a second coat of the same color. Final painted drywall was dried overnight at ambient conditions and then placed into a 120°C oven for 1 week. Samples were removed from oven and cut into desired dimensions using draw knife. Samples were dusted off using Kim wipes, tissue, paper towels, or air (no cleaning with solvents) to remove dust left over from cutting before use in testing.

A standard static shear test was performed at elevated temperature according to Pressure Sensitive Tape Council (Chicago, IL./USA) PSTC- 107 (procedure G). The test was performed at

70°F/50% Relative Humidity as called for by the method. The sample area of adhesive bonded to the prepared drywall surface was 2.54 cm in the vertical direction by 2.54 cm in the width direction (rather than 1.27 cm by 1.27 cm as called for by the method). Then a 6.8 kg weight was placed on top of the bonded sample area for 1 minute. After a dwell time of 60 seconds, the test specimen was hung in the shear stand at desired temperature and loaded immediately with a 250 g weight. The time to failure for the adhesive bond was recorded in minutes. The test was discontinued at 20,000 minutes and samples that passed the test are reported as 20,000+ minutes.

This same shear test was also conducted with other surfaces (cinderblock, ceramic tile). Such surfaces were prepared for testing as follows: Preparation of Cinderblock for Testing

Cinderblock was obtained from and cut down to 2" x 3" squares and 1 ½" x 5" strips by Total Construction & Equipment, Inc. (10195 Inver Grove Trl, Inver Grove Heights, MN, USA). Cinderblock was primed using paint roller with Zinsser Bulls Eye 1 -2-3 ® (Rusto-Oleum Corp, 1 1 Hawthorn Pkwy, Vernon Hills, IL, USA). Surfaces were dried for a minimum of 4 hours at ambient conditions before applying next coat of paint. White paint (Valspar Signature, Hi-def Advanced Color, Eggshell Interior, #221399, Ultra White / Base A) was applied to primed drywall using a new paint roller and allowed to dry at ambient conditions until tackless before applying a second coat of the same color. Final painted drywall was dried overnight at ambient conditions and then placed into a 120°C oven for 1 week.

Samples were removed from oven and cut into desired dimensions using draw knife. Samples were dusted off using Kim wipes, tissue, paper towels, or air (no cleaning with solvents) to remove dust left over from cutting before use in testing.

Preparation of Ceramic Tile for Testing

Tile was cleaned using a 50:50 (wt%) of Isopropyl alcohol : deioinized water mixture twice using Surpass tissues or Kim wipes.

Test Method 3 : Dynamic Mechanical Analysis

Comparative Example A, which is also the same as Adhesive Skin 1 (at 26.6 mil thickness) and examples 3-8 and 1 1-13 were analyzed by Dynamic Mechanical Analysis (DMA) using a Discovery Hybrid parallel plate rheometer (TA Instruments) to characterize the physical properties of each sample a function of temperature. Rheology samples were prepared by punching out a section of the PSA with an 8 mm circular die, removing it from the release liners, centering it between 8 mm diameter parallel plates of the rheometer, and compressing until the edges of the sample were uniform with the edges of the top and bottom plates. The furnace doors that surround the parallel plates and shafts of the rheometer were shut and the temperature was equilibrated at 20°C and held for 1 minute. The temperature was then ramped from 20°C to 125 or 130°C at 3°C/min while the parallel plates were oscillated at an angular frequency of 1 Hertz and a constant strain of 5 percent. The results are depicted in FIG. 6-8.

Examples

As used herein, all percentages are parts are by weight. Amounts of additives, e.g., crosslinkers, photoinitiator, tackifiers, etc. are also expressed in parts per hundred resin (pph) in which 100 parts of the resin represents the total weight of the monomers that form the (meth)acrylic polymer, e.g., IOA, 20A, AA, with the exception of the crosslinking monomer. The weight % of the major components relative to the total adhesive composition is also reported.

Comparative Example A (no second skin layer)

Comparative A was prepared by charging a 500 mL jar with 350 g of IOA and 0.14 g (0.04 pph) of 651. The monomer mixture was purged with nitrogen for 10 minutes then exposed to low intensity UV A radiation until a coatable syrup was formed, after which another 0.70 g (0.20 pph) of 651 and 1.58 g SR 306 HP was added. Next, 52.5 g (15 pph) of trade designation Aerosil R972 fumed silica (Evonik Industries) were added and the syrup was mixed with a trade designation Netzsch Model 50 Dispersator, degassed, and jar rolled until used. The coated syrup was coated at a thickness of about 15 mils between a release liner and a primed 3 mil PET film and cured by UVA light with a total dosage of 1332 mJ/cm². The average values of three samples were as follows:

This same composition was tested at a thickness of 26.6 mils (about 665 microns). The results were as follows:

Preparation and Characterization of Multilayer Adhesive

Preparation of Adhesive Skin 1

Skin 1 -was prepared by charging a 500 mL jar with 350 g of IOA and 0.14 g (0.04 pph) of 651. The monomer mixture was purged with nitrogen for 10 minutes then exposed to low intensity UV A radiation until a coatable syrup was formed, after which another 0.70 g (0.20 pph) of 651 and 1.58 g SR 306HP was added. Next, 52.5 g (15 pph) of trade designation Aerosil R972 fumed silica (Evonik Industries) were added and the syrup was mixed with a trade designation Netzsch Model 50 Dispersator, degassed, and jar rolled until used.

The wt-% of each of the major components of the total adhesive skin composition was as follows

Examples 1-8

Examples 1-8 were made by charging a quart jar with 300 g of low Tg monomer (IOA or 2-OA), 0.12 g of 651, and a quantity of crosslinker as shown in the following tables(TMPDE-90 and CiA, respectively). The monomer mixture was purged with nitrogen for 5 minutes then exposed to low intensity ultraviolet radiation until a coatable syrup was prepared. Subsequently, 5.1 g of HDK HI 5 fumed silica was added, and the syrup was mixed with a Netzsch Model 50 Dispersator. An additional 0.57 g of 651 and 24 g of glass bubbles were then added. Pre-adhesive formulations were mixed thoroughly by rolling over night and degassed. The Adhesive Skin 1 composition and coatable syrup were coated sequentially between a release liner and a primed 3 mil PET film was in contact with the release liner and had a thickness of 2 mils and the coated syrup was in contact with the PET film and had a thickness of 22 mils. UVA dosage, shear holding power and peel adhesion properties of resulting PSAs are shown in the following table. For rheological measurements, the coatable syrup was coated at 25 mil thickness and cured in the same manner.

Ex Low Tg 70 °C / 50% 90° Peel

Monomer CiA UVA Dose RH Shear to Adhesion to

CiA (g)

(pph) (mJ/cm²) Orange Peel Boise copy

Dry Wall (min) paper (N/dm)

6 20A 5.49 1.83 2664 5741 1 17.2

7 20A 4.1 1 1.37 2664 20000 144.1

8 20A 2.76 0.92 2664 20000 141.9

The wt-% of each of the major components of Examples 1-8 in the total adhesive composition were as follows:

Examples 9-13

Samples were made by charging a gallon jar with 2000 g of 2-OA, and 0.8 g of 651. The monomer mixture was purged with nitrogen for 10 minutes then exposed to low intensity ultraviolet radiation until a coatable syrup was prepared. Subsequently, 34 g of HDK HI 5 fumed silica was added, and the syrup was mixed with a Netzsch Model 50 Dispersator. An additional 3.8 g of 651 and 160 g of glass bubbles were then added. The formulations were mixed thoroughly by rolling over night and degassed. A quart jar with 200 g of the compounded syrup was combined with the amount of HDDA indicated in the following table and rolled overnight. The Adhesive Skin 1 composition and coatable syrup were coated sequentially between a release liner and a primed 3mil PET film such that the Adhesive Skin 1 was in contact with the release liner and had a thickness of 3 mils and the coated syrup was in contact with the PET film and had a thickness of 22 mils. Light intensity during cure and shear holding power and creep properties of resulting PSAs are shown in the following table. For rheological measurements, the coatable syrup was coated at 25 mil thickness and cured in the same manner.

The wt-% of each of the major components of Examples 9-13 in the total adhesive composition were as follows:

Examples 14-18

Samples were prepared by combining 2-OA and acrylic acid at the amounts indicated in the following table with 0.04 pph of 651 as a photoinitiator in a glass vessel. This was partially polymerized to provide a coatable syrup of ~ 2200 cPs viscosity (measured with a Brookfield viscometer, T = 25°C, spindle S63, 30 rpm) by exposure to ultraviolet radiation. Additional 0.19 pph 651, 0.055 ppH HDDA crosslinker and 1.7 pph HDK HI 5 fumed silica were added to the syrup and shear mixed until the 651 and HDDA had dissolved. Samples were then shear mixed at 4000 rpm for -240 seconds (delta T = ~7.5°C) for proper dispersion of the fumed silica. K15 glass bubbles (8 pph) were then mixed into the syrup using Jiffy mixing blade at low rpm (-200-300). Final mixtures were measured for viscosity, degassed and rolled until coated. Samples were frothed as described in U.S. Patent No. 4,415,615 using about 2-4 wt- % of the copolymer surfactant described in Example 44 of U.S. Patent No. 6,852,781. The Adhesive Skin 1 composition and coatable syrup were coated sequentially between a release liner and a primed 3mil PET film such that the Adhesive Skin 1 was in contact with the release liner and had a thickness of 3 mils and the coated syrup was in contact with the PET film and cured by UVA light with a total dosage of 1482 mJ/cm². For rheological measurements, the coatable syrup was coated at 25 mil thickness and cured in the same manner.

The cured samples were then tested for peel, shear, density, and caliper (of the adhesive layers by subtraction of the thickness of the PET and release liner) as reported in the following table.

The wt-% of each of the major components of Examples 14- 18 in the final adhesive composition were as follows:

Samples were made with Examples 14- 18 in the same manner as previously described except that the skin layer (i.e. Adhesive Skin 1) was omitted. The results were as follows:

Examples 19-22

Samples were made by charging a gallon jar with 2000 g of 2-OA, and 0.8 g of 651. The monomer mixture was purged with nitrogen for 10 minutes then exposed to low intensity ultraviolet radiation until a coatable syrup was prepared. Subsequently, 34 g of HDK HI 5 fumed silica was added, 2.2 g of HDDA, and 3.8 g 651 were added to the syrup and mixed with a Netzsch Model 50 Dispersator. Next 160 g of glass bubbles were added and mixed thoroughly by rolling over night and degassed. The Adhesive Skin 1 composition and coatable syrup were coated sequentially between a release liner and a primed 3mil PET film such that the Adhesive Skin 1 was in contact with the release liner and had a thickness of 3 mils and the syrup was in contact with the PET film and cured by 998 mW/cm² UVA light. The syrup was coated at various thicknesses as indicated in the following table. The cured samples were then tested for peel, shear and caliper as reported in the following table.

Examples 23-27

Samples were made by charging a gallon jar with 2000 g of 2-OA, and 0.8 g of 651. The monomer mixture was purged with nitrogen for 10 minutes then exposed to low intensity ultraviolet radiation until a coatable syrup was prepared. Subsequently, 34 g of HDK HI 5 fumed silica was added, 2.2 g of HDDA, and 3.8 g 651 were added to the syrup and mixed with a Netzsch Model 50 Dispersator. Next 160 g of glass bubbles were added and mixed thoroughly by rolling over night and degassed. The Adhesive Skin 1 composition and coatable syrup were coated sequentially between a release liner and a primed 3mil PET film such that the Adhesive Skin 1 was in contact with the release liner and the syrup was in contact with the PET film and cured by 998 mW/cm² UVA light. The adhesive skin was coated at various thicknesses as indicated in the following table, while concurrently reducing the thickness of the coatable syrup such that the total thickness of the adhesive layers was 25 mils. The cured samples were then tested for peel and shear as described in the following table.

Reusability

Example 9 was tested for adhesive reusability. The results are as follows:

Adhesive Performance on Various Surfaces

Claims

What is claimed is:

1. An adhesive coated article comprising:

a substrate comprising a first major surface and a second opposing major surface and a multilayer pressure sensitive adhesive layer disposed on the first major surface of the substrate; wherein the multilayer pressure sensitive adhesive comprises a first adhesive layer disposed on the first major surface of the substrate, and a second pressure sensitive adhesive skin layer disposed upon the first layer wherein at least the second skin layer is an acrylic adhesive comprising no greater than 1 wt-% of polymerized units derived from acid functional monomers.

2. The article of claim 1 wherein the first and second adhesive layers are acrylic adhesives comprising no greater than 1 wt-% of polymerized units derived from acid functional monomers.

3. The article of claims 1-2 wherein the first and second adhesive layers comprise at least 50 wt % of low Tg alkyl(meth)acrylate polymerized units.

4. The article of claims 1-2 wherein the first adhesive layer and optionally the second adhesive layer further comprise fumed silica.

5. The article of claims 1-4 wherein the first adhesive layer further comprises glass bubbles.

6. The article of claims 1-5 wherein the second adhesive layer is substantially free of glass bubbles.

7. The article of claims 1-6 wherein the first adhesive layer and optionally the second adhesive layer is crosslinked by a crosslinking monomer comprising at least two (meth)acrylate groups.

8. The article of claims 1-7 wherein the first adhesive layer is crosslinked with a crosslinking monomer comprising at least one C3 to C20 olefin group.

9. The article of claim 8 wherein the crosslinking monomer comprises at least one C3 to C20 olefin group and at least of (meth)acrylate group.

10. The article of claim 8 wherein the crosslinking monomer comprises at least two (meth)allyl groups.

1 1. The article of claims 1 -10 wherein the first adhesive layer comprises 0 to no greater than 10 wt-% of polymerized units derived from high Tg monomers.

12. The article of claims 1 -1 1 wherein the first adhesive layer has a tan delta of at least 0.4 at 25°C and 1 hertz.

13. The article of claim 1 wherein the substrate is a release liner and a release liner is disposed upon the second adhesive layer.

14. The article of claim 1 wherein the substrate is a backing and a release liner is disposed upon the second adhesive layer.

15. The article of claim 14 where the backing is a transparent film.

16. The article of claim 1-15 wherein the backing further comprises a graphic.

17. The article of claim 1 wherein the substrate is a backing and a pressure sensitive adhesive is disposed on the opposing surface of the backing forming a double-faced tape.

18. The article of claim 16 wherein the pressure sensitive adhesive disposed on the opposing surface of the backing is the multilayer adhesive according to claims 1-17.

19. The article of claim 16 wherein the pressure sensitive adhesive disposed on the opposing surface of the backing is a different pressure sensitive adhesive than the multilayer adhesive according to claims 1 - 12.

20. The article of claims 1 -12 wherein the substrate is a mounting article.

21. The article of claims 1 -20 wherein the first layer(s) of the multilayer adhesive has a thickness ranging from about 20 to 40 mils.

22. The article of claims 1 -21 wherein the second layer(s) of the multilayer adhesive has a thickness ranging from 1 to 5 mils.

23. An adhesive coated article comprising:

a substrate comprising a first major surface and a second opposing major surface; and a pressure sensitive adhesive layer disposed on the first major surface of the substrate wherein the pressure sensitive adhesive layer is cleanly removable from paper, reusable, and has a shear to orange peel dry wall with a 250 g weight of at least 500 minutes.

24. The article of claim 23 wherein the adhesive coated article comprises a multilayer pressure sensitive adhesive layer according to claims 1-22.

25. A method of using an adhesive coated article comprising

providing an article according to claims 1-24;

adhering the pressure sensitive adhesive to a surface.

26. The method of claim 25 wherein the surface has an average roughness of greater than 25 microns.