WO2018080929A1

WO2018080929A1 - Repositionable sheets

Info

Publication number: WO2018080929A1
Application number: PCT/US2017/057685
Authority: WO
Inventors: Maria A. FREITAS; Joao R. Talamoni; Susana SHIMIZU; Rodrigo M. TAFURI
Original assignee: 3M Innovative Properties Company
Priority date: 2016-10-26
Filing date: 2017-10-20
Publication date: 2018-05-03
Also published as: BR112019008391A2

Abstract

A repositionable sheet comprising a backing having front and back major surfaces and an adhesive on at least a portion of the back major surface, wherein the adhesive is an acrylic pressure sensitive adhesive derived from the reaction product of: (a) an acrylic acid ester of monohydric alcohol having an alkyl group of 5 to 10 carbon atoms; and (b) a nonpolar acrylic monomer having a solubility of less than about 9.2 as measured by the Fedors method using a homopolymer of the nonpolar acrylic monomer, wherein the reaction product has side chain crystallinity.

Description

REPOSITIONABLE SHEETS

Field of Invention

The present invention relates to repositionable sheets, in particular, repositionable sheets comprising acrylic adhesives that provide effective shear holding characteristics in combination with clean removal from adherend substrates.

Background

Repositionable sheets are widely known and commercially available in a variety of embodiments. Illustrative examples include the family of POST-IT® Products from 3M Company (e.g., notes, flags, tabs, easel pads, dry erase material, etc.).

Summary

The present invention provides novel repositionable sheets which provide surprising results.

In brief summary, a repositionable sheet of the invention comprises a backing having front and back major surfaces and an adhesive on at least a portion of the back major surface,

wherein the adhesive is an acrylic pressure sensitive adhesive derived from the reaction product of:

(a) an acrylic acid ester of monohydric alcohol having an alkyl group of 5 to 10 carbon atoms; and (b) a nonpolar acrylic monomer having a solubility of less than about 9.2 as measured by the Fedors method using a homopolymer of the nonpolar acrylic monomer, wherein the reaction product has side chain crystallinity.

The repositionable sheets described herein are well suited for a variety of applications including repositionable adherence to vertical surfaces and to sensitive substrate adherends.

Detailed Description of Illustrative Embodiments

Adhesive

This invention is directed at repositionable sheets comprising specific acrylic adhesives that are capable of achieving a desired balance of adhesive characteristics, particularly with applications involving substrates with delicate surfaces sensitive to tearing or delamination. In certain embodiments, the acrylic adhesives are non-polar adhesives that possess a low peel adhesion at relatively higher peel rates coupled with low adhesion build up and high shear strength values. This combination of performance

characteristics enables the adhesive and resultant repositionable sheet to function in certain embodiments for application to substrate adherends that are sensitive to delamination or tearing upon removal of the PSA from the substrate. The adhesive properties enabled by certain embodiments described herein offer sufficient bond strength and the subsequent clean removal of the adhesive after prolonged attachment to such delicate surfaces. In certain embodiments, the acrylic adhesive is derived from the reaction product of (i) an acrylic acid ester of monohydric alcohol having an alkyl group of 5 to 10 carbon atoms; and (ii) a nonpolar acrylic monomer having a solubility of less than about 9.2 as measured with the Fedors method using a homopolymer of the nonpolar acrylic monomer. The acrylic adhesive exhibits side chain crystallinity as indicated by fusion enthalpy of at least about 2.5 J/g. Side chain crystallinity modifies the performance of the adhesive in certain applications due to the reduced segmental mobility of these side chains that limit adhesion build up over extended application time. The adhesives of noted composition also possess desirable cohesive properties as indicated by a relatively high shear holding strength. The acrylic adhesives may optionally comprise other monomers, crosslinking agents, and other additives such as tackifiers.

An acrylic adhesive assembly may be created by applying the adhesive derived from the reaction product of (i) an acrylic acid ester of monohydric alcohol having an alkyl group of 5 to 10 carbon atoms; and (ii) a nonpolar acrylic monomer having a solubility of less than about 9.2 may be applied onto various backing substrates. The assembly has the acrylic adhesive layer disposed on at least a portion of a surface of the substrate. In some embodiments, the acrylic adhesive assembly may possesses a desired low adhesion, high tack and appropriate cohesive strength to enable the assembly to function as a PSA for applications involving articles with delicate surfaces. In other embodiments, the acrylic adhesive assembly may exhibit a peel adhesion value of less than about 3 N/dm according to the Peel Adhesion Test, at a peel rate of 300 mm/min and a peel adhesion value of less than about 4.5 N/dm according to the Peel Adhesion Test, at a peel rate of 2290 mm/min. The relatively high peel rate of 2290 mm/min replicates the speed at which a person would remove a PSA from the surface of an article and therefore is more closely representative of at least some of the intended applications embodied in this disclosure, such as the separation of individual packages from a multipack. In certain applications such as a PSA for delicate surfaces, a low peel adhesion followed by a low adhesion build up is desirable otherwise the adhesive becomes permanent and may cause damage when attempting to separate the adhesive assembly from a package having a delicate surface.

The acrylic adhesive of this disclosure derived from an acrylic acid ester of monohydric alcohol and a nonpolar acrylic monomer may be produced utilizing conventional polymerization practices such as solvent polymerization, emulsion polymerization, or bulk polymerization.

Certain embodiments of the acrylic adhesive provide the desired balance of peel adhesion, tack, and shear holding strength.

The following terms used in this application are defined as follows:

"Acrylate" or "Acrylic" is inclusive of both acrylate and (meth)acrylate or acrylic and

(meth)acrylic.

"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.

"Solubility Parameter" refers the solubility of the homopolymer derived from a select monomer using the Fedors method.

Acrylic adhesive s of the invention are derived from the reaction product of (i) an acrylic acid ester of monohydric alcohol having an alkyl group of 5 to 10 carbon atoms; and (ii) a nonpolar acrylic monomer having a solubility of less than about 9.2. The reaction product also exhibits side chain crystallinity in the acrylic adhesives resulting in a reduced segmental mobility of these side chains. The acrylic adhesive may be created in the form of a hot melt adhesive of a pressure-sensitive adhesive.

For purposes of this disclosure, a pressure-sensitive adhesive or PSA can be identified by a means known as the Dahlquist criterion. This criterion defines a PSA as an adhesive having a 1 second creep compliance of greater than about 1 x 10^"6 cm²/dyne as described in Handbook of PSA Technology, Donatas Satas (Ed.), 2^nd Edition, p. 172, Van Nostrand Reinhold, New York, N.Y., 1989. Alternatively, since modulus is, to a first approximation, the inverse of creep compliance, PSA's may be defined as adhesives having a Young's modulus of less than about 1 x 10⁶ dynes/cm². Another common

characterization means of identifying a PSA is that it is aggressively and permanently tacky at room temperature and firmly adheres to a variety of dissimilar surfaces upon mere contact without the need of more than finger or hand pressure, and that it may be removed from smooth surfaces without leaving a residue as described in Glossary of Terms Used in the Pressure Sensitive Tape Industry provided by the Pressure Sensitive Tape Council, 1996. Another suitable definition of a suitable PSA is that it preferably has a room temperature storage modulus within the area defined by the following points as plotted on a graph of modulus versus frequency at 25°C: a range of moduli from about 2 x 10⁵to about 4 x 10⁵ dynes/cm² at a frequency of about 0.1 radians/sec (0.017 Hz), and a range of moduli from about 2 x 10⁶to about 8 x 10⁶ dynes/cm² at a frequency of about 100 radians/sec (17 Hz) (for example see Fig. 8-16 on p. 173 of Handbook of PSA Technology (Donatas Satas, Ed.), 2^nd Edition, Van Nostrand Rheinhold, NY., 1989). Any of these methods of identifying a PSA may be used to identify suitable PSA's in accordance with this invention.

Conventional acrylic ester adhesives are typically an elastomeric polymer comprised primarily of a low T_g non-polar acrylate monomer, as well as a small amount of polar acrylic monomer such as acrylic acid. Two widely used low T_g acrylates in the acrylic adhesives 2-ethylhexyl acrylate (EHA) and isooctyl acrylate (IOA), each providing an alkyl chain of eight carbon atoms (Cs). Some embodiments copolymerize a higher T_g non-polar acrylate monomer that possesses a solubility of less than about 9.2 with the noted low T_g non-polar acrylate monomer. The resulting non-polar copolymer demonstrates a unique combination of physical characteristics such as low adhesion, high tack and sufficient cohesion to permit removal of the adhesive from an adherend. The T_g of the acrylic adhesive are generally in the range of about -35 to about -50°C. Certain embodiments exhibit a T_g of about -40 to about -45°C.

An acrylic acid ester of monohydric alcohol having an alkyl group of 5 to 10 carbon atoms is one of the monomers in the acrylic adhesive. The number of carbon atoms are selected to achieve a balance between sufficient T_g values and modulus. A lower number of carbon atoms may adversely impact T_g value and a higher number of carbon atoms may impact the desired tack. The homopolymer of the selected monomer has a T_g less than about 0°C. Non-limiting examples of the acrylic acid ester of monohydric alcohol include 2-ethylhexyl acrylate, iso-octyl acrylate, n-octyl acrylate, nonyl acrylate, hexyl acrylate, heptyl acrylate, 2-heptyl acrylate, ethylbutyl acrylate, 3-methylbutyl acrylate, plant-based 2-octyl acrylate and fusel oil acrylate and combinations thereof. In some embodiments, the acrylic acid ester monomers are included in the polymerizable composition at about 40 percent by weight to about 90 percent by weight. In other embodiments, the acrylic acid ester monomers are comprise about 50 percent by weight to about 80 percent by weight of the polymerizable composition.

The acrylic adhesives of this disclosure employ a nonpolar acrylic monomer having a homopolymer with a solubility parameter of less than about 9.2 as measured by the Fedors method. The T_g value of the homopolymer is greater than 19°C. The non-polar nature of this monomer limits the adhesion build up over extended application time. It also provides the smooth peel characteristics to the adhesive. Suitable non-polar acrylic monomers are those having alkyl group from 12 to 26 carbon atoms. Non-limiting examples include octadecyl acrylate, octadecyl methacrylate, cyclodecyl acrylate, cyclohexyl acrylate, hexadecyl acrylate, isobornyl acrylate, lauryl acrylate, lauryl methacrylate and combinations thereof. The nonpolar acrylic monomer comprises about 10 percent by weight to about 60 percent of the polymerizable composition. In other embodiments, the non-polar acrylate monomers comprise about 20 percent by weight to about 50 percent by weight of the polymerizable composition.

The resulting copolymer from the reaction components of an acrylic acid ester of monohydric alcohol and a nonpolar acrylic monomer possesses side chain crystallinity. The side chain crystallinity reduces segmental mobility of these side chains limiting adhesion build up over time. As a result of the crystallinity, reaction product exhibits a fusion enthalpy of at least about 2.5 J/g, at least about 5.5 J/g, or at least about 6.0 J/g.

In some embodiments, the acrylic adhesives of this invention can be derived from plant based or renewable resources. In particular, the acrylic adhesive may be derived, in part, from plant materials.

In some embodiments, the acrylic adhesives may also contain one or more conventional additives. Preferred additives include tackifiers, plasticizers, dyes, antioxidants, and UV stabilizers. Such additives can be used if they do not affect the superior properties of the acrylic adhesives. Those of ordinary skill in the art are capable of selecting an appropriate amount of the optional components to achieve desired end properties. The monomers can be polymerized by conventional techniques including, but not limited to, solvent polymerization, emulsion polymerization, and bulk polymerization. The monomer mixture may comprise a polymerization initiator, of a type and in an amount effective to polymerize the comonomer.

An optional crosslinking agent may be used in forming the acrylic adhesive. The optional crosslinking agent may be used to achieve a specific balance of adhesive properties for a selected application. A crosslinking agent is generally included in the composition for subsequent crosslinking upon application of the polymer in its desired end state. Upon activation, the crosslinking agent interacts with the functional moieties from the acrylate to improve cohesive strength. The crosslinking agent generally comprises compounds containing hydroxyl, carboxylic acid, isocyanate, azilidine or epoxy functional groups. Non-limiting example of crosslinking agents include benzophenone, triazine and acetophenone derived photocrosslinking compounds; multifunctional acrylates and methacrylates; silanes, organo-titanium compounds, or combinations thereof. Those of ordinary skill in the art are capable of selecting a specific crosslinking agent compatible with the chosen monomers and capable of withstanding the intended adhesive manufacturing environment. The crosslinking agent is included in the acrylic adhesive in an amount of about 0.1 to about 2.0 percent by weight.

The acrylic adhesive may be self-tacky or, in alternative embodiments, may be tackified. Useful tackifiers for acrylic adhesives are rosin esters such as that available under the trade name FORAL® 85 from Eastman, Inc., aromatic resins such as that available under the trade name PICCOTEX® LC from Eastman, Inc., aliphatic resins such as that available under the trade name PICCOTAC® 95 from

Eastman, Inc., and terpene resins such as that available under the trade names PICCOLYTE® A-l 15 and ZONAREZ® B-100 from Arizona Chemical Co. Plant based tackifiers may be well suited in certain applications, such as for example, FORAL® 85. Those of ordinary skill in the art with knowledge of this disclosure are capable of selecting an appropriate tackifier in an amount necessary to achieve desired end results for a selected application.

Many of the acrylate monomers used herein may be derived from plant based resources. In some embodiments, the plant based acrylic acid ester of monohydric alcohol is 2-octyl acrylate or fusel oil acrylate. As desired, the acrylic adhesive in certain embodiments comprises a plant based content of from about 25 to about 99 percent by weight, using ASTM D6866-10, method B. Those of ordinary skill in the art will additionally recognize that many of the components in an adhesive assembly, such as tackifiers and backing materials, may be derived from plant based resources. In certain embodiments, an adhesive assembly may comprise about 25 weight percent or more plant based content.

The above-described acrylic PSA compositions are 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 gravure roll coating, roller coating, flow coating, dip coating, spin coating, spray coating knife coating, and die coating. 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 from a few microns to a few hundred microns. Those of ordinary skill in the art are capable of selecting an appropriate coating technique to match the backing and desired end use application.

Various forms of radiation may be employed to cure the adhesive using crosslinking agents once acrylic adhesive is applied onto a backing. For example, actinic radiation is well suited to initiate crosslinking. For purposes of this disclosure actinic radiation means electromagnetic radiation capable of inducing a chemical change in a material. Non-limiting examples of actinic radiation include

wavelengths in the ultraviolet (UV) and/or visible regions of the spectrum, and electron beam radiation.

The acrylic adhesives of this disclosure are well suited for applications involving requiring easily removable tape that can be firmly adhered to a substrate, and subsequently removed without damaging the substrate and without transferring adhesive to the substrate. In some embodiments, the adhesive assembly of this disclosure is capable of binding two or more containers together. The binding of two or more containers may be referred to as a multipack. In selected applications, the adhesive assembly possesses the requisite balance of adhesive properties to enable sufficient shear holding strength and then subsequently permit the clean removal of the acrylic adhesive after prolonged attachment to delicate surfaces of containers in a multipack.

For purposes of this disclosure, delicate surfaces refers to articles, such as containers or packages, that are sensitive to delamination or tearing upon removal of an adhesive from the article. Non-limiting examples include paper, cartons, cardboard, film, films of cellophane, monoaxially, biaxially or non-oriented polyolefins or polyvinyl chloride films. The adhesive properties enabled by certain embodiments of this disclosure possess a low peel adhesion at relatively higher peel rates coupled with low adhesion build up and high shear strength values. This combination of performance characteristics enables the adhesive to function in certain embodiments as a PSA for application to substrate adherends with delicate surfaces. The term "delicate surfaces," as used herein, refers to surface films with tear resistance lower than 300 g-f according to method ASTM D 1004- 13, paper, paperboard, cardboard or combinations thereof. Upon subsequent removal of the acrylic pressure sensitive adhesive assembly or repositionable sheet of the invention, the acrylic pressure sensitive adhesive exhibits no cohesive failure and the surfaces of the two or more containers remain whole. Also, for purposes of this disclosure, the term "whole" indicates that the condition of the substrate surface, is substantially similar to its condition prior to application of the acrylic PSA, with certain substrates, the removal of the adhesive assembly will not cause tearing or delamination.

Some embodiments of the acrylic adhesive are capable of forming an acrylic adhesive assembly that exhibits a peel adhesion value of less than about 3 N/dm according to ASTM D3330 test method A and peel angle of 180°, peel rate 300 mm/min and a peel adhesion value of less than about 4.5 N/dm according to the Peel Adhesion Test, at a peel rate of 2290 mm/min on a stainless steel pane conforming to Type 302 of Specification A666.

The adhesive assembly may also possess other desirable characteristics suitable for binding the repositionable sheet to challenging substrate applications as desired. For example, the adhesive assembly may comprise one or more of (i) a loop tack value greater than about 6 N/dm according to ASTM D6195-03 test method B, and (ii) shear value of greater than about 10,000 shear min according to ASTM D3654 test procedure A. In certain embodiments, the shear value may be greater than about 12,000 shear min, greater than about 15,000 shear min, or even greater than about 17,000 shear min.

The acrylic adhesives balance of adhesive properties to enable sufficient shear holding strength and then subsequently permit the clean removal of the acrylic adhesive is not the only defining attribute of the composition of this disclosure. The acrylic adhesive has at least a 1 second creep compliance of greater than about 1 x 10^"6 cm²/dyne.

Backing

In typical embodiments, the backing is selected from the group consisting of paper, cardboard, and plastic films. Selection of suitable backing material is dependent in part upon the intended

application for the repositionable sheet. Non-limiting examples of materials that can be included in the backing include polyolefins, such as polyethylene, polypropylene, polystyrene, polyester, polyvinyl chloride, polyurethane, polyvinyl alcohol, poly(ethylene terephthalate), poly(butylene terephthalate), poly(caprolactam), poly(vinylidene fluoride), polylactides, cellulose acetate, ethyl cellulose, paper, silicone and combinations thereof. Other non-limiting examples of commercially available backing materials include kraft paper, spun-bond polyolefins, porous films obtained from polyolefins, and multi- layered constructions. In some embodiments involving an adhesive assembly well suited for application onto delicate surfaces, monoaxially, biaxially or non-oriented polyolefins or polyvinyl chloride substrates may be used.

Typically, the backing is writable on its front major surface.

Typically, the backing and sheet of the invention are flexible.

Typically, sheets of the invention are arranged in assemblies such as a plurality of such sheets arranged in a stack, or one or more sheets of the invention wound in roll form.

In some embodiments, sheets of the invention may consist essentially of a backing and adhesive as described herein with no use of primer to achieve adherence of the adhesive to the back surface of the backing as desired or release of the adhesive of an overlying sheet from an underlying sheet from stack or roll form. As a result, desirably performing repositionable sheets may be made in economical fashion.

In some embodiments, the backing is a writable plastic film (e.g., non-oriented, monoaxially oriented, or biaxially oriented polypropylene), such as VITOPAPER™ films from Vitopel. Such material can provide bleed proof performance, thereby protecting underlying substrate adherend surfaces, as well as being made desirably light transmissive to permit "seeing" the substrate surface through the sheet repositionably mounted thereon.

The size and shape of the sheet, size and shape of backing, and amount and pattern of adhesive thereon is dependent in part upon the desired application. For example, a note pad composed by sheets of 75 mm x 75 mm and an adhesive strip of 12.5 mm width with 10 g/m². Larger sheets, as well as repositionable sheet intended for use in vertical or other challenging applications may be made with greater amounts of adhesive.

Examples

Test Procedures

90° peel adhesion to stainless steel

90° peel adhesion was measured following the procedure generally outlined in FINAT Test Method no.2, a standard 90° peel test method (from Federation Internationale des Fabricants Europeens et

Transformateurs d'Adhesifs et Thermocollants sur Papiers et autres Supports (FINAT)), with the exception of: (i) while FINAT 2 requires a glass substrate, a stainless steel plate in testing the present examples; and (ii) the dwell time was essentially zero rather than 20 min and 24 hrs, respectively, as specified by the FINAT 2 method.

Samples of repositionable sheets measuring 25 mm in width and 175 mm in length were cut and adhered to a Type 302 stainless steel plate. A 2 kg roller was rolled over each sample twice. The stainless steel plate was cleaned prior to adhering the adhesive tape by wiping the plate with isopropyl alcohol using a tissue paper. The force required to peel the repositionable sheet was measured using an IMASS™ Adhesion Tester SP-2100 (from Imass, Inc., Hingham, Mass) equipped with a 2 kg load cell. At a peel angle of 90°, peel adhesion was measured in Newton / 25 mm -width at a speed of 300 millimeters / minute. Failure mode was noted. Each sheet was evaluated using five different samples and the results reported as average in Newton/25 mm -width (N/25mm).

90° peel adhesion to paper substrate, initial and aged

Repositionable sheets were cut into 1 inch (2.45 cm) wide and 17.5 cm long sample strips having an adhesive layer disposed therewith. A portion of the sample strip was applied to either a 75 g/m² bond paper or to a 62 g/m² glossy magazine paper, both of which were disposed on horizontal surfaces. A 4.5 pound (2 kg) hard rubber roller was used to firmly adhere the sample strip to the bond paper and to the glossy magazine paper. The remaining portion of the strip was attached to a load cell in such a way that it formed a removal angle of about 90° with the paper substrate. The strip was peeled from the paper substrate at a constant rate of 300 mm/minute. The force required to peel the strip of repositionable sheet was measured using the Instron® 5965 equipped with a 5 kg load cell and an apparatus that allow a peel angle of 90° and results are reported as average of triplicate measurements in g-f/in-width in Tables 5 and 6

Similarly, to the procedure described above, sample strips of repositionable sheets were adhered to either bond paper of gloss magazine paper, forming test laminates. The laminates were aged for three days (72 hours) at one of temperature of 150°F (65°C) / no humidity, or temperature of 70°F (21°C) / 80% relative humidity. After aging, 90° peel adhesion of the samples were measured and % of adhesion build up is defined as % (aged adhesion to paper - initial adhesion to paper) / initial adhesion to paper. It is considered the adhesive has no adhesion build (i.e., 0%) if the calculated number is 0 or negative.

Breaking Strength and Elongation:

Breaking strength and elongation was measured according to test method C described in ASTM D3759/D3759M. Samples of 12 mm wide by 20 cm long of adhesive label were cut and mounted between two clamps of an INSTRON® Machine, model 5965. A 5 cm gauge length and a rate of 30 cm/min was used. The breaking strength was measured in kg-f/12 mm-width and elongation in %.

Adhesion loss (%)

This test was used to evaluate repositionability by adhering a repositionable sheet to the bond paper substrate for 10 consecutive times, measuring and recording adhesion to the substrate each time the sheet was applied thereof. 90° peel adhesion was measured as described in "90° peel adhesion to paper substrate" test method above, except that the same sample was applied to and removed from the substrate 10 times. Adhesion loss was calculated with the first value of adhesion (1^st peel=Xl) and the 10^th value of adhesion (10^th peel= X10) after 10 times removing and repositioning and testing, in this case, the rate loss is calculated as (X10-X1)/X10 and is reported as %.

Probe Tack

A TA-XTPlus Texture Analyser made by Texture Technologies Corp. was used for tack measurement. Samples were held with the adhesive side up by a brass test fixture. A 6 mm stainless steel probe was brought into contact with the specimen until a specific force was reached, usually, 100 g. After one second contact time, the probe was raised at speed of 0.5 mm/sec and the force to separate the probe from adhesive was measured and reported as function of peak force in g-f/area, in this case g-f/28.26 mm².

Static Shear

Shear strength was measured following the test procedure A described in ASTM D3654-06, "Standard Test Methods for Shear Adhesion of Pressure-Sensitive Tapes". A 25.4 mm strip of sample was adhered to a previously cleaned stainless steel plate. The strip was subsequently cut leaving a 25.4 mm by 25.4 mm square sample. A 2 kg roller was rolled over each sample, one pass in each direction. Load of 1 kg were attached to the tape sample using a hook. Each sample was suspended until failure. Failure time and mode of failure were recorded. 10 replicate test samples were used to establish confidence in the mean results.

Loop Tack

Loop tack was measured following the test method B procedure described in ASTM D6195-03, "Standard Test Methods for Loop Tack". Samples of adhesive tape measuring 25 mm by 100 mm were cut and a loop was formed and attached to a mobile arm of a Loop Tack tester (LT-500, Chemlnstruments, Inc.). The force required to remove the tape at 300 mm/min was measured in grams/25 mm width. Measurements were done in triplicate. Average loop tack is reported in gram/25 mm -width (g/25 mm).

Tack Loss %

This test was used to evaluate repositionability by adhering a repositionable sheet to the bond paper substrate with a 2 kg roller passed over the sample. Sample was removed by hand at a 90° peel angle at a rate of about 30 cm/min. This procedure was repeated for 10 times. After the tenth removal, the tack was measured according to the loop tack method described above. Measurements were done in triplicate. Loop tack after ten removals from bond paper is reported in gram-f/25 mm-width (g-f/25 mm). Loop tack loss was calculated using the equation (Y10-Y1)/Y10, where Yl is the initial loop tack measured according to the loop tack method described above and Y10 is the loop tack value after 10 removal from the bond paper. The rate loss is calculated as and is reported as %.

Inherent Viscosity

Inherent viscosity is based on a comparison of cinematic viscosity of a diluted solution of adhesive and the pure solvent used to prepare this diluted solution. In the present examples, the solvent used was ethyl acetate. Cinematic viscosity was measured using an Ostwald-Fenske viscometer, using an automatic equipment from Lauda DR. R. Wobser GMBH & Co. KG, from Germany, model Lauda Viscotemp 15. A diluted solution of adhesive was prepared and 10 ml of this diluted solution was added to the equipment where it measured cinematic viscosity. The adhesive solution was then replaced by pure solvent and the cinematic viscosity of the solvent was measured. The polymer solution concentration (% solids) was calculated after a sample of the adhesive composition was left in a convection oven set at a temperature of about 120°C for 30 minutes (0.5hours). Inherent viscosity was calculated by the following equation:

where C is the polymer solution concentration (g/dL) and ¾¾?S is relative viscosity, defined as

_

'^{^} %

where Π is the viscosity of the solution and % is the viscosity of the pure solvent. Inherent viscosity is reported as dL/g. Fusion enthalpy

Samples of adhesive were prepared for thermal analysis by weighing and loading the material into TA Instruments aluminum DSC sample pans. The samples were analyzed using a TA Instruments Q2000 Modulated® Differential Scanning Calorimeter (MDSC) utilizing a heat-cool-heat method in temperature modulated mode (-90 to 200°C at 4°C/min. with a modulation amplitude of ±0.64°C and a period of 60 sec).

After data collection, the thermal transitions were analyzed using the TA Universal Analysis program. Any peak transitions were evaluated using the heat flow (HF), reversing heat flow (REV HF) or non- reversing heat flow (NR HF) curves. Peak area values and/or peak minimum / maximum temperatures are also determined; peak integration results are normalized for sample weight and reported in J/g. Fusion enthalpy was calculated and is reported in J/g.

Materials

Preparation of Examples

Preparation of Adhesive Composition 1

Adhesive Composition 1 was prepared by adding to a 1000 ml four-necked reaction vessel, equipped with a stirrer, nitrogen line, condenser, and a PT100 thermocouple the following ingredients in order: 121.3 g of 2-ethylhexyl acrylate, 96.7 g of a solution of ODA in toluene (45.2% solids), 155 g of ethyl acetate and 0.825 g of AEBP (50% solids in ethyl acetate). A slight nitrogen purge was placed in the solution and this solution reaction was heated to 58°C. When the temperature reached 58°C, a solution of 0.35 grams of VAZO'™ 64 in 5 grams of ethyl acetate was added to the solution reaction. This solution was kept in reaction for about 24 hours, and a 98-99% conversion was obtained. Inherent viscosity of the adhesive was measured using the procedure described above. Inherent viscosity (IV) and fusion enthalpy are shown, in Table 1, below.

Table 1

Comparative Example C 1

A commercially available repositionable sheet was obtained under the trade designation "POST-IT® Big Pad", a 30 count pad of removable self-stick paper (size 55.8 cm x 55.8 cm) by 3M Company of St. Paul, MN, and is hereinafter referred to as Comparative Example CI .

Example 1

Repositionable sheet of Example 1 was prepared using the following procedure: adhesive

composition 1 was coated onto a Corona treated non-oriented polypropylene backing film (NOPP, 62 micra, 42 dyn/cm) using a fluid bearing die. Tensile strength of the NOPP was about 4.4 kg-f/12 mm and elongation was about 823%. The adhesive composition was dried to evaporate the solvent in an oven set at a temperature of about 70°C. After drying, the adhesive layer had a coating weight was from about 19 to about 21 g/m². The adhesive layer was cured using germicidal (GEMS) UVC irradiation of 300 mJ/cm² to crosslink the adhesive.

Example 2

composition 1 was coated onto a Corona treated non-oriented polypropylene backing film (NOPP, 55 micra, 42 dyn/cm) using a fluid bearing die. Tensile strength of NOPP was about 2.8 kg-f/12 mm and elongation was about 657%. The adhesive composition was dried to evaporate the solvent in an oven set at a temperature of about 70°C and after drying, the adhesive composition was coated in seven stripes, each stripe having a width of about 2 mm and wherein the distance between each stripe was 2 mm. After drying, the total adhesive coating weight was from about 9 to about 11 g/m². The adhesive layer was cured using germicidal (GEMS) UVC irradiation of 300 mJ/cm² to crosslink the adhesive.

Example 3

Repositionable sheet of Example 3 was prepared using the following procedure: adhesive composition 1 was coated onto a Corona treated non-oriented polypropylene backing film (NOPP, 62 micra, 42 dyn/cm) using a fluid bearing die. Tensile strength of the NOPP was about 4.4 kg-f/12 mm and elongation was about 823%. The adhesive composition was dried to evaporate the solvent in an oven set at a temperature of about 70°C. After drying, the adhesive layer had a coating weight was from about 30 to about 35 g/m². The adhesive layer was cured using germicidal (GEMS) UVC irradiation of 200 mJ/cm² to crosslink the adhesive.

Example 4

Repositionable sheet of Example 4 was prepared using the following procedure: adhesive composition 1 was coated onto Vitopaper (37g/m²) obtained by Vitopel backing film (Vitopaper, 37g/m², 42 dyn/cm) using a fluid bearing die. The adhesive composition was dried to evaporate the solvent in an oven set at a temperature of about 70°C. After drying, the adhesive layer had a coating weight was between 13 and 15 g/m². The adhesive layer was cured using germicidal (GEMS) UVC irradiation of 200 mJ/cm² to crosslink the adhesive.

90° peel adhesion to stainless steel of Examples 1, 2, 3, and 4 (examples with different backings, adhesive coating weights and different curing energies) and Comparative Example CI were measured using the procedures described above to yield the results reported in Table 2.

Table 2

Static shear, probe tack and repositionability in bond paper (measured as a function of % loss in adhesion) of Examples 1 and 2 and Comparative Example 1 were measured using the procedures described above. Probe tack was used to compare the tack of comparative example 1 and examples 1 and 2, once this method does not have high impact of different backings. Results are reported in Table 3. Table 3

Loop Tack and Loop tack loss of example 3 and Comparative Example 1 are reported on table 4. Loop tack was used to measure the loop tack loss because the tack is measured in a higher surface area than probe tack.

Table 4

% of loop tack loss is defined as % (loop tack after 10 removals from bond paper - initial loop tack)/ initial loop tack. It is considered the adhesive has no tack loss (i.e., 0%) if calculated number is 0 or positive.

Examples 1, 2 and Comparative Example 1 were adhered to bond paper and gloss magazine paper and aged, using the procedure described above. 90° peel adhesion results are reported in Tables 5 and 6 as average adhesion in gf/in initial and after aging, and % adhesion build up on bond paper and average adhesion in gf/in initial and after aging, and % adhesion build up on gloss magazine paper, respectively. Adhesive transfer to the substrate is reported as "transferred" and "not transferred", wherein "transferred" means that 100% of adhesive transferred to the substrate and "not transferred", means clean removal (0% adhesive residue). Results are reported in Table 7.

Table 5

Table 6

% adhesion build up is defined as % (aged adhesion to paper - initial adhesion to paper) / initial adhesion to paper. It is considered the adhesive has no adhesion build (i.e., 0%) if calculated number is 0 or negative.

Table 7

Claims

What is claimed is:

1. A repositionable sheet comprising a backing having front and back major surfaces and an adhesive on at least a portion of the back major surface,

(a) an acrylic acid ester of monohydric alcohol having an alkyl group of 5 to 10 carbon atoms; and

(b) a nonpolar acrylic monomer having a solubility of less than about 9.2 as measured by the Fedors method using a homopolymer of the nonpolar acrylic monomer, wherein the reaction product has side chain crystallinity.

2. The sheet of claim 1 wherein the reaction product exhibits a fusion enthalpy of at least about 2.5 J/g.

3. The sheet of claim 1 wherein the reaction product exhibits a fusion enthalpy of at least about 5.5 J/g.

4. The sheet of claim 1 wherein the reaction product exhibits a fusion enthalpy of at least about 6.0 J/g.

5. The sheet of any of the preceding claims wherein the nonpolar acrylic monomer having alkyl group from 12 to 26 carbon atoms.

6. The sheet of any of the preceding claims further comprising a crosslinking agent.

7. The sheet of claim 4 wherein the crosslinking agent comprises a benzophenone, a triazine or acetophenone derived photocrosslinking compound; a multifunctional acrylate or methacrylate; a silane, an organo-titanium compound, or combinations thereof.

8. The sheet of any of the preceding claims wherein the acrylic acid ester of monohydric alcohol comprises 2-ethylhexyl acrylate, iso-octyl acrylate, 2-octyl acrylate, n-octyl acrylate, nonyl acrylate, hexyl acrylate, heptyl acrylate, 2-heptyl acrylate, ethylbutyl acrylate, 3-methylbutyl acrylate, fusel oil acrylate and combinations thereof.

9. The sheet of any of the preceding claims wherein the nonpolar acrylic monomer comprises an octadecyl acrylate, an octadecyl methacrylate, a cyclodecyl acrylate, a cyclohexyl acrylate, a hexadecyl acrylate, an isobornyl acrylate, a lauryl acrylate, a lauryl methacrylate or combinations thereof.

10. The sheet of claim 8 wherein the two octyl acrylate and fusel oil acrylate are biobased.

11. The sheet of any of the preceding claims further comprising a tackifier.

12. The sheet of any of the preceding claims wherein the acrylic adhesive is a pressure sensitive adhesive or a hot melt adhesive.

13. The sheet of claim 1 wherein the backing is selected from the group consisting of paper, cardboard, and plastic films.

14. An assembly comprising a plurality of sheets of claim 1 arranged in stack.

15. A sheet of claim 1 arranged in roll form.