The invention relates to label-wrapped foam cups and particularly to such cups in which the labels wrap around the cups and contribute to the structural integrity of the cups and to such labels and their manufacture.
Foam cups reinforced by wrap-around labels are widely used as drinking cups, particularly for beverages served warm such as coffee. The foam cups, which are typically made of beaded polystyrene, are shaped for holding a liquid and exhibit good insulating properties. The wrap-around labels, which are typically made of paper or plastic film, reinforce sidewalls of the foam cups and provide good printing surfaces for applying text and graphics to the reinforced foam cups.
Sidewalls of the foam cups have a generally frusto-conical shape and the wrap-around labels are shaped to match the unrolled form of the frusto-conical shape. The wrap-around labels are generally attached to the foam cups with a pressure-sensitive adhesive that bonds the labels to the cups. Within a region of overlap, the pressure-sensitive adhesive bonds opposite ends of the wrap-around labels to each other.
Generally, the pressure-sensitive adhesive completely covers a back surface of the label to provide an uninterrupted bond with the underlying foam cup. The continuous bond between the wrap-around label and the foam cup can provide a smooth outer surface for displaying text and graphics. In addition, the smooth outer surfaces of the label-wrapped cups enable the cups to be collected into stacks and released individually from the stacks with a consistently low force. However, heating, cooling, stretching, or bending the sidewalls of the cups can produce unsightly wrinkles in the labels.
Pressure-sensitive label stocks can add cost to the label-wrapped cups because a release liner is required to protect the pressure-sensitive adhesive until the labels are in position for application to the cups. Once the pressure-sensitive labels are removed from the release liner, the release liner is discarded. As much as one-third of the cost of the pressure-sensitive label stocks is attributable to the release liners that form no part of the finished label-wrapped cups.
The invention among its preferred embodiments reduces the cost of label-wrapped foam cups, enhances bonding between the labels and the foam cups, improves grip, avoids unsightly wrinkles, and contributes to the appearance of the label-wrapped foam cups. Cost can be reduced by obviating the release liner and by patterning adhesive on a back surface of the linerless labels. Bonding can be enhanced by using an externally activated adhesive, such as a heat-activated adhesive, that provides a more permanent bond between the labels and the foam cups and by applying the externally activated adhesive in beads or ridges that melt, flow, or otherwise migrate into pores within the foam cups for providing rigid mechanical locks. Grip can be improved by patterning the externally activated adhesive at a thickness such that the surface of the label is correspondingly textured by underlying beads or ridges of the adhesive. Unsightly wrinkles can be avoided by stronger bonds and by surface undulations in the labels that accommodate limited amounts of expansion and contraction of the underlying foam cups. Contributions to the appearance of the label-wrapped foam cups can be made by coordinating the patterning of the adhesive on a back surface of the labels with printing on a front surface of the labels to produce desired visual effects.
One version of the invention features a label-wrapped foam cup combining a foam cup having an open end and a closed end joined by a peripheral wall including inner and outer wall surfaces with a label wrapped in a frusto-conical form around the outer wall surface of the foam cup. Printed matter is applied to a front surface of the label, and a patterned adhesive is applied between a back surface of the label and the outer wall surface of the foam cup. The patterned adhesive includes discontinuous deposits of adhesive that bond the label to the foam cup and form corresponding undulations in the front surface of the label.
Preferably, the foam cup is made of expanded polystyrene and the adhesive is a heat-activated adhesive. Deposits of adhesive melt into surface interstices between beaded structures of the foam cup. The deposits of adhesive can have a thickness prior to melting that is greater than an average depth of the surface interstices for both forming strong mechanical bonds and texturing the surface of the label.
The label can be divided into different annular sections along the height of the foam cup. For example, a continuous adhesive can be deposited within a first annular section and a discontinuous adhesive can be deposited within the second annular section. The first annular section can be adjacent to the open or closed end of the foam cup to provide a continuous seal or a smooth surface for stacking the cups, and the second annular section can be located intermediate of the cup ends to provide the desired texturing. The patterned adhesive can be deposited as a plurality of parallel or crisscrossed lines or as an array of beads. The form, density, or thickness of the adhesive deposits can be varied progressively between the opposite ends of the cup or discontinuously to produce more localized variations. For example, the printing and patterning of the adhesive can be registered to produce such effects as raised lettering or angularly sensitive images.
Another version of the invention features a web for forming a succession of labels for wrapping in a frusto-conical form around foam cups. A continuous web has inner and outer surfaces. Graphics can be printed on the outer surface of the web defining a succession of labels having a fixed length in a direction for wrapping around the cups. An externally activated adhesive can be printed on the inner surface of the web in registration with the graphics printed on the outer surface of the web in a succession of adhesive lengths less than the fixed length of the labels.
A label 10 is shown in in a flat state with an overall shape intended for efficiently wrapping around a foam cup 12 as shown in for forming a label-wrapped foam cup 14. A front surface 16 of the label 10, as shown in , 3, and 4, contains various text and graphics including a trade name 23, a graphic illustration 24, and a set of descriptors 25 for describing the intended contents of the label-wrapped foam cup 14.
The foam cup 12 is preferably made in a conventional manner from plastic materials, such as foamed or expanded polystyrene. Typically, pre-expanded polystyrene beads are filled into a mold of suitable shape and heated with steam to further expand and fuse the foam beads into an integrated cup structure. The foam cup 12, which has an overall frusto-conical shape, includes an open end 32 and a closed end 34 joined by a peripheral wall 36 having conically tapered inner and outer wall surfaces 38 and 40. The labels 10 are wrapped around and bonded to the outer wall surface 40 using a patterned externally activated adhesive 26 as shown in . In addition, one end 27 of the labels 10 preferably overlaps another end 29 of the labels 10 so that the labels 10 also bond to themselves to compete a closed frusto-conical shape. However, the label ends 27 and 29 could also be arranged to abut one another.
A back surface 18 of the label 10 is shown in with the externally activated adhesive 26 applied in a crisscross pattern 28 of elongated beads (or ridges) 30 over much of the back surface 18. A margin 20 between a boundary of the adhesive pattern 28 and a periphery 22 of the label 10 is free of the adhesive 26 so that when the label 10 is applied to the foam cup 12, the adhesive 26 does not leak beyond the periphery 22 of the label 10. The margin 20 also provides for cleanly die cutting individual labels 10 from a web 92 (shown in , 12, and 13). Preferably, the margin 20 has an average width of at least one-half millimeters but less than 2 millimeters.
The externally activated adhesive 26 is preferably a low-temperature heat-activated adhesive that transitions from a solid state to a tacky state at less than the temperature at which the foam cup 14 breaks down from heat. For example, the heat-activated adhesive, also referred to as a hot-melt adhesive, turns tacky at an elevated temperature such as approximately 200 degrees Fahrenheit or less and preferably at a temperature of between 170 degrees Fahrenheit to 180 degrees Fahrenheit. The foam comprising the peripheral wall 36 provides insulation to inhibit transfers of heat from hot liquids within the foam cup 12 to the adhesive pattern 28, which largely precludes any significant re-melting or undue softening of the heat-activated adhesive. However, even if some softening of the heat-activated adhesive does occur, the result is expected to be merely an increase in tackiness similar to the ordinary state of a pressure-sensitive adhesive.
The greatly enlarged breakaway sectional side view of shows one of the beads 30 of the heat-activated adhesive forming a bond between the back surface 18 of the label 10 and the outer wall surface 40 of the foam cup's peripheral wall 36. The bead 30 is shown melted into interstices 42 in the outer wall surface 40 formed between fused polystyrene beads 44. When hardened upon cooling, the bead 30 forms a mechanical interlock in addition to the customary chemical bonding of the heat-activated adhesive for forming a strong bond with the peripheral wall surface 40. Similar physical and chemical bonding occurs between the bead 30 and the back surface 18 of the label 10, which is preferably made of paper or film. In addition, a barrier layer 48 can be applied between the back surface 18 of the label 10 and the pattern of adhesive 28 including the beads 30 to enhance the bonding of the adhesive to the back surface 18 and to inhibit ingress of discolorants or other visual or structural impairments into the labels 10. The barrier layer can be a varnish or other protective agent.
As also shown in and similarly apparent in the less enlarged view of , the beads 30 have a thickness “T” well beyond an average depth of the interstices 42 for spacing the label 10 from the outer wall surface 40 and for supporting local undulations 46 in the label 10 that provide a textured look and feel to the label-wrapped cup 14. The undulations 46 accommodate relative expansions and contractions of the label 10 and the foam cup 12 by varying amplitudes of the undulations and thereby avoiding permanent wrinkling or creasing of the labels 10. The bonds formed by the beads 30 of the heat-activated adhesive remain unbroken by allowing the unbonded portions of the label 10 to vary in spacing with respect to the outer wall surface 40 to compensate for externally induced variations in the periodicity of the beads 30. For example, mechanically or thermally induced variations in the size of the foam cup 12 relative to the label 10 can be dispersed by the beads 30 over the columnar supported areas of the label 10 to avoid local concentrations of stress between the label 10 and the foam cup 12 that might otherwise result in a wrinkling or creasing of the label 10. The undulations 46 also provide for improving grip so that the label-wrapped foam cups 14 are less likely to the unintentionally dropped or spilled. The thickness “T” of the beads 30 also creates air spaces between the label 10 and the foam cup 12, which further improves the insulating properties of the label-wrapped foam cup 14.
depict different patterns with which the externally activated adhesive 26 can be deposited onto the back surfaces 52, 62, 72, and 82 of similar labels 50, 60, 70, and 80. For example, a heat-activated adhesive applied to the back surface 52 of label 50 has the form of a regular array pattern 54 of hemispheric beads 56. A margin 58 separates the array pattern 54 from a periphery 59 of the label 50 so that upon melting, the beads 56 do not extend beyond the periphery 59 of the label 50 and so that upon die cutting individual labels 20 from a web 92 (shown in , 12, and 13), the cutters remain free of adhesive. Although shown as regularly spaced hemispheric beads 56 of similar size and shape, the adhesive elements of the array pattern 54 could be formed by one or more other shapes including ovals, crosses, or line segments and can vary in both size and distribution throughout the array pattern 54.
The externally activated adhesive 26 is applied to the back surface 62 of the label 60 shown in in three distinct annular zones 64, 65, and 66. Within the annular zones 64 and 66 near the top and bottom of the label 60, a heat-activated adhesive is applied as a continuous deposit of adhesive covering all or nearly all of the annular zones 64 and 66 without interruption. However, within the annular zone 65, which is straddled by the annular zones 64 and 66, a heat-activated adhesive is applied as a discontinuous deposit of adhesive in the form of elongated beads 68 similar to the crisscross pattern 28 of the label 10. The annular zones 64 and 66 containing patches of continuous adhesive provide for sealing the corresponding top and bottom portions of the label 10 to the outer wall surface 40 of the foam cup's peripheral wall 36. In addition, the corresponding portions of the front surface 16 of the label 10 remain smooth for purposes of stacking similar label-wrapped cups 14 together and for separating individual cups 14 from the stack. The adhesive patterns within the annular zones 64, 65, and 66 can also differ from one another in other ways such as by incorporating different combinations of continuous and discontinuous adhesive patterns or different types of discontinuous adhesive patterns. The sizes and number of annular zones can be varied, and the zones can subdivide the label 10 in other ways, such as zones that contain different adhesive patterns in different circumferential positions around the label-wrapped cup 14.
The back surface 72 of the label 70, as shown in , includes a discontinuous deposit of the heat-activated adhesive in the form of a distribution 74 of hemispheric beads 76 that varies in density between a top and bottom of the label 70. While the distribution 74, as shown, progressively increases in density towards the top of the label 70 other orientations and kinds of variation can also be used. For example, the variation in the density of the hemispheric beads 76 can increase toward the middle of the label 70 and progressively decrease towards both the top and the bottom of the label 70.
In addition to or as an alternative to avoiding wrinkles and improving the grip and insulating properties of the label-wrapped cups, such as the label-wrapped cup 14, deposits of the externally activated adhesive (e.g., a heat-activated adhesive) can be registered with some or all of the printing on the front surface of the labels to augment the printing or to produce other visual effects. For example, the back surface 82 of the label 80, as shown in , includes in addition to a regular crisscross pattern 84 of adhesive beads 86, a graphic pattern 88 intended to match or otherwise complement a graphic pattern such as the graphic illustration 24 appearing on the front surface 16 of the label 10. The graphic pattern 88 of adhesive renders the graphic illustration 24 more pronounced when viewed on the cup 14 and can also contribute to an apparent three-dimensional image. Other visual effects are also possible from registering the adhesive patterns with corresponding patterns of print, such as an angularly sensitive visual effect by registering the printing on the front surface of the label 80 with the expected undulation patterns of the labels 80 based on the spacing of the adhesive beads 86.
An in-line press 90, as shown in , is arranged for producing a succession of fixed length and width wrap-around labels 110 along a web 92 also shown in . Following an unwinder 94, one of more printing stations 96 apply multiple color graphics and text to an outer surface 98 of the web 92 in successive positions corresponding to front surfaces 112 of the labels 110. The printing stations 96 can be repetitive or variable printing stations including such repetitive printing processes as flexography, letterpress, lithography, rotogravure, and screen-printing, and such variable printing processes as inkjet, thermal transfer, and laser printing.
One or more adhesive patterning stations 100 apply an externally activated adhesive, such as a heat-activated adhesive, in a repeating pattern 114 to an inner surface 102 of the web 92 corresponding to a succession of back surfaces 116 of the labels 110. Similar repetitive format printers can be used for applying the adhesive patterns 114. Preferably, a fixed length and a fixed width of the adhesive pattern 114 is less than the fixed length and width of the labels 110 to leave a surrounding margin that recesses the adhesive pattern 114 from peripheries 118 of the labels 110. Although not shown, an additional applicator station could be used to apply a barrier layer to the inner surface 102 of the web 92 between the back surfaces 116 of the labels 110 and the adhesive patterns 114 to prevent the ingress of discolorants or other visual or structural impairments into the labels 110. Alternatively, the inner surface 102 of the web 92 could be pretreated with a similar barrier layer.
The adhesive patterning stations 100 are registered with the printing stations 96 in a conventional manner by relating the printing and adhesive stations 96 and 100 to each other or to the common web 92. One or more die cutting stations 104 provide for trimming the web 92 to a desired width and for partly forming the peripheries 118 of the labels 110, such as by cutting out the top and bottom profiles of the labels 110. A rewinder 106 rewinds the in-line processed web 92 for delivery to a label applicator machine for applying the labels 110 to a succession of foam cups 12. Such applicators are known in the art, such as disclosed in U.S. Pat. No. 4,332,635 to Holbrook et al., which patent is hereby incorporated by reference in all relevant and consistent respects.
Preferably, the externally activated adhesive is a heat-activated adhesive, but other forms of externally activated adhesive could also be used having limited tackiness prior to activation for obviating the need for a release liner. For example, the adhesive patterns can be formed from solvent-activated adhesives, moisture-activated adhesives, or light-activated adhesives.
The invention relates to pressure sensitive adhesives. The invention also relates to the use of pressure sensitive adhesives in the manufacture of pressure sensitive adhesive articles and other types of articles, including but not limited to impact resistant articles, prepared using the adhesive or pressure sensitive articles of the invention. The pressure sensitive adhesive used in the practice of the invention is prepared by combining a silane-functional polymer and an acrylic polymer. The compositions of the invention have properties that make them particularly well suited for end use applications requiring high impact resistance.
Typical acrylic pressure sensitive adhesive formulations are copolymers of alkyl ester monomers, a functional monomer such as acrylic acid, and may be crosslinked using, for example, aluminum or titanium chelates. These adhesives may be further tackified to improve adhesion on different types of substrates, although usually with limitations in resistance to degradation and aging for most graphics and industrial tape applications in which acrylic solutions are conventionally used.
U.S. Pat. Appl. No. 2005/0142357 discloses a high strength pressure sensitive adhesive comprising a blend of a cross-linked liquid polymer, at least one tackifying resin which is compatible with the liquid polymer, and at least one resin which is incompatible or at least partially incompatible with the liquid polymer. Although the formulated products described in this disclosure provide very high performance at ambient temperature, their high temperature performance will be limited by the Tg of the incompatible phase.
U.S. Pat. No. 5,625,005, No. 6,642,298 and No. 6,670,417 disclose hybrid rubber-acrylic pressure sensitive adhesives described as having good UV resistance and aging characteristics along with high adhesion to non-polar surfaces.
Despite these advancements in the art, there continues to be a need for high performance pressure sensitive adhesives having high adhesion and heat resistance properties that are able to meet higher requirements in applications such as industrial tapes and transfer films. There is also a need for a pressure sensitive product with extremely good performance in other areas, such as impact resistance, that can be used to prepare articles, such as glass/plastic laminates, that will pass the UL-972 Testing for Burglary Resistant Glazing Materials standard. The present invention addresses these needs.
The invention provides adhesive formulations having outstanding adhesion properties. These performance properties are maintained at high impact speed in their dried state. The invention provides the art with pressure sensitive adhesives that will pass the UL-972 standard when used to bond glass to plastic. The invention also provides the art with pressure sensitive adhesive articles and articles prepared using the pressures sensitive adhesive and articles of the invention, such as high impact resistant articles. Methods of making such articles, in particular articles that pass the UL-972 standard when used to bond a brittle or breakable substrate such as glass to a flexible substrate such as a plastic film are encompassed by the invention.
One embodiment of the invention is directed to articles, including impact resistant articles, manufactured using a pressure sensitive adhesive prepared by combining an acrylic polymer and a silane-functional polymer having a glass transition temperature of below −20° C. In one preferred embodiment, the pressure sensitive adhesive is prepared by combining an acrylic polymer and a silane-functional polymer that contain —Si(CxH2x-1)n(OCyH2y+1)3−n end groups where n is 0, 1 or 2, and x and y are independently integral numbers of from 0 to 12. In another preferred embodiment, the pressure sensitive adhesive prepared by combining an acrylic polymer and a silane-terminated polyurethane
In one embodiment, the acrylic polymer used in the practice of the invention is a pressure sensitive acrylic polymer. In another embodiment the acrylic polymer used in the practice of the invention is one that does not itself contain silane functional groups. In yet another embodiment, the acrylic polymer used in the practice of the invention is prepared from monomers comprising (i) acrylate monomers, homopolymers of which have a glass transition temperature less than 0° C., which acrylate monomers contain from about 4 to about 18 carbon atoms in the alkyl group and (ii) monomers, homopolymers of which have a glass transition temperature greater than 0° C. Monomers used to prepare the acrylic polymer may also desirably include acid containing monomers and/or hydroxy containing monomers. In one embodiment, the acid functional monomer is acrylic acid. Useful acrylic polymers include, for example, acrylic polymers prepared from 2-ethyl hexyl acrylate, acrylic acid, and vinyl acetate or methyl acrylate. In one preferred embodiment, the acrylic polymer comprises 2-ethyl hexyl acrylate, methyl acrylate and acrylic acid.
Encompassed articles include articles comprising a glass substrate bonded to a plastic film. In one preferred aspect, the plastic film is a plastic laminate. Impact resistant glass laminates used, for example in windows, doors, partitions, picture glass, show case panels, and storefronts are included.
Another embodiment of the invention is directed to methods of preparing articles or products having high impact resistance. The method comprising applying a pressure sensitive adhesive to at least a first substrate, the pressure sensitive adhesive prepared by combining an acrylic polymer and a silane-functional polymer, and bringing at least a second substrate in contact with the adhesive applied to the first substrate. The substrates may be the same or different. In one embodiment, both the first and the second substrates are both transparent and clear.
High impact resistant articles/products include impact resistant laminates, in particular laminates made by bonding a brittle or breakable surface to a flexible facestock. Nonlimiting examples of high impact resistant articles prepared using the method of the invention include windows for homes, storefronts such as convenience stores, automobiles, and sliding glass doors, LCD displays, display cabinets, and the like.
Preparation of High Impact Resistance Products Using the Method of the Invention provides the art with a method of preparing burglary resistant products, such as high impact resistant windows, doors and show cases, that will pass the UL-972 testing standard. High impact products comprising a glass substrate bonded to a plastic substrate such as a polyester film. The plastic films used may desirably be plastic film laminates bonded together, preferably, with the adhesive of the invention. In one embodiment the laminate comprises two glass substrates and one or more interlays of a plastic film. Such may be used in the manufacture of windows, doors, partitions, show case panels, storefronts and the like.
The invention also provides the art with novel pressure sensitive adhesives.
In one embodiment, the adhesive of the invention is prepared by combining a pressure sensitive acrylic polymer with a silane-functional polymer.
In another embodiment, the adhesive of the invention is prepared by combining an acrylic polymer with a silane-functional polymer, wherein the acrylic polymer used lacks silane-functional groups.
In still another embodiment, the adhesive of the invention is prepared by combining an acrylic polymer with a silane-functional polymer, wherein the silane-functional polymer is a silane terminated polyurethane.
The pressure sensitive adhesives of the invention may be used to prepare pressure sensitive articles such as tapes and labels, and, as described above, may advantageously be used to laminate a breakable substrate, such as glass, to flexible facestock material, such as a plastic film to prepare impact resistant glass laminates.
The novel pressure sensitive adhesives of the invention may advantageously be used in the manufacture of adhesive articles including, but not limited to, industrial tapes and transfer films. Single and double face tapes, as well as supported and unsupported free films are encompassed by the invention. Also included, without limitation, are labels, decals, name plates, decorative and reflective materials, reclosable fasteners, theft prevention and anti-counterfeit devices. The adhesive and adhesive articles may advantageously, as described above, be used to prepare other types of articles, including but not limited to articles requiring impact resistance.
The disclosures of all documents cited herein are incorporated in their entireties by reference.
As used herein, the term “pressure-sensitive adhesive” refers to a viscoelastic material which adheres instantaneously to most substrates with the application of slight pressure and remains permanently tacky. A polymer is a pressure-sensitive adhesive within the meaning of the term as used herein if it has the properties of a pressure-sensitive adhesive per se or functions as a pressure-sensitive adhesive by admixture with tackifiers, plasticizers or other additives.
An accepted quantitative description of pressure sensitive polymers and adhesives is given by the “Dahlquist Criterion” that relates modulus data to tack-temperature studies. Materials that have a storage modulus (G′) of less that about 3×105 Pascal (measured at 10 radians/second at a temperature of about 20° C. to about 22° C.) have pressure sensitive adhesive properties. A second criterion for pressure sensitivity is that the glass transition temperature of the material be below the use temperature, which is usually room temperature. Generally, the Tg will be about 30 to 70° C. below room temperature, depending on the base polymer and any added modifiers. See, Everaerts and Clemens, Chapter 11, “Pressure sensitive adhesive” In: Adhesion Science and Engineering—2, Surfaces, Chemistry and Applications, Eds., Chaudhury and Pocius, pp. 466.
It has been discovered that certain types of adhesives, when used in the manufacture of glass/plastic laminates, produce laminates that show a minimum amount of delamination of a glass substrate from a polyester facestock following impact. The pressure sensitive adhesive used in the practice of the invention bonds strongly under a very high speed delamination process, i.e., about 0000× fold higher than regular peeling test speed of 12″/min. Current pressure sensitive adhesive products used for this application do not give satisfactory results when tested by the UL-972 standard.
The adhesive polymer used in the practice of the invention is prepared by combining an acrylic polymer and silane-functional polymer. In one embodiment, the acrylic polymer is a pressure sensitive adhesive polymer. In another embodiment, the acrylic polymer is a non-silylated acrylic polymer. In one embodiment the silane-functional polymer is a silane terminated polyurethane. In another embodiment, the silane-functional polymer is a polymer that comprise a silane or silyl end group represented by Si(CxH2x+1)n(OCyH2y−1)3−n, wherein n=0, 1 or 2; and x and y are, independently, integral numbers from 1 to 12, linked to a polymer backbone.
The acrylic polymer backbone used in the practice of the invention may be formed by polymerizing acrylate monomers of one or more low glass transition temperature (Tg) alkyl acrylates. Low Tg monomers are those having a Tg of less than 0° C. Preferred alkyl acrylates which may be used to practice the invention have up to about 18 carbon atoms in the alkyl group, preferably from about 4 to about 10 carbon atoms in the alkyl group. Useful alkyl acrylates include butyl acrylate, amyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, isooctyl acrylate, decyl acrylate, dodecyl acrylates, isomers thereof, and combinations thereof. One preferred alkyl acrylate for use in the practice of the invention is 2-ethyl hexyl acrylate.
The monomer system used to make the acrylic backbone polymer may include high Tg monomers (i.e., a Tg greater than 0° C.) and may also include functional comonomers, in particular carboxy-containing functional monomers and/or hydroxy-containing functional monomers.
High Tg monomer components include vinyl acetate, methyl acrylate, ethyl acrylate, isobutyl methacrylate and combinations thereof. The high Tg monomers may be present in a total amount of up to about 50% by weight, preferably from about 5 to about 50% by weight, more typically from about 10 to about 40% by weight, based on total weight of the acrylic polymer.
As described above, the acrylic backbone polymer may also comprise one or more functional monomers. Preferred are carboxy and/or hydroxy functional monomers. While the acrylic polymer may itself contain silane-functional groups, in one embodiment, the acrylic polymer used to prepare the adhesive does not contain silane-functional groups.
Carboxy functional monomers, when used, will typically be present in the polymer in an amount of up to about 10% by weight, more typically from about 1 to about 6% by weight, based on the total weight of the monomers. Useful carboxylic acids preferably contain from about 3 to about 5 carbon atoms and include acrylic acid, methacrylic acid, itaconic acid, and the like. Acrylic acid, methacrylic acid and mixtures thereof are preferred.
Hydroxy functional monomers include hydroxyalkyl (meth)acrylate esters, and acrylic polymers used to form the backbone of the invention are preferably acrylic ester/hydroxy (meth)alkyl ester copolymers. Specific examples of hydroxy functional monomers include hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate and hydroxypropyl methacrylate. When used, hydroxy functional monomers will generally be present in an amount of from about 1 to about 10%, preferably from about 3 to about 7%.
Other comonomers can be used to modify the Tg of the acrylic polymer, to further enhance adhesion to various surfaces and/or to further enhance high temperature shear properties. Such comonomers include N-vinyl pyrrolidone, N-vinyl caprolactam, N-alkyl (meth)acrylamides such as t-octyl acrylamide, vinyl esters such as vinyl neodecanoate, cyanoethylacrylates, diacetoneacrylamide, N-vinyl acetamide, N-vinyl formamide, glycidyl methacrylate and allyl glycidyl ether.
The monomer proportions of the acrylic polymer will typically be adjusted in such a way that the backbone polymer has a glass transition temperature of less than about −10° C., and more preferably from about −20° C. to about −60° C.
In one particularly preferred embodiment the acrylic polymer is prepared using 2-ethylhexyl acrylate or similar low Tg acrylic monomer, vinyl acetate or similar high Tg monomer, and also a carboxylic acid functional monomer such as acrylic acid or hydroxy functional monomer such as hydroxyethyl acrylate.
Silane functional polymers that may be used in the practice of the invention will preferably have a molecular weight range of from about 2,000 to about 100,000. In one embodiment the silane functional polymers will have a glass transition temperature of about −20° C. or less, as determined by differential scanning calorimetry (DSC) using a scan rate of 20° C./min and taking the inflection point of the baseline shift as the measure of Tg. In another embodiment the silane-functional polymers have a glass transition temperature of about −30° C. or less, as determined by DSC. In yet other embodiments the silane-functional polymers will have a glass transition temperature of from about −50° C. to about −70° C. or less, as determined by DSC. The silane-functional polymers will typically be present in an amount of from about 1 to about 95 percent by weight of the adhesive polymer of the invention, preferably from about 5 to about 50%, and more typically from about 10 to about 30% by weight.
Useful silane functional polymers include silane-terminated polyurethanes. Silane-terminated polyurethanes that can be used in the practice of the invention may be obtained, for example: (i) from the reaction of an isocyanto-terminated polyurethane prepolymer with an organofunctional silane containing active hydrogens, such as an amino-silane, that can react with isocyanate and thus link to the prepolymer; (ii) from the reaction of a polyol with an isocyanatosilane; and (iii) from the reaction of a hydroxyl terminated polyurethane prepolymer with an isocyanatosilane. (The starting polyurethane prepolymers with hydroxyl or isocyanato termination are obtained by reacting polyols with polyisocyanates using an excess of equivalents of hydroxyl or isocyanate groups respectively.) Mixtures of (i) and/or (ii) and/or (iii) may also be used in the practice of the invention.
Suitable polyols that can be used to make the silane terminated polyurethanes include polyoxyalkylene diols (especially polyethylene glycol, polypropylene glycol, polytetramethylene glycol), polyoxyalkylene triols, polycaprolactone diols and triols, and the like. Other polyol compounds, including tetraols thereof, may also be used, including pentaerythritol, sorbitol, mannitol and the like. Preferred polyols used in the present invention are polypropylene glycols with equivalent weights in the range of from about 500 to about 50,000; preferably, between about 2000 and 30,000. Mixtures of polyols of various structures, molecular weights and/or functionalities may also be used.
Suitable polyurethane prepolymer intermediates include any from polyurethane polymers that can be prepared by the chain extension reaction of polyols with diisocyanates. Useful diisocyanates include, for example, 2,4-toluene diisocyanate; 2,6-toluene diisocyanate; 4,4′-diphenyl-methanediisocyanate; isophorone diisocyanate; dicyclohexylmethane-4,4′-diisocyanate; various liquid diphenylmethanediisocyanates containing a branch or a mixture of 2,4- and 4,4′ isomers and the like, and mixtures thereof.
Silane endcappers suitable for endcapping of isocyanate terminated urethane prepolymers are represented by the general formula:
wherein R is a divalent alkylene group; R′ is alkyl or aryl, preferably having from 1 to 8 carbon atoms, X is a hydrolyzable alkoxy, or alkyloximido group, preferably having from 1 to 4 carbon atoms; and n is an integer from 1 to 3. Group R″ is an organo-functional group, which can react with either isocyanato or hydroxyl terminated polymers, such as isocyanato, primary or secondary hydroxyl, amino, mercapto, or ureido functional groups.
A more detailed description of methods to prepare silane terminated polyurethane may be found in U.S. Pat. No. 6,197,912 and U.S. Pat. Appl No. application 2006/0142532. Silane-terminated polyurethanes are commercially available from chemical companies such as Bayer, Wacker, Momentive Performance Materials Inc. and Henkel Co and KGaA.
Other useful silane functional polymers are polymers that comprises a silane or silyl end group represented by Si(CxH2x+1)n(OCyH2y+1)3−n, wherein n=0, 1 or 2; and x and y are, independently, integral numbers from 1 to 12, linked to a polymer backbone, whose backbone composition include, but is not limited to, polyether, aliphatic polyolefin, polyacrylate, polyurethane, EVA, SBS, SIS. Examples of end groups include, but are not limited, to trimethoxy —Si(OCH3)3, triethoxy-Si(OC2H5)3, methyl dimethoxy-Si(CH3)(OCH3)2 etc. These types of silane-functional polymers, such as SAX 725 and MAX 951, are commercially available from Kaneka Co.
Preferred for use are adhesive compositions that have been crosslinked using a chemical crosslinking agent. The use of aluminum crosslinking agents may be used to practice the invention. Titanium containing metal alkoxide may also be used as crosslinking agent. The crosslinker is typically added in an amount of from about 0.3% to about 2% by weight of the polymer in final product.
The adhesive compositions used in the practice of the invention may, optionally, be tackified. Tackifiers that are compatible with the acrylate polymer can be used. Non-limiting examples include polar tackifiers such as terpene phenolics such as Sylvares TP300 and TP96, and rosin esters such as Sylvalite RE80HP, etc., all available from Arizona Chemical Co. Non-polar tackifier may also be used to improve adhesion on low surface energy substrate. The tackifying resin will normally be present at a level of 0 to 60% by weight of the adhesive composition.
The formulated adhesive may also include, diluents, plasticizers, antioxidants, UV stabilizers, adhesion promoters, anti-irritants, fillers, such as clay and silica, pigments and mixtures thereof, excipients, preservatives, as well as other components or additives.
In one preferred embodiment, the adhesive is prepared by combining a silane-functional polymer and an acrylic polymer prepared using 2-ethylhexyl acrylate or similar low Tg acrylic monomer, vinyl acetate or similar high Tg monomer, and preferably also a carboxylic acid functional monomer or hydroxy functional monomer such as acrylic acid or hydroxyethyl acrylate.
The pressure sensitive adhesives described herein may advantageously be used in the manufacture of adhesive articles including, but not limited to, industrial tapes and transfer films, including both single and double face tapes, as well as supported and unsupported free films. Also included, without limitation, are labels, decals, name plates, decorative and reflective materials, reclosable fasteners, theft prevention and anti-counterfeit devices. Articles requiring impact resistance may advantageously be manufactured using the described pressure sensitive adhesive as a laminating adhesive to bond breakable or otherwise brittle substrates such as glass to flexible substrates made of, e.g., polymer films such as polyvinyl butylral (PVB), polypropylene, polyamide and polyester. Included are LCD displays, plate glass for use in windows, doors, partitions and the like for commercial and residential uses. The adhesive is advantageously used in end use applications where the manufacture article is subjected to vibration, stress or is vulnerable or prone to impact.
The invention provides laminated glass panels and panes that are able to pass the Underwriters Laboratory test standard UL 972. This test considers the ability of a laminated glass to resist burglary or forced entry (e.g., “smash and grab” type burglaries). The test consists of dropping a 3.25 inch, 5 lb (2.25 kg) steel ball through a designated vertical distance onto a sample measuring 24 in by 24 in (61 cm×61 cm). Resistance is determined by whether the steel ball, after 5 impacts per sample, is able to penetrate the laminate. It will be appreciated that when impacted or otherwise or attacked, the glass unit will crack. The structural integrity once the glass is cracked becomes dependent on the plastic layer of the laminate. In one preferred embodiment, the polymer film used will be a plastic film laminate of 2 or more film layers, more preferable 3 or more film layers bonded together using the adhesive of the invention. Individual films within the film laminate may be of the same, or may be of different thicknesses. Individual films used to prepare the film laminate will generally range from about 2 to about 10 mils. The adhesive will typically be applied in the 0.5 mil to 3 mils range.
While glass laminates are tested and rated in the industry by Underwriters Laboratory according to standards set forth in UL-972, in the following test examples impact resistance was measured by a Pendulum Impact Tester using the procedure described below.
In the following examples, the following adhesive test methods were used.
Preparation of Coatings:
The adhesive solutions were cast on a silicone coated release liner, air dried for 15 minutes, and then dried for 3 minutes at 250° F. in a forced air oven. The films were then laminated to a backing film and conditioned overnight at 22° C. and 50% relative humidity. Unless otherwise indicated the dried adhesive film thickness was 1 mil (25 microns) and the backing film was 2 mil PET (polyethylene terephthlate) film.
Peel adhesion at 180° between the backing and the adherend test panel was measured according to Test Method number 1 of the Pressure Sensitive Tape Council (PSTC), Northbrook, Ill., adapted as follows. The peel strength was measured after wetting out a stainless steel (SS) test panel for 20 minutes or as otherwise indicated. The testing was also carried out on high density polyethylene (HDPE) test panels. Unless otherwise indicated, all testing was performed at 22° C. and 50% relative humidity.
Shear Holding Power:
Shear holding power was measured according to PSTC Test Method number 7, adapted as follows. The holding power was measured under a shear load of 1 kg on a 0.5 inch wide by 1 inch long area, applied after wetting out the test panel for 15 minutes. Unless otherwise indicated, all testing was performed at 22° C. and 50% relative humidity.
Shear Holding was also measured at elevated temperature conditions. 5 lb weight with 1″×1″ overlap area. Samples conditioned at 150° F. for 15 minutes before applying weight.
As noted above, the industrial standard, UL 972 for Burglary Resisting Glazing material, consists of multiple impact tests wherein a 5 lb steel ball is dropped onto 2′×2′ laminated glass substrate over different distances (8-40 feet) and under different temperatures (−10 to 49° C.).
The ideal pressure sensitive adhesive (PSA) adhesive used in this laminate will lead to minimum amount of delamination of glass from polyester facestock. This requirement translates into a strong bonding of PSA under very high speed delamination process, about 10000× fold higher than regular peeling test speed of 12″/min.
To screen the impact resistance of PSA, a Pendulum Impact tester, with a 2.5 lb metal ball dropping in pendulum motion over 2 feet in perpendicular distance. The laminated glass test panel consisted of 0.25 inch thick glass bonded with the adhesive sample to a PET laminate consisting of three films bonded together with the same adhesive sample. The percentage of PET film delaminated from glass plate was measured after the collision, less of which indicates a better impact resistance of the product. Broken glass pieces that remained attached to PET film, with minimum amount of delamination taking place had better impact resistance.
The following abbreviations are in the Examples and Tables.
- 2-EHA: 2-ethylhexyl acrylate
- MA: methyl acrylate
- VAc: vinyl acetate
- Veova-10: vinyl neodecanoate
- AA: acrylic acid
- GMA: glycidyl methyacrylate
- Silquest A-187: γ-glycidoxypropyltrimethoxysilane
- Spur+1050 mM: silylated polyurethane resin based on polypropylene glycol from Momentive Performance Materials Inc.
- Max 951: a silyl-terminated polyether with silyl-modified acrylics from Kaneka Co.
- Al(acac)3: aluminum acetylacetonate
- SAX 725: silyl terminated polyether from Kaneka Co.
- Sylvares TP300: terpene phenolic tackifier resin from Arizona Chemical Co.
- AF: adhesive failure to substrate
- CF: cohesive failure
- SS: stainless steel substrate
An initial charge mixture containing 8.95 g 2-ethylhexyl acrylate (2-EHA), 19.14 g Vinyl Acetate (VAc), 0.57 g of Acrylic Acid (AA), 9.64 g ethyl acetate (EtOAc), 13.06 g heptanes (a standard mixed isomer grade), and 0.048 g azobis(isobutyronitrile) (AIBN) was prepared and charged to a 3 liter 4-neck round bottomed flask equipped with stainless steel stirrer, thermometer, condenser, water bath, and slow addition funnels. The initial charge was heated to reflux while stirring. After 10 minutes at reflux a monomer mix containing 62.38 g 2-EHA, 8.94 g Acrylic Acid and an initiator mix containing 5.93 g EtOAc, 7.62 g heptanes, 0.24 g AIBN were simultaneously, separately, and uniformly added over a period of 2 hours and 3 hours, respectively. At the end of the additions the flask contents were held at reflux for a further 2 hours. Next the residual monomers were scavenged using a short half-life initiator added over a one hour period and the solution was held under reflux for a further hour. Then diluent consisting of 28.30 g Heptanes, 43.15 g of Isopropanol (IPOH) and 10.66 g of Xylene were slowly added to the reactor contents while cooling the contents to room temperature. The polymer solution maintained a fluid viscosity throughout the process and showed no tendency to climb the reactor stirring shaft.
The polymer solution had a solids content of 43.18% and a Brookfield viscosity of 2924 cps. The molecular weight averages, determined by gel permeation chromatography, were Mw=422,349 and Mn=82,098.
Acrylic polymer samples B-F were prepared in a similar way as sample A. Samples A-F were used as base polymers to make the adhesive formulations, the composition in percent by weight and physical properties of the acrylic polymer samples are shown in Table 1.
This example described the performance improvements in peel adhesion and shear holding when using an adhesive formulation made by combining a silane functional polymer and an acrylic polymer. SPUR+ 1050 mM and Spur+ 1015 LM, available from Momentive Performance Materials Inc., are organofunctional silane terminated polyurethane prepolymers. In Table 2, formulation A-1 served as control and comprised of 100 parts of acrylic polymer A and 0.6 part of Al(acac)3 as crosslinking agent and coated as described above. Its peel adhesion after 20 min dwell time on stainless steel substrate was 73.7 oz/in, with hot shear holding of 0.21 hour. In formulation A-2, 100 parts of polymer A were combined with 10 parts of silane functional polymer Spur+1050 mM with 0.4 part of Al(acac)3 as crosslinking agent and coated as described above. Its peel adhesion after 20 min dwell time on stainless steel substrate was 80 oz/in, with hot shear holding of 0.6 hour. These values were significantly better than those of formulation A-1. Similar results were obtained using formulation A-3.
Similarly, formulation B-1 served as control and comprised of 99.65 parts of acrylic polymer B and 0.35 part of Al(acac)3 as crosslinking agent and coated as described above. Its peel adhesion after 20 min dwell time on stainless steel substrate is 64.4 oz/in, with hot shear holding of 7.4 hours. In formulation B-2, 54.65 parts of polymer B were combined with 20 parts of Spur+1050 mM with 0.35 part of Al(acac)3 as crosslinking agent, 50 parts of Sylvares TP300 as tackifier and coated as described above. Its peel adhesion after 20 min dwell time on stainless steel substrate was 92.4 oz/in, significantly better than those of formulation B-1. Similar results were obtained using formulation B-3 where silane functional polymer SAX 725 from Kaneka Co. was used to combine with polymer B.
Different approaches were used in order to improve the impact resistance, including using more low Tg monomer as comonomer, adding polar functional monomer to increase specific adhesion, adding functional monomer, etc. The composition of acrylic Samples C to F are shown in Table 1. These polymers were formulated with Al(acac)3 crosslinker as A-1, and tested with their performance shown in Table 3.
Acrylic sample C was used as the control product. Batches D-F were modifications based on the control sample. In spite of better peel adhesion shown by these polymers in comparison to the control C, none of them gave significant improvement in pendulum screening test as indicated by large percentage of glass delamination after the collision.
Low Tg silane-terminated polyurethanes Spur+1050MM and 1015LM were combined with control polymer C. The amounts are shown in Table 4 (parts per hundred), along with performance in pendulum screening test and peel, shear results.
From the results shown in Table 4, it can be seen that by combining these silane-functional polymers with an acrylate pressure sensitive adhesive polymer, impact resistance was greatly improved (2-5% glass delamination compared to −20% delamination of control product). Peel results at 20 minutes decreased to various degrees, but increased to a level comparable to control over time. Also the shear holding results increased to an extraordinarily high level.
Many modifications and variations of this invention can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. The specific embodiments described herein are offered by way of example only, and the invention is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled.