Stock material or miscellaneous articles – Composite – Of addition polymer from unsaturated monomers
Reexamination Certificate
2000-06-28
2003-12-16
Harlan, Robert (Department: 1713)
Stock material or miscellaneous articles
Composite
Of addition polymer from unsaturated monomers
C526S319000, C526S326000, C526S329200
Reexamination Certificate
active
06663978
ABSTRACT:
FIELD OF INVENTION
This invention relates to pressure-sensitive adhesives. More particularly, this invention relates to pressure-sensitive adhesives having a high refractive index.
BACKGROUND OF THE INVENTION
Pressure-sensitive adhesives (“PSAs”) are defined herein as adhesives which exhibit permanent tack at room temperature. This property allows pressure-sensitive adhesives to adhere tenaciously upon application with only light finger pressure. PSAs have a balance of properties: adhesion, cohesion, stretchiness, and elasticity. Adhesion refers both to immediate adhesion to a surface and to the bond strength which develops upon application of pressure (often measured as “peel strength”). Cohesion refers to the “shear strength” or resistance of the applied PSA to failure when subjected to shearing forces. Stretchiness refers to the ability to elongate under low stresses. Elasticity refers to a property wherein the material exhibits a retractive force when stretched and retracts when the force is released.
Pressure-sensitive adhesives have many diverse applications including applications in optical products. For certain optical applications, it is useful to match the refractive index (RI) of the adhesive to that of the substrate to which it is applied. This matching of refractive index enhances the optical properties of the construction by reducing glare and reflectance. Glare is defined herein as the average reflectance over a range of 450-650 nanometers and reflectance is defined herein as the process where a fraction of the radiant flux incident on a surface is returned into the same hemisphere whose base is the surface and which contains the incident radiation (see Handbook of Optics, 2
nd
ed., McGraw-Hill, Inc., 1995). Often, the substrate is a polymeric material having refractive indexes in the range of 1.48 to 1.65, for example, polymethyl(meth)acrylate (PMMA) has a RI of 1.489; polycarbonate has a RI of 1.585; and polyethylene terephthalate (PET) has a RI of 1.64.
Known PSAs have RIs of about 1.47 or less. If these PSAs are used in optical applications, glare and reflectance may occur.
Therefore, the need exists for pressure-sensitive adhesives which have high refractive indexes.
SUMMARY OF THE INVENTION
The present invention provides pressure-sensitive adhesives which have a refractive index of at least 1.48. These pressure-sensitive adhesives are particularly suitable for optical applications where the substrate similarly has a high refractive index. The pressure-sensitive adhesives of the present invention advantageously allow for the matching of refractive index which reduces glare and reflectance.
The pressure-sensitive adhesives of the present invention comprise at least one monomer containing a substituted or an unsubstituted aromatic moiety.
One aspect of the present invention is a pressure-sensitive adhesive comprising the reaction product of: (a) at least one monomer selected from the group consisting of a monomeric acrylic or methacrylic acid ester of a non-tertiary alcohol, the alkyl group of which comprises from about 1 to about 12 carbon atoms, preferably from about 4 to about 8 carbons; and (b) at least one monomer containing a substituted or an unsubstituted aromatic moiety.
Another aspect of the present invention is a pressure-sensitive adhesive comprising the reaction product of: (b) at least one monomer containing a substituted or an unsubstituted aromatic moiety; and (c) at least one polar monomer copolymerizable with component (b).
Yet, another aspect of the present invention is a pressure-sensitive adhesive comprising the reaction product of: (a) at least one monomer selected from the group consisting of a monomeric acrylic or methacrylic acid ester of a non-tertiary alcohol, the alkyl group of which comprises from about 1 to about 12 carbon atoms, preferably from about 4 to about 8 carbons; (b) at least one monomer containing a substituted or unsubstituted aromatic moiety; and (c) at least one polar monomer copolymerizable with the monomer(s) of components (a) and (b).
The pressure-sensitive adhesives of the present invention may optionally comprise other monomers, crosslinkers, and additives.
Another embodiment of the present invention is a substrate coated with the pressure-sensitive adhesives of the present invention.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
The present invention relates to pressure-sensitive adhesives having a refractive index of at least 1.48. Preferably, the pressure-sensitive adhesives have a refractive index of at least 1.50.
The pressure-sensitive adhesives of the present invention have a high refractive index and yet have a good balance of the four properties relevant for pressure-sensitive adhesives: adhesion, cohesion, stretchiness, and elasticity.
Refractive index is defined herein as the absolute refractive index of a material (e.g., a monomer) which is understood to be the ratio of the speed of electromagnetic radiation in free space to the speed of the radiation in that material, with the radiation being of sodium yellow light at a wavelength of about 583.9 nanometers (nm). The refractive index can be measured using known methods and is generally measured using an Abbe Refractometer.
The pressure-sensitive adhesives of the present invention are acrylate adhesives comprising at least one aromatic monomer which is either substituted or unsubstituted. The pressure-sensitive adhesives may further comprise at least one acrylic monomer selected from the group consisting of a monomeric acrylic or methacrylic acid ester of a non-tertiary alcohol and/or at least one polar monomer. The pressure-sensitive adhesives of the present invention optionally comprise other monomers which may be added to improve the properties of the adhesives, such as crosslinkers, and other additives such as tackifiers or plasticizers.
Acrylic Monomers
The acrylic monomers useful in the pressure-sensitive adhesive of the present invention are typically present at ranges from about 0 to about 93 parts by weight. Useful acrylic monomers include at least one monomer selected from the group consisting of a monomeric acrylic or methacrylic acid ester of a non-tertiary alkyl alcohol, the alkyl group of which comprises from about 1 to about 12 carbon atoms, preferably from about 4 to about 8 carbon atoms, and mixtures thereof.
Suitable acrylic monomers include, but are not limited to, those selected from the group consisting of the esters of acrylic acid or methacrylic acid with non-tertiary alkyl alcohols such as 1-butanol, 1-pentanol, 2-pentanol, 3-pentanol, 2-methyl-1-butanol, 1-methyl-1-butanol, 1-methyl-1-pentanol, 2-methyl-1-pentanol, 3-methyl-1-pentanol, 2-ethyl-1-butanol, 2-ethyl-1-hexanol, 3,5,5-trimethyl-1-hexanol, 3-heptanol, 2-octanol, 1-decanol, 1-dodecanol, and the like, and mixtures thereof. Such monomeric acrylic or methacrylic esters are known in the art and are commercially available.
Aromatic Monomers
The following aromatic monomers are high refractive index acrylic monomers, preferably all of which have homopolymer glass transition temperatures at or below 50° C. These aromatic monomers, when polymerized alone or in the presence of other acrylic monomers, result in PSAs having RIs higher than are otherwise available. By adjusting the ratio of monomers, it is possible to make PSAs having RIs of at least 1.48.
The aromatic monomers of the present invention are represented by the following general Formula (I):
wherein:
Ar is an aromatic group which is unsubstituted or substituted with a substituent selected from the group consisting of Br
y
and (R
3
)
z
wherein y represents the number of bromine substituents attached to the aromatic group and is an integer from 0 to 3;
R
3
is a straight or branched alkyl of 2 to 12 carbons; and
z represents the number of R
3
substituents attached to the aromatic ring and is an integer from 0 to 1,
provided that both y and z are not zero;
X is either oxygen or sulfur;
n is 0 to 3, preferably n is 0 or 1;
R
1
is an unsubstituted straight or branched alkyl linking group of 2 to 12 carbons, pre
Fong Bettie C.
Lu Ying-Yuh
Moore Cheryl L.
Olson David B.
Williams Todd R.
3M Innovative Properties Company
Black Bruce E.
Harlan Robert
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