Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1995-10-25
2001-06-19
Copenheaver, Blaine (Department: 1771)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S3550RA, C428S3550AC
Reexamination Certificate
active
06248438
ABSTRACT:
The present invention relates to a method for preparing a pressure sensitive paper label. In particular, the method of the present invention produces a label from paper filled with inorganic filler containing multivalent cation. The filled paper label of the present invention resists deterioration of the label's adhesive strength, which is known in the industry as age-resistance. Age-resistant pressure sensitive paper labels prepared by the method of the present invention may be applied to a wide variety of substrates.
Age-resistance is the ability of a label to retain adhesive strength over time. Loss of adhesive strength results in a label that may not stick to a substrate or may easily fall off after being applied to a substrate. Age resistance is particularly a problem in labels made from filled paper having inorganic fillers which contain multivalent cation. Paper having inorganic fillers, such as clay and calcium carbonate, is finding increasing use in the label industry due to its lower cost. Unfortunately, the increasing use of filled paper makes the associated age-resistance problem an increasing concern.
One attempt to improve the age-resistance of filled paper is disclosed in Japanese patent application J 03-265678A by Hori, et al. (“Hori”). Hori discloses that the problem of age-resistance is attributed to crosslinking of carboxylic acid groups in the polymer adhesive by cations in the filler. This crosslinking reduces the adhesive strength of the label adhesive. Hori discloses minimizing the age-resistance problem by reducing the level of carboxylic acid in the pressure sensitive adhesive polymer to between 0.1-1.0% by weight. Unfortunately, reducing the level of carboxylic acid has two disadvantages. First, the lower level of carboxylic acid only reduces, rather than eliminates the cross-linking problem, and second, the lower level of carboxylic acid reduces the polymer stability.
Carboxylic acid groups are added into an emulsion polymer to help stabilize the polymer. Reducing the level of carboxylic acid correspondingly reduces the stability of the composition. To compensate for the decrease in stability, Hori, discloses adding a water soluble acrylic resin to the composition.
The present invention has overcome the problem of age-resistance on filled paper by eliminating carboxylic acid groups from the adhesive composition, without requiring additional stabilizers. We have found that age-resistant, filled-paper labels can be prepared using a stable copolymer made from selected acid monomers. Filled paper labels prepared by the method of the present invention are useful for application to various substrates such as paper, glass, metal, cardboard, wood, corrugated board and plastic.
In a first aspect of the present invention, there is provided a method for preparing a paper label comprising:
a) forming a copolymer comprising, as polymerized units:
1) from 0.1 percent to 5 percent by weight of an acid monomer or monovalent salts thereof, said acid monomer being selected from the group consisting of vinyl sulfonic acid, methallyl sulfonic acid, phosphoethylmethacrylate, (meth)acrylate sulfonic acid, acrylamido alkyl sulfonic acid, N-(2-sulfo-1,1-dimethylethyl)acrylamide, 2-acrylamido-2-methylpropanesulfonic acid and mixtures thereof; and
2) from 99.9 percent to 95 percent by weight of at least one ethenically unsaturated monomer;
wherein the glass transition temperature of said copolymer is in the range of from 0° C. to −80° C.; wherein said copolymer has a molecular weight in the range of from 5,000 to 10,000,000;
b) formulating said copolymer into an adhesive composition; and
c) applying said adhesive composition to a paper label comprising inorganic filler to form a pressure sensitive adhesive label; wherein said inorganic filler comprises multivalent cation.
In a second aspect of the present invention, there is provided a pressure sensitive adhesive composition comprising a copolymer comprising, as polymerized units:
a) from 0.1 percent to 5 percent by weight of an add monomer, or monovalent salts thereof, said acid monomer being selected from the group consisting of sodium vinyl sulfonate, sodium methallyl sulfonate, phosphoethylmethacrylate, and mixtures thereof; and
b) from 99.9 percent to 95 percent by weight a second monomer comprising at least one ethenically unsaturated monomer; wherein said copolymer has a glass transition temperature in the range of from 0° C. to −80° C.; and wherein said copolymer has a molecular weight in the range of from 5,000 to 10,000,000.
In a third aspect of the present invention, there is provided an article comprising a filled paper basestock coated on at least one side with a pressure sensitive adhesive composition.
The present invention provides a method for preparing a paper label from paper filled with inorganic fillers using an adhesive composition containing a copolymer made from selected monomers.
Copolymer
The adhesive composition of the present invention contains a copolymer of at least one selected acid monomer and at least one ethenically unsaturated monomer. As used herein, “(meth)acrylate” shall mean either acrylate or methacrylate. “Alkyl” herein shall mean either straight chain or branched carbon groupings having in the range of from one to twenty carbon atoms.
Selected acid monomers, and mixtures of those acid monomers, are useful in the present invention. “Acid monomer” as used herein includes the acid monomer as well as monovalent salts of the monomer. Selected acid monomers resist crosslinking by multivalent cation when incorporated into a copolymer. Selected acid monomers useful in this invention include vinyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, phosphoethylmethacrylate, (meth)acrylate sulfonic acid, acrylamido alkane sulfonic acid, N-(2-sulfo-1,1-dimethylethyl)acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid. Monovalent salts useful in this invention are preferably lithium, sodium, potassium, rubidium and cesium salts, more preferably sodium and potassium salts and most preferably sodium salts such as, for example, sodium vinyl sulfonate, sodium styrene sulfonate, and sodium methallyl sulfonate.
The copolymer of this invention contains from 0.1 percent to 5 percent of the acid monomer by weight of the copolymer, and preferably from 0.2 percent to 4 percent acid monomer by weight of the copolymer. The use of lower levels of acid monomer results in a loss of latex polymer stability in water. Higher levels of acid monomer result in excessive thickening during polymerization.
The polymers of this invention are copolymers of the acid monomer and at least one ethenically unsaturated monomer. The ethenically unsaturated monomer is present in the polymer at 99.9% to 95% by weight. Examples of useful ethenically unsaturated monomers include simple olefins such as ethylene, alkyl (meth)acrylates where the alkyl group has 1 to 20 carbon atoms (preferably 1 to 12 carbon atoms), vinyl acetate, acrylonitrile, styrene, isobornyl methacrylate, acrylamide, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, N-vinyl pyrolidinone, butadiene, isoprene, vinyl halides such as vinyl chloride and vinylidene chloride, alkyl maleates, and alkyl fumarates.
Generally, the polymer of the present invention is prepared by means known in the art, such as dispersion or emulsion polymerization in water. Preferably, the copolymer is prepared by aqueous emulsion polymerization using a suitable free radical initiator and appropriate heating. Conventional dispersants may be used at levels in the range of from 0.1 percent to 6 percent by weight based on the weight of total monomer. Initiation can be by either thermal or redox initiation using conventional free radical initiators such as, for example, hydrogen peroxide, organic hydroperoxides, and organic peroxides, at levels of from 0.05 percent to 3.0 percent by weight based on the weight of total monomer. Frequently, a low level of chain transfer agent such as, for example, a mercaptan at 0.05 percent to 6 percent by weight based on
Ho Kim Sang
Pierson Don Gordon
Copenheaver Blaine
Greenblatt Gary D.
Rohm and Haas Company
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