Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reissue Patent
1999-11-18
2002-02-26
Moore, Margaret G. (Department: 1712)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C523S221000, C524S460000
Reissue Patent
active
RE037563
ABSTRACT:
TECHNICAL FIELD
This invention relates to a microsphere adhesive and in particular to a microsphere adhesive that exhibits enhanced adhesion to substrates while remaining repositionable.
BACKGROUND OF THE INVENTION
Repositionable adhesives are commonly used for temporary messaging or signage in the home and office environment. This type of product is typified by Post-it® brand notes. When using such a product it is desired that the note adhere to a variety of surfaces yet be cleanly removable from the surface without leaving adhesive residue, while maintaining the repositionable characteristics of the notes.
References can be cited for the preparation and/or use of inherently tacky, polymeric microsphere adhesives (see for example, U.S. Pat. Nos. 3,691,140 and 4,166,152). Such microsphere adhesives are typically used for the commonly recognized repositionable notes.
Various investigators have sought to improve or further enhance adhesion to surfaces other than the commonly used paper surfaces. Various techniques have been used, such as chemical modification of the microsphere, alteration of the adhesive composition, including the use of binders and the like, or process modifications. For example, U.S. Pat. No. 5,053,436 describes a hollow microsphere, wherein the microsphere provides increased resistance to adhesive transfer and an increased adhesion level. Along the same line, U.S. Pat. No. 4,988,567 describes microspheres having multiple small voids.
In yet another attempt, U.S. Pat. No. 5,326,842 describes a dual polymerization process wherein high tack adhesives are produced wherein a chain transfer agent is used in the first step (suspension polymerization) and the second step (emulsion polymerization) provides stability of the final material.
However, to date, control of the solvent soluble portion of the microsphere to produce a stable repositionable microsphere adhesive with enhanced adhesion has not been contemplated.
SUMMARY OF THE INVENTION
Briefly, in one aspect of the present invention, a microsphere adhesive composition is provided comprising a 30-98% solvent soluble portion.
In particular, the present invention comprises a microsphere adhesive composition comprising:
(a) a plurality of polymeric, elastomeric microspheres wherein the microspheres are the reaction product of reactants comprising polymerizable starting materials comprising at least one C
4
-C
14
alkyl (meth)acrylate monomer and optionally at least one comonomer,
(b) optionally, a polymeric stabilizer in an amount of between about 0.1 and about 3 parts by weight per 100 parts by weight of the microspheres, preferably about 0.1 to about 1.5 parts by weight per 100 parts by weight of the microspheres;
(c) a surfactant in an amount of no greater than about 5 parts by weight per 100 parts by weight of the microspheres, preferably no greater than 3 parts by weight and most preferably in the range of 0.5 to about 1.5 parts by weight per 100 parts by weight of the microspheres;
(d) a modifier, wherein the modifier can be at least one of a chain transfer agent, a tackifier, a solvent or the like in an amount that is sufficient to provide microspheres with a solvent soluble portion in the range of 30-98%, preferably in the range of 40-95%; and
(e) an initiator present in amounts ranging from 0.1 to approximately 2 parts by weight per 100 parts by weight of the polymerizable monomer starting material.
As used in this application, the notation “(meth)acrylate” refers to acrylate and methacrylate.
A modifier may be used to regulate the solvent soluble portion of the microspheres and it is added to the polymerization mixture in an amount sufficient to provide a solvent soluble portion that is in the range of 30-98%, preferably in the range of 40-95%. Various modifiers may be used within the scope of this invention and the amounts used are those that sufficiently provide the microspheres with a solvent soluble portion. Such amounts would range, for example for solvents from 1-30%, for tackifiers from 1-30% and for chain transfer agents, up to about 0.15%.
Particularly useful modifiers are chain transfer agents. To control the molecular weight of the polymer being formed in the microsphere a chain transfer agent or modifier is used. Many halogen-and sulfur-containing organic compounds function well as chain transfer agents in free radical polymerizations. Non-limiting examples of such agents are: carbon tetrabromide, carbon tetrachloride, dodecanethiol, iso-octylthioglycolate, butyl mercaptan, and tertiarydodecyl mercaptan. Particularly useful chain transfer agents are long chain mercaptans, such as dodecanethiol. The amount of chain transfer agent suitable for microsphere polymerizations is calculated on a weight basis to the entire polymerizable content. The chain transfer agent is preferably added at up to about 0.15%, more preferably up to about 0.12% and most preferably up to about 0.08%. These levels are adequate to provide a solvent soluble polymer component in the microsphere of up to about 98%.
Other useful modifiers are solvents. Examples of which are but not limited to: aliphatic or aromatic solvents such as heptane, benzene, toluene and the like; alcohols such as methanol, isopropyl alcohol, and the like; and ketones such as acetone, methyl ethyl ketone and the like. The amount of solvent suitable for microsphere polymerizations is calculated on a weight basis to the entire polymerizable content. The solvent is preferably added at up to about 30%, more preferably up to about 15% and most preferably up to about 5%. These levels are adequate to provide a solvent soluble polymer component in the microspheres of up to about 98%.
Still other useful modifiers include tackifiers and/or plasticizers. Examples of which are but not limited to: hydrogenated rosin esters commercially available from such companies as Hercules, Inc. under the tradenames of Foral™, Regalrez® and Pentalyn™. Tackifying resins also include those based on t-butyl styrene. Useful plasticizers include but are not limited to dioctylphthalate, 2 ethylhexyl phosphate, tricresyl phosphate, mineral oil and the like. The tackifier and/or plasticizer are preferably added at up to about 30%, more preferably up to about 15% and most preferably up to about 5%. These levels provide a solvent soluble polymer component in the microsphere of up to about 98%.
In another aspect of the present invention a one step suspension polymerization process is provided for preparing polymeric elastomeric microspheres comprising the steps of:
(a) stirring or agitating a mixture comprising polymerizable monomer starting materials comprising:
(i) at least one C
4
-C
14
alkyl (meth)acrylate monomer and, optionally at least one comonomer;
(ii) an initiator for the polymerizable monomer starting materials present in amounts ranging from 0.1 to approximately 2 parts per weight per 100 parts by weight of the polymerizable monomer starting materials;
(iii) optionally, a polymeric stabilizer in an amount in the range of 0.1 to about 3 parts by weight per 100 parts by weight of the polymerizable monomer starting materials;
(iv) a surfactant in an amount no greater than about 5 parts by weight per 100 parts by weight of polymerizable monomer, preferably no greater than about 3 parts by weight and most preferably in the range of 0.5 to 1.5 parts by weight;
(v) water to form an oil in water suspension; and
(vi) a modifier in an amount sufficient to provide a solvent soluble portion in the range of 30-98%; and
(b) polymerizing the (meth)acrylate monomer(s) and the comonomer(s), if present; wherein microspheres are provided.
In yet another aspect, the present invention provides a two-step suspension polymerization process for preparing polymeric elastomeric microspheres from polymerizable monomer stating materials, wherein the process comprising the steps of:
(a) stirring or agitating a mixture comprising:
(i) at least one C
4
-C
14
alkyl (meth)acrylate monomer;
(ii) an initiator for the monomer present in amounts ranging from 0.1 to approximately 2 parts per weight per 100 par
Cooprider Terrence E.
Crandall Michael D.
Garbe James E.
Goetz Richard J.
Kesti Michael R.
3M Innovative Properties Company
Moore Margaret G.
Peters Carolyn V.
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