Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-05-02
2003-11-04
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S352000, C428S3550RA, C427S208000, C427S208800, C427S209000, C427S411000, C427S412100, C525S477000, C525S478000
Reexamination Certificate
active
06641922
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention discloses a water-reducible isocyanate adduct having dimethylsiloxane segment and ionic group. Emphasis is being placed on the use of the compound as release coating in adhesive-coated products as well as a process for creating adhesive tapes and labels.
2. Description of the Prior Art
A pressure-sensitive adhesive tape is generally manufactured and sold with the tape wound upon itself in convolutions to form a roll of some suitable length of tape. Consequently, when it is necessary to use the tape, it must be possible to unwind the desired length from the roll without excessive force or delaminating of the backing, offsetting of the adhesive, or the like, regardless of the time or conditions under which the tape has remained in roll form prior to use. For these reasons, a coating known as a release coat or backsize is generally provided on the backside of the tape backing member, i.e., the side opposite that on which the adhesive mass is applied. Such a coat, compared to an uncoated backing member, as is its objective, offers relatively low adhesion to the adhesive mass.
Although various release agents and compositions thereof have been developed over the years, none of them, to my knowledge, accomplishes all the objects desired by their use. With some release agents, the release characteristics diminish with time, and particularly at high temperatures, because of some chemical or physical change in the release material per se. Others interact with the adhesive mass so that adhesion to various substrates to which the tape is applied is adversely affected.
Whether a material is suitable or not as a release agent, in particular for pressure-sensitive adhesive tapes, depends upon a number of factors. The lower the interfacial tension between the adhesive mass and the material used as a release coating, naturally the better release provided. However, low interfacial tension alone is not enough. The material, to be useful as a release coat, should also be of a suitable cohesive strength and possess good adhesion with the backing member.
In the 1970's, silicone emulsions in water were introduced. Generically, they were dimethylsiloxane oligomers with Si—H reactive groups. They had to be mixed with a catalyst prior to application to paper or plastic film, which made them inconvenient 2-component systems. Upon evaporation of water, a surface film of the oligomer was deposited, which built up in molecular weight, crosslinked, and a solid coating resulted. This process, called “cure”, needed either high temperatures or long time at moderate temperatures.
The necessity for curing the polymeric material after deposition has placed certain restrictions on the use of silicones. This is because the temperature needed for curing, at least to the extent desired, has often exceeded the temperature, which a substrate on which a release coating is deposited could withstand. This has been particularly true where the substrate is a thermoplastic film or a paper-thermoplastic film laminate, care being needed to avoid melting or distorting the thermoplastic film. In paper substrates, high temperatures result in over-drying of paper.
A further disadvantage associated with silicone release polymers is their relatively poor adhesion to certain plastic films on which they are coated. This poor adhesion is thought to be due to the scarcity of polar groups in the silicone. Consequently, the use of a primer is often needed to obtain better anchorage of the silicone film to the substrate. In addition, the release characteristic in itself is sometimes a problem in that too good a release is provided. Thus, tape rolls may be too easy to unwind and, in some cases, the adhesion between the adhesive mass and release coat may be so low that the roll doesn't remain tightly wound.
U.S. Pat. 4,287,109 of Schlak et al. discloses an aqueous resin of a Silicone-Si—O—C-Polyester block copolymer.
B.P. 1,128,642 of Keberle et al. and G.P. DE 37 30 780 A1 of Nagorski et al. disclose water base silicone-modified polyurethanes. Keberle suggests their use for impregnating and coating fabrics, leather, paper, glass, wood, laminates and foamed plastics for anti static finishes and hydrophobic coatings, and as binder, lubricant, mold release agent, cleaning agent, leveling agent and corrosion inhibitor. Nagorski suggests usage as coating for wood, metal, paper, synthetic fabric, flock and leather.
EPA 0 342 826 of Higgins and its corresponding U.S. Pat. No. 5,082,704 disclose a silicone-modified polyurethane dispersion in water which may be used to fabricate a release liner for adhesives, most notably for asphalt roofing materials.
EPA 0 380 236 A2 of Leir discloses an amino-terminated silicone, its preparation, the preparation in a solvent of an anionic, nonionic and cationic silicone modified polyurea and its dilution with water, and its use as an elastomer, a pressure sensitive adhesive and a low adhesion backsize.
My own inventions, U.S. Pat. Nos. 5,356,706 and 5,543,171, disclose processes for manufacturing aqueous release coatings for pressure sensitive adhesive tapes by reacting a siloxane oligomer having 2-3 isocyanate-reactive groups and a diol having an acidic group with an excess polyisocyanate, and further reacting, in water, with a tertiary amine to form a salt and a primary or secondary polyamine to extend the prepolymer into a polymeric chain.
U.S. Pat. No. 5,679,754 of Larson et al. disclose fluorinated polyurethane with sulfonate groups as release agent dispersion in water.
U.S. Pat. Nos. 5,750,630 and 6,072,019 of Sengupta disclose a “polyurethane polymer whose chain includes silicone-containing segments and whose polymer chain is end-capped with a single isocyanate-reactive silane group” and a 2.5-30 weight percent solution in water of the polyurethane.
SUMMARY OF THE INVENTION
A coating can be prepared from polyisocyanates and reactants having only one isocyanate-reactive group. The reactions product is an isocyanate adduct that may have urethane/urea/amide bond. For simplicity it is hereon referred to as urethane, or isocyanate adduct, with many advantages as coating materials over the prior art polymeric urethanes. Examples of coatings are release agents for pressure sensitive adhesive tapes and labels. Other examples are mold release agents, finish materials for fibers, fabrics or paper products, overprint varnishes, printing inks and write-on office products, such as note pads coated with a pressure sensitive adhesive.
This invention comprises an isocyanate adduct comprising the reaction product of a composition comprising in admixture:
A. Polyisocyanate,
B. Silicone having dimethylsiloxane segments and one or more isocyanate-reactive group bonded to said segment through an intermediate organic group,
C. Reactant with one or more isocyanate-reactive group, and one or more acid group or amine group,
D. Optionally organic substance having one or more isocyanate-reactive groups, and
E. Compound providing a counterion for said acid or amine group,
Wherein either silicone B, or reactant C, or both, have a single isocyanate-reactive group.
This invention further discloses a process for manufacturing a pressure sensitive adhesive-coated product comprising the steps of:
i. providing an isocyanate adduct comprising the reaction product of a composition comprising in admixture:
A. Polyisocyanate,
B. Silicone having dimethylsiloxane segments and one or more isocyanate-reactive group bonded to said segment through intermediate divalent organic group,
C. Reactant with one or more isocyanate-reactive group and one or more acid or amine groups, and optionally
D. Organic substance having one or more isocyanate-reactive groups,
Wherein either silicone B, or reactant C, or both, have single isocyanate-reactive group,
ii. reacting said acid or amine group with a compound providing counterion,
iii. mixing with water to form dilute solution or dispersion,
iv. coating a substrate with said solution or dispersion and removing water by heat, and
v. c
Dawson Robert
Keehan Christopher M.
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