Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-02-22
2003-08-05
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C156S226000, C524S401000, C524S442000, C524S450000, C524S457000, C524S493000, C524S500000, C525S054100, C525S242000, C525S244000, C525S254000
Reexamination Certificate
active
06602944
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
U.S. Pat. Nos. 4,918,128 and 5,190,818 provide pressure sensitive adhesives/cohesives that are revolutionary in their utility when utilized with mailers or like type documents or business forms. These patented adhesives have allowed the practical implementation in the mailer industry of mailers which may be quickly and effectively produced and sealed without the drawbacks associated with conventional heat or moisture activated adhesives.
While the adhesives in the above-identified patents are extremely effective, it is desirable to be able to produce an adhesive that has even better properties. While the adhesives in the above-identified patents are not tacky after the application to paper, and do not adhere/seal unless a high level of pressure is applied (which prevents the adhesive from blocking during the printing, which would slow down the processing due to paper jams or the like), sometimes the adhesive action may be hampered by contamination of the printing surface and adhesive with silicone lubricants used in conventional printers (particularly laser printers).
The adhesive according to the present invention, when coated on paper or like substrates used in mailer-type business forms, or the like, has the same advantageous properties as the adhesives in the above-identified patents and also has enhanced functionality when contaminated by silicone lubricants.
Like the preferred embodiments in the above-identified patents, the cohesive according to the present invention contains a natural rubber graft, an appropriate acrylate monomer or monomers such as methyl methacrylate, or cyclohexyl methacrylate, or benzyl methacrylate, or isobornyl methacrylate or trimethyl cyclohexyl methacrylate or isobornyl acrylate), and finely divided hard particles such as silica. When cyclohexyl methacrylate is employed it is typically present in an amount of about 0.5-1.5 weight %, more usually about 1 weight % based in the weight of the modified latex. Methyl methacrylate and polymethylmethacrylate when employed are typically present in an amount of about 10-18 weight %, more usually about 15 weight %.
The cohesive according to the present invention also may include starch, acrylic acid and/or 4-acetoxystyrene, and optionally ethyl hexyl acrylate.
According to the present invention a pressure sensitive adhesive/cohesive is provided comprising the following components: 100 parts by weight natural rubber; about 5-35%, by weight of the rubber, acrylate monomer; about 0.5-8% by weight of the rubber acrylic acid and/or about 0-10%, typically 1-10%, by weight of rubber, 4-acetoxystyrene, and 1-50%, by weight of the rubber, a finely divided hard particulate material having substantially no thermoplasticity.
The composition may also comprise advantageously about 0-10%, for example 1-10%, by weight of rubber, 4-acetoxystyrene. The composition may further comprise about 0-20%, by weight of the rubber, ethyl hexyl acrylate, 0-50%, by weight of the rubber, starch; and 0-40%, by weight of the rubber, carboxylated styrene-butadiene latex, or carboxylated polychloroprene latex, or vinyl-pyridine styrene-butadiene latex or pre-crosslinked natural rubber latex, or a tackifier, or combinations thereof.
In the case of 4-acetoxystyrene as a comonomer in the graft/block of the rubber, grafted rubber has built-in antioxidant as a result of hydrolysis of acetoxy group which provides the cohesive antioxidant property helping its shelf-life as a coated cohesive by acting as a free radical scavenger.
The pressure sensitive adhesive/cohesive according to the present invention is typically coated on a piece of paper. More typically, since the material according to the invention is best as a cohesive, it is coated on two portions of a piece of paper, the cohesive portions being in contact with each other as a result of folding the paper (such as by forming a mailer), or bringing a like sheet in contact therewith, and pressure sealed together (such as by running through conventional pressure sealing equipment, such as “Speedisealer®” equipment available from Moore USA of Lake Forest, Ill.), so as to cause paper fiber tear if attempted to be pulled apart.
In the following discussion, percentages are by weight unless otherwise stated. Preferably, the adhesive/cohesive comprises at least 1% ethyl hexyl acrylate, and at least 1% starch, e.g. about 10-30% starch (such as about 20% starch) having an average particle size of about 5-25 microns. The hard particulate material preferably comprises silica gel, e.g. about 10-30% (such as about 20%), the silica gel having an average particle size of about 0.2-20 microns (e.g. about 0.3-0.4 microns), or a fumed silica (e.g. 0.1-0.3 microns). There also may be at least 5% carboxylated styrene-butadiene latex, or carboxylated polychloroprene latex, or vinyl-pyridine styrene-butadiene latex, or pre-crosslinked natural rubber latex, or a styrene-acrylate-acrylonitrile latex, or a tackifier, or combinations thereof.
The acrylate monomer preferably comprises methyl methacrylate, e.g. about 5-30%, or 0.5-8% of 4-acetoxystyrene, cyclohexyl methacrylate, benzyl methacrylate, trimethyl cyclohexyl methacrylate or isobornyl methacrylate. The acrylic acid typically is present between about 0.5-4%, and the 4-acetoxystyrene between about 1-3%. The modified natural rubber latex is preferably electrosterically stabilized natural rubber graft and block terpolymer.
Generally, the acrylate monomer is selected from cyclohexyl methyl methacrylate, methyl methacryate and mixtures of the two. Trimethyl cyclohexyl methyl methacrylate, methyl methacryate and mixtures thereof may also be used. In both instances, the natural rubber may be electrostatically stabilized latex of natural rubber graft/block terpolymer.
In the present case, the term “electrosterically” is used when there are ionizable/hydrolyzable groups grafted onto the natural rubber, e.g. acrylic acid or 4-acetoxystyrene. These ionizable groups impart a negative charge to the latex particles which stabilizes the emulsion. The term “electrostatically” is used when non-ionizable/hydrolyzable groups grafted onto the natural rubber and, hence, the only charge on the latex particles arises from an electric double layer.
According to a further embodiment, the cohesive may be manufactured by synthesizing a modified natural rubber latex through reaction of 1,4 cis polyisoprene (natural rubber) with two or more acrylate monomers, followed by further reactions and processing. Typically, the modification carried out using cyclohexyl methacrylate (CHMA) (approx. 1 to about 5% by weight) and/or methyl methacrylate (MMA) (approx. 10-18% by weight).
For purposes of discussion, the synthesis of the modified natural rubber latex graft/block terpolymer with CHMA/MMA will be described below. However, it will understood that the invention is not limited to modified natural rubber latexes using those two acrylate monomers. Examples of other acrylates which may be used are benzyl methacrylate and/or isobornyl methacrylate and/or trimethyl cyclohexyl methacrylate and/or isobornyl acrylate.
A graft/block terpolymer of natural rubber latex with CHMA/MMA may be synthesized by conducting a seeded emulsion polymerization of natural rubber latex (for example about 100 parts by weight) with CHMA (for example about 5 parts by weight), by initiating a graft polymerization by a redox couple under a nitrogen atmosphere in a reaction vessel at 35° C. After CHMA starts to polymerize and starts to be consumed, MMA (about 11 parts by weight) is added to the reaction mixture by initiating a reaction with the redox couple initiator system. MMA polymerizes along with the growing polymer CHMA chains creating partial blocks of poly CHMA poly MMA grafted onto the 1,4-cis-polyisoprene.
This results in a modified natural rubber latex molecular architecture which is a graft/block terpolymer latex. Some polymethylmethacrylate (PMMA) is also formed during synthesis of the modified natural rubber latex because surfactant concentration is far above the cmc (
Moore North America Inc.
Niland Patrick D.
Nixon & Vanderhye P.C.
LandOfFree
Pressure sensitive cohesive does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Pressure sensitive cohesive, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Pressure sensitive cohesive will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3096223