Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
1999-09-03
2001-06-12
Nakarani, D. S. (Department: 1773)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C106S287120, C106S287130, C106S287140, C106S287150, C106S287170, C523S202000, C523S205000, C523S209000
Reexamination Certificate
active
06245833
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to abrasion resistant protective coatings and methods of making the same. This invention also relates to abrasion resistant coatings derived from a ceramer composite.
BACKGROUND OF THE INVENTION
Thermoplastic and thermosetting polymers are used to form a wide variety of structures for which optical clarity, i.e., good light transmittance, is a desired characteristic. Examples of such structures include camera lenses, eyeglass lenses, binocular lenses, retroreflective sheeting, non-retroreflective graphic displays, automobile windows, building windows, train windows, boat windows, aircraft windows, vehicle headlamps and taillights, display cases, eyeglasses, watercraft hulls, road pavement markings, overhead projectors, stereo cabinet doors, stereo covers, furniture, bus station plastic, television screens, computer screens, watch covers, instrument gauge covers, bakeware, optical and magneto-optical recording disks, and the like. Examples of polymer materials used to form these structures include thermosetting or thermoplastic polycarbonate, poly(meth)acrylate, polyurethane, polyester, polyamide, polyimide, phenoxy, phenolic resin, cellulosic resin, polystyrene, styrene copolymer, epoxy, and the like.
Many of these thermoplastic and thermosetting polymers have excellent rigidity, dimensional stability, transparency, and impact resistance, but unfortunately have poor abrasion resistance. Consequently, structures formed from these polymers are susceptible to scratches, abrasion, and similar damage.
To protect these structures from physical damage, a tough, abrasion resistant “hardcoat” layer may be coated onto the structure. Many previously known hardcoat layers incorporate a binder matrix formed from radiation curable prepolymers such as (meth)acrylate functional monomers. Such hardcoat compositions have been described, for example, in Japanese patent publication JP02-260145, U.S. Pat. No. 5,541,049, and U.S. Pat. No. 5,176,943. One particularly excellent hardcoat composition is described in WO 96/36669 A1. This publication describes a hardcoat formed from a “ceramer” used, in one application, to protect the surfaces of retroreflective sheeting from abrasion. As defined in this publication, a ceramer is a hybrid polymerizable composite (preferably transparent) having inorganic oxide particles, e.g., silica, of nanometer dimensions dispersed in an organic binder matrix.
Many ceramers are derived from aqueous sols of inorganic colloids according to a process in which a radiation curable binder matrix precursor (e.g., one or more different radiation curable monomers, oligomers, or polymers) and other optional ingredients (such as surface treatment agents that interact with the colloids of the sol, surfactants, antistatic agents, leveling agents, initiators, stabilizers, sensitizers, antioxidants, crosslinking agents, and crosslinking catalysts) are blended into the aqueous sol. The resultant composition is then dried to remove substantially all of the water. The drying step may also be referred to as “stripping”. An organic solvent may then be added, if desired, in amounts effective to provide the composition with viscosity characteristics suitable for coating the composition onto the desired substrate. After coating, the composition can be dried to remove the solvent and then exposed to a suitable source of energy to cure the radiation curable binder matrix precursor.
SUMMARY OF THE INVENTION
The manufacture of ceramer compositions can be challenging due to the extremely sensitive characteristics of the colloids of the aqueous sol. Particularly, adding other ingredients, such as binder matrix precursors or other additives, to such sols tends to destabilize the colloids, causing the colloids to flocculate, e. g., precipitate out of the sol. Flocculation is not conducive to forming high quality coatings. First, flocculation results in local accumulations of particles. These accumulations are typically large enough to scatter light which results in a reduction of the optical clarity of the resultant coating. In addition, the accumulation of particles may cause nibs or other defects in the resultant coatings. In short, flocculation of the colloids causes the resultant ceramer composition to be cloudy, or hazy, and thus, coatings formed from the ceramer composition could be cloudy or hazy as well. Conversely, if colloid flocculation were to be avoided, the resultant ceramer composition would remain optically clear, allowing coatings containing the ceramer composition to be optically clear as well.
Thus, the manufacture of ceramer compositions may require special processing conditions that allow binder precursors or additives to be incorporated into a sol to avoid colloid flocculation. Unfortunately, the processing conditions developed to manufacture one ceramer composition are often not applicable to the manufacture of a ceramer containing different components.
One method of manufacturing ceramers from aqueous, colloidal sols involves incorporating one or more N,N-disubstituted (meth)acrylamide monomers, preferably N,N-dimethyl (meth)acrylamide (hereinafter referred to as “DMA”), into the binder matrix precursor. The presence of such a radiation curable material advantageously stabilizes the colloids, reducing the sensitivity of the colloids to the presence of other ingredients that might be added to the sol. By stabilizing the colloids, the presence of materials like DMA makes ceramers easier to manufacture. In addition to enhancing colloid stability, DMA provides other benefits. For example, ceramer compositions containing DMA show better adhesion to polycarbonate or acrylic substrates and better processability as compared to otherwise identical ceramer compositions lacking DMA.
Unfortunately, the use of DMA also has some drawbacks. A ceramer composition incorporating DMA tends to attract or bind with acidic contaminants (coffee, soda pop, citrus juices, and the like) in the environment. Thus, ceramers incorporating DMA tend to be more vulnerable to staining.
Accordingly, it would be desirable to find an alternative approach for making ceramers without DMA, or with reduced amounts of DMA, such that (1) the colloids are sufficiently stable during ceramer manufacture, (2) the resultant ceramer is stain resistant, or (3) the resultant ceramer retains excellent hardness and abrasion resistance.
Fluorochemicals have low surface energy characteristics that would satisfy at least one of the aforementioned criteria. Specifically, because compositions with lower surface energy generally tend to show better stain resistance, the incorporation of a fluorochemical into a ceramer would be likely to enhance the ceramer's stain resistance. Unfortunately, however, the incorporation of fluorochemicals into a ceramer sol is extremely difficult. For example, because fluorochemicals are both hydrophobic (incompatible with water) and oleophobic (incompatible with nonaqueous organic substances), the incorporation of a fluorochemical into a ceramer sol often results in phase separation, e.g., colloid flocculation. This undesirable colloid flocculation can also result during the stripping process, when water is typically removed from the blended aqueous sol.
Consequently, it would further be desirable to find a way to provide ceramers with good stain resistance using fluorochemicals or other stain resistant additives, while avoiding compatibility and hardness problems generally associated with fluorochemicals.
The present invention provides a method for effectively incorporating a fluorochemical into a ceramer composition. According to the invention, a nonionic fluorochemical containing both a fluorinated moiety and a hydrolyzable silane moiety (the “fluoro/silane component”) can be successfully incorporated into a ceramer sol, without causing appreciable colloid flocculation, to provide ceramer coatings with surprisingly long shelf lives and excellent stain resistant characteristics. Ceramers incorporating such a fluorochemical also retain a high level o
Kang Soonkun
Moore George G. I.
3M Innovative Properties
Buckingham Stephen W.
Cleveland David
Fagen Lisa M.
Nakarani D. S.
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