Record receiver having plural interactive leaves or a colorless – Having a colorless color-former – developer therefor – or... – Method of use – kit – or combined with marking instrument or...
Reexamination Certificate
2000-03-10
2002-02-19
Hess, Bruce H. (Department: 1774)
Record receiver having plural interactive leaves or a colorless
Having a colorless color-former, developer therefor, or...
Method of use, kit, or combined with marking instrument or...
C503S209000, C503S213000, C503S217000, C503S218000, C503S221000, C503S224000, C526S329700
Reexamination Certificate
active
06348432
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to heat sensitive coatings. More specifically, the invention relates to heat sensitive coatings which do not require a protective coating.
BACKGROUND OF THE INVENTION
Generally, heat sensitive recording materials include a color producing or heat sensitive layer coated onto a substrate with a protective layer coated over the heat sensitive coating to protect it from exposure to water and/or oils.
Typical heat sensitive coatings are aqueous dispersions of a color former, a color developer, an optional organic sensitizer and a water soluble polymeric binder. The polymeric binder, e.g., polyvinyl alcohol, polyvinylpyrrolidone, or the like, typically is highly soluble in water. Accordingly, heat sensitive layers which contain water soluble polymers, like polyvinyl alcohol, have a high affinity for water such that the resulting recording material may be easily damaged by the presence of moisture. In addition, organic sensitizers and bisphenol-type developers in typical heat sensitive coatings often arc soluble in oil such that contact between the recording material and an oil may result in reversal of an image formed by development at the area of contact.
Protective coatings generally include water soluble polymer binders such as, for example, polyvinyl alcohol crosslinked with a crosslinker such as, for example, melamine-formaldehyde. These top coat layers tend to reduce the incidence of damage to the recording material by water and/or oil, however, they do not protect the recording material from prolonged exposure to water.
The use of a protective coating also increases the cost of the heat sensitive recording material, for example, the costs of the protective coating materials and the processing costs involved in preparing and coating the protective coating are added to the overall costs of the commercial product. Moreover, protective coatings typically reduce the tint strength of the heat sensitive layer due to increased spacing between the thermal head of the thermal printer and the color producing layer when printing. Additionally, protective layers typically include a plastic binder and/or fillers comprising pigment. Plastic binders typically are heat insulating which further reduces the potential tint strength and pigments which tend to mask the developed color of the heat sensitive layer.
SUMMARY OF THE INVENTION
A heat sensitive coating has been developed which is environmentally resistant. That is, the heat sensitive coating is resistant to water, oil, cleaning solutions and plasticizers, as well as other environmental stresses including scuffing and scratching, thus obviating the necessity and expense of a protective coating. The heat sensitive coating and recording materials of the present invention may be used with a variety of printers and processes, including, but not limited to, offset and flexo printing.
An environmentally resistant heat sensitive coating of the present invention includes an acrylate polymer of the formula:
wherein R
1
is a hydrogen or a methyl group; R
2
is a hydrogen or a methyl group; and R
3
is nitrile or chlorine or
wherein, when c is 0, R
4
is methyl, phenyl, or substituted phenyl, and when c is greater than 0, R
4
is methyl, phenyl, substituted phenyl, halogen, nitrile or hydroxyl; m is greater than 1; n is greater than 1; b is greater than or equal to 0; and c is an integer from 0 to 38.
In one embodiment of the present invention, the acrylate polymer is soluble in an alkaline aqueous solution. In another embodiment, the acrylate polymer is a methylmethacrylate/ethylacrylate/methacrylic acid polymer, a methylmethacrylate
-butylmethacrylate/methacrylic acid polymer, a methylmethacrylate/methylacrylate/methacrylic acid polymer, a methylmethacrylate/hydroxyethylmethacrylate/methacrylic acid polymer, a methylmethacrylate/hydroxypropylmethacrylate/methacrylic acid polymer, or a methylmethacrylate/propylacrylate/methacrylic acid polymer.
In another embodiment, an organic sensitizer is included with the acrylate polymer. Suitable sensitizers include, but are not limited to, polyaromatic waxes, methylbenzyl oxalates, for example, di-p-methylbenzyl oxalate, terphenyls, for example p-terphenyl, benzobiphenyls, fatty acids, fatty acid esters, for example, stearate, fatty amides, for example, stearamide, fatty acid salts, polyethylene waxes, dimethylphenyl ethane, for example, 1,2 bis(3,4-dimethylphenyl)ethane, carnauba waxes, microcrystalline waxes, and carboxy-modified paraffin waxes.
Optionally, the present invention may include a crosslinking agent. Preferably, the crosslinking agent is one that is suitable for use with polymers containing functional carboxylic acid groups. Suitable crosslinking agents include, for example, aziridine, epichlorohydrine, zinc oxide, and ammonium zirconium carbonate.
In yet another embodiment, a heat sensitive coating of the present invention may include a color former. Suitable color formers include fluorans, thiofluoranes, spiropyrans, triarylmethanes, xanthenes, and methynes.
In a further embodiment, the present invention may include a color developer. Suitable color developers include 4,4′-isopropylidenediphenol, 4,4″-diphenolsulfoxide, benzyl p-hydroxybenzoate, and phenol oligomers.
Optionally, the present invention may further include a filler selected from the group consisting of silica, zinc oxide, aluminum hydroxide, kaolin clay, talc, calcium carbonate, nylon powder, and polyethylene powder.
Another aspect of the present invention is a recording material which includes a heat sensitive coating of the present invention.
Yet another aspect of the present invention is a method of making an environmentally resistant heat sensitive recording which includes the following steps: (a) providing a heat sensitive coating comprising an acrylate polymer of the formula:
wherein R
1
is a hydrogen or a methyl group; R
2
is a hydrogen or a methyl group; and R
3
is nitrile or chlorine or
wherein, when c is 0, R
4
is methyl, phenyl, or substituted phenyl, and when c is greater than 0, R
4
is methyl, phenyl, substituted phenyl, halogen, nitrile or hydroxyl; m is greater than 1; n is greater than 1; b is greater than or equal to 0; and c is an integer from 0 to 38; (b) coating a substrate with the heat sensitive coating; and (c) thermally activating the heat sensitive coating.
The invention will be understood further upon consideration of the following description.
DETAILED DESCRIPTION OF THE INVENTION
An environmentally resistant heat sensitive coating has been developed. That is, the heat sensitive coating is resistant to water, oil, cleaning solutions and plasticizers, as well as other environmental stresses including scuffing and scratching, thus obviating the necessity and expense of a protective coating.
Generally, the invention disclosed herein includes an environmentally resistant heat sensitive coating including an acrylate polymer of the formula:
wherein R
1
is a hydrogen or a methyl group; R
2
is a hydrogen or a methyl group; and R
3
is nitrile or chlorine or
wherein, when c is 0, R
4
is methyl, phenyl, or substituted phenyl, and when c is greater than 0, R
4
is methyl, phenyl, substituted phenyl, halogen, nitrile or hydroxyl; m is greater than 1; n is greater than 1; b is greater than or equal to 0; and c is an integer from 0to 38.
In one embodiment of the invention, the acrylate polymer is soluble in an alkaline aqueous solution. This solubility is due in part to the presence of carboxylic acid groups, which are neutralized in alkaline aqueous solutions. Without wishing to be bound to any particular theory, it is believed that the acrylate polymers of the present invention, being not readily soluble in neutral and acidic water, increase the resistance of the coating to water damage. Preferably, the acrylate polymer also has a glass transition temperature (Tg) equal to or greater than about 100° C.
One polymer suitable for use in accordance with the present invention is methylmethacrylate/ethylacrylate/methacrylic acid. This po
Hess Bruce H.
Nashua Corporation
Testa Hurwitz & Thibeault LLP
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