Substrates for heat transfer labels

Details Substrates for heat transfer labels Substrates for heat transfer labels

1998-10-08

2001-07-03

Hess, Bruce H. (Department: 1774)

Stock material or miscellaneous articles

Structurally defined web or sheet

Discontinuous or differential coating, impregnation or bond

C428S202000, C428S211100, C428S343000, C428S347000, C428S913000, C428S914000, C428S480000, C428S484100, C428S474400

Reexamination Certificate

active

06254970

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the field of heat transfer labels. More particularly, the invention relates to improvements in the substrates used to carry labels prior to heat transfer of the labels onto a surface.
BACKGROUND OF THE INVENTION
Heat transfer label technology has been used since the early 1900's for decorating textiles and leather. In the late 1950's and early 1960's, the process was first applied to plastics. More recently, the technology has been used to provide labels on numerous surfaces, including plastic bottles.
The most common form of heat transfer label uses a wax layer as a transfer agent. In particular, the conventional heat transfer label is a multi-layered structure which incorporates a carrier or substrate, a transfer agent, inks and an adhesive layer. Optionally, a protective lacquer layer may be included as well. One such label is shown in FIG.
1
. In
FIG. 1
, the heat transfer label
10
includes a carrier substrate
11
comprised of a supporting carrier
12
and a wax transfer agent
14
, an optional protective lacquer
16
, one or more inks
18
, and an optional adhesive lacquer
20
. Typically, the adhesive lacquer is provided, however, certain inks having a high binder content adhere well to surfaces, thereby eliminating the need for the adhesive lacquer. The supporting carrier
12
typically is a paper material, and can comprise a calendered paper or a coated paper, such as a clay coated paper. Other carrier substrates that have been used include wax-coated papers, papers coated with polymeric extrusions such as polyethylenes, polypropylenes and nylons, laminates of polyethylene or polypropylene to paper, silicone-coated papers, and polyester films having release coatings.
The transfer agent
14
is typically a layer of a material, such as wax, that melts when heated, thereby allowing the inked portion of the label to be removed from the carrier substrate
12
and adhered to a bottle or other item to be labeled. Various waxes have been used as the heat transfer agent
14
. Such waxes are typically used in the form of mixtures of various waxes and typically comprise mixtures including montan waxes, victory white wax, ethylene vinyl acetate resins, paraffins, low molecular weight polyethylenes, and the like. Typically, the wax layer is approximately 2.0 to 2.5 mils in thickness. Optionally, a protective lacquer
16
, is applied to the transfer agent. The protective lacquer can be any of a wide variety of known materials including polyesters, acrylics, nitrocellulose, vinylidene chloride copolymers, etc. The protective lacquer serves as a protective coating over the ink once the label has been adhered to the desired item.
Heat transfer labels of the type described above may be applied to a surface, such as the outer surface of a plastic bottle, in the manner depicted in FIG.
2
. As can be seen in
FIG. 2
, the heat transfer label
10
formed of the supporting carrier
12
, the wax transfer agent
14
, the optional protective lacquer layer
16
, the ink(s)
18
, and the optional adhesive lacquer
20
are pressed against the outer surface of a bottle
22
. More specifically, the label
10
is placed against the bottle
22
such that the adhesive lacquer
20
or the binders contained in the inks
18
are in contact with the bottle surface, while heat and pressure are simultaneously applied to the reverse (carrier substrate
11
) side of the label. The elevated temperature resulting from the thermal application causes the wax forming the heat transfer agent
14
to melt and split. At the same time, the adhesive lacquer
20
and/or the binder in the inks
18
becomes tacky. The tackified label is thus caused to adhere to the bottle surface while the carrier substrate
11
is removed. The result is a carrier substrate
11
comprising a supporting carrier
12
having a thinner layer of the heat transfer agent
14
on its surface, and a bottle
22
, having the heat transferred label on its surface. The adhered label will retain a portion of the heat transfer agent
14
on its exposed surface.
One problem associated with the heat transfer labels described above is a result of the heat transfer agent. Specifically, the commonly used waxes leave a thin wax layer on the label surface. This wax layer is undesirable in that it often has a residual or natural tackiness that causes it to become soiled, thereby obscuring the label and producing an unappealing product. Additionally, being relatively soft, the wax is susceptible to physical damage (i.e., scratching, scraping, etc.) that detracts from the appearance of the label and the labeled product, as well as to chemical damage that can result if the label is exposed to certain chemical agents such as caustics.
Accordingly, a need exists for a heat transfer label and labeling system that substantially eliminates the residual heat transfer agent from the label once the label has been transferred to a surface. A need also exists for heat transfer labels and labeling systems that result in a label that has a tendency to remain clean and undamaged throughout its shelf life.
SUMMARY OF THE INVENTION
Broadly, the present invention relates to a heat transfer labeling system which comprises a carrier substrate, a polymeric layer disposed upon at least one surface of the carrier substrate, a transfer release agent disposed upon the polymeric layer and a label formed on the transfer release agent. The label comprises one or more inks, an optional adhesive lacquer and an optional protective lacquer. The invention is characterized in that it employs a novel carrier substrate and transfer release agent to minimize or eliminate the transfer of the transfer release agent to the label during the process in which the label is transferred to a substrate such as a package. Alternatively, in some embodiments of the present invention, the entire transfer release agent is transferred with the label, however, in these embodiments, the transfer release agent is a material which does not impart the disadvantages of conventional thick wax transfer release coatings.
As will be described in detail below, the carrier substrate may be a paper having a polymeric coating upon which the transfer release agent is coated. Alternatively, in one embodiment, the transfer release agent may be incorporated directly into the polymeric coating. Preferred polymeric coatings include cured epoxy acrylates, latex materials, and polyester, polyethylene or polypropylene films. Suitable transfer release agents include aqueous release coatings and polyacrylamides.


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