Prelaminate pressure-sensitive adhesive constructions

Details Prelaminate pressure-sensitive adhesive constructions Prelaminate pressure-sensitive adhesive constructions

2000-06-06

2003-04-01

Mayes, Curtis (Department: 1734)

Adhesive bonding and miscellaneous chemical manufacture

Methods

Surface bonding and/or assembly therefor

C156S184000, C156S297000, C156S267000, C156S289000, C156S320000, C156S324000, C427S208800

Reexamination Certificate

active

06540865

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to pressure-sensitive adhesive constructions and methods for making the same and, more particularly, to prelaminate pressure-sensitive adhesive constructions having a detackified surface to provide anti-blocking characteristics for facilitating subsequent handling and/or treatment of the construction before lamination to a second substrate.
BACKGROUND OF THE INVENTION
Pressure-sensitive adhesive (PSA) constructions such as labels, tapes, decals and the like are known in the art. For example, PSA label constructions are commonly used to apply a particular face stock having a specific nature of printing to an object or article, and are especially useful where objects having low surface energies are to be labeled. PSA label constructions typically comprise a face stock, a liner, and a PSA layer interposed between the face stock and liner.
In accordance with well known practice in the industry, the liner may be coated with a releasable material, forming a release liner. The releasable surface of the release liner may be coated with a layer of PSA for subsequent transfer of the adhesive to the face stock with which the release liner is employed. When the face stock is combined with the release liner, the adhesive is laminated to the face stock. Alternatively, the adhesive may have been directly coated on or combined with the face stock prior to combining the face stock with the release liner. In either approach, in a later step the release liner is removed from the PSA and face stock construction to expose the adhesive, which remains permanently joined to the face stock.
Thus, as indicated in
FIG. 1
, a PSA
10
may be applied to the release surface of the release liner
12
at a station
14
following drying or curing of a release coat
16
previously applied to the release liner at station
18
. This may be a tandem coating operation, or the adhesive coating
10
may be applied on a separate coating line. The PSA may be formed from a material that requires drying before application of the face stock, in which case the face stock is applied to the dried PSA layer. In some cases the release surface
16
is precoated onto the release liner
12
, and the adhesive
10
is applied at a later time prior to laminating the release liner
12
to a face stock
20
. The combining of the release liner and face stock is diagrammatically illustrated in FIG.
2
.
Most commonly, the resulting laminated construction takes the form of a continuous ribbon or web that is collected on a roll. This roll may be transported to a converter for further operations such as printing, die cutting, and matrix stripping, in order to create labels, signs, or other PSA products. Thus for example,
FIG. 3
illustrates the die cutting of the face stock
20
at a station
22
into a series of PSA labels
24
of desired shape and size, carried by the release liner
12
.
The manufacturing processes described above share the characteristic that the lamination of the release liner, PSA, and face stock occur at a common production facility. To promote flexibility in the production of PSA constructions, it is desired to devise a method for coating the release liner with a PSA (thereby forming a “prelaminate construction”) in a separate and independent operation from laminating the prelaminate construction to face stock. These operations should be capable, for example, of allowing the prelaminate construction to be produced at a different geographic location, or in a separate and independent production line, than that at which the prelaminate construction is laminated to the face stock.
One way in which this desire has been addressed has been to make PSA constructions having a subsequent layer of material applied to the exposed surface of the adhesive in an effort to detackify the adhesive surface. Detackifying the PSA construction in such manner has been thought to be an effective way of forming a nonblocking PSA construction that, in theory, would permit the prelaminate PSA construction to be rolled upon itself and stored or transported for subsequent lamination without adhering to a backside surface of the construction, or to anything else. In practice, however, detackified PSA constructions known in the art have not been entirely effective at providing a completely nonblocking construction.
As used herein, the term “nonblocking” is intended to mean that the prelaminate PSA construction is capable of preventing any significant bonding or adhering to contiguous layers of the label construction, i.e., the backside surface of the release liner, during storage, transportation and handling of the construction so that the removal or separation of the prelaminate PSA construction from contiguous layers of the construction, when collected and/or stored in sheet or roll form, will not be impaired.
For example, U.S. Pat. No. 4,135,033 discloses a two-layer adhesive coating having a dry, nontacky surface that is convertible to a permanently adhesive surface by application of heat over a period of ten seconds. The two-layer adhesive coating can be used with silicone treated release paper. In manufacturing PSA constructions it is desired that the step of heating and laminating the PSA construction be completed quickly to maximize the web speed and, thereby maximize manufacturing efficiency. The need to heat activate such nontacky surface over the relatively long period of ten seconds is contrary to the goal of achieving manufacturing efficiency, and thus is not economically practical.
Additionally, in practice it is known that the patented two-layer adhesive coating is not effective at forming a completely nonblocking PSA construction, thereby permitting adhesional interference to occur between contiguous PSA construction surfaces. Such blocking is believed to be caused by the failure of nontacky surface to form a completely continuous film to cover the underlying adhesive layer.
U.S. Pat. No. 3,843,480 discloses a process for preparing a surface-detack layer on a PSA that is carried releasably upon a supporting release liner. The process includes the steps of applying a PSA layer onto a release liner and dusting a surface portion of the PSA layer with a mineral powder to detackify the PSA layer. The resulting detackified PSA layer is said to permit the prelaminate construction to be wound upon itself or sheeted and stacked without adhesional interference. However, in practice it is known that such patented prelaminate constructions are not completely effective at preventing blocking, as adhesional interference between contiguous construction layers is known to occur. A reason for such blocking is believed to be the failure of the mineral powder to form a continuous PSA covering film.
The surface detack layer of such patented construction is subsequently attached to another substrate surface, such as printing paper and the like, by a single process step of simultaneously heating the surface of both the detack layer and the printing paper, while applying pressure to the printing paper and heated detack layer to form a completed laminate construction.
Simultaneous heat activation of the detack layer and pressure lamination, however, is problematic because it limits the types of substrate materials that can be used. For example, thermally-sensitive substrates such as thermal print paper, films of polymers having a low glass transition temperature, and oriented polymer films cannot be used with this process because the step of heating such substrates is known to adversely impact the desired performance of these materials.
The need to simultaneously heat activate and laminate the PSA construction is also not desired because of the related problems that are known to occur at the nip, such as wrinkling and buckling of the laminated construction that is caused by the different coefficients of expansion between the prelaminate PSA construction and the laminated substrate. Additionally, simultaneous heat activation and lamination is also known to cause shrinkage in paper face stocks due to

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