Label face stock

A multilayer label stock structure comprising a label stock of polypropylene film having on one side thereof a highly printable blend of (A) alkylene acrylate copolymer and (B) an interpolymer of an alkyl acrylate, an alkyl methacrylate and an alkyl acrylate acid.

FIELD OF THE INVENTION 
This invention relates to the field of adhesively adhered labels. In 
particular, the invention relates to biaxially oriented polymer film 
structures employed as adhesively adhered labels. 
BACKGROUND OF THE INVENTION 
Of recent years polymeric films have been utilized to take the place of 
paper for product labels and the like. Synthetic film labels are stronger 
and in some respects easier to handle in automatic machinery employed for 
applying labels to products. 
A typical system employs a release layer which carries one or more 
removable labels therefrom. The label carried by the release substrate has 
a pressure sensitive adhesive on one side and a product identifying 
indicia or other information on the other. The release layer is composed 
of a substrate which has a surface to which the label adhesive will not 
aggressively adhere. The release characteristics of the substrate and the 
adhesive are such that when the substrate is bent through a certain angle, 
the stiffness of the label will cause it to separate from the release 
surface in spite of the presence of the adhesive. This will permit a 
container or product to be interfaced with the adhesive layer so that the 
label will transfer from the release surface to the product to be labeled. 
This technique happens rapidly and sequentially in automated mechanisms. 
One shortcoming in general with the use of polymeric films with label 
stock is that they may not have excellent printability with high speed dot 
matrix and thermal transfer printers. Thermoplastic label stock is also 
much desired in contrast to paper labels from the standpoint of 
recyclability. Paper labels intermixed with recyclable plastic film 
present a significant problem since the two materials are not easily 
separable. Thus, there is an ever increasing need for plastic film label 
stock as opposed to paper labels. 
Therefore, it is an object of the present invention to present a synthetic 
film-adhesive label face stock having excellent printability. 
SUMMARY OF THE INVENTION 
The label stock of the present invention includes the following multilayer 
structure: 
A base structure comprising an oriented polypropylene film having on one 
side thereof a blend of (A) one or more alkylene acrylate copolymer and 
(B) an interpolymer of (a) from 2.5 to about 6 parts by weight of an 
alpha-beta monoethylenically unsaturated carboxylic acid selected from the 
group consisting of acrylic acid, methacrylic acid and mixtures thereof 
and (b) from about 97.5 to about 94 parts by weight of neutral monomer 
esters, said neutral monomer esters comprising (1) methyl acrylate or 
ethyl acrylate and (2) methyl methacrylate, said interpolymer comprising 
from about 30% to about 55% by weight of methyl methacrylate when said 
alkyl acrylate is methylacrylate, and from about 52.5% to about 69% by 
weight of methyl methacrylate when said alkyl acrylate is ethyl acrylate; 
said mixture containing inert inorganic fillers; and on the other side 
thereof an adhesive layer. 
In many instances the adhesive will be a pressure sensitive adhesive. In 
other cases the adhesive may be one activatable by any means, such as, 
heat, solvent, etc. For its best utility the above described label 
structure is carried by a release surface wherein the release 
characteristics of the surface of the release sheet permits the label 
stock to be readily removed therefrom so as to be applied to some other 
surface.

DETAILED DESCRIPTION OF THE INVENTION 
For use as a base or core layer for label stock purposes, this material can 
be transparent or opaque, preferably white opaque. For the opaque version, 
this provides an excellent contrasting background for printed material 
applied to the outer surface of the label stock. A material which has the 
good characteristics of excellent tensel strength, low permeability to 
moisture and other liquids, is oriented polypropylene. A preferred 
transparent polypropylene base or core layer has two or more coextruded 
polypropylene layers, one layer of which is thicker than the skin or outer 
layers. These outer layers may be filled or unfilled with appropriate 
additives. A preferred opaque base or core material is an oriented 
polypropylene structure containing a core layer cavitated in a special way 
so as to produce a pearlescent opaque appearance. A material of this type 
is described in U.S. Pat. No. 4,377,616 issued to Ashcraft et al. This 
patent is incorporated herein by reference in its entirety. In accordance 
with this patent, the process of preparing the opaque film structure is as 
follows: a major proportion of a first thermoplastic material, e.g. 
polypropylene, is mixed with a minor proportion of second material of a 
higher melting point or of a high glass transition temperature than the 
first material. This mixture is heated to a temperature at least above the 
melting point of the first material. Thereafter, the second material is 
uniformly dispersed throughout the molten first material in the form of 
microspheres. The microspheres can be conveniently prepared in a master 
batch of, e.g. polybutylene terephthalate, micro dispersed in molten form 
in molten polypropylene. This combination is then coextruded with clear 
unfilled polypropylene so as to have a thin skin layer on opposite 
surfaces of the core combination of the materials. Thereafter, this 
arrangement is biaxially oriented at a temperature and to a degree to form 
a strata of opacifying closed cell voids of dimensions X, Y and Z. 
Dimensions X & Y are major dimensions and dimension Z is a minor dimension 
at least generally corresponding to the diameter of the microspheres. In 
some cases, it may be advantageous to include inorganic filler materials 
therein for example, to promote the roughness of the surface of the skin. 
The material dispersed as microspheres throughout the molten core material 
can be polybutylene terephthalate, nylon, solid or hollow preformed glass 
spheres, metal beads or spheres, ceramic spheres, calcium carbonate, etc. 
As indicated, the preferred core material is polypropylene, particularly 
preferred is an isotactic polypropylene containing at least 80% by weight 
of isotatic polypropylene. It is also preferred that the polypropylene 
have a melt flow index of about 2-10 g/10 min. 
It is preferred that the average diameter of the void-initiating particles 
be from about 0.1 to about 10microns. These particles may be of any 
desired smooth shape, although it is preferred that they be substantially 
spherical. 
The skin material coextruded onto one surface of the base or core material 
to be cavitated, preferably is a medium density polyethylene. This is 
meant that the density of the polyethylene can be anywhere from about 
0.926-0.945. A material of this type is described in U.S. Pat. No. 
5,194,324 issued to Poirer. This patent is incorporated herein by 
reference in its entirety. 
It is also contemplated that one side may carry the medium density 
polyethylene layer while the opposite surface may carry no skin layer or 
may have any one of a variety of other skin surfaces. For example, the 
opposite skin material can be noncavitated polypropylene, a copolymer of 
ethylene and propylene, where the proportion of ethylene is from 2-8%, a 
terpolymer of ethylene, propylene and butene-1, etc. This skin surface can 
be any material which will aggressively receive thereon a coating of a 
pressure sensitive adhesive. This aggression must be sufficient to 
maintain the adhesive in contact with the skin layer when separation 
occurs between the adhesive and a release surface carrying the same. 
The essence of the present invention involves employing a particular 
polymeric blend which results in a layer having excellent receptivity to 
impact and thermal printing methods. The resulting surface can be printed 
with high speed equipment that is present in the industry, i.e., 400 lines 
per minute. The resulting coating has excellent ink adhesion and smear 
resistance both dry and in the presence of water. This ensures that bar 
coding is not jeopardized by ambient conditions. 
This polymeric blend is a combination of a mixture of (A) and (B). (A) is 
one or more alkylene acrylate copolymer. These copolymers have an alkylene 
group having 2-6 carbon atoms and an alkyl ester group having from 1-8 
carbon atoms. These compounds are disclosed, for example, in U.S. Pat. No. 
3,845,163 incorporated herein in its entirety by reference. This type of 
polymer is prepared by copolmerizing an olefin, for example, ethylene or 
propylene, with one or more of the following monomers: a C.sub.1 -C.sub.8 
alkyl acrylate, for example, methacrylate, ethylacrylate, hexylacrylate 
and the like; a C.sub.1 -C.sub.8 alkyl methacrylate, for example, methyl 
methacrylate, ethyl methacrylate, hexyl methacrylate and the like; and 
acrylic acid or methacrylic acid. Preferred are copolymers of ethylene 
with an alkyl ester of acrylic acid. In general, the acrylate content or 
methacrylate content of the copolymer may be from approximately 10 to 
approximately 30% by weight. The olefin content of the copolymer may be 
from approximately 70 to approximately 90% by weight. An example of the 
last-mentioned copolymer is an ethylene-ethylacrylate copolymer with a 
weight ratio of ethylene to ethylacrylate of approximately 4.1 to 1. 
Commercially available material of this type includes ethylene-methyl 
acrylate copolymer identified as Chevron Chemical Company PE 2205, having 
a methylacrylate content of 20% by weight, and a melt flow index of 2.4 
gm/10 min. (ASTM D-1238), ethylene-acrylate acid copolymer having an 
acrylic acid content of about 6.5% and a melt flow index of 9.0 gm/10 
min., available as Dow Primacor 3340 grade; ethylene-acrylic acid 
copolymer available as Dow Primacor 1430; and ethylene acrylic acid 
copolymer available as Dow Primacor 5991. A particularly preferred 
copolymer is obtained as a water emulsion from Michelman, Incorporated and 
is a 25% solids dispersion of Dow Primacor 5980. This material consists of 
ethylene copolymerized with acrylic acid. 
The (B) component of the blend is typified by an interpolymer of (a) from 
2.5 to about 6 parts by weight of an alpha-beta monoethylenically 
unsaturated carboxylic acid selected from the group consisting of acrylic 
acid, methacrylic acid and mixtures thereof and (b) from about 97.5 to 
about 94 parts by weight of neutral monomer esters, said neutral monomer 
esters comprising (1) methyl acrylate or ethyl acrylate and (2) methyl 
methacrylate, said interpolymer comprising from about 30% to about 55% by 
weight of methyl methacrylate when said alkyl acrylate is methylacrylate, 
and from about 52.5% to about 69% by weight of methyl methacrylate when 
said alkyl acrylate is ethyl acrylate; said mixture containing inert 
inorganic fillers; and on the other side thereof an adhesive layer. 
Material of this type is described in U.S. Pat. No. 3,753,769 the 
disclosure of which is incorporated in its entirety. A preferred material 
is that described in Example 1 of the '769 patent. 
The polymeric blend of (A) and (B) is prepared as a water based coating 
formulated as a 20-40% solids dispersion, preferably 30% solids 
dispersion. The composition can include absorptive, opacifying or 
whitening inert particles, such as, absorptive silica, calcium carbonate, 
TiO.sub.2, etc. A typical coating composition can include the following: 
______________________________________ 
COATING INGREDIENT PERCENT DRY 
______________________________________ 
(A) alkylene acrylate copolymer 
35-55% 
(B) interpolymer 4-10 
Silica 20-40 
Calcium carbonate 5-20 
______________________________________ 
This coating composition is applied to the selected base or core material. 
For example, a product sold by Mobil Chemical Company and identified as 
140LL302 LabelLyte.RTM. can be employed. This product is a 3 mil, white 
opaque label product consisting of a cavitated homopolymer polypropylene 
core with skin layers on opposite surfaces. The layer which is coated with 
the polymer blend of the present invention is a medium density 
polyethylene with a titanium dioxide filler. The opposite skin layer is a 
homopolymer polypropylene with a calcium carbonate filler. The coating can 
be applied in a secondary coating process. This refers to a process by 
which the film is coated in a process separate from the process forming 
the base or core material. A polymer blend composition can be applied by 
rod coating technology or by reverse direct gravure techniques. The 
coating weight of the label stock material can range from approximately 
1-5 grams, preferably 2 grams per MSI. The following example illustrates a 
coated label stock within the scope of the present invention. 
EXAMPLE 
A 3 mil thick three layer LabelLyte.RTM. film as described above, was 
coated on the medium density polyethylene side with 2 grams per MSI of the 
following 30% solids water based composition: (A) Dow 5980-ethylene 
copolymerized with acrylic acid, % dry 45%; (B) the interpolymer of methyl 
acrylate, methyl methacrylate, and methacrylic acid, % dry 5%, silica 35% 
and calcium carbonate 15%. 
This coating structure has been found to be excellently compatible with 
impact and thermal printing methods and can be printed at 400 lines per 
minute. 
In the art of labeling, the label which is to be applied to a surface or a 
product is normally carried by a release sheet or surface. A common 
example of this type of label structure, familiar to most automobile 
owners, is the county or city registration sticker which must be applied 
to the windshield of a car. This type of structure comprises a release 
sheet, one side of which has a release surface of a silicon material or 
the like. Carried on this surface is a pressure sensitive adhesive and 
applied to the pressure sensitive adhesive is the label or decal to be 
applied to the windshield. The adhesive may be applied either to the label 
or the release liner. When the decal or label is separated from the 
release sheet the pressure sensitive adhesive preferentially adheres to 
the label or decal and by this means is affixed to the windshield of the 
car. For the labeling of cans or bottles, obviously a more automated 
system must be employed. Providing for a more or less continuous labeling 
system, a continuous release roll is prepared by applying to one side of a 
continuous substrate which is preferably a polymeric film and still more 
preferably a polypropylene film and which may be of a single or multiple 
layers, a release coating of silicon or the like. Thereafter, for example, 
the release face of the release liner of the type described above is 
coated with a layer of pressure sensitive adhesive. Thereafter, a label 
stock as described above which has been or will be printed with the 
appropriate label indicia, is brought into mating contact with the 
pressure sensitive adhesive. Following this mating, printing can be 
accomplished, if not already completed and individual labels can be 
die-cut severed in a manner well known to the art. Following this 
procedure, labels then can be sequentially, individually applied to a 
product surface by causing the individual labels to separate from the 
release surface and having the adhesive side of the label contact and 
product to be labeled. 
As indicated above, instead of a pressure sensitive adhesive, activatable 
adhesives can be employed for certain labeling techniques. For instance, 
when a label is to be applied about the full circumference of a package or 
bottle, a water or other solvent can activate an adhesive stripe or strip 
applied to one end of the label. The label is then fixed in place by a 
slight overlap of the other end of the label. 
It should be evident that this disclosure is by way of example and that 
various changes may be made by adding modifying or eliminating details 
without departing from the fair scope of the teaching contained in this 
disclosure. The invention is, therefore, not limited to particular details 
of this disclosure except to the extent that the following claims are 
necessarily so limited.