High friction package retainer

In order to stabilize stacks of cartons of consumer products which have ultra-low friction, glossy, point of sales graphics surfaces, on a pallet, without having to package the cartons in an outer container such as a corrugated cardboard box or the like, high-friction tie sheets are used between each superimposed layer of the carton. Each tie sheet has opposed ultra-high friction surfaces with a coefficient of friction of at least 0.8, up to 0.9 or even higher to itself.

BACKGROUND OF THE INVENTION 
This invention relates to the handling of cartons which have an ultra-low 
friction outer surface, such as cartons of consumer products and the like. 
More and more commonly, consumer products such as soap powders, breakfast 
cereals, beverages and the like are packaged in containers having a 
vividly printed graphic outer surface, to provide advertising and to 
attract consumers' attention at points of sale. This trend toward high 
visibility graphics minimizes the need for display ads in self-service 
stores because the packages themselves function to present information in 
up to seven colors. Moreover, new retailing entities, such as the 
so-called club stores or discount stores, which are increasing in 
popularity, find they can sell more merchandise if is displayed in highly 
visible, eyecatching packaging. 
The demand for more attractive containers has revolutionized the packaging 
surface itself so that it is more receptive to the new panoply of high 
visibility inks, graphics, and even hologram displays. All of these 
surfaces require a glossy overprint varnish which enhances the attractive 
presentation and maintains the integrity of the package graphics during 
filling, transportation and handling of the containers in general. Almost 
without exception, these high gloss overcoats produce ultra-low friction 
surfaces which are extremely slick or slippery. In fact, in the absence of 
these very low friction surfaces, the packages would rub together and 
thereby abrade and distort or destroy the graphic presentation. Also, with 
the high speed filling equipment currently in use, less slippery container 
surfaces tend to cause jam-ups, slow-downs and other undesirable 
production problems. 
For all of the foregoing reasons, and others, this demand for ultra-low 
friction packaging surfaces will undoubtedly intensify with time. However, 
the very slipperiness of the product containers presents particular 
problems with respect to transporting the merchandise from manufacturer to 
wholesaler to retailer, and ultimately to display areas for the consumer 
in the store. 
Due, at least in part, to their high gloss outer surfaces, it is generally 
difficult to directly palletize the product packages for transfer through 
the merchandise chain. Therefore, the individual cartons are commonly 
packed batchwise in containers or boxes which may themselves be more 
readily palletized. The boxes, generally made of corrugated paper or 
cardboard inherently have a higher coefficient of friction than the high 
gloss cartons and are, therefore, more readily handled and transported. 
Sometimes, even the cardboard boxes are treated with a heavy coating of a 
normal or conventional nonskid material, such as colloidal silica or 
alumina, to increase their frictional properties, and, thereby, facilitate 
palletizing the boxes for handling and transportation. 
The use of such corrugated cardboard boxes obviously increases the cost of 
merchandising the product. For example, one must consider the cost of the 
boxes themselves, as well as the economic and environmental costs of 
recycling or destroying the boxes after use. Further, the labor and 
equipment costs in packing and unpacking the boxes exceeds the cost of the 
boxes themselves by many times. Such costs are undesirable, at best. In 
certain instances, such as in the club stores where prices are discounted 
and profit margins are limited to start with, these additional costs can 
become totally unacceptable. 
Various concepts have been tried to minimize these problems. Packing boxes 
have been devised with almost "picture frame" sides, so that the inner 
contents are visible. Half-height trays have been used to facilitate 
displaying the high gloss merchandise. These "solutions" present their own 
obvious problems. 
Entire pallets of individual product cartons have been stabilized for 
shipping by overwrapping horizontally with multiple turns of thin plastic 
film material such as stretch wrap. This approach effectively cocoons the 
cartons and avoids the needs for packing and unpacking cardboard boxes. 
However, palletized product cartons wrapped in this manner are still 
highly unstable and difficult to transport without carton movement. With 
high gloss product cartons, the instability of the pallet is such that 
simply transferring the stacked cartons to the stretch wrapper causes the 
cartons to slide relative to each other. Moreover, removing the stretch 
wrap, or attempting to move the pallet by a conventional fork lift truck 
from the receiving area in a club store or the like, to the merchandising 
floor for display once the stretch wrap has been removed, will also 
disrupt and destroy the stack. Therefore, further handling of the product 
cartons, either by individually placing them on shelves, or restacking 
them in some other fashion for display, becomes necessary. 
The use of paper sheets between the layers of a pallet to help stabilize 
the pallet is a well-established, but infrequently used, practice. These 
sheets are variously known as tier sheets or tie sheets, or slip sheets in 
the case of one on the bottom for full pallet handling. They can be made 
of light to heavy weight kraft paper, or recycled chipboard sheets of 
various calipers, from 0.010 to 0.030 inches, depending on costs and 
conditions of use. In some rare instances, these pallet-sized sheets have 
had a conventional non-skid, such as colloidal alumina or silica, applied 
to one side to impart a modicum of slip resistance. The benefit, however, 
is usually minimal and in the instant case, with glossy, high graphic 
cartons, usually of no apparent benefit in handling. 
SUMMARY OF THE INVENTION 
It is evident that economies in materials and handling costs will accrue if 
the need for batchwise packing and unpacking of high gloss product 
packages in corrugated boxes and the like could be eliminated, and the 
individual cartons could be palletized directly. It is, therefore, a 
primary object of this invention to provide a means to stabilize a pallet 
of ultra-low friction, high gloss, product cartons so as to permit 
palletized stacks of such products to be delivered to a merchandising 
outlet and displayed for consumers with a minimum of labor intervention. 
More specifically, the instant invention provides tie (or slip) sheets 
treated to provide both sides of the sheet material with an ultra-high 
coefficient of friction, and a pallet carrying a plurality of layers of 
high gloss product cartons having point of sales graphics, stabilized by; 
interposition of such tie sheets between adjacent layers. 
A generally accepted test for slipperiness is TAPPI T-815, which is the 
inclined plane slip angle method and all references herein to slip angles 
are with reference to that test method. 
When the surface of the product container exhibits a slip angle to itself, 
according to the TAPPI test, that is, two like surfaces placed against 
each other, of 10.degree. or less (coefficient of friction of about 
0.194), handling becomes an impossibility--on the order of new plastic 
playing cards. If the slip angle between two adjacent like packages is 
about 12.degree.-14.degree. (coefficient of friction about 0.21 to 0.25 ), 
handling of such packages on a pallet is difficult, at best. Generally 
speaking, any two things that exhibit a slip angle against each other 
below about 16.degree.-17.degree. (coefficient of friction about 0.3) is 
quite difficult to handle, and without special care and handling will 
engender some damage. Therefore, the instant inventive concepts are 
directed to palletizing high gloss product cartons with point of sales 
graphics having an outer surface with a slip angle to itself of less than 
18.degree., according to TAPPI T-815. 
The invention provides tie sheets (or slip sheets) having a substrate which 
is preferably made of chipboard, i.e., board material made from recycled 
paper, similar to that used as shirt boards or tablet backs, or heavy 
liner (or kraft) paper, i.e., the paper commonly used to make the inside 
and outside of an ordinary corrugated box. Both surfaces of the substrate 
are treated to provide an ultra-high coefficient of friction (on the order 
of at least about 0.8, and, preferably, even 0.9 or more), to itself, and 
a slip angle to itself in the range of at least about 40.degree., even up 
to 50.degree. or more. The sheets are used between juxtaposed layers of 
rows of cartons having a high gloss, ultra-low friction surface, to enable 
the cartons to be stacked with sufficient stability against slippage for 
normal handling. By using the sheets in this manner, the slip angle 
between the surface of a stacked carton and a juxtaposed tie sheet 
surface, i.e., the effective slip angle between one layer of cartons and 
the next, can be increased to a level of 22.degree.-35.degree.. This 
resistance to movement enables the cartons to be palletized and handled or 
transferred without the need to batchwise pack the individual cartons in 
an outer container such as a corrugated box or the like. 
Additional features and advantages of the invention will become apparent 
from the ensuing description and claims read in conjunction with the 
accompanying drawing.

DESCRIPTION OF PREFERRED EMBODIMENTS 
FIG. 1 shows a stack 10 illustratively comprising three layers 12, 14 and 
16, of individual high gloss cartons 20 formed on a conventional wooden or 
other pallet 25, with tie sheets 30 according to this invention interposed 
between the adjacent layers of the stack. An optional wrapping of plastic 
material securing the stack 10 for shipment is shown partially broken away 
at 35. 
The cartons 20 may, for example, comprise packages of consumer products, 
such as breakfast cereal, soap powder or the like which have printed outer 
surfaces with point of sales graphics schematically shown at 22, covered 
by a high gloss, ultra-low friction coating typically having a slip angle 
against itself of less than 18.degree. (coefficient of friction of less 
than 0.3). Because of the low slip angle between such cartons, the stack 
would heretofore collapse when moved while the stack was being taken to 
the stretch wrapper, during transportation, even after stretch wrapped, 
and when the stretch wrap was removed, making direct display, or even 
limited movement of the palletized stack, virtually impossible. 
According to the instant invention, however, the tie sheets 30 interposed 
between the respective layers 12, 14 and 14, 16, dramatically increase the 
slip angle therebetween. In order to accomplish this result, the tie 
sheets must have both sides treated to provide an ultra-high friction 
surface, typically on the order of about 0.8 to 0.9 or higher (to each 
other), so that when positioned between the cartons, the slip angle 
between each carton and the juxtaposed tie sheet is 18.degree. or more, 
preferably from about 22.degree.-25.degree.. 
When a conventional wooden pallet is used, as illustrated at 25, it is not 
generally necessary to provide an ultra-high friction slip sheet according 
to this invention under the lowest row 12 of cartons 20. For pallets with 
lower friction surfaces, however, a slip sheet similar to the tie sheets 
30 may be used. 
The preferred construction of a tie sheet 30 according to this invention is 
schematically shown in FIGS. 2 and 3. Each sheet 30 comprises a central 
substrate 32 dimensioned to suit the stack of cartons, and which may be a 
chipboard, or a kraft linerboard paper or the like. Each surface of the 
substrate is coated with an ultra-high friction tackified coating 34, 
providing a surface coefficient of friction of about 0.8 -0.9 to itself. 
To manufacture tie sheets 30 according to their invention, a suitable 
substrate 32 of chipboard, for example, can be provided on each side with 
a coating 34 of a pressure-sensitive latex formula that has been modified 
to retain a slightly tacky character. Any pressure sensitive resin or 
latex may be employed that is capable, upon modification, of providing a 
slightly tacky surface when coated on paper over long periods of time and 
which will release from itself when stacked or in roll form. Of course, 
the relative thickness of the coating layers 34 is exaggerated in the 
drawing for illustrative clarity. In practice each layer will generally be 
less than 1% of the total thickness of a tie sheet 30. 
While unsized chipboard or kraft paper may be used as a substrate, this can 
lead to variable results where the degree of tackiness and release may 
vary with age. Therefore, particularly in the case of chipboard, it is 
preferred that the substrate 32 be sized to a standard 10 minutes water 
drop test (according to the TAPPI T-432 test, the time for a predetermined 
drop of water to wet the board). In the case of linerboard, further 
treatment is usually not necessary since such materials are commonly sized 
to industry standards, which are sufficient for use in this invention. 
With linerboard, the preferred material for this invention has a weight of 
from about 26 to about 90 pounds per thousand square feet. 
The paper or chipboard substrate can be coated by any one of many coating 
techniques known in the paper coating art, and by known coating apparatus 
such as three roll coaters, air knife coaters, wound wire coaters, and the 
like, followed by a conventional drying oven. The coating may be applied 
separately to opposite sides of the substrate, or simultaneously in a 
suitable device capable of coating and drying both sides of the substrate 
in one path. Also, the coating may be applied to cover each entire surface 
of a tie sheet 30, or the coating may be patterned, for example, as 
checkerboard squares, stripes, grid work or the like. 
The invention is further illustrated in the following example: 
EXAMPLE 1 
Pallet-sized tie sheets according to this invention were made from 
substrates of 30 point chipboard, sized to 10 minutes water drop test. The 
substrates are passed through a three roll coater with rubber-coated, 5 
inch diameter, rolls containing a coating consisting of 90 weight % PS-61 
from Rohm & Haas and 10 weight % Jonwax 39 from Johnson Wax Co. PS-61 is a 
modified acrylic backbone pressure sensitive adhesive; Jonwax 39 is a wax 
emulsion which provides for release between the coated sheets and modifies 
the PS-61 so as to provide an enduring, slightly tacky character to the 
finished coated board. The sheets are then passed through a forced air 
convection drying oven to produce a 25.degree. slide angle against typical 
8.degree.-10.degree. angle slippery cartons, according to the TAPPI T-815 
test. The sheets are again passed through the equipment to coat the 
reverse side. 
The tie sheets made in this fashion were used between every layer of large 
soap box cartons having high gloss outer surfaces with point of sales 
graphics and a slip angle to themselves of about 8.degree.. Use of the tie 
sheets in the manner illustrated in FIG. 1 produced a slip angle between 
the respective tie sheets and the juxtaposed carton surfaces of 
22.degree., enabling the palletized cartons to be handled as required for 
normal merchandising without disruption to the stack, and with no need for 
the standard corrugated cardboard boxes commonly used to package such 
merchandise. 
The following Table illustrates the advantages of building a pallet using 
tie sheets according to this invention. In this Table, all slip angles are 
the average results of three tests according to the TAPPI T-815 test 
procedures. 
TABLE 
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2 
Slip Angle to 
3 
50% Recycled 
Slip Angle to Tie 
4 
Product with 
1 Corrugated Board 
Sheet According to 
Approximately Average 
Point of Sales 
Slip Angle 
a b Example 1 of this 
Change in Slip Angle 
Surface To Itself 
Untreated.sup.1 
Heavy NS.sup.2 
Invention a.sup.3 
b.sup.4 
__________________________________________________________________________ 
Tide Cartons 
10.degree. 
9.degree. 
9.degree. 
22.degree. 
-1.degree. 
12.degree. 
Coke 12 pak Cartons 
9 13 12 26 3 17 
Duralast Auto Parts 
13 14 14 32 1 19 
Preprint Corrugated 
Cartons 
Gordon's Gin 
14 12 12 32 -2 18 
Preprinted Corrugated 
Carton 
Chevron Preprint 
16 14 14 35 -2 19 
Corrugated Cartons 
Dove Preprint 
16 11 16 30 -2 14 
Corrugated Cartons Avg. 0 
+16.5.degree. 
__________________________________________________________________________ 
.sup.1 The recycled corrugated board has a slip angle to itself according 
to TAPPI T815 of about 18.degree.. 
.sup.2 When the same corrugated board surface is treated with a heavy 
coating of a normal or conventional nonskid (NS) such as colloidal silica 
the slip angle to itself is increased to about 36.degree.. 
.sup.3 Difference between Column 1 slip angle and average of Columns 2a 
and 2b. 
.sup.4 Difference between Column 1 slip angle and Column 3. 
In the above Table, Column 1 shows representative slip angles for a number 
of commercial point of sale high graphics packages. These packages range 
from glossy coated large and small cartons to different kinds of preprint 
corrugated, i.e., where the outside liner of the corrugated sandwich is 
preprinted with multicolor graphics and coated with a gloss varnish so 
that when the corrugated box is completed, it has a most striking graphic 
impact. As can be seen, the slip angles of such common commercial packages 
to themselves, range from 9.degree. to 16.degree., all below the level at 
which they could be effectively palletized without need for batchwise 
packaging in corrugated boxes or the like. 
The comparison of Column 2 with Column 1 shows the ineffectiveness of 
ordinary corrugated board, whether untreated, or even treated with a heavy 
coating of conventional nonskid, such as colloidal silica, in stabilizing 
a stack of such high gloss commercial cartons. Column 2a shows that the 
slip angle, when the high gloss containers are tested against an untreated 
corrugated board, are essentially unchanged. Even with the use of a 
nonskid treated corrugated board, unacceptably low slip angles are seen. 
This minimal improvement in slip angle, when the high gloss containers are 
tested against corrugated boards having a heavy nonskid coating, is 
surprising when it is recognized that the slip angle of the corrugated 
board against itself is raised from 18.degree. to 36.degree. when provided 
with a nonskid coating. Compare footnotes 1 and 2 to the Table. 
In any event, it is clear that tie sheets, whether untreated, or treated 
with a heavy coating of conventional nonskid, fail to provide sufficiently 
better handling when interposed between the slippery high graphics 
surfaces of common commercial products. 
Column 3 tabulates the results of testing the commercial package surfaces 
against tie sheets treated on both sides according to Example 1 above. The 
results, taken in aggregate are listed in Column 4 and show that, in 
contrast to the relative ineffectiveness using tie sheets of the prior 
art, whether treated with nonskid or not, (average increase in slip angle 
as compared to the use of no tie sheet at all equals zero), the use of tie 
sheets according to this invention evidence an appreciable increase in the 
slip angle (average increase of 16.5.degree.). This increase in slip angle 
provides a significant improvement in the stability of the stacked cartons 
and in handling effectiveness. 
While only preferred embodiments of the invention have been described 
herein in detail, the invention is not limited thereby, and modifications 
can be made within the scope of the attached claims.