Method of producing a non-tacky hot melt adhesive containing package

A method of producing a tackless hot melt adhesive package by using a hydrogenated castor oil coating material and a low pressure, melt blow application technique, wherein the hydrogenated castor oil is melt blown through orifices to form droplets which deposit a thin adherent coating in a cavity, then a hot melt adhesive is cast into the cavity.

BACKGROUND OF THE INVENTION 
This invention relates to a package containing a tackless or nonblocking 
hot melt adhesive and to the method for producing such packaging wherein a 
selected wax coating material and a low pressure, melt blow application 
technique are used. 
Hot melts adhesives which are generally applied and distributed while in 
the molten or liquid state are solid at room temperature. Typically, these 
adhesives are provided in the form of blocks and because of the nature of 
these materials, particularly the pressure sensitive hot melts, there are 
problems associated with handling and packaging them. Blocks and other 
forms of these materials not only stick or adhere to hands or mechanical 
handling devices and to each other, but they also pick up dirt and other 
contaminants. Additionally, certain applications which require high tack 
formulations result in blocks that will deform or cold flow unless 
supported during shipment. The need and advantage of providing a tackless 
or non-blocking adhesive is therefore quite apparent and various ways of 
accomplishing this have been tried and developed over many years. 
Japanese Patent Bulletin 48-103635 published Dec. 26, 1973 discloses a 
granular adhesive which is tacky at room temperature and coated or 
enveloped with a non-tacky, hot meltable material that is the same type or 
is miscible or mixable with it. 
French Patent 2,544,654 published Oct. 26, 1984 discloses forming a 
tackless hot melt by adding molten hot melt to a mold containing a 
preformed support layer having a transfer film thereon and which is 
compatible with the hot melt. 
U. S. Pat. Nos. 4,748,796 issued Jun. 12, 1988 and 4,755,245 issued Jul. 5, 
1988 disclose forming a protective coating for an adhesive material by 
electrostatically coating a mold or cavities with a powder screen and then 
pouring hot melt into the mold. 
French Patent 2,601,616 published Oct. 22, 1988 discloses forming blocks of 
hot melt pressure sensitive adhesives by casting the pressure sensitive 
adhesive into molds precoated by spraying with a film of non self-sticking 
hot melt material thereby forming a fusible non-tacky veil around the 
pressure sensitive block. 
Various other methods of making tackless hot melt adhesives have also been 
developed. However, despite all these techniques which include many 
alleged compatible, non-adhesive coating materials and a number of 
different application systems and equipment, there are still problems in 
producing a thin, continuous, adherent coating which is completely 
compatible with the hot melt adhesive and most important is not brittle 
and will not flake or rub off during handling. 
SUMMARY OF THE INVENTION 
Now in accordance with this invention, a package containing a tackless 
pressure sensitive hot melt adhesive is provided by the use of a selected 
high melting, hard wax coating material which is applied using a low 
pressure, melt blow application technique. 
More particularly, the tackless pressure sensitivity hot melt adhesive 
package of this invention is provided by melt blowing molten hydrogenated 
castor oil through orifices of a heated die plate into a fine stream of 
hot inert gas which surrounds or curtains the molten hydrogenated castor 
oil forming droplets which deposit a thin, adherent and uniform coating 
into a preformed support cavity, the molten hydrogenated castor oil being 
at a temperature of about 190.degree. F. to 300.degree. F., the gas being 
at a temperature of from about 190.degree. to 300.degree. F. and a 
pressure of from about 10 to 50 psig, the hydrogenated castor oil flow 
rate being sufficient to deposit a thin, uniform coating of about 0.05 to 
1% by weight of hydrogenated castor oil based on the weight of hot melt 
adhesive, and after coating, casting the pressure sensitive hot melt into 
the coated cavity. The invention provides a convenient means of storing 
and shipping hot melt adhesives, including those susceptible of blocking 
when shipped and stored in accordance with conventionally known procedures 
.

DETAILED DESCRIPTION OF THE INVENTION 
The tackless pressure sensitive adhesive package of this invention involves 
two distinct and significant aspects, i.e., a selected hard wax coating 
material and a particular melt blow application technique. 
While various compatible materials have been suggested for use as a coating 
material for forming tackless adhesives including the hot melt polymers 
and copolymers, waxes and paraffins, not all have given the results 
desired especially being able to provide a thin, uniform compatible 
coating which will adhere to the hot melt and is not brittle or flaky, 
particularly when a release agent such as silicone is first applied to the 
cavity package. In this invention, a very selected high melting, hard wax 
is used to provide the tackless or non-tacky coating. This hard wax is 
hydrogenated castor oil or the triglyceride of 12-hydroxystearic acid. The 
hydrogenated castor oil wax material is a well known commercially 
available material sold under tradenames such as Castorwax, Opalwax, 
Ric-syn Wax, Cenwax G and Sanfol 101-E. This wax material which is 
compatible with hot melt adhesives has a melting point of about 
185.degree. to 192.degree. F. (85.degree. to 89.degree. C.), a hydroxy 
value of about 155 to 160 and a penetration hardness of about 2. Other 
variations of this wax such as Castorwax MP 70 and 80 which have similar 
properties may also be used. 
In combination with the selected wax coating composition described above, 
the ability to provide the desired coating results from the use of a 
particular low pressure melt blow application technique. Many different 
application procedures have been used or tried to provide tackless 
coatings on an adhesive including brushing, rolling, spraying and 
electrostatic coating. The suitability of a particular application 
technique depends on the selected coating material and the desired 
characteristics of the coating. It has been difficult to find a suitable 
coating material and application system which will provide a thin, 
uniform, compatible coating for the pressure sensitive hot melt adhesive 
that is not only completely compatible and does not reduce adhesion but 
also is not brittle or flaky, particularly when used in a flexible cavity, 
including one that is coated with a release agent. The melt blow 
application, as described hereinafter, when used in combination with the s 
defined hard waxy material surprisingly provides a desired thin, 
continuous coating that adheres well and does not flake off when handled. 
The coating application technique as used in this invention is a low 
pressure, melt blow procedure similar to that described in U.S. Pat. Nos. 
3,755,527 issued Aug. 28, 1973; 3,978,185 issued Aug. 31, 1976 and 
4,048,364 issued Sep. 13, 1977 and can be better understood from a review 
of FIG. 1 which schematically illustrates the process. As shown in the 
drawing, the wax coating material is added through inlet hopper 1 and 
melted in heating chamber 2 before it is pumped by pump 4 into the nozzle 
die head 3. The die head contains heating means (not shown) with leads to 
the heater as shown, to control the temperature of the nozzle die head. 
The gas or air stream which blows or disperses the molten wax into small 
droplets is provided through gas outlet slots or jets (not shown) in the 
die head. As shown in FIG. 2, the hot gas curtains or envelopes the molten 
coating material as it exits one of the orifices in the die plate. These 
gas slots are supplied with hot gas by inlet gas lines shown in FIG. 1. 
The molten wax is forced out of a row of nozzle orifices or die openings 
in the nozzle die head into a gas stream which provides a fine spray or 
stream of wax droplets into an open cavity which is moving on a conveyor 
belt or other moving device. 
The wax coating material is heated in the heating chamber to a temperature 
of from about 190.degree. to 300.degree. F. and preferably from about 
200.degree. to 250.degree. F. and remains at this temperature when it 
reaches the orifices in the heated nozzle or die head. The gas, which is 
an inert gas, preferably air, is provided at a temperature of about 
190.degree. to 300.degree. F., preferably from about 200.degree. to 
250.degree. F., and is generally at the same or slightly higher 
temperature than the nozzle die temperature. Air pressure is generally at 
about 10 to 50 psig, preferably from about 20 to 40 psig. 
The flow rate for the wax coating material will vary depending on the 
amount of coating deposit desired and the rate of speed at which the 
support cavities are being fed into the system. Generally, the rate of the 
wax and air flows will be an amount that will effectively provide a thin, 
uniform coating deposit and more particularly this will be from about 0.05 
to 1% by weight, preferably 0.1 to 0.5% and more preferably 0.1 to 0.3% by 
weight of wax based on the total weight of the hot melt adhesive. When 
feeding cavities at the rate of 16 ft/min, the wax flow rate will 
typically vary from about 50 to 750 g/min and preferably from about 70 to 
400 g/min. The air will be at a flow rate of generally from about 3 to 50 
SCFM and more particularly from about 5 to 20 SCFM. The distance between 
the die head and the bottom of the cavity as shown in FIGS. 1 and 2 can be 
varied as desired depending on other conditions to get the desired 
coating. Generally the distance may vary between 1 to 10 inches and more 
particularly between 1 to 5 inches. 
While the conditions, particularly temperatures and flow rates and pressure 
may be varied as described above, the important aspect of this invention 
is that the discrete molten droplets of coating wax that are formed when 
leaving the die head remain at a relatively high, near molten or higher 
temperature when it is deposited in the cavity to obtain a good adherent 
coating. 
The hot melt adhesive used in the invention may be any of the known 
materials used for this purpose including polymers and copolymers of 
synthetic resins, rubbers, polyethylene, polypropylene, acrylics, vinyl 
acetate, ethylene vinyl acetate and polyvinyl alcohol. Examples of 
representative adhesives include those based on: 
a) rubber polymers such as block copolymers of monovinyl aromatic 
hydrocarbons and conjugated diene, e.g., styrene-butadiene, 
styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), 
styrene-ethylene-butylene-styrene (SEBS), and 
styrene-ethylene-propylene-styrene (SEPS); 
b) ethylene-vinyl acetate polymers, other ethylene esters and copolymers, 
e.g., ethylene methacrylate, ethylene n-butyl acrylate and ethylene 
acrylic acid; 
c) polyolefins such as polyethylene and polypropylene; 
d) polyvinyl acetate and random copolymers thereof; 
e) polyacrylates; 
f) polyamides; 
g) polyesters; and 
h) polyvinyl alcohols and copolymers thereof. 
Most often such adhesives are formulated with tackifying resins in order to 
improve adhesion and introduce tack into the adhesive. Such resins include 
(a) natural and modified resins, (b) polyterpene resins, (c) phenolic 
modified terpene resins, (d) coumarons-indene resins, (e) aliphatic and 
aromatic petroleum hydrocarbon resins, (f) phthlate esters and 
g)hydrogenated hydrocarbons, hydrogenated rosins and hydrogenated rosin 
esters. 
Desirable optional ingredients include diluents, e.g., liquid polybutene or 
polypropylene, petroleum waxes such as paraffin and microcrystalline 
waxes, polyethylene greases, hydrogenated animal, fish and vegetable fats, 
mineral oil and synthetic waxes. In some cases, an essentially hydrocarbon 
oil is required in the formulation, typically called naphthenic or 
paraffinic mineral oils. 
Other optional additives may include stabilizers, antioxidants, colorants 
and fillers. 
The selection of components and preparation of hot melt adhesives is well 
known in the art and described in the literature. 
The cavity or support or tray which forms part of the pressure sensitive 
hot melt package may be any of the materials known to be useful for this 
purpose including polypropylene and polyethylene, polyester sheets, 
polycarbonate, rubber modified polystyrene, polyamide (nylon), paper 
including paper coated with polyester or cardboard, silicone rubber and 
teflon. Filled polypropylene (e.g., filled with talc or titanium dioxide) 
is a preferred material for the preformed support cavity. The term support 
cavity as used herein includes cavities, supports, trays and other forms 
made of the above and similar materials and which make up this package 
containing the pressure sensitive hot melt adhesive. It is further noted 
that the support cavity used in making up the adhesive package of this 
invention and containing the tackless hot melt adhesive can be used as a 
shipping and or storage container. It is also noted that after the hot 
melt adhesive is cast into the open and coated preformed support cavity, a 
similar melt blown deposit may be coated on the uncoated hot melt adhesive 
(surface) or a lid or top (may be made of same material as rest of support 
cavity) precoated with hydrogenated castor oil can be pressed against the 
uncoated hot melt adhesive surface. 
A release agent is most often used to ease separation of the package or 
support cavity from the tackless hot melt adhesive at the time of use. 
Materials useful as release agents include silicone, fluoropolymers and 
polyolefins with silicone being preferred in this application. 
The following examples will further illustrate the embodiments of this 
invention. In the examples all parts are by weight unless otherwise 
indicated. 
EXAMPLE 1 
A tackless pressure sensitive hot melt adhesive package was produced as 
follows. An open flexible polypropylene filled (talc) film capable of 
withstanding high temperatures was initially given a thin coating of 
silicone and this film was thermoformed to form cavities of a desired size 
(4.5.times.10.5.times.4 inches). Following this, with the silicone coating 
on the interior surface, a thin, continuous coating of hydrogenated castor 
oil (Castorwax) was melt blown using an application technique similar to 
that shown in FIGS. 1 and 2 and described in the specification. 
Application conditions were as follows: a wax temperature of about 
230.degree. F., an air temperature of about 230.degree. F. with air 
pressure of 25 psig. The wax and air flow rates were adjusted to give 
droplets forming a suitable continuous thin coating corresponding to a 
coating of about 0.2% by weight based on the total weight of the hot melt 
adhesive. 
A hot melt adhesive comprising a Kraton styrene-butadiene rubber elastomer, 
paraffin oil and a hydrocarbon tackifying resin was cast into the coated 
open cavity. A similar thin, continuous coating was applied to the 
previously uncoated top of the hot melt adhesive package. 
Separating the polypropylene package material from the hot melt showed a 
tackless smooth adhesive block with an adherent coating that did not flake 
or rub off when handling either the full package or separated block. 
Further use of the adhesive indicated good compatibility between the hot 
melt and the adhesive and most important the properties of the hot melt 
adhesive were not altered or modified in any significant way.