Anti-blocking coating for pressure sensitive adhesives using cellulose acetate butyrate

A composition comprising a hot melt adhesive; and a coating for the adhesive comprising cellulose acetate butyrate, wherein the cellulose acetate butyrate is coated on the hot melt adhesive, and a method to prevent blocking of hot melt adhesives comprising coating cellulose acetate butyrate on at least a portion of the surface of a hot melt adhesive.

FIELD OF THE INVENTION 
This invention relates to a new anti-blocking agent for hot melt pressure 
sensitive adhesives (HMPSAs). The anti-blocking agent is a cellulose 
acetate butyrate (CAB) containing a high butyrate content. The agent is 
compatible with most commonly used HMPSA's and provides unexpected 
improvement in performance. 
BACKGROUND OF THE INVENTION 
The packaging, transportation, and storage of hot melt pressure sensitive 
adhesives presents a problem to industry because once formed, HMPSA 
particles tend to agglomerate or "block". HMPSAs are produced in a molten 
state at high temperatures. From the molten state, the adhesives are 
cooled to solid form and packaged in a form usable by application 
equipment. In order to reduce the thermal decomposition of the HMPSA at 
application temperatures, the melt reservoir of most application equipment 
is kept small enough to turn over the adhesive rapidly. For this reason, 
it is necessary to produce blocks, slats, or pellets of HMPSAs which can 
be manipulated easily by equipment operators and will fit into the 
openings of the melt reservoirs. 
There are two common methods to produce easily handled presentations of 
HMPSAs. One method is to produce relatively large (0.5-2 kg) blocks of 
material packaged in strippable containers such as silicone coated paper 
boxes or plastic films. Another approach is to produce smaller particles 
such as slats (an extruded ribbon of material cut into individual 
rectangular shaped pieces weighing 2-10 grams each) or pellets. Pelletized 
or slatted adhesives must be protected by the use of non-adhesive coatings 
to prevent the adhesives from blocking. 
In order to be effective, an anti-blocking coating must fulfill four basic 
requirements. First, the coating must be easily and efficiently applied to 
the adhesive particles. Second, the coating must provide storage stability 
for the adhesive under normal transportation, storage, and handling 
conditions. Third, the coating should combine with the adhesive when 
placed in the applicator. Finally, the coating should not diminish the 
adhesive properties of the HMPSA. 
Materials used for anti-blocking coatings include talc, powdered 
polyethylene, co-extruded polyethylene films, and polymeric coatings. 
Powders in general are of limited utility due to the tendency of HMPSAs to 
flow past the powder coating and block. Additionally, inorganic 
non-thermoplastic powders such as talc or calcium carbonate are insoluble 
in the HMPSA and can separate, causing plugging of the applicator. 
Co-extrusion or "sausage" wrapping of anti-blocking films require costly 
extra steps in the HMPSA production process. The most desirable types of 
anti-blocking coatings are those which can be applied to cooling molds or 
directly to the particles of adhesive. 
SUMMARY OF THE INVENTION 
We have discovered a new anti-blocking agent for HMPSA's which is thermally 
stable and compatible with most HMPSA's. The new anti-blocking agent is 
cellulose acetate butyrate ("CAB"). The most preferred CAB contains about 
55% by weight of the butyrate component and is compatible with most 
HMPSA's in a percentage range of 0.1 to 2.5 wt. %. The CAB unexpectedly 
improves the performance of the adhesive. 
In accordance with the purpose(s) of this invention, as embodied and 
broadly described herein, this invention, in one aspect, relates to a 
composition comprising: a hot melt adhesive; and a coating for the 
adhesive comprising cellulose acetate butyrate, wherein the cellulose 
acetate butyrate is coated on the hot melt adhesive. 
In another embodiment the invention provides a method to prevent blocking 
of hot melt adhesives comprising coating cellulose acetate butyrate on at 
least a portion of the surface of a hot melt adhesive. 
Additional aspects and advantages of the invention will be set forth in 
part in the description which follows, and in part will be obvious from 
the description, or may be learned by practice of the invention. The 
advantages of the invention will be realized and attained by means of the 
elements and combinations particularly pointed out in the appended claims. 
It is to be understood that both the foregoing general description and the 
following detailed description are exemplary and explanatory only and are 
not restrictive of the invention, as claimed. 
DISCUSSION OF THE INVENTION 
Before the present compounds, compositions, articles, devices and/or 
methods are disclosed and described, it is to be understood that this 
invention is not limited to specific synthetic methods, or specific 
compositions as such may, of course, vary. It is also to be understood 
that the terminology used herein is for the purpose of describing 
particular embodiments only and is not intended to be limiting. 
Use of Terms 
It must be noted that, as used in the specification and the appended 
claims, the singular forms "a," "an" and "the" include plural referents 
unless the context clearly dictates otherwise. Thus, for example, 
reference to "an adhesive" includes mixtures of adhesives compounds, 
reference to "a butyrate" includes mixtures of two or more such butyrates, 
and the like. 
Ranges may be expressed herein as from "about" one particular value, and/or 
to "about" another particular value. When such a range is expressed, 
another embodiment includes from the one particular value and/or to the 
other particular value. Similarly, when values are expressed as 
approximations, by use of the antecedent "about," it will be understood 
that the particular value forms another embodiment. When multiple 
embodiments are disclosed as successively narrower ranges, other 
embodiments include all of the mathematically possible ranges formed by 
combining the various endpoints. 
Definitions 
References in the specification and concluding claims to parts by weight, 
of a particular element or component in a composition or article, denotes 
the weight relationship between the element or component and any other 
elements or components in the composition or article for which a part by 
weight is expressed. Thus, in a compound containing 2 parts by weight of 
component X and 5 parts by weight component Y, X and Y are present at a 
weight ratio of 2:5, and are present in such ratio regardless of whether 
additional components are contained in the compound. 
A weight percent of a component, unless specifically stated to the 
contrary, is based on the total weight of the formulation or composition 
in which the component is included. 
A residue of a chemical species, as used in the specification and 
concluding claims, refers to the moiety that is the resulting product of 
the chemical species in a particular reaction scheme or subsequent 
formulation or chemical product, regardless of whether the moiety is 
actually obtained from the chemical species. Thus, an ethylene glycol 
residue in a polyester refers to one or more --OCH.sub.2 CH.sub.2 O--units 
in the polyester, regardless of whether ethylene glycol was used to 
prepare the polyester. Similarly, a sebacic acid residue in a polyester 
refers to one or more --CO(CH.sub.2).sub.8 CO--moieties in the polyester, 
regardless of whether the residue is obtained by reacting sebacic acid or 
an ester thereof to obtain the polyester. 
"Optional" or "optionally" means that the subsequently described event or 
circumstance may or may not occur, and that the description includes 
instances where the event or circumstance occurs and instances where it 
does not. For example, the phrase "optionally substituted lower alkyl" 
means that the lower alkyl group may or may not be substituted and that 
the description includes both unsubstituted lower alkyl and lower alkyl 
where there is substitution. 
By the term "effective amount" of a compound or property as provided herein 
is meant such amount as is capable of performing the function of the 
compound or property for which an effective amount is expressed. As will 
be pointed out below, the exact amount required will vary between 
processes and/or compounds, depending on recognized variables such as the 
compounds employed and/or the processing conditions observed. Thus, it is 
not possible to specify an exact "effective amount." However, an 
appropriate effective amount may be determined by one of ordinary skill in 
the art using only routine experimentation. 
Discussion 
We have discovered that a solution of cellulose acelate butyrate such as 
CAB-551-0.01 can be applied to particles of HMPSA to form an easily 
applied anti-blocking coating that provides storage stability, 
compatibility with common HMPSA systems, and does not detract from the 
adhesive performance of the coated adhesives. The only exception to the 
use of CAB is that systems subject to cold flow at room or elevated 
temperatures may rupture the coating and block. 
Thus, in one embodiment the invention provides a composition comprising: a 
hot melt adhesive; and a coating for the adhesive comprising cellulose 
acetate butyrate, wherein the cellulose acetate butyrate is coated on the 
hot melt adhesive. In another embodiment the invention provides a method 
to prevent blocking of hot melt adhesives comprising coating cellulose 
acetate butyrate on at least a portion of the surface of a hot melt 
adhesive. 
The cellulose acetate butyrate preferably comprises from about 17 wt. % 
butyryl to about 58 wt. % butyryl, from about 1 to about 38 wt. % acetyl, 
and from about 0.5 to about 5 wt. % hydroxyl. Even more preferably the 
cellulose acetate butyrate comprises from about 50 to about 58 wt. % 
butyryl, from about 1 to about 30 wt. % acetyl, and from about 1 to about 
2 wt. % hydroxyl. 
The compositions of this invention preferably comprise from about 95 to 
about 99.99 wt. % adhesive, and from about 0.01 to about 5 wt. % coating. 
The adhesive preferably comprises a styrene-isoprene-styrenc block 
copolymer, a styrene-butadiene-styrene block copolymer, a 
styrene-ethylene-butylene-styreiie block copolymer, an amorphous 
polyolefin, an ethylene-vinyl acetate, an acrylic, or a polyester. Of 
these, styrene-isoprene-styrene block copolymers, 
styrene-butadiene-styrene block copolymers, 
styrene-ethylene-butylene-styrene block copolymers, amorphous polyolefins, 
and ethylene-vinyl acetates are most preferred. 
The cellulose acetate butyrates of this invention preferably comprise 
repeat units having the following structure: 
##STR1## 
wherein: (i) R, R', and R" are independently butyryl, hydroxyl, or acetyl, 
(ii) the cellulose acetate butyrate comprises from about 17 wt. % to about 
58 wt. % butyryl, preferably from about 50 wt. % to about 58 wt. % 
butyryl, 
(iii) the cellulose acetate butyrate comprises from about 1 to about 38 wt. 
% acetyl, preferably from about 1 to about 30 wt. % acetyl, 
(iv) the cellulose acetate butyrate comprises from about 0.5 to about 5 wt. 
% hydroxyl, preferably from about 1 to about 2 wt. % hydroxyl, and 
(v) n gives a molecular weight of from about 10,000 to about 70,000, 
preferably from about 12,000 to about 30,000. 
In the methods of this invention the cellulose acetate butyrate is 
preferably present in the form of a solution or dispersion comprising from 
about 90 to about 60 wt. % solvent, and from about 10 to about 40 wt. % 
cellulose acetate butyrate. The solvent is preferably acetone, 
methyl-ethyl ketone, 80% toluene/20% ethanol, or 2% ethylene glycol 
monobutyl ether/98% acetone. 
The CAB can be easily applied to the adhesive by brushing, spraying or 
dipping, or can be applied to the mold prior to molding of the adhesive. 
This solution is ideal for adhesive manufacturers employing cooling molds 
for their products in that the CAB solution can be spray applied to the 
molds. The molds can then be filled with molten HMPSA and after cooling 
the CAB film provides easy release from the mold and an anti-blocking 
coating for the individual adhesive blocks. In order to provide mold 
release it is preferred to use molds constructed of polyethylene or 
polypropylene since CAB has high adhesion to metals. Once de-molded, the 
blocks of HMPSA can be packaged as seen fit by the manufacturer. The CAB 
coating has sufficient integrity to prevent blocking under normal 
transportation and storage conditions. 
An alternative application method for coating an HMPSA with CAB is to dip a 
cooling ribbon of adhesive in a CAB solution. High volume production of 
HMPSA utilizes an extruded ribbon of adhesive that passes through a 
cooling water system. At the end of the cooling bath or belt the 
solidified ribbon of HMPSA can be passed through a CAB solution which 
would then dry into an anti-blocking, coating. 
Thus, in further embodiments, the methods of this invention further 
comprise the preceding step of applying the cellulose acetate butyrate to 
the interior surface of an adhesive mold. In another embodiment the method 
of this invention further comprises the preceding step of applying the 
cellulose acetate butyrate to the interior surface of an adhesive mold, 
wherein the adhesive mold is constructed from polyethylene or 
polypropylene. In still another embodiment of the methods of this 
invention the coating is performed by dipping a ribbon of the adhesive in 
a solul ion or dispersion of cellulose acetate butyrate.

EXAMPLES 
The following examples are put forth so as to provide those of ordinary 
skill in the art with a complete disclosure and description of how the 
compounds, compositions, articles, devices and/or methods claimed herein 
are made and evaluated, and are intended to be purely exemplary of the 
invention and are not intended to limit the scope of what the inventors 
regard as their invention. Efforts have been made to ensure accuracy with 
respect to numbers (e.g., amounts, temperature, etc.) but some errors and 
deviations should be accounted for. Unless indicated otherwise, parts are 
parts by weight, temperature is in .degree. C. or is at ambient 
temperature, and pressure is at or near atmospheric. 
In examples 1-6 presented in Table 1, an evaluation was made of four CABs, 
cellulose acetate, and cellulose nitrate to determine their compatibility 
with a common HMPSA system based on styrene-isoprene-styrene ("S-I-S") 
block copolymers such as Kraton D1107 or Kraton D1112 from Shell Chemical 
Company. The samples were blended with the adhesive at various 
concentrations to reflect the concentrations expected if the samples were 
used as anti-blocking coatings. 
The results indicate that only the CAB products with the highest butyrate 
content (55% by weight) were found to be compatible with the adhesive in 
concentrations of 0.1% to 2.5%. Nitrocellulose was incompatible with the 
adhesive and rapidly formed a black char. 
TABLE 1 
__________________________________________________________________________ 
Ex. 
Material 
Wt % 
Wt % 
Wt % 
Wt % 
Wt % 
Wt % 
Wt % 
Wt % 
Wt % 
Wt % 
Wt % 
__________________________________________________________________________ 
Adhesive Base 
99.5 
99.5 
99.5 
99.5 
99.5 
99.0 
97.5 
99.5 
99.0 
97.5 
95 
1 Par-Cell R1/2 sec. 
0.5 
2 CA 398-3 0.5 
3 CAB 171-15 0.5 
4 CAB 381-0.2 0.5 
5 CAB 551-0.2 0.5 
1.0 
2.5 
6 CAB 551-0.01 0.5 
1.0 
2.5 
5.0 
Molten Solubility 
No.sup.b 
No No No Yes 
Yes 
No Yes 
Yes 
Yes 
No 
Room Temp. 
Appearance 
Char.sup.b 
T.sup.c 
T T C.sup.d 
SH.sup.e 
T C C SH T 
__________________________________________________________________________ 
.sup.a Adhesive Base Composition: 
Kraton D1107 10% 
Kraton D1112 20% 
Eastotac H100W 54% 
Shelflex 371 15% 
Irganox 1010 1% 
.sup.b Nitrocellulose charred within 5 minutes when added to molten 
adhesive at 175.degree. C. 
.sup.c = Turbid 
.sup.d = Clear/Compatible 
.sup.e = Slight Haze 
Examples 7-11 show the compatibility, storage stability, and effect of 
adhesive properties of a CAB 551-0.01 anti-blocking coating on various 
HMPSA systems. Five reference systems were selected to represent a typical 
range of base polymers, tackifiers, and plasticizers commonly used in 
HMPSA's. The compositions of the selected adhesives are shown in Table 2. 
Each of these adhesives was produced and formed into samples using a 
polypropylene cubicle ice tray suspended in a water bath to simulate 
adhesive production conditions. The tray was completely coated with a 25% 
solids solution of CAB551-0.01 in acetone, and then adhesive was poured 
into the mold chambers at 170-190.degree. C. The resultant formed adhesive 
pieces were then removed from the molds, with the CAB coating allowing 
easy demolding as well as forming an anti-block coating. The pieces of the 
adhesive cubes were then dipped in the CAB solution to coat the tops of 
the cubes. Several of the cubes were then weighed and washed with acetone 
to remove the coating. The cubes were reweighed to determine the weight of 
the add-on coating. In this manner it was determined that coaling add-on 
was between 0.75 and 1% by weight for each cube. 
The samples were placed in an oven at 60 degrees C., for 30 days to 
determine the stability of the anti-block coating. Four of the samples 
were still essentially free flowing after the heat-aging period. The one 
sample which was not stable was the AQ14000 based HMPSA. This sample 
exhibited cold flow, ruptured the CAB coating and completely fused after 
two days in the oven. 
TABLE 2 
______________________________________ 
HMPSA FORMULATIONS INCLUDED IN THE STUDY 
______________________________________ 
Example 7 
Kraton 10% Example 9 
Eastoflex 
65% 
D-1107 E1200 
APE 
S-I-S Based 
Kraton 20% APO Based 
Eastotac 
20% 
HMPSA D-1112 HMPSA H-100R 
Control Eastotac 54% Control Indopol 
5% 
H-100W H-100 
Shelflex 15% Irganox 
1% 
371 1010 
Irganox 1% 
1010 
Example 8 
Stereon 14% Example 10 
Stereon 
27% 
840A 840A 
S-I-S/S-B-S 
Kraton 6% S-B-S Based 
Permalyn 
27% 
Based D-1107 HMPSA 505 
HMPSA Eastotac 16% Control Zonatac 25% 
Control H-100R 1100 
Eastotac 32% White Oil #1 
20% 
H-130R 
Permalyn 17% Irganox 
1% 
305 1010 
White Oil #1 
20% 
Irganox 0.5% 
1010 
Example 11 
AQ 14000 70% 
AQ 14000 
Staybelite 
20% 
Based Benzoflex 
10% 
HMPSA 9-88 
Control Irganox 0.5% 
1010 
______________________________________ 
Examples 12-21 show the effect of the addition of the CAB coating to 
adhesives. Each formula with and without the CAB coating was drawn down on 
2 mil Mylar (Dupont, Wilmington, Del.) film at an adhesive thickness of 2 
mils. The resultant adhesive tapes were tested for 180.degree. peel 
adhesion and quick tack to both steel and LDPE using ASTM Method D903, and 
the rolling ball tack using an Eastman Chemical Company procedure based on 
PSTC Method 6. The results of these tests are summarized in Table 3. Since 
CAB 551-0.01 is a hard, high T.sub.g material with low compatibility with 
the components of the adhesive, it was expected that its addition to the 
system would be detrimental. In the case of an anti-blocking coating, 
however, the CAB is added to the adhesive at concentrations at or below 
its solubility limits and therefore would be expected to have minimal or 
no effect on the adhesive properties. 
The surprising result of these evaluations was that in some cases the CAB 
significantly improved the adhesive properties. This effect was most 
pronounced in the S-I-S and APO (Amorphous polyolefin) based HMPSAs, 
examples 12-15 in Table 3. In the case of the S-I-S based HMPSA, the 
180.degree. peel adhesion to both steel and LDPE was increased by a factor 
of 2. Also, in the case of adhesive to steel, the mode of failure changed 
from adhesive to cohesive failure. In the case of the APO based HMPSA, all 
failure modes were cohesive with and without the CAB addition, so that all 
that was being measured was the internal strength of the adhesive. The APO 
based HMPSA, however, did exhibit higher tack to steel when the CAB was 
added. In those adhesives with a measurable rolling ball tack, the CAB did 
appear to reduce the average number, but when the standard deviation of 
the tests were taken into consideration the changes were not statistically 
significant. 
TABLE 3 
__________________________________________________________________________ 
RESULTS OF ADHESIVE PROPERTY COMISONS WITH/WITHOUT CAB-551-0.01 
COATING 
Example Number 
12 13 14 15 16 17 18 19 20 21 
Adhesive Identification 
S-I-S/ AQ 
S-I-S APO S-I-S/ 
S-B-S S-B-S 
AQ 14000 
S-I-S 
+ APO + S-B-S 
+ S-B-S 
+ 14000 
+ 
Control 
CAB Control 
CAB Control 
CAB Control 
CAB Control 
CAB 
__________________________________________________________________________ 
180.degree. Peel to 
107.1 
203.0 
121.8 
111.1 
203.0 
151.8 
40.1 
40.9 
6.1 31.4 
steel, g/mm 
Standard 
5.69 
13.16 
4.36 
6.69 
13.01 
10.93 
1.55 
1.30 
2.16 
20.91 
deviation 
180.degree. Peel to PE, 
87.3 
101.6 
121.1 
111.3 
22.7 
9.4 36.4 
34.2 
14.2 
17.5 
g/mm 
Standard 
11.07 
6.83 
3.63 
3.7 9.56 
4.33 
6.24 
4.93 
6.20 
6.15 
deviation 
Quick Tack to 
119.5 
150.1 
28.6 
75.3 
19.4 
3.7 53.0 
46.4 
4.7 4.1 
Steel, g/mm 
Standard 
12.02 
5.15 
24.5 
28.6 
8.84 
2.36 
10.44 
5.69 
1.24 
2.47 
deviation 
Quick Tack to 
82.5 
92.6 
33.4 
27.5 
4.4 0.7 32.0 
34.9 
6.3 3.9 
PE, g/mm 
Standard 
5.90 
15.54 
7.46 
5.25 
2.02 
0.62 
5.15 
3.46 
4.39 
3.09 
deviation 
Rolling Ball 
19.28 
30.35 
148.8 
123.9 
No No 22.20 
30.23 
No No 
Tack, cm Tack 
Tack Tack 
Tack 
Standard 
5.79 
5.87 
46.74 
23.62 
N/A N/A 4.39 
6.30 
N/A N/A 
deviation 
__________________________________________________________________________ 
These examples show that CAB, when applied to HMPSA's at rates that reduce 
blocking, is sufficiently soluble in most HMPSA's to be universally useful 
as an anti-blocking agent. The examples also showed storage stability at 
60 degrees for 30 days, maintaining anti-blocking properties, and 
unexpectedly improving adhesive performance on steel and LDPE. All 
materials used in the examples are shown below: 
______________________________________ 
IDENTIFICATION OF REFERENCED MATERIALS 
Material Trade 
Name Description Vendor 
______________________________________ 
CAB 551-0.01 
Cellulose Acetate 
Eastman Chemical Company 
Butyrate (55 wt. % 
Kingsport, TN 
butyrate) 
CAB-551-0.2 
Cellulose Acetate 
Eastman Chemical Company 
Butyrate (55 wt. % 
butyrate) 
CAB-381-0.2 
Cellulose Acetate 
Eastman Chemical Company 
Butyrate (38 wt. % 
butyrate) 
CAB-171-15 
Cellulose Acetate 
Eastman Chemical Company 
Butyrate (17 wt. % 
butyrate) 
CA-398-3 Cellulose Acetate 
Eastman Chemical Company 
Par-Cell R1/2 sec 
Nitrocellulose 
Hercules Chemical Company 
Wilmington, DE 
Stereon 840A 
S-B-S Block Firestone Synthetic Rubber & 
Copolymer (Styrene- 
Latex Co., Akron, OH 
butadiene-styrene) 
Kraton D-1107 
S-I-S Block Shell Chemical Company 
Copolymer (Styrene- 
Houston, TX 
isoprene-styrene) 
Kraton D-1111 
S-I-S Block Shell Chemical Company 
Copolymer 
Eastotac H-100R 
Aliphatic hydrocarbon 
Eastman Chemical Company 
tackifying resin 
Eastotac H-130R 
Aliphatic hydrocarbon 
Eastman Chemical Company 
tackifying resin 
Eastoflex E1200 
Amorphous propylene- 
Eastman Chemical Company 
ethylene copolymer 
Eastotac H-100W 
Aliphatic hydrocarbon 
Eastman Chemical Company 
tackifying resin 
Indopol H-100 
Polybutene plasticizer 
Amoco Chemical Company 
Shelflex 371 
Naphtenic plasticizing 
Shell Chemical Company 
oil 
White Oil #1 
Mineral Oil Texaco Chemical Co. 
Austin, TX 
Irganox 1010 
Antioxidant Ciba Additives Div. 
Hawthorne, NY 
Zonatac 1100 
Polyterpene tackifying 
Arizona Chemical Company 
resin Div. Of Intl. Paper 
Panama City, FL 
Benzoflex 9-88 
Diethylene glycol 
Velsicol Chemical Company 
dibenzoate plasticizer 
Rosemont, IL 
AQ 14000 Water dispersible 
Eastman Chemical Company 
polyester polymer 
Staybelite 
Acid rosin tackifier 
Hercules Chemical Company 
Permalyn 303 
Rosin Ester tackifying 
Hercules Chemical Company 
resin 
Permalyn 505 
Rosin Ester tackifying 
Hercules Chemical Company 
resin 
______________________________________ 
It will be apparent to those skilled in the art that various modifications 
and variations can be made in the present invention without departing from 
the scope or spirit of the invention. Other embodiments of the invention 
will be apparent to those skilled in the art from consideration of the 
specification and practice of the invention disclosed herein. It is 
intended that the specification and examples be considered as exemplary 
only, with a true scope and spirit of the invention being indicated by the 
following claims.