Compositions for the manufacture of hot-melt adhesives

A composition for the manufacture of hot-melt adhesives, in which the improvement comprises a terpolymer of ethylene having a melt index between 5 and 500 dg/minute and comprising from 1 to 10 mol % of units derived from an ester selected from alkyl acrylates and methacrylates, the alkyl group having from 1 to 6 carbon atoms, and from 0.3 to 3 mol % of units derived from maleic anhydride. The composition also contains at least one tackifying resin and may contain at least one compound selected from paraffin, microcrystalline polymeric wax, and esters of a hydrogenated rosinic acid and of a lower alcohol.

BACKGROUND OF THE INVENTION 
The present invention relates to the field of compositions that can be used 
in the manufacture of hot-melt adhesives. 
In general, a hot-melt adhesive is manufactured from a mixture comprising 
three essential components: 
a petroleum resin having a tackifying effect, 
a thermoplastic resin capable of providing the cohesion of the mixture, and 
a paraffin or a microcrystalline polymeric wax capable of adapting the 
viscosity of the mixture to the processing and use conditions of the 
adhesive. 
To choose the thermoplastic resin forming part of this mixture, good 
properties are sought both in respect to heat stability and in respect to 
adhesiveness. The thermoplastic resins commonly used in compositions for 
the manufacture of hot-melt adhesives have been on the one hand, 
copolymers of ethylene and vinyl esters, in particular vinyl acetate, and, 
on the other hand, copolymers of ethylene and alkyl acrylates, in 
particular ethyl acrylate and butyl acrylate. 
For example, U.S. Pat. No. 3,869,416 describes an adhesive composition 
comprising: 
(a) 100 parts by weight of a petroleum wax reinforced by an 
ethylene/C.sub.3 -C.sub.18 .alpha.-olefine copolymer, and 
(b) an adhesion-promoting system consisting of a mixture of 25 to 50 parts 
by weight of a tackifying resin and 10 to 30 parts by weight of a polar 
polymeric additive. This additive is selected from: 
copolymers of ethylene and vinyl esters, 
copolymers comprising at least 85 mol % of ethylene and at least 7 mol % of 
alkyl (meth)acrylates, and 
copolymers comprising at least 85 mol % of ethylene and from 0.15 to 5 mol 
% of carboxylic acids, carboxylic acid partial esters, or carboxylic 
anhydrides (methacrylic acid and maleic anhydride are preferred). 
The users of hot-melt adhesives are constantly seeking to improve their 
properties, in particular their adhesiveness on a given substrate and 
their ability to adhere to very diverse types of substrate. From this 
viewpoint, the compositions previously used are not satisfactory, 
irrespective of the type of substrate in question. For example, a hot-melt 
adhesive manufactured from a composition comprising a copolymer of 
ethylene and vinyl acetate has good adhesiveness on leather and on a panel 
made of agglomerated particles, but moderate adhesiveness on rubber, poor 
adhesiveness on polyvinyl chloride, aluminum, and steel, and very poor 
adhesiveness on glass. 
SUMMARY OF THE INVENTION 
The object of the present invention is therefore to provide compositions 
for hot-melt adhesives that simultaneously have improved properties with 
respect to a given substrate and good ability to adhere to very diverse 
types of substrate. 
Additional objects 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 
objects and advantages of the invention may be realized and attained by 
means of the instrumentalities and combinations particularly pointed out 
in the appended claims. 
To achieve the foregoing objects and in accordance with the purpose of the 
invention, as embodied and broadly described herein, the improvement of 
the invention comprises selecting a particular thermoplastic resin 
comprising a terpolymer of ethylene, an ester selected from alkyl 
acrylates and methacrylates, and maleic anhydride. Thus, the compositions 
according to the invention comprise, per 100 parts by weight: 
(a) from 20 to 45 parts of at least one tackifying resin, 
(b) from 0 to 45 parts of at least one compound selected from paraffin, 
microcrystalline polymeric wax, and esters of a hydrogenated rosinic acid 
and of a lower alcohol, and 
(c) from 20 to 70 parts comprising a terpolymer of ethylene having a melt 
index between 5 and 500 dg/minute and comprising: 
from 1 to 10 mol% of units derived from an ester selected from alkyl 
acrylates and methacrylates, said alkyl group having from 1 to 6 carbon 
atoms, and from 0.3 to 3 mol% of units derived from maleic anhydride. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Reference will now be made in detail to the presently preferred embodiments 
of the invention. 
The tackifying resins that can be used in the composition according to the 
invention are preferably resins prepared from hydrocarbon cuts originating 
from naphtha steam-cracking. The resins may be mixed with an ester of a 
hydrogenated rosinic acid and of a higher alcohol. In particular the 
hydrocarbon cuts used for the preparation of the said resins may be, for 
example, aromatic cuts originating from petroleum or coal and containing 
at least one monomer selected from styrene and its derivatives, indene and 
its derivatives, vinyltoluenes, and allyl-benzene. 
By lower alcohol according to the present invention, there is intended a 
mono-alcohol comprising from 1 to 4 carbon atoms. By higher alcohol 
according to the present invention, there is intended on the one hand 
mono-alcohols comprising at least 12 carbon atoms and on the other hand 
polyols. 
Some terpolymers that can be used in the compositions according to the 
invention have been described in French Pat. No. 1,323,379. Particular 
terpolymers that can also be used, characterized namely by a 
polydispersity index above 6, have been described in French patent 
specification No. 81/1,430 in the name of the applicant. The process for 
the manufacture of these products consists in copolymerizing a mixture 
comprising 94 to 99% by weight of ethylene, 0.7 to 5% by weight of (meth) 
acrylic acid ester, and 0.2 to 0.9% by weight of maleic anhydride, in the 
presence of at least one free-radical initiator, in a reactor kept under a 
pressure of 1,000 to 3,000 bars and at a temperature of 170.degree. to 
280.degree. C., in relaxing the pressure and then separating the mixture 
of monomer and terpolymer formed in the reactor, and finally in recycling 
the previously separated mixture of ethylene and monomers into the 
reactor, the recycled stream comprising from 99 to 99.8% of ethylene and 
from 0.2 to 1% of (meth)acrylic acid ester. 
The compositions according to the invention may also comprise one or more 
mineral or organic fillers, such as carbon black, calcium carbonate, and 
the like. 
It should be observed that, due to the particular characteristics of the 
terpolymers described above, and contrary to the teaching of the prior 
art, the presence of a compound such as a paraffin or a microcrystalline 
polymeric wax is not essential in the composition according to the 
invention. 
The compositions described above possess improved properties, compared with 
the state of the art, and a good ability to adhere to very diverse types 
of substrate. These performance characteristics are further improved, 
however, by the addition, per 100 parts by weight of the composition, of 
up to 1 part of a heat-reversible modifier or crosslinking agent, such as 
an involatile alcohol, a mono-, di- or tri-alcoholamine, or a 
polyfunctional alcohol. Examples of alcoholamines are ethylene glycol and 
benzyl alcohol. Examples of alcoholamines are monoethanolamine and 
diethanolamine. Pentaerythritol is an example of a polyfunctional alcohol 
that can be used according to the present invention. 
Likewise, the performance characteristics of the compositions according to 
the invention may be still further improved if the component (c) of the 
compositions is a mixture comprising at least 40% by weight of the 
terpolymer and up to 60% by weight of a copolymer of ethylene and a vinyl 
ester such as vinyl acetate. 
The preparation of the compositions according to the invention does not 
present any difficulty and is carried out by homogeneous mixing of the 
various components at a temperature between 100.degree. and 250.degree. C. 
The compatibility of the main components is good if the proportions of the 
compositions according to the invention and the range of temperatures 
indicated above are observed. In the case where a heat-reversible modified 
or crosslinking agent is added to the mixture, it is introduced gradually 
in an amount such that the viscosity of the mixture remains between about 
2 and 5,000 poises if the temperature remains between 100.degree. and 
200.degree. C. In fact, if the viscosity of the crosslinked mixture 
becomes too high, a gel is obtained that is difficult to handle for 
subsequent use. 
The compositions prepared in this way are particularly useful as hot-melt 
adhesives, on the one hand because of their improved properties with 
respect to the given substrate, and on the other hand because of their 
ability to adhere to very diverse types of substrate. The property which 
best distinguishes the compositions according to the invention from the 
compositions according to the prior art, comprising an ethylene/vinyl 
acetate copolymer or an ethylene/ethyl acrylate copolymer, is the ultimate 
shearing strength, designated as USS below, which is determined according 
to the method below and expressed in kgf/5 cm.sup.2.

The purpose of the following examples is to illustrate several embodiments 
of the present invention without implying a limitation. 
EXAMPLES 1 TO 4 
Manufacture of Ethylene/Ethyl Acrylate/Maleic Anhydride Terpolymers 
A cylindrical autoclave reactor comprised three zones, each having a volume 
of 1 liter, and was equipped with a blade stirrer. The zones were 
separated by valve-screens. Fresh ethlene, compressed by a first 
compressor, fed the first zone. The second zone was fed with a homogeneous 
mixture of ethylene, maleic anhydride (MA), and ethyl acrylate (EA). 
Finally, a solution of tert-butyl 2-ethyl-perhexanoate in a hydrocarbon 
cut was injected into the third zone. The latter therefore constituted the 
only reaction zone because it brought the three comonomers into contact 
with a free-radical initiator. Table I below shows, on the one hand, the 
proportions by weight of maleic anhydride and ethyl acrylate in the 
reaction zone, relative to the ethylene, and, on the other hand, the 
temperature in the zone. The reactor was kept under a pressure of 1,600 
bars. An expansion valve, which makes it possible to lower the pressure to 
300 bars, was located at the bottom of the third zone of the reactor. 
After having passed through the expansion valve, the mixture of the molten 
polymer on the one hand and the gaseous monomers on the other hand passed 
into a separating hopper. While the polymer was collected at the bottom of 
the hopper, the monomers, after passage through a degreasing hopper, were 
led into a second compressor. Furthermore, a solution of maleic anhydride 
in ethyl acrylate was pumped in under pressure and led into the inlet of a 
Venturi-type homogenizer, where it was mixed with the stream of the 
recycled monomers coming from the second compressor. At the outlet of this 
Venturi device, the mixture of the three monomers was led into a sprial 
homogenizer and then transferred to the second zone of the reactor. 
On leaving the separating hopper, the resulting terpolymer was analyzed by 
infra-red spectrophotometry and the molar proportions of ethyl acrylate 
units and maleic anhydride units were determined; these are indicated in 
Table I below. Furthermore, the melt flow index of the polymer was 
determined according to ASTM Standard Specification D 1238-73 and 
expressed in dg/minute. 
EXAMPLES 5 (COMISON) AND 6 
Adhesion of Hot-Melt Adhesive Composition to Various Substrates 
A mixture was prepared that comprised, by weight, 100 parts of a 
thermoplastic resin, 50 parts of an aliphatic petroleum resin marketed 
under the reference ESCOREZ 5320, 20 parts of a colophony hydrogenated and 
esterified by glycerol (marketed under the reference STAYBELITE ESTER 10), 
and 0.4 part of an antioxidant. 
In Example 5 (comparison), the thermoplastic resin was an ethylene/vinyl 
acetate copolymer marketed under the reference ELVAX 260, while in Example 
6, the thermoplastic resin was the terpolymer of Example 4 above. 
The specific adhesion of the compositions thus obtained to various 
substrates was then evaluated, under identical conditions, by means of a 
qualitative and uniform notation for the substrates in question. 
The results of this evaluation are collated in Table II below. 
TABLE I 
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Reactor Polymer 
Example 
T .degree.C. 
% MA % EA % MA % EA MFI 
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1 180 0.26 2.6 0.9 6.5 200 
2 185 0.52 5.2 0.9 8.2 38 
3 175 0.94 4.4 2.1 7.7 50 
4 180 0.30 3.5 0.9 6.1 7.1 
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TABLE II 
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Substrate Example 5 Example 6 
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Leather Good Good 
Rubber Moderate Good 
Rigid polyvinyl Poor Very good 
chloride 
Panel made of Good Good 
agglomerated particles 
Aluminum Poor Good 
Steel Poor Good 
Glass Very poor Moderate 
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EXAMPLES 7 TO 10 (COMISON) AND 11 TO 22 
The object of the examples below is to describe the value of using, for 
adhesion to wood, compositions obtained from various copolymers according 
to the prior art (Examples 7 to 10) and from the terpolymers of Examples 1 
to 3, optionally modified by the addition of a heat-reversible 
crosslinking agent (Examples 11 to 22). 
All the compositions tested in this series of examples consist of 50 parts 
by weight of an aromatic petroleum resin marketed under the reference 
NORSOLENE M 1080, 50 parts of a paraffin having a melting poing of 
53.degree. C., and 50 parts of a thermoplastic resin. 
In Examples 7 and 8, the thermoplastic resin used was a commercial 
ethylene/ethyl acrylate copolymer comprising, respectively, 15.7% (Example 
7) and 21.3% (Example 8) by weight of acrylate. In Examples 9 and 10, the 
thermoplastic resin used was a commercial ethylene/vinyl acetate copolymer 
comprising, respectively, 28% (Example 9) and 18% (Example 10) by weight 
of acetate. The melt flow indices MFI of the resins used are indicated in 
Table III below. 
In Examples 11 and 12, the thermoplastic resins used were, respectively, 
the terpolymers of Examples 3 and 4 above. In Examples 13 and 14, the 
thermoplastic resins used were, respectively, the terpolymers of Examples 
1 and 2 above. 
In Examples 15 to 18, the thermoplastic resin used was the terpolymer of 
Example 1 modified by the gradual addition, during the preparation of the 
composition, of a heat-reversible modifier or crosslinking agent. The 
nature and the amount of this modifier or crosslinking agent, measured in 
parts by weight, were as follows: 
Example 15: 0.9 part of ethylene glycol. 
Example 16: 0.5 part of diethanolamine. 
Example 17: 1.5 parts of benzyl alcohol. 
Example 18: 0.5 part of triethanolamine. 
In Examples 19 to 21, the thermoplastic resin used was the terpolymer of 
Example 2, modified by the gradual addition, during the preparation of the 
composition, of a heat-reversible modifier or crosslinking agent. The 
nature and the amount of this modifier or crosslinking agent, measured in 
parts by weight, were as follows: 
Example 19: 0.9 part of ethylene glycol. 
Example 20: 1.4 parts of benzyl alcohol. 
Example 21: 0.1 part of diethanolamine. 
The resin used in Example 22 was a mixture of 30 parts of a commerical 
ethylene/vinyl acetate copolymer comprising 25% by weight of acetate, and 
20 parts of the terpolymer of Example 1, modified by the addition of 0.2 
part of triethanolamine as a heat-reversible crosslinking agent. 
The following properties, the values of which are shown in Table III below, 
were measured on the compositions prepared in this way: 
Ultimate shearing strength: the hot-melt composition was applied hot, with 
the aid of a spatula, to the central part, having a surface area of 10 
cm.sup.2, of a beechwood test-piece of dimensions 10.times.2 cm. A second 
wooden test-piece, of dimensions 5.times.2 cm, was rapidly placed on the 
part coated with adhesive, while exerting a pressure so as to obtain a 
uniform thickness of adhesive. After standing for three days, the larger 
test-piece is cut through the middle, with the aid of a saw, and the 
resistance to separation is measured with the aid of a Lhomargy tensile 
tester. The resistance to separation is expressed in kgf/5 cm.sup.2. 
Viscosity: the measurement was carried out at two temperatures with the aid 
of a Rheomat 30 viscometer, and the results are expressed in poises. 
TABLE III 
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Viscosity 
Example MFI USS 200.degree. C. 
100.degree. C. 
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7 5.6 57 21 306 
8 20 55 12 170 
9 25 85 12 155 
10 180 41 3.5 45 
11 50 84 3.7 21 
12 7.1 126 16 248 
13 200 85 3.3 30 
14 38 90 9.5 93 
15 200 98 3 42 
16 200 146 14 * 
17 200 90 3 34 
18 200 161 3.8 * 
19 38 101 8 159 
20 38 112 8 83 
21 38 131 15 150 
22 320 108 2.7 48 
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*The viscosity, which was very high, could not be measured by the 
instrument used. 
It will be apparent to those skilled in the art that various modifications 
and variations could be made in the composition of the invention without 
departing from the scope or spirit of the invention.