Resins based on .alpha.-methyl styrene, styrene and a phenol

Resins suitable for adhesives are based on .alpha.-methyl styrene, styrene and phenol in certain percentages, viz. 25 to 63, 35 to 73 and 2 to 15 percent by weight, respectively, Combinations of resin, ethylene vinyl acetate copolymer or thermoelastomer and optionally a wax or tackifying oil yield excellent adhesives, in particular hot-melt adhesives.

The invention relates to resins, based on .alpha.-methyl styrene, styrene 
and a phenol as constituents, and their application in adhesives, such as 
hot-melt adhesives and pressure-sensitive adhesives. 
Resins based on the above constituents are known in the art for various 
purposes, GB Specification No. 1,131,163 discloses water-soluble resins 
obtained by reacting formaldehyde and a Friedel Crafts catalyzed 
condensation product of phenol optionally with some cresol and styrene or 
.alpha.-methyl styrene. This intermediate condensation product is prepared 
by reacting styrene (or .alpha.-methyl styrene) with an excess of phenol, 
i.e. 0.1-0.5 mole styrene per mole of phenol resulting in phenolic resins 
containing 10 to 30% by weight of styrene and 64 to 90% of phenol. 
U.S. Pat. No. 3,189,569 discloses polymeric compositions containing about 
65-80% by weight of vinylaryl compounds, about 20-35% by weight of 
acrylonitrile, less than 1% of a trisubstituted phenol and optionally less 
than 1% of an epoxidized compound. 
U.S. Pat. No. 2,558,812 discloses resins comprising about 5-25 mole percent 
of phenol, about 24-45 mole percent of an aromatic hydrocarbon and 50-60 
mole percent of a conjugated aliphatic diene hydrocarbon such as 
butadiene, isoprene or cyclopentadiene. Fr. Specification No. 7,419,993 
(Nat. Reg. No. 2,232,554) and the equivalent G.B. Specification No. 
1,457,356 disclose resins based on .alpha.-methylstyrene, styrene, a 
phenol and 5-50% by weight of isobutene, resulting in a relatively low 
softening point of the resins. 
However, for use in hot melt and pressure-sensitive adhesives relatively 
high softening points, good compatability with natural or synthetic 
elastomers, satisfactory peel strength, shear adhesion and tack are 
required. 
The resins according to the present invention possess a good combination of 
properties satisfying the above requirements and also show improved 
compatibility with ethylene-vinyl acetate copolymers (EVA), atactic 
polypropylene (APP) and ethylacrylate copolymers (EEA). 
It has now been found that certain resins useful in adhesives, in 
particular hot-melt pressure-sensitive adhesives, are based on a mixture 
of .alpha.-methyl styrene, styrene and a phenol as the sole constituents, 
in such a way that the resin consists of 25-63% by weight of 
.alpha.-methyl styrene, 35-73% by weight of styrene and 2-15% by weight of 
a phenol. These percentages add up to 100 or substantially 100, because 
technical grade constituents may contain minor impurities. For instance, 
technical grade .alpha.-methyl styrene typically is more than 98% pure, 
the impurities being aromatic solvents and styrene. Technical grade 
styrene typically has a purity of more than 99%, the main impurities being 
aromatic solvents. Certain technical grades, containing these starting 
materials together with non-polymerisable aromatic solvents, may however 
also be used yielding a resin consisting for more than 98% of above 
constituents. 
In a preferred embodiment of the invention the resin consists of 25-57% by 
weight of .alpha.-methyl styrene, 40-72% by weight of styrene and 3-10% by 
weight of phenol. 
The .alpha.-methyl styrene, the styrene and a phenol, which may have the 
structural formula 
##STR1## 
in which R represents hydrogen or a C.sub.1 -C.sub.12 alkyl group, 
preferably a C.sub.6 -C.sub.10 alkyl group, can be used in the form of 
technical grade compounds (purity above 95%). Depending on the nature and 
reactivity, some of these impurities may be built into the resin. 
Those resins are preferred which comprise a combination of a phenol and a 
C.sub.6 -C.sub.10 monoalkyl phenol such as e.g. octyl phenol, for use in 
adhesives. 
The resins according to the invention usually show softening points (Ring & 
Ball according to ASTM E28) of about 70.degree. to 120.degree. C., unless 
high amounts of phenol and/or .alpha.-methyl styrene with respect to 
styrene are used. The compatability with elastomers, such as natural and 
synthetic rubbers, is excellent, giving typical cloud points below 
30.degree. C. and yielding clear mixtures. The average molecular weight of 
these resins ranges from about 400 to 2,000, depending on the percentage 
of phenol present. 
The resins according to the present invention can be prepared by reacting, 
optionally in the presence of a hydrocarbon solvent e.g. methylcyclohexane 
or toluene, the desired amounts of starting materials and a small amount 
of a Friedel-Crafts type catalyst, for instance BF.sub.3, AlCl.sub.3, 
TiCl.sub.4 or a complex thereof with e.g. ether or phenol, and keeping the 
reaction temperature between 0.degree. and 80.degree. C., preferably 
between 20.degree. and 50.degree. C. 
Slow addition of the catalyst--which is preferably BF.sub.3 or a complex 
thereof--may be recommendable in view of the exothermic nature of the 
reaction. Special measures to control the temperature during the reaction 
may be required to secure satisfactory and reproducible technical results. 
The reaction mixture is kept for several hours at the desired reaction 
temperature (0.degree.-80.degree. C.), after which the catalyst is 
destroyed, preferably by precipitating with an aqueous hydroxide and 
filtering, whereafter the volatiles e.g. solvent and any unreacted 
starting material, are removed. 
The resins according to the present invention can advantageously be used in 
adhesives, more particularly in hot-melt adhesives which do not require 
the presence of organic solvents. The compatability of the resin with 
rubber is excellent (50:50) mixtures). 
In some instances elastomers like rubber and certain ethylene-vinyl acetate 
copolymers (EVA), ethylacrylate copolymers (EEA) and amorphous 
polypropylene (APP) can be used either in combination or separately 
together with these resins in hot-melt pressure-sensitive adhesive 
formulations. 
The present invention also provides pressure-sensitive adhesives which are 
mixtures of a resin based on .alpha.-methyl styrene, styrene and a phenol 
in the above-specified amounts, and an elastomer such as natural or 
synthetic rubber. As natural rubber crude gum can be used and as synthetic 
rubbers any thermo-elastomer, such as styrene butadiene styrene (SBS) and 
e.g. styrene isoprene styrene (SIS) block copolymers. 
The resins and elastomers can be combined in weight ratios of between 0.3 
to 3 parts of resin per part of rubber, preferably between 0.5 and 2. 
Optional further ingredients such as waxes, tackifying oils (usually a 
napthenic oil) and stabilizers against oxidation and ultraviolet light can 
be incorporated in minor amounts. The resin and rubber are melted at a 
temperature ranging from about 80.degree. to 200.degree. C. and kept at 
this temperature for 10-30 minutes. Sometimes, better results are obtained 
by combining more than one type of rubber or more than one type of resin. 
The use of solvents (aliphatic or aromatic hydrocarbons, chlorinated 
derivatives thereof or e.g. ketones) is often superfluous, though the 
usual adjuncts, such as anti-oxidants, fillers and the like may be 
incorporated in minor amounts. 
In a further embodiment the present invention provides hot-melt 
pressure-sensitive adhesives which comprise a mixture of ethylene-vinyl 
acetate copolymer containing 38% and at most 55% of vinyl acetate and the 
same hydrocarbon resin as described above, and optionally a tackifying 
oil. The amounts by weight of resin and polymer can range between 35:65 
and 60:40, preferably 40:60 and 50:50. The ethylene vinyl acetate 
copolymer to be applied contains from 38-50, preferably from 40-45% by 
weight of vinyl acetate. 
In another embodiment of the present invention hot-melt adhesives are 
provided, which comprise substantially a mixture of an 
ethylene-vinyl-acetate copolymer containing at least 25, and at most 55% 
by weight of vinyl acetate, and a resin obtained by catalytic reaction of 
a mixture comprising .alpha.-methyl styrene, styrene and phenol in the 
mutual weight ratios as specified above, optionally with a 
microcrystalline and/or paraffin wax and/or a tackifying oil. The amounts 
by weight of resin and copolymer can then range between 35:65 and 60:40, 
preferably between 40:60 and 50:50. The ethylene-vinyl acetate copolymer 
to be applied contains from 25 to 55%, preferably 28 to 50%, by weight of 
vinyl acetate. 
Mixing of resin and copolymer is effected in the melt at a temperature of 
150.degree.-200.degree. C., preferably 160.degree.-180.degree. C. for 
15-60 minutes. Also minor quantities of antioxidants may be present. As 
the Examples show, by this process hot-melt adhesives can be provided 
which are particularly suitable for packaging, bookbinding or the 
manufacture of disposables, such as diapers, sanitary towels, disposable 
dressings. 
The balance of the essential properties of certain adhesives, when 
formulated as pressure-sensitive adhesives, such as compatibility with 
rubber, peel strength (determined according to PSTC-1) tack (determined 
according to PSTC-6, modified in that the adhesive is applied in a layer 
of 25-50 micrometers (.mu.m) using a hot knife) and shear adhesion 
(determined according to PSTC-7) is improved as compared with those resins 
based exclusively on .alpha.-methyl styrene, styrene, isobutene and 
optionally a phenol. 
The adhesives according to the invention are especially useful in the 
manufacture of disposables, e.g. diapers and sanitary towels, tapes of 
various types such as e.g. packaging tapes, masking tapes for automobile 
windows, carpet-laying tapes, labels, floor tiles, wall coverings, 
automobile upholstery, etc. 
The non-pressure-sensitive hot melts as formulated herein are characterized 
by superior adhesion, hot and cold resistance and stability and as such 
are suitable for packaging, bookbinding and non-pressure-sensitive 
disposables applications.

The invention is illustrated by the following Examples. 
EXAMPLE 1 
64% by weight of styrene, 34% by weight of .alpha.-methyl styrene and 2% by 
weight of phenol were dissolved in 60 parts by weight, calculated on 
monomeric starting material, of methylcyclohexane and subsequently 0.2 
part by weight of BF.sub.3 gas was introduced. A reaction temperature of 
30.degree.-35.degree. C. was maintained for four hours, after which the 
catalyst was neutralized with sodium hydroxide and filtered, while solvent 
and some unreacted starting material were stripped off. A resin was 
obtained with a softening point of 97.degree. C., which was soluble in 
polystyrene-polybutadiene-polystyrene and 
polystyrene-polyisoprene-polystyrene block copolymers (ratio of resin to 
elastomer 50:50), yielding a solution with a cloud point below 30.degree. 
C. The resin was very useful for hot-melt adhesive compositions, 
especially for hot-melt pressure-sensitive adhesives. 
EXAMPLE 2 
70% by weight of styrene, 28% by weight of .alpha.-methyl styrene and 2% by 
weight of phenol were dissolved in 60 parts by weight of toluene, and 0.2 
part by weight of BF.sub.3 gas was introduced (these parts by weight are 
calculated on the monomeric starting material). Reaction and working-up 
conditions were as described in Example 1. A resin was obtained with a 
softening point of 85.degree. C. 
EXAMPLE 3 
63.5% by weight of styrene, 31.3% by weight of .alpha.-methyl styrene and 
5.2% by weight of octyl phenol were dissolved in 60 parts by weight of 
methyl cyclohexane, after which 0.3 part by weight of BF.sub.3 gas was 
introduced. Reaction and working-up conditions were as described in 
Example 1. The resin obtained had a softening point of 85.degree. C., was 
completely soluble in polystyrene-polyisoprene-polystyrene and 
polystyrene-polybutadiene-polystyrene block copolymers (50:50), yielding a 
clear solution with a cloud point below 30.degree. C. 
EXAMPLE 4 
61% by weight of styrene, 32% by weight of .alpha.-methyl styrene and 7% by 
weight of phenol were dissolved in 80 parts of methylcyclohexane, and 0.25 
part of BF.sub.3 was introduced. Reaction and working-up conditions were 
as described in Example 1. Resin was obtained having a softening point of 
80.degree. C., which resin was fully compatible with ethylene-vinyl 
acetate containing 40% of vinyl acetate and with 
polystyrene-polybutadiene/polyisoprene-polystyrene block copolymers 
(50:50). 
EXAMPLE 5 
60% by weight of styrene, 31.5% by weight of .alpha.-methyl styrene and 
8.5% by weight of phenol were dissolved in 70 parts of toluene and 0.2 
part of BF.sub.3 gas was introduced. Reaction and working-up conditions 
were as described in Example 1. The resin thus obtained showed a softening 
point of 70.degree. C. and as regards compatibility it had properties 
equivalent to those of the resin of the preceding Example. 
EXAMPLE 6 
60% by weight of styrene, 31% by weight of .alpha.-methyl styrene and 9% by 
weight of phenol were dissolved in 70 parts by weight of toluene, 
calculated on the total weight of monomeric material, and 0.2 part of 
BF.sub.3 gas was introduced. The reaction temperature was 
50.degree.-55.degree. C., which was maintained for four hours, after which 
the catalyst was neutralized with an aqueous NaOH solution and was 
filtered off, and volatiles were stripped off. The resin thus obtained 
showed a softening point of 65.degree..+-.5.degree. C. and was fully 
compatible with an ethylene-vinyl acetate copolymer containing 40% of 
vinyl acetate and also with a polystyrene-polybutadiene-polyisoprene block 
copolymer in a weight ratio of 50:50. 
EXAMPLE 7 
50 parts by weight of the resin obtained according to Example 5 were mixed 
with 100 parts by weight of a thermoelastomer (a 
polystyrene-polyisoprene-polystyrene block copolymer, specific density 
0.93, shear adhesion 250) and 16 parts of naphthenic oil. Mixing was 
effected at 100.degree. C. for 15 minutes, after adding 5 parts of zinc 
dibutyl dithiocarbamate. The mixture thus obtained was a useful hot-melt 
pressure-sensitive adhesive especially suitable for permanent labels on 
bottles, showing the following properties: 
______________________________________ 
peel strength 450 g/cm 
shear adhesion above 24 hours 
tack 17 cm. 
______________________________________ 
EXAMPLE 8 
30 parts by weight of the resin of Example 5, 70 parts by weight of 
thermoelastomer as described in Example 6, and 3 parts of zinc dibutyl 
dithiocarbamate were mixed at 130.degree. C. for 15 minutes, yielding a 
homogeneous hot-melt pressure-sensitive adhesive, especially useful for 
carpet-laying tapes. The properties of the adhesive were as follows: 
______________________________________ 
peel strength 805 g/cm 
shear adhesion above 25 hours 
tack 9 cm. 
______________________________________ 
EXAMPLE 9 
120 parts by weight of the resin of Example 5, 100 parts of thermoelastomer 
as described in Example 6, 40 parts of naphthenic oil and 5 parts of zinc 
dibutyl dithiocarbamate were mixed at 100.degree. C. for 15 minutes, 
yielding a pressure-sensitive adhesive, especially suitable for packaging 
tapes. The properties were as follows: 
______________________________________ 
peel strength 300 g/cm 
shear adhesion above 24 hours 
tack 15 cm. 
______________________________________ 
EXAMPLES 10 AND 11 
50 parts by weight of the resin of Example 5 and 50 parts by weight of an 
ethylene-vinyl acetate copolymer containing 40% by weight of vinyl acetate 
(melt index determined according to ASTM D 1238: 40-70 g/10 minutes) were 
mixed in the melt at a temperature of about 165.degree. C. Thus a hot-melt 
pressure-sensitive adhesive was obtained which was very suitable for use 
in the production of diapers, sanitary towels, and the like. 
By a similar process an excellent adhesive was obtained by mixing resin and 
polymer in a ratio of 40:60. 
The following properties were determined for 50:50 and 40:60 mixtures 
respectively: 
______________________________________ 
peel strength 670 580 g/cm 
shear adhesion 
above 24 above 24 hr 
tack 3.5 6.5 cm 
______________________________________ 
EXAMPLES 12 AND 13 
By the process described in Example 10 two hot-melt pressure-sensitive 
adhesives were prepared by mixing an amount of the resin of Example 6 with 
an ethylene-vinyl acetate copolymer containing 45% vinyl acetate (melt 
index determined according to ASTM 1238: 25 g/10 minutes). The ratios by 
weight of the mixture of resin and copolymer were 50:50 and 40:60. The 
melting/mixing temperature was 180.degree. C. Also these hot-melt 
pressure-sensitive adhesives proved to be especially suitable for bonding 
diapers, sanitary towels, and other disposables. 
The following properties were determined for 50:50 and 40:60 mixtures 
respectively: 
______________________________________ 
peel strength 640 500 g/cm 
shear strength 
above 24 above 24 hr 
tack 3.6 6.6 cm 
______________________________________ 
EXAMPLE 14 
A standard hot-melt was prepared according to the formulation: 
30 parts ethylene-vinyl acetate resin (containing 28% of vinylacetate); 
50 parts of resin; 
20 parts of microcrystalline wax (m.p. 82.degree. C.); 
0.5 parts of di-tert-butyl-p cresol. 
Two such compositions were evaluated and compared; in the first the resin 
was the resin described in Example 5, in the second it was a commercially 
available copolymer, .alpha.-methyl styrene-styrene (without phenol), 
having the following characteristics: 
softening point: 85.degree. C. (R+B) 
colour: water-white 
acid value and saponification value: &lt;1 
specific gravity (25.degree. C.): 1.06 
Both compositions were evaluated as a hot-melt adhesive to seam 
polyethylene to non-wovens. 
The adhesive based on the commercial resin gave poor (zippery) bonds 
between polyethylene and non-wovens, whereas the other adhesive according 
to the invention gave strong (destructive or polytearing) bonds.