U.S. patent number 3,695,477 [Application Number 05/038,491] was granted by the patent office on 1972-10-03 for plastisols and gaskets.
Invention is credited to Robert P. Edmonston, George C. Keller, John W. Lefforge.
United States Patent |
3,695,477 |
Edmonston , et al. |
October 3, 1972 |
PLASTISOLS AND GASKETS
Abstract
Plastisols, preferably of polyvinyl chloride, having a high
yield value and low high shear viscosities are obtained by
thickening conventional plastisol preparations with about 1 to 40
parts of certain block copolymers of the A-B-A type in which B is
an elastomeric polymer core and A stands for a thermoplastic
polymerized alkenyl aromatic compound. Tough, resilient gaskets can
be manufactured from these improved materials.
Inventors: |
Edmonston; Robert P.
(Billerica, MA), Lefforge; John W. (Lynnfield, MA),
Keller; George C. (East Derry, NH) |
Family
ID: |
21900261 |
Appl.
No.: |
05/038,491 |
Filed: |
May 18, 1970 |
Current U.S.
Class: |
215/341; 521/139;
525/96; 525/98; 525/177; 525/239; 521/75; 525/57; 525/166;
525/222 |
Current CPC
Class: |
C08L
57/00 (20130101); C08L 27/06 (20130101); C09K
3/10 (20130101); C08L 27/06 (20130101); C08L
27/06 (20130101); C08L 57/00 (20130101); C08L
57/00 (20130101); C08L 2666/24 (20130101); C08L
53/02 (20130101); C08L 2666/04 (20130101); C08L
53/02 (20130101); C09K 2200/0635 (20130101); C08L
53/02 (20130101); C09K 2200/0642 (20130101) |
Current International
Class: |
C08L
27/00 (20060101); C08L 27/06 (20060101); C08L
57/00 (20060101); C09K 3/10 (20060101); C08L
53/00 (20060101); C08L 53/02 (20060101); C08f
029/24 (); C08f 029/12 (); B65d 053/00 () |
Field of
Search: |
;260/876B,31.8M
;215/40 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Blech; Samuel H.
Claims
What is claimed is:
1. A container closure comprising a flowed-in gasket consisting of
a fluxed layer of a plastisol of a resin selected from the group
consisting of homopolymers and copolymers of vinyl chloride
containing up to 20 percent of vinyl acetate, containing, for each
100 parts by weight of the resin, from about 1 to 40 parts of a
block copolymer having an A-B-A structure in which B represents an
elastomeric core of polymerized diene units selected from the class
consisting of conjugated diene hydrocarbon compounds having four to
eight carbon atoms and elastomeric copolymers of ethylene with
propylene, said core having an average molecular weight within the
range of 10,000 to 200,000, and A represents a thermoplastic
segment of a polymerized alkenyl aromatic compound of average
molecular weight within the range of about 2,000 to 30,000, wherein
the total polymerized alkenyl aromatic compound content constitutes
from about 10 to 50 percent by weight of the block copolymer
molecule.
2. The container closure of claim 1 wherein the plastisol contains
about 5 to 25 parts by weight of a copolymer of styrene and
butadiene having average over-all molecular weight of about 60,000
to 160,000 and a copolymerized styrene content within the range of
25 to 30 percent of the weight of the molecule.
3. The container closure of claim 1 wherein in the block copolymer
the diene unit of the elastomeric segment is derived from isoprene.
Description
THE PRIOR ART
In the bottling of carbonated beverages, an air-tight pressure
crown seal is applied on the orifice of the container, for instance
a bottle, to retain the carbonation of the contents and to protect
the beverage against contamination. Crowns for such bottles are
made of metal having uniform ductility, gage and even temper and
are lined with a sealing gasket which may consist of cork,
polyethylene, fluxed plastisols or other plastic materials. It is
with fluxed plastisol linings or gaskets of this general type that
the present invention is concerned.
Basically, plastisols comprise a dispersion of finely divided
thermoplastic resin particles in a liquid non-volatile plasticizer
in which the resin is insoluble or only very slightly soluble at
room temperature. At elevated temperatures, the resin becomes
substantially completely solvated by the plasticizer, yielding a
homogeneous solution which transforms itself into a rubbery
thermoplastic mass upon cooling. In addition to the basic
components, other ingredients may enter the plastisol compositions
to accomplish conventional purposes. Thus the compositions may
contain fillers, pigments, stabilizers, wetting agents and
thickeners. Also, when a fluxed cellular liner is desired, a gas
may be dispersed in the plastisol or a gas-evolving agent, i.e., a
blowing agent, may be incorporated which will decompose at the
fluxing temperature of the composition.
Plastisols are widely used in the manufacture of sealing gaskets
for crown closures, where the gasket comprises an over-all liner
coextensive with the inside surface of the closure panel. According
to one method of lining closures, a measured quantity of plastisol
is deposited in an inverted closure shell and the closure is
rotated at high speed to cause the deposit to spread over the inner
surface of the closure panel. The deposit is then heated at a
temperature and for a period of time sufficient to completely flux
the composition. In bottle capping operations, the lined crown
closure thus obtained is placed over the orifice of the bottle and
the skirt of the crown is crimped around the locking ring of the
bottle to form a seal.
The operations and manipulations that the plastisols must undergo
in the procedures just described and in other similar sealing
applications require that the liquid compositions involved possess
certain characteristic rheological properties. The compositions
must be fluid enough at high shear rates to permit easy disposition
through a nozzle and rapid distribution over the inner surface of
the closure when the spin lining technique is employed. Yet, they
must possess a viscosity sufficiently high so that the gasket
material remain in position until it is solidified by heat
treatment. This type of property is conventionally imparted to
plastisols by incorporating into them a small quantity of a finely
divided material, generally of siliceous nature.
It is an object of this invention to provide improved plastisol
preparations which yield tougher closure gaskets that can better
survive the abuse to which such closures are conventionally
subjected in their ultimate application. It is also an object of
this invention to provide plastisols possessing a more easily
controlled thixotropy than that of conventional materials. Another
object is to prepare plastisols capable of yielding sealing gaskets
of increased shear and tensile modulus under high strain and of
lesser hardness than normally available. A further object is to
provide fluxed plastisols that are more resistant to extraction of
their plasticizer by certain organic liquids to which they may be
exposed.
SUMMARY OF THE INVENTION
It has now been discovered that the yield value of unfluxed
plastisols, i.e., the low shear viscosity, can be successfully
increased, without significantly affecting the high shear
viscosity, by incorporating into the plastisols relatively small
quantities of certain thermoplastic elastomeric block copolymers of
conjugated dienes with certain alkenyl aromatic comonomers,
dissolved in conventional plasticizers. It has also been discovered
that sealing gaskets obtained from plastisols of this type will be
stronger, more resilient and softer than those obtained from
plastisols containing conventional siliceous materials.
While the quantity of block copolymer that will achieve desirable
improvement will vary with such factors as the nature and molecular
weight of specific block copolymers, the plasticizer contents of
the composition and the particular application contemplated, the
preferred proportions lie within the range of about 5 to 25 parts
by weight of block copolymer per 100 parts of plastisol resin.
However, useful compositions may be devised with as little as 1
part and as much as 40 parts of copolymer per 100 parts
thermoplastic resin.
DETAILED DESCRIPTION
The block copolymers that are added to plastisols according to the
present invention are thermoplastic elastomers composed of
polymerized alkenyl substituted aromatic segments attached to the
ends of an elastomeric polymerized hydrocarbon chain core. Usable
hydrocarbon monomers for forming the core preferably contain four
to eight carbon atoms. This includes butadiene, isoprene,
pentadiene-1,3 and 2,3-dimethylbutadiene. The elastomeric core
material may also consist of saturated ethylene-propylene
copolymers. The alkenyl aromatic hydrocarbon monomers used to form
the rest of the block copolymer molecule are preferably of the
monovinyl substituted type such as styrene, methylstyrene, vinyl
toluene, vinyl naphthalene and the like. More than one monomer may
be employed for each section of the block copolymer.
The structure of the block copolymers being described may be
represented by the formula A-B-A in which B is the elastomeric core
while A stands for the aromatic alkene polymer segments. While,
obviously such copolymers may possess a gradation of properties
ranging from those of relatively homogeneous polymerized aromatic
vinyl compounds to those of relatively homogeneous elastomers, the
polymers of particular interest here possess a thermoplastic
segment content of about 10 to 50 percent by weight, an average
elastomeric core molecular weight of about 10,000 to 200,000, and
an average thermoplastic segment molecular weight of 2,000 to
30,000. The preferred copolymers within the class just described
are styrene-butadiene block copolymers containing from about 25 to
30 percent by weight polymerized styrene and having an average
overall molecular weight of between about 60,000 and 160,000.
To carry out the invention, as mentioned earlier, the selected
copolymer is dissolved in a conventional liquid plasticizer and the
solution is incorporated into the plastisol by mixing. Between
about 1 and 40 parts by weight of block copolymer per hundred parts
of plastisol resin will yield the desired results.
The plasticizers that may be employed to dissolve the block
copolymer as well as to form the plastisol may be dialkyl
phthalates, such as dioctyl phthalate, butyl decyl phthalate and
octyl decyl phthalate; alkyl phthalyl alkyl glycollates, such as
butyl phthalyl butyl glycollate and methyl phthalyl ethyl
glycollate; and dialkyl esters of alkane dicarboxylic acids, such
as dioctyl and dibutyl sebacates, dioctyl azelate and diisobutyl
adipate. Secondary plasticizers that may be incorporated in the
plastisol include trialkyl and triaryl phosphates, acetyl trialkyl
citrates, alkyl esters of high fatty acids, epoxy derivatives and
polymeric polyester plasticizers, such as glycol sebacate
polyesters. If desired, mixtures of plasticizers may be employed
including one or more primary plasticizers and blends of primary
and secondary plasticizers.
The following examples are given to illustrate the practice of the
invention.
EXAMPLE 1
A block copolymer preflux is formed by heating with agitation at
250.degree. to 280.degree.F, one part by weight of a block
copolymer of styrene and butadiene containing 25 percent bound
styrene and having an average overall molecular weight of about
120,000, with 4 parts dioctylphthalate.
A conventional polyvinyl chloride (PVC) plastisol is prepared from
the following ingredients:
Parts by weight PVC resin, plastisol grade 100 Dioctylphthalate
(DOP) 50 Azodicarbonamide, 33% in DOP 1.08 Zinc/calcium stearates
in epoxidized soybean oil (stabilizer) 0.5 Eicosane 4 Paraffin wax,
melting range 120.degree.-131.degree.F 3 Block copolymer preflux,
20% concentration 25
A wax-plasticizer blend is formed by melting the wax in a few parts
of the plasticizer at a temperature of approximately 130.degree.F.
The hot wax blend is mixed with about half the plasticizer, the
mixture stirred and allowed to cool to about 110.degree.F. The
eicosane, the stabilizer, the azo compound and the resin are added
with stirring. The remaining plasticizer is also added and the
resulting composition stirred until a homogeneous mixture results.
The preflux is then blended in to obtain a product having a 60 rpm
viscosity of 14,000 centipoises and a 6 rpm viscosity of 45,000 cps
as measured on a Brookfield viscosimeter (model LVF-SX) at
110.degree.F with a No. 3 spindle.
EXAMPLE 2
A plastisol is prepared as in Example 1 except that it contains 3
parts of fumed silica, a conventional thickener. The SBR block
copolymer preflux is omitted.
The plastisol thus obtained has a 6 rpm viscosity of 60,000 cps and
a 60 rpm viscosity of 20,000 cps.
The plastisols of Example 1 and 2 were applied to bottle crowns and
fluxed in the conventional manner. The crowns were then affixed to
bottles filled with simulated soft drink pack and the packages
obtained were subjected to an abuse test.
In this test, a static load pressure of 100 lbs is applied to
capped bottles and maintained constant for a period of one week.
This treatment duplicates conditions found in soft drink bottling
plants where cases of packed soda are stacked on top of one another
with the weight of the upper cases being applied to the bottle
crowns in the lower cases. After one week, the static pressure is
released. The carbon dioxide pressure retained in each bottle is
measured, 24 hours after release, by means of a head sampler and a
pressure gage. The results are recorded in terms of gas volumes,
4.0 gas volumes indicating a perfect performance since that is the
amount of gas originally charged into the bottles. A 3.8 gas volume
retention is considered acceptable by the industry, while ratings
below 3.8 failures. One failure in a sample of six bottles suffices
to rule a compound unsatisfactory.
The essential properties of the plastisols of Examples 1 and 2 as
well as the performance of crowns sealed with them under static
load abuse are summarized in the following table:
ABUSE TEST RESULTS
Example 1 2
__________________________________________________________________________
Thickener SBR Block Silica gel Copolymer Viscosity: 6 rpm 45,000
60,000 60 rpm 14,000 20,000 6/60 ratio 3.2 3.0 Abuse Data: No. of
failures/6 bottles 0 5 Average gas volumes 4.02 3.35
__________________________________________________________________________
It becomes apparent from these results that SBR block copolymer
reinforced plastisols show increased resistance to static load
abuse as compared to the conventional silica thickened
materials.
EXAMPLE 3
Another illustrative composition can be prepared in the
conventional manner from the following ingredients:
Parts by weight PVC resin, plastisol grade 100 Dioctyl phthalate
105 Paraffin wax 4.6 Diatomaceous earth 3.5 Azodicarbonamide 0.7
Zinc oxide 0.6 Titanium dioxide 5.6 Hematite 0.16 Limonite 0.13
Carbon black 0.03
To this plastisol is added 20 parts of a 15 percent preflux of an
isoprene-styrene block copolymer having an average core molecular
weight of 200,000 and an average styrene segment molecular weight
of 30,000. The resulting unfluxed plastisol has a 110.degree.F
viscosity of about 10,000 cps at 6 rpm and about 3,400 cps at 60
rpm. When fluxed and subjected to the static load abuse test
described earlier, it behaves substantially as the preparation of
Example 1 in that the average gas volume retained in 6 sample
bottles is at least 3.8 after a 4 volume charge.
EXAMPLE 4
A fluxed plastisol with greatly decreased compressive modulus and
only moderately increased shear strength, thus particularly suited
for sealing and capping without any decrease in blow-off pressure,
is prepared by incorporating 25 parts per 100 parts resin by weight
of a styrene-butadiene block copolymer such as Kraton*(*Registered
trademark, Shell Chemical Co.) 1102 which has a Brookfield
viscosity of about 1000 cp at room temperature for a 25 percent
concentration by weight in toluene. A 50 percent by weight solution
of the block copolymer in the plasticizer is prepared by prolonged
stirring and heating, for instance at 280.degree.F, and this
solution is added to a plastisol which has otherwise been prepared
in the conventional manner.
A representative formulation would thus appear as follows:
Parts by Weight Total Plasticizer
__________________________________________________________________________
PVC resin, plastisol grade 400 -- PVC resin, suspension polymerized
100 -- Epoxydized soybean oil 25 25 Azodicarbonamide, 33% 7.5 5
Zinc oxide, 20% 15 12 Dioctyl phthalate (DOP) 258 258 Block
copolymer 250 125 Total 1055.5 425
__________________________________________________________________________
Solutions or suspensions of the various ingredient in DOP are first
prepared at the solids concentration indicated and the resulting
mixtures are combined in the proportions indicated in the "total"
column of the above table. The block copolymer solution is added
last to a thorough mixture of all the other components and it is
mixed in until a uniform product is obtained. The net amount of
plasticizer used is tabulated in the next column and adds up to 425
parts by weight for a final ratio of 85 parts per 100 parts
resin.
For comparison purposes, a similar preparation can be made without
the 125 parts styrene-butadiene block copolymer. A silica aerogel,
45 parts by weight is used instead; all other component quantities
and ratios are maintained unchanged including the DOP to resin
ratio.
Both formulation yield thixotropic mixtures with viscosities too
high for measurement by ordinary means. On lining closures with 400
mg of these plastisols and fluxing for 3 minutes at 410.degree.F, a
number of interesting differences can be observed.
For instance, the block copolymer-containing structures have been
found to possess an average 15 second blow-off pressure 17 psi
higher than their silica-containing analogs over the range of
32.degree. to 212.degree.F. Also, in the closing or capping
operation, the closing force required for the block copolymer
plastisol is only 50 to 70 percent of that needed with the
conventional silica preparations. Furthermore, exposure of fluxed
gaskets to 50 percent aqueous solution of ethyl alcohol at
100.degree.F results in a loss of only 8 percent of the plasticizer
when the block copolymer is present while 18 percent of the
plasticizer is extracted with silica present. In general, the use
of block copolymers results in increased shear and tensile modulus
while providing relatively lower durometer values.
The plastisol compositions that can benefit from the incorporation
of block copolymers of the styrene-butadiene type as described in
this invention are those of vinyl chloride homopolymers as well as
copolymers containing up to 20 percent of vinyl acetate. Although
such polymers are preferred, other acid-resistant thermoplastic
resins may be used, including polyvinyl acetate, polyvinyl
butyrate, polyvinyl alcohol, polyvinylidene chloride, and so on.
These materials, as well as the other modifying components of the
plastisols such as blowing agents, fillers, stabilizers, pigments
and dispersing agents are well known to the art and are listed in
numerous publications including, for example, U. S. Pat. No.
3,447,710. No need exists therefore for re-numerating all the
possible elements that can be combined by the man skilled in the
art to yield compositions that can be improved in the manner
disclosed by the present invention.
* * * * *