Diffusion resistant rubber liner and laminates formed therefrom

A rubber liner having resistance to fluid diffusion is disclosed. The rubber liner is compounded from natural or synthetic rubber in combination with a thiuram compound such that the blend upon curing has a durometer hardness no greater than about 75 on the Shore D. Scale. The rubber liner may be combined with a heat-resistant rubber layer to form a rubber laminate resistant to heat and fluid diffusion. The heat-resistant rubber layer may be composed of natural or synthetic rubber in combination with a salt of a benzimidazole which resists oxidation at elevated temperature over extended time periods with a retention or increase tensile strength. The rubber laminate may also have a metal-adhesive rubber layer to secure the laminate to metal substrates of industrial production tanks, vessels, pipes, and other containers where industrial processing continually exceeds 180.degree. F. The use of a rubber liner having diffusion resistant properties with a durometer hardness less than 75 on the Shore D Scale resists structural weaknesses developed upon continuous exposure to temperatures of about 180.degree. F.

TECHNICAL FIELD 
This invention relates to rubber laminates resistant to heat and fluid 
diffusion, and individual rubber lining compositions comprising the rubber 
laminate. 
BACKGROUND ART 
Heretofore, linings for industrial surfaces transferring or holding 
corrosive material have typically included rubber liners in a multi-layer 
form. These rubber laminates have been compounded to prevent the corrosive 
material from reacting with the typically metal storage tank or transfer 
pipe. In the industrial production of corrosive acids such as phosphoric 
acid, diffusion of fluids through the rubber liner creates pockets of 
corrosion between the liner and the metal pipe or tank, which causes a 
corrosive delamination and bursting of the liner or the entire laminate. 
The entire protective features of the rubber laminate are lost upon this 
corrosive destruction, and industrial production is halted while the 
entire tank or pipe is replaced. 
U.S. Pat. No. 4,215,178, granted to this inventor, and the references cited 
therein, as well as U.S. Pat. No. 4,115,614 granted to this inventor, and 
the references cited therein, describe the general state of the art for a 
variety of rubber laminates serving to protect tanks, pipes, reactors, and 
other vessels. 
However, it has been found that these various rubber laminates used in the 
art do not provide adequate resistance to fluid diffusion and fail 
especially at processing temperatures which exceed 185.degree. Fahrenheit. 
In the production of phosphoric acid, a greater concentration of 
phosphoric acid or a greater volume of phosphoric acid production may be 
achieved when the processing temperatures exceed 185.degree. Fahrenheit 
and approach 220.degree. Fahrenheit. Rubber laminates presently known in 
the art are incapable of resisting fluid diffusion at such higher 
processing temperatures. Therefore, the need exists for a rubber liner 
capable of resisting fluid diffusion while serving as a protective lining 
for tanks, pipes, and other vessels. The need also exists for a rubber 
laminate resistant to heat degradation to protect that section of the 
laminate which resists fluid diffusion. 
DISCLOSURE OF INVENTION 
It is an object of the invention to provide a rubber liner resistant to 
fluid diffusion wherein the rubber liner is compounded with a 
concentration of curing agents sufficient to limit the curing of the 
rubber liner to a durometer hardness of less than about 75 on the Shore D 
Scale. 
It is another object of the invention to provide a rubber liner resistant 
to fluid diffusion, wherein the rubber liner is uncured when installed 
upon the pipe, tank, or other vessel and cures to a durometer hardness of 
no greater than about 75 on the Shore D Scale. 
Another object of the invention is to provide a rubber liner which is 
resistant to fluid diffusion thereby maintaining protection of the pipe, 
tank, or other vessel during industrial processing at temperatures in 
excess of 185.degree. Fahrenheit from the degrading effect of corrosive 
materials upon the tank, pipe, or other vessel. 
It is yet another object of the invention to provide a rubber liner 
resistant to fluid diffusion which may be laminated to other liners 
assisting in the resistance to heat and other degrading effects caused by 
passage of corrosive material at elevated temperatures for extended 
periods of time. 
It is another object of the invention to provide a rubber liner resistant 
to fluid diffusion which may be laminated to other liners assisting in the 
resistance to heat and other degrading effects including attack by oil 
based anti-foaming agents. 
It is moreover an object of the invention to provide a rubber laminate 
resistant to heat and fluid diffusion, wherein the curing of the 
diffusion-resistant liner to a durometer hardness of less than about 75 on 
the Shore D Scale prevents a rupture of the entire rubber laminate, and 
wherein the heat resistant liner prevents oxidative degradation of the 
rubber laminate. 
The objects of the invention are achieved by a rubber liner resistant to 
fluid diffusion, comprising: a composition, having upon curing, a 
durometer hardness of from about 15 to about 75 on the Shore D Scale, said 
blend comprising (a) about 100 parts by weight of a rubber elastomer 
selected from the group consisting of (1) natural rubber, (2) a polymer 
made from diene monomers having from 4 to 12 carbon atoms, (3) a copolymer 
made from diene monomers having from 4 to 12 carbon atoms, and (4) a 
copolymer made from vinyl substituted aromatic monomers having from 8 to 
12 carbon atoms and diene monomers having from 4 to 12 carbon atoms; and 
(b) from about 1 part to about 4 parts by weight of a thiuram compound 
having the following formula: 
##STR1## 
where R is hydrogen or alkyl group having from 1 to 6 carbon atoms and 
where Q is selected from the group of thio radicals consisting of --S--, 
--S--S--, and combinations thereof; whereby said composition resists 
structural cracking under continuous exposure to temperatures above about 
180.degree. F. 
The objects of the invention are also achieved by a rubber laminate 
resistant to heat and fluid diffusion, comprising: a heat resistant rubber 
layer and a diffusion-resistant rubber layer; said diffusion-resistant 
layer comprising a composition having, upon curing, a durometer hardness 
of from about 15 to about 75 on the Shore D Scale, said composition 
comprising (a) about 100 parts by weight of a rubber elastomer selected 
from the group consisting of (1) natural rubber, (2) a polymer made from 
diene monomers having from 4 to 12 carbon atoms, (3) a copolymer made from 
diene monomers having from 4 to 12 carbon atoms, and (4) a copolymer made 
from vinyl substituted aromatic monomers having from 8 to 12 carbon atoms 
and diene monomers having from 4 to 12 carbon atoms; (b) from about 1 part 
to about 4 parts by weight of a thiuram compound having the following 
formula: 
##STR2## 
where R is hydrogen or an alkyl group having 1 to 6 carbon atoms and where 
Q is selected from the group of thio radicals consisting of --S--, 
--S--S--, and combinations thereof; whereby said composition resists 
structural cracking under continuous exposure to temperatures above about 
180.degree. F.; said heat resistant layer comprising a blend having less 
then ten percent (10%) change in percentage elongation after exposure to 
temperatures of about 212.degree. F. for periods greater than about 70 
hours, said blend comprising (1) about 100 parts by weight of a rubber 
elastomer selected from the group consisting of (a) natural rubber, (b) a 
polymer made from diene monomers having from 4 to 12 carbon atoms, (c) a 
copolymer made from diene monomers having from 4 to 12 carbon atoms, and 
(d) a copolymer made from vinyl substituted aromatic monomers having from 
8 to 12 carbon atoms and diene monomers having from 4 to 12 carbon atoms, 
(e) homopolymers made from chloro-substituted diene monomers having from 4 
to 12 carbon atoms, (f) copolymers made from cyano-substituted olefin 
monomers having from 2 to 8 carbon atoms and diene monomers having from 4 
to 12 carbon atoms; and (2) about 1 part by weight of a salt of a 
benzimidazole having the following formula: 
##STR3## 
where Y is selected from the group of radicals consisting of hydrogen and 
mercapto and where Z is selected from the group of radicals consisting of 
hydrogen and alkyl groups having from 1 to 6 carbon atoms; whereby said 
heat resistant layer resists oxidation at elevated temperatures over 
extended time periods to retain or increase its tensile strength.

BEST MODE FOR CARRYING OUT THE INVENTION 
According to the concepts of the present invention, a rubber liner 
resistant to fluid diffusion must be capable of withstanding continual 
exposure to elevated temperatures for extended periods of time. For the 
diffusion-resistant rubber liner to be effective, according to the 
concepts of the present invention, the rubber liner must prevent diffusion 
of fluids to form pockets of corrosion between the rubber laminate and the 
metal substrate. A rubber liner which is diffusion resistant must be 
resistant to structural cracking of its composition upon exposure to 
elevated temperatures for continuous periods of time. By limiting the 
concentration of curing agents, the maximum cure of the rubber liner 
resistant to fluid diffusion does not exceed the point where the durometer 
hardness of the rubber composition exceeds about 75 on the Shore D Scale. 
It has been found by the inventor that structural integrity of the rubber 
liner is maintained when the durometer hardness of the rubber composition 
is less than about 75 on the Shore D Scale upon curing of the blend. 
The rubber liner of the present invention resistant to fluid diffusion is 
indicated by the number 15 as seen in FIG. 1. The cross-sectional rubber 
laminate 11 in which rubber liner 15 is a component may be seen in FIG. 2 
and the applications of the laminate to straight and curved metal 
substrates as seen in FIGS. 3 and 4, respectively. 
The rubber liner 15 can generally be prepared from any type of rubber 
elastomer which resists diffusion and may be limited by other compounds to 
a cure less than about a durometer hardness of about 75 on the Shore D 
Scale. Rubber elastomers for liner 15 include natural rubber, that is 
cis-1, 4-polyisoprene obtained from "rubber trees," various homopolymers 
or interpolymers such as copolymers made from diene monomers, containing 
from 4 to 12 carbon atoms, and various copolymers made from vinyl 
substituted aromatic monomers containing from 8 to 12 carbon atoms and the 
diene monomers containing from 4 to 12 carbon atoms. Specific examples of 
diene monomers include isoprene (that is containing both cis and trans 
isomers), butadiene, piperylene, hexadiene, heptadiene, octadiene, 
decadiene, dodecadiene, 2,3-dimethyl-1,3-butydiene, 2-methyl-1, 
3-pentadiene, 3,4-dimethyl-1,3-hexadiene, 4,5-diethyl-1,3-octadiene, 
3-butyl-1,3-octadiene and the like. Preferred monomers include isoprene, 
and butadiene. An example of a homopolymer of diene monomers is cis-1, 
3-polyisoprene (synthetic natural rubber). Examples of various copolymers 
made from said dienes include butadiene-isoprene, piperylene-isoprene, 
butadiene-hexadiene, and the like. 
Examples of specific vinyl substituted aromatic monomers include styrene, 
alpha-methylstyrene, ortho-, para-, and meta-methyl, ethyl styrenes, and 
the like. Specific examples of copolymers containing vinyl substituted 
aromatic monomers include styrene-butadiene (SBR), styrene-isoprene, 
alpha-methylstyrene-butadiene and the like. A desirable copolymer is 
styrene-butadiene. The highly preferred rubber elastomer is natural 
rubber, that is cis-1,4-polyisoprene. Generally, the number average 
molecular weight of the rubber elastomer in liner 15 may range from about 
10,000 to about 500,000 with a range of from about 100,000 to about 
400,000 being preferred. 
Based upon 100 parts by weight of said rubber elastomer, from about 1 to 
about 4, desirably from about 2 to about 4, and preferably about 2.5 parts 
by weight of a thiuram compound is added. The thiuram compound is defined 
to be that group of compounds having the following formula: 
##STR4## 
where R is hydrogen or an alkyl group having from 1 to 6 carbon atoms, and 
where Q is selected from the group of thio radicals consisting of --S--, 
--S--S--, and combinations thereof. Examples of thiuram compounds include 
tetramethyl thiuram monosulfide, tetramethyl thiuram disulfide, tetraethyl 
thiuram monosulfide, and tetraethyl thiuram disulfide. Of the compounds 
having the above described formula, tetramethyl thiuram disulfide and 
tetramethyl thiuram monosulfide are desirable, and tetramethyl thiuram 
monosulfide (TMTM) is preferred. 
In addition to the rubber elastomer and the thiuram compound, other 
ingredients may be added to the rubber liner composition. It has been 
found that from about 30 parts to about 60 parts by weight of sulfur and 
from about 5 parts by weight to about 15 parts by weight of zinc oxide aid 
in the processing and curing of the rubber liner 15. Preferably, about 50 
parts of sulfur and about 8 parts by weight of zinc oxide may be added. 
Finally, about 0.2 parts by weight of a peptizer may be added to the blend 
for rubber lining 15 to aid in processing. The peptizer is available by 
the commercial name of Pepton, a powder peptizer produced by American 
Cyanamide. 
In addition to the above-identified compounds which, when mixed with the 
rubber elastomer, yield a rubber liner having diffusion resistance, 
desirable amounts of various conventional compounds or compounding agents 
may be added to the rubber to improve its physical properties as is known 
in the art. For example, carbon black, silica, various clays, waxes and 
fibers may be utilized along with a host of other compounds such as 
fillers, antioxidants, anti-ozonants, accelerators, processing agents, and 
the like. In addition to a curing agent such as sulfur, organic peroxides 
may be added in sufficient amounts to cure the rubber upon heating. 
However, control of the concentration of the thiuram compound is necessary 
to limit the durometer hardness to about 75 on the Shore D Scale. 
Once the rubber elastomer having these various components has been 
compounded, it is generally mixed on a mill. Mixing on the mill may occur 
from about 100.degree. to about 180.degree. Fahrenheit. Following mixing, 
the rubber elastomeric blend is formed into rubber liner 15 on a calendar 
roll at a temperature from about 125.degree. F. to about 180.degree. F. 
Various thicknesses may be created for the liner 15 depending upon the 
particular application. However, it has been found that a thickness from 
about 0.035 to about 0.100 inches will provide adequate diffusion 
resistance for the predominant number of applications. Preferably, the 
thickness is about 0.088 inches for most pipes, tanks, and other vessels 
in industrial production of phosphoric acid. 
The application of rubber liner 15 to a metal substrate will prevent the 
diffusion of moisture and other corrosive fluids from the phosphoric acid 
or other corrosive material through the liner 15 to the metal substrate. 
Moisture and other corrosive materials may diffuse through rubber 
materials in only one direction. Once the moisture or other corrosive 
material is trapped between a rubber liner and the metal substrate, with 
no route for removal, the moisture or other corrosive material will attack 
the metal substrate. Therefore, continued maintenance of the diffusion 
resistance in the rubber liner 15 maintains longer production life for the 
metal substrates forming the tanks, pipes, and other vessels of industrial 
production of corrosive materials. 
Diffusion resistance is seriously weakened by a continual hardening or 
curing of the rubber liner 15 upon continued exposure to elevated 
processing temperatures. With production temperatures for phosphoric acid 
typically around 185.degree. Fahrenheit, the uncured rubber liner 15 is 
cured continually under these conditions. As the curing and hardening 
continues, cracks and other structural weaknesses in the rubber liner 15 
develop making diffusion of moisture and other corrosive materials more 
likely to the metal substrate. Therefore, preventing a continual hardening 
or curing of the rubber liner 15 is necessary to maintain the diffusion 
resistant characteristics of rubber liner 15 as compounded using materials 
described above. Regulation of the concentration of the thiuram compound 
greatly alters the surface structure of the rubber liner 15, by altering 
the durometer hardness properties of the liner 15. 
The rubber liner 15 was prepared according to the following recipe: 
TABLE I 
______________________________________ 
RUBBER LINER RECIPES 
(Parts by Weight) 
COMPOUNDS Sample 1 Sample 2 Sample 3 
Sample 4 
______________________________________ 
Natural Rubber 
100 100 100 100 
(constant vicosity 60- 
premasticated) 
Sulfur (spider type) 
50 50 50 50 
Zinc Oxide 8.00 8.00 8.00 8.00 
Tetramethyl Thiuram 
0 1 2 4 
Monosulfide (TMTM) 
Pepton (Peptizer from 
0.2 0.2 0.2 0.2 
American Cyanamide) 
______________________________________ 
As shown in Table I, four samples of rubber liner 15 were prepared, with 
varying amounts of the thiuram compound. Each of the samples were 
subjected to a temperature of about 212.degree. F. for a constant period 
of 48 hours. As seen with reference to Table II, below, Sample 1 exhibited 
0 Shore D hardness and was too soft for effective resistance. However, 
progressing from Sample 2 to Sample 4 as seen in Table II, the hardness 
was in an acceptable range on the Shore D Scale from about 15 to about 75. 
Adding one part by weight of the thiuram compound formed a rubber liner 15 
which was acceptable for diffusion resistance, though at the soft area of 
the acceptable range. Likewise, Sample 4, yielded a rubber liner 15 within 
the acceptable range at the hard end of the spectrum. 
TABLE II 
______________________________________ 
Sample 
1 2 3 4 
______________________________________ 
Durometer Hardness 
0 15 35 75 
(Shore D Scale) 
______________________________________ 
The rubber liner 15 having from 1 to 4 parts of the thiuram compound 
maintains its diffusion resistance property over extended periods of time 
and elevated temperatures. Without a controlled durometer hardness 
property, the rubber liner 15 would continue to cure, weakening its 
structure and rendering it more susceptible to moisture and corrosive 
material diffusion than is permitted for industrial processing at 
temperatures of about 185.degree. F. or greater. It has been found by the 
inventor that the weakened structure of liner 15 weakens all other layers 
of a laminate, despite different curing properties. By employing a rubber 
liner 15 of the present invention, it may be possible to raise 
temperatures in the reaction vessels, pipes, and tanks of industrial 
production of phosphoric acid, because the rubber liner 15 of the present 
invention may maintain its diffusion resistance properties without a 
weakening structural degradation during constant elevated temperatures and 
periods of time. At higher temperatures such as about 220.degree. F., 
greater concentrations of phosphoric acid are produced as well a greater 
volume of material being processed. The rubber liner 15 of the present 
invention increases the production efficiency for that industrial process. 
As described above, the thiuram compound is mixed with the rubber 
elastomer, the sulfur, and the zinc oxide. If there is a delay in 
production between the mixing stage and calendar steps, the thiuram 
compound should be withheld from the rubber compound during storage and 
added immediately prior to the calendaring of the rubber compound into 
rubber liner 15. Whereas the original mixing on the mill occurs for about 
30 minutes, the rubber compound is not adversely affected by subsequent 
mixing of the thiuram compound therein immediately prior to calendaring. 
FIG. 2 shows a preferred 3-layer laminate 11. The above-described rubber 
elastomer blend having the thiuram compound controlling durometer hardness 
constitutes intermediate or central layer 15. The interior layer 20 is 
made from any soft rubber material, that is a rubber elastomer which has a 
Shore A hardness of from about 30 to about 40, with approximately 35 being 
preferred. The soft layer permits maximum rubber-to-metal adhesion between 
the laminate 11 and the metal substrate 30, whether straight or curved as 
seen in FIGS. 3 and 4, respectively. On the opposite side of liner 15 is 
the exterior liner 10 which is also made from a soft rubber material 
having a Shore A hardness of from about 30 to about 40, with approximately 
35 being preferred. As described below, either layer 10 or layer 20 or 
both may have particular heat resistant properties suitable for combining 
with the rubber liner 15 of the present invention to prevent degradation 
of the overall laminate 11. Laminate 11 may also contain any number of 
layers in addition to the three layers mentioned, as long as a soft rubber 
layer creates the rubber-to-metal adhesion. The rubber liner 15 of the 
present invention provides diffusion resistance, and the soft outer layer 
10 prevents direct contact of the corrosive material and its by-product 
with the rubber liner 15 of the present invention. 
While the layers 10 and 20 have been described as any soft rubber material, 
it has been found by the inventor that the combination of a particular 
known formulation for layer 10, in combination with the rubber liner 15 of 
the present invention, provides unexpected improvements to the overall 
structural integrity of the laminate 11 when subjected to constant 
temperatures in excess of 185.degree. F. for continuous periods of time in 
the presence of the corrosive material and its by-products. The rubber 
elastomer for layer 10 may be any of the rubber elastomers previously 
described for rubber liner 15 including natural rubber, polymers made from 
diene monomers having from 4 to 12 carbon atoms, copolymers made from 
diene monomers having from 4 to 12 carbon atoms, and copolymers made from 
vinyl substituted aromatic monomers having from 8 to 12 carbon atoms and 
diene monomers having from 4 to 12 carbon atoms. Additionally homopolymers 
made from chloro substituted diene monomers having from 4 to 12 carbon 
atoms, and various copolymers made from cyano-substituted olefin monomers 
containing from 2 to 8 carbon atoms and diene monomers containing from 4 
to 12 carbon atoms, may become rubber elastomers for layer 10. 
In addition to the rubber elastomers, layer 10 may also have various 
antioxidants which contribute to its heat resistant properties. In a 
formulation prepared by the Malaysian National Rubber Bureau, it has been 
found that the zinc salt of 2-mercapto-4(5)-methylbenzimidazole provides 
oxidation resistance which resists heat for rubber layer 10. Therefore, 
rubber layer 10 should have about 1 part by weight of a salt of a 
benzimidazole having the following formula 
##STR5## 
where Y is selected from the group of radicals consisting of hydrogen and 
mercapto and where Z is selected from the group of radicals consisting of 
hydrogen and alkyl radicals having from 1 to 6 carbon atoms. These 
compounds are commercially available from Mobay Chemical Corporation under 
the trade name of Vulcanox ZMB. 
In addition to the rubber elastomer and the benzimidazole compound, the 
Malaysian Rubber Bureau formulation includes AgeRite resin D, manufactured 
by R. T. Vanderbuilt Co. This resin is polymerized 1, 
2-dihydro-2,2,4-trimethylquinoline. The combination of the rubber 
elastomer, the benzimidazole compound and the AgeRite resin D contribute 
greatly to antioxidant properties which give good aging properties with 
limited effect on the modulus of the layer 10 during periods of constant 
exposure to elevated temperatures. 
In addition to the rubber elastomer, the benzimidazole compound, and the 
quinoline compound, the formulation of the Malaysian Rubber Bureau 
includes about 3.2 parts of a compound having the following formula, which 
is the reaction product of a nitrosophenols and a di-isocyanate. 
##STR6## 
This material is commercially available from Durham Chemicals Limited 
under the trade name of Novor 924, and this compound serves as a 
vulcanizing agent providing a pseudo-urethane crosslinking for the 
compound comprising rubber layer 10. 
Other materials included in the formulation by the Malaysian Rubber Bureau 
are about 0.90 parts by weight of 4,4 dithiodimorpholine, and about 0.10 
parts by weight of N-tert-butyl-2-benzothiazolesulfenamide. The first 
compound is commercially available from the Monsanto Company under the 
trade name of Sulfasan R, and the latter is commercially available from 
the same company under the trade name Santocure NS. An additional material 
in the blend for rubber layer 10 is about 1.3 parts of tetramethylthiuram 
monosulfide. 
As seen with reference to Table 3, there are several other materials in the 
rubber layer recipe of the Malaysian Rubber Bureau commonly used in rubber 
compounding. 
TABLE III 
______________________________________ 
RUBBER LAYER RECIPE 
MALAYSIAN RUBBER BUREAU 
COMPOUND TS BY WEIGHT 
______________________________________ 
Natural Rubber 100 
(Number 1 Ribbed Smoke Sheet) 
Pepton 0.20 
Zinc Oxide 1.05 
Stearic Acid .50 
AgeRite Resin D 2.00 
Novor 924 3.20 
TMTM 1.30 
Sulfasan R 0.90 
Santocure NS 0.10 
Vulkanox ZMB-Z 1.00 
Circolite Oil 1.85 
(a lightweight processing oil) 
______________________________________ 
After mixing the ingredients in Table III for a period of about 30 minutes 
on a mill at a temperature from about 100.degree. F. to about 180.degree. 
F., the blend is calendared at a temperature from about 125.degree. to 
about 180.degree. F. to form a layer 10. This layer may have a varying 
thickness depending upon the thicknesses of the layers 15 and 20 in 
laminate 11 and the desired protection for the metal substrate 30. 
Typically, the layer 10 has a thickness of about 0.112 inches. Generally, 
it may be stated that the greater the thickness of the layer 10 to provide 
heat resistance for the entire laminate 11, the greater the overall 
resistance of laminate 11 to diffusion of moisture or other corrosive 
materials. 
As stated above, layer 20 may be any soft rubber compound which permits 
maximum rubber-to-metal adhesion. However, it is desirable to use the 
rubber layer recipe described in Table III for layer 20 as well as layer 
10. It has been found that this recipe of the Malaysian Rubber Bureau 
exhibits good rubber-to-metal adhesion necessary for laminate 11. 
The properties of rubber layer 10 exhibit excellent sustained tensile 
strength and percentage elongation which benefits the overall laminate 11. 
As seen in Table IV, the tensile strength of layer 10 increases and the 
percentage elongation does not endure a percentage change greater than ten 
percent (10%). 
TABLE IV 
______________________________________ 
Standard Cure 
Layer of Recipe 
10 mins. Cure for 70 Hrs. 
Percent 
in Table III 
320.degree. F. 
At 212.degree. F. 
Change 
______________________________________ 
TENSILE STRENGTH (PSI) 
1st Reading 
2475 3275 +32 
2nd Reading 
2200 2825 +28 
3rd Reading 
2125 3225 +52 
% ELONGATION 
1st Reading 
680 650 -4 
2nd Reading 
670 640 -4 
3rd Reading 
650 690 +6 
______________________________________ 
While it may appear that the overall laminate 11 is improved by layer 10 
having the recipe described in Table III, it has been found by the 
inventor that rubber liner 15 of the present invention controls the 
performance of the heat resistant layer 10 for the laminate 11. The rubber 
liner 15 must not cure beyond a durometer hardness of 75 on the Shore D 
Scale to prevent a significant loss in percentage elongation which will 
crack or fissure layer 10. It has been found by the inventor that, despite 
the excellent percentage elongation of layer 10, it is not capable of 
preventing a structural weakness when the same is first generated in the 
liner 15. Further, the diffusion resistance of the rubber liner 15 
maintains its effectiveness over great periods of time at elevated 
temperatures, and layer 10 supplements the formulation of rubber liner 15 
to slow the curing of liner 15, and never beyond a durometer hardness of 
75 on the Shore D Scale. The combination of layers, one having the recipe 
of Table I and the other having the recipe of Table III combine to produce 
a laminate 11 having the unexpected properties of diffusion resistance 
maintained by heat resistant materials. 
Whenever an anti-foaming agent such as kerosene is employed in the reaction 
processing, or when kerosene is employed in uranium ore floatation 
recovery methods, the laminate 11 may also have a layer 10 resistant to 
heat and the degrading effects of petroleum and its derivatives upon 
layers 10, 15, and 20. Such rubber elastomers as nitrile rubber and 
polychloroprene (neoprene) are particularly suitable for blending with the 
heat resistant formulation of the Malaysian Natural Rubber Bureau. It has 
been found a nitrile rubber having a composition found in Table V may be 
blended with the Malaysian Natural Rubber Bureau Formulation of Table III 
to provide protection against kerosene degradation against layer 10 while 
maintaining high temperature resistance, as seen in Table VI. The blend of 
heat resistant rubber and anti-foaming agent resistant rubber may be from 
10 percent by weight/90 percent by weight anti-foamer resistant 
rubber/high temperature resistant rubber to 90 percent/10 percent 
anti-foamer resistant rubber/high temperature resistant rubber. Desirably, 
the blend may be from 30 percent/70 percent to 70 percent/30 percent 
anti-foamer resistant rubber/high temperature resistant rubber. 
TABLE V 
______________________________________ 
RESISTANT RUBBER OIL 
Compound Parts By Weight 
______________________________________ 
Nitrile Rubber 100.00 
(Hycar 1052-30 by B. F. Goodrich) 
Carbon Black 30.00 
(N 762 Black) 
Stearic Acid 1.00 
Zinc Oxide 5.00 
Dibutyl Pathalate Oil 15.00 
(A Plasticizer) 
Sunolube 240 Wax 0.50 
(Sun Oil Co.) 
AgeRite Resin D 1.00 
AKROCHEM P 90 Resin 5.00 
(phenol formaldehyde resin tactifier, 
Akron Chemical Co.) 
Santocure NS 2.00 
Tetramethyl Thiuram Disulfide 
2.00 
Sulfasan R 2.00 
______________________________________ 
TABLE VI 
______________________________________ 
50% BY WEIGHT OF RUBBER OF TABLE III/ 
50% BY WEIGHT OF RUBBER OF TABLE V 
Standard Cure 
10 minutes Cure for 70 Hrs. 
Percent 
Sample 320.degree. F. 
212.degree. F. 
Change 
______________________________________ 
TENSILE STRENGTH 
1st Reading 
2100 2250 +7% 
2nd Reading 
2020 2300 +13% 
3rd Reading 
2040 2250 +10% 
% ELONGATION 
1st Reading 
600 600 0% 
2nd Reading 
600 620 +3% 
3rd Reading 
630 630 0% 
______________________________________ 
It is apparent from an examination of Table VI that a blend of oil 
resistant rubber and heat resistant rubber have a durometer hardness of 
about 40 on the Shore A Scale, synergistically provides a maintained 
resistance to heat, as measured by tensile strength and percent 
elongation. Further, with nitrile rubber or neoprene rubber, the oil 
resistant rubber portion of the blend resists the degradation of laminate 
11 from kerosene degradation. Comparison of Tables VI and IV demonstrates 
the addition of the blended oil resistant rubber does not affect the 
tensile strength or the percent elongation properties of the heat 
resistant rubber either alone or in combination with the oil resistant 
rubber. 
In accordance with the Patent Statutes, the best mode for carrying out the 
invention has been provided. However, the invention is not to be limited 
thereto or thereby. Consequently, for an understanding of the scope of the 
invention, reference is had to the following claims.