Process for the production of permeation resistant containers

A multi-step blow molding process for producing fuel containers having excellent resistance to permeation by hydrocarbon fuels and organic fuel additives such as lower alkanols and ethers. In blow molding, a parison is formed from a thermoplastic material, expanded within a closed mold by means of an inflating gas for conforming the parison to the shape of the mold and fluorinated under conditions sufficient to effect surface fluorination of the interior of the parison. The parison is evacuated and the article recovered. The improvement in the blow molding operation comprises pressurizing the parison with a reactive fluorine containing gas containing from 0.1 to 1% fluorine by volume while the parison is at a temperature above its self supporting temperature and for a time sufficient to effect fluorination of the interior surface of the parison. Subsequently, the interior surface of the pre-fluorinated parison is pressurized with a reactive fluorine containing gas containing at least twice the initial concentration but not less than about 1% fluorine by volume for a time, typically from about 2 to 30 seconds to form said fluorinated parison having reduced permeability.

FIELD OF THE INVENTION 
This invention pertains to a process for the fluorination of polymeric 
materials, e.g. polyethylene, to produce containers resistant to 
permeation by hydrocarbons, polar liquids and mixtures of hydrocarbons and 
polar liquids. 
BACKGROUND OF THE INVENTION 
Fluorination of polyethylene and other polymeric materials to improve their 
resistance to solvents and to vapor permeation has long been practiced. 
Early work was reported by Joffre in U.S. Pat. No. 2,811,468 and Dixon et 
al. in U.S. Pat. No. 3,862,284. The '468 patent showed the early room 
temperature fluorination of polyethylene materials to improve the barrier 
properties thus enhancing the material as a wrapping material for 
foodstuffs and perishable materials and for the generation of containers 
via a blow molding operation utilizing a reactive fluorine containing gas 
for conforming the shape of the molten polyethylene parison to the mold. 
Joffre carried out fluorination of polyethylene film and of container 
walls in chambers by contacting the polyethylene surface with a fluorine 
containing gas at room temperature for a period of about 20 to 150 minutes 
to achieve fluorine concentrations of 0.03 to 3.5 percent by weight of 
fluorine based on the weight of the polyethylene. 
Dixon et al., in '284 disclosed fluorination of a variety of polymeric 
materials in blow molding operations to enhance their barrier properties. 
A treatment gas containing from about 0.1 to 10% by volume of fluorine in 
an inert gas was injected into the parison and inflated or expanded into 
shape utilizing the reactive gas. Due to the higher temperature, a blowing 
time of approximately 5 seconds was utilized at which time the parison was 
cooled and the reactive gas and container recovered. 
Commercially fuel tanks having enhanced resistance to hydrocarbon 
permeation have been marketed under the Airopak trademark wherein the fuel 
tanks were produced utilizing blow molding techniques. In these processes 
the parison is initially conformed to the desired shape by inflating or 
expanding with an inert gas, followed by evacuation of the parison and 
subsequent injection of the parison with a reactive gas containing from 
0.1 to 10% fluorine. The reactive gas is removed from the parison, 
recovered and the container ejected from the mold. 
There have been substantial modifications to the early processes for the 
production of containers having enhanced barrier properties via blow 
molding. Some of these processes are described in the following patents, 
they are: 
U.S. Pat. No. 4,142,032 discloses an apparent improvement in the Dixon et 
al., process utilizing a reactive gas containing both fluorine and a 
reactive bromine source at temperatures below the softening point of the 
polymer and pressures one atmosphere or less. Basically, then, the '032 
process is similar to that of Joffre '468 in that the fluorination is 
effected at low temperature, thus requiring long reaction times. 
U.S. Pat. Nos. 4,404,256; 4,264,750; and 4,593,050 disclose a low 
temperature fluorination of polyolefins, e.g. polyethylene and 
polypropylene, to form low energy surfaces utilizing wave energy in 
association with the fluorination process. The '256 and '750 patents 
disclose contacting the polymer surface with ions or radicals comprising 
fluorine or fluorinated carbon as a cold plasma. The '050 discloses 
fluorination of polymer surfaces utilizing a fluorinating gas and 
enhancing the fluorination by exposing the surface to ultraviolet 
radiation to assist in the fluorination process. 
U.S. Pat. No. 4,701,290 discloses the production of high density 
polyethylene fuel tanks having increased barrier resistance to hydrocarbon 
vapor permeation via off-line-fluorination. The key to enhancing barrier 
permeation resistance lies in the precise control of fluorination of the 
polyethylene fuel tank and this is achieved by passing the treatment gas 
through a container filled with aluminum oxide. By measuring the quantity 
of oxygen generated from the Al.sub.2 O.sub.3, one controls the 
concentration of fluorine contained in the treatment gas and thereby 
controls the level of fluorine acting upon the surface of the container 
within a predefined reaction time. 
Improvements in blow molding processes have also been made since the 
discovery of the Dixon, et al. higher temperature blow molding process and 
these are reported in U.S. Pat. Nos. 4,830,810; 4,617,077 and 4,869,859. 
The '810 patent discloses a blow molding process for producing containers 
comprising inserting the preform or parison into the mold, injecting inert 
gas into the parison at a first level of pressure to expand and conform it 
to the shape of the mold, raising the pressure to a level above the first 
level by injecting a fluorine containing reactant gas into the parison 
after pressure tightness has been determined. The reactant gas typically 
comprises a mixture of fluorine and nitrogen with the fluorine 
concentration being about 1% by volume; the injection pressures are from 4 
to about 10 bar and reaction times of about 30 seconds. The process 
eliminates some of the hazards associated with blow molding using a 
reactive gas to conform the parison to the mold since pressure tightness 
at the time of injection of the reaction gas may not have been 
established. The '077 patent modifies the '810 process in that inflation 
of the parison in the mold with an inert gas is conducted at high pressure 
followed by treatment of the interior of the parison with a fluorine 
containing gas at substantially lower pressure than that used for 
initially expanding the parison or preform. After reaction, the reaction 
gas is replaced with a flushing and cooling gas at a pressure 
substantially higher than the pressure of the reaction gas and even higher 
than the initial injection gas used to preform the parison. 
U.S. Pat. No. 4,869,859 discloses a blow molding process for the 
preparation of high density polyolefin fuel tanks. The patentees indicate 
that severe wrinkling of the thermoplastic occurs at temperatures close to 
or above the melting point. Fluorination is carried out at temperatures 
from 50.degree. to 130.degree. C., preferably 80.degree. to 120.degree. 
C., and below the molding temperature, in an effort to achieve uniform 
temperature distribution and fluorination of the interior surface of the 
material. 
SUMMARY OF THE INVENTION 
This invention relates to an improved in-line multi-step fluorination 
process for the blow molding of thermoplastic containers such as fuel 
containers and bottles which have enhanced barrier properties. The fuel 
tank containers have enhanced barrier properties with respect to vapor 
permeation by hydrocarbons, polar liquids, and hydrocarbon fuels 
containing polar liquids such as alcohols, ethers, amines, carboxylic 
acids, ketones, etc. In the basic process for the production of blow 
molded thermoplastic articles via in-line fluorination wherein a parison 
of thermoplastic material is formed, expanded within a closed mold by 
means of a gas for conforming the parison to the shape of the mold, 
fluorinated under conditions sufficient to effect surface fluorination of 
the interior of said parison and then evacuating the parison, purging, and 
recovering the parison from the mold. The improvement resides in the 
multi-stage fluorination of the parison comprising the steps: 
effecting a fluorination of the surface of the parison by contacting the 
parison with a reactant gas comprising a reactive fluorine containing gas 
containing from about 0.1 to 1% fluorine by volume while the thermoplastic 
is at a temperature above its self-supporting temperature for a time 
sufficient to effect fluorination of the surface of the parison; and then, 
contacting the initial fluorinated surface of the parison while at an 
elevated temperature with a reactive fluorine containing gas having a 
fluorine concentration of at least twice that used in the initial 
fluorination but such fluorine concentration in said gas being not less 
than about 1%. 
There are several advantages associated with the in-line multi-step 
fluorination process to produce containers having improved barrier 
properties, and these include: 
the ability to form permeation resistant containers having enhanced barrier 
properties, particularly with respect to hydrocarbons, polar liquids and 
hydrocarbons containing polar liquids such as alcohols, ethers, amines, 
carboxylic acids, ketones, etc.; 
the ability to produce permeation resistant containers via an in-line blow 
molding process while achieving fluorination at commercial production 
rates; 
the ability to produce high density polyethylene fuel containers 
particularly suited for the automotive industry, such containers having 
reduced permeation associated with hydrocarbon fuels blended with lower 
alcohols such as methanol, ethanol, ethers such as methyl tertiary butyl 
ether, ketones, etc.; and 
the ability to produce thin-walled containers having excellent permeation 
resistance. 
DETAILED DESCRIPTION OF THE INVENTION 
Automotive standards regarding vapor permeation rates associated with 
hydrocarbon fuels and particularly hydrocarbon fuels containing minor 
portions of lower alkanols have been established for some times. Fuel 
tanks constructed of fluorinated high density polyethylene and produced 
via in-line fluorination processes meet current environmental emission 
requirements from the automobile manufacturers. However, such fuel 
containers do not meet the proposed environmental emission requirements, 
particularly when those hydrocarbon fuels are blended with polar liquids 
such as lower alkanols, e.g., methanol, ethanol, ethers such as methyl 
tertiary butyl ether, ketones, amines and other fuel additives. The 
California Air Resources Board (CARB) has proposed regulations suggesting 
that a final permeation rate of less than 0.2 g/day would be desirable for 
future fuel tanks. 
Blow molding of thermoplastic materials to produce containers of various 
sizes, wall thicknesses and shapes is well known. Thermoplastic material 
such as polymers and copolymers of polystyrene, polyacrylonitrile, 
polyvinylchloride and particularly polyolefins such as low density and 
high density polyethylene and polypropylene often are used in producing 
containers and they can be treated via in-line fluorination to enhance 
their barrier properties in accordance with this process. The process is 
particularly adapted for the fluorination of thick-walled containers, 
e.g., 3 millimeters (mm) and greater, typically 3 to about 6 mm high 
density polyethylene for the fabrication of fuel tanks for the automotive 
industry and thin-walled, e.g., 2 mm and less wall thickness, bottle-type 
containers. 
In a typical blow molding process for producing hollow articles or 
containers, a thermoplastic is heated to a temperature above its softening 
point, formed into a parison and injected into a mold. The parison is 
inflated or expanded in its softened or molten state via sufficient 
pressurization with a gas to conform the parison to the contour of the 
mold. In many processes, fluorine-containing gases initially are used to 
inflate and conform the parison to the contour of the mold. However, 
releases may occur during the initial pressurization of the parisons, 
particularly thick-walled containers such as fuel tanks and cause a 
release of fluorine and contaminate the workplace. In recent years, the 
parison initially is conformed to the mold via pressurization with a 
substantially inert gas, e.g. nitrogen, helium, or argon, to ensure that a 
seal is formed, then fluorinated in an effort to reduce environmental 
contamination and occupational hazards. 
Although fuel tanks constructed via the above described in-line 
fluorination process have provided acceptable barrier to permeation by 
hydrocarbon solvents and meet current environmental emission requirements, 
the in-line processes have not produced containers having acceptable 
barrier resistance to permeation by hydrocarbon solvents containing polar 
liquids to meet future environmental emission requirements. Thin-walled 
products such as bottles also are noted to have high permeation rates and 
greater barrier resistance is required. 
In the conceptual development of the invention it was postulated that 
surface damage in the form of "molecular pinholes", if you will, which 
rendered the container permeable to alcohols, ethers, and other organic 
fuel additives, were being generated in prior art processes by the high 
temperature reaction of fluorine with the polymer at its surface. The key 
to reducing permeation was visualized as controlling the level of CF.sub.x 
sites at the surface of the polymer, these sites indicating a high degree 
of reaction and high localized temperatures during the initial contact 
with the reactant gases. The high localized temperature lead to the 
formation of molecular pinholes at the surface of the container thereby 
leading to excessive permeation. Barrier properties were believed to be 
relatively independent of fluorine concentration in the polymer. The 
development, had as its objective, the modification of fluorination 
processes for effecting reduction and elimination of the molecular 
pinholes from the surface of the container while at the same time 
effecting fluorination of the container at levels sufficient to provide 
the necessary and desired physical properties for fuel containers and 
bottles, e.g., abrasion and solvent permeation resistance, etc. 
An in-line, multi-step process for fluorinating fuel tanks and thin-walled 
bottle type polymer containers was considered the viable way to produce 
containers having an acceptable barrier to hydrocarbon solvents containing 
polar liquids as well as to meet future environmental emission 
requirements. The in-line, multi-step fluorination process would require 
carefully controlling the polymer temperature, concentration of fluorine 
in the reactant gas used during fluorination and the contact time of 
fluorination. The parison initially would be contacted with an initial 
reactant gas containing a low concentration of fluorine, the balance 
thereof being inert under the reaction conditions, at a temperature above 
the self-supporting temperature of the thermoplastic and for a time 
sufficient to effect surface fluorination. The self-supporting temperature 
here is defined as the temperature at which the parison or container will 
collapse if removed from the mold. If a reactant gas having a high 
concentration of fluorine were used to contact the polymer initially while 
it is at a temperature above the self-supporting temperature of the 
polymer, damage at the polymer surface may occur thereby reducing its 
barrier properties. 
The pre-fluorinated parison then would be contacted with a reactant gas 
containing a relatively high concentration of fluorine in subsequent 
steps. The pre-fluorinated polymer may be at a temperature above the 
self-supporting temperature of the polymer, but then cooled to a 
temperature below the self-supporting temperature, but elevated. The 
exposure of a pre-fluorinated parison to an ambient temperature reactant 
gas containing a substantially higher concentration of fluorine than used 
initially would cause further fluorination of the polymer without causing 
damage to the polymer surface. Excessive localized heating would be 
reduced since many of the available reactive sites would have reacted with 
fluorine in the initial treatment and because the surface temperature of 
the pre-fluorinated parison would have been reduced on contact with the 
ambient temperature gas. 
The in-line, multi-step fluorination process of the present invention 
therefore proposes to utilize an extremely dilute fluorine-containing gas, 
e.g., generally not greater than about 1%, preferably not greater than 
about 0.7% and most preferably not greater than about 0.5% by volume as 
the fluorinating agent in the initial fluorination of thick walled 
containers, e.g., 3 mm and greater, while the thermoplastic is at a 
temperature above the self-supporting temperature of the polymer. For 
example, a temperature generally varying from about and above 105.degree. 
to 130.degree. C. would be required for high density polyethylene (HDPE). 
For thick-walled containers, the fluorine concentration of the initial 
reactant gas preferably should be about 0.25% to 0.7%; for thin-walled 
containers the fluorine concentration preferably should be from about 0.7 
to 1% by volume. If higher concentrations of fluorine in the reactant gas, 
e.g. &gt;1%, were injected into the parison while the polymer is above the 
self-supporting temperature and for extended times, e.g., greater than 
about 3 seconds, it appears that there is a searing or singeing effect, if 
you will, caused by the aggressive reaction of fluorine with carbon 
causing surface damage, leading to increased solvent permeation. Reaction 
or contact pressures are conventional and range from 2 to 50 bar. 
Since the initial fluorine treatment is carried out above the 
self-supporting temperature of the polymer, it is very important to 
carefully control the time involved in expanding and conforming the 
parison to the mold with an inert gas, if such initial step is used. The 
temperature of the polymer surface is largely dependent on the thickness 
of the wall, the temperature of the inflating gas and the contact time 
necessary for expanding and conforming the parison to the mold. For 
example, thin-walled containers cool rapidly on contact with room 
temperature inflation gas, thereby permitting the use of higher fluorine 
concentrations in the reactant gases. Thick-walled containers maintain 
temperature for a longer period of time and lower fluorine concentrations 
in the reactant gases are often required because of excessive surface 
temperatures. In any case, it is important to carefully control the 
expanding and conforming time in such a way that the initial fluorine 
treatment on contact with a reactant gas containing a low concentration of 
fluorine is carried out at a temperature above the self-supporting 
temperature of the polymer. Contact times range for a reaction period of 
about 2 to 30 seconds, preferably from about 5 to 20 seconds. Although 
reaction times can extend for dilute streams beyond 30 seconds, no 
significant advantages appear to be achieved. 
Once the surface of the container is fluorinated and the initial 
permeability substantially reduced, further fluorination of the surface to 
achieve the final reduction in permeability and achieve enhanced physical 
properties is effected. Secondary fluorination of the prefluorinated 
parison is achieved by contacting the surface with a fluorine-containing 
gas containing from above about 1 to 20% fluorine and preferably from 1 to 
10% fluorine by volume and more preferably from about 2 to 6% fluorine by 
volume of a period of 2 to 30 seconds, preferably a period of 5 to 20 
seconds for both the thick and thin-walled containers when the container 
wall temperature is at an elevated temperature but below the 
self-supporting temperature. It is treatment of the pre-fluorinated 
parison with the higher concentration of fluorine in the subsequent 
reactant gas that causes a second fluorination of the parison to occur, 
thereby creating a second fluorine-polymer gradient. Because of the 
initial surface treatment of the polymer via contact with the dilute 
fluorine-containing gas, contact of the polymer surface with the reactive 
gas containing the higher concentration of fluorine does not singe or sear 
the surface and thereby causing surface damage. 
Secondary treatment or fluorination of the pre-fluorinated parison can be 
achieved in more than one step by contacting reactive fluorine containing 
gases containing 1% and higher fluorine concentration with the surface of 
thick and thin-walled containers at an elevated temperature. For example, 
enhanced secondary fluorination can be achieved by utilizing a reactant 
gas containing 1% and higher fluorine for a period of 1 to 20 seconds, 
partially releasing the pressure and then undergoing a third or fourth 
treatment utilizing a reactive fluorine containing gas containing 1% and 
higher concentrations of fluorine for a period of 1 to 20 seconds. With 
each secondary fluorine treatment step, enhanced fluorination is achieved 
and essentially no surface disruption is observed by the reaction of 
reactant gas having a high concentration of fluorine gas with the 
thermoplastic polymer. 
In a preferred embodiment, solvent permeation resistant containers are made 
from polyethylene. Initial fluorination of the parison, and preferably at 
least the first treatment associated with the secondary fluorination, is 
to be conducted at above the self-supporting temperature of polyethylene. 
For polyethylene, this temperature will vary from 105.degree. C. to 
130.degree. C. and with final temperatures reaching below about 
100.degree. C. prior to ejection of the parison from the mold. If more 
than two fluorination stages are used in the multi-step process, 
subsequent stages may be carried out at temperatures below the 
self-supporting temperature. 
To summarize, in the multi-stage, in-line process, in contrast to the early 
methods of fluorination, initial contact of the parison is made with a 
dilute fluorine containing reactant gas for fluorinating the surface of 
the parison while the thermoplastic in its softened state and above while 
it is at a temperature above the self-supporting temperature for limited 
times. The dilute fluorine-containing reactant gas will have a fluorine 
concentration not greater than about 1% and preferably not greater than 
about 0.7 to 0.5% by volume for thick-walled containers and preferably not 
less than about 0.7 to 1% fluorine for thin-walled containers. Reaction 
periods of about 2 to 30 seconds, preferably from about 5 to 15 seconds, 
are employed. Initial surface fluorination at these concentrations effects 
an initial fluorinated polymer gradient. Secondary fluorination requires a 
reactant gas having a significantly higher fluorine concentration, 
typically from 2 to 5% for thick-walled containers and 5 to 10% for 
thin-walled containers. Contact times range from 2 to 30 seconds, 
preferably from 5 to 15 seconds for both initial and secondary treatment. 
The following examples are provided to illustrate various embodiments of 
the invention and are not intended to restrict the scope thereof.

COMATIVE EXAMPLE 1 
Multi-Step Production of Thin-walled Containers from High Density 
Polyethylene 
Cylindrical high density polyethylene (HDPE) thin-walled containers with a 
nominal wall thickness of 0.9 mm were prepared by the extrusion blow 
molding process. During the inflation process the containers were 
pressurized to approximately 100 psig with either an inert nitrogen or a 
reactive treatment gas containing 1 to 10% fluorine in inert nitrogen for 
a period of 6 or 12 seconds, after which the pressure was released from 
the containers for a period of one and one-half seconds to allow the inert 
nitrogen or reactive gas to escape. The containers were then repressurized 
to a second time to approximately 100 psig with inert nitrogen for a 
period of six seconds. After this the pressure was released from the 
containers for a period of one and one-half seconds to allow inert 
nitrogen to escape. They were pressurized a third time to approximately 
100 psig with inert nitrogen for 6 seconds. Finally, the containers were 
vented to atmospheric pressure and removed from the mold. According to the 
above procedure, the containers were treated with fluorine containing gas 
only in the first step at above the self-supporting temperature of HDPE. 
Containers prepared in the above manner were filled with a hydrocarbon 
solvent mixture consisting of eighty-five percent (85%) toluene and 
fifteen percent (15%) methanol by volume. The mouths of the filled 
containers were then heat sealed with foil-backed low density polyethylene 
film and capped. The sealed containers were stored in an ambient pressure 
air circulating oven at 50.degree. C. for 28 days, and their weight loss 
was monitored periodically. 
Table 1 indicates the composition of the reactive treatment gas, treatment 
times and the resultant solvent permeability. 
TABLE 1 
______________________________________ 
Treatment 
Concentration of Fluorine in Nitrogen 
Solvent 
Permeated, 
Gas Gas Gas 
Run No. 1 Time 2 Time 3 Time g/day 
______________________________________ 
1 0% 6 Secs 0% 6 Secs 
0% 6 Secs 
6.16 
2 1% 12 0% 6 0% 6 0.37 
3 10% 6 0% 6 0% 6 0.89 
______________________________________ 
Run 1 shows, as was known, that HDPE is not resistant to hydrocarbon 
permeation absent fluorination. Run 2 shows a one-step treatment of HDPE 
using a reactant gas having a fluorine concentration (1% fluorine in 
nitrogen) at above the self-supporting temperature of HDPE significantly 
reduces the solvent permeation, but the solvent permeation value is rather 
high. Run 3 shows that a one-step treatment of HDPE with high fluorine 
containing gas (10% fluorine in nitrogen) at above the self-supporting 
temperature of HDPE is not as desirable as the use of a more dilute 
reactant gas because it provides HDPE containers with considerably lower 
resistance to solvent permeation. Although Run 2 provided good results, 
barrier properties may not meet future requirements. 
COMATIVE EXAMPLE 2 
Multi-Step Production of Thin-Walled Containers from High Density 
Polyethylene 
Cylindrical high density polyethylene (HDPE) thin-walled containers similar 
to ones described in Example 1 were prepared by the extrusion blow molding 
process. During the inflation process the containers were pressurized to 
approximately 100 psig with an inert nitrogen reactant gas for a period of 
6 or 12 seconds (Step 1 or Gas 1), after which the pressure was released 
from the containers for a period of one and one-half seconds to allow the 
nitrogen gas to escape. The containers then were repressurized a second 
time to approximately 100 psig with a reactive treatment gas containing 1 
or 10% fluorine in inert nitrogen for a period of 6 seconds (Step 2 or Gas 
2). After this the pressure was released from the containers for a period 
of one and one-half seconds to allow reactive gas to escape. The 
containers were pressurized a third time to approximately 100 psig with a 
reactive treatment gas containing 1 or 10% fluorine in inert nitrogen for 
a period of 6 seconds. Finally, the containers were vented to atmospheric 
pressure, purged with an ambient pressure air stream or an inert gas to 
remove any traces of reactive treatment gas and removed from the mold. 
Since the containers were thin-walled, they were quickly cooled from a 
temperature above the self-supporting temperature to a temperature below 
the self-supporting temperature of HDPE within a time estimated to be 
about 2 to 3 seconds by the pressurizing and purging with inert nitrogen 
gas used in the Step 1 and prior to the reactant gas treatment in Step 2. 
The containers were, therefore, treated with a fluorine containing gas in 
multiple steps first at above and then below the self-supporting 
temperature of HDPE. The solvent permeability of these containers was 
determined following the procedure similar to the one described in Example 
1. Table 2 indicates the composition of the reactive treatment gas, 
treatment times in seconds and the resultant solvent permeability. 
TABLE 2 
______________________________________ 
Treatment 
Concentration of Fluorine in Nitrogen 
Solvent 
Permeated, 
Gas Gas Gas 
Run No. 1 Time 2 Time 3 Time g/day 
______________________________________ 
1 0% 6 Secs 1% 6 Secs 
1% 6 Secs 
3.29 
2 0% 12 10% 6 10% 6 0.36 
______________________________________ 
Run 1 shows that a multi-step treatment of HDPE with low fluorine 
containing gas (1% fluorine in nitrogen) at below the self-supporting 
temperature of HDPE marginally improves the resistance to solvent 
permeation of treated containers. Run 2, on the other hand shows, that a 
multi-step treatment of HDPE with high fluorine containing gas (10% 
fluorine in nitrogen) at below the self-supporting temperature of HDPE 
significantly improves the resistance to solvent permeation of treated 
containers. The solvent permeation value was very similar to that noted 
with one-step treatment with low concentration of fluorine at above the 
self-supporting temperature of HDPE (compare results of Run 2 of Ex 2 with 
Run 2 of Ex 1). However, the solvent permeation value is still high. 
EXAMPLE 3 
Multi-Step Production of Thin-walled Containers from High Density 
Polyethylene 
Cylindrical high density polyethylene (HDPE) thin-walled containers similar 
to ones described in Example 1 were prepared by the extrusion blow molding 
process. During the inflation process the containers were pressurized to 
approximately 100 psig with a reactive treatment gas containing 1 or 10% 
fluorine in inert nitrogen gas for a period of 6 or 12 seconds, after 
which the pressure was released from the containers for a period of one 
and one-half seconds to allow the reactive gas to escape. The containers 
were then repressurized a second time to approximately 100 psig either 
with an inert nitrogen or a reactive treatment gas containing 10% fluorine 
in inert nitrogen for a period of 6 seconds. After pressurizing, pressure 
was released from the containers for a period of one and one-half seconds 
to allow reactive gas to escape. The containers were pressurized a third 
time to approximately 100 psig with a reactive treatment gas containing 1 
or 10% fluorine in inert nitrogen for a period of 6 seconds. Finally, the 
containers were vented to atmospheric pressure, purged with an ambient 
pressure air stream or an inert gas to remove any traces of reactive 
treatment gas and removed for the mold. Containers were, therefore, 
treated in the first step with fluorine containing gas at above the 
self-supporting temperature of HDPE. They were treated further in the 
second and third steps with fluorine containing gas at below the 
self-supporting temperature of HDPE. 
The solvent permeability of these containers was determined following the 
procedure similar to the one described in Example 1. Table 3 indicates the 
composition of the reactive treatment gas, treatment times and the 
resultant solvent permeability. 
TABLE 3 
______________________________________ 
Treatment 
Concentration of Fluorine in Nitrogen 
Solvent 
Permeated, 
Gas Gas Gas 
Run No. 1 Time 2 Time 3 Time g/day 
______________________________________ 
1 1% 6 Secs 0% 6 Secs 
1% 6 Secs 
0.55 
2 1% 12 10% 6 10% 6 0.22 
______________________________________ 
Run 1 shows that a multi-step treatment of HDPE with low fluorine 
containing gas (1% fluorine in nitrogen) first at above the 
self-supporting temperature of HDPE and then at a temperature below the 
self-supporting temperature of HDPE improves the resistance to solvent 
permeation of the container. Run 2, on the other hand, shows that a 
multi-step treatment of contacting HDPE with an initial low fluorine 
containing gas (1% fluorine in nitrogen) at above the self-supporting 
temperature of HDPE and then contacting with a fluorine containing gas 
having a higher fluorine concentration than used initially (10% fluorine 
in nitrogen) at below the self-supporting temperature of HDPE greatly 
improves the resistance to solvent permeation of the container. 
The result of Run 2 suggests that it is desirable to treat HDPE containers 
at above the self-supporting temperature with low fluorine containing gas 
first and, then, at some point, contacting HDPE at a temperature below the 
self-supporting temperature with high fluorine containing gas to 
significantly reduce solvent permeation of treated containers. 
COMATIVE EXAMPLE 4 
Multi-Step Production of Thick-walled Automobile Fuel Tanks from High 
Density Polyethylene 
The procedure of Example 2 was repeated utilizing a multi-step process for 
the production of thick-walled automobile fuel tanks with a nominal wall 
thickness of 4.0 mm wherein in the first step an inert nitrogen gas (Gas 
1) was used to pressurize and inflate the parison for a period of 9 
seconds, after which the pressure was released from the tanks. Because of 
relatively thick walls of the fuel tanks, the temperature remained above 
the self-supporting temperature of HDPE. The fuel tanks were treated in 
the second step with a reactive gas containing 1% fluorine by volume and 
the balance being nitrogen followed by tertiary treatment with reactive 
gases containing from 1% to 10% fluorine by volume. The secondary 
treatment times in the second (Gas 2) and third steps (Gas 3) were for a 
period of 9 seconds each. The fuel tanks were vented to atmospheric 
pressure, purged with an ambient pressure air stream or an inert gas to 
remove any traces of reactive treatment gas and removed from the mold. The 
tanks were, therefore, treated first with a fluorine containing gas at 
above the self-supporting temperature of HDPE. They were treated further 
with a fluorine containing gas at a temperature above or below the 
self-supporting temperature of HDPE or both above and below. 
The hydrocarbon solvent permeability of these fuel tanks was determined 
following the procedure similar to the one described in Example 1. The 
hydrocarbon solvent mixture consisting of 92.5% indolene, 5.0% methanol, 
and 2.5% ethanol by volume was used for determining solvent permeability 
instead of using a hydrocarbon mixture of eighty-five percent (85%) 
toluene and fifteen percent (15%) methanol by volume. Table 4 indicates 
the composition of the reactive treatment gas, treatment times and the 
resultant solvent permeability after 8 weeks of storing in an ambient 
pressure air circulating oven at 40.degree. C. 
TABLE 4 
______________________________________ 
Treatment 
Concentration of Fluorine in Nitrogen 
Solvent 
Permeated, 
Gas Gas Gas 
Run No. 1 Time 2 Time 3 Time g/day 
______________________________________ 
1 0% 9 Secs 1% 9 Secs 
1% 9 Secs 
0.36 
2 0% 9 1% 9 10% 9 0.29 
3 0% 9 1% 9 10% 9 0.26 
______________________________________ 
The data in Table 4, as with Table 3, again shows that a multi-step 
treatment of HDPE with low fluorine containing gas (1% fluorine in 
nitrogen) at above the self-supporting temperature of HDPE first and then 
with high fluorine containing gas (10% fluorine in nitrogen) initially at 
above and then ending below the self-supporting temperature of HDPE 
provides good solvent permeation value for the treated fuel tanks. 
However, the solvent permeation value is still higher than the desired 
value. For thick-walled containers such as fuel tanks, it is believed that 
a 1% and higher initial fluorine concentration may be too high of a 
concentration, or the contact time may have been too long for the process 
temperature. 
EXAMPLE 5 
Multi-Step Production of Automobile Fuel Tanks from High Density 
Polyethylene 
The procedure of Example 4 was repeated for the production of thick-walled 
automobile fuel tanks wherein in the second step a reactive gas containing 
0.5% fluorine by volume and the balance being nitrogen at above the 
self-supporting temperature of HDPE was used followed by tertiary 
treatment at above or below the self-supporting temperature of HDPE with 
reactive gas containing from 0 to 10% fluorine by volume. The treatment 
times in the second and third steps were for a period of nine seconds 
each. The fuel tanks were vented to atmospheric pressure, purged with an 
ambient pressure air stream or an inert gas to remove any traces of 
reactive treatment gas and removed from the mold. The fuel tanks were, 
therefore, treated first with a reactant gas containing a low level of 
fluorine at above the self-supporting temperature of HDPE. They were 
treated further with high fluorine containing gas at above or below the 
self-supporting temperature of HDPE. 
The solvent permeability of these containers was determined following the 
procedure similar to the one described in Example 4. Table 5 indicates the 
composition of the reactive treatment gas, treatment times an the 
resultant solvent permeability. 
TABLE 5 
______________________________________ 
Treatment 
Concentration of Fluorine in Nitrogen 
Solvent 
Permeated, 
Gas Gas Gas g/ 
Run No. 1 Time 2 Time 3 Time day 
______________________________________ 
1 0% 9 Secs 0.5% 9 Secs 
0% 9 Secs 
0.35 
2 0% 9 0.5% 9 0% 9 0.30 
3 0% 9 0.5% 9 1% 9 0.18 
4 0% 9 0.5% 9 1% 9 0.18 
5 0% 9 0.5% 9 2.5% 9 0.08 
6 0% 9 0.5% 9 5% 9 0.10 
7 0% 9 0.5% 9 5% 9 0.09 
8 0% 9 0.5% 9 10% 9 0.21 
9 0% 9 0.5% 9 10% 9 0.21 
______________________________________ 
Runs 1-2 show enhanced resistance to permeability after an initial one-step 
treatment with low concentration of fluorine containing inert gas above 
the self-supporting temperature of the polymer. Runs 3 and 4 show that 
after initial fluorination, contacting the containers with a gas having a 
higher fluorine content than otherwise would be acceptable for reducing 
permeability and improving barrier properties. Runs 8 & 9 show that 
additional reaction occurs over and beyond that shown in Runs 3-7. Higher 
permeability of the container, as noted in Runs 8 & 9 vis-a-vis Runs 6 & 7 
is attributed to an increase in the polymeric degradation from aggressive, 
high fluorine concentration treatment, thereby damaging the surface. The 
institution of a secondary treatment reactant gas having too high a 
fluorine concentration may lead to reduced permeation relative to that 
obtained from using a reactant gas having a significantly higher 
concentration of fluorine (10 fold) from that used initially but less than 
the 20 fold increase used in Runs 8 & 9. In any case, the use of a 
reactant gas having a low concentration of fluorine prior to the 
introduction of reactant gas having the higher concentration permits one 
to obtain added benefits as illustrated in runs 4-6 of Table 4. 
The data in Table 5 clearly show that a multi-step treatment of HDPE with 
low fluorine containing gas (0.5% fluorine in nitrogen) at above the 
self-supporting temperature of HDPE first and then with high fluorine 
containing gas (above 1% fluorine in nitrogen) at above or below the 
self-supporting temperature of HDPE provides excellent solvent permeation 
resistance to the treated fuel tanks. The solvent permeation value in some 
cases was noted to be well below the desired value.