CA2071813A1

CA2071813A1 - Sulfonated multilayer container and a method for producing the same

Info

Publication number: CA2071813A1
Application number: CA002071813A
Authority: CA
Inventors: Yutaka Takado
Original assignee: Individual
Current assignee: Tonen Chemical Corp
Priority date: 1989-12-15
Filing date: 1990-12-13
Publication date: 1991-06-16
Also published as: WO1991009732A1; JPH03184845A

Abstract

The present invention relates to a multilayer container having good gasoline barrier properties which is suitable for use as the automotive fuel tank, and also to a method for producing the same.
More particularly, the present invention relates to a sulfonated multilayer container having an interlayer of highly sulfonated high-density polyethylene, and also to a method of producing the same.

Description

"091/09732 PCT/US90/07~05 - 1 - 2~7~ ~13 SULFONATED ,~lULTILAYER CO~ITAINEn~_AND A METHOD
FOR PRODUCIN~ THE SAME
Prior art For the weight reduction of automobiles, many attempts are being made to make the fuel tank from plas-tics and a variety of plastics are being offered to this end. The fuel tank is.required to have gasoline barrier 5 properties as well as qood mechanical strength and impact resistance. None of the plastics avai~able meet this .
requirement.
In general, polyamides are ~uperior in gasoline barrier properties but poor in impact resistance. By con-trast, polyolefins are inferior in gasoline barrier prop-erties but superior in impact resistance. For this reason, many attempts ~ave been made to produce a con-tainer superior in both impact resistance and gasoline barrier properties from a polyamide and polyolefin i~
combination.
For example, Japanese Patent Publlcation No.
14695~19B5 discloses a molded article of composite mate-rial composed of polyolefin, polyamide, and alkylcarboxyl-substituted polyolefin, with the polyolefin forming a co~-ti~uous matrix phase, t~e po~yamide existing in layer formin the cont~nuous matrix phase,~ and the alkylcarboxyl-su~stituted polyolefi~ ex$stlng between the polyamid~
layer~. ~ container for~ed ~rom this compo~ite mater~al is poor i~ low-temperature.impact resistance despite the modified polyolefin incorporated therein a~d the polyamlde SUIE~5TITUTE SHET

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dispersed therein in layer for~, because the polyamide layer is poor in adhesion to the continuous matrix phase of polyolefin. Another disadvantage is that t~e composite material of multilayer structure makes it difficult to recycle flash.
on the other hand, there has been proposed a means to improve the gasoline barrier properties by substituting sulfonated or fluorinated polyolefin for polyamide having a poor affinity (adhesion) for polyolefin. For example, Japanesc Patent Pu~lication No. Z3914/1971 discloses a polyolefin container having a sulfonated surface which is substantially impermeable to fuels and organic solvents.
Problems to be solved by the invention The above-mentioned impe~eable container, howe~er, has a disadvanta~e that the sulfonation for surface treat-ment costs much time and expenses. Moreover, it has been found t~at the sulfonation itself is not satisfactory.
Accordingly, it is an object of the present invention to provide a sulfonated multilayer container which exhib its good gasoline barrier properties owing to the high degree of s~lfonation. It is anothex object of the present invention to prov~de a method for produc~ng the - sulfonated multilayer contalner efficiently.
~e~ns to solve the problems -25 ~ In order to`achieve the ibo~e-mentioned objects, the - presene inventors carried out a serieS of researches ~hich led to the finding that the gcGd gasoline ~arrier proper-( .

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. . , ~ . ,:` . ' .. . . .. ~; . , , ~ . ., ' ~ 91/09732 2 ~ ~ ~ 8 ~ ~ PCT~USgo/07s05 tles and impact resistance are obtained by multilayer blow molding from sulfonated high-density polyethylene in combination with untreated hig~-density polyethylene instead of sulfonating the molded container, the former S component being prepared by sulfonating high-density poly-ethylene in the form of powder ha~ing a large surface area. This finding led to the present invention.
The sulfonated multilayer container pertaining to the present invention co~prises an interlayer formed from sulfon~ted high-density polyethylene powder and inner and outer layers of high-density polyethylene.
According to the present invention, the sulfonated multilayer container may have, if necessary, an additional layer of modified high-density polyethylene between the interlayer and each of the inner and outer layers, said first layer having good adheslon to the other layers.
Also, the method for pros~ucing the sulfonated multi-layer container according to the present invention com-~prises the steps of sulfonating high-density polyethylene ~ powder having a particle dia~eter of 100-3000 ~m with a ~as ~ontaining 12-25 vol~ of S03 at 45-60 C, and subjecting the sulfonated high-den~ity polyethylene tog~ther with untreated high-density polyethylene to ~ultilayer blow .. ~ . . . . . . . ... .. . . .~, .
mold ~ process, so that the sulfonated hig~-density poly-~, 25 ethylene forms the interlayer and the untreated high-density polyethylene forms t~e inner and outer Iayers.

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W091/~9732 r~l PCT/US90io750 C~2 In what follows, the present invention will be described in more detail.
The in~erlayer in the sulfonated multilayer container of the present invention is made of high-density polyeth-S ylene having a density higher than 0.93 g/cm3~ preferably0.94-0.97 g/cm~, a weight-average molecular weight higher than 100,000, prefera~ly higher than 150,000, a melt index ~ML: l90 C, 2.16 kg load) lower than 1.0 g/lO min, prefer-ably 0.2-0.01 g/10 min (which translates into a high-load melt index (HLMI: l90'C. 21.6 kg load) lower than 70 g/10 min, preferably 20-1 g/10 min).
The greater the weight-average m~lecular weight, the better the molded product in barrier properties and impact resistanca. Therefore, it is necessary that the high-density polye~hylene have a wei~ht average molecularwei~ht higher than 100,000, preferably higher than l50,000 ~say 200,000~.
With a melt i~dex higher than 1.0 g/lO min, the high-density polyethylene is liable to dra~down during multi-layer blow moldlng. The one.having a melt. index of 0.2-0.01 gllO min is desirable in vie~ of moldability and ....
impact resis~ance. Incidentally, the MI of small values may be replaced by the HLMI (high-load melt index) in ` ` order to avold errors in measurements. With an HL~I higher :

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than 70 g/10 min, the high-density polyethylene is liable to excess drawdown. The preferred HLMI ranges ~rom 20 to 1 g~10 min.
Incidentally, the high-density polyethylene is not limited to homopolymers. It may also include copolymers of ethylene with an ~-olefin such as propylene, butene-l, and hexene-1.
According to the present invention, the h1gh-density polyethylene is sulfonated in the form of powder. Having a large surface area, powder is capable of rapid and effi-cient sulfonation. For the object of the present inven-tion to be achieved, the hiqh-density polyethylene powder should have a particle diameter smaller than 5,000 ~m, preferably from 100 to 3,000 ~m. With a particle diameter larger than 5,000 ~m, the high-density polyethylene powder undergoes sulfon~tion so inef~iciently that it is a non-~ sense to use powder. Reducing the particle diameter belo~
;~ 100 ~m produces no effect commensurate with iS.
The sulfonàtion of high-density polyethylene powder is acco~plished by exposing the powder to an SO~-containing gas. The treatlng gas usually contains SO~ ln an amounE of 12-25 vol%, with the remainder being an inert gas such as , . . ..
~ nitrogen. For effici`ent sulfonation, the SO~-containinq ....
gas should be passed through the high-density polyethylene ;` powder held in a breathable container such as a wire net.

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WO91/09732 ~_ PCT/US9~io750 An alternative method for sulfonation consists of fluidiz-ing the ~igh-density polyethylene powder with the SO~-containing gas in a fluidized bed. In either cases, t~e sulfonation should be performed at 40-70 C, preferably 45-60'C, for 3-lO minutes.
After the completion of sulfonation, the S03-containing gas should be purged with nitrogen gas, and residual S03 should be removed by absorption into sulfuric acid in a vent scrubber.
In this way, there is obtained a sulfonated high-density polyethylene powder having a degree of sulfonation of 1-5 wt%. With a degree of sulfonation lower than 1 w~.~, the sulfonated high-density polyethylene powder does not provide.satisfactory gasoline barrier properties.
Reducing the degree of sulfonation below S wt% produces not effect commensurate with it.
The sulfonated high-density polyethylene powder sub-sequen~ly undergoes ~he step oE neu~cralizi-~g s~llfonic groups contalned therein~ Neutralization ~ay he accom-plished ~ith a neutralizing agene such as sodium hydrox-- ide, potassium hydroxide, lithium hydroxide, sodium car-bonate, sodium bicarbonate, potassium carbonate, potassium .
carbonate, lithium bicarbonate, and ammonia.~ ~mmonia is preferable because of i~s.ability to be used for gas phase r - `---25 reactiOn.

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~091/09732 2 ~ 7 ~ ~13 PCT/~S90/07~05 The neutralization is accomplished ~ith a neutraliz-ing agent in an amount of 2 mol for l mol of sulfonic groups. Therefore, the volume of ammonia yas should be twice that of SO~ gas that has bonded to the high-density S polyet~ylene. Neutralization with ammonia gas should be perfonmed at 45-60 C for 4-9 minutes. After the neutral-ization is complete, the residual ammonia gas should be purged with nitrogen gas.
In the meantime, basically the high-density polyeth-10 ylene for the inner and outer layers may be the same as that used for the interlayer. It should preferably be a high-~olecular weight high-density polyethylene having a weig~t-average molecular weight higher than 150,000 from the standpoint of impact resistance.
According to the first embodiment of the present ~` invention, the multilayer comtainer is composed of three layers, that is, an interlayler 1 of sulfo~ated higb-1 density polyethylene and an inner layer 2 and an outer layer 2' of untraated high-density polyethylene, as shown 20 in Fig. l. The interlayer 1 should have a thickness of 10-500 ~. With a t~ickness less than lO ~m, the inter-layer l does not pro~ide th~ multilayer container ~it~

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satisfactory gasoline barrier properties. With a thickness in excess of 500 ~, the i~terlayer 1 does ?.5 not produce any effect commensurate with the increased ~ ... .,, . . , . : . . , - ..
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c~ - 8 -preferred thickness of the interlayer 1 is 100-200 ~m. On t~e other hand, the inner layer 2 and the outer layer 2' both should have a thickness of 1.5-5 mm. With a thick-ness less than 1.5 mm, they do not provide the multilayer container with sufficient ~echanical strength and impact resistance. With a thickness in excess of 5 mm, they do not produc~ any effect commensurate with ~he increased thickness.
According to the second embodiment of the present 10 invention, the multilayer container is composed of an interlayer 1 of sulfonated high-density polyethylene, an inner layer 2 and an outer layer 2' of untreated high-density polyethylene, and additional layers 3 and 3' of modified high-density polyethylene each interposed between 15 the interlayer 1 and the inner layer 2 and between the interlayer 1 and the outer layer 2', as shown in Fig. 2.
The modified high-density polyethylene is one which is ohtained by modifying t~e same high-density polyethyl-ene as mentioned above wlth an unsaturated carboxylic acid 20 or anhydride t~ereof; Examples o~ t~e unsaturated carbox-- ylic acid or anhydxide thereof include monocarboxylic acid lsuch as acrylic acld and methacryIic acid), dicarboxylic acid (such as Maleic acid, fumaric acid, and itaconic acid), and dicarboxylic acid anhydride lsuch as.maleic .
~ 25 an~ydride and itaconic anhydride). Preferable among them ~ I

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The modified high-density polyethylene should contain the unsaturated carboxylic acid or anhydride thereof in an amount of 0.2-0.6 mol%. With an amount less than 0.2 mol%, it does not permit the modified high-density poly-ethylene to firmly bond to the high-density polyethylene.
With an amount in excess of 0.6 mol%, it does not produce any effact commensurate with the increased amoun~.
In the second embodiment, the additional layers 3 and 3~ of the modified high-density polyethylene, each inter-posed between the interlayer l and each of the inner and outer layers 2 and 2', should have a thickness of 10-500 ~m. With a thickness smaller t~an lO ~m, the additional layers 3 and 3' of the modified high-density polyethylene do not exhibit good adhesion to the interlayer 1 and the inner and outer layers 2 and ~', and hence contribute little to the improvement in impact resistance. With a thickness in excess of $00 ~m, they do not produce any effect commensurate wit~ the increased thickness. Inci-dentally, the interlayer l and the inner and outer layers2 and 2' may have the same thicknesses as mentioned above.
; ~ ~ In either cases of the first and second embodiments, the multilayer container may be produced by multilayer - blow molding process, which is carri~d out as follows:

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- 10 _ The sulfonated ~igh density polyethylene for the inter-layer and the untreated high-density polyethylene for the inner and outer layers are melted and mixed separately at 180-220-C. The melts are fed simultaneously to the multi-layer blow molding die and then extruded from it into a parison. The parison is blown up in a mold by hot com-pressed air to be made into a molded article of desired shape and size. ID the case where ~he additional layers of the modified high-density polyethylene are to be formed, the melt of the modified high-density polyethylene should be fed to the multilayer blow molding die simulta-neously with other melts.
. Exampl es The invention will be explaine~ in more detail with reference to the following examples.
J, ~xample 1 High-density p~lyethylene ~B-5742~ (a product of Tonen SeklyukagakU XOK~ having an HLMI of 4 g/10 . , .
min and a density of 0.945 gtcm~ in the fon~ of powder - 20 ~ha~ing a partiele diameter of 150-2gO0 ~) was sulfonated ln the following manner. The powder, held in a wire net container, was exposed at 53'C or 4 minutes to nitrogen --- gas containing 18 vol% of 503 which waa flow'ng at a flow ra~e of 5 L/min. ~he remaining gas was purged with nitro-gen gas and the residual S03 was absorbed into H2SO4 by :

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~ 91~09732 2~7 ~ ~3 PCT/US90/07505 .' means of a vent s~rubber.
The high-density polyethylene powder was subsequently exposed to an ammonia gas stream at 53 C for 6 minutes for the n~utralization of sulfonic groups. The remaining S ammonia gas was purged with nitrogen gas. Thus there was obtained a sulfonated high-density polyethylene powder having an ~LMI of 5 g/lO min and a density of O.9S0 g/cm3 .
- She degree of sulfonation was measured by fluores-cence X-ray analysis. In actual pr~ctice, a working curve was prepared for a sulfonated hi~h-density polyethylene plate, and a table showing the relationship between the degree of sulfonation and the number of counts was pre-pared from the working curve, so that measurements ~ere made by comparing the number of counts of sulfonated high-lS density polyethylene powder with that of reference in the table. The results of the analysis showed that the degree of sulfonation was about 2 wt%. In the meantime, it is considered that the sulfonated lligh-density polyethylene has a structure as s~lown below. , ~ ~1 H 1 H
- C --C - C ---C -3 H ~1. n ! SO; , ~NH4. (NH~j~ ) A 40-liter mult~layer container of the following struCture was produced by multilayer blo~ molding process SUB5TITIJTE~SS~EE~T

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from ~he sulfonated high-density polyethylene powder (for the interlayer~, maleic anhydride-modified high-density - j polyethylene containing 0.4% of maleic anhydride ~made by Tonen Sekiyukagaku K.~ or the adhesion layers), and untreated high-density polyet~ylene ~-S742) ~for the inner and outer layers). Blow molding was accomplished by using a large-sized multilayer blow molding machine with an accumulator head (made ~y The Japan Steel Works, Ltd.).
Inner layer: HDPE (B-5742), 1.5-5 mm thick Adhesion layer: maleic anhydride-modified high-density polyethylene, 150 ~m thick Interlayer: sulfonated %DPE ~B-5742), l00 ~m thick Adhesion layer: maleic anhydride-modified high-density - polyethylene, 150 ~m thick 15 ~ Outer layer: HDP~ ~B-5742), l.5-5 mm thick This multilayer cc.~tainer was tested for impact resistance and gasoline barrier properties in the follow-ing manner. - ~
~l) Low-temperature drop impact test This ~est was perr'ormed on the multilayer container, co~pletely filled with water, under the following condi-tion. ' .
Temperature: -40 C ~~
I Drop heigh~: 6 m, 9 m, and-12 m .. I

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',' ' . ' , , ~'~91/09732 2 0 7 ~ 3 1 3 PCT/US90/07505 Drop direction: with the pinch-off part parallel to the ver~ical direction Minimum wall thickness of the container: 3.0 mm Total weight: 46 kg (completely filled with water) (2) Gasoline permeability The multilayer container (90 liters) was filled with 20 liters of gasoline, and tAe half-filled container was allowed to stand at 40 C for 8 weeks. The amount of gaso-line lost during this period was recorded to calculate the permeability to gasoline. This test conforms to the stan-dards of the Ministry of ~ransport (No. 1327~ ~echnical Standards for Plastics Fuel Tank for Passenger Cars). The results are shown in Table 1.
Example 2 A 40-liter multilayer container of the following three-layer structure was produced from t~e sulfonated high-density polyethylene prepared in.Example 1 and - untreated high-density polyethylene ~B-5742).
Inner layer: H~PE (B-5742j, 1.5-5 mm thi~k ~ Interlayer sulfonated HDPF, ~B-5742), 100 ~m thick - Outer layer: HDPE (~-5742~, 1.5-5 mm thick ` This~multilayer container was tested ln the same ... . - .. ~
- manner as in Example 1. The results are shown in Table 1.
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The same procedure as in Example l was repeated for sulfonation, except that B-5742 (powder of high-density polye~hylene for sulfonation) was replaced by a powder S t200-2~00 ~m in particle diameter~ o~ ~-6012 having an MI
of 0.15 g/l0 min and a density o~.O.q52. g/cm~ ~a product of Tonen Sekiyukagaku K.K.). There was obtained a powder of sulfonated HDPE having an MI of 0.l5 ~l0 min and a density of 0.957 g/rm~.
A 40~ er mul~ilayer container of the following three-~ayer structure was produced by mult.ilayer blow molding process from the sulfonated high-density polyeth-ylene (for the interlayer) and untreated high-density polyethylene ~B-57421.
Inner layes: HDPE (B-5742), 1.5-5 mm thick Interlayer: sulfonated HDPE ~B-6012), 100 ~m thick Ou~er layer: HDPE (B-5742), 1.5-5 mm thic~
This multilayer container ~as tes~ed i~ the same ; manner as in Example l. The results are shcwn in Table lo Comparative Example 1 ~, , A 40-liter container of single-layer structure having the same shape and size as that in Exampl~ 1 was produced by blow ~olding process from a-s742 . high-density polyethylene. This single-layer container was tested in the same manner as in ~xample l. The .

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- , O91/09732 2 ~ 7 ~ ~ ~ 3 PCT/VS90io7505 results are shown in Table 1.
Comparati~e Exampl a 2 A 40-iiter five-layer container of the following structure having the same shape and size as that in Example 1 was produced by multilayer blow molding process .
rom high-density polyethylene lB-5742), nylon 6 (CM-1046,-made by Toray Industries, Inc.), and maleic anhydride-modified high-dens~ty polyethylene containing 0.9~ sf maleic anhydride (made by Tonen Sekiyukagaku K.K.).
~ Inner layer: HDPE ~-5742), l.S-5 mm thick Adhesion layer: maleic anhydride-modified high-density . polyethylene, 200 ~m thick :~ Interlayer: nylon S, 100-200 ~m thick : Adhesion layer: maleic anhydride-modified ~igh-density polyethylene, 200 ~m thick Outer layer: ~DPE ~B-5742), 1.5-5 mm thic~
This multilayer con~ainer was tested i~ the same manner as in Example 1. T~e resules are shown in Table 1 Tabl~l .___ _ _ - ~ampleNo. Dr~ ~ _ C~n~t~e 6m 9m 12m Penneab~-~ d ~ampleNo.~ . ~asoline~day) . . . ... _ ` 1 _ not broken nol broken not broken .
- -~ - 2 not broken not broken nol broken 0.7 ,.~ , 3 - ~ n~t blokënnot broken~ ~` r~ot broken . _ . . - - !~ . nbt br~k-n not broken- nol broken . ' (2) r ot b~oken ~ ken broken 0.5 _ .. _ .

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WO 91/09732 C~o P~r/lJS90iO750 ~ - 16 -For any fuel tank to meet the requirement for gaso-line barrier properties set up by the SHED regulation in the U.S., it must have a gasoline permeability lower than 2 g/day. It is noted from Table l that the multilayer containers in Example 1 to 3 all meet this requirement.
By contract, the single-layer container in Comparative Example l has a gasoline permeability as high as 8.0 g/day.
on the other hand, there are no regulations for impact xesi~tanoe; however, it is necessary that the fuel tank, an important component, should not be broken at the worst. The ~ultilayer container having a nylon interlayer does not have sufficient impact resistance.

Effect of the invention As mentioned above, the present invention provides a sulfonated multilayer container which is composed o an interlayer of highly sulfonated high-density polye~hylene and inner and outer-layers of high-density polyethylene.
- Because of this structure, the multilayer container exhib~
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` 20 its good gasoline barrier properties as well as high - impact resistance. The interlayer of sulfonated high-density polyethylene is not affected by gasoline because .. _ ~ . . . . .. . ..
-- - it--is isolated f~om gasoline.by~ the inner layer. There- r fore, the multilayer container of the presënt invention is - 25 suitable for use as the automotive fuel tank and other . .

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4. arief Description of the Drawings:
Fig 1 is a partial sectional view showing the struc-ture of the multilayer container in one embodiment of the present invention.
Fig. 2 is a partial sectional view showing the struc-ture of the multilayer container in another embodiment of the present invention.

1 ... Interlayer 2, 2' ... Inner and outer layers 3, 3' ... Modified high-density polyethylene layers .` ; .

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Claims

CLAIMS:

1. A sulfonated multilayer container which comprises an interlayer formed from sulfonated, high-density polyethylene powder and inner and outer layers of high-density polyethylene.

2. A sulfonated multilayer container as claimed in Claim 1, wherein the interlayer has a thickness of 10-500 µm and the inner and outer layers each have a thickness of 1.5-5 mm.

3. A sulfonated multilayer container as claimed in Claim 1 or Claim 2, wherein the high-density polyethylene is a high-molecular weight high-density polyethylene having a weight-average molecular weight higher than 100,000.

4. A sulfonated multilayer container which comprises an interlayer formed from sulfonated high-density polyethylene powder, inner and outer layers of high-density polyethylene, and additional layer of modified high-density polyethylene each interposed between said interlayer and each of said inner and out layers.

5. A sulfonated multilayer container as claimed in Claim 4, wherein the interlayer has a thickness of 10-500 µm, and the additional layers of modified high-density polyethylene each have a thickness of 10-500 µm.