BACKGROUND OF THE INVENTION The present invention relates to irradiated molding compositions having improved mechanical service, to methods of making such compositions, to articles made from said compositions, and to methods of making said articles.

Stress cracking or environmental stress cracking (ESC) is the brittle failure of plastic parts when simultaneously subjected to static mechanical stress and chemical exposure. In a similar fashion, environmental fatigue (EF) is the failure or cracking of a part when simultaneously subjected to dynamic mechanical stress and chemical exposure. Insufficient environmental stress cracking resistance or environmental fatigue resistance leads to greatly shortened service life of a part.

Flexible molded articles are used in various packaging, dispensing, pumping, footwear, or protective mechanical boot applications. Ideally, these flexible molded articles will retain essentially the same mechanical properties during the desired service life. However, in a less than ideal world, especially mechanical service in the presence of aggressive chemical environments, such exposure can attack or alter these flexible molded articles and hence the performance or service life of such articles.

It is desired that these flexible molded articles withstand, without cracking, mechanical cycling during exposure to a wide range of chemicals. These articles preferably retain dimensional stability after long periods in a compressed state. Dimensional stability permits the springing back of said articles toward their natural uncompressed position as opposed to becoming set to the compressed shape. Additionally, when these articles are held under compression in contact with chemicals and for an extended period of time, it is desired that they withstand environmental stress cracking that could create cracks or openings through the wall of the part and/or alter the mechanical properties.

It is desirable that the flexible molded articles be suitable for service in a wide range of chemical environments. However, designing a suitable polymeric material for such a flexible molded article useful in a wide range of chemical environments has proven difficult.

For example, numerous elastomeric materials can be used to make flexible spring-like moldings that satisfy mechanical design criteria in the absence of an aggressive chemical environment, or in one particular type of aggressive chemical

environment. For example, a material that is suitable for an acidic solution can be ill-suited for an alkaline or oxidizing medium; a material that is resistant to stress cracking in a dilute alcoholic solution can crack after the addition of a perfume, for example, a terpene-based perfume. More specifically, thermoplastic elastomers such as polyesters and polyamides provide spring-like behavior in an article. However, these materials lack chemical resistance to extreme pH conditions because of chemical degradation. Thermoplastic urethane elastomers provide a wide range of mechanical properties and could satisfy the mechanical design requirements of a flexible spring-like device. However, these materials can degrade from exposure to alkaline solutions. Resins such as poly(vinyl chloride) or propylene and styrene- ethylene-butylene-styrene block copolymer blends, when highly plasticized, exhibit greater chemical resistance but lack either the compression set resistance or dynamic response required for a flexible spring-like device. Low crystallinity or low density polyethylene or ethylene copolymers typically provide favorable moduli and good chemical resistance. However, these materials can often undergo environmental stress cracking unless very high molecular weight resins, that are ill-suited for injection molding, are used. Thus, selection of a material for a flexible spring-like article for use in a wide variety of chemical environments, preferably aqueous solutions or emulsions, becomes difficult.

Alternatively, if several materials are chosen for particular types of chemical service, then fabrication costs can be large. For example, because each material can exhibit unique shrinkage during molding, achieving dimensional tolerances often requires the fabrication of individual molds that are tailored to the shrinkage of each material. Accordingly, use of several molds to accommodate the shrinkage of a variety of thermoplastic materials for the production of the same part but for service in different fluids leads to higher fabrication costs. It is desired to minimize this cost by use of a few materials as possible, ideally, by the use of one material.

One type of application of particular interest, is the use of a flexible spring¬ like device, such as a bellows, in chemical service. Techniques for fabricating a bellows are known in the art. For example, U.S. Patent No. 5.236,656, issued August 17, 1993 to Nakajima discloses a method of injection blow molding synthetic resin bellows. U.S. Patent No. 5,439,178, issued August 8, 1995 to Peterson, discloses a pump having a bellows which can be constructed from polyolefins such as polypropylene, low density polyethylene, ethylene vinyl acetate, rubber and thermoplastic elastomers. World Patent No. WO 88/06088 to Cheynol et al.. published August 25. 1988, discloses a process and apparatus for the manufacture of a protective bellows for a transmission device, in which rough

molded bellows are injected during a primary stage into a first mold, then, in a second mold, the rough molding is blown rib by rib, or by groups of ribs, until the required form of the bellows is achieved.

However, these patents do not address the fabrication of a bellows suitable for use in a wide variety of chemical environments. Specifically, for a flexible spring-like device in chemical service, an enhancement of one or more material properties is required for any material to satisfy the requirements of such service.

Methods to enhance the environmental stress cracking resistance of, for example, polyethylene and ethylene copolymers are known. These methods include crosslinking of polyethylene by peroxides or irradiation. Crosslinking with peroxides has disadvantages such as increased viscosity, localized scorching, and health concerns. Crosslinking by irradiation avoids these disadvantages.

Irradiation of thermoplastics is known in the art as shown by the following prior art references.

U.S. Patent No. 2,855,517, issued October 7, 1958, to Rainer et al.; Lanza, V. L., in "Effect of radiation on polyethylene", Modern Plastics, vol. 34, No. 1 1, pp. 129-132, 134 and 136 (1957); U.S. Patent No. 2.906,678, issued September 29, 1959 to Lawton et al.; Olander, John, in "A guide to radiation equipment". Modern Plastics, vol. 38, No. 10, pp. 105-106, 109, 1 10, 1 13, 1 16, 1 19, 190 and 192 (1961); U.S. Patent No. 3,102,303, issued September 3, 1963 to Lainson; U.S. Patent No. 3,130.139, issued April 21, 1964 to Harper et al.; U.S. Patent No. 3,563,870. issued February 16. 1971 to Tung et al.; U.S. Patent No. 3,734,843, issued May 22. 1973 to Tubbs: U.S. Patent No. 3,773,870. issued November 20, 1973 to Spillers; U.S. Patent No. 3,783,1 15, issued January 1, 1974 to Zeppenfeld; U.S. Patent No. 4,049.757, issued September 20, 1977 to Kammel et al.; U.S. Patent No. 4.264.661, issued April 28, 1981 to Brandolf; U.S. Patent No. 4,367,186, issued January 4, 1983 to Adelmann et al.; U.S. Patent No. 4.582,656, issued April 15. 1986 to Hoffman; U.S. Patent No. 5,061,415, issued October 29, 1991 to Depcik; and JP 098850, published December 27, 1991.

However, none of the above prior art references disclose or suggest how to enhance the environmental fatigue life for a flexible product in aggressive chemical service.

SUMMARY OF THE INVENTION

The present invention provides a process for producing a treated non-planar article, having improved mechanical service in an aggressive chemical environment. The process includes forming a thermoplastic into a first non-planar article having a flexible portion; and exposing the first non-planar article to an amount of radiate

energy to form a treated thermoplastic. The exposure to the radiate energy should be such that the temperature of the thermoplastic during irradiation does not exceed its melting point, while being sufficient to improve the mechanical service of the article in an aggressive chemical environment.

The improvement in mechanical service can be an improvement in the compression set index of the treated non-planar article while exposed to the aggressive chemical environment, as compared to the compression set index of the first untreated non-planar article in the same aggressive chemical environment.

The improvement in mechanical service can also be an improvement in the resistance to environmental stress cracking or environmental fatigue of the treated non-planar article while exposed to the aggressive chemical environment, as compared to the environmental stress cracking or environmental fatigue, respectively, of the first untreated thermoplastic article in the same aggressive chemical environment, while maintaining the mechanical properties, such as the compression set index, of the untreated thermoplastic.

The improvement in mechanical service can also be an improvement both in the compression set index, and in the environmental stress cracking or environmental fatigue of the non-planar article while exposed to the aggressive chemical environment, as compared to compression set index and environmental stress cracking or environmental fatigue of the first untreated non-planar article in the same aggressive chemical environment.

The invention also provides that the thermoplastic can first be irradiated, optionally ground into particles, and then formed into a desired shape. The ground particles can be mixed with unirradiated thermoplastic, which mixture is then formed into a desired shape (which shape can optionally be further irradiated).

The invention also provides that the thermoplastic can first be irradiated and then molded into an article of a desired shape, so long as the melt viscosity of the irradiated thermoplastic remains low enough to permit molding.

The invention also provides a non-planar article comprising a flexible portion which comprises an irradiated thermoplastic.

The invention also provides a non-planar article comprising a potential energy section. This potential energy storage section comprises an irradiated thermoplastic, where the section is suitable for cyclic movement between a position of lower potential energy, and another position of higher potential energy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a perspective of a bellows 30 of Example 1

FIG. 2 is side view of bellows 30 of FIG. 1.

FIGs. 3A, 3B and 3C are a schematic representation of bellows 30 undergoing compression set testing.

FIGs. 4 A and 4B are a schematic representation of bellows 30 undergoing environmental stress cracking resistance testing or environmental fatigue testing.

FIG. 5 is a schematic representation of a bellows 30 undergoing environmental fatigue testing.

DETAILED DESCRIPTION OF THE INVENTION The following definitions of terms are used in this specification.

Aggressive Chemical Environment is any vapor, liquid or solid environment which can adversely diminish the chemical or physical properties or nature of a thermoplastic article into which the article is placed, or in which the article is in contact in service.

Compression Set Testing is a test wherein a flexible portion of an article, such as a standard bellows as shown in FIG. 1, is compressed by a Force FI from a first position wherein the flexible portion has a length LI, to a second position wherein the flexible portion has a compressed length L2, and is held at the compressed length L2 for a period of time and temperature in a fixed aggressive chemical environment. After the period of time, the flexible portion is removed from the environment and permitted to expand free of strain to a third position wherein the flexible portion has a length L3. Thereafter, a force F2 is applied to the article to compress the flexible portion from the third position (L3) to the second position (L2). Alternatively, the article can be returned to the compressed second position (length L2) and placed into the environment for additional periods of time.

Compression Set Resistance is the resistance of the flexible portion of an article such as a bellows to become permanently set at a fixed temperature into or approaching the second position after the Compression Set Testing.

Compression Force Residual (CFR) is the ratio of the force F2 to the force FI, or F2/F1, wherein FI and F2 are as defined by the Compression Set Testing.

Compression Force Ratio is the ratio of the Compression Force Residual (CFR) of an irradiated article to the CFR of a non-irradiated or non-treated article.

Compression Set Index (CSI) is the ratio of the difference between length LI and length L3, to the difference between length LI and length L2. times 100. wherein lengths LI, L2 and L3 are as defined by the Compression Set Testing.

Compression Set Ratio (CSR) is the ratio of the Compression Set Index (CSI) of the irradiated flexible portion of a thermoplastic article to the Compression Set Index (CSI) of the flexible portion of the thermoplastic article before irradiation.

Environmental Stress Cracking Resistance (ESCR) is the resistance of a flexible portion of a thermoplastic article to developing cracks in the thermoplastic flexible portion as a result of holding or restraining the flexible portion in a compressed or strained state while exposed to an aggressive chemical environment.

Environmental Fatigue Resistance (EFR) is the resistance of a flexible portion of a thermoplastic article to developing cracks in the thermoplastic flexible portion as a result of prolonged cyclic loading of the flexible portion from a first position free of strain prior to said testing (of length LI) to a compressed second position (of said length L2), while exposed to an aggressive chemical environment.

In the present invention, an article can be modified to permit its service in a wide variety of chemical environments, preferably, aqueous based environments. The chemical environment of the end application is first determined, and then an appropriate thermoplastic selected for that environment. The material of the article is chosen from thermoplastic resins that resist chemical attack in an aggressn e chemical environment, that resist excessive swelling by the fluid of the aggressive chemical environment, that are crosslinkable with irradiation and that have low moduli. The polymer is preferably selected to have a melt index suitable to permit use of injection molding manufacturing methods.

Suitable materials are generally crosslinkable by irradiation. It is preferred that these materials undergo more crosslinking reactions rather than chain scission (degradation through bond rupture leading to lower molecular weight) reactions from irradiation.

The thermoplastics materials generally provide mechanical service in aggressive chemical environments after irradiation and are generally flexible or can be modified to permit flexibility at application temperatures. Accordingly, these irradiated thermoplastic articles can offer mechanical and chemical advantages over the uncrosslinked articles as specified by this invention.

Furthermore, the irradiated thermoplastic articles are generally intractable. These articles substantially resist flowing when heated above the melting point. Application of compressive forces such as 10,000 lbs force from heated plates to said articles once heated above the melting point still does not create significant flow of said articles. Contrarily, non-irradiated or gel-free thermoplastic articles can be formed into thin films when heated above the melting point and compressed between heated plates with 10,000 lbs force.

The present invention enables an improvement in either the physical properties or nature, or the chemical properties or nature, or both, in a flexible portion of a thermoplastic article which has been treated with radiate energy. In one embodiment, an article can be made from a untreated thermoplastic which exhibits good environmental stress cracking or environmental fatigue in aggressive chemical environment, but which has poor to moderate physical properties or nature in the aggressive chemical environment, such as compression set index. As an example, a bellows made from an ethylene vinyl acetate copolymer (EVA) containing 28 weight % vinyl acetate would offer good EFR but poor CSR. Treatment of the thermoplastic with radiate energy in accordance with the present invention provides improved physical properties, such as improved compression set index, to the treated thermoplastic article.

In another embodiment, an article can be made from a untreated thermoplastic which exhibits good physical properties or nature, such as compression set index, in an aggressive chemical environment, but which has poor to moderate environmental stress cracking or environmental fatigue in the aggressive chemical environment. As an example, a bellows made from an ethylene vinyl acetate copolymer (EVA) containing 9 weight % vinyl acetate would exhibit improved CSR but poor EFR. Treatment of the formed thermoplastic article with radiate energy in accordance with the present invention provides improved environmental stress cracking or environmental fatigue properties to the treated thermoplastic article, compared to the untreated thermoplastic. Environmental stress cracking is generally improved with less radiate energy dosage than it requires to improve compression set resistance.

In another embodiment, an article can be made from an untreated thermoplastic which exhibits poor to moderate environmental stress cracking or environmental fatigue in the aggressive chemical environment, as well as poor to moderate physical properties or nature, such as compression set index. Such a thermoplastic can be selected for cost or other reasons. As an example, a bellows made from an ethylene vinyl acetate copolymer (EVA) containing 19 weight % vinyl acetate would exhibit moderate EFR and CSR, especially at temperatures at or above 100°F. Treatment of the formed thermoplastic article with radiate energy in accordance with the present invention provides improved environmental stress cracking or environmental fatigue properties, as well as improved physical properties or nature, such as compression set index, to the treated thermoplastic article.

/49543 PC17US97/09699

8

In an alternative embodiment of this embodiment, the thermoplastic can first be irradiated, optionally ground into particles of less than about 10 microns in size, and then formed into a desired shape. Alternatively, the thermoplastic can first be irradiated and then formed into a desired shape, which shape can be further irradiated. Or, the thermoplastic can first be irradiated, then mixed with unirradiated thermoplastic, which mixture is then formed into a desired shape (which shape can optionally be further irradiated).

Examples of such thermoplastic materials which can be utilized in the present invention include but are not limited to poly alpha-olefins, copolymers of one or more alpha-olefins, copolymers of an alpha-olefin and an ethylenically unsaturated carboxylic ester, poly(vinyl chloride), poly(dimethyl siloxane), natural rubber, poiybutadiene, and butadiene-styrene copolymer. and blends of the above.

The alpha-olefins utilized in the present invention generally comprise at least 2 carbon atoms. Preferably, the alpha-olefin utilized in the copolymers of the present invention comprise from 2 to 8 carbon atoms, more preferably from 2 to 4 carbon atoms, and most preferably from 2 to 3 carbon atoms. Preferable examples include ethylene. propylene and butylene, most preferably, ethylene.

Polyethylenes are generally selected according to the desired use to have a high elongation at yield, high elongation at yield at elevated temperatures, suitable modulus, resistance to stress relaxation, and suitable dynamic response. Generally the polyethylene will have a density less than about 0.94 g/cm->, and will generally include those known commercially as low density, very low density, or linear low density polyethylenes. Methods of making such polyethylenes are well known, and include high pressure processes, Ziegler-Natta catalyst processes, or single cite catalyst processes such as metallocene catalyst processes, any of which can be utilized.

The ethylenically unsaturated carboxylic ester monomers are selected from the group of vinyl esters of saturated carboxylic acids and alkyl esters of an alpha, beta-ethylenically unsaturated carboxylic acids. Examples of suitable ester monomers include alkyl acrylates, non-limiting examples of which include, methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate and methyl methacrylate. Other non-limiting examples of suitable ester monomers include, diethyl maleate, dimethyl fumarate, vinyl acetate, vinyl propionate and the like. Preferably the copolymer contains one of the following ester monomers: methyl acrylate, ethyl acrylate and vinyl acetate. Most preferably, the copolymer is an ethylene vinyl acetate copolymer, ethylene ethylacrylate copolymer, or ethylene methylacrylate copolymer.

A preferred material is a copolymer of olefins and either vinyl or alkyl esters, and more preferred are copolymers of ethylene and either vinyl or alkyl esters. The copolymers of olefins and vinyl or alkyl esters generally comprise in the range of 1 to 40 weight percent ester, preferably 5 to 30 weight percent ester, and most preferably 10 to 30 weight percent ester.

The melt flow index of the material must be suitable to allow sufficient filling of the selected mold shapes and to withstand operating conditions of forming process. For example, for a spring-like flexible article such as a bellows, it is preferred to use a resin having a medium melt flow index (MFI) in the range of 3 to 40. more preferably of 5 and 35, and most preferably of 7 to 30. The melt flow index is defined in ASTM test method D 1238. This range of MFI permits shaping of the article with such methods as injection molding or injection blow molding.

After treatment by the methods of the present invention, resins suitable for making a spring-like flexible article (such as a bellows) generally have a Young's modulus of at least 2000 psi (pounds per square inch), and preferably of less than 100,000 psi. More preferably, resins have a Young's modulus after treatment in the range of 2.000 to 50,000 psi for such flexible articles, and even more preferably in the range of 2,000 to 35,000 psi. Most preferably, the resins have a Young's modulus after treatment in the range of 3,000 to 12,000 psi.

Any high energy radiation suitable to impart the desired properties can be used. Suitable high energy radiation includes, ultraviolet light, high energy electrons, neutrons, protons, and deuterons, as well as X-rays, beta-rays, and gamma-rays.

Devices for generating radiate energy are well known, and any device suitable in the practice of the present invention can be utilized. Preferably, energy sources used are gamma rays as generated by Cobalt 60, or high energy electrons as generated by electron accelerators.

Ultraviolet light can be conveniently provided utilizing commercially available UV lamps, for example Philips HTQ 4 or 7, Hanovia lamps or others. Electron beam energy can be conveniently provided by commercially available electron beam curing units, for example a Dynamitron direct electron accelerator available from Radiation Dynamics of Edgewood, N.Y.

The radiation dose levels which will provide improved performance and/or service life will vary from thermoplastic material to material. In general, it is desirable that the irradiation process not cause any undue distortion of the formed article. This is generally accomplished by making sure that the temperature of the irradiated material does not exceed its melting point during the irradiation process.

The suitable radiation dosage levels can be estimated depending upon the G values for crosslinking of the material. The G values are defined as the number of molecules reacted per 100 eV of energy absorbed. The G values for crosslinking (or scission) refer to the number of molecules undergoing crosslinking (or bond rupture) per 100 eV of absorbed energy.

For example, the crosslink (scission) G values for polyethylene and natural rubber are 3.0 molecules undergoing crosslinking (0.88 molecules undergoing bond rupture) and 1.1 molecules undergoing crosslinking (0.22 molecules undergoing bond rupture) per 100 eV absorbed, respectively. For these materials, crosslinking occurs preferentially over chain scission reactions. For polyethylene, a dosage in the range of about 2 to about 40 Mrad is suitable to impart the desired properties. Preferably, for polyethylene, a dosage in the range ofabout 3 to about 35 Mrad. and most preferably in the range of about 3 to about 30 Mrad is utilized. In contrast, for natural rubber, a dose 2.7 times higher than that for polyethylene would be required.

The radiation dose level required for a desired level of performance can change based on additives in the polymer. It is known that crosslinking enhancers and crosslinking retarders modify the required dose level. Additionally, it is known that conditions such as temperature or atmosphere can modify the required dose level. These should all be taken into consideration.

The irradiation levels utilized must be suitable to impart desired properties to the molding. For example, for ethylene-vinyl acetate copolymer, irradiation levels from 1 to 35 Mrad are used to impart desired properties to the molding. For the same polymer, doses between 5 and 25 Mrad are preferred for increased compression set resistance, with the most preferred dosage being in the range of 5 to 15 Mrad.

At its upper level, any irradiation dose absorbed by the article should not cause undue or substantial permanent dimensional distortions or undesired mechanical property changes. Heating of an article to the melting point, or with some materials to the softening point, can lead to permanent dimensional distortions or undesired mechanical properties changes. Thus, for an article that can be heated above its thermoplastic softening point temperature without undue or substantial permanent dimensional distortions or undesired mechanical property changes, it is generally heated to a temperature less than its melting point temperature, preferably to a temperature between its melting point temperature and its softening point temperature. Most preferably the thermoplastic materials are not heated above their softening point temperatures.

A high radiation dose can be delivered without excessively heating the article either by use of a low radiate flux such as obtained using gamma rays or by using multiple passes of incremental dosing from high flux sources such as electron beam radiation. The article must be permitted to cool, or be cooled, prior to absoφtion of an additional radiation dose if the article ^' s temperature approaches a melting or softening point. The sum of all dosages received by an article since the creation of the molded part is termed the accumulated dose. Provided that melting of crystals or softening or melting of the article does not occur, then the performance of the article should be directly related to the accumulated dose and exhibit little to no relationship to the number of irradiation sessions, or to the level of radiate flux.

A measurement of the effectiveness of radiation to provide cross-linking of the material, and thus a measure of the relative amount of cross-linking of the material, can be determined by measuring the amount of gel by ASTM Standard D2765-90.

While fabrication of the irradiated polymer of the present invention has been illustrated mainly with respect to injection molding, it should be understood that the polymer should also find use in a broad range of polymer fabrication processes, including injection blow molding, stamp molding, extrusion, pultrusion, pressing, blow molding, rotational molding, and the like.

The benefits obtained from radiation-induced crosslinking are several-fold. First, the environmental stress cracking resistance (ESCR) is significantly improved. Second, the environmental fatigue resistance (EFR) is also significantly improved. Third, with sufficient radiation dosage, the compression set resistance (CSR) is significantly improved.

For an irradiated article undergoing compression set testing in an aggressive chemical environment at a temperature of interest, the ratio of the compression force residual after (for example) 16 weeks will generally be improved, as compared to the compression force residual of a non-irradiated article. The improvement of the compression force ratio resulting from irradiation is preferably at least 5 percent, more preferably at least by 20 percent, even more preferably at least by 50 percent, and most preferably at least by 200 percent. In a similar way, the improvement of the compression set index resulting from irradiation is preferably at least 5 percent, more preferably at least by 10 percent, even more preferably at least by 15 percent, and most preferably at least by 20 percent.

The materials of the present invention are useful for making flexible molded articles for various packaging, dispensing, pumping, or protective mechanical boot applications.

The materials of the present invention will find utility in the making of products subject to static or cyclic loading conditions in an aggressive chemical environment, for example, bellows, diaphragms, and boots. Such products have a flexible, resilient, spring-like or potential energy storage portion, which can be subject to static or cyclic loading. Such a portion can comprise one or more folds, pleats, coils, bends, curves, helixes, bows, twists, or the like, to form a section which functions as a potential energy storage section, for example a pleated section as with a bellows, or a coiled section as with a spring.

The articles of the present invention are generally non-planar having a potential energy storage section, and undergoing cyclic movement of the potential energy storage section between a position of lower potential energy, and another position of higher potential energy.

An article of the present invention is the form of a bellows is particularly useful as a means of pumping and dispensing fluids from containers, such as bottles, cans, and the like. Bellows and bellows pumps and dispensers in general are well known in the art. Techniques for fabricating a bellows and use of a bellows as a pump or dispensing means for a container are known in the art. For example. U.S. Patent No. 5.236,656, issued August 17, 1993 to Nakajima discloses a method of injection blow molding synthetic resin bellows, and U.S. Patent No. 5.439,178, issued August 8, 1995 to Peterson, discloses a pump having a bellows which can be constructed from polyolefins such as polypropylene, low density polyethylene, ethylene vinyl acetate, rubber and thermoplastic elastomers. Non-limiting products that can be dispensed using such bellows pump include liquid hair care compositions such as shampoos and conditioners, cosmetic and skin care products, and liquid dishcare, hard surface and laundry detergent compositions. Such products can come in a variety of liquid forms including, but not limited to. lotions, gels, oils, aqueous liquids, emulsions and dispersions

In the practice of the present invention, there can be utilized, as desired and/or necessary, accelerators to advance the formation of cross-linking of the polymer, or inhibitors to diminish the formation of cross-linking of the polymer. Examples of accelerators include polyfunctional unsaturated monomers such as diemylene glycol diacrylate or dipropargyl maleate; examples of inhibitors include antioxidants such as butylated hydroxytoluene.

In the practice of the present invention, there can also oe utilized, as desired and/or necessary, antioxidants, cross-linking agents, stabilizers, ultraviolet ray absorbers, lubricants, foaming agents, antistatic agents, organic and inorganic flame retardants, plasticizers, slip agents, dyes, pigments, talc, calcium carbonate, carbon

black _, mica _, glass fibers, carbon fibers, aramid resin, asbestos, as well as other fillers as are known in the art.

Examples The invention is further illustrated by the following examples:

Example 1

An ethylene-co-vinyl acetate copolymer having a MFI of 30 and containing 19% by weight vinyl acetate (UE652-059 made by Quantum Chemical Co.) was injection molded into one or more pleated bellows as shown in FIG. 1.

The bellows 30 illustrated in FIG. 1 and FIG. 2 were made in an automatic unit cavity mold. The bellows 30 has a top portion 40 having a shoulder 45, a bottom portion 50. and a flexible portion 60 intermediate to the top portion 40 and the bottom portion 50, the flexible portion 60 consisting a plurality of pleats 65a and 65b.

The injection molding machine was a Engel 200 ton tie-barless machine, model EC88, made in Canada. The range of conditions used for manufacture of these bellows are specified in Table 1 -A.

Table 1-A. Typical Injection Molding Parameters

Parameter Setting Units

Melt Temperature 195-225 °C

Screw RPM 200-400 rpm

Back pressure 20-60 psi

Injection Time 0.5-0.7 s

Hold Pressure 5000-8000 psi

Hold Time 2-6 s

Cooling Time 8-12 s

Mold Temperature 90 °C

The bellows formed above are equilibrated to room temperature and are irradiated (E-Beam Services, Inc. of Cranbury N.J.) with a total exposure of 25 Mrad utilizing a Dynamitron direct electron accelerator (available from Radiation Dynamics of Edgewood, N.Y.) The amount of radiate energy absorbed for each pass of the article through the accelerator is controlled at between 1-2.5 Mrad, for as many passes through the accelerator to achieve the total of 25 Mrad. The rate of irradiation exposure and the frequency of passage of the article through the accelerator is selected to minimize (preferably avoid) heating the article above the melting point of the thermoplastic.

a) Environmental Fatigue Resistance (EFR)

Referring to FIGs. 4A and 4B. environmental fatigue resistance testing was performed by placing the bellows 30 into a test solution 200 of FIG. 5 consisting of Vidal Sassoon™ Straight Hair Shampoo, sold in Japan by Procter & Gamble Far East. Inc. (June 1995), and cycling the flexible portion 60 of the bellows from a first position near full height (where the flexible portion has a length LI) to a second position near the end of a full stroke (where the flexible portion has a length L2). For the bellows shown in FIG. 1, the bottom portion 50 is substantially incompressible relative to the flexible portion 60, and is held stationary. The shoulder 45 of the bellows is cycled at 2 cycles per second from the first position wherein length LI is 1.64 inches (4.166 cm), down to a second position wherein the length L2 is 1.14 inches (2.896 cm).

The cycling is effected by a mechanical apparatus 100 as shown in FIG. 5, with motor 1 10 driving flywheel 120 as shown by direction arrow 152 to create a sinusoidal stroke pattern. Bellows 30 are held between top retaining plate 135 and bottom retaining plate 130, which are all submerged in aggressive chemical 200 in tank 160 having lid 162. Retaining plate 135 is moved toward and away from bottom retaining plate 130, guided by retaining plate guides 137. Pushrod 145 is connected to flywheel 120 by adjustable linkage 140, and to top retaining plate 135 by linkage 147. The rotation of flywheel 120 in the direction of arrow 152 as shown, drives pushrod 145 up and down as represented by arrow 151 , which in turn moves retaining plates 135 relative to retaining plate 130. thus repeatedly compressing bellows 30. After cycling 10.000 times, the bellows is inspected for cracks and holes, and is graded to characterize the extent of cracks and holes (indicating a failure of the bellows) using the Environmental Fatigue Resistance Testing Index shown in Table 1-B. The adjustable linkage 140 is adjusted to create a 0.5 inch (1.27 cm) stroke in push rod 145 and top plate 135. The bottom plate 130 is raised to ensure nearly full compression of the flexible portion of the bellows.

Table 1-B

Index Description _^

1 No cracks

2 Less than 10 small cracks

3 No holes but more than 10 cracks

4 One or more holes

5 Opening connecting two or more holes

An environmental failure index based on the average of the indices of four bellows is reported in Table 1-C.

b) Compression Force Residual (CFR) and Compression Set Ratio (CSR) Referring to FIGs. 3A, 3B and 3C, the flexible portion 60 of a bellows 30 prior to testing is compressed from a first position near full height (wherein the flexible portion has a length LI) to a second position which generally is slightly compressed as could be found after assembly of a bellows into a fixture such as a bellows pump (wherein the flexible portion has a length L2), and the force needed to compress the flexible portion of the bellows from length LI to length L2 is recorded as compression force FI . The compressed bellows is held at the second position while in contact with (submerged in) a test solution at a fixed temperature for a period of time. The test solution can be air, or can be an aggressive chemical environment for the thermoplastic of interest. After the period of time, the compressed bellows is removed from the test solution and removed from compression, and allowed to expand to an unrestrained length and return to room temperature, wherein the flexible portion of the unrestrained bellows will achieve a length L3. The force needed to again compress the flexible portion of the bellows from length L3 back to length L2 at room temperature is recorded as compression force F2. Alternatively, the article can be returned to the compressed second position (L2) and placed into the environment for additional periods of time. The ratio of F2 to FI (or F2/F1) is the Compression Force Residual (CFR) for the bellows tested. The Compression Set Index (CSI) of the irradiated bellows is represented by the Equation 1 :

CSI = (LI - L3) _x 1 Q0 (Equation 1)

(L1 - L2)

For the bellows 30 shown in FIG. 1, the flexible portion 60 of the bellows is compressed from a first position wherein length LI is 1.41 inches (3.58 cm) to the second position wherein the length L2 is 1.23 inches (3.12 cm), and held in compression in the second position for a fixed time in the test solution at a fixed temperature. The test solutions used included air and Pantene™ Damage Care Treatment Shampoo, sold by Max Factor K.K. in Japan (Dec. 1995). Results of the Compression Force Residual and Compression Set Index are recorded for both the irradiated bellows 30 and the non-irradiated bellows in Table 1-C and Table 1-D, respectively.

Table 1-C

Fatigue Index and Compression Force Ratio

Dose Test Fatigue FI F2 @ 16 Compression

(Mrad) Environmen Index (+/- 0.2 weeks Force t lbs.) (+/- 0.2 Residual - lbs.) CFR

0 air 1 1.85 0.83 0.449

25 air 1 2.15 1.17 0.544

0 Pantene™ 5 1.88 0.20 0.106

25 Pantene™ 1 2.19 0.72 0.329

Table 1-D

Compression Set Index

Dose Test LI L3 Compression Set

(Mrad) Environme (+/-0.02 (+/- 0.02 Index - CSI nt in) in) (L2 - 1.23 inches)

0 air 1.45 1.35 45.5

25 air 1.50 1.39 40.7

0 Pantene™ 1.47 1.28 79.2

25 Pantene™ 1.50 1.34 59.3

From Table 1-C, for bellows treated in air after 16 weeks at 70°F. the Compression Force Residual (CFR) for the non-irradiated bellow is 0.449, while the CFR for irradiated bellows is 0.544. The improvement in CFR in air due to irradiation is 21%. For bellows treated in the Pantene™ shampoo after 16 weeks.

the CFR for the non-irradiated bellows is 0.106, while the CFR for irradiated bellow is 0.329. The improvement in CFR in the Pantene™ due to irradiation is 210%.

Example 2

An ethylene-co-vinyl acetate copolymer having a MFI of 30 and containing 19% by weight vinyl acetate (UE652-059 made by Quantum Chemical Co.) was injection molded into pleated bellows as shown in FIG. 1, by the method as described in Example 1. Irradiated bellows received total accumulated dosages of 3, 7, 12, 15, and 25 Mrad from a direct electron accelerator, as described in Example 1. The results of environmental fatigue testing are shown in Table 2-A for bellows tested in the Pantene™ Damage Care Treatment shampoo of Example 1, and in Comet™ Pine Bathroom Cleaner, sold by The Procter & Gamble Company (Dec, 1995)..

Table 2-A

Fatigue Index

Dosage Pantene™ Shampoo - Comet™ Pine Bathroom

(Mrad) Japan Cleaner

0 4 5

3

7

12

15

25

Referring now to FIGs. 4A and 4B, the Environmental Stress Cracking Resistance (ESCR) test is conducted by compressing a flexible portion of a bellows from a first position near full height wherein the length of the flexible portion is L 1 , to a second compressed position near the end of a full stroke, wherein the length of the flexible portion is L2. The compressed flexible portion of the bellows is held in a static compressed state while immersed in a test solution consisting of a harsh chemical environment of interest. The assembly is then transferred to a 100°F constant temperature room or oven. At predetermined time periods, the flexible portion is removed from the test solution which is still held under compression. If no cracks are observed in the compressed flexible portion, the bellows sample is again submerged into the test solution at the 100°F constant temperature. The total

time at which a crack is first observed in a bellows is reported as the failure time. and the test is terminated.

For the bellows as shown in FIG. 1. the flexible portion 60 of the bellows is compressed from a first position wherein length LI is 1.41 inches (3.581 cm) to the second position wherein the length L2 is 0.77 inches (1.956 cm), and submerged into one of the Pantene™ Damage Care Treatment Shampoo of Example 1. or the Comet™ Pine Bathroom Cleaner, The average time for the failure of four bellows tested in each of the test solutions is listed in Table 2-B.

Table 2-B

ESCR (hours)

Dosage Pantene™ Shampoo - Comet™ Pine (Mrad) Japan of Example 1 Bathroom Cleaner

0 2 2

25 >1000 >1000

Example 3 Irradiated and non- irradiated bellows made as described in Example 1 separately from two ethylene methyl acrylate (EMA) copolymers and from one very low density polyethylene (VLDPE). The EMA resins were SP2220 and SP2207, purchased from Chevron Chemical Co. These resins have methyl acrylate weight percentages of 20 wt% and melt flow indices of 20 and 6, respectively. The VLDPE utilized was obtained from Enichem Chemical Co. of Italy (MFI of 13). and sold under the tradename MQFO. The Environmental Fatigue Resistance Index (determined in accordance with the method described in Example la) of these bellows when tested in the Vidal Sassoon™ Shampoo described in Example 1 -A are shown in Table 3.

Table 3

Fatigue Index

Dosage SP2220 SP2207 MQFO (Mrad)

0 4.0 2.0 2.25

25 1.0 1.0 1.0

The above examples illustrate how the properties of molded articles comprised of properly chosen thermoplastic radiation-crosslinkable resins that are loaded in cyclic or static states of stress are enhanced by irradiation. Enhanced properties include but are not limited to ESCR. environmental resistance fatigue and compression set resistance. Other properties that can also be enhanced include but are not limited to heat, chemical, and abrasion resistance. Articles as described herein include, but are not limited to, bellows used for pumping or dispensing of fluids, such as aqueous based fluids. Another example application for an irradiated flexible article includes but, is not limited to a protective boot such as used in an automotive application. Thus, irradiated crosslinkable thermoplastic materials can provide for long service lives of these and other articles loaded in cyclic and static states of stress while exposed to aggressive chemical environments.