CA2101787A1 - Fabricated articles with improved resistance to hydrohalocarbons - Google Patents

Abstract

A multiple layer article of a thermoformable structural polymeric layer (11) which is susceptible to damage upon exposure to hydrohalocarbon blowing agents and a polymeric layer (13) which is a barrier to such hydrohalocarbon blowing agents provides a useful refrigerator liner. Related structures are useful for preventing the migration of hydrohalocarbons.

Description

21U17~7 :::

TITLE
FABRICATEDARTICLES WITH ~MPROVED ~;
RESISTANCE TO HYDROHALOCARBONS
BACKGROUND OF THE INVENTION
This Application is a continuation-in-part of U.S. Application 07/648,007, filed 30 January 1991.
This irlvention relates to articles wi~h barrier properties toward hydrohalocarbons and a method for providing a barrier against penetration by hydrohalocarbons.
Chlorofluorocarbons such as Freon~11 (CFCl3) have been widely used as refrigerants, blowing agents, and propellants. Recent concern about the environIIiental effects of such materials, however, has prompted efforts to seek replacement in various applications by partially halogenated blowing agents or refrigerants, such as hydrochlorofluorocarbon ("HCFC") 123 ~ ; -(CHCl2CF3~ or HFC 134A (CH2FCF3). Such materials are a liquid or gas (thus mobile) at or near room temperature and are believed to be significantly more benign to the environment. Unfortunately it has been found that these replacements can often more readily penetrate polymers which are good barriers to the fully halogenated materials. Such penetration can lead to loss of refrigerant through hoses or tubing in certain applications.Other problems may also result, including solvent-induced stress cracking, distortion, or other interaction of polymers which may come into contact with ~he HCFC. Structural polyrners such as acrylonitrile-butadiene-styrene polymer (ABS) or high impact polyst.yrene (HIPS) are commonly used to ~5 form the plastic liners of refrigerators, and they may exhibit severe disfigllration or cracking when HCFCs are used as blowing agents for insulative foam adjacent to the liner. The present invention provides a solution to these problems.
Insulative liners for refrigerators and freezers are well known.
They are commonly formed by a process which has been described in U.S.
Patent 3,960,631. This patent discloses a liner which includes a plastic wall provided with a release layer Oll one surface. The release layer has a limited adhesion with an insulating foam which is subsequently foamed in place against the release layer. The release layer perrnits separation of the liner from the foam as ~ result of differential therrnal contraction of the liner and foam, and thereby avoids stress cracking of the liner.

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2 1 0 1 7 8 7 Pcr/US92/oo~o2 2 `

A variety of polymers have been used to provide a fuDctional barIier. For example, Japanese Application 62 044,446 discloses a laminate of of a saponified terpolymeric layer of 0.1-3 mol% acrylonitrile units, 2~55 mol% ethylene units, and vinyl acetate units, greater than 98% saponified, 5 and a ~hermoplastic resin l~yer. The laminate has good barrier properties.
Japanese application 02 035,291 discloses a low permeabili~
hose for use in a refrigerant. An intermediate layer is a permeation preventing layer comprising an ethylene vinyl alcohol copolymer. The hose is useful ;n transferring a re~igerant such as Freon'D gas, or gasoline or lightoil. . -~
S~J~MAE~Q~I~Nl~oN
The present inve~tion provides a method for preventing migration of a mobile hydrohalocarbon from a iirst volume containing said hydrohalocarbon to a second volume substantially free from said 5 hydrohalocarbon, comprising interposing a substantially continuous layer of vinyl alcohol polymer composition betwee~ said first and second volumes.
The invention further provides an article compnsing a substantially cont~uous layer of ~nnyl alcohol polymer composition which at least partially encloses a volume designed to sontain a mobile 20 hydrohalocarbon, whereby n~igration of the hydrohalocarbon from said volume is reduced. More specifically, the invention provides such an article in the form of a refrigerator liner.
In addition, the invention provides a multiple layer sheet suitable for combination with at least one thermoformable polymeric 25 structural layer of a styrene-based polymer to form a multiple layer, thermoforrnable article having barrier properties, said multiple layer sheet comprising at least one layer of an ethylene vinyl alcohol copolymer and at least one layer of a polymeric compatibilizer, said compaffbilizer being present in a sufficient ~nount and having sufficient compatibility with the 3 0 ethylene vinyl alcohol copolymer and with the polymer of said therrnoformable polymeric structural layer to compatibilize a melt blend prepared by comminuting and melting the layers of said thermoformable article.
Furthermore, the invention provides a process for preparing a 3 s liner for an insulated cabinet, comprising the steps of:
(a) preparing a multiple layer structure comprising a WO g2/13716 Pcr/uS92/oooo2 21017~

thelmofonnable structural polymeric layer which is susceptible to damage upon exposure to hydrohalocarbon blowing agents and a polymeric layer which is a barrier to such hydrohalocarbon blowing agents, said layer extending substantially continuously over said structural layer and 5 comprising a thermoformable vinyl alcohol polymer composition;
~ b) ther noforming the multiple layer structure to take a th~ee-dimensional shape suitable for use as at least a portion of a liner for an insulated cabinet;
(c) supplying an outer member of a suitable si~e and shape 10 that said thermoformed structure can be assembled thereinto while maintaining a clearance between said outer shell and said thermoformed structure;
(d) assembling the thermoformed structure to said outer member, the polymeric barrier layer of said thermoformed structure facing 15 towards said outer member, while leaving a clearance between said outer member and said thermoformed structure sufficient to contain an insulative amount of foamed polymer; and (e) injecting a foamable polymeric composition comprising a foamable polymer or polymer precursor and a hydrohalocarbon blowing 20 agent into the clearance between said thermoformed structure and said outer member, whereby said foamable composition expands to substantially fill said clearance, thereby forming an insulative foamed polymer layer.
BRI~ DE~lPrlON OF THE l~RAWINGS
Figure 1 is a cross sectiofial view of an embodiment of the 25 invention.
Figures 2, 3, and 6 show further embodiments of the invention.
Figure 4 is a detailed cross sectional view of an embodiment of the invention including a foamed polymer layer and an outer member.
Figure S shows a partially cut-away view of a refrigerator 3 0 incorporating the present invention.
Figure 6 is a cross sectional diagram of an embodiment of the -present invention in the form of a tube.
Figure 7 is a cross sectional diagram of an embodiment of the invention in which a layer of regrind material is incorporated.
DET~ILED D~SC}~PTION OF THE ~NVENT~ON
The present invention generally includes an article comprising W0 9211371~ 1 PCr/US92~ 2 -~
21U17~7 4 a substantially continuous layer of vinyl alcohol polymer composition which at least partially encloses a volume designed to contain a mobile hydrohalocarbon. The term "encloses" in the context of this invention is to -be interpreted broadly. It includes, at one cxtreme, embod~ments in which 5 the vinyl alcohol polymer substantially surrounds the designated volume, as in a tube or a container. It also includes, however, embodiments in which the vinyl alcohol polymer at least partially separates or seals off one or more Q~faces of a volume which may be largely defined by other structural members. A common feature of such embodiments is that ~he vinyl alcohol 0 polymer serves to prevent or minimize migration of a hydrohalocarbon into or out of a volume in which it is to be contained (or excluded).
One embodiment of the present invention is a multiple -layered article in which a thermoformable structural layer is protected from damage from exposure to certain mobile hydrohalocarbons when used as e.g. blowing agents. The structural layer is thus protected by the present --invention ~om the effects of such blowing agents during the process of injecting and foaming an adjacent polymer. A number of s~ructural - -polymeric materials are susceptible to damage under such conditions, when certain halocarbons, particularly certain hydrohalocarbons, are employed, 2 o because hydrohalocarbons are more aggressive solvents than their fully halogenated counterparts, perhaps because of their greater polarity.
Polymeric materials which are thus susceptible to damage include semiamorphous polymers such as polystyrene, styrene-ac~yloI~itrile copolymers such as aclylonitrile-butadiene-s1yrene copolymer, high impact polystyrene, polycarbonate, acrylics, styrene-maleic anhydride copolymers, polyvinyl chloride, and amorphous polyesters such as PETG (glycol modified PET copolyesters). Most typically such a layer is a styrene-based polymer such as high impact polystyrene or ABS copolymer, since these materials are comrnonly used as inner liners for refrigerators, freezers, and 3 o other insulated cabinets. High impact polystyrene (HIPS) is polys~rene modified by styrene-butadiene rubber. ABS copolymer is acrylonitrile butadiene styrene terpolymer, containing monomer units in various proportions, knuwn to those skilled in the art. Such materials are particularly useful because they are comparatively strong, tough, and rigid 3s and can be easily thermoformed into three-dimensional shapes characteristic of inner liners of refrigerators and the like. The thickness of wo 92/13716 2 1 0 1 7 8 7 Pcr/US92/oooo2 , . . . . .

the structural polymeric layer will depend on the particular application at hand; for a refrigerator liner, the thickness is ~pically about 0.25 to about 2.5 mm.
Adjacent to the structural polymer layer in this embodiment is 5 a layer of a polymeric material which is a barrier to such hydrohalocarbon blowing agents. This relationship is shown m Figure 1, wbere 11 represents the structural layer and 13 represents the barrier layer. The barrier layer extends substantially continuously over tbe structural layer and serves to protect the structural layer from damage caused by exposure to the 0 hydrohalocarbons. The polymeric barrier layer therefor must not only have excellent barrier properties towards hydrohalocarbons used as foam blowing agents, but it must also be suitable for thermoforming. That is, it should either adhere to the structural layer or it must be capable of being adhered by means of a suitable adhesive. Furthermore, it should be thermoformable 5 at a temperature compatible with the thermoforming conditions used for the structural polymer layer.
The barrier layer is preferably a vinyl alcohol polymer composition. In particular, an ethylene vinyl alcohol copolymer composition is preferred, although other related polymers can also be used. For 20 example, partially hydrolyzed polyvinyl acetate may be suitable for some applications; polyvinyl alcohol itself may be useful under certain circumstances if it is adequately plasticized. The preferred ethylene vinyl ~lcohol copolymer composition is largely or entirely a copolymer of about 25 to about 60 mole percent ethylene monomer moieties and about 40 to about ;
25 75 mole percent vinyl alcohol (i.e. saponified vinyl acetate) monomer moieties. For applications for which barrier properties are particularly ~ -important, the copolymer will preferably comprise about 30 to about 45 mole percent ethylene monomer and about 65 to about 70 mole percent vinyl alcohol. For applications in which ease of thermoformability is 30 particularly important, the copolymer will preferably comprise about 35 to about 60, and more preferably about 40 to about 50, mole percent ethylene monomer. Other alkenes such as propylene may also be used; and additional comonomers such as vinyl acetate, aclylates, aclylic or methac~ylic acid or their derivatives may also be present in amounts suitable 35 to provide processability and toughness to the polymer. If the copolymer comprises less than about 40 mole percent viDyl alcohol, the barrier 2 1 0 1 7 8 7 ~ Pcr/us92/oooo2 ~ ~
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properties of the polymer are dimiI~ished. If it comprises more than about 75 mole percent vinyl alcohol, the processability of the copolymer is diminished, and in particular the thermoprocessability is diminished. In either event it becomes less suitable as a barrier layer for thermoformed 5 structures. The vinyl alcohol moieties preferably should be substantially completely saponified, being, for example, at least 90%, preferably at least 9S%, or most preferably at least 98% or even 99% saponified. Incomplete saponification leads to a reduction in barrier properties of the polymer, but can lead to improved processability; for this reason polymers with degrees of -~ -saponification as low as 80% can be used if desired.
Alternatively, the barrier layer may be a blend of polymers.
Several particularly useful blends which exhibit good barner properties and improved thermoformability properties are desc ibed in European Applications 305,146 and 380,123. In particular, compositions of at least about 50 percent by weight of EVOH copolymer and up to about 50 percent by weight of a polyamide component, including semicrystalline or preferably amorphous polyamide, provide improved thermoformability. Also preferred are blends of at least about 50 percent by weight EVOH and up to about 50 weight percent of a polyamide blend, which consists essentially of at least ~ ;
2 o about 30 weight percent of at least one amorphous polyarnide and up to -~
about 70 percent of at least one miscible semicrystalline polyamide. A
particularly suitable amorphous polyamide is a copolymer of hexamethylenediamine with isophthalic acid and terephthalic acid;
preferred semicrystalline polyarnides include nylon 6 and Dylon 66.
Likewise, the barrier layer may comprise at least about 30weight percent, ~; -and preferably at least about 50 weight percent, of an ethylene vinyl alcohol ~ -copolymer and up to about 70 weight percent (preferably up to about S0 weight percent) of at least one ethylene copolymer other than ethylene vinyl ;~
alcohol copolymer. The other copolymer component can comprise a 3 o polymer of ethylene and acrylic or methacrylic acid moieties and a polymer of ethylene and glycidyl acrylate or methacrylate moieties.
Tbe barrier layer may also contain customary amounts (e.g up to about 30 weight percent) of other modi~lers as are known in the art for improving toughness, processability, thermal stability and the like, especially 3 5 polymeric modi~lers such as polyolefirLs, ethylene copolymers, ionomers, vinyl ester polymers, polyesters, polyethers, polyurethanes, and elastomers.

Wo 92/13716 2 1 0 1 7 g 7 Pcr/US92/oooo2 Modest amounts of fillers, especially plate-like ~llers such as mica and talc, can be added to further improvç the barrier properties of this layer provided they do not interfere with the thermoformability of the barrier layer.
The thickness of the barrier layer (after thermoforming) will depend on the degree of barrier protection that is desired and on the effectiveness of the bamer material itself. For use in a refrigerator liner, typical thicknesses will ra~ge from about Q002 to about 05 mm, preferably about 0.01 to about 0.1 mm, as measured after thermoforming. The thickness of the barrier layer before thermoforming is typically about 0.0l to 0.8 mm, preferably about Q05 to 0.4 mm. When thinner layers are used, proportionately greater permeation can occur; use of layers thicker than this provides little added protection and is less economical.
The barrier layer is normally applied to the structural layer by lamination, a manufacturing process which is well known to those skilled Ln the art, although other processes such as coextrusion, extrusion coating, spray coating, powder coating, or solution coating may be used.
Often it is preferable for an adhesive layer to be used between ~
the structural and barrier layers. Such an arrangement is shown in Figure 2, -:
where 15 represents the adhesive layer. Suitable adhesives include 2 0 copolyrners of ethylene with one or more of acrylic or methaclylic acids or esters thereof, vinyl acetate, carbon monoxide, and the IL~ce, as well as maleicanhydride grafted polymers of the above, and styrene-containing copolymers. Preferred adhesives include those prepared from ethylene vinyl acetate copolymers, maleic anhydride grafted ethylene vinyl acetate ~
copolymers and styrene butadiene copolymers, as described in U.S. Patent ~ -4,861,677. Such an adhesive layer may be quite thin, for example, about 0.025 to 0.050 mm (before thermoforming). In addition, when certain highly preferred adhesive materia-ls are used, unexpected improvements in processing appear, as is discussed below. It is often convenient to combine 3 o the adhesive and barrier as a single sheet, prepared by coex~usion. The sheet is then laminated onto the structural polymer layer by known techniques. In a suitable lamination process, a film of EVOH and an adhesive layer passes through a nip roll along with a melt of a structural polymer in a sheet extrusion process. The adhesive layer is in contact with a 3 5 hot melt of the structural polymer layer. The film of EVOH should not be exposed to excessive heat from the molten structural polymer or from other WO g2/13716 ` ' Pcrfuss2/oooo2 211)1787` 8 ` ~;

sources before it enters the nip roll, to prevent softening of the EVOH layer and possible wrinlcing or sagging. The film should be laminated under sufficient tension to mamtain a flat surface. A similar lamination procedure can be employed using a subsequent polishing roll rather than a nip roll, provided that the surface of the sheet is sufficiently heated to provide good adhesion.
It will sometimes be desirable to provide an additional polymeric layer atop the barrier layer, as shown in Figure 3. For example, a layer of polyethylene, 17, can be used as a release layer, since it will ~ -normally have limited adhesion to the foam layerwhich will be described in detail below. Use of a release layer permits separation of the liner from the foamed material as a result of differential thermal contraction of the liner -~ -and foam, thereby avoiding stress cracking of the liner. This layer and its use are described in more detail in U.S. patent 3,960,631. Such a layer can also be useful to prevent physical damage to the barrier layer, for example ;
protection from scratches.
A layer of foamed polymer is applied to the multiple layered structure described above, in such a way that the barrier layer is interposed between the foam and the structural layer. Tbe layer of foarned polymer ~
may be applied by methods known to those skilled in the art, but preferably ~ -by injection of the reactive polymers plus foanung agent into a confined -space bounded on one side by the above multiple layered structure and on the other side by another structural member. Such an application is shown in Figure 4, where 19 is the foam and 21 is the second structural member (not drawn to scale). The foarn can be any of a number of polymeric materials well known in the art, preferably a polyurethane. Ihe blowing -agent is a material which is designed to form cells in the polymeric material -~
and thus convert it into a foam. (The blowing agent can also itseif provide additional insulative value after the foaming is completed.) Blowing agents 3 o are generally liquids at ordinary temperatures and under pressure, but they readily fonn a gas upon release of pressure or upon heating. While hydrocarbons such as butane, pentane, and the like have been used as blowing agents, halocarbons are preferred for their relative inertness, low flammabili~ and toxicity, and low heat of vaporization. Recently hydrohalo-carbon blowing agents have become increasingly important because of environmental concerns. A preferred hydrohalocarbon blowing agent is WO 92/13716 2 1 0 1 7 ~ 7 PCr/US92/00002 ~. , .

HCFC 123, CHCl2CF3. Others which may be used include HCFC 141B
(C~ICI2CH2F). It is when such hydrohalocarbons are used that the ~ -advantages of the present invention are fully realized, because of the damaging nature of such materials on the styrene-based polymers commonly used as liners for refrigerators and the like.
The present invention is most effectively employed when the multiple layered structure of the structural and the barrier layer is thermoformed into a desired shape before application of tbe polymeric foam. It is under such conditions that the desirable combination of 0 thermoformability and barrier protection of the present invention is most completely realized. Thermoforming is a process which is well known to those skilled in the art. It is particularly useful for fonning shaped articles,and is distinct from the initial melt processing step. Ex~unples of articles that can be prepared by thermoforming include containers such as bowls, trays, and dishes. Most importantly for the present invention is the formation of shaped articles in the form of liners for refrigerators, freezers, and similar insulated cabinets. The liners for such articles can be prepared by thermoforming a single composite sheet of structural and barrier polymers to form the back wall and the side, bottom, and top walls of the interior storage compartment. A similar thermoforming process can be used to prepare the inner liner for the refrigerator door, which is also considered a part of the liner for purposes of this invention. The extent of deformation necessary to form a door liner is less than that for the refrigerator cavity itself, but most ref~igerator doors do have a definite three-dimensional 2 5 structure, with molded-in shelves and the lLke. It is preferable to assure that the barrier layer of the multiple layer structure is at or slightly above its softening temperature before undertaking the thermoforming process.
The thickness of the multiple layer structure, prior to thermoforming, will depend on the extent of drawing or stretching to be 3 o introduced by the thermoforming process. For formation of a full ref~igerator liner the overall draw ratio may be a factor of 3-6x. Thus in order to obtain a final liner with a total thickness of about 0.4 mm, the initial sheet should be about 2 mm in total thickness. This relationship can be readily adjusted as necessary by one skilled in the art.
Whenever a formed'article such as a refrigerator liner is prepared from a sheet, there will necessarily be some excess ~aterial at the ```` 2101~7 .>

edges of the sheet after forming. This material must be trimrned away from the formed article and discarder or recycled in some appropriate way. A
particularly preferred embodiment of the present invention permits this scrap material to be efficiently recycled.
S 1 he key to this aspect of the inve~tion is the use of a select adhesive ~ ~
material which serves both as an adhesive and as a compatibilizer. That is, -~-when a suf~lcient quantity of the adhesive/compatibilizer is present in the structure, the scrap material can be reground and melted into a substantially uniform material which can be supplied as a separate layer without causing ~ -deterioration of the structural properties of the final structure. The resultingstructure is illustrated in Figure 7. Layers 11, 13, and 15 are, as before, the structural layer, the barrier layer, and the a&esive layer. Layer 31 represents the regrind layer and is composed of a vinyl alcohol polymer (preferably ethylene vinyl alcohol copolymer) from layer 13, the styrenic polymer from layer 11, and the adhesive from layer 15. Layer 31 can, of course, also include recycled materi~l generated from layer 31 itself, which will normally be the ~ -case inacommercial operation.
The ability to recycle the regrind material as shown in Fig. 7 ~
depends on selection of a material as the adhesive which will also serve to ~;
compatibilize the barrier material and the structural m~terial so as to form a blend which retains reasonable structural strength. It has been found that a suitable class of adhesives/compatibilizers are copolymers of about 40 to about 79 weight percent ethylene comonomer, about 0.5 to about 30 weight percent of at least one comonomer selected from the group consisting of ~5 carbon monoxide and sulfur dioxide, about 20 to about S0 weight percent of at least one comonomer selected from the group consisting of unsaturated carboxylic acids, unsaturated derivatives of carboxylic acids other than anhydrides, and alkyl vinyl ethers; and about 0.01 to about 5 weight percent of at least one comonomer containing pendant carbo~ylic acid anhydride functionality. Such adhesives are described in copending U.S. Application S/N 07/734,771.
The CO or SO2 component of this copolymer is believed to serve to increase the polarity of the copolymer, thereby incr~asing the level of inter-action with the EVOH copolymer and thus improving the compatibilizing ability. It should be present in an amount at least sufficient to lead to such improvement. The upper limit of these comonomers is not clearly defined; 30 5~ " ~ ,T~

6 21017 ~ I pcr/uss2/oooo2 weight percent is considered to be a practical limit to the amount of such comonomer which can be copolymerized. Preferably this comonomer is carbon monoxide, and is present in an amount of 7-25 weight percent, more preferably about 8 to about 15 weight percent, and most preferably about 10 to about 14 weight percent.
The unsaturated acid or derivative component of this copolymer is preferably selected from the group consisting of unsaturated mono- or dicarboxylic acids having 3-18 carbon atoms, alkyl esters of such acids having 1-18 carbon atoms in the allyl group, unsaturated alkyl nitriles having 3-18 0 carbon atoms, vinyl esters of saturated carboxylic acids where the acid group -has 3-18 carbon atoms, and aL~cyl vi~yl ethers wberein the alkyl group has 1-18 carbon atoms. Suitable comonomers include acrylic acid, methacrylic acid, vinyl acetate, aLIicyl acrylates and methacrylates baving allyl groups such as methyl, ethyl, propyL isopropyL n-butyl, isobutyl, t-butyL n-pentyL n-hexyl, 2-ethylhexyl, and the like, propyl vinyl ether, acrylonitrile, and methacrylonitrile. Preferred comonomers are aL~cyl acrylates and methacrylates, in particular is n-butyl acrylate. The comonomer selected from this group will preferably comprise about 25 to about 45 weight percent, and more preferably about 27 to about 40 weight percent, and most preferably about 28 to about 30weight percent, of the main chain of the copolymer.
The final comonomer of this copolymer is at least one comonomer containing penda~nt carboxylic acid anhydride functionality.
This comonomer can be incorporated in the polymer chain itself by well-lcnown radical initiated polymerizations processes. Preferably, however, this comonomer is grafted onto the main chain of the polymer. The grafting monomer is selected from the group consisting of ethylenically unsaturated di-, or polycarboxylic acid anhydrides and ethylenically unsaturated carboxylic acid anhydrides. Examples of suitable anhydAdes include itaconic anhydride, maleic anhydAde, and dimethyl maleic anhydride;
3 o maleic anhydride (which may also be prepared from fumaric acid) is preferred.
The method for grafting of the comonomer onto the ethylene copolymer can be any of tbe processes which are well known in the art. For example, grafting can be carried out in the melt without a solvent, as disclosedin European Patent Application 0 266 994, or in solution or dispersion. Melt grafting can be done using a heated extruder, a Brabendern' or Banburyn' wo 92/13716 Pcr/uss2/oooo2 2 1 O 1 ~ 8 7 12 mLxer or other internal mixers or kneading machines, roll mills, and the like.
The grafting may be carried out in the presence of a radical initiator such as asuitable organic pero~de, organic perester, or organic hydropero~ade. The graft copolymers are recovered by any method which separates or utilizes the 5 graft polymer that is formed. Thus the graft copolymer can be recovered in the form of precipitated flu~, pelletsS powders, and the like.
The amount of monomer grafted onto the ethylene copoly ner is not particularly limiting, and may be as low as about O.Ol weight percent or as much as about S percent or even more, based on the weight of the grafted o ethylene copolymer. Preferably the amount of graft comonomer is QOS to about 1.0 or 15 percent of the composition, and more preferably about O.l to about 05 percent. ~;
It is possible that cerhin amounts of ungrafted copolymer can also be present. Sometimes, for example, an~rdride grafted copolymer 5 compositions comprise a cerhin fraction of copolymer which is grafted and a fraction which is not grafted. This might arise as an artifact of the ~rafting process or it may be the result of a mixing process designed to reduce the cost of the relatively expensive grafted material. The presence of an ungrafted copoly ner portion, otherwise chemically similar to the grafted copolymer, is 2 0 specifically contemplated as an equivalent included within the scope of the present invention, provided that the overall amount of pendant anhydride ;
functionality in the composition remains sufficiently high to provide the desired improvements.
The relative-amount of this adhesive present in the structure 25 (and therefore the amount present in the regrind layer) is that which is sufficient to provide a degree of compatibility among the layers of the multiple layer structure when they are ground and melted. A suitable degree of compatibility is that whicb leads to an increase in the mechanical proper~iesof the mixture, such as impact strength, when compared with the comparable 3 o mixture prepared v~/ithout use of the selected adhesive/compatibilizer. In particular, the amount of the adhesive should be about 1 to about 500 parts based on lOO parts by weight of the vinyl alcohol polymer. Preferably the amount is about lO to about 200 parts by weight, and most preferably about 100 to about 200 parts by weight, based on lOO parts by weight of the vinyl 3 5 alcohol polymer. Likewise, in structures of the present invention the relative thicknesses of the vinyl alcohol polymer layer or layers and the adhesive layer wo 92/13716 Pcr/us92/oooo2 or layers should likewise be approximately in these ratios. The amount of the styrenic polymer is most preferably about 87 to about 95 percent by weight of the blend (or by thickness, of the struc~ure).
Accordingly, the present invention encompasses a multiple layer 5 struchlre comprising a layer of a styrenic structural polymer, as described above, a layer of a vinyl alcohol polymer composition, as described above, and a layer of the above-described polymeric compatibilizer or adhesive, which is present in a sufficient amount to compatibiLize a melt blend prepared by comminuting and melting the layers.
The present invention further comprises the process of .. ~.
preparing such a multiple layer structure with a re~ind l~yer. This process specifically can include ~e steps of extrudi~g at least one layer of the thermofolmable structural polymer and at least one layer prepared from co~uting and melting materials recovered from t~mming of other such 5 multiple layer structures, onto a preformed sheet of ethylene vinyl alcohol copolymer and polyrneric compatibilizer. It is desirable tha~ the melt comprising the regrind stream should be sufficiently well mixed in order to assure the maximum compatibilizing effect. It is also permissible to add a certain amount of virgin structural polymer to the regrind stream in order to 20 further improve its structural properties, as will be apparent to a person skilled in the art.
When the present invention is used in the formation of a refrigerator liner, the thermoformed s~ructure is assembled to an outer member, which is norrnally the outer metal body or shell of the ref~igerator or 25 the refrigerator door, shown in Figure S as 21 and 21'. A clearance is maintained between the thermoformed struc~re and the outer shell, adequate to contain a customary amount of foamed polymeric insulation, 19 and I9'. The bar~ier layer faces this clearance or space. A foamable polymeric composition is injected into the ope~ space, by processes which are 3 o well known to those skilled in the art, so that the space between the outer shell and the inner liner (23 and 23') is effectively filled with insulating foam. ~ -Because of the presence of the barrier layer, the HCFC is substantially retained in the volume I9 defined by the liner 23 and the outer body 21. The HCFC blowing agent thus does not contact the inner polymeric liner, which 3 5 thereby remains f~ee from solvent-induced cracking or distortion.
It vill be recognized that the present invention is not limited to wo 92~13716 21 D ~ 7 8 7 ~- PCr/US92/00002 liners for re~igerators and the like, but may be employed effectively in other embodiments where it is desirable to prevent penetration of a mobile hydrohalocarbon from one volume to another volume. For example, a substantially continuous layer of a vinyl alcohol polymer can reduce or 5 eliminate loss of refrigerant from domestic or automotive air conditioners or other refrigeration systems, when used for instance as part of a tube or hose which contains a hydrohalocarbon. Such a tube is shown schematically in Figure 6. Refrigerant is carried within the tube, in volume 25. The bulk of the tube, 27, is a material such as an elastomer which may not provide a lO particularly effective barner to penetration of hydrohalocarbon. The layer ofvinyl alcohol polymer, 29, provides the needed barrier. Of course, the barrier layer need not be on the inside of the tube, as shown, but may be an exterior layer, and additional layers may also be present.as may be desired. Suitable tubes can be made by crosshead extrusion, as is known to those sl~lled in the 15 art. This process involves extrusion of an elastomeric layer atop a preformed tube or layer of EVOH.
xamples 1-7 and C~Qmparativç Ex~mp]ç~Ç1-C~2:
Permeability Measurements.
The permeability of hydrohalocarbons through a layer of a 20 variety of polymeric materials was measured by the process described in ASTM-D-1434, procedure M (November, 1982) except that a vacuum gauge rather than a manometer was used to measure differential vacuum. The materials measured were approximately 03-0.9 mm (0.01-0.03 inches) thiclc Steady state permeation coefficient for 25 hydrochlorofluorocarbon 134A (CH2FCF3) through polymeric materials, measured at 93C, are reported in Table I, and for hydrochlorofluorocarbon 123 (CHCI2CF3) in Table II. The results show that ethylene vinyl alcohol copolymer exhibits barrier properties to these hydrohalocar~ons which are ~ -about an order of magnitude better than those of many other commonly used 3 o barrier materials. Although some samples of polyesters appear to exhibit good barrier properties (Table II), such materials do not exhibit the ease of thermoformability required for many applications. For example, they often ;
exhibit significantly higher forming temperatures than those of ABS or HIPS
(about 145-160C for ABS). It is believed that good barrier properties are 35 more uniformly and reproducibly achievable using EVOH.

WO 92/13716 21017 8 ~PCr/US92/00002 ~, PQ1~ner Permeati~n Coefficienta EVOH (32 mol % ethylene) ~.034 2 blend of EVOH of Ex. 1 (80%) + amorphouspolyamideb(20%~ 0.Q36 3 blend of EVOH of Ex. 1 (60~o) + ionomerC (40%) 0.04 4 blend of EVOH of Ex. 1 (50~)+ ionomerC (42.S%) + E/nBA/GMA terpo1ymerd (6%) 0.05 5 3 layers: EVOH of Ex. 1 (0.1 rnrn) + adhesivee (0.04 mm)+ polypropylene (0.1 mm) 0.04 C1 butadiene/acrylonitrile rubber 13 C2 nylon 66,6 copolymer with 18%
n-butylbenzene sulfonamide plasticizer 1.79 C3 nylon 6 toughened with 19% EPDM
rubber and compatibilizer 0.21 C4 Nylon 12 052 CS Nylonl212 0.64 C6 Clystalline polyethylene terephthalate (annealed) Q13 .
20 a. 10-10(cm3-STP)(cm)/~sec)(~cm2)(cmHg . amorphous polyamide is the copolyrner of hexamethylenediamine with 70 percent isophthalic acid and 30 percent terephthalic acid. - ~ -c. terpolymer of ethylene, 24 wt.% n-butyl acrylate, and 9 wt.% methacrylic acid, 70% neutralized with zinc ions.
25 d. terpolymer containing 26 wt.% n-butyl acrylate and 1.4 w~.% glycidyl methacrylate. (The blend also contains 1% Zn stearate and 0.5%
IrganoxT~ 1010 antioxidant.) e. polypropylene grafted with 0.11% maleic anhydride.

WO 92~13716 2 1017~ g 7 ? ~- ; PCI/US92/0000' Ex. Po]ymer PermeationCoefficienta 6 EVOH (32 mol% E) 0.121 7 EVOH (44 mol% E) 0.0Q6 5 C7 highdensi~ypolyethylenewithCaCO3 filler 19.7 C8 Modified PET with ionomer + low dens. polyethylene 3.34 C9 PET, 0.7 i.v., with ionomer + low dens. polyethylene 0~035 C10 PET, i. v. 0.68 0.016 C11 Modified polyester of ethylene glycol 0.011 o with terephthalic and isophthalic acids (ca. 92/8) C12 Modified polyester similar toC12 0.002 (t/i ratio ca. 86/14) a 10-1 (cm3-STP)(cm)/(sec)(cm2)(cm-Hg) Examples 8-9 and CQ~tive Examples C13 and C14:
Solvent Stress ~cking.
Samples of a polymer (ABS) which is subject to solvent stress cracking were prepared in the form of injection molded ilex bars, 127 mm x 13 20 mm x 3.2 mm. For Examples S and 6 the flex bar was lamLnated witb the ethylene-vinyl alcokol copolymer of Example 1. The test bar was placed between two sheets of EVOH each about 0.76 mm thick (without adhesive) ~ -and this structure was placed in a mold in a heated press. The resulting - ~ -lamination covered both faces and the edges of the test bar. Each sample was 25 held in a three-point metal jig which imparted 3% bending strain to the bar.
The jig and the sample bar were placed in a covered glass jar which contained Freon~ 123 (CHCl2CF3). The sample was held above the liquid so that it was exposed only to the solvent vapors. The results are shown in Table m.

WO92/13716 2101 1~7 . PCr/US92/00002 TABLE III
Ex. $ample Results C13 ABS ("Cycolac~ DFA-lOOOR") cracked throug~ in ca 3 minutes.
C14 ABS (Monsanto) started to crack in 4 minutes badly cracked at 9 minutes, fully cracked through at 13 minutes.

8 ABS of C9 + EVOH lamination surface whiteI~ing behind the EVOH
layer, with cracks devel~ping over time.

9 Repeat of Ex. 3 severely cracked after 1 hour (appears to initiate at flaws in lamination.) (An experiment in which coating of ABS by EVOH was attempted by solvent dipping resulted in severe cracldng within 6 minutes, presumably because of incomplete coating by the EVOH.) Examples lQ and lL~n~Qm~veEx~e C15.
Two- or three-layer films were prepared by extrusion lamination :
of a 127 micrometer (5 mil) layer of an ethylene vinyl alcohol copol~ner 2 0 containing 44 mole percent copolymerized ethylene to a layer 127 ~ ~ -micrometers (5 mil) thick of an adhesive composition (Film A) or to two layers, each 64 micrometers (2.5 mils) thick of the adhesive composition, one layer on each side of the EVOH layer (Film B). In both cases the adhesive composition was a blend of 80 parts of a copolymer of ethylene with 28 weight % n-butyl acrylate and 14 weight % CO, grafted with 1.0weight % maleic -anhydride 20 parts of an ungrafted copolymer of ethylene, 30 wt.% n-butyl ;
acIylate, and 10 wt.% CO, melt index 100 dg/min. The films can be used directly in larnination ~nth an ABS sheet to provide a multiple layer structure in which the graft copolymer blend serves as an adhesive layer. To 3 o demonstrate regrind capability, samples of Film A and Film B, respectively,were cut into pieces about 1 cm square and d~y blended with acrylonitrile-butadiene-styrene copolymer ("ABS," Cyclolacn' N14 from General Electric Plastics) in the proportions indicated in Table VI. The dry blends were melt blended and then formed into test plaques as described above, and Gardner impact strength (ASTM D-3029) was measured. The results, reported in Table VI, indicate that the adhesive layer functions as a compatibilizer in the WO 92/13716 2 1 0 1 7 8 7 PCI~/US92/00002 melt blend to provide blends with good impact strength.

TABLEVI :
. . -- .
Ex. ABS, Film A, Film B, Impact __ ~o Strength C15 100 O O 35.2 ... _ ..
91 9 O ~36.1 11 91 O 9 34.7 a. in N-m

Claims (24)

WHAT IS CLAIMED IS:

1. A method for preventing migration of a mobile hydrohalocarbon from a first volume containing said hydrohalocarbon to a second volume substantially free from said hydrohalocarbon, comprising interposing a substantially continuous layer of vinyl alcohol polymer composition between said first and second volumes.

2. The method of claim 1 wherein the vinyl alcohol polymer composition consists essentially of an ethylene vinyl alcohol copolymer.

3. An article comprising a substantially continuous layer of vinyl alcohol polymer composition which at least partially encloses a volume designed to contain a mobile hydrohalocarbon, whereby migration of the hydrohalocarbon from said volume is reduced.

4. The article of claim 3 wherein the vinyl alcohol polymer composition consists essentially of an ethylene vinyl alcohol copolymer.

5. The article of claim 3 comprising a multiplicity of layers including:
(a) a thermoformable structural polymeric layer which is susceptible to damage upon exposure to hydrohalocarbon blowing agents;
and (b) a polymeric layer which is a barrier to such hydrohalocarbon blowing agents, said layer comprising a thermoformable vinyl alcohol polymer composition and extending substantially continuously over said structural layer.

6. The article of claim 5 further comprising a layer of adhesive located between said structural polymeric layer and said barrier layer, said adhesive being prepared from at least one ethylene vinyl acetate copolymer, at least one maleic anhydride grafted ethylene vinyl acetate copolymer, and at least one styrene butadiene copolymer.

7. The article of claim 6 in the form of a liner for an insulated cabinet.

8. The article of claim 3 comprising a multiplicity of layers in a tubular form, including:
(a) a structural polymeric layer which is at least partially permeable to hydrohalocarbon refrigerants; and (b) a substantially continuous polymeric layer which is a barrier to such hydrohalocarbon refrigerants, said layer comprising a vinyl alcohol polymer composition.

9. The article of Claim 5 further comprising a layer of a polymeric compatibilizer which has sufficient compatibility with said thermoformable structural polymeric layer and said vinyl alcohol polymer layer and is present in a sufficient amount to compatibilize a melt blend prepared by comminuting and melting said layers, wherein the polymeric compatibilizer serves as an adhesive between the structural polymeric layer and the barrier layer.

10. The article of claim 9 wherein the polymeric compatibilizer comprises a copolymer of about 40 to about 79 weight percent ethylene comonomer, about 0.5 to about 30 weight percent of at least one comonomer selected from the group consisting of carbon monoxide and sulfur dioxide, about 20 to about 50 weight percent of at least one comonomer selected from the group consisting of unsaturated carboxylic acids and unsaturated derivatives of carboxylic acids other than anhydrides; and about 0.01 to about 5weight percent of at least one comonomer containing pendant carboxylic acid anhydride functionality.

11. The article of claim 9 further comprising a recycled regrind layer of a melt blend of the polymers of the thermoformable structural polymeric layer, the vinyl alcohol polymer layer, and the layer of polymeric compatibilizer.

12. A multiple layer sheet suitable for combination with at least one thermoformable polymeric structural layer of a styrene-based polymer to form a multiple layer, thermoformable article having barrier properties, said multiple layer sheet comprising at least one layer of an ethylene vinyl alcohol copolymer and at least one layer of a polymeric compatibilizer, said compatibilizer being present in a sufficient amount and having sufficient compatibility with the ethylene vinyl alcohol copolymer and with the polymer of said thermoformable polymeric structural layer to compatibilize a melt blend prepared by comminuting and melting the layers of said thermoformable article.

13. The multiple layer sheet of claim 12 wherein the polymeric compatibilizer comprises a copolymer of about 40 to about 80 weight percent ethylene comonomer, about 0.5 to about 30 weight percent of at least one comonomer selected from the group consisting of carbon monoxide and sulfur dioxide, about 20 to about 50 weight percent of at least one comonomer selected from the group consisting of unsaturated carboxylic acids and unsaturated derivatives of carboxylic acids other than anhydrides; and about 0.01 to about 5 weight percent of at least one comonomer containing pendant carboxylic acid anhydride functionality.

14. A process for preparing a liner for an insulated cabinet, comprising the steps of:
(a) preparing a multiple layer structure comprising:
(i) a thermoformable structural polymeric layer which is susceptible to damage upon exposure to hydrohalocarbon blowing agents;
and (ii) a polymeric layer which is a barrier to such hydrohalocarbon blowing agents, said layer extending substantially continuously over said structural layer and comprising a thermoformable vinyl alcohol polymer composition;
(b) thermoforming the multiple layer structure to take a three-dimensional shape suitable for use as at least a portion of a liner for an insulated cabinet;
(c) supplying an outer member of a suitable size and shape that said thermoformed structure can be assembled thereinto while maintaining a clearance between said outer shell and said thermoformed structure;
(d) assembling the thermoformed structure to said outer member, the polymeric barrier layer of said thermoformed structure facing towards said outer member, while leaving a clearance between said outer member and said thermoformed structure sufficient to contain an insulate amount of foamed polymer;
(e) injecting a foamable polymeric composition comprising a foamable polymer or polymer precursor and a hydrohalocarbon blowing agent into the clearance between said thermoformed structure and said outer member, whereby said foamable composition expands to substantially fill said clearance, thereby forming an insulative foamed polymer layer.

15. The process of claim 14 wherein the multiple layer structure further comprises a layer of a polymeric compatibilizer which has sufficient compatibility with said thermoformable structural polymeric layer and said polymeric barrier layer and is present in a sufficient amount to compatibilize amelt blend prepared by comminuting and melting said layers.

16. The process of claim 15 wherein the multiple layer structure further comprises a recycled regrind layer of a melt blend of the polymers of the thermoformable structural polymeric layer, the polymeric barrier layer, and the polymeric compatibilizer layer.

17. A multiple layer article comprising:
a) a thermoformable structural layer comprising a styrene-based polymer;
b) a thermoformable barrier layer adjacent to the structural layer, comprising a vinyl alcohol polymer, and c) an adhesive layer between the structural and barrier layers comprising an adhesive copolymer wherein:
i) from about 40 to about 79 wt% is copolymerized ethylene;
ii) from about 0.5 to about 30 wt% is selected from copolymerized carbon monoxide and copolymerized sulfur dioxide;
iii) from about 20 to about 50 wt% is selected from copolymerized unsaturated carboxylic acid, copolymerized unsaturated carboxylic acid derivatives other than anhydrides, and copolymerized alkyl vinyl ethers; and iv) from about 0.01 to about 5 wt% is copolymerized-comonomer containing pendant carboxylic acid anhydride functionality.

18. The multiple layer article of claim 17 wherein the adhesive copolymer comprises 1) from about 10 to 14 wt% copolymerized carbon monoxide;
2) from about 27 to 40 wt% selected from copolymerized alkyl acrylate and copolymerized alkyl methacrylate; and 3) from about 0.1 to about 0.5 wt% selected from copolymerized itaconic anhydride, copolymerized maleic anhydride and copolymerized dimethyl maleic anhydride.

19. The multiple layer article of claim 18 further comprising a regrind layer prepared from comminuting and melting materials recovered from trimming such multiple layer articles.

20. The multiple layer article of claim 19 wherein the regrind layer contains virgin styrene-based polymer.

21. The multiple layer article of claim 17 wherein the adhesive copolymer is present from 1 to about 500 weight parts per hundred weight parts vinyl alcohol polymer in the barrier layer and the thickness of the adhesive layer is from 1 to about 500% of the barrier layer thickness.

22. The multiple layer article of claim 21 wherein about 87 to 95 of the thickness of the article is the styrene-based polymer.

23. The multiple layer article of claim 17 wherein the styrene-based polymer is selected from high impact polystyrene and acrylonitrile-butadiene-styrene copolymer.

24. A liner for a refrigeration cabinet comprising a multiple layer article as recited in any of claims 17-23.