Umted States Patent [19]
`Nojiri et a1.
`
`[54] COMPOSITION FOR A CROSSLINKED
`POLYOLEFIN FOAM
`[75] Inventors: Akio Nojiri, Kawasaki; Takashi
`Sawasaki; Isamu Noguchi, both of
`Tokyo; Shinji Onobori, Hatano; I
`Junnosuke Sasazima, Hiratsuka’ all‘of
`Japan
`
`[73] Assignee: The Furukawa Electric Co., Ltd.,
`Tokyo, Japan
`[21] Appl. No: 358,684
`.
`I
`[22] Flled'
`
`Mar‘ 16’ 1982
`
`_
`
`_
`
`Related US. Application Data
`Continuation-impart of Ser. No. 179,477, Aug. 18,
`1980, abandoned.
`Foreign Application Priority Data
`
`[63]
`
`[301
`
`Japan .............................. .. 54-110063
`Aug. 29, 1979 [JP]
`[51] Int. cu ............................ .; ................ .. C08J 9/12
`[52] US. Cl. ...................................... .. 521/82; 521/88;
`521/134; 521/140; 521/915; 525/240
`
`[11]
`[45]
`
`4,421,867
`Dec. 20, 1983
`
`[58] Field of Search ................. .. 521/82, 88, 134, 140;
`525/240
`
`[56]
`
`References Cited
`
`U'S' PATENT DOCUMENTS
`3,549,563 12/1910 H111 et a1. .......................... .. 521/134
`3,846,349 11/1974 Harada et a1.
`521/134
`3,929,689 12/1975 Walton et a1. ..
`521/134
`3,950,278 4/ 1976 Wada et a1.
`521/134
`3,965,054 6/1976 Nojiri et a1. .
`521/134
`4,055,695 10 1977 L t
`t
`1. ...... ..
`.. 521 134
`/
`as e a
`/
`Primary Examiner~Morton Foelak
`Attorney, Agent, or Firm-Frishauf, Holtz, Goodman &
`
`Woodward
`
`ABSTRACT
`[57]
`A composition for a crosslinked polyole?n foam is pre
`pared from 20 to 75% by weight of a crystalline propy
`lene copolymer containing 1 to 15% by weight of ethyl
`ene and having a crystallinity higher than 50% and 80
`to 25% by weight of polyethylene‘
`
`12 Claims, 1 Drawing Figure
`
`700
`
`600
`
`500
`
`1%)
`
`400
`
`300
`
`ELONGATION 200 '
`
`|
`
`| Ii 1|
`
`l
`'
`|
`l
`l
`I
`l
`||
`|
`'
`II.
`|
`l
`I
`||
`1
`|
`||
`1!
`l
`|
`O
`2030
`O
`. 100
`7O 75
`50
`PROPYLENE COPOLYMER (%BY WEIGHT)
`
`100
`
`I
`
`I
`
`1
`‘I00
`
`I
`l
`zioés
`so
`80 70
`POLYETHYLENE (% BY WEIGHT)
`
`o
`
`Page 1 of 8
`
`BOREALIS EXHIBIT 1091
`
`

`
`U.S. Patent
`
`Dec. 20, 1983
`
`4,421,867
`
`7 6 5 4 3 2 .1
`O O O O O O O
`O O O O O O O O
`
`- _ _ _ _ _ O
`
`
`
`O lllllll 13E m
`
`
`I I I I I l ‘ I lllww
`, P
`P O R
`
`5 |||||||| 1-7
`||||||| 1m
`
`0 w
`% BY WEIGHT)
`
`R m
`
`'0
`5w. 0 w C
`
`l
`‘IOO
`
`8O 7O
`3025
`50
`POLYETHYLENE (
`% BY WEIGHT )
`
`|
`
`. 0
`
`Page 2 of 8
`
`

`
`1
`
`COMPOSITION FOR A CROSSLINKED
`POLYOLEFIN FOAM
`
`4,421,867
`
`2
`met and polyethylene which corresponds to the propor
`tions (% by weight) of the respective components of
`said mixture. Detailed description is given of the above
`mentioned elongation in Example 3 and Control 5.
`A composition embodying this invention for a cross
`linked polyoletin foam provides a crosslinked foam
`which displays an unexpectedly high elongation and
`prominent thermoformability.
`Detailed description is now given of said composition
`embodying the invention. A propylene copolymer used
`in the preparation of said composition contains 1 to 15%
`by weight of ethylene, has a melt index (M.I.) of 1 to 20
`and a crystallinity higher than 50% and is preferred to
`be a random or block copolymer containing 2 to 9% by
`weight of ethylene. These copolymers can be distin
`guished from a homopolymer by the differential scan
`ning calorimeter (DSC). A polymer which indicates
`only one endothermic peak at a temperature from 162°
`to 170° C. as measured at a heating rate of 5° C./min is
`a propylene homopolymer. A polymer which displays a
`broad small endothermic peak in the proximity of 120°
`C. and a large endothermic peak in the proximity of
`160° C. is a propylene block copolymer. A polymer
`which shows a broad fusion curve over a temperature
`range of 100° to 160° C. is a propylene random copoly
`mer. In view of the required crosslinking, extrudability
`and thermoformability, the above-mentioned propylene
`copolymer is preferably used in this invention. It is
`more preferred to apply the type which shows a fusion
`peak at a temperature as over 138° to less than 158° C.
`(a shoulder section in the fusion curve is not regarded as
`a peak). A most preferred type of propylene copolymer
`for high extrudability is that which indicates a fusion
`peak at a temperature of less than 150° C.
`The propylene copolymer used in this invention is
`crystalline, the crystallinity of which can be measured
`by the infrared absorption method. The relationship
`between the absorbance ratio and the tacticity of the
`polymer is known to the art, i.e., absorbance ratio be
`tween 995 cm“1 band and 974 cm—1 band. In general,
`the crystallinity is determined from the above-noted
`relationship on the assumption that the tacticity is sub
`stantially equal to the crystallinity. The propylene co
`polymer used in this invention has at least 50% of crys
`tallinity. Incidentally, the crystallinity of atactic poly
`propylene is substantially zero. Also, the propylene
`component of the ordinary ethylene-propylene rubber
`has a tacticity of at most 10%.
`The type of polyethylene used in this invention is not
`subject to any particular limitation. However, the so
`called medium density polyethylene is preferred whose
`density ranges between 0.920 to 0.945 g/cm3. More
`preferred medium density polyethylene is the type
`whose density ranges between 0.923 and 0.937 g/cm3.
`These types of polyethylene are, to be precise, copoly
`mers of ethylene and a small amount of any of the other
`a-ole?ns such as propylene, butene-l and hexene-l. The
`above-mentioned polyethylene is generally manufac
`tured by the low and medium pressure polymerization
`method such as the Ziegler and Phillips processes. More
`preferred polyethylene is the type which has a density
`falling within the above-mentioned range and in which
`the absorptivity coefficient K’770 cm—l (expressed by
`the following equation) of an infrared absorption spec
`trum which shows the presence of a longer chain
`branch than an ethyl branch
`
`This application is a continuation-in-part of applica
`tion Ser. No. 179,477, ?led on Aug. 18, 1980, now aban
`doned.
`This invention relates to a composition well adapted
`for thermoforming, for example, vacuum forming or
`compression forming of a crosslinked polyole?n foam,
`and also to a foam prepared from the composition.
`A crosslinked polyole?n foam, particularly cross
`linked polyethylene foam which generally has good
`?exibility and heat insulation is widely accepted as heat
`insulating material or sundry goods after subjected. to
`secondary processing such as laminating and thermo
`forming. In recent years, the crosslinked polyethylene
`foam is much desired, for example, as a heat-insulating
`member of a car cooler, or a box-shaped heat insulating
`member of an icebox or cushioning medium, etc. There
`fore, a heat-insulating product and sundry goods are
`often manufactured by the vacuum forming or com
`pression forming of a crosslinked polyethylene foam
`sheet. However, a commercially available crosslinked
`polyole?n foam has low thermoformability, presenting
`considerable difficulties in effecting a higher draw ratio
`than 0.7 (the draw ratio is represented by the ratio of the
`depth of a box-shaped foam sheet by draw forming to
`the length of the longer side of the bottom plane), and
`consequently failing to provide formings sufficiently
`withstanding application.
`The present inventors have conducted studies in view
`of the above-mentioned circumstances, and as a result
`have succeeded in developing a composition capable of
`producing a crosslinked polyole?n foam which not only
`retains heat resistance, heat insulation, shock absorbing
`properties and ?exibility which are possessed by the
`conventional crosslinked polyole?n foam, but also
`prominently excels in thermoformability, particularly
`vacuum formability and compression formability.
`Namely, this invention relates to a composition for
`use in a crosslinked polyole?n foam having a closed cell
`structure which comprises a mixture of 20 to 75% by
`weight of a crystalline propylene copolymer containing
`1 to 15% by weight of ethylene and having a crystallin
`ity higher than 50% and 80 to 25% by weight of poly
`ethylene.
`A crosslinked polyole?n foam with a closed cell
`structure prepared from a composition embodying this
`invention has an elongation of more than 250% at room
`temperature, which is a far larger value as compared
`with crosslinked polyethylene foam and crosslinked
`polypropylene foam, made by the prior art, having an
`elongation of not more than 150% and 100% respec
`tively at room temperature. In other words, the cross
`linked polyole?n foam of the invention ensures deep
`draw vacuum forming with a high draw ratio of 0.7 to
`2 or more.
`The accompanying drawing graphically shows the
`elongation characteristic of a crosslinked polyole?n
`foam prepared from a composition embodying this in
`vention. Curve A denotes that percentage elongation of
`a crosslinked foam prepared from a mixture of a propy
`lene copolymer and polyethylene which corresponds to
`the proportions (% by weight) of the respective compo
`nents of said mixture. Curve B represents that percent
`age elongation of a nonfoamed but only crosslinked
`product prepared from a mixture of a propylene copoly
`
`25
`
`35
`
`45
`
`55
`
`60
`
`65
`
`Page 3 of 8
`
`

`
`3
`
`K770 Cm“l = %' - loglTo
`
`has a value falling within the range of 0.5 to 7.
`In the above-mentioned equation,
`d =density (g/cm3)
`l=f1lm thickness (cm)
`I,,=transmittance of a base line at 770 cm—1
`I=transmittance of an absorption at 770 cm-1
`The melt indices of polyethylene and propylene co
`polymer used to prepare a composition embodying this
`invention are not subject to any particular limitation.
`Where, however, a foamable sheet for a crosslinked
`polyole?n foam is prepared, for example, by an extruder
`from a mixture of both polymers blended with a blow
`ing agent and, if necessary, a crosslinking agent, then
`the polyethylene is chosen to have a melt index ranging
`between 1 and 10 or preferably between 1 to 8, and the
`propylene copolymer is desired to have a melt index
`ranging between 1 and 20, or preferably between 4 and
`
`15.
`
`'
`
`10
`
`30
`
`35
`
`45
`
`4,421,867
`4
`anurate and trimethylol propane triacrylate and apply»
`ing heat and pressure to the blended mass. Further, it is
`possible to conduct the crosslinking process by blending
`the composition embodying this invention with silane
`compounds such as vinyl trimethoxy silane and vinyl
`triethoxy silane, and a small amount of organic perox
`ides such as dicumyl peroxide and di-t-butyl peroxide,
`thereby grafting the polymer contained in the composi
`tion embodying this invention, and further mixing said
`grafted polymer with a silanol condensation catalyst
`such as dibutyl tin dilaurate in the presence of water.
`Any of the above-mentioned crosslinking processes
`should advisably be undertaken before the foaming of
`the composition or at the same time as said foaming.
`The crosslinking degree varies with, for example, the
`method of manufacturing a crosslinked polyolefin foam,
`the proportions of polyethylene and propylene copoly
`mer contained in the composition and the molecular
`weights of the respective component polymers. How
`ever, the crosslinking well serves the purpose if it is
`carried out to’such degree that where a crosslinked
`foam is extracted for 12 hours at 135° C. with tetralin
`used as an extraction solvent, the resultant gel content
`ranges between 20 and 80% by weight. Said gel content
`preferably ranges between 20 and 50% by weight. The
`reason for this is that a smaller gal content than 20% by
`weight causes the crosslinked foam to decrease in me
`chanical strength, though increased elongation; and
`conversely a larger gel content than 80% undesirably
`causes the crosslinked foam to have a low elongation
`even upon application of heat and be reduced in the
`vacuum formability.
`The above-noted gel content of the crosslinked poly
`ole?n foam of this invention represents the sum of gel
`content of polyethylene and gel content of propylene
`copolymer, i.e., percentage of the sum based on the
`total weight of the foam. Also, the polyethylene gel
`content based on the total weight of the polyethylene
`contained in the polymer blend is about 10 to 50%, with
`the propylene copolymer gel content based on the total
`weight of the copolymer contained in the polymer
`blend being about 30 to 90%.
`In the manufacturing process of a crosslinked poly
`olefm foam, a preferred crosslinked polyole?n foam is
`produced by mixing the composition embodying this
`invention with a blowing agent, triacrylate or trimeth
`acrylate of aliphatic polyhydric alcohol and phenolic
`derivative, irradiating the mixture at an absorbed dose
`of 0.5 to 5 Mrad and thermally foaming it.
`The triacrylate or trimethacrylate of aliphatic poly
`hydric alcohol used in this invention includes trimethac
`rylate, trimethylol ethane triacrylate, tetramethylol
`methane triacrylate. The added proportion of these
`acrylates is chosen to be 0.5 to 4.0 parts per hundred
`parts of resin (phr). A lower phr rate than 0.5 does not
`give rise to crosslinking. A higher gas rate than 4.0
`results in the growth of a foam full of voids. The pre
`ferred added proportion of said acrylates is chosen to
`range between 1.0 and 2.5 phr.
`Derivatives of phenolic compounds also usable in this
`invention include, for example, 2,6-di-t-butyl-4-methyl
`phenol; 2,5-dimethyl hydroquinone; 2,2-bis(4-hydroxy
`3,5-dimethyl phenyl) propane; 2,4,6-trimethyl phenol;
`bis(4-hydroxy-3,5-di-t-butyl phenyl) sul?de; bis(2
`hydroxy-3,5-dimethyl phenyl) methane; bis(3-hydroxy
`2,5-tetramethyl phenyl) methane; l,3,5-trimethyl-2,4,6
`tris-(3,5-di-t-butyl-4-hydroxybenzyl)benzene; 1,1,3-tris
`
`For the object of this invention, 80 yo 25% by weight
`of polyethylene is mixed with 20 to 75% by weight of
`propylene copolymer. It is preferred to mix 70 to 30%
`25
`by weight of polyethylene with 30 to 70% by weight of
`a propylene copolymer.
`A polyolefm foam embodying this invention having
`the above-mentioned composition has a density of about
`0.25 to 0.02 g/cm3, a closed cell structure, a greater
`elongation than 250% at 20° C. and a satisfactory ther
`moformability. Further, a crosslinked foam produced of
`65 to 45% by weight of polyethylene having a medium
`density of 0.920 to 0.945 g/cm3 and 35 to 55% by
`weight of a propylene-ethylene random copolymer
`containing 1 to 15% by weight of ethylene is extremely
`preferred because said foam has a greater elongation
`than 300% at 20° C., and is noticeably improved in the
`property of thermoforming including vacuum forming
`and allows for a deep draw ratio having as high a draw
`40
`ratio as 2.0.
`A composition embodying this invention for a cross
`linked polyolefm foam comprises a mixture of polyeth
`ylene and propylene copolymer blended with the
`above-de?ned proportions. However, it is possible to
`add any other polymer to said mixture. The proportion
`of said additional polymer is chosen to be less than 50%
`or preferably less than 30% by weight. Said additional
`polymer is desired to be a polymer compatible with the
`aforesaid polyole?ns such as polybutene-l, polypropyl
`ene homopolymer, ethylene-vinyl acetate copolymer,
`ethylene-ethyl acrylate copolymer, polystyrene, ethy
`lene-propylene rubber and styrenebutadiene rubber
`alone or a mixture thereof. It is also possible to blend the
`above-mentioned mixture with such additives as an
`inorganic ?ller, pigment, antioxidant, ultraviolet ab
`sorber and other processing aids.
`The crosslinking of a composition embodying this
`invention for a crosslinked polyolefm foam is com
`monly carried out by irradiating electron beams on the
`composition containing polyfunctional compounds
`such as divinylbenzene, triallyl cyanurate, diethylene
`glycol diacrylate, and diallyl phthalate prepolymer and,
`if necessary, monofunctional monomers such as styrene
`and vinyl toluene. The crosslinking process may also be
`effected by blending the composition embodying this
`invention with organic peroxides such as dicumyl per
`oxide, and 2,S-dimethyl-2,5-di(t-butylperoxy)hexyne-3,
`and polyfunctional compounds such as triallyl isocy
`
`60
`
`65
`
`Page 4 of 8
`
`

`
`10
`
`15
`
`20
`
`25
`
`40
`
`45
`
`4,421,867
`5
`6
`(5-t-butyl-4-hydroxy-2-methyl phenyl) butane; octade
`A process adapted to produce a crosslinked polyole
`cyl-3-(3',5’-di-t-butyl-4’-hydroxy phenyl) propionate;
`?n foam from a foamable sheet for a crosslinked poly
`pentaerythrityl-tetrakis
`[3-(3,5-di-t-butyl-4-hydroxy
`ole?n foam is known which comprises placing a foam
`phenyl) propionate]; and tris-(3,5-di-t-butyl-4-hydroxy
`able polyole?n composition sheet on a stainless steel net
`benzyl) isocyanate. Particularly preferred are com
`endless conveyor traveling through a hot air furnace at
`pounds having at least three hydroxyl groups such as
`its entrance, carrying out the foaming of said sheet and
`l,1,3-tris-(5-t-butyl-4-hydroxy-2-methyl phenyl) butane;
`taking out the foamed sheet at the exit of the furnace.
`octadecyl-3-(3’,5’-di-t-butyl-4’-hydroxy phenyl) propio
`The polyole?n melts during foaming process. Unless,
`nate; tris-(3,5-di-t-butyl-4~hydroxybenzyl) isocyanurate;
`therefore, properly supported, the molten foamable
`l,3,5-trimethyl-2,4,6-tris-(3,5-di-t-butyl-4-hydroxyben
`sheet is stretched by its self weight. Consequently, it is
`zyl) benzene and pentaerythrityltetrakis [3-(3,5-di-t
`necessary to foam said sheet while it is carried by a
`butyl-4-hydroxy phenyl) propionate].
`support like a wire net. The wire net is adapted for
`foaming. The reason for this is that since the molten
`The phenolic compound derivative serves to enhance ’
`sheet during the foaming process is ready to stick to a
`the crosslinking effect even when added in a small
`support, the wire net not only reduces the area of the
`amount. Further, if foaming is carried out in the air in
`support to which the molten sheet is ready to adhere but
`the absence of the phenolic compound derivative, the
`also effects the uniform application of heat to the upper
`produced foam tends to shrink. The reason for this is
`and lower sides of the sheet by facilitating the passage
`unclear‘.
`or hot air.
`The amount of the phenolic compound derivative
`A composition embodying this invention for a cross
`ranges from 0.01 to 5.0 phr. If the amount exceeds 5.0
`linked polyole?n foam is particularly suited for the
`phr, the crosslinking reaction is adversely affected.
`above-mentioned conventional foaming process.
`Conversely, if the amount of the phenolic compound
`Though fundamentally suited for the production of a
`derivative is smaller than 0.01 phr, then the above-men
`foamed polyole?n sheet, said conventional foaming
`tioned effect is not produced. The amount of a phenolic
`process, does not always fully serve the purpose. For
`compound derivative having at least. three hydroxy
`instance, depending on the kind and composition of
`groups used in this invention is preferred to range be
`polyole?ns and the crosslinking degree thereof, the
`tween 0.05 and 1.0.
`molten sheet undesirably sticks to a wire net, failing to
`A composition embodying this invention for a cross
`provide a properly foamed sheet, or otherwise that side
`linked polyole?n foam is irradiated by ionizing radia
`of the foamed sheet which contacts the wire net is
`tions which include 'y rays and B rays emitted from a
`marked with the pattern of said wire net.
`radioactive isotope and electron beams and X-rays from
`However, a composition embodying this invention
`an electron accelerator. The absorbed dose of said ion
`for a crosslinked polyole?n foam is not adhesive to a
`izing radiations is chosen to be from 0.1 to 10 Mard,
`wire net, thereby providing a foamed sheet free from
`preferably from 0.5 to 5 Mrad, more preferably from 1
`the pattern of the wire net. Therefore, the composition
`to 3 Mrad.
`of the invention is particularly suited for the above
`A preferred crosslinked polyole?n foam is produced
`mentioned conventional foaming process.
`by foaminga composition embodying this invention by
`A composition embodying this invention for a cross
`the steps of mixing the prescribed polymer blend with
`linked polyole?n foam is generally foamed to 4 to 60
`0.5 to 30 phr of a solid blowing agent such as azodicar
`times the original volume. However, the foamed com
`bon amide, dinitrosopentamethylene tetramine, and
`position used for vacuum forming is generally the type
`p-toluenesulfonyl semicarbazide and applying thermal
`foamed to 10 to 40 times the original volume.
`decomposition or effecting said foaming by 0.5 to 40
`This invention will be more fully understood with
`phr of aliphatic hydrocarbons such as butane and pen
`reference to the examples which follow.
`tane or halogenated hydrocarbons such as dichlorodi
`?uoromethane. Or said foaming may be carried out by
`a normally gaseous inorganic gas such as nitrogen gas.
`A foamable shaped sheet is commonly prepared by
`supplying the prescribed polymer blend previously
`mixed with a blowing agent to an extruder or supplying
`said polymer blend, said blowing agent and other addi
`tives to the extruder at the same time. In some cases,
`however, a crosslinked foamable sheet is directly drawn
`out from a die of an extruder with crosslinking carried
`out in the extruder. Where solvent or gas is applied as a
`blowing agent, there may be used the conventional
`process comprises introducing said polymer blend and
`the blowing agent into the extruder and extrusion foam
`ing the mixture after or at the same time with crosslink
`ing.
`Further the composition for a crosslinked polyole?n
`foam is sometimes previously subjected to crosslinking
`in the form of pellet or shaped article. Later, the cross
`linked mass is impregnated with a blowing agent, fol
`lowed by thermal foaming.
`Heating for foaming is generally carried out by hot
`air, infrared rays, salt bath, or oil bath. Or as previously
`described, heating is applied in an extruder itself.
`
`EXAMPLE 1
`55% by weight of medium density polyethylene pro
`duced by the low pressure process (M.I.: 4; density:
`0.925 g/cm3; and absorptivity coef?cient: K’770
`cm-l: 1.5) was mixed with 45% by weight of propy
`lene-ethylene random copolymer (M.I.: 7; ethylene
`content: 4% by weight; melting point: 147° C.; and
`crystallinity: 85%). 100 parts by weight of the mixture
`were blended with 15 parts by weight of azodicarbon
`amide as a blowing agent, 2.0 parts by weight of triallyl
`trimellitate as a crosslinking promoter and 0.2 part by
`weight of penthaerythrityl-tetrakis [3-(3,5-di-t-butyl-4
`hydroxy phenyl) propionate] as a phenolic compound
`derivative (manufactured by Ciba Gigy under the trade
`mark “Irganox 1010”).
`'
`.
`The mixture was extruded into a sheet having a thick
`ness of 1.5 mm. Electron beams were irradiated on the
`sheet with an absorbed dose of 4.0 Mrad. The irradiated
`sheet was foamed while being carried on a wire net
`endless belt traveling through a foaming furnace with
`hot air of 230° C. The foamed sheet had a thickness of
`4.5 mm, density of 0.032 g/cc (corresponding to an
`expansion ratio of 30 times), and a ?ne and closed cell
`
`55
`
`65
`
`Page 5 of 8
`
`

`
`4,421,867
`
`8
`TABLE l-continued
`Tensile strength and elongation
`of polyole?n foams
`
`.
`
`7
`structure. Heating was applied to both sides of the
`foamed sheet for about 15 seconds by a pair of 10 KW
`infrared heaters respectively spaced 80 mm from both
`sides of the sheet. The heated sheet was subjected to
`vacuum forming with a draw ratio of 1.3, thereby fabri
`cating a box-shaped glass case cushioning member mea
`suring 260 mm (depth)X200 mmX200 mm. The vac
`uum forming was easily carried out. The box-shaped
`cushioning member was free from edge breakage and
`creases.
`
`Control 1
`It was tried to fabricate a box-shaped cushioning
`member of the previously mentioned dimensions of 260
`mm (depth)><200 mm><200 mm by vacuum forming
`with a draw ratio of 1.3 as in Example 1 from a commer
`cially available 4.5 mm thick crosslinked polyethylene
`foam sheet with a foamed density of 0.035 g/cm3, which
`had been produced from the polyethylene of a density
`of 0.915 g/cm3, a melt index of 1.0 and an absorptivity
`coefficient K'770 Cm-l of 0. It was also tried to produce
`by vacuum forming with a draw ratio of 1.3 as in Exam
`ple l, a similar box-shaped cushioning'member having
`the same dimensions as described above from a com
`mercially available 4.5 mm thick crosslinked polypro
`pylene foam sheet with a foamed density of 0.034 g/cc,
`which had been produced from the polypropylene of a
`random copolymer containing 2.0% by weight of ethyl
`ene, and having a melt index of 10, melting point of 150°
`C. and a crystallinity of 90%. In both cases, however,
`the box-shaped cushioning member was broken at the
`edge, failing to provide a cushioning box of prescribed
`dimensions.
`
`35
`
`EXAMPLE 2
`As in Example 1, 50% by weight of medium density
`polyethylene was mixed with ‘50% by weight of a pro
`pylene-ethylene random copolymer (containing 4% by
`weight of ethylene and having a melt index of 9.0, melt~
`40
`ing point of 143° C. and a crystallinity of 78%. The
`mixture was further blended with the same blowing
`agent, crosslinking agent and phenolic compound deriv
`ative as used in Example 1 and was foamed as in Exam
`ple 1. The resultant crosslinked foam (having a closed
`cell structure and a density of 0.028 g/cc) indicated a
`tensile strength (kg/cm2) and elongation (%) given in
`Table 1 below.
`
`45
`
`Controls 2 to 4
`For comparison with Example 2, determination was
`made of the tensile strength (kg/cm2) and elongation
`(%) of a commercially available crosslinked polyethyl
`ene foam (Control 2), commercially available cross
`linked polypropylene foam (Control 3), and non-cross
`linked polyethylene foam (Control 4), the results being
`also set forth in Table 1 below.
`'
`
`TABLE 1
`Tensile strength and elongation
`of polyole?n foams
`
`Density
`(g/cc)
`0.028
`0.035
`
`Tensile
`strength
`(kg/cm2)
`6.5
`5.5
`
`Elonga
`tion
`(%)
`310
`110
`
`Kind of foam
`Example 2 Crosslinked foam
`Control 2 Crosslinked
`polyethylene foam
`(M.I. = 1.0;
`K'77o cm-l = ;
`density
`
`50
`
`55
`
`60
`
`65
`
`Density
`(g/ cc)
`
`Elonga
`Tensile
`tion
`strength
`(kg/m2) (%)
`
`0.034
`
`6.9
`
`80
`
`Control 3
`
`Kind of foam
`= 0.914 g/cm3)
`Crosslinked
`polypropylene foam
`(M.I. = 10;
`ethylene content
`
`Control 4
`
`= 4.0%.
`
`_
`
`random copolymer;
`melting point
`= 141° C.
`crystallinity
`= 69%)
`Noncrosslinked
`polyethylene foam
`(M.I. = 0.7;
`K'770 cm-l = ;
`density
`= 0.918 g/cm3)
`
`0.037
`
`4.2
`
`70
`
`As seen from Table 1 above, a crosslinked foam (Ex
`ample 2) prepared from a composition embodying this
`invention has a far larger elongation than those of Con
`trols 2 to 4. Example 2 was still found to retain heat
`resistant and heat-insulating properties originally pos
`sessed by a polyolefin foam. Therefore, a cross-linked
`foam of Example 2 proved to be extremely useful as a
`heat-resistant and heat-insulating covering material to
`be required for large elongation.
`
`EXAMPLE 3
`Sample mixtures of medium density polyethylene
`(density:0.925 g/cm3; M.I.=4; K'770 cm—1=2.l) and
`propylene-ethylene random copolymer (M.I. =9; ethyl
`ene content=4% by weight; melqing point 141° C.;
`crystallinity=70%) were provided with the propor-'
`tions of the component polymers varied. 100 parts by
`weight of each sample mixture was blended with 15
`parts by weight of azodicarbon amide as a blowing
`agent, 2 parts by weight of trimethylol propane triacryl
`ate as a crosslinking promoter, and 0.3 part by weight of
`pentaerythrityltetrakis
`[3-(3-5-di-t-butyl-4-hydroxy
`phenyl)] propionate (manufactured by Ciba Gigy under
`the trademark “Irganox 1010”). The mixture was ex
`truded into a 2 mm thick sheet, which was subjected to
`crosslinking by irradiating electron beams with an ab
`sorbed dose of 2.0 Mrad. All the crosslinked sample
`sheets were foamed at 230° C., producing several kinds
`of crosslinked foams with closed cells containing differ
`ent amounts of polypropylene. Determination was
`made of the elongation (%) of said sample foams, the
`results being indicated by Curve A in the appended
`drawing. As apparent therefrom, sample crosslinked
`foams prepared from compositions whose propylene
`copolymer content falls outside of the range of 20 to
`75% by weight defined for a composition embodying
`this invention showed a smaller elongation than the
`crosslinked foam of the invention. A crosslinked foam
`prepared from a composition embodying the invention
`whose polyethylene content is particularly de?ned to
`range between 70 to 30% by weight is shown to indi
`cate a prominently large' elongation as over 250%.
`
`Control 5
`
`Electron beams were irradiated with an absorbed
`dose of 2.0 Mrad on a sheet prepared from substantially
`
`Page 6 of 8
`
`

`
`4,421,867
`9
`the same composition as used in Example 3 (except that
`15 phr of azodicarbon amide was omitted). Determina
`tion was made of the elongation of the resultant cross
`linked sheet, the results being indicated by Curve B in
`the accompanying drawing. As apparent from Curve B,
`a composition formed of a mixture of polyethylene and
`propylene copolymer whose proportions are de?ned in
`accordance with the present invention rather indicates a
`small elongation if the composition is simply cross
`linked without being foamed. Conversely where said
`composition is foamed, its elongation is prominently
`increased as seen from Curve A.
`
`EXAMPLES 4 AND 5
`Determination was made of the tensile strenght
`(kg/cmZ), elongation (%) and vacuum formability of
`sample crosslinked foams with closed cells prepared
`from compositions speci?ed in Table 2 below, the re
`sults being given in Table 3 below.
`'20
`
`15
`
`Control 6
`Determination was made of the tensile strength
`(kg/cmz), elongation and vacuum formability of a sam
`ple crosslinked foam prepared from a composition spec
`i?ed in Table 2 below, the results being indicated in
`Table 3 below.
`
`TABLE 2
`Polyethylene
`Polypropylene
`Example 4 55% by weight of
`45% by weight of
`medium density
`propylene-ethylene
`polyethylene
`copolymer
`(M.I. = 4.5;
`(M.I. = 10;
`Density; 0.927;
`Melting point = 138° C.;
`K’77Q em‘1 = 1.8)
`Ethylene content
`= 6% by weight
`Crystallinity = 66%)
`45% by weight of
`propylene homopolymer
`(M.l. = 6;
`Melting point = 164“ C.)
`45% by weight of
`propylene-ethylene
`copolymer
`(M.I. = 7;
`Melting point = 143° C.;
`Ethylene content
`= 4.5% by weight
`Crystallinity : 72%)
`
`Control 6
`
`Same as above
`
`Example 5 55% by weight of
`high density
`polyethylene
`(M.I. = 6;
`Density = 0.950;
`K'770 cm_1 = 0.6)
`
`Tensile
`strength
`(kg/cmz)
`6.3
`6.9
`7.2
`
`TABLE 3
`Elonga-
`Crosslinking
`tion
`degree
`(%)
`(%)
`340
`38
`85
`60
`200
`48
`
`Vacuum
`formability
`Good
`Bad
`Good
`
`Example 4
`Control 6
`Example 5
`
`25
`
`30
`
`40
`
`45
`
`50
`
`Note:
`The crosslinking degree denotes a gel content. The
`vacuum formability was determined by a test for vac
`60
`uum formability with the draw ratio set at 1.0.
`As seen from Table 3 above, sample crosslinked
`foams of Example 4 and 5 prepared from compositions
`consisting of polyethylene of medium and high densities
`and propylene-ethylene copolymer have far larger elon
`gations than a sample crosslinked foam of Control 6
`prepared from a composition consisting of medium
`density polyethylene and propylene homopolymer.
`
`65
`
`10
`EXAMPLE 6
`Controls 7 and 8
`Sample sheets each having a thickness of 1 mm were
`prepared from compositions shown in Table 4 below in
`the same manner as in Example 1. The sample sheets
`were foamed while being carried on a 20-mesh stainless
`steel net endless belt traveling at a speed of 2 meters/
`min through a foaming furnace through which air
`streams heated to 230° C. were circulated, providing
`closed cell foams shown in Table 5 below.
`TABLE 4
`Control 7
`
`Example 5
`
`Control 8
`
`100 parts
`by weight
`of resin
`
`the same resin
`mixture as in
`Example 2
`
`15 parts
`by weight
`of blowing
`agent
`Cross-
`linking
`promoter
`
`Absorbed
`dose
`
`Azodicarbon
`amide
`
`1.8 parts by
`weight of
`trimethylol
`propane
`triacrylate
`2.0 Mrad
`
`the same
`propylene-ethylene
`random copolymer
`as in Example 2
`Same as left
`
`Same as left
`
`Same as left
`
`Same as left
`
`4.0 parts by
`weight of
`divinyl
`benzene
`
`2.0 Mrad
`
`8.0 Mrad
`
`Density (g/cm3)
`Gel content (%)
`Elongation (%)
`Surface
`condition
`
`35
`
`TABLE 5
`Example 5
`Control 7
`0.032
`0.040
`35
`55
`350
`160
`Very
`Noticeably
`smooth
`marked with
`a wire net
`pattern
`
`Control 8
`0.038
`62
`120
`Same as
`left
`
`Table 5 above shows that a crosslinked foam embody
`ing this invention is prominently impr