Note: Descriptions are shown in the official language in which they were submitted.
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~ETHOD QF P~QDUCING
PEN~-CELL FO~ED ARTICLE~ OF CROSS-LXNKED pOLYOLEFINS
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'i E~CK~ROUND OF THE INVENTION
Il . ,
¦ (1) Field of the InYention.
ll This invention relates to a method for the production
¦~of open-cell foamed articles of cross-linked polyolefins.
5 ¦1 (2) Description of the Prior Art:
ll Among the methods heretofore suggested for the manu-
jifacture of cellular articles of cross-linked polyolefins,
l~particularly of polyethylene, the methods which use the organic
¦I`decomposition type blowing agents are generally known in the art.
10 ¦IThese methods, as dlsclosed in Japanese Patent Publication
¦!NOS. 8840/1965, 18832/1967 and 22674/1968, generally comprise
j~the steps of first cross-linking polyethylene by means of an
!iorganic peroxide or by exposure to electron beams and thereafter
~ decomposing the blowing agent thereby imparting a cellular
structure to the cross-linked polyethylene.~ In addition, there
have been known a method in which a foamable and cross-linkable
composition containing a polyolefin,~a blowing agent and a cross-
linking agent is heated in a closed mold under increased pressure
and thereafter the pressure applied to the composition in the
mold is released resulting in the foamed cross-linked polyethylene,
and also so-called "two-step" method, as disclosed in Japanese
Patent Publication No. 29381/1970, in which the foamable and
cross~linkable polyolefin compos~ti~on ~is heated in the s~e manner
~as aboye tQ paxtlai~ly decQmpose the blowin~ agent and thereafter
further heated under atmospheric pressure to deco~pose the
~remainl~ng blowing agent. In the latter two methods, since the
decomposition of bl~ing agent and cross-linking agent is effected'
¦ by heating t~e compos~tion in the closed mold under pressure, the
cross-linking react~on of pol~ethylene takes place but the
foam~ng is suppressed, and the expansion of polyethylene
lloccurs only after the release of applied pressure. Therefore,
10 i the latter methods are same as the former methods in principle
that polyethylene is first cross-linked and thereafter expanded.
The foamed products of cross-linked polyolefins obtained
by the above mentioned methods have a closed cell structure. By
I these methods, it will be difficult to obtain a foamed product
15 1l having an open cell structure. This is because, unlike the
~reactive foaming such as is involved in the production of poly-
urethane foam, the foaming of cross-linked polyolefin according
Ito the prior methods produces closed cells, and the membranes
¦¦enclosing these cells are so tough that, even under application
¦of compressive force, they will not be ruptured to transform such
¦closed cells into open cells and, even if the membranes are
¦forcibly ruptured somehow or other, the ruptured cell membranes
~will not be retained as they are. Owing to the melt elasticity
¦possessed commonly by polyolefins, such ruptured cell membranes
cannot be reta~ned as they are, ~ithout reference to the particular
type of blow~n~ agent and the presence or absence of cross-linking
reaction. With the escape of the expanding gas r there ensues
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the .~heno~enon of..contxactl~on o,f.cell me~bxanes~ F occuX~ence of
!lempty caYitie$. Thi:s ~henomen~n becomes more.conspicuous with
¦ the increasi~ng expans;~.on degree of polyolefin ~oam.
¦~ In the aboYe circums;tances! the ~reater part of the
5 ¦ii commercially a~ilable open-cell foamed articles is polyurethane
,,.foam. However, pol~olefins exhibit excellent weathering resis-
¦Itance as compared with the soft urethane resin typifying those
resins which are capable of producing open-cell foamed articles
land also have very good resistance to chemicals and to water.
¦Thus, debut of an open-cell foamed article made from this resin
~has long been awaited.
So far, a few methods aimed at the production of open- ¦
cell foamed articles of polyolefins have been proposed, for
ijinstance the method which comprises blending polyolefin with a
15 ll water-soluble powder such as starch and thereafter dissolving out ¦
¦the water-soluble powder from the mixture, and the sintering
method in which the polyolefin powd.er is sintered. By these
methods however, there are barely obtained cellular products of
very low expansion ratio of the order of about 2 to 3 times the
original volume.
Recently, there have been proposed methods which effect
rupture of the membranes of closed cells of a foamed cross-linked
. ¦polyethylene by the action of compressi~e force. One of these
methods is disclosed in Japanese Patent Publication No. 10350/1974.
This method comprises cooling the foamed article of a thermoplastic
resin having closed cells to a temperature below the second~order
transition temperature (brittle temperature) of the thermoplastic
11 7V416
~resin and ~oll ~xessin~ th~ cooled ,f,o,a,m,ed 7axt~cle the~eby
~,producing a cellul~r arti,cle ,h,a,Yin~ open cells. ThIS ~ethod 1,
~,accom~lishes the trans-~o~m~tion of closed cells to open cells by l~
I~sacri~icing the strength o~ t~e thexmoplastic resin itself to 1,
5 i,some extent. Another of the methods is disclosed in Japanese
, Patent Application la~d open to public inspection No. 63172/1979.
¦,This method cc,mprises producin~ a foamed article of polyethylene
¦Icontaining an inorganic filler and subjecting the formed article
! to compressive force there~y rupturing the membrances of closed
10 llicells and trans~orming the cells into open cells~ This method
'attains the transformation of closed cells into open cells by
adding to the resin a large amount of the inorganic filler enough
.
to lower the strength of the resin.
,, The former method, however, has a disadvantage that a
15 ¦I~very long time is required t~ cool the foamed article having
¦lextremely low thermal conductivity to a temperature below the
'brittle temperature (-100C) of the resin and the method, when
desired to be carried through in a short period of time, is
',applicable only to foamed sheets of very small thickness.
~ The latter method also has a disadvantage that the
method itself is hardly practicaL~,le and, if it is materialized by
special technical efforts, the addition of the large amount of
inorganic filler inevitably decreases the degree of expansion
and increases the bulk density.
In any event, successful transformation of closed cells
of a foamed cross-linked polyolefin to open cells on a commercial
scale remains yet to be accomplished. This is because the poly-
ethylene resin, etc. used as the raw material of the foamed
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cross-linked polyolefin are so tough, b~ nature, that
the membranes of closed cells in the foamed article will
not be ruptured under application of compressive force
and, even if the compressive force is great enough to
rupture such membranes, the compressive force is transmitted
only in the surface region of the foamed article. The
compressive force transmitted to the deep portion of the
; foamed article is no longer great enough to rupture the
membranes in that portion. Thus, the desired transformation
of closed cells into open cells has not been accomplished
to date.
SUMMARY OF T~IE INVENTION
An object of an aspect of this invention, therefore,
is to provide a method for easily producing an open-cell
foamed article of cross-linked polyolefin merely by imparting
mechanical deformation to the foamed article without requir-
ing any other special treatment or the addition of a filler.
An object of an aspect of this invention is
to provide a method for the production of an open-cell
foamed article of cross-linked polyolefin of a great thickness
with a high degree of expansion.
An object of an aspect of this-invention is
to provide open-cell foamed articles of cross-linked poly
olefin possessing highly advantageous properties and having
desired thicknesses with a high degree of expansion.
- To accomplish the objects described above and other
objects, according to the present invention, there is provided
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a method for the production of open-cell foamed
articles of cross-linked polyolefins comprising the
; steps of:
. blending with heating a polyolefin, a chemical
blowing agent and a cross-linking agent to obtain a
foamable and cross-linkable composition,
:- forming the foamable and cross-linkable
composition into a desired shape under pressure and at
a temperature of from 115 to 155C and which is lower
than the foaming temperature of said composition while
maintaining its gel percent at zero,
heating the shaped composition at a suitable
foaming temperature under atmospheric pressure in such
conditions that the peak of the ratio of the degree of
cross-linking to the degree of decomposition of the
blowing agent is not more than 20 to decompose the
cross-linking agent and the blowing agent concurrently,
thereby giving rise to a foamed product of cross-linked
polyolefin havi.ng cells enclosed with very thin
2~ membranes capable of being easily ruptured by the
action of mechanical force, and ~`
mechanically deforming said foamed product to
cause the membranes of the cells to rupture;
wherein the gel percent is the ratio of the
foamable and cross-linkable composition after
extraction to that before extraction, the extraction
.being carried out under reflux of trichloroethylene for
24 hours by means of a soxhlet extractor using a glass
filter of from 45 to 50~ ; the degree of cross-lin~ing
is the gel percent of the composition at a given
heating time and the degree of decomposition of the
blowing agent is the ratio of the degree of expansion
at said given heating time to the final degree of
expansion of the foamed composition.
BRIEF DESCRIPTION OF T~E DRAWING
'' The single figure is a graph showing the change of
the ratio of the degree of cross-linking to the degree
of decomposition of the blowing agent along the course
of heating time at a suitable foaming temperature.
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DETAILED DESCRIPTION OF THE INVENTION
The method for the production of an open-cell
foamed article of cross-linked polyolefin in accordance
.; with the present invention consists primarily in
utilizing the adjustment of the
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decompositiQn Xate o~ the blow~ing a~ent relatiYe to the xate of
cxoss~link~n~ ~e~c~i~on, I
~n thè theory ~ the ~Qa~ing o~ cross-linked polyolefin,
' the so-called "preceding cross-linkin~ ~ ~ollowing foaming", as
5 ~ ~entioned a~ove, is common sense to those skilled in the art.
'In other words, ~ere has heen considere~ that the expanding gas
¦~is leaked out from the resin at the time of expansion, unless
the yiscosity of xesln is increased by ~irtue of its cross-linking.l
l However, it has been found that the dilation of precedently cross-¦
10 Ililinked resin is poor and thus it is hardly possible to produce a
foamed product having cells enclosed with very thin membranes
`suitable for obtaining an open-cell foamed article. Now it has
been found, according to the present invention, that it is
l possible to produce said foamed product by concurrently effecting ¦
15 ~the cross-linking reaction and the foaming of the foamable and
~¦cross-linkable composition being maintained at the state where its
,gel percent is zero.
1 Now, the meaning of the expression "concurrent decom-
¦lposition of cross-linking agent and blowing agent" will be
lexplained.
When the foamable and cross-linkable composition is
heated under atmospheric pressure, the cross-linking reaction
and the decomposition of blowing agent take place, and the cross-
linking curve and the dec~mposition curve of blowing agent are
respectiyely obtained. Now then, when the foamable and cross-
linkable composition of which ~el percent is maintained at zero
is heated ulder atmospheric pressure and th~ ratio (y) oE the
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,deg,ree of, c,rjos,s,~linki~ng,to, the de~.ee o,f, decomposition o,f, the
blow,~n~ a~ent agai~nst.the ~eatin~ time is plotted on.lo~axi.thmic
~graph paper! the.re can ~e o~tained the curye as shown in the
~iacc.ompanyin~ dra~ing. Howevex, in case:the ~oamable composition
5 I cro~s-linked in adyance as. in the prior methods is heated under
~,atmospheric pressure, the similar curve ~ay not be obtained.
¦, ... Degr.ee of. cross--l.inkin~
Y - .
, Degree of decomposition of blowing agent
i Degree of cross-linking: Gel percent o~ resin at a certain
10 ll heating time
Degree of decomposition of blowing agent: Ratio of the
, degree of expansion at the same
,~ heating time as above to the final
lll degree of expansion of the foamed
15 il product obtained.
Ii Where, the term "gel percent" means the ratio of the
.weight of the sample after extraction to that before extraction,
¦~wherein the extraction is carried out under reflux of trichloro- "
lethylene used as a solvent during 24 hours by means of a soxhlet
¦extractor using a glass filter of from 40 to 50~ . The gel percent .
¦is calculated by the following equation. The degree of cross-
linking is proportional to the increase of gel percent.
. W, 1 ' { ~ ~1 ~ X, ) +, ,, ,~ } ,~o , , ,
Gel ,percent ~ - x 100
W _ { AT (l = x) + 0~7 T~X ~,.T ~
Where~
WO: Weight of the sample before extraction,
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: r~l; Wei.~ht o~. the s~$a~1e af.ter. extr.action,
' T; Total weIght pa~ts of.the.co~ponents~,
A: ~.e ght parts o~.the blowin~ ~yent,:.
Il C: ~ei~ht parts o$ the ~illers,
5 'I x: Decomposition.degree of the blowing agent,
, AT (l-x)Wo^ Weight of the remaining blowing agent in
the sample,
I' ,.. .
-7 - ~T x WO:: Weight of the residue of decomposed blowing
, agent in the sample, and
10 " T WO: Weight of the fillers in the sample.
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In the figure, the peak A of the curve indicates the
. ratio (y) of the degree of cross-linking to the degree of
, decomposition of the blowing agent at which the decomposition of
¦Iblowing agent most lags behind the cross-linking of resin compound
15 1i That is to say, at the heating time of this point A the distance
~ibetween the cross-linking cur~e and the decomposition curve of
! blowing agent is most wide. The greater value of this ratio (y) j
at the peak means that the foaming is more delayed to the cross- ¦
linking accordingly. On the other hand, the smaller value of
20 said peak ratio means that the delay of the foaming to the cross-
linking is little, that is to say, the cross-linking reaction
and the foaming phenomenon of the foamable and cross-linkable
. lcomposition concurrently took place.
Surprisingl~ it has now been disco~ered that there is
a limit of peak in said ratio (y) for obtaining a foamed product
having ~el membranes capable of being easily r~ptured by the
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action o~ ~echanical.~o~.ce, The.peak yalue o~ said r.atio (y)
is ~n~luenced h.~ the ty~e ~ xe~ins.u~ed and.the ~ounts of the
c~os;s-.link~ny agent or the ~lowin~ agent. HoweYer ! in spite of
' thes~e paXametexs, it has been ~ound that in case said peak ratio
5 ', is not more than 20, there can be obtained a ~oamed product
1. haying cell mem~ranes suita~le for manu~acturing the open-cell
¦ foamed art~cle. Sa;d Yalue "20" of the peak ratio is critical,
¦~ but it is preferable to control said peak ratio in the range of
jl not more than 15, ~ecause in case o~ the particular type of
lO i resins the rigidity is required for the reaction conditions, etc.
at the value close to 20.
Therefore, the expression"concurrent décomposition of
..cross-linking agent and blowing agent" as used herein means that
Il the decomposition of cross-linking agent and blowing agent is
1 effected in such consitions that the peak of the ratio (y) is not
more than 20. It will be a good practice to subject various
polyolefins to a preliminary foaming to determine the range of the,
¦¦amounts of cross-linking agent, blowing agent, foaming aid, if
¦Irequired, and their optimum foaming temperatures which satisfy
said conditions. In the actual operations, one can select the
amounts of each components within the range thus determined.
To describe the present invention more specifically,
a given polyolefin is mixed with a blowing agent, a cross-linking
lagent and, if required, a foaming aid, a filler and a pigment,
¦and the resultant mixture is kneaded with a mixing roll heated
or the like, Then, the obtained composition is placed in the
mold ha~ing a desired cavity profile and, under the pressure
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~pplied w~ th.a p~ess.! the~ally sha~ed.~t a t~mFeX~atu~e within
. the ~an~e of ~xom 115C .to 155C! pxefe~ably fxo~ 12QC.to 140C,
. and therea~ter removed ~xqm-the mold. In place of said shaping
,, at an eleyated temperature and under pressure,: the:composition
5 j after knea`d~n~ may be sIlaped by heating it in the mold to which
. the pressure is not applied or by directly passing it through. I
an ext~uder or a calendering roll. HoweYer, since the heating in ¦
~I this shaping step rise the foama~le and cross-linkable composition
¦I to the thermally excited state and, as a result, contributes to
10 .~ the more smooth concurrent decomposition of the cross-linking
.agent and the blowing agent in the following foaming and cross-
;linking step, it is preferable to carry out the shaping of the
. composition under the heating. For instance, in case the shaplng
`,is carried out without heating and without applying a pressure, I
15 I~the cells of the foamed product obtained in the following foaming ¦
l~and cross-linking step are coarse and un-uniform, which is some-
what undesirable. In this thermal shaping it is significant that ,
the foamable and cross-linkable composition should be shaped -i
llmaintaining its gel percent at zero, namely at the predetermined
20 ¦¦ heating time and temperature whereby the cross-linking of
¦polyolefin will not occur. Therefore, the shaping temperature
is required to be lower, preferably by more than 20C,than the
jfoaming temperature in the following foaming and cross-linking
Istep. If the cross-linking of polyolefin occurs in this thermal
shaping step, as being apparent from the comparative examples
described here~nafter, there will be obtained a final product
having an open cell ratio of less than 50~ which cannot possibly
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se~ s to he the open cell foamed pxoduct. In addition! if said
shapin~ ~s ca~ied QUt at an eleyated tempe~atuXe and under
pressure, as bein~ apparent ~rom Examples 11 to 15 described
~I hereinafter! t~e cell s-ize of the obtained foamed product becomes I
I more fine as the heatin~ time increases. Therefore, it is possible
to delicatel~ vary the ap~eaxance and the tactile impression of
I, the final foamed article with ~arying heating time. By the way,
,l in this thermal shaping step a ~ery few amounts of blowing agent
~I may be pre-decomposed, and as a result the shaped composition
10 iimay expand to the degree of about 2 times larger than the original
il Yolume ~hen removed from a mold. However, this phenomenon is
' not within the concept of the foaming and/acceptable to the
present invention. There can be considered that the above-
, mentioned difference in cell size is due to the fact that the
i nuclei for cells may be formed by this pre-decomposition of
' blowing agent.
The foamable and cross linkable composition shaped as
¦ above is then heated under atmospheric pressure thereby con-
l¦currently decomposing the blowing agent and cross-linking agent.
¦ The meaning of the expression "concurrent decomposing of blowing
¦agent and cross-linking agent" and the condltions thexefore has
¦ already been explained. In this foaming and cross-linking step
I the shaped composition is heated in an atmosphere of nitrogen or
in a heating medium, for instance metal bath containing Rose's
metal, ~ood~s metal or the like, oil bath, molten salt bath
containing one or more of the salt such as sodium nitrate,
potassium nitrate, potassium nitrite or the like. The shaped
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composltion ls ~re~e~ablx placed ~in an openable ~old o~ ~etal
hox wfi~ch is not a~rti~g~t and ~eated in said heatin~ ~edium kept
at a su~ta~le foam~ng temperatuxe~ ~therwise, t~e openable mold
'1 or metal box Whic~ IS not airtI~ht may ~e provided with a heater
5 ,l on the s~rface o~ its ~etal plate or with a jacket through which
a heating medium such as steam, heating oil, etc. is circulated.
I By the use of th~s openable mold~ the foamable composition is
I indirectly heated ~y the heater or heating medium. Besldes, the
~i shaped composition may be coYered with a metal sheet, etc. capable
10 ,, of moying up and down and heated in such a state. After the
heating for a predetermined period, the composition is cooled to
obtain a cooled and foamed product. The foaming temperature is
selected within the range of from 145C to 210C, preferably
1, from 160C to 190C, to suit the particular type of polyolefin
15 ¦1 actually used, and the heating time is within the period of from
j 10 to 90 minutes, preferably from 15 to 40 minutes. Thus, there
Il can be obtained a foamed article having closed cells which
¦~i membranes are able to be easily ruptured by exerting a mechanical
¦I deformation and the degree of cross-linking similar to that of
¦ the foamed product produced by the prior methods (up to about
¦ 95% of gel percent).
In accordance with the present invention, the heating
in said foaming and cross-linking step may be carried ou-t in two
steps. In this two-step process, the conditions for foaming and
cross-~linkin~ polyolefin is mild~ and thus the decompositions of
cross--l~nking agent and blowing agent can be accomplished more
concurrently in two steps. By this two-step process, the
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hete~ogeneous heat cond~cti~on in the dixectiQn o~ thickness of
the ~oama~le and c~os~-l;nkable composition may he eliminated
and the composition may~e'homo~eneously~ heated. As a result,
there ~ill not arise'the phenomena such as the su~face cracking
5 ', resultin~ from the partial uneYenneSS of ~oamin~ in the composi-
l~l tion, the collapse and the escaping of gas. Furthermore, it is
¦~ possible to ~ncrease'the expansion ratio of the foamed article
1' obtained up to about 70 times the original volume at will and
,i the thickness up to about 15~mm. Therefore, this two-step process!
`~ 10 1' is particularly su~table for producing thickex foamed articles or
the foamed articles having higher expansion ratios more than
20 times the original ~olume.
To describe this two-step foaming and cross-linking
.; ~ I
process more specifically, in the first step the foamable and
15 li cross-linkable composition shaped as mentioned above is heated
' in the same manner as mentioned hereinbefore, i.e. in the
~ atmosphere of nitrogen or in the metal bath, molten salt bath, I
¦~ etc. at a temperature of from 145C to 180C for a period of from ¦
1, 5 to 60 minutes, preferably from 10 to 45 minutes, and thereafter
20 ¦i the intermediate product is removed from the heating medium.
In the second step, the intermediate product is further heated
in the same manner as mentioned hereinbefore at a temperature of
from 170C to 210C for a period of from 5 to 50 minutes,
l preferably from 15 to 40 minutes, and subsequently cooled to
giye rise to a foamed art1cle with low density. In said first
step, it is preferable to decompose from 5 to 70% of blowing
agent, whereat the gel percent of resin composition is reached
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to fxom ahout 20. to ~b.o;ut 8Q~ ..th.e de~xee of, decomposition
of the blowin~ a~ent ~nd the ~el per:cent are ~exy hl~h, the
aforement~Qned advantages of th~s two-step process will not be
I deriYed.
5 , The ~oamed article obtained as aboYe is compressed by
being passed between two rolls rotated at an equal speed, with
the result that t~e compression so applied will rupture the
membranes o~ closed cells ~f the ~oamed article and consequently
Iconvert the closed cell structure to th.e open cell structure.
10 ill The open-cell foamed article obtained by the method of
.this invention possessed outstanding properties fa~orably
comparable with the properties of the foamed article of poly-
urethane, and the open cell ratio thereof determined in the
similar manner to Remington Pariser Method (ASTM D 1940-62T) is
jequal or nearly equal to 100%.
The polyolefins which are preferably used in this
linvention are low-density polyethylene, medium-density poly-
.l~ethylene, high-density polyethylene, poly-1,2-butadiene, ethylene-
Ilpropylene copolymer, ethylene-butene copolymer, ethylene-Yinyl
20 ¦1 acetate copolymer, copolymers of ethylene with up to 45~of
l¦methyl-, ethyl-, propyl- or buthyl-acrylate or methacrylate, I
¦,chlorinated products of the above homopolymers or copolymers whichj
¦chlorine content being up to 60% by weight, mixtures of two or more
lof the above polymers and mixtures of the above polymers with
isotactic or atactic polypropylene.
To suit the purpose of.this invention,. the cross-linking
.. agent ought to decompose in polyolefin at a temperature at least
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higher than the flow point of polyolefin. Organic peroxides
which decompose upon being heated to liberate free radicals
capable of giving rise to intermolecular or intramolecular
cross-linked bonds and, therefore, serve advantageously as
S radical generators meet this requirement. Examples of such
organic peroxides include~ but are not limited to: dicumyl
peroxide, l,l-ditertiary-butyl-peroxy-3,3,5-trimethyl cyclo-
hexane, 2~5-dimethyl-2,5-ditertiary-butyl peroxyhexane,
2,5-dimethyl-2,5-ditertiary-butyl p~roxyhexane, ~ , ~
10 -ditertiary-butyl peroxydiisopropyl benzene, tertiary-butyl
peroxy ketone, tertiary-butyl peroxy benzoate, etc. The
organic peroxide which best suits the particular type of
poleolefin used should be selected.
The blowing agents which are usable in this inven-
tion are chemical blowing agents having the decomposition
temperature higher than the melting point of poleolefin.
Examples of such chemical blowing agents include, but are
not limited to: azo type compounds such as azodicarbona-
mide and barium azodicarboxylate; nitroso type compounds
such as dinitrosopentamethylene tetramine and trinitroso-
trimethyl triamine; hydrazine type compounds such as p,p'-
oxybis ~benzene sulfonyl hydrazide); sulfonyl semicarbazide
type compounds such as p,p'-oxybis (benzene sulfonyl semi-
carbazide3 and toluenesulfonyl semicarbazide, etc.
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Besides the particular type of polyelefin used
and the foaming temperature selected, the amounts of
the cross-linking agent and the blowing agent are the
significant factor exerting influence on the ratio Iy~
5 of the degree of cross-linking to the degree of decom-
position of the blowing agent. If the amount of
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cxQ~ nkin~ ;a~ent ~s~ tqo much o~ the amount of blowin~ a~ent
is ve~y l~ttler the ~eak o~ s~aid X~tio ~ will e~sily exceed 20
and~ as a natural consequence, ~t is hardl~ possible to p~oduce
' an open-cell ~oamed article. There~re~ the amounts of the cross-
5 , linking agent and the blow-in~ agent should be selected within the
range in which the peak of sa;d ratio (y) will no exceed 20.
Besides the above factors, it is possible to control the
peak of ratio (y) by adding a ~oaming aid (See Example 1 and
IlComparative Example 1 described hereinafter). Thus, in the
present invention, a foaming aid may be used depending on the
! particular type of blowing agent to be used. Examples of such
aids include, but are not limited to: compounds having urea as a
principal component; metal oxides such as zinc oxide and lead
oxide; compounds having salicylic acid, stearic acid, etc~ as a
15 ,,principal component, i.e. higher fatty acids, metal compounds of
~higher fatty acids, etc.
i i
In the present invention, to effect the improvement
~lof the properties of composition prepared and the reduction of
¦Icost, if desired, there may be added into the composition the
20 ¦~compounding additives or fillers which do not exert very harmful
¦influence on the cross-linkage of polyo-lefi~, for example metal
¦oxidessucllascarbon black, zinc oxide, titanium oxide, calcium
oxide, magnesium oxide and silicon dioxide; carbonates such as
magnesium car~onate and calcium carbonate; fibrous filler material
such as pulp; various dyes; pigments; fluorescent materials; and
rubber compounding ingredients commonly used.
UDlike the co~ven~ional technique w~hi-h ~,,~
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~7~4~
Il i
,iohtain xe~uixed ~educti~on o~ the st~en~th of the XeSin as b~
, cooli~n~ the closed-cell ~oame~ R~qduct to ~ tempexatu~e below the
,Ibrittle tempe~ature of the resin o~ addin~ lar~e amounts of
inorganic ~lllers to the foaming composition, the method of this
5 ' invention utilizes the adjustment of the decomposition rate of
the blow~ng agent relatiYe to the rate of cross-linking of the
. i
resin. Conse~uently, this inYent~on enables open-cell foamed
~articles of cross-linked polyolefins to be easily obtained
llwithout impairing the advantageous properties of polyolefins.
10 ,~In addition, the final foamed articles can be obtained by this
, inyention with high open-cell ratios falling within the range of
from 97 to 100~ and in large thickness. The method of this
` invention has further advantages of easy operation, short working ~,
, time and high productivity.
15 iI The open-cell foamed articles of cross-linked polyolefins
obtained by the method of this invention can be suitably used for
,cushioning media, filters, heat insulating materials, coaters, etc.
,Particularly, ~hen said foamed articles are used in clothes, noise
,abating materials and heat insulating materials so far produced
~0 ¦by using soft polyurethane foams, they exhibit outstanding
¦resistance to weathering and chemicals and high flame retardance
Iland, therefore, warrant safe use. I
¦l For more specific illustration of the present invention,l
l the following examples are presented which are intended to be
merely illustrative of and not in any sense limitative of the
inyention.
- 18 -
~. . -I
. , . : . ,
1~L7~L6
.,
I . .
Exam~le l; ,
' A compos~ti,on con,~i,stin~ o,f, ethylene-yinyl acetate
I copolymer ~proprietary product of Mitsui Polychemical co. ! Ltd.,
marketed under trade name o~ "EYerflex P-14Q3"~ YAC 14% by
5 i`weight), 17 parts ~y~ weight per hundred parts by weight of resin
,'(phr~ of azodicarbonamide Cproprietar~ product of Eiwa Chemical
~,Industry Co., Ltd., marketed under trade name of "Vinyhol , f
AC#50s~ 0.83 phr o~ dicum~l peroxide and 0.5 phr of zinc oxide
`'was kneaded in a mixing roll at 85C. the resultant blend was
10 I,charged in a mold (150 X 150 X 7mm) within a press kept at 126C
and heated under increased pressure for 30 minutes to form a
foamable and cross-linkable sheet. The gel percent of this sheet
Iwas zero. The sheet obtained was then heated for 40 minutes in a
llmetal bath kept at 170C to obtain an intermediary foamed product
15 l in which 30.5% of the blowing agent was decomposed. Thereafter,
the intermediary foamed product was further heated in a metal bath
¦kept at 190C for 20 minutes to obtain a foamed product in which
~he remaining blowing agent was completely decomposed. The peak
¦value of the ratio(y) in said foaming and cross-linking step was
20 ¦10.4. After the cooling, the foamed product was passed between
two rolls separated by a space of 3mm and rotated at an equal
speed to rupture the cell membranes. The foamed article obtained
had a thickness of 23~0mm, a bulk density of 0.03g/cm3 and an open
: ¦cell ratio of 100%.
25Wherein, the open cell ratio was measured in a similar
manner to ~em~ngton Par~ser-method ~ASTM D 1940-62T) and
I ^~ ;rrc7Jcs ~rrks
.
, 3 ~7~94~6
~,
i l
i.
~deter~ined bx the ~Qllo~in~ c~lculation ~ox~ula.
.. '(V.s'~ ~). ~ (~' ~ Y~
j Open cell r~tio ~ 100
~$ ~ ~R
~ ~s = ~Y X lQQ
~s ~ ~R
~here,
i~ !
Vs: Yolume of sample,
, VR: Volume of resin ~atrix (= weight of sampls Ws/
~ density of resin)/ and
10 ~ aV: Increase in Yolume.
Examples 2 - 4:
The procedure oE Example 1 was repeated using the
varying amounts of zinc oxide and dLcumyl peroxide shown in Table
~ l. In each Example the complete open-cell foamed article havingi
'the open cell ratio of 100% was obtained. The degree of decompo-
sition of the blowing agent in the intermediary foamed product
~¦w~as respectively 51.7% in Example 2, 69.0% in Example 3 and 11
¦lin Example 4, and the peak value of the ratio (y) was 5.0 in
¦Example 2, 1.27 in Example 3 and 4.0 in Example 4.
20 ~I Comparative Example 1:
l'he procedure of Example 1 was repeated without using
zinc oxide. The peak Yalue of the ratio (y) in the ~oaming and
cross-linkin~ step was 20.5. The foamed article obtained had
an open cell ratio of 55.3~, which exhibits that the rupture of
, , . -, , ~ ,
~ ,,
~7(~416
i. ,
.
cell ;me~h~ane~ waS e~ected only pa~ti~all~.
, i , . .
EXample 5s
A foamed art~cle ~as producea ~x~m a composition
consisting of ethylene-~inyl acetate copolymer (pxoprietary
'product of ~itsubishi Petrochemical Co., Ltd. marketed under
tradename of "Yukalon EVA-41H~ AC 16% b~ weight), 17 phr of
~azodicarbonamiae and 0.53 phr of dicumyl peroxlde in the same
manner and under the same conditions as in Example 1. The open
cell ratio of the foamed article o~tained was 100%.
Example 6:
Il A composition consisting of the same resin as used in
'I Example 5, 17phr of azodicarbonamide, 0.08phr`of zinc oxide and
,0.73phr of dicumyl peroxide was kneaded in the same manner as in
iiExample 1. The resultant blend was~rged in a mold (140 X 140 X
15 ~l28mm) within A press kept at 126C and heated under increased
pressure for 30 minutes to form a foamable block. The foamable
¦block obtained was then heated in a metal bath kept at 170C for
40 minutes to obtain an intermediary foamed product in which 27%
lof blowing agent was decomposed. Thereafter, the intermediary
Ifoamed product was placed in an openable mold (370 X 370 X llOmm)
¦which is not air-ti~ht, and heated in a metal bath kept at 190C
for 30 minutes to decompose the remaining blowin~ agent completely.
After the cooling, the ~oamed product was removed from the mold.
The foamed product was passed between two rolls separated I
t~ ~ J~ ~narks
- 21 -
~1L7~
, I
hy a space of lO~m and ~otated at an equal speed to ~uptuxe the
I cell membxanes. The thick open-cell foamed article haying a
thickness of lOQmm! a ~ulk dens-ity of 0.03 g/cm3 and an open cell
ratio of 100% was obtained.
Example 7:
i '
.1 .
A foamable sheet was obtained from a composition
consisting of the same resin as used in Example 1, 17 phr of
azodicarbonamide, 0.2 phr of zinc oxide and 0.63 phr of dicumyl
peroxide in the same ~anner and under the same conditions as
in Examplel. The foamable sheet obtained was heated in a metal
bath kept at 190C for 15 minutes to completely decompose the
blowing agent and cross-linking agent in a single stage, resulting
~ in a foamed product. After the cooling, the foamed product was
!i converted to an open~cell foamed article ha~ing an open-cell ratio~
15 l, of 100~ by passing between two rolls rotated at an equal speed in
¦Ithe same manner as in Example 1.
¦~ Example 8: 1
An open-cell foamed article was produced from a
l¦composition consisting of the same resin as used in Example 5,
20 1!35 phr of azodicarbonamide, 0.53 phr of dicumyl peroxide under
the same conditions as in Example 1. The open-cell foamed article
highly expanded had an open-cell ratio of 100%, a thickness of
30mm and a bulk density of 0.019 g/cm3.
. I
- 22 - I
1~7(~4~6
i
li . .
- ~` Ex~mple 9;
A composi,tLon cons~i~sting of low-density pQlyethylene
,~ (proprietary product o~ Mi,ts,u~i$h~ Petrochemical Co.~ Ltd.
-
~marketed under the tradename of "~ukalon LK-30," density;
0.918 g/cm3, MFR 40), 17 phr of azodicarbonamide and 0.2 phr of ,
~zinc oxide was intimately kneaded in a mixing roll at 100C.
The resultant blend was placed in a mold (150 X lS0 X 7mm) within
a press kept at 136C and heated under increased pressure for
,, i
,,30 minutes to form a foamable sheet. This sheet was cross-linked
and expanded under the same conditions as in Example,l, and
"
thereafter passed between two rolls rotated at an equal speed in
the same manner as in Example 1.~ An open-cell foamed article
having an open-cell ratio of 100% and a thickness of 23mm was thus
,lobtained.
' Example 10:
An open-cell foamed article was produced from a compo-
,1 . i
¦Isition consisting of low density polyethylene (proprietary product,
¦of Mitusbishi Petrochemical Co., Ltd. mark~ted under the tradename
¦¦of "Yukalon HE-30", density; 0.92 g/cm3, MFR 0.5), 17 phr of
20 llazodicarbonamide and 0.13 phr of dicumyl peroxide under the same
jlconditions as in Example 9. The open-cell foamed article had an
¦lopen-cell ratio of 100~ and a thickness of 23mm.
Examplesl1 ~ 15:
-The procedure of Example 1 was repeated using the same
-~ ~a~ m~ks
~17V4~6
:.
., ,
'composition as in Ex~ple 1 ,a,nd the y~xying heatin~ t~me within
a, press ~ l! 5! lQJ 20 ~a,nd 3Q ~i~nutes. Ea,ch ~oamed article had
` an open-cell ratio o~ lQQ%~ and the thickness of shaped article
and ~ts appearance was unchanged regardless of the heating time.
Howeyerr the`cell size was reduced ~ith the increase of heating
'~time.
i
, Comparative Examples 2 and 3:
The foamed articles were produced from the same
composition as used in Example 5, under the same conditions as
in Example 5 except that the heating temperature within a press
was changed to 145C (comparatlve example 2) and 151C (comparative
~' ` example 3) respectively. After the step of compressing, the
,foamed articles were found by test to possess the open-cell ratios
llof 47.2~ and 45.2~ respectively, which exhibit that the rupture
15 ,of cell membranes was obtained partially and the foamed articles
will not function as an open-cell`foamed article. Under the ,
conditions, the gel percents of foamable sheets removed from a
Ilmold within a press were 20.0% at 145C and 31.2~ at 151C
¦Irespectively. I
20 1~ The operating conditions involved in the examples and
comparatives examples cited above and the results respectively
obtained are shown in the following Table 1. And the relation
between the cell size of the final foamed product and the heating
Itime in the shaping step in examples 11 to 15 is shown in
ITable 2.
- ` -
1~7~6
Tahle 1 ~
1 CQ~POS~I~TIQN AND SHAPIN~ CONDI~TION$
`, No. of Composit~on (ph~) Shapiny Gel
1~ -- Conditlons
! examplesi: Foamlng Cross- under of shaped
i and ~lo~ing l~n~Ln~ pressure sheet
1 ccmparatiye Res~n agent (z~nc a~ent Temp. Time (%)
~les* ~ADCA) oxide) (DC~? (c) (min. )
1E~ "P-1403" 17 0.08 0.83126 30 o
'I P-1403 17 0.20 0.83126 30 0
3 P-1403 17 2.50 0.83126 30 0
4 P-1403 17 0 0.33126 30 0
5EV~ "EV~-41H" 17 0 0.53126 30 0
` 6EV~-4IH 17 0.08 0.73126 30 0
7EV~ "P-1403" 17 0.2 0.63126 30 0
8EV~ "EY~-41H" 35 0 0.53126 30 0
9LDPE "LK-30" 35 0.2 0.53136 30 0
10LDPE "HE-30" 35 o ~ 0.13136 30 0
11EV~ "P-1403" 35 0.08 0.83126 1 0
12 P-1403 35 0.08 0.83126 5 0
13 P-1403 35 0.08 0.83126 10 0
14 P-1403 35 0.08 0.83126 20 0
15 P-1403 35 0.08 0.83126 30 0
I
l*EY~ "P-1403" 17 O 0.83126 30 0
2*EV~ "EY~-41H'i 17 0 0.53145 3020.0
3*Ey~-4IH 17 0 0.53- 151 3031.2
~ L7~3~L3L~ ~
,, ~
Table 1 (2)
FOAMING CONDITIONS AND PROPERTIES OF FINAL PRODUCT
j:
of one step Conditions of tw~ Thickness Bulk Open-cell i
e~amples . step foaming of flnal r ~ :
; foam mg Of Lmal ratio
and openrcell open-cell .
. first step .second step foam %
I cGmparatlve T T- foam ( )
examples* (C)P ~in )Temp. Tlme Temp. Time (mm) (g/cm )
- 170 40 lgo20 23 0.030 loo
!
2 - ~ 170 40 lgo20 23 0.030 loo
3 - - 170 40 lgo20 23 0.030 loo
` 4 - - 170 40 19020 23 0.030 loo
- - 170 40 lgo20 23 0Oo30 loo
6 - - 170 40 l9o30 loo 0.030 loo
7 lgo 15 - - ~ 23 0.030 loo
~ 8 - - 170 40 lgo20 30 o.olg loo I -
`' 9 - - 170 40 lgo20 23 0.030 loo
i lo - - 170 40 lgo20 23 0.030 loo
!
- - 170 40 lgo20 23 0.030 loo
2 _ - 170 40 lgo20 23 0.030 loo
3 - - 170 40 190~ 20 23 0.030 loo
4 - - 170 40 lgo20 23 0.030 loo
- - 170 40 l9o20 23 0.030 loo
* - - 170 40 lgo20 23 0.030 55.3
2* - - 170 40 lgo20 20 0.030 47.2
3* - - 170 40 lgo20 20 0.030 45.2
1 - 26- . . .~
. , ' , .
117V4~L~
. '
' Table 2
,, '.
No. of Heating time in
examples shaping step Cell size
,~ (min.) (mm) f
I . ~
ll 1 1.5
12 5 0.9
. 13 10 0.8
. 14 20 0.6
` 15 30 0.6
. ~ .
;l !
i,
I~ f
,
; ~ .
