CA1085549A - Foamable and crosslinkable polyethylene composition, process for its production, and process for producing crosslinked polyethylene foams using said composition - Google Patents
Foamable and crosslinkable polyethylene composition, process for its production, and process for producing crosslinked polyethylene foams using said compositionInfo
- Publication number
- CA1085549A CA1085549A CA248,315A CA248315A CA1085549A CA 1085549 A CA1085549 A CA 1085549A CA 248315 A CA248315 A CA 248315A CA 1085549 A CA1085549 A CA 1085549A
- Authority
- CA
- Canada
- Prior art keywords
- weight
- polyethylene
- parts
- composition
- heat
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J9/00—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof
- C08J9/04—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent
- C08J9/06—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a chemical blowing agent
- C08J9/10—Working-up of macromolecular substances to porous or cellular articles or materials; After-treatment thereof using blowing gases generated by a previously added blowing agent by a chemical blowing agent developing nitrogen, the blowing agent being a compound containing a nitrogen-to-nitrogen bond
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F230/00—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and containing phosphorus, selenium, tellurium or a metal
- C08F230/04—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and containing phosphorus, selenium, tellurium or a metal containing a metal
- C08F230/08—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and containing phosphorus, selenium, tellurium or a metal containing a metal containing silicon
- C08F230/085—Copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and containing phosphorus, selenium, tellurium or a metal containing a metal containing silicon the monomer being a polymerisable silane, e.g. (meth)acryloyloxy trialkoxy silanes or vinyl trialkoxysilanes
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F255/00—Macromolecular compounds obtained by polymerising monomers on to polymers of hydrocarbons as defined in group C08F10/00
- C08F255/02—Macromolecular compounds obtained by polymerising monomers on to polymers of hydrocarbons as defined in group C08F10/00 on to polymers of olefins having two or three carbon atoms
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
- C08J2323/00—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers
- C08J2323/26—Characterised by the use of homopolymers or copolymers of unsaturated aliphatic hydrocarbons having only one carbon-to-carbon double bond; Derivatives of such polymers modified by chemical after-treatment
Abstract
Abstract of the Disclosure Polyethylene foams, and a process for their preparation, wherein a silane-modified polyethylene is melt-kneaded with a higher carboxylic acid zinc salt and a heat-decomposable blowing agent, at a temperature below the decomposition point of the blowing agent. Foaming is effected by heating to above this temperature. Such materials find use in preparing foam articles of large dimensions.
Description
This in~ention relate~ to a foamable and cro-CZ~-linkable polyethylene compo~ition, and more specifically, to a foamable and crosslinkable polyethylene compo~ition, a proce~s for it~ production, and a crosslinked poly-ethylene foam u~ing the above composition.
A number of techniques for preparing cro~linked polyethylene foams from polyethylene have heretofore been sugge~ted. For example, Japanese Patent Publication No.
6?.78/66 disclose~ a proce~Y which compri~es applying ioniz-ing radiation to a sheet prepared from polyethylene con-taining a heat-decompo~able blowing agent, and heating the resulting cro~linked polyethylene sheet at atmospheric pressure to expand it. Furthermore, Japanese Patent Publi-catlon No. 17436/64 sugge~ts a proces~ which compriseJ
mixing polyethylene with an organic peroxide (chemical crosslinking agent) and a blowing agent, heating the mixture to croJJlink it, and foamlng it at atmo~pheric pres~ure.
The ~ugge~ted proce~ses are called "general atmo~-pherlc pressure foaming method", and are utilized commercially for the production of polyethylene foams. In radiation-initiated cro~linking and foaming techniques typified by the procos~ of Japanese Patent Publlcation No. 6278/66 cited above, electron beams are usually the only source of com-I mercially availablo radiation. Since electron beams have 25 a weak penetrating power, their effect doe~ not extend tothe inside of a polyethylene ~heet having a large thickness.
-~ Tho utilization of the radiation-initiated cros~linking - and foaming techniques i~ thorefore limited to ~heets having ~,~ a thickne~ of about 10 mm at mo~t. On the other hand, the .. . . .
~, .. .. . ~
- process of Japanese Patent Publication No. 17436?64 uging chemical crosslinking agents ~uffers from the defect that cro~slinking tend~ to begin at the time of melt-kneading polyethylene containing a chemical crosslinking agent, and this makes it~ sub~equent molding difficult. Further- ~-more, since crosslinking and foaming proceed almo~t simul-taneously in this proce~s, it is difficult to maintain the form of a molded article which is being cro~slinked and foamed. Another defect is that because there is a dif- I
ference in the degree of crosslinking reaction between the surface layer and the inside layer, the resulting foamed article i8 non-uniform with different cell diameter~ between the surface layer and the inside layer. This tendency be-comes greater when it is desired to obtain foamed articles of larger thickness. With the latter method, it i8 also difficult to obtain foamed article having a fine cellular ~tructure.
In an attempt to remedy these defects~ Japanese La1d-Open Patont Publications Nos. 100470~73 and 130460/74 suggest a proce~s which comprises chemically bonding a silane compound containing at lea~t one un~aturated bond to pol~ethylene in the presence of a radical generator to form silyl-modified polyethylene, and heating the silyl-modified polyethylene together with a silanol condensation catalyst and a heat-decomposable blowing agent ~uch as ~ azodicarbonamide to a temperature above the decomposition - tomperature o~ the blow~ng agent, thereby to expand and crosslin~ the modified polyethylene. This process can re-mo~e the above-mentioned defects to a somewhat ~atisfactory -:- - . . , extent, but has the serious defect that when an organo-metallic compound such as dibutyltin dilaurate di~closed specifically as the silanol condensation catalyst in the above cited Patent Publication is used, the polyethylene composition prior to heat-foaming has poor storage cta-bility, and when it is heat-foamed after storage for a long period of time for rea~ong of transportation or otherwise, it is impossible to obtain a foamed article having the de~ired expansion ratio because the gel con-tent of the composition becomes extraordinarily high by the influence of the moisture in the air and by the actlon of the catalyst.
It has now been found that when a zinc salt of a hlgher carboxylic acid not disclosed in the Japanese Laid Open Patent Publications cited above is used as the ~ilanol condensation catalyst in the process of these Publications~
polyethylene compositions which have very good ~torage sta-bility prior to heat-foaming can be obtained.
Accordingly, it is an object of this invention to 1 20 provide a foamable and crosslinkable polyethylene compo-~ition which has superior storage stability, can be expanded uniformly throughoutl and can be shaped into a foamed art-icle of large thickne~s.
Another ob~ect of this invention is to provide a process for producing the above foamable and crosslinkable polyethylene composition.
Still another object of this invention is to pro-vide a process for preparin~ a crosslinked polyethylene foam from the above foamable and crosslinkable polyethylene ,.
,.' ,.
. . .. .. . . ., . :
composition.
Other objects and advantages of the present in-vention will become apparent from the following detailed description.
Accordin~ to the present invention, there is provided a foamable and crosslinkable polyethylene com-position comprising (a) modified polyethylene obtained by chemically bonding a silane compound containing at least one unsatu-rated group to polyethylene in the presence of a radical generator, (b) zinc stearate as the silanol condensation catalyst, and (c) azodicarbonamide as heat-decomposable blowing agent, said ingredients (a), (b) and (c) having been melt-kneaded with one another at a temperature lower than the decomposition temperature of the heat-decomposable blowing agent.
The term "polyethylene", used in the present specification and appended claims, is meant to include not only a homopolymer of ethylene, but also an ethylene co-polymer composed of at least 50 mole%, preferably at least 70 mole%, of an ethylene unit and a minor proportion of a monomer copolymerizable with ethylene, and a blend of at -~
least 50~ by weight, preferably at least 60% by weight, of the ethylene homopolymer or copolymer with another polymer.
Examples of monomers copolymerizable with ethylene are vinyl acetate, propylene, butene and hexane. The other polymer that can be blended with the ethylene homopolymer or copolymer may be any type of polymer compatible with it. Examples are polypropylene, polybutadiene, polyisoprene, n S
V
polychloroprene, chlorinated polyethylene, a ~tyrene~
butadiene copolymer, a vinyl acetate,'ethylene copolymer, chlorinated polyethylene, and a vinyl chloride'vinyl acetate copolymer. Eopecially preferred species are polypropylene, polybutadiene ar.d styrene~butadiene co-polymer.
Examples of polyethylene that can be advantage-ously employed in the present invention are lo~-, medium-and high-den~ity polyethylene, an ethylene/vinyl acetato copolymer, an ethylene'propylene copolymer, a blend of polyethylene and polypropylene, a blend of polyethylene -and an ethylene/vinyl acetate copolymer, and a blend of polyethylene and an ethylene/propylene copolymer. Of these, the medium density polyethylene, low denslty polyethylene, and ethylene/propylene copolymer are especially suitable.
Preferably~ the polyethylene resins have a soften~
ing point of le~ than 130C, Furthermore, it is preferred ¦ that the polyethylene resins have a melt index of 2.0 to 20~ a number average molecular ~reight of ~0,000 to 60,000, ~ 20 an intrinsic viscoyity, at 75C. in xylene, of o.8 to 1.1, j and a density of 0.910 to 0.940.
According to the present invention, the poly-ethylene described above is converted to modified poly-ethylene by chemically bonding a ~ilane compound contain-
A number of techniques for preparing cro~linked polyethylene foams from polyethylene have heretofore been sugge~ted. For example, Japanese Patent Publication No.
6?.78/66 disclose~ a proce~Y which compri~es applying ioniz-ing radiation to a sheet prepared from polyethylene con-taining a heat-decompo~able blowing agent, and heating the resulting cro~linked polyethylene sheet at atmospheric pressure to expand it. Furthermore, Japanese Patent Publi-catlon No. 17436/64 sugge~ts a proces~ which compriseJ
mixing polyethylene with an organic peroxide (chemical crosslinking agent) and a blowing agent, heating the mixture to croJJlink it, and foamlng it at atmo~pheric pres~ure.
The ~ugge~ted proce~ses are called "general atmo~-pherlc pressure foaming method", and are utilized commercially for the production of polyethylene foams. In radiation-initiated cro~linking and foaming techniques typified by the procos~ of Japanese Patent Publlcation No. 6278/66 cited above, electron beams are usually the only source of com-I mercially availablo radiation. Since electron beams have 25 a weak penetrating power, their effect doe~ not extend tothe inside of a polyethylene ~heet having a large thickness.
-~ Tho utilization of the radiation-initiated cros~linking - and foaming techniques i~ thorefore limited to ~heets having ~,~ a thickne~ of about 10 mm at mo~t. On the other hand, the .. . . .
~, .. .. . ~
- process of Japanese Patent Publication No. 17436?64 uging chemical crosslinking agents ~uffers from the defect that cro~slinking tend~ to begin at the time of melt-kneading polyethylene containing a chemical crosslinking agent, and this makes it~ sub~equent molding difficult. Further- ~-more, since crosslinking and foaming proceed almo~t simul-taneously in this proce~s, it is difficult to maintain the form of a molded article which is being cro~slinked and foamed. Another defect is that because there is a dif- I
ference in the degree of crosslinking reaction between the surface layer and the inside layer, the resulting foamed article i8 non-uniform with different cell diameter~ between the surface layer and the inside layer. This tendency be-comes greater when it is desired to obtain foamed articles of larger thickness. With the latter method, it i8 also difficult to obtain foamed article having a fine cellular ~tructure.
In an attempt to remedy these defects~ Japanese La1d-Open Patont Publications Nos. 100470~73 and 130460/74 suggest a proce~s which comprises chemically bonding a silane compound containing at lea~t one un~aturated bond to pol~ethylene in the presence of a radical generator to form silyl-modified polyethylene, and heating the silyl-modified polyethylene together with a silanol condensation catalyst and a heat-decomposable blowing agent ~uch as ~ azodicarbonamide to a temperature above the decomposition - tomperature o~ the blow~ng agent, thereby to expand and crosslin~ the modified polyethylene. This process can re-mo~e the above-mentioned defects to a somewhat ~atisfactory -:- - . . , extent, but has the serious defect that when an organo-metallic compound such as dibutyltin dilaurate di~closed specifically as the silanol condensation catalyst in the above cited Patent Publication is used, the polyethylene composition prior to heat-foaming has poor storage cta-bility, and when it is heat-foamed after storage for a long period of time for rea~ong of transportation or otherwise, it is impossible to obtain a foamed article having the de~ired expansion ratio because the gel con-tent of the composition becomes extraordinarily high by the influence of the moisture in the air and by the actlon of the catalyst.
It has now been found that when a zinc salt of a hlgher carboxylic acid not disclosed in the Japanese Laid Open Patent Publications cited above is used as the ~ilanol condensation catalyst in the process of these Publications~
polyethylene compositions which have very good ~torage sta-bility prior to heat-foaming can be obtained.
Accordingly, it is an object of this invention to 1 20 provide a foamable and crosslinkable polyethylene compo-~ition which has superior storage stability, can be expanded uniformly throughoutl and can be shaped into a foamed art-icle of large thickne~s.
Another ob~ect of this invention is to provide a process for producing the above foamable and crosslinkable polyethylene composition.
Still another object of this invention is to pro-vide a process for preparin~ a crosslinked polyethylene foam from the above foamable and crosslinkable polyethylene ,.
,.' ,.
. . .. .. . . ., . :
composition.
Other objects and advantages of the present in-vention will become apparent from the following detailed description.
Accordin~ to the present invention, there is provided a foamable and crosslinkable polyethylene com-position comprising (a) modified polyethylene obtained by chemically bonding a silane compound containing at least one unsatu-rated group to polyethylene in the presence of a radical generator, (b) zinc stearate as the silanol condensation catalyst, and (c) azodicarbonamide as heat-decomposable blowing agent, said ingredients (a), (b) and (c) having been melt-kneaded with one another at a temperature lower than the decomposition temperature of the heat-decomposable blowing agent.
The term "polyethylene", used in the present specification and appended claims, is meant to include not only a homopolymer of ethylene, but also an ethylene co-polymer composed of at least 50 mole%, preferably at least 70 mole%, of an ethylene unit and a minor proportion of a monomer copolymerizable with ethylene, and a blend of at -~
least 50~ by weight, preferably at least 60% by weight, of the ethylene homopolymer or copolymer with another polymer.
Examples of monomers copolymerizable with ethylene are vinyl acetate, propylene, butene and hexane. The other polymer that can be blended with the ethylene homopolymer or copolymer may be any type of polymer compatible with it. Examples are polypropylene, polybutadiene, polyisoprene, n S
V
polychloroprene, chlorinated polyethylene, a ~tyrene~
butadiene copolymer, a vinyl acetate,'ethylene copolymer, chlorinated polyethylene, and a vinyl chloride'vinyl acetate copolymer. Eopecially preferred species are polypropylene, polybutadiene ar.d styrene~butadiene co-polymer.
Examples of polyethylene that can be advantage-ously employed in the present invention are lo~-, medium-and high-den~ity polyethylene, an ethylene/vinyl acetato copolymer, an ethylene'propylene copolymer, a blend of polyethylene and polypropylene, a blend of polyethylene -and an ethylene/vinyl acetate copolymer, and a blend of polyethylene and an ethylene/propylene copolymer. Of these, the medium density polyethylene, low denslty polyethylene, and ethylene/propylene copolymer are especially suitable.
Preferably~ the polyethylene resins have a soften~
ing point of le~ than 130C, Furthermore, it is preferred ¦ that the polyethylene resins have a melt index of 2.0 to 20~ a number average molecular ~reight of ~0,000 to 60,000, ~ 20 an intrinsic viscoyity, at 75C. in xylene, of o.8 to 1.1, j and a density of 0.910 to 0.940.
According to the present invention, the poly-ethylene described above is converted to modified poly-ethylene by chemically bonding a ~ilane compound contain-
2~ ing at least one un~aturated group to it in the presence of A radical generator. -~
~;~ The silane compound used in this invention is an ~- or$anosilicon compound containing at least one unsaturated ~; group capable of being chemically bonded to the sites of , ' :
t~
'` ;~ - , ' ~ :
free radicals generated in the polymer chain of the poly-ethylene a~ a result of radical reaction, and typically include3 organo~ilane compound3 of the following formula R
R? ~ Si - R4 (I) R
wherein one or two, preferably only one, of Rl, R~, R3 and R4 represent a hydrocarbon or hydrocarboxy group containing a radical-poly-merizable double bond~ and the re.~t r~pre~ent organic residues capable of being split off by , 10 hydrolysis.
-¦ In the above formula, example~ of the hydro-carbon group containing a radlcal-polymerizable double bond arQ vinyl, allyl, 2-methylallyl, butenyl, cyclohexenyl, cyclopentadienyl, and octadienyl, and example~ of the hydro-c~rbonoxy group containing a radical-polymerizable double bond lnclude allyloxy and 2-methyl allyloxy. Of the-ae, vinyl i~ most proferred.
Examples of the organic residues capable of being ~ split off by hydroly~is include an alkoxy group such a~ -¦~ 20 methoxy~ ethoxy or butoxy, an acyloxy group such as formyl-j~ oxy, acetoxy or propionoxy, and a substituted amino group ~uch a~ methylamino or ethylamino. Of the~e, the aIkoxy group~ are espectally preferred.
Thus, vinyltrimethoxysilane and vinyltriethoxy-~ilane are ~ilane compounds which can be conveniently u.~ed in the present invention.
The amount of the silane compound is not critical, , but can be varied widely according, for example, to the type of polyethylene~ Generally, its amount is 0~1 to 30 parts by weight, preferably 0.5 to 10 parts by weight, per 100 partY by weight of the polyethylene.
Advantageously, radical generators used in the reaction between the polyethylene and the silane compound are those which decompose upon heating and generate radi~
cals. The radical generator acts as a reaction initiator at the time of chemically bonding the silane compound to the polyethylene. Preferably, these radical generators generally have a half life of 3 minutes or less at the -~
melting temperature of the polyethylene. Examples of such radical generators include organic peroxides such as benzoyl peroxide or lauroyl peroxide, and oragnic peroxide such as tert-butyl peracetate, tert.-butyl peroxy-~-ethyl hexanoate, ~ ;
or tert.-butylperoxy isobutyrate, tert.-butylperoxy benzo-ate, dlcumyl peroxide, ~,5-dimethyl-2,5-di~tert.-butyl-peroxy)hexane, 2.~5-dimethyl-?,5-di(tert.-butylperoxy) hexyne.
~0 The amount of the radical generator i8 not limited in particular, but can be varied over a wide range accord-in~, for example, to the type of the polyethylene u~ed or the amount of the ~ilane compoun~. Generally, its suitable amount is 0.01 to 1.5 parts by weight, preferably 0.1 to 1.0 2~ part by weight, per 100 parts by weight of the polyethylene.
The bonding of the silane compound to the poly-ethylene can be performed easily bv the method to be des-cribed.
The ~inc salt of a higher carboxylic acid acts ~ J.. . `
~ - 8 _ .:
. ~ . . . . . . . .
~ ~ .
.
as a silanol condensation catalyst, and preferably in-cludes zinc salts of aliphatic or alicyclic carboxylic acids containing 8 to 20 carbon atoms, preferably 8 to 17 carbon atoms. Examples of these zinc salts include zinc stearate, zinc octanoate, zinc naphthenate and zinc laurate, and the use of the zinc stearate is especially preferred.
The amount of the zinc salt of higher carboxylic acid can be varied according to the amount of the silane compound bonded to the modified polyethylene. Generally, its amount is 0.01 to 5 parts by weight, preferably 0.1 to
~;~ The silane compound used in this invention is an ~- or$anosilicon compound containing at least one unsaturated ~; group capable of being chemically bonded to the sites of , ' :
t~
'` ;~ - , ' ~ :
free radicals generated in the polymer chain of the poly-ethylene a~ a result of radical reaction, and typically include3 organo~ilane compound3 of the following formula R
R? ~ Si - R4 (I) R
wherein one or two, preferably only one, of Rl, R~, R3 and R4 represent a hydrocarbon or hydrocarboxy group containing a radical-poly-merizable double bond~ and the re.~t r~pre~ent organic residues capable of being split off by , 10 hydrolysis.
-¦ In the above formula, example~ of the hydro-carbon group containing a radlcal-polymerizable double bond arQ vinyl, allyl, 2-methylallyl, butenyl, cyclohexenyl, cyclopentadienyl, and octadienyl, and example~ of the hydro-c~rbonoxy group containing a radical-polymerizable double bond lnclude allyloxy and 2-methyl allyloxy. Of the-ae, vinyl i~ most proferred.
Examples of the organic residues capable of being ~ split off by hydroly~is include an alkoxy group such a~ -¦~ 20 methoxy~ ethoxy or butoxy, an acyloxy group such as formyl-j~ oxy, acetoxy or propionoxy, and a substituted amino group ~uch a~ methylamino or ethylamino. Of the~e, the aIkoxy group~ are espectally preferred.
Thus, vinyltrimethoxysilane and vinyltriethoxy-~ilane are ~ilane compounds which can be conveniently u.~ed in the present invention.
The amount of the silane compound is not critical, , but can be varied widely according, for example, to the type of polyethylene~ Generally, its amount is 0~1 to 30 parts by weight, preferably 0.5 to 10 parts by weight, per 100 partY by weight of the polyethylene.
Advantageously, radical generators used in the reaction between the polyethylene and the silane compound are those which decompose upon heating and generate radi~
cals. The radical generator acts as a reaction initiator at the time of chemically bonding the silane compound to the polyethylene. Preferably, these radical generators generally have a half life of 3 minutes or less at the -~
melting temperature of the polyethylene. Examples of such radical generators include organic peroxides such as benzoyl peroxide or lauroyl peroxide, and oragnic peroxide such as tert-butyl peracetate, tert.-butyl peroxy-~-ethyl hexanoate, ~ ;
or tert.-butylperoxy isobutyrate, tert.-butylperoxy benzo-ate, dlcumyl peroxide, ~,5-dimethyl-2,5-di~tert.-butyl-peroxy)hexane, 2.~5-dimethyl-?,5-di(tert.-butylperoxy) hexyne.
~0 The amount of the radical generator i8 not limited in particular, but can be varied over a wide range accord-in~, for example, to the type of the polyethylene u~ed or the amount of the ~ilane compoun~. Generally, its suitable amount is 0.01 to 1.5 parts by weight, preferably 0.1 to 1.0 2~ part by weight, per 100 parts by weight of the polyethylene.
The bonding of the silane compound to the poly-ethylene can be performed easily bv the method to be des-cribed.
The ~inc salt of a higher carboxylic acid acts ~ J.. . `
~ - 8 _ .:
. ~ . . . . . . . .
~ ~ .
.
as a silanol condensation catalyst, and preferably in-cludes zinc salts of aliphatic or alicyclic carboxylic acids containing 8 to 20 carbon atoms, preferably 8 to 17 carbon atoms. Examples of these zinc salts include zinc stearate, zinc octanoate, zinc naphthenate and zinc laurate, and the use of the zinc stearate is especially preferred.
The amount of the zinc salt of higher carboxylic acid can be varied according to the amount of the silane compound bonded to the modified polyethylene. Generally, its amount is 0.01 to 5 parts by weight, preferably 0.1 to
- 3 parts by weight, per 100 parts by weight of the poly-ethylene.
j According to the present invention, the silanol condensation catalyst may be a mixture of the above higher carboxylic acid zinc salt with a minor amount of a con-ventional silanol condensation catalyst, for example, organo-tin compounds such as dibutyltin dilaurate, dibutyltin maleate or dibutyltin diacetate. The amount of the con-ventional silanol catalyst in the mixture should be mini-mized, and preferably limited to not more than 5% based on the total weight of the mixed silanol catalyst.
Ordinary heat-decomposable blowing agents used heretofore in the production of polyethylene foams can be used in the present invention. Especially preferred spe-cies are those which decompose at a temperature between 170 and 220C. to generate gas. Specific examples include azo-dicarbonamide, dinitrosopentamethylene tetramine, benzene-sulfonyl hydrazide and toluenesulfonyl hydrizide. Azodi-carbonamide is especially advantageous because of its good _ g _ thermal stability and optimal decomposition temperature.
These blowing agents can be used either alone or in ad-mixture, and the amount of the blowing agent can be varied over a wide range according, for example, to the degree of expansion required of the final foamed shaped article. Usually, its amount is 3 to 30 parts by weight, preferably 10 to 20 parts by weight, per 100 parts by weight of the polyethylene.
If desired, the composition of this invention may further include a chain transfer agent. The chain transfer agent used in this invention has an action of de-activating any portion of the radical generator which re-mains unreacted at the time of modifying polyethylene in J the presence of the radical generator. Examples of suit-able chain transfer agents are dodecyl mercaptan, t-butyl mercaptan, n-butyl mercaptan, octyl mercaptan, and ~-methylstyrene. The chain transfer agent inhibits the cross-linking reaction of polyethylene and permits the silane -compound-bonding reaction to proceed effectively. When such a chain transfer agent is used, its amount is 0.01 to 0.5 part by weight, preferably 0.03 to 0.1 part by weight, per I 100 parts by weight of polyethylene.
¦ If desired, the composition of this invention may contain conventional additives such as coloring agents, lubricants, foaming assistants, and deterioration in-hibitors in the amounts usually employed in the art.
According to the present invention, the poly-ethylene composition can be prepared by melt-kneading ~a) modified polyethylene obtained by chemically bonding , - 10 -, :
~.. . . . . . . .
a silane compound containing at least one unsaturated group to polyethylene in the presence of a radical gene-rator, (b) zinc stearate as the silanol condensation catalyst and (c) azodicarbonamide as a heat-decomposable blowing agent at a temperature below the decom~osition temperature of the heat-decomposable blowing agent.
The modified polyethylene can be prepared in advance of melt-kneading, or can be formed in situ at the time of melt-kneading.
When it is to be prepared in advance, polyethylene is mixed (e.g., dry-blended) with the radical generator and the silane compound in the proportions indicated herein-above, and the mixture is melted and kneaded at a tempera-ture above the melting temperature of the polyethylene, pre-ferably at a temperature higher than 150C. The melt-knead-ing can be carried out using an ordinary extruder, calender roll, roll mill, injection molding machine, or the like.
The reaction time is generally about 1 to 10 minutes when the reaction system is in the molten state.
The molded polyethylene so formed can be molded into a suitable form such as pellets. Or it can be used in the molten state, and successively kneaded with the higher carboxylic acid zinc salt and the blowing agent to afford the composition of this invention.
The resulting modified polyethylene is blended with the higher carboxylic acid zinc salt and the heat-decomposable blowing agent in the amounts indicated here-inabo~e, and the mixture is melt-kneaded with or without other optional in~redients at a temperature belo~ the :' , ,~
~085549 decomposition temperature of the heat-decompo~able blow-ing agent.
A~ an alternative ~ethod, the polyethylene, radical generator, silane compound, higher carboxylic acid zinc ~alt and blowing agent and other optional ingredients are mixed, and the resulting mixture is melt-kneaded at ``
a temperature below the decomposition temperature of the heat-decomposable blowing agent, preferably at a tempera- ~
ture of 110C. to 150C., to afford the composition of thi~ ~-inventlon. This alternative method ~imultaneou~ly achieve~
the bonding of the ~ilane compound to the polyethylene and the melt-kneading of the resulting modified polyethylene, -~
-.
- higher carboxylic acid zinc salt and heat-decomposable blow- ~ -ing agent.
Mlxing of the ingredient~ can be performed by con-ventional mean~ for example, using a kneader, blender or ~ mixer. The melt-kneading can be carried out u~ing~ for i~
! example, an extruder, roll, or in~ection molding machine in which the polyethylene i8 melted by heat and kneaded with , ?.0 the other lngredient~.
The temperature for melt-kneading i~ above the melting temperature of the modified polyethylene u~ed and below the decompo~ition temperature of the heat-decompos-able blowing agent. Usually~ the melt-kneadin$ temperature is preferably about 110 to 150C. It i~ ~ufficient that kneading is carried out for about l to lO minutes at this .
temperature.
Thu~, according to the present invention, a foam-able and crosslinkable polyethylene composition having a .,~ - 1~. -.~ ~
gel content of not more than 40% by weight, preferably not more than 20% by weight can be obtained.
In the present specification and appeded claims, the term "gel content" i9 defined as the weight percent of an insoluble portion of polyethylene which has been left after immer~in~ the polyethylene in xylene at 110C.-for 48 hours, based on the weight of the polyethylene before immer~ion.
The foamable and cro~slinkable polyethylene com-positlon of this invention can be converted into foamed ~haped article~ crosslinked to a high degree by sub~equent I molding and heat-foaming. The gel content of the final ~-foamed shaped article can be raised to at least 509b by '~ weight, usually 60 to 80% by weight. Thus, polyethylene 1 15 foams having superior thermal stability can be prepared from ¦ the composition of this invention.
The polyethylene composition of this invention ha~
~ery good ~torage stability~ and does not undergo any change at all even uhen allowed to stand for long periods of time without heat-foaming. Even when it is heated after storage for long periods of time, the state of the cells and the expan~ion ratio are scarcely different from those with a composltion immediately after preparation. FoAms of good quality can be prepared from such a polyethylene composition f this invention.
Another advantage of the present in~ention is that it can be fabricated into any de~ired shape such as a board, pipQ and rod as well as a thin sheet because there is no re~triction on the shape or thickness of the shaped structure.
, : . - ,;.~ --- .
Thus, according to the present invention, there is provided a process for preparing crosslinked poly-ethylene foams, which comprises melt-kneading (a) modified polyethylene obtained by chemically bonding a silane com-pound containing at least one unsaturated group in the presence of a radical generator, (b) zinc stearate as the silanol condensation catalyst and (c) azodicarbonamide as a heat-decomposable blowing agent at a temperature below the decomposition temperature of the heat-decomposable blowing agent, shaping the kneaded mixture into a desired shape, and heating the shaped article to a temperature above the decomposition temperature of the heat-decomposable blowing agent to expand and crosslink the shaped article.
The polyethylene composition of this invention can be shaped in accordance with this invention into any desired shape such as a sheet, rod, cylinder, board or block. The shaping can be effected by various conventional shaping methods such as injection molding, extrusion mold-ing or blow molding.
The resulting shaped article can be expanded and crosslinked by heating it, either immediately after shap-ing or after storage for long periods of time, to a tem-perature above the decomposition temperature of the heat-, decomposable blowing agent. The heating temperature varies according to the type of the blowing agent used. Usually, however, it is at least 180C., preferably 200 to 230~C.
Generally, the foaming and crosslin~ing can be completed within 1 to 20 minutes. ~-As a result of such heating, a s~all amount of moisture in the shaped article or the moisture in the am-bient atmosphere and the zinc salt of higher carboxylic acid act together to hydrolyze the silane compound bonded to polyethylene, and then a condensation reaction occurs to cause the chemical crosslinking of the silane. This in turn re~ult~ in the cros~linkage of the modified poly-ethylene to increase its viscoela~ticity.
When the zinc ~alt of higher carboxylic acid is uffed as a silanol condensation catalyst in accordance with this invention, a crosslinking reaction of the polyethylene I compo~ition becomes vi~orous only at temperature far higher than the temperature employed in the melt-kneading, and is not particularly active when the decompo~ition of the ! heat-decomposable blowing agent does not occur. For this 1 15 reason~ the formation of a main crosslinkage in the modi-fied polyethylene is effected in a step of heating the j 8haped article to a temperature above the decompositlon ! temperAture of the blowing agent.
~ Substantially at the same time as the proceeding ¦ 20 of the crosslinking reaction, the heat-decomposable blow-ing agent decomposes under heat to generate gas such a~
nltrogen, and therefore, the shaped article softened by heat converted to a foamed structure.
. ~
The heating of the shaped article can be effected, for example, by radiation from an infrared lampl application of a hot air, or immersion in a heated liquid bath.
The present invention thus provides a polyethylene foam which is highly crosslinked and has superior thermal stability.
,,~ .
.`
, "
The advantages brought about by the present in-vention are summarized belolr.
In the present invention, polyethylene is re-acted ~ith the silane compound before or during the melt-kneading operation to form modified polyethylene contain-ing the silane compound in its side chain. When this modified polyethylene is subjected to high temperAtures in the presence of the higher carboxylic acid zinc salt, the silane compound is chemically bonded to itself by hydrolysis and conden~ation caused by the moisture in the -ambient atmosphere, which results in the crosslinking of the polyethylene. The crosslinking reaction is promoted --( in the presence of a product formed by the decompo~ition ; of the heat-decomposable blowing agent, especially azo-dicarbonamide. In the present invention, the polyethylene -i resin ig foamed and crosglinked simultaneously in the ste~p of heating the shaped article to a temperature above the decompositlon temperature of the blowing agent. The use of this method can increase the density of crosslinXages in the final product.
For this reason, a polyethylene foam having a high crosslinkage density, that is, having ~uperior ther-mal stability can be obtained. In contrast, in the con-ventional method in which a resin is first crosslinked and then foamed, too high a density of cro3slinkage makes ~ the ~oaminy of the crosslinked resin difficult, which in - turn leads to the difficulty of obtaining foams having superior thermal stability.
Furthermore~ in the present invention, the crosslinking of the resin by the higher carboxylic acid z~nc salt scarcely occurs at the time of melt-kneading and shapin$ the resin composition, and therefore, no abrupt rise in viscosity of the resin occurs in these steps. Thuq, conventional procedures employed for shaping polyethylene can be applied in these steps. The -~
resin can be fabricated into various shapes such as a rod, cylinder, and spherical container as well as a sheet, and by foaming such a shaped article under heat, a foamed shaped article having a complicated shape conforming to the shape of the above ~haped article can be obtained.
Moreover, the present invention does not require the application of ionizing radiation for crosslinking polyethylene, and therefore, can obviate the use of lar~e-scale dangerous equipment required for radiation. --The most characteristic advantage in the present invention is that shaped article of the polyethylene com-position need not to be heat-foamed immediately, but ~an be stored for relatively long periods of time before foam-ing. Even after such a long-term storage, the shaped article~ can be converted to foamed product~ without ~i adverse effects on the expansion ratio or the state of i the cells in the heat-foaming step. Thus, even after storing or transporting the resulting shaped structures for long periods of time, foamed articles having satis-factory quality and commercial value can be obtained therefrom.
The polyethylene foams prepared by the present invention can be u~ed in various applicati~ns, for example, , ~
~, .. . .. .... . .
- ~ : - . : . . .
as a cushioning material, a warmth-retaining material for hot water supply pipes, and a heat insulating or sound-proofing material to be embedeed in house walls. Since the polyethylene foams in accordance with thi~ invention have especially good thermal stability, they can be suit-ably used as a heat insulating material for pipes that transport a cooling or heating ~edium in the form of a cylindrical shaped structure.
The following Examples and Comparati~e Examples illustrate the present invention specifically.
Example 1 100 Parts by weight of polyethylene having an average particle diameter of ?.0 mesh, a melt index of 4.0, and a density of 0. 9?A4 was uniformly mixed with 3 parts by weight of ~inyltriethoxysilane, 0.4 part of t-butyl-~ peroxy ?.-ethylhexanoate, ? parts by weight of zinc ~tearatej and 15 parts by wei~ht of azodicarbonamide (havin~ a de-composition temperature of 190C.) in a ribbon blender.
; The mixture WaB fed into an extruder, and melt-kneaded at a temperature of 135C.
When the melt-kneading was performed for about 5 ~ minutes, the vinylethoxysilane was bonded to the poly-j ethylene. The resulting composition was then extruded into , a sheet.
;, 25 Example 2 i~ A sheet was prepared by extrusion in the same way as in Example 1 except that the amount of the zinc stearate ~; was charged to 0.4 part by weisht.
Example 3 ~i, ' ..
--... . . . . . .. .
.~ - . "
~0~5S49 A sheet was prepared by extrusion in the same way as in Example 1 except that 0.4 part by weight of zinc octanoate was used instead of the zinc stearate.
Example 4 A sheet was prepared by extrusion in the same way as in Example 1 except that 0.4 part by weight of zinc naphthenate was used instead of the zinc stearate.
Exam~le 5 A sheet uaa prepared by extruslon in the same way as in Example 4 except that the amount of the zinc naphthe-nate was changed to 200 parts by weight.
i Example 6 A sheet was prepared by extrusion in the same way as in Example 1 except that ?.0 parts by weight of zinc laurate was used instead of the zinc stearate.
Comparative Example 1 A sheet was prepared by extrusion in the same way as ln Example 1 except that the zinc stearate was not used.
Comparative Example 2 A ~heet was prepared by extrusion in the same way as in Example 4 except that 0.4 part by weight of cobalt naphthenate was used instead of the zinc naphthenate.
Com~arative Example 3 A ~heet was prepared by extrusion in the ~ame way as in Example 1 except that 0.4 part by weight of dibutyltin dilaurate was used instead of 2.0 parts by weight of zinc stearate.
Samples of the sheets prepared in the above examples, either as obtained, after standing for 6 days, or after , - 19 _ .
standing for 14 days, ~ere each allowed to stand in a hot air having chamber held at ?.~0C. for about 3 minutes to expand them.
The expansion ratio and the state of the cells -.5 were determined with regard to all the foams obtained, and the results are shown in Table 1.
: Table 1 i Immediately After stand- After stand- ~. .
after pre- ing for ing for : paration 6 day~ . 14 days State Expan- State Expan- State Expan-of sion of sion of sion Samples cells ratio cellg ratio cell~ ratio .. . ~ .' ; Examples i 1 Good 33 Good33 Good 3?.
2 Good 3~ Good 3~. Good 31 3 Good 31 Good31 Fair 31 :
j According to the present invention, the silanol condensation catalyst may be a mixture of the above higher carboxylic acid zinc salt with a minor amount of a con-ventional silanol condensation catalyst, for example, organo-tin compounds such as dibutyltin dilaurate, dibutyltin maleate or dibutyltin diacetate. The amount of the con-ventional silanol catalyst in the mixture should be mini-mized, and preferably limited to not more than 5% based on the total weight of the mixed silanol catalyst.
Ordinary heat-decomposable blowing agents used heretofore in the production of polyethylene foams can be used in the present invention. Especially preferred spe-cies are those which decompose at a temperature between 170 and 220C. to generate gas. Specific examples include azo-dicarbonamide, dinitrosopentamethylene tetramine, benzene-sulfonyl hydrazide and toluenesulfonyl hydrizide. Azodi-carbonamide is especially advantageous because of its good _ g _ thermal stability and optimal decomposition temperature.
These blowing agents can be used either alone or in ad-mixture, and the amount of the blowing agent can be varied over a wide range according, for example, to the degree of expansion required of the final foamed shaped article. Usually, its amount is 3 to 30 parts by weight, preferably 10 to 20 parts by weight, per 100 parts by weight of the polyethylene.
If desired, the composition of this invention may further include a chain transfer agent. The chain transfer agent used in this invention has an action of de-activating any portion of the radical generator which re-mains unreacted at the time of modifying polyethylene in J the presence of the radical generator. Examples of suit-able chain transfer agents are dodecyl mercaptan, t-butyl mercaptan, n-butyl mercaptan, octyl mercaptan, and ~-methylstyrene. The chain transfer agent inhibits the cross-linking reaction of polyethylene and permits the silane -compound-bonding reaction to proceed effectively. When such a chain transfer agent is used, its amount is 0.01 to 0.5 part by weight, preferably 0.03 to 0.1 part by weight, per I 100 parts by weight of polyethylene.
¦ If desired, the composition of this invention may contain conventional additives such as coloring agents, lubricants, foaming assistants, and deterioration in-hibitors in the amounts usually employed in the art.
According to the present invention, the poly-ethylene composition can be prepared by melt-kneading ~a) modified polyethylene obtained by chemically bonding , - 10 -, :
~.. . . . . . . .
a silane compound containing at least one unsaturated group to polyethylene in the presence of a radical gene-rator, (b) zinc stearate as the silanol condensation catalyst and (c) azodicarbonamide as a heat-decomposable blowing agent at a temperature below the decom~osition temperature of the heat-decomposable blowing agent.
The modified polyethylene can be prepared in advance of melt-kneading, or can be formed in situ at the time of melt-kneading.
When it is to be prepared in advance, polyethylene is mixed (e.g., dry-blended) with the radical generator and the silane compound in the proportions indicated herein-above, and the mixture is melted and kneaded at a tempera-ture above the melting temperature of the polyethylene, pre-ferably at a temperature higher than 150C. The melt-knead-ing can be carried out using an ordinary extruder, calender roll, roll mill, injection molding machine, or the like.
The reaction time is generally about 1 to 10 minutes when the reaction system is in the molten state.
The molded polyethylene so formed can be molded into a suitable form such as pellets. Or it can be used in the molten state, and successively kneaded with the higher carboxylic acid zinc salt and the blowing agent to afford the composition of this invention.
The resulting modified polyethylene is blended with the higher carboxylic acid zinc salt and the heat-decomposable blowing agent in the amounts indicated here-inabo~e, and the mixture is melt-kneaded with or without other optional in~redients at a temperature belo~ the :' , ,~
~085549 decomposition temperature of the heat-decompo~able blow-ing agent.
A~ an alternative ~ethod, the polyethylene, radical generator, silane compound, higher carboxylic acid zinc ~alt and blowing agent and other optional ingredients are mixed, and the resulting mixture is melt-kneaded at ``
a temperature below the decomposition temperature of the heat-decomposable blowing agent, preferably at a tempera- ~
ture of 110C. to 150C., to afford the composition of thi~ ~-inventlon. This alternative method ~imultaneou~ly achieve~
the bonding of the ~ilane compound to the polyethylene and the melt-kneading of the resulting modified polyethylene, -~
-.
- higher carboxylic acid zinc salt and heat-decomposable blow- ~ -ing agent.
Mlxing of the ingredient~ can be performed by con-ventional mean~ for example, using a kneader, blender or ~ mixer. The melt-kneading can be carried out u~ing~ for i~
! example, an extruder, roll, or in~ection molding machine in which the polyethylene i8 melted by heat and kneaded with , ?.0 the other lngredient~.
The temperature for melt-kneading i~ above the melting temperature of the modified polyethylene u~ed and below the decompo~ition temperature of the heat-decompos-able blowing agent. Usually~ the melt-kneadin$ temperature is preferably about 110 to 150C. It i~ ~ufficient that kneading is carried out for about l to lO minutes at this .
temperature.
Thu~, according to the present invention, a foam-able and crosslinkable polyethylene composition having a .,~ - 1~. -.~ ~
gel content of not more than 40% by weight, preferably not more than 20% by weight can be obtained.
In the present specification and appeded claims, the term "gel content" i9 defined as the weight percent of an insoluble portion of polyethylene which has been left after immer~in~ the polyethylene in xylene at 110C.-for 48 hours, based on the weight of the polyethylene before immer~ion.
The foamable and cro~slinkable polyethylene com-positlon of this invention can be converted into foamed ~haped article~ crosslinked to a high degree by sub~equent I molding and heat-foaming. The gel content of the final ~-foamed shaped article can be raised to at least 509b by '~ weight, usually 60 to 80% by weight. Thus, polyethylene 1 15 foams having superior thermal stability can be prepared from ¦ the composition of this invention.
The polyethylene composition of this invention ha~
~ery good ~torage stability~ and does not undergo any change at all even uhen allowed to stand for long periods of time without heat-foaming. Even when it is heated after storage for long periods of time, the state of the cells and the expan~ion ratio are scarcely different from those with a composltion immediately after preparation. FoAms of good quality can be prepared from such a polyethylene composition f this invention.
Another advantage of the present in~ention is that it can be fabricated into any de~ired shape such as a board, pipQ and rod as well as a thin sheet because there is no re~triction on the shape or thickness of the shaped structure.
, : . - ,;.~ --- .
Thus, according to the present invention, there is provided a process for preparing crosslinked poly-ethylene foams, which comprises melt-kneading (a) modified polyethylene obtained by chemically bonding a silane com-pound containing at least one unsaturated group in the presence of a radical generator, (b) zinc stearate as the silanol condensation catalyst and (c) azodicarbonamide as a heat-decomposable blowing agent at a temperature below the decomposition temperature of the heat-decomposable blowing agent, shaping the kneaded mixture into a desired shape, and heating the shaped article to a temperature above the decomposition temperature of the heat-decomposable blowing agent to expand and crosslink the shaped article.
The polyethylene composition of this invention can be shaped in accordance with this invention into any desired shape such as a sheet, rod, cylinder, board or block. The shaping can be effected by various conventional shaping methods such as injection molding, extrusion mold-ing or blow molding.
The resulting shaped article can be expanded and crosslinked by heating it, either immediately after shap-ing or after storage for long periods of time, to a tem-perature above the decomposition temperature of the heat-, decomposable blowing agent. The heating temperature varies according to the type of the blowing agent used. Usually, however, it is at least 180C., preferably 200 to 230~C.
Generally, the foaming and crosslin~ing can be completed within 1 to 20 minutes. ~-As a result of such heating, a s~all amount of moisture in the shaped article or the moisture in the am-bient atmosphere and the zinc salt of higher carboxylic acid act together to hydrolyze the silane compound bonded to polyethylene, and then a condensation reaction occurs to cause the chemical crosslinking of the silane. This in turn re~ult~ in the cros~linkage of the modified poly-ethylene to increase its viscoela~ticity.
When the zinc ~alt of higher carboxylic acid is uffed as a silanol condensation catalyst in accordance with this invention, a crosslinking reaction of the polyethylene I compo~ition becomes vi~orous only at temperature far higher than the temperature employed in the melt-kneading, and is not particularly active when the decompo~ition of the ! heat-decomposable blowing agent does not occur. For this 1 15 reason~ the formation of a main crosslinkage in the modi-fied polyethylene is effected in a step of heating the j 8haped article to a temperature above the decompositlon ! temperAture of the blowing agent.
~ Substantially at the same time as the proceeding ¦ 20 of the crosslinking reaction, the heat-decomposable blow-ing agent decomposes under heat to generate gas such a~
nltrogen, and therefore, the shaped article softened by heat converted to a foamed structure.
. ~
The heating of the shaped article can be effected, for example, by radiation from an infrared lampl application of a hot air, or immersion in a heated liquid bath.
The present invention thus provides a polyethylene foam which is highly crosslinked and has superior thermal stability.
,,~ .
.`
, "
The advantages brought about by the present in-vention are summarized belolr.
In the present invention, polyethylene is re-acted ~ith the silane compound before or during the melt-kneading operation to form modified polyethylene contain-ing the silane compound in its side chain. When this modified polyethylene is subjected to high temperAtures in the presence of the higher carboxylic acid zinc salt, the silane compound is chemically bonded to itself by hydrolysis and conden~ation caused by the moisture in the -ambient atmosphere, which results in the crosslinking of the polyethylene. The crosslinking reaction is promoted --( in the presence of a product formed by the decompo~ition ; of the heat-decomposable blowing agent, especially azo-dicarbonamide. In the present invention, the polyethylene -i resin ig foamed and crosglinked simultaneously in the ste~p of heating the shaped article to a temperature above the decompositlon temperature of the blowing agent. The use of this method can increase the density of crosslinXages in the final product.
For this reason, a polyethylene foam having a high crosslinkage density, that is, having ~uperior ther-mal stability can be obtained. In contrast, in the con-ventional method in which a resin is first crosslinked and then foamed, too high a density of cro3slinkage makes ~ the ~oaminy of the crosslinked resin difficult, which in - turn leads to the difficulty of obtaining foams having superior thermal stability.
Furthermore~ in the present invention, the crosslinking of the resin by the higher carboxylic acid z~nc salt scarcely occurs at the time of melt-kneading and shapin$ the resin composition, and therefore, no abrupt rise in viscosity of the resin occurs in these steps. Thuq, conventional procedures employed for shaping polyethylene can be applied in these steps. The -~
resin can be fabricated into various shapes such as a rod, cylinder, and spherical container as well as a sheet, and by foaming such a shaped article under heat, a foamed shaped article having a complicated shape conforming to the shape of the above ~haped article can be obtained.
Moreover, the present invention does not require the application of ionizing radiation for crosslinking polyethylene, and therefore, can obviate the use of lar~e-scale dangerous equipment required for radiation. --The most characteristic advantage in the present invention is that shaped article of the polyethylene com-position need not to be heat-foamed immediately, but ~an be stored for relatively long periods of time before foam-ing. Even after such a long-term storage, the shaped article~ can be converted to foamed product~ without ~i adverse effects on the expansion ratio or the state of i the cells in the heat-foaming step. Thus, even after storing or transporting the resulting shaped structures for long periods of time, foamed articles having satis-factory quality and commercial value can be obtained therefrom.
The polyethylene foams prepared by the present invention can be u~ed in various applicati~ns, for example, , ~
~, .. . .. .... . .
- ~ : - . : . . .
as a cushioning material, a warmth-retaining material for hot water supply pipes, and a heat insulating or sound-proofing material to be embedeed in house walls. Since the polyethylene foams in accordance with thi~ invention have especially good thermal stability, they can be suit-ably used as a heat insulating material for pipes that transport a cooling or heating ~edium in the form of a cylindrical shaped structure.
The following Examples and Comparati~e Examples illustrate the present invention specifically.
Example 1 100 Parts by weight of polyethylene having an average particle diameter of ?.0 mesh, a melt index of 4.0, and a density of 0. 9?A4 was uniformly mixed with 3 parts by weight of ~inyltriethoxysilane, 0.4 part of t-butyl-~ peroxy ?.-ethylhexanoate, ? parts by weight of zinc ~tearatej and 15 parts by wei~ht of azodicarbonamide (havin~ a de-composition temperature of 190C.) in a ribbon blender.
; The mixture WaB fed into an extruder, and melt-kneaded at a temperature of 135C.
When the melt-kneading was performed for about 5 ~ minutes, the vinylethoxysilane was bonded to the poly-j ethylene. The resulting composition was then extruded into , a sheet.
;, 25 Example 2 i~ A sheet was prepared by extrusion in the same way as in Example 1 except that the amount of the zinc stearate ~; was charged to 0.4 part by weisht.
Example 3 ~i, ' ..
--... . . . . . .. .
.~ - . "
~0~5S49 A sheet was prepared by extrusion in the same way as in Example 1 except that 0.4 part by weight of zinc octanoate was used instead of the zinc stearate.
Example 4 A sheet was prepared by extrusion in the same way as in Example 1 except that 0.4 part by weight of zinc naphthenate was used instead of the zinc stearate.
Exam~le 5 A sheet uaa prepared by extruslon in the same way as in Example 4 except that the amount of the zinc naphthe-nate was changed to 200 parts by weight.
i Example 6 A sheet was prepared by extrusion in the same way as in Example 1 except that ?.0 parts by weight of zinc laurate was used instead of the zinc stearate.
Comparative Example 1 A sheet was prepared by extrusion in the same way as ln Example 1 except that the zinc stearate was not used.
Comparative Example 2 A ~heet was prepared by extrusion in the same way as in Example 4 except that 0.4 part by weight of cobalt naphthenate was used instead of the zinc naphthenate.
Com~arative Example 3 A ~heet was prepared by extrusion in the ~ame way as in Example 1 except that 0.4 part by weight of dibutyltin dilaurate was used instead of 2.0 parts by weight of zinc stearate.
Samples of the sheets prepared in the above examples, either as obtained, after standing for 6 days, or after , - 19 _ .
standing for 14 days, ~ere each allowed to stand in a hot air having chamber held at ?.~0C. for about 3 minutes to expand them.
The expansion ratio and the state of the cells -.5 were determined with regard to all the foams obtained, and the results are shown in Table 1.
: Table 1 i Immediately After stand- After stand- ~. .
after pre- ing for ing for : paration 6 day~ . 14 days State Expan- State Expan- State Expan-of sion of sion of sion Samples cells ratio cellg ratio cell~ ratio .. . ~ .' ; Examples i 1 Good 33 Good33 Good 3?.
2 Good 3~ Good 3~. Good 31 3 Good 31 Good31 Fair 31 :
4 Good 33 Good33 Good 30 ! . Good 31 Good31 Good 3 . 6 Good 3?. Good3? Good 3 . .. _._ :.' ,,1 Coimvpe aErX-i amples :
l 1 Very Very 9 Very 11 .- ~oor 5 poor poor ~ ? Very 3 Very 4 Very 5 :' ~ poor poor poor , . 3 600d ~.7 Poor?~1 Poor 8 .
!::
li The gtate of the cells was e~aluated on a scale of good, fair, poor, and very poor as follows:
Good: Uni~orm fine cell~ occurred all o~er.
- ?.0 -, Fair: Irregular cells partly occurred.
Poor: Irregular cellg occurred all over.
Very poor: The shape collapsed, and the sample assumed a cast ~tate.
Example 7 -~
100 Parts by weight of polyethylene having an average particle size of 30 me~h, a melt index of 4.0 and a density of 0.924 was dry-blended with ~ part~ by .
weight of vinyltriethoxysilane and 0.12 part by weight of dicumyl peroxide~ and the blend was fed into an extruder where it WaY melt-kneaded at 190C. and pelletized. The resulting pellets of modified polyethylene were pulverized to a size of about 30 mesh A composition consisting of 100 parts by weight of the pul~erized modified polyethylene, 15 parts by weight of azodicarbonamide and 1 part by weight of zinc stearate wa~ fed into an extruder, melt-~neaded at 134C. and ex-truded into a ~heet.
Example 8 A sheet was prepared by extrusion in the same way a~ in Example 7 except that 1 part by weight of zinc naph-! thenate wa~ used instead of the zinc stearate ,: .
,~ Comptarati~e Example 4 A sheet was prepared by extru~ion in the same way as in Example 7 except that 1 part by weight of dibutyltin dilaurate was used instead of the zinc stearate.
Com~arative Exam~le 5 A sheet was prepared in the same way as in Example 1 7 exeept that 1 part of cobalt naphtenate was prepared ~, , - ?.1 _ ~ -~ ~ .
- ~ ~, - .
~085S49 instead of the zinc stearate.
Samples of the sheets prepared in Examples 7 and 8 and Comparative Exam~les 4 and 5, either as obtained, after standing for 7 days, or after standin$ for 50 days, were each allowed to stand in a hot air heating chamber held at ~30C. for about 3 minutes.
The expansion ratio and the state of the cells were determined ~ith regard to all the foams obtained, and the results are shown in Table ?.. The determinations were made by the same methods as described hereinabove.
Table 2 Immediately After stand- After stand-after pre- ing for ing for parati on 7 days 50 days -State Expan- State Expan- State Expan-of sion of sion of sion Samples cell~ ratio cells ratio cells ratio , .... .
,Example 7Good 31 Good 31 Good 31 Example 8 Good 32 Good 32 Good 31 _ . _ Comparative &ood 26 Poor 5 Poor 3 Example 5 Good 29 Poor 20 Poor 15 ~;
' '' The shaped articles obtained in the above examples ~ere examined for gel content immediately before foaming ¦ 15 and after foaming. The results are shown in Table 3 below.
The method of measuring the gel content was as defined here-inabove.
.1 , .
. ~
Table 3 Immediately After stand- After stand-after pre- ing for i;~g for paration 6 days 14 day~
Before AfterBeforeAfter Before ¦ After foam-foam- foam-foam-foam- foam-Samples inging inging ing ing Exampleq 1 063.o 1.565.o 4.0 6~.. 3 2 059. 0 58-3 1.5 59.5 3 060~5 561.3 34.5 65.8 4 055~3 054.6 1.5 56.3 o58-3 1.559.5 6.o 61.2 6 060.0 1.558.5 1.5 58.5 7 071.~ 1.573.51~.5 73~
8 065.8 1.571.519.0 72.0 :
Comparative Example~
1 020.3 021.8 0?,5.0 2 08.5 0 8.o 0 9~3 3 O 53- 45.055.045.&~ 53-8 4 065.o 43.066.349.0 59.5 068.o 11.072.141.0 69.o , -- ~3 --
l 1 Very Very 9 Very 11 .- ~oor 5 poor poor ~ ? Very 3 Very 4 Very 5 :' ~ poor poor poor , . 3 600d ~.7 Poor?~1 Poor 8 .
!::
li The gtate of the cells was e~aluated on a scale of good, fair, poor, and very poor as follows:
Good: Uni~orm fine cell~ occurred all o~er.
- ?.0 -, Fair: Irregular cells partly occurred.
Poor: Irregular cellg occurred all over.
Very poor: The shape collapsed, and the sample assumed a cast ~tate.
Example 7 -~
100 Parts by weight of polyethylene having an average particle size of 30 me~h, a melt index of 4.0 and a density of 0.924 was dry-blended with ~ part~ by .
weight of vinyltriethoxysilane and 0.12 part by weight of dicumyl peroxide~ and the blend was fed into an extruder where it WaY melt-kneaded at 190C. and pelletized. The resulting pellets of modified polyethylene were pulverized to a size of about 30 mesh A composition consisting of 100 parts by weight of the pul~erized modified polyethylene, 15 parts by weight of azodicarbonamide and 1 part by weight of zinc stearate wa~ fed into an extruder, melt-~neaded at 134C. and ex-truded into a ~heet.
Example 8 A sheet was prepared by extrusion in the same way a~ in Example 7 except that 1 part by weight of zinc naph-! thenate wa~ used instead of the zinc stearate ,: .
,~ Comptarati~e Example 4 A sheet was prepared by extru~ion in the same way as in Example 7 except that 1 part by weight of dibutyltin dilaurate was used instead of the zinc stearate.
Com~arative Exam~le 5 A sheet was prepared in the same way as in Example 1 7 exeept that 1 part of cobalt naphtenate was prepared ~, , - ?.1 _ ~ -~ ~ .
- ~ ~, - .
~085S49 instead of the zinc stearate.
Samples of the sheets prepared in Examples 7 and 8 and Comparative Exam~les 4 and 5, either as obtained, after standing for 7 days, or after standin$ for 50 days, were each allowed to stand in a hot air heating chamber held at ~30C. for about 3 minutes.
The expansion ratio and the state of the cells were determined ~ith regard to all the foams obtained, and the results are shown in Table ?.. The determinations were made by the same methods as described hereinabove.
Table 2 Immediately After stand- After stand-after pre- ing for ing for parati on 7 days 50 days -State Expan- State Expan- State Expan-of sion of sion of sion Samples cell~ ratio cells ratio cells ratio , .... .
,Example 7Good 31 Good 31 Good 31 Example 8 Good 32 Good 32 Good 31 _ . _ Comparative &ood 26 Poor 5 Poor 3 Example 5 Good 29 Poor 20 Poor 15 ~;
' '' The shaped articles obtained in the above examples ~ere examined for gel content immediately before foaming ¦ 15 and after foaming. The results are shown in Table 3 below.
The method of measuring the gel content was as defined here-inabove.
.1 , .
. ~
Table 3 Immediately After stand- After stand-after pre- ing for i;~g for paration 6 days 14 day~
Before AfterBeforeAfter Before ¦ After foam-foam- foam-foam-foam- foam-Samples inging inging ing ing Exampleq 1 063.o 1.565.o 4.0 6~.. 3 2 059. 0 58-3 1.5 59.5 3 060~5 561.3 34.5 65.8 4 055~3 054.6 1.5 56.3 o58-3 1.559.5 6.o 61.2 6 060.0 1.558.5 1.5 58.5 7 071.~ 1.573.51~.5 73~
8 065.8 1.571.519.0 72.0 :
Comparative Example~
1 020.3 021.8 0?,5.0 2 08.5 0 8.o 0 9~3 3 O 53- 45.055.045.&~ 53-8 4 065.o 43.066.349.0 59.5 068.o 11.072.141.0 69.o , -- ~3 --
Claims (31)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A foamable and crosslinkable polyethylene composition compris-ing (a) modified polyethylene obtained by chemically bonding a silane compound containing at least one unsaturated group to polyethy-lene in the presence of a radical generator, (b) zinc stearate as the silanol condensation catalyst, and (c) azodicarbonamide as heat-decomposable blowing agent, said in-gredients (a), (b) and (c) having been melt-kneaded with one another at a temperature lower than the decomposition tempera-ture of the heat-decomposable blowing agent.
2. The composition of claim 1 which has a gel content of not more than 40% by weight,
3. The composition of claim 1 comprising 100 parts by weight of polyethylene, 0,01 to 1,5 parts by weight of said radical generator, 0.5 to 10 parts by weight of the silane compound, 0.01 to 5 parts by weight of said zinc stearate, and 3 to 30 parts by weight of the heat-decomposable blowing agent.
4. The composition of claim 1 wherein said silane compound is a member selected from the group consisting of vinyltrimethoxysilane and vinyl-triethoxysilane.
5. The composition of claim 1 wherein said radical generator has a half life of not more than 3 minutes at a temperature between the melting temperature of the polyethylene and 150°C.
6. The composition of claim 5 wherein said radical generator is a member selected from the group consisting of tert-butylperoxy pivalate, di-cumyl peroxide, tert-butylperoxy 2-ethyl hexanoate, tert-butyl peracetate, tert-butylperoxy isobutyrate benzoyl peroxite and lauroyl peroxide.
7. The composition of claim 1 wherein said heat-decomposable blow-ing agent has a decomposition temperature of 170° to 220°C.
8. The composition of claim 7 wherein said heat-decomposable blow-ing agent is a member selected from the group consisting of azodicarbonamide, dinitrosopentamethylene tetramine, benzenesulfonyl hydrazide and toluene-sulfonyl hydrazide.
9. The composition of claim 1 which further includes a chain trans-fer agent.
10. The composition of claim 9 wherein said chain transfer agent is dodecyl mercaptan.
11. The composition of claim 9 wherein the amount of said chain transfer agent is 0,01 to 0.5 part by weight per 100 parts by weight of the polyethylene.
12. The composition of claim 1 comprising 100 parts by weight of polyethylene, 0,1-1,0 parts by weight of said radical generator, 0,5-10 parts by weight of the silane compound, 0,1-3,0 parts by weight of said zinc stea-rate, ant 10-20 parts by weight of the heat-decomposable blowing agent, said silane compound being a member selected from the group consisting of vinyl-trimethoxysilane and vinyltriethoxysilane and said radical generator being a member selected from the group consisting of tert-butylperoxy pivalate, di-cumyl peroxide, tert-butylperoxy 2-ethyl hexanoate, tert-butylperacetate, tert-butylperoxy isobutyrate, benzoyl peroxide and lauroyl peroxide, said composition having a gel content of not more than 20% by weight,
13. The composition of claim 11 wherein the amount of said chain transfer agent is 0.03-0.1 parts by weight per 100 parts by weight of the polyethylene.
14. A process for preparing crosslinked polyethylene foams, which comprises melt-kneading (a) modified polyethylene obtained by chemically bond-ing a silane compound containing at least one unsaturated group to polyethy-lene in the presence of a radical generator, (b) zinc stearate as the silanol condensation catalyst and (c) azodicarbonamide as a heat-decomposable blow-ing agent at a temperature below the decomposition temperature of the heat-decomposable blowing agent, shaping the kneaded mixture, and heating the shaped article to a temperature above the decomposition temperature of the heat-decomposable blowing agent to expand and crosslink the shaped article.
15. Crosslinked polyethylene foams prepared by the process of claim 14.
16. The polyethylene foams of claim 15 which are in the form of a sheet, rod, cylinder, board or block.
17. A process for preparing a foamable and crosslinkable polyethy-lene composition, which comprises melt-kneading (a) modified polyethylene ob-tained by chemically bonding a silane compound containing at least one un-saturated group to polyethylene in the presence of a radical generator, (b) zinc stearate as the silanol condensation catalyst ant (c) azodicarbonamide as heat-decomposable blowing agent at a temperature lower than the decomposi-tion temperature of the heat-decomposable blowing agent.
18. The Process of claim 17 wherein said silane compound is a mem-ber selected from the group consisting of vinyltrimethoxysilane and vinyl-triethoxysilane.
19. The process of claim 17 wherein the amount of the silane com-pound is 0.5 to 10 parts by weight per 100 parts by weight of the polyethy-lene.
20. The process of claim 17 wherein said radical generator has a half life of not more than 3 minutes at a temperature between the melting temperature of the polyethylene and 150°C.
21. The process of claim 20 wherein said radical generator is a mem-ber selected from the group consisting of tert.-butylperoxy pivalate, dicumyl peroxide, tert.-butyl-peroxy 2-ethyl hexanoate, tert.-butyl peracetate, tert.-butylperoxy isobutyrate, benzoyl peroxide and lauroyl peroxide.
22. The process of claim 17 wherein the amount of the radical gene-rator is 0.01 to 1.5 parts by weight per 100 parts by weight of the poly-ethylene.
23. The process of claim 17 wherein the amount of said zinc stearate is 0.01 to 5 parts by weight per 100 parts by weight of the polyethylene.
24. The process of claim 17 wherein said heat-decomposable blowing agent has a decomposition temperature of 170° to 220°C.
25. The process of claim 24 wherein said heat-decomposable blowing agent is a member selected from the group consisting of azodicarbonamide, dinitrosopentamethylene tetramine, benzenesulfonyl hydrazide and toluene-sulfonyl hydrazide.
26. The process of claim 17 wherein the amount of the heat-decom-posable blowing agent is 3 to 30 parts by weight per 100 parts by weight of the polyethylene.
27. The process of claim 17 wherein a chain transfer agent is further kneaded into the mixture.
28. The process of claim 27 wherein the chain transfer agent is dodecyl mercaptan.
29. The process of claim 27 wherein the amount of the chain transfer agent is 0,01 to 0,05 part by weight per 100 parts by weight of the polyethy-lene.
30. The process of claim 17 wherein the melt-kneading is carried out by means of an extruder.
31. The process of claim 17 wherein components (a), (b) and (c) are melt-kneaded at a temperature in the range of from 110° to 150°C.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP33,763/75 | 1975-03-20 | ||
| JP50033763A JPS51109069A (en) | 1975-03-20 | 1975-03-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1085549A true CA1085549A (en) | 1980-09-09 |
Family
ID=12395461
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA248,315A Expired CA1085549A (en) | 1975-03-20 | 1976-03-19 | Foamable and crosslinkable polyethylene composition, process for its production, and process for producing crosslinked polyethylene foams using said composition |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS51109069A (en) |
| CA (1) | CA1085549A (en) |
| DE (1) | DE2611491C3 (en) |
| FR (1) | FR2304644A1 (en) |
| GB (1) | GB1541271A (en) |
| IT (1) | IT1058629B (en) |
| NL (1) | NL7602918A (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1575961A (en) * | 1977-09-07 | 1980-10-01 | Sekisui Chemical Co Ltd | Foamable compositions and their use in preparing foams |
| JPS559611A (en) * | 1978-07-05 | 1980-01-23 | Mitsubishi Petrochem Co Ltd | Cross-linkable polyethylene resin composition |
| DE3129515C2 (en) * | 1980-07-29 | 1986-07-24 | Hitachi Chemical Co., Ltd., Tokio/Tokyo | Foamable styrene resin composition and process for its production |
| JPS581530A (en) * | 1981-06-28 | 1983-01-06 | Dainichi Nippon Cables Ltd | Method for continuously preparing crosslinked polyolefin tubular body |
| FI70916C (en) * | 1983-11-04 | 1986-10-27 | Neste Oy | MEDICAL UPHOLSTERY SHEETS WITH A SILK TV POLYOLFINSKUMOCH FOERFARANDE FOER FRAMSTAELLNING AV DETTA |
| CH667659A5 (en) * | 1984-02-03 | 1988-10-31 | Neste Oy | MODIFIED POLYOLEFIN. |
| US4734440A (en) * | 1984-12-21 | 1988-03-29 | Union Carbide Corporation | Foamable compositions |
| DE4107665A1 (en) * | 1991-03-09 | 1992-09-10 | Basf Ag | PARTLY NETWORKED PLASTIC MATERIAL FROM PROPYLENE AND ETHYLENE POLYMERS |
| DE19637602A1 (en) * | 1996-09-16 | 1998-03-26 | Fritz Hans Gerhard Prof Dr | Polypropylene foam films or sheets |
| DE19831278A1 (en) | 1998-07-13 | 2000-01-27 | Borealis Ag | Heterophase polyolefin alloys |
| WO2008070022A1 (en) * | 2006-12-04 | 2008-06-12 | Ingenia Polymers Inc. | Cross-linked polyolefin foam |
Family Cites Families (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS556051B2 (en) * | 1972-01-18 | 1980-02-13 | ||
| GB1406680A (en) * | 1972-10-10 | 1975-09-17 | Dow Corning Ltd | Crosslinking process |
-
1975
- 1975-03-20 JP JP50033763A patent/JPS51109069A/ja active Pending
-
1976
- 1976-03-18 IT IT21393/76A patent/IT1058629B/en active
- 1976-03-18 DE DE2611491A patent/DE2611491C3/en not_active Expired
- 1976-03-19 CA CA248,315A patent/CA1085549A/en not_active Expired
- 1976-03-19 NL NL7602918A patent/NL7602918A/en not_active Application Discontinuation
- 1976-03-19 GB GB11293/76A patent/GB1541271A/en not_active Expired
- 1976-03-19 FR FR7608104A patent/FR2304644A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| FR2304644B1 (en) | 1980-05-09 |
| FR2304644A1 (en) | 1976-10-15 |
| NL7602918A (en) | 1976-09-22 |
| DE2611491B2 (en) | 1979-04-19 |
| DE2611491A1 (en) | 1976-09-23 |
| IT1058629B (en) | 1982-05-10 |
| DE2611491C3 (en) | 1980-01-10 |
| GB1541271A (en) | 1979-02-28 |
| JPS51109069A (en) | 1976-09-27 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4160072A (en) | Foamable and crosslinkable polyethylene composition, process for its production, and process for producing crosslinked polyethylene foams using said composition | |
| CA1247816A (en) | Lightly crosslinked linear olefinic polymer foams and process for making | |
| US5532282A (en) | Polyolefin-based composition for rotational molding | |
| CA1056550A (en) | Foamed plastics of resin compositions comprising pullulan type resins and thermoplastic resins and process for producing the same | |
| US4554293A (en) | Lightly crosslinked linear olefinic polymer foam blends and process for making | |
| EP1188785B1 (en) | Polyolefin foam and polyolefin resin composition | |
| CA1085549A (en) | Foamable and crosslinkable polyethylene composition, process for its production, and process for producing crosslinked polyethylene foams using said composition | |
| US4581383A (en) | Lightly crosslinked linear olefinic polymer foam blends and process for making | |
| EP0054183B1 (en) | Ethylene-chlorotrifluoroethylene copolymer foam | |
| US3491032A (en) | High density polyolefin foams | |
| CA1197049A (en) | Fast-curing foamable composition based on ethylene terpolymers | |
| CA1247817A (en) | Process for the production of closed celled foamed shaped bodies formed of cross-linked polyolefins | |
| US4391922A (en) | Blowing agents as curatives for ethylene/carbon monoxide copolymers | |
| US4369257A (en) | Foaming synthetic resin compositions stabilized with certain naphthyl amine compounds | |
| US4701472A (en) | Expandable polyvinyl chloride resin composition and foamed sheet prepared from the same | |
| US4391923A (en) | Low density closed-cell foamed articles from ethylene copolymer/vinyl or vinylidene halide blends | |
| US3544490A (en) | Ethylene polymer foam compositions and process for making same | |
| EP0138265B1 (en) | Process for the production of expanded reticulated polyethylene | |
| US4394459A (en) | Fast-curing foamable composition based on ethylene terpolymers | |
| US4434253A (en) | Low density closed-cell foamed articles from ethylene copolymer/vinyl or vinylidene halide blends | |
| US4501711A (en) | Process and composition for producing open-cell cross linked polyolefin film | |
| JPH10259268A (en) | Crosslinked polyethylene resin foam and its production | |
| SU474156A3 (en) | The method of producing foams | |
| CA1228200A (en) | Heat-foamable olefinic resin composition and process for production of olefinic resin foam from said composition | |
| CA1111200A (en) | Process for preparing foamed and crosslinked shaped articles having improved heat-sealability and foamable and crosslinkable polyethylene resin composition used therefor |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |