Patent Application: US-99897307-A

Abstract:
the invention pertains to a process for producing a cross - linked polyolefin foam in a continuous process using standard processing equipment without using a moisture cross - linking step after processing . in this method , a vinyl functional silane compound is melt grafted onto a low density polyethylene in the presence of a free radical generator . the resulting silane grafted polyethylene resin is mixed and melted with a blowing agent in a continuous process in the presence of water to form a vinyl functional silane foam .

Description:
as a result of a broad investigation , it has been found that a mixture of a silane grafted polyethylene resin , polyethylene resin , silanol condensation catalyst masterbatch , a blowing agent and / or a water releasing agent forms a silane cross - linking expandable polyolefin foam . ( a ) 10 - 99 . 5 % by weight of a silane grafted polyethylene resin obtained by melt extruding i ) a low density polyethylene with ii ) 0 . 1 - 5 % by weight of a vinyl functional silane compound and iii ) 0 . 05 - 0 . 5 % by weight of a free radical generator ; ( b ) 90 - 0 % by weight of a low density polyethylene resin as described above ; ( c ) 0 - 5 % by weight of a silanol condensation catalyst masterbatch obtained by melt extruding i ) 95 % by weight of a low density polyethylene ii ) 5 % by weight of a silanol condensation catalyst and optionally iii ) 0 . 01 - 1 % by weight of a primary or secondary antioxidant ; and ( d ) 0 . 5 - 20 % by weight of a chemical or physical blowing agent . if the blowing agent does not release water on decomposition , 0 - 10 % by weight of a water releasing additive is required . wherein for item ( c ) above , the silanol condensation catalyst may be a higher or lower % by weight to produce a masterbatch of different silanol condensation catalyst % by weight . if so , the corresponding letdown of said masterbatch can be used according to the specified range of 0 - 5 % by weight into the polyethylene resin . weight % is calculated by dividing the weight of a reagent by the total weight of a mixture to which it is added subsequent to the addition of the reagent . for example , adding 1 gram of a reagent a to 99 grams of a reagent b , thereby forming 100 grams of a mixture a + b would constitute adding 1 weight % of the reagent a to the mixture . weight % is equivalent to % by weight . the low density polyethylene used herein can be any materials falling within the scope of a low density polyethylene having a melt index of 0 . 1 - 100 g / 10 min and a density of 0 . 870 - 0 . 945 g / cm 3 , most preferably a melt index of 0 . 1 - 2 and a density of 0 . 870 to 0 . 920 g / cm 3 . the low density polyethylene can be attained through various polymerization methods such as gas phase method , solution method , and suspension polymerization method under medium , low or high - pressure conditions , using ethylene and an α - olefin in the presence of various catalysts such as ziegler - based catalysts , metallocene - based catalysts , vanadium - based catalysts , and chromium - based catalysts . examples of the α - olefin include α - olefins having 3 - 12 carbon atoms such as propylene , butene - 1 , pentene - 1 , octene - 1 , 4 - methylpentene - 1 , 4 - methylhexene - 1 , 4 , 4 - di - methylpentene - 1 , nonene - 1 , decene - 1 , undecene - 1 , and dodecene - 1 . the vinyl functional silane compound used to graft onto the low density polyethylene is represented by the formula : where r is a monovalent olefinic unsaturated hydrocarbon group , y is a hydrolysable organic group , and r &# 39 ; is a monovalent hydrocarbon group other than aliphatic unsaturated hydrocarbons or is identical with y . the presumed purpose of the vinyl functional silane is to create a crosslinking point among the low density polyethylene molecular chains . examples of silane compounds may include vinyl trimethoxysilane , vinyltriethoxysilane , vinyl tributoxysilane , allyl trimethoxysilane and allyl triethoxysilane . the amount of vinyl functional silane added is approximately 0 . 1 to 5 weight % and most preferably approximately 0 . 1 to 3 weight %. the free radical generator used acts as an initiator of the silane graft reaction . examples of free radical generators that may be used include organic peroxides such as dicumyl peroxide , di - t - butyl peroxide , t - butylcumyl peroxide and dibenzoyl peroxide . the amount of free radical generator added is approximately 0 . 05 to 0 . 5 weight % and most preferably approximately 0 . 05 to 0 . 25 weight %. the silane grafted polyethylene can be processed using conventional extrusion or melt mixing methods including a brabender mixer , banbury mixer , single screw or twin screw extruders . most preferably the vinyl functional silane and organic peroxide used is vinyltrimethoxy silane and dicumyl peroxide . the silanol condensation catalyst masterbatch consists of low density polyethylene , an organotin catalyst , and an antioxidant . the organotin catalyst acts as an initiator for the cross linking reaction in the presence of water . organotin catalysts include dibutyltin dilaurate , dibutyltin oxide , dibutyltin diacetate , butyl stannoic acid , dioctyltin dilaurate , dioctyltin maleate , butyltin tris ( 2 - ethylhexoate ), and hydrated monobutyltin oxide . the antioxidant used in the catalyst masterbatch may include all forms of primary phenolic antioxidants , secondary phosphate or thioester antioxidants or a combination of primary and secondary antioxidants . the catalyst masterbatch can be processed using conventional extrusion or melt mixing methods including a brabender mixer , banbury mixer , single screw or twin screw extruders . the blowing agent used generates a gas suitable to foam the silane grafted polyethylene resin . the blowing agent may be a chemical or physical blowing agent . the chemical blowing agent may be organic or inorganic . the organic blowing agent decomposes during melt processing to generate a gas resulting in subsequent foaming and also generates an acidic compound and or water on decomposition at foaming to promote moisture cross linking of the silane grafted polyethylene resin . examples of organic blowing agents include azo compounds ( azodicarbonamide , azohex - hydrobenzonitrile , diazoaminobenzene ), nitroso compounds ( n , n ′- dinitrosopentamethylenetetramine , n , n ′- dinitroso - n , n ′- dimethylphthalamide ) and diazide compounds ( terephthaldiazide , p - t - butylbenzazide ). most preferably , an inorganic chemical blowing agent is used in combination with an organic acid and surfactant in a masterbatch formulation . the inorganic agent used as a blowing agent may include sodium bicarbonate , ammonium bicarbonate and ammonium carbonate . the blowing agent masterbatch consists of approximately 60 - 80 % by weight of a low melting point polymer carrier resin , approximately 2 - 10 % by weight of an organic surfactant , approximately 5 - 20 % by weight of an organic acid and approximately 5 - 20 % by weight of an inorganic blowing agent . the low melt carrier resin used herein can be any materials falling within the scope of having a melting point range of approximately 40 - 105 ° c ., most preferably a melting point range of approximately 80 - 100 ° c . the carrier resin may include acrylate copolymers including vinyl , butyl , ethyl and methyl acrylates . the organic surfactant used are long chain fatty acid amides such as behenamide , erucamide , oleamide , stearamide , oleyl palmitamide , stearyl erucamide , ethylene bis - stearamide and ethylene bis - oleamide . the organic acid used reacts with the inorganic blowing agent generating a gas and an acidic substance and / or water as a decomposition product at foaming to promote moisture crosslinking of a silane graft group . examples of organic acids include citric , stearic , oleic , phthalic and maleic acids . the blowing agent masterbatch can be processed using conventional extrusion or melt mixing methods including a brabender mixer , banbury mixer , single screw , or twin screw extruders . alternatively , a physical blowing agent in combination with a water releasing additive can be used . physical foaming agents include low molecular weight organic compounds including c 1 - c 6 hydrocarbons such as acetylene , propane , propene , butane , butene , butadiene , isobutane , isobutylene , cyclobutane , cyclopropane , ethane , methane , ethene , pentane , pentene , cyclopentane , pentene , pentadiene , hexane , cyclohexane , hexene , and hexadiene , c 1 - c 5 organohalogens , c 1 - c 6 alcohols , c 1 - c 6 ethers , c 1 - c 5 esters , c 1 - c 5 amines , ammonia , nitrogen , carbon dioxide , neon , or helium . the preferred physical foaming agent concentration prior to expanding the foam is between 0 . 1 and 20 weight %. the water releasing compounds include compounds which release water at normal processing temperatures where foaming and crosslinking can occur simultaneously . examples include alumina trihydrate , hydrated calcium sulfate , hydrotalcite and the like . water may also be directly added to the process as a source for moisture . the invention may comprise any combination of a blowing agent , either physical or chemical , as well as water molecules , whether chemically released or directly added to the process . the preparation of the silane crosslinking polyolefin foam can be processed continuously using conventional extrusion methods including single or twin screw extruders . the silane crosslinking foam has a gel fraction of approximately 1 % by weight or more , preferably approximately 1 - 10 % by weight . the gel fraction was measured by the following technique . a sample of the silane crosslinked polyolefin foam was immersed in boiling xylene at approximately 144 ° c . and refluxed for around 16 hours . the samples were dried in an oven at approximately 170 ° c . for around 2 hrs . the gel fraction was calculated by dividing the residual weight by the weight of the foam before immersion . the invention is described in more detail in the following examples . it is understood that the invention is not limited thereto . 3 wt % of vinyltrimethoxysilane ( vtms ) is melt grafted onto a low density polyethylene ( ldpe ) ( lfy 819a — nova chemicals ) using 0 . 05 wt % of dicumyl peroxide as a catalyst . melt grafting is achieved via a zsk - 30 ( coperion ) twin screw extruder with a melt temperature of 180 ° c . and screw speed of 400 rpm . a 50 gram foam masterbatch consisting of 76 wt % ethylene vinyl acetate ( eva 2030 — at plastics ), 10 wt % air milled sodium bicarbonate ( usp grade 3 ), 10 wt % citric acid and 4 wt % behenamide is prepared in a brabender mixer . mixing conditions are 100 ° c . for 1 minute . the masterbatch is subsequently cold pressed at 70 ° f . 86 . 4 wt % ldpe , 9 . 6 wt % of a 3 % grafted vtms ldpe and 4 wt % foam masterbatch are dry blended , fed and extruded through a blown film line . the resultant cross linked foam has a gel content of 2 . 6 % and foam density of 0 . 576 g / cc . 3 wt % of vinyltrimethoxysilane ( vtms ) is melt grafted onto a low density polyethylene ( ldpe ) ( lfy 819a — nova chemicals ) using 0 . 05 wt % of dicumyl peroxide as a catalyst . melt grafting is achieved via a zsk - 30 ( coperion ) twin screw extruder with a melt temperature of 180 ° c . and screw speed of 400 rpm . a 50 gram foam masterbatch consisting of 76 wt % ethylene vinyl acetate ( eva 2030 — at plastics ), 10 wt % air milled sodium bicarbonate ( usp grade 3 ), 10 wt % citric acid and 4 wt % behenamide is prepared in a brabender mixer . mixing conditions are 100 ° c . for 1 minute . the masterbatch is subsequently cold pressed at 70 ° f . 96 wt % of a 3 wt % grafted vtms and 4 wt % foam masterbatch are dry blended , fed and extruded through a blown film line . the resultant cross linked foam has a gel content of 51 . 3 % and foam density of 0 . 718 g / cc . examples 3 and 4 demonstrate how the use of a tin catalyst can aid in the cross linking reaction . 1 wt % of vinyltrimethoxysilane ( vtms ) is melt grafted onto a low density polyethylene ( ldpe ) ( lfy 819a — nova chemicals ) using 0 . 05 wt % of dicumyl peroxide as a catalyst . melt grafting is achieved via a zsk - 30 ( coperion ) twin screw extruder with a melt temperature of 180 ° c . and screw speed of 400 rpm . a 50 gram foam masterbatch consisting of 76 wt % ethylene vinyl acetate ( eva 2030 — at plastics ), 10 wt % air milled sodium bicarbonate ( usp grade 3 ), 10 wt % citric acid and 4 wt % behenamide is prepared in a brabender mixer . brabender mixing conditions are 100 ° c . for 1 minute . the masterbatch is subsequently cold pressed at 70 ° f . 96 wt % of a 1 % grafted vtms and 4 wt % foam masterbatch are dry blended , fed and extruded through a blown film line . the resultant cross linked foam has a gel content of 53 . 5 % and foam density of 0 . 714 g / cc . 1 wt % of vinyltrimethoxysilane ( vtms ) is melt grafted onto a low density polyethylene ( ldpe ) ( lfy 819a — nova chemicals ) using 0 . 05 wt % of dicumyl peroxide as a catalyst . melt grafting is achieved via a zsk - 30 ( coperion ) twin screw extruder with a melt temperature of 180 ° c . and screw speed of 400 rpm . a tin catalyst masterbatch is prepared by melt mixing 5 wt % of dibutyl tin dilaurate ( fascat 4020 — arkema ) with 94 . 9 wt % ldpe and 0 . 1 wt % antioxidant ( irganox 1010 - ciba ). melt mixing is achieved via a zsk - 30 ( coperion ) twin screw extruder with a melt temperature of 180 ° c . and screw speed of 300 rpm . a 50 gram foam masterbatch consisting of 76 wt % ethylene vinyl acetate ( eva 2030 — at plastics ), 10 wt % air milled sodium bicarbonate ( usp grade 3 ), 10 wt % citric acid and 4 wt % behenamide is prepared in a brabender mixer . brabender mixing conditions are 100 ° c . for 1 minute . the masterbatch is subsequently cold pressed at 70 ° f . 91 . 2 wt % of a 1 % grafted vtms , 4 . 8 wt % of a tin catalyst masterbatch and 4 wt % foam masterbatch are dry blended , fed and extruded through a blown film line . the resultant cross linked foam has a gel content of 57 . 1 % and foam density of 0 . 658 g / cc . example 5 demonstrates how the crosslinking reaction occurs in situ during processing and does not require additional moisture curing as in typical cross - linking applications of polyethylene . 3 wt % of vinyltriethoxysilane ( vtes ) is melt grafted onto a low density polyethylene ( ldpe ) ( lfy 819a — nova chemicals ) using 0 . 05 wt % of dicumyl peroxide as a catalyst . melt grafting is achieved via a zsk - 30 ( coperion ) twin screw extruder with a melt temperature of 180 ° c . and screw speed of 300 rpm . a tin catalyst masterbatch is prepared by melt mixing 5 wt % of dibutyl tin dilaurate ( fascat 4020 — arkema ) with 94 . 9 wt % ldpe and 0 . 1 wt % antioxidant ( irganox 1010 — ciba ). melt mixing is achieved via a zsk - 30 ( coperion ) twin screw extruder with a melt temperature of 180 ° c . and screw speed of 300 rpm . a 50 gram foam masterbatch consisting of 76 wt % ethylene vinyl acetate ( eva 2030 — at plastics ), 10 wt % air milled sodium bicarbonate ( usp grade 3 ), 10 wt % citric acid and 4 wt % behenamide is prepared in a brabender mixer . brabender mixing conditions are 100 ° c . for 1 minute . the masterbatch is subsequently cold pressed at 70 ° f . 91 . 2 wt % of a 3 % grafted vtes , 4 . 8 wt % of a tin catalyst masterbatch and 4 wt % foam masterbatch are dry blended , fed and extruded through a blown film line . the gel content of the foam was 69 . 7 %. the foam was treated in a hot water bath at 80 ° c . for a 24 hour period . after 5 hours a sample of foam was pulled . the gel content of the foam after 5 hours was 66 . 7 %. after 24 hours , a sample of foam was pulled from the bath . the gel content of the foam after 24 hours was 65 . 2 %. the following references and patents , to the extent that they provide exemplary procedural or other details supplementary to those set forth herein , are specifically incorporated herein by reference . u . s . patent documents u . s . pat . no . 4 , 186 , 068 u . s . pat . no . 3 , 646 , 155 u . s . pat . no . 4 , 870 , 111 u . s . pat . no . 5 , 589 , 519 u . s . pat . no . 5 , 844 , 009 u . s . pat . no . 4 , 591 , 606 u . s . pat . no . 6 , 812 , 262 u . s . pat . no . 5 , 844 , 009 u . s . pat . no . 4 , 591 , 606 u . s . pat . no . 6 , 812 , 262 international patent documents british patent 1 , 286 , 460 japanese patent a - 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