CA2063478A1

CA2063478A1 - Scorch extending curing/crosslinking compositions

Info

Publication number: CA2063478A1
Application number: CA002063478A
Authority: CA
Inventors: Michael F. Novits; Chester J. Kmiec; Edward P. Hibbard
Original assignee: Michael F. Novits; Chester J. Kmiec; Edward P. Hibbard; Atochem North America, Inc.; Elf Atochem North America, Inc.
Current assignee: Arkema Inc
Priority date: 1991-03-22
Filing date: 1992-03-19
Publication date: 1992-09-23
Also published as: US5876624A; DE69226108T2; EP0504920A3; MX9201255A; US5869580A; US5849214A; JPH05209085A; DE69226108D1; EP0504920B1; US6765058B1; EP0504920A2; US5912304A; JP3182199B2; ATE168123T1; US6197213B1; BR9200992A; US6069208A

Abstract

ABSTRACT OF THE DISCLOSURE

A crosslinkable composition of a polymeric thermoplastic and/or elastomeric material which is susceptible to scorching when processed at elevated temperatures, prior to crosslinking, in the presence of a free radical initiator, is protected against such scorching by the incorporation therein of a mixture of at least one hydroquinone compound and a sulfur accelerator.
this mixture may also contain at least one monomeric allylic, methacrylic, acrylic or diene type coagent. The mixture exhibits a synergistic effect resulting in improved scorch protection for peroxide cured systems when compared with the protection afforded by the components singly.

Description

2~3~78 SCORCH EXTENDING CURING/CROSSLINKING COMPOSITIONS

(IR 3177) BACKGROUND OF THE INVENTION

This invention relate~ to the prevention of scorchlng prior to cros~linking of a peroxide or azo compound crosslinkable thermoplastic and/or elastomeric composition.
A major difficulty in using organic peroxides or azo compounds in cro~slinking (curing) elastomeric and thermoplastic materials applications is that they may initiate premature crosslinking (i.e. scorch) during compounding and/or processing prior to the actual phase in the overall process when curing is desired. With conventional methods of compounding, such a~ milling, Banbury, or extrusion, scorch occurs when the time-temperature relationship results in a condition where the peroxide or azo initiator undergoes thermal decompositlon, initiating the crosslinking reaction whereby gel particles in the mass of the compounded polymer may be formed. The presence of the~e gel particle~ lead~ to inhomogeneity of the final product.
Exce~sive 3corch reduces the plastic propertie~ of the material so that it can no longer be pr3cessed, re~ulting in the 1088 of the entire batch.
Therefore, it has been widely accepted that the peroxide of choice must have a high enough activation temperature 80 th~t compounding and/or other processing steps can be successfully completed prior to the final curing ~tep. ~hu~ one method of avoiding scorch i~ to uqe an initiator that is characterized by having a high _ 3 _ 2~ 7g 10 hour half-life temperature. The disadvantage to thi~
approach i~ that one subsequently obtains a longer cure time, which results in lower throughput. High cure temperatures can ~e used but this runs into the disadvantaqe of higher energy costs.
A further way of avoiding ~corch is to lower the compounding and/or proce~sing temperature to improve the scorch safety margin of the crosslinking agent. This option however may be somewhat limited in scope depending upon the polymer and/or process involved. In addition, curing at the lower temperature requires longer cure times and results in lower throughput. Prior to the pre~ent lnventLon, certain additLves were incorporated into compo~itions whlch reduced the tendency for ~corchlng. For example, Brltish patent 1,535,039 disclose~ the u~e of organic hydroperoxides as scorch inhibitor~ for peroxide-cured ethylene polymer compo~ition~ U.S. patent 3,751,378 di~close~ the use of N-nltroso diphenylamine or N,N'-dinitro~o-para-phenylamine as retarders incorporated in a polyfunctional acrylate cros~linking monomer for providing long Mooney scorch times in variou~ elastomer formulatlons. U.S.
patent 3,202,648 dlscloses the use of nitrites such as isoamylnitrite, tert-decyl nitrite and others as ~corch inhibitors for polyethylene. U.S. patent 3,954,907 2 1~ 3 ~ g discloses the use of monomeric vinyl compounds as protection agains~ Qcorch. U.S. patent 3,335,124 describes the use of aromatic amines, phenolic compounds, mercaptothiazole compounds, bis(N,N-disubstituted thiocarbonyl)sulfides, hydroquinones and dialkyldithiocarbamate compounds. The use of mixtures of the actLve compounds in preventing scorch is neither taught nor suggested. U.S. patent 4,632,950 di~close~
the use of mixture~ of two metal salts of disubstituted dithiocarbamic acid, wherein one metal salt is based on copper. This reference does not teach the u~e of such mixtures with neat peroxides. For some applications, it is desirable or mandatory to use liquid or neat peroxide~, as described in this current invention. One ~uch application 19 in extruded compounding. A common commercial process technique employs a liquid peroxide which i8 sprayed onto polymer pellets or granules to coat them prior to extrus~on compounding. This can provide increased production efficiency and eliminates physical handling of hazardous compounds. This reference patent teaches that at least one filler must be present. The scorch re~istant sy~tems described in this reference are not effective in polyolefins specifically LDPE, LLDPE, or HDPE. The present invention Ls effective in palyolefin systems. Moreover, this reference doe~ not teach the use of mixtures of hydroquinones and metal salts of disubstituted dithiocarbamic acid.
When employing these prior art methods for extending scorch time, the cure time and/or final crosslink density of the cured composition can be adversely affected, leading to a decrease in productivity and/or product performance. The present invention overcomes the disadvantages of the prior art in that an improvement in scorch at compounding temperatures is achieved without significant impact on the final cure time or crosslink density. Thiq is achieved by incorporation of the cure retarding composition at low additive levelq, there~y limiting the effect on propertie~. In addition, significsnt worch protection is achieved, since the use of the combinatlon of the hydroquinones and a sulfur accelerator of the dithiocarbamate or thluram class result~ ln a synergistic effect on scorch time at the low additive levels employed.
SUMMARY OF THE INVENTION
The present invention provides in a first composition aspect a scorch retarding compositlon comprising a hydroquinone and at least one ~ulfur accelerator.

7 ~

The tangible embodiments of this composition aspect of the invention possess the inherent applied use characteristics of being scorch retarders showing greater effect than equivalent amounts of either component used separately when incorporated into polymeric compositions which are crosslinkable by free radical initiation while not substantially affecting final cure time or properties.
Special mention is made of compositions of the first composition aspect of the invention which additionally comprise a coagent.
The invention al30 provides in a second compo~ition aspect a scorch retardlng, curing/crosslinking compo~ltlon comprlsing a free radical initiator selected from the group consi~ting of organic peroxides, azo compound~ and mlxtures thereof, and the scorch retarding compo~ition of the fir~t compo~ition aspect of the invention.
The tangible embodiments of this second composition aspect of the invention possess the inherent applied use characteri~tics, when blended into conventional thermopla~tic and/or ela~tomeric polymers as a cro~linking agent, of providing improved scorch protection for the blended ~ystem while not substantially affecting final cure times or characteristic~.

2 ~

This invention also provides in a third composition aspect a crosslinkable composition comprising a peroxide or azo compound crosslinkable thermoplastic and/or ela~tomeric polymer, and a scorch retarding curing/crosslinking composition as defined in the second composition aspect of the inventions.
The invention also provides in an improved process for the preparation of a crosslinkable composition comprising a peroxide or azo compound crosslinkable thermoplastic and/or elastomeric polymer and a free radical initiator selected from the group of organic peroxides, azo compounds and mixtures thereof wherein ~aid polymer i8 compounded with said free radical lnitiator, the improvement comprising performing said compounding $n the presencs of a scorch retarding composition of the first composition aspect of the invention.
Special mention i8 made of processes of this process aspect of the invention wherein the scorch retarding composition additionally comprises a coagent.
In the practice of this invention, the preferred blends of hydroquinones and sulfur accelerators exhibit acceptable ~olubillty in the free ~adical initiators when the ~elected free radical initiator is a liquid or low melting so1id. Thus, this new technology w~ll allow for L~ ~ g a pumpable or a meterable homogeneous cros~linking sy~tsm that provides ease of handling and greater worker safety as well as longer compounding times for better mixing due to the improved scorch protection provided.
Where homogenous liquid or low melting solid crosslinking compositions are not normally used ~uch as in rubber compounding, and the selected scorch retarding crosslinking composition is liquid, the hydroquinone, peroxide, sulfur accelerator and optional coagent(s) either as individual portions, or the entire combined ~corch retarding crosslinking composition may be di~persed on an inert filler (preferably an inorganic filler) for ease of addition during compounding such as on a rubber mill. A masterbatch on a polymeric bindar may be used ln the same fashlon for the same purpose.

DETAI~ED DESCRIPTION
The superior scorch resistance for peroxide and azo cros~linkable elastomeric and/or thermoplastic polymeric systems may be obtained by admixing, conveniently by employlng conventional compounding means, with the thermoplastic and/or elastomeric polymer which is desired to be cros01inked, a scorch retarding crosslinking compo~it~on comprising a free radical initiator selected from the group consisting of organic peroxide~, azo compounds and mixture~ thereof, a hydroquinone compound, 2 ~ i 7 ~

at least one sulfur accelerator, and optionally any of the known acrylic, methacrylic or allylic monomers.
The scorch retarding curing/crosslinking composition may preferably be blended into the desired polymer as a S preformed mixture or the individual ingredients thereof may be incorporated into the polymer separately or even as subcombinations of one or more but not all the ingredients. If incorporation a~ individual or subcombinations of ingredients is desired, it is preferred that the hydroquinone, monomers, and/or the sulfur accelerator be blended into the polymer prior to blending of the free radical initiator.

In accordance wlth the preent invention, compounds well known in the art such as azo initiators and/or organlc peroxlde~ (with the exception of hydroperoxides and peroxydicarbonates) which upon thermal decomposition generate free radical~ that facilitate the curing/
cro~alinking reaction may be employed. Of the free radical initiators used as cros~linking agents, the dialkyl pernxides and diperoxyketal initiator~ are preferred. A detailed description of the~e compounds may ~e found in the Encyclopedia of Chemical Technology, 3rd edition, Vol. 17, pp 27-90. (1982) ~l53~A ~i8 In the group of dialkyl peroxide~, the preferred initiators are:
dicumyl peroxide di-t-butyl peroxide t-butyl cumyl peroxide 2,5-dimethyl-2,5-di(t-butylperoxy)-hexane 2,5-dimethyl-2,5-di(t-amylperoxy~)-hexane 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 2,5-dimethyl-2,5-di(t-amylperoxy)hexyne-3 alpha,alpha-di[(t-butylperoxy)-i~opropyl]-benzene di-t-amyl peroxide 1,3,5-tri-[(t-butylperoxy)-isopropyl]benzene 1,3-dimethyl-3-(t-butylperoxy)butanol 1,3-dimethyl-3-(t-amylperoxy) butanol and mlxture~ thereof.
In the group of diperoxyketal initiator~, the preferred lnitiator~ are:
1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane 1,1-di(t-butylperoxy)cyclohexane n-butyl 4,4-di(t-amylperoxy)valerate ethyl 3,3-di(t-butylperoxy)butyrate 2,2-di(t-amylperoxy)propane 3,6,6,9,9-pentamethyl-3-ethoxycarbonylmethyl-1,2,4,5-tetraoxacyclononane;
n-butyl-4,4-b$~(t-butylperoxy)-valerate;

~&3~ ~8 ethyl-3,3-di(t-amylperoxy)-butyrate and mixtures thereof.
Other peroxide, e.g., 00-t-butyl-0-hydrogen monoperoxysuccinate; 00-t-amyl-0-hydrogen-monoperoxysuccinate and/or azo initiators e.g., 2,2~-azobis-(2-acetoxypropane) may also be used to provide a crosslinked polymer matrix. Mixtures of two or more free radical initiators may also be used together a~ tha initiator within the scope of this invention.
Other suitable azo compounds include those described in U.S. Patents 3,862,107 and 4,129,531 which are incorporated herein by reference.
The amount of the scorch retarding crosslinking compo~ition a~pect of this invention to be incorporated in a crosslinkable compo~ition will readily be ~elected by one of skill in the art to be suffLcient to afford the de~ired degree of cros~linking. When the free radical initiator component i~ an organic peroxide, the scorch retarding crosslinking composition may be employed in quantities to provide a concentration of peroxide in the cro~linkable composition ranging from 0.01 to 30 parts by weight, preferably, from 0.01 to 20 part~ by weight, moat preferably from 0.5 to 4.0 part~ by weight for each 100 parts by weight of polymer.

~3~ q8 Sulfur Accelerators Any of the known sulfur accelerators as understood by one of skill in the art to be employed in curing of elastomers are contemplated for use in the practice of ~he invention. One sulfur accelerator class that is suitable for use in the practice of this invention comprise~ metal salts of disubstituted dithiocarbamates.
The metal ~alts of disubstituted dithiocarbamic acid, which are suitable in the practice of this invention , may be represented by the structure:

X-[S-C-N ]n whereln X 1~ an ion derived from a metal selected from the group consi~ting of nickel, cobalt, ironl chromium, tin, zinc, copper, lead, bismuth, cadmium, ~elenium, and tellurium, n may vary from 1 to 6 and is equal to the formal valence of the metsl, R1 and R2 are independently alkyl of 1 to 7 carbon atoms.
Example~ of the metal salts of disubstituted dithiocarbamic acid ares bi~muth dimethyldithiocarbamate cadmium diamyldithlocarbamate cadmium diethyldithiocarbamate copper dimethyldithiocarbamate lead diamyldithiocarbamate ~ t~

lead dimethyldithiocarbamate selenium dimethyldithiocarbamate tellurium diethyldithiocarbamate zinc diamyldithiocarbamate S zinc diethyldithiocarbamate zinc dimethyldithiocarbamate selenium dimethyldithiocarbamate A second sulfur accelerator cla~s that is also sultable for use in the practice of thi~ invention comprises the thiurams. Thiuram accelerators are prepared from secondary amines and carbon disulfide.
They may be repre3ented by the following structure:

\ ~ I /
N-C-Sn-C-N

wherein R3 i~ an alkyl group of 1 to 7 carbon atoms and n may have a positlve value from greater than zero up to 6.
20 Examples of thluram type accelerators lnclude:
tetrabutylthluram disulflde tetraethylthiuram disulfide tetramethylthiuram disulfide tetramethylthiuram mono~ulfide These cla~e~ of sulfur accelerators as well as other~suitable classe~ of sulfur accelerator3 such as the sulfenamides, thiazoles, thioureas and xanthateR are described in further detail in The Vanderbilt Rubber 2 ,~` 7 3 Handbook, pp 339-380. The sulfur accelerators described therein encompass the classes of sulfur compounds which would be comprehended by one of skill in the art of curing elastomeric polymers as sulfur accelerators.
Simple mercaptans of the formula RSH are not included in this class of sulfur accelerators.
Hydroquinones The hydroquinones which are suitable in the practice of this invention are described in detail in the Encyclopedia of Chemical Technology, Third Edition, vol.
19 pp 572-606. Examples of hydroquinones particularly useful in the practice of this invention are:
hydroquinone hydroquinone di(beta-hydroxyethyl)ether hydroquinone monomethyl ether mono-tert-butyl hydroquinone di-t-butyl hydroquinone dl-t-~myl hydroquinone The sulfur accelerator and the hydroquinone are employed in amounts that are sufficient to achieve the desired balance in cure characteristics. The weight ratio of hydroquinone compound to sulfur accelerator is from 1:50 to 500sl preferably from ls25 to 250:1 more preferably from 1:25 to 25:1, still more preferably from 1:10 to 10:1 and most preferably from 1:1 to 5:1. The 2 ~ 7 8 weight ratio of this blend to peroxide can range from 0.5:100 to 1:2, preferably from 1:100 to 1:2, more preferably from 1:100 to 1:4 and still more preferably from 1:25 to 1:20.

_ _ ///

/

Coagents Various vinyl and/or allyl monomer~ are used to enhance cros~linking and as such are often called crosslinking coagents. The effective coagents are generally difunctional or polyfunctional vinyl and/or allyl monomers.
The use of the~e monomers or crosslinking coagents in the practice of this invention provides a number of advantages:
1) The extent of crosslinking as mea~ured by MH, the maximum torque shown by an oscillating disc rheometer i~ enhanced or maintained in the final cured polymer when scorch retarding compared with formulations not employing coagento.
2) ~he solubility and ease of preparation of ~olution~ of the peroxide, quinone and sulfur accelerator are ~urpri~lngly facilitated;
3) An important and unexpected enhanced phase and color ~tability i8 provided in scorch retarding curing/cro~slinking peroxide solution formulations contemplated by the second compo~ition of the invention.

4) It ha~ surprisingly been found, for those compositions tested, when ingredient~ are combined in the proper order, the speed and ease of dissolution and thus the preparatlon of the second compositlon aspect compositions of the invention are made more rapid and easier. This order is first coagent, second hydroquinone, third sulfur accelerator, last peroxide or azo compound.
~lends of coagents may also be used in the practice of this invention wherein monofunctional monomers may be used in combination with the di- or poly-vinyl and/or allyl monomers.
Representative monomers include but are not limited to the following: methyl methacrylate, lauryl methacrylate, allyl methacrylate, trimethylol propane triacrylate, triallyl cyanurate, triallyl isocynaurate, trlallyl phosphate, tetraallyloxyethane, allyldiglycol, carbonate, triallyltrimellitate, triallylcitrate, diallyl adlpate, dlallylterephthalate, diallyl oxalate, diallyl fumarate, ethylene glycol dimethacrylate, 2-hydroxyethyl methacrylate.
Other polyfunctional vinylic compound~ such aq liquld 1,2 - polybutadiene may also be used.
Particular preferred monomers are selected from:
allyl methacrylste, triallylcyanurate, triallyltrimellitate, triallylisocyanurate, allydiglycolcarbonate, diallyl oxalate, methyl methacrylate and blends thereof.

2~3~78 The monomeric compounds, when incorporated into any of the composition aspects of the invention, may be used in ratios of 100:1 to 1:100 pref~rably 50:1 to 1:50, most preferably 10:1 to 1:10 with respect to the combined amount of sulfur accelerators and quinones present.
Polyme~s The thermoplastic and/or elastomeric polymers encompassed in the pre~ent invention may be defined as those natural or qynthetic polymers which are thermoplastic and/or elastomeric in nature, and which can be crosslinked (cured) through the action of a croselinking agent. Rubber World, ~Ela3tomer Cros~linking with Diperoxyketals," October, 1983, pp.26-32, and Rubber and Plastic Newe, "Organic Peroxides for Rubber Cros~linking," September 29, 1980, pp. 46-50, describe the crosslinking action and crosslinkable polymer~. Polyolefin~ suitable for use in thle lnvention are deecribed in Modern Plastics ~ncyclopedia 89 pp 63-67, 74-75. Illu~trative polymers include linear low density polyethylene, low density polyethylene high density polyethylene, chlorinsted polyethylene, ethylene-propylene terpolymers, ethylene vlnyl acetate ethylene-propylene copolymers, silicone rubber, chlorosulfonated polyethylene, fluoroelastomers.

In addition, blends of two or more polymers may be employed. The polymers described above and the crosslinkable compositions prepared therefrom may contain variou~ other additives known to those s~illed in the art including fillers such as carbon black, titanium dioxide, and the alkaline earth metal carbonates. Monomeric co-agent3 such as triallylcyanurate, allyldiglycolcarbonate, triallylisocyanurate, trimethylolpropane diallylether, trimethylolpropane trimethacrylate, various allylic compounds, methacrylates and acrylate compound~ may also be added separately to the various polymerq above. It is al~o well known in the art that polymer containing compo~itions in general may al~o contain antloxidants, stabilizers, plasticizer~, and proces~ing oils. The cro~llnkable compositions of this invention may al~o contain such conventional additive~.
The novel compositions can be incorporated into a ma~terbntch or carrier compri~ing various polyolefins and/or ela~tomers at levelq from about 5 to 80 percent by weight.
For ease of addition for certain procesqes, the ~corch retarding cros~linking compoqition, in the form of a homogenou~ liquid or meltable solid, may be dispersed on an inert filler ~uch as CaC03, silica or clay at levels from about 10 to 80 percent by weight.

The scorch retarding crosslinking composition can be incorporated into a polymeric thermoplastic and/or elastomeric material, as a preformed mixture or with the addition of each component separately, resulting in S improved scorch protection. The weight ratio of hydroquinone compound to sulfur accelerator in the first compo~ition aspect of the invention may be from l:S0 to 500:1, preferably from ls25 to 250:1, more pre~erably from 1:25 to 25:1, still more preferably from 1:10 to lOsl, and mo~t preferably from 1:1 to 5:1. The weight ratio of the first composition aspect to peroxide in the second composition aspect of the invention may range from O.5slO0 to ls2, preferably from 1:100 to 1:2, more preferably lslO0 to ls4, and ~till more preferably ls25 to ls20. The peroxide, guinone, sulfur accelerator and optlonal coagent containing second compo~ition aspect of the invention may be lncorporated into the polymeric thermoplastlc and/or ela~tomeric material in quantitie~
to provide a peroxide concentration in the cro~slinkable compo~ition ranglng from 0.01 to 30 parts by weight, preferably from 0.01 to 20 part3 by weight, mo~t preferably from 0.5 to 4.0 parts by welght for each 100 parts by weight of polymer.
The crosslinkable composition may be heat cured to a time sufficient to obtain the desired degree of 2 ~ 7 g crosslinking. The heat curing ha~ a temperature-time relationship which is primarily dependent on the polymeric compound and the peroxide initiator present, but that relationship may be affected by other ingredients in the formulation. It is customary to use a time equal to about 6 to 8 half-lives of the initiator, but this may be varied based on experience at the option of the operator depending on the exact properties desirad in the final product. The inclusion of the scorch retarding compositions of this invention has no substantial effect on the time-temperature relationship when comp~red to the relationship in a similar sy~tem without the scorch retarding composition.
Cro~linking (curing) msy be carried out at a temperature of 100-300C or more. The cure time is inv-r~ely related to the temperature. Sy~tem~ employing the preferred lnitiators heat cure at temperature-time relatlon~ of about 120-200C and 0.5 to 30 minutes.
The heat curing may be carried out in any conventional fashion such as mold cures, oil bath cures ( where oil does not harm the polymeric compound), oven cures, steam cure~, or hot metal salt bath cures.
9~nQ~al Ex9erimental Procedures All formulations were compounded utilizing the ~ Q 'f~ 3 ~

C.w.srabender Plastigraph with type-5 mixing blades.
~ixer temperatures are specified below for various resin types.
Resin Type Temp (C) high density polyethylene tHDPE) 140 low den~ity polyethylene (~DPE) 110 linear low density PE (LLDPE) 125 ethylene-vinyl acetate (EVA) 105 or less ethylene-propylene-diene (EPDM) ambient temperature monomers terpolymer fluoroelastomer ambient temperature To prepare crosslinkable compo~itions, except for the polymer, all components of the composition, for example, the peroxide, a disubstituted dithiocarbamic lS acld, and hydroquinone were weighed at the desired parts by weight resin into a ten dram vial and mixed to form a homogeneou~ ~olutlon. The quantity of each ingredient expre~ed ln part~ per 100 parts of polymer is listed in each example.
Por both thermoplastic and rubber (elastomeric) compo~itions, 100 parts by weight of polymer were fluxed in the mixer using a mixing speed of 30 rpm at a mixing temperature de~ignated in the specific examples. The preweighed component mixture in the vial was then 810wly added to the fluxing resin. The composition wa~ then allowed to mix for six (6) minute~, after which the ~3~

composition was removed and subsequently pressed into a flat plaque ~of no specific thickness)~ using a Carver laboratory press ~Model C) set at the polymer melting point, folded and pressed at least six times to remove air bubbles and smooth out sample, and then the plaque was allowed to cool to room temperature.
mesting Crosslinking evaluations were carried out on the prepared compositions using a Monsanto O~cillating Disk Rheometer (Model R-100).
The Monsanto ~heometer test procedure consists of an uncured sample enclosed, under positive pre~sure, in a heated die cavity containing a biconical disk. The disk 18 osclllated (100 cycles/min) through an arc of 1 or 3 or 5. The force, or torque, required to oscillate the di~k 18 recorded as a function of time. This shear modulu~ is proportional to the extent of crosslinking, and i~ a repre~entation of the cure reaction. The shear modulus increases as percent crosslinking increases. The test variables recorded from the rheometer were:
MH - Maximum torque (in-lbs), a measure of cros~linking ~ttained.
ML - Minimum torque (in-lbs), a measure of visco~ity of the compound and an indicator of 2 ~ ~3~
scorch. Increased ML values are indicative of scorch.
MH-ML - Difference between maximum and minimum torque value~. ~his is useful in determining extent of crosslinking.
Tcgo - Cure Time (minutes), time to reach 90% of maximum torque a~ defined by (MH-ML) 0.9 + ML.
TS2 - Scorch time (minutes), time required for torque to increase two inch-pounds above NL
Tv - Vulcanization time, calculated by Tcgo-TS2~ a measure of cure rate, in which the curing rate is isolated from the scorch or processing phase.
TS2- Delta ~S2 (minutes), the difference in ~corch time calculated by the TS2 of a scorch retarded peroxlde containing polymer formulation minus the TS2 for a comparable reference or control peroxide containing polymer formulation. The cure i8 ad~usted ~o that (MH) is virtually identical for both formulations.
Other reported "Delta" (~) values have been determined in similar fashion from the differences detexmined for the particular variable.
Torque values reported (MH-ML) are rounded off to the nearest whole number. Scorch time values are rounded off to the nearest tenth of a minute.

The following examples ara provided to illustrate preferred embodiments of the invention, and are not intended to restrict the scope thereof.

This example illustrates the desirable increase in scorch ~ime change, delta TS2~ when using a synergistic blend of a hydroquinone such as hydroquinone monomethyl ether (HQMME) and a dithiocarbamate ~uch as zinc diamyldithiocarbamate (ZnDADTC) as a scorch retarding composition as compared to the use of the~e additives separately ln a dicumyl peroxide cure of a LLDPE (Union Carbide DFDA7530). Six scorch retarding crosslinking compo~itions were evsluated (A-F) Component~A B C ,,D E ,_~
(Quantities in parts by weight) Dicumyl Peroxide100 100 100 100 100 100 (100% a~ay) HOMME O 6.0 9.0 0 0 6.0 ZnDADTC~pure ba~i~)0 0 0 3.0 9.0 3.0 In order to accurately compare change in scorch time, delta TS2~ for each peroxide composition on the curing of LLDPE, the parts per hundred rubber (phr) use level of each blend (A-F) was adju~ted to provide the same magnitude of cure (MH) for the LLDPE con~aining cros~linkable compositions (G-L) below.

- 26 - ~ B~

LLDPE COMPOSITIONS
MH = 60 in-lbs. for all sample~ (Monsanto ODR R-100 at 360F, +3 arc).

parts of(A-F) G H I J K L
5peroxide compo-~itions per 100 parts of LLDPE1.5A 1.94B2.24C 1.72D 2.03E 2.19F
(by weight) The use level~ of HQMME and/or ZnDADTC present in each composition are provided below, along with the resulting changes in ~corch time, delta TS2~ obtained at the equivalent degree of cure for the samples shown above.

SQm~Ç~n~8 G H I J K L
(~arts by~eigh~L

Dlcumyl peroxide 1.5 1.83 2.05 1.62 1.72 1.95 ~100% asaay) HQMME 0 0.12 0.18 0 0 0.12 ZnDADTC(pure b~8is) 0 0 0 0.06 0.18 0.06 Ts2(min) 5.9 8.0 9.3 6.1 8.5 10.1 ~Ts2(min) ~ +2.1 +3.4 +0.2 +2.6 +4.2 Monsanto ODR at 290F,+ 3arc The equ~l we$ght usage of HQMME and ZnDADTC singly in compositions H and J provide~ a +2.1 and +0.2 improvement in scorch time respectively for a total change in scorch time ~ TS2) of only + 2.3 min.

_ 27 - 2 ~ 3 ~ ~ ~

as compared to + 4.2 min. improvement in scorch time for the synergistic combination in composition L.
U~ing significantly higher concentrations of either additive, as in compositions I or K does not provide the S scorch time improvement attained by the novel additive blend in composition L.

This example illustrates the desirable increase in scorch time change, delta TS2, when using a blend of a hydroquinone such as mono-t-butylhydroquinone (MTBHQ)and a thiuram such as tetrabutylthiuram disulfide (TBTD) as compared to the singular use of these additives in a dicumyl peroxide cure of EVA (U.S.I. EY901). Six peroxlde compositions were evaluated (P~-F).
~Q~LQn~n~ A B C _ D ~_ F
(Quantitie~ in parts by weight) Dicumyl Peroxide 100 100 100 100 100 100 (100~ Ass~y) ~TLHQ 0 2.0 0 0 2.0 2.0 TB~D O 0 2.0 4.0 2.0 4.0 In order to accurately compare change in scorch time delta TS2 for each peroxide composition on the curing of EVA, the phr u~e level of each blend (A-F) was ad~usted to provlde the same magnitude of cure (MH) for the EVA compositions (G-L) below.

~ ~ ~ 3 ~

EVA COMPOSITIONS
parts of (A-F) G H I J R L
peroxide compositions per 100 parts of EVA 1. 49A 1. 60B 1. SOC 1. 55D 1. 60E 1. 70F
~H = 45 in.-lb. for all samples Monsanto ODR at 360F, +3 arc The use level~ of MTBHQ and/or TBTD pre ent in each composition are provided below, along with the resulting change in scorch time, delta TS2, obtained at equivalent degree of cure as indicated above.

Compo~e~$~ G H I J K L
(paxts by weight) Dicumyl peroxide 1.49 1.57 1.47 1.52 1.54 1.61 (100~ As~y) MTBHQ 0 0.03 0 0 0.03 0.03 TBTD 0 0 0.03 0.06 0.03 0.06 Ts2(min) 4.4 6.0 7.0 8.4 9.4 10.8 /\TS2(min) +1.6 +2.6 +4.0 +5.0 +6.4 Monsanto ODR at 290F,+ 3arc The equal weight u8age of MTBHQ and TBTD ~ingly in composition3 H and I provide a +1.6 and +2.6 min.
improvement in w orch time for a total of + 4.2 min. as compared to + 5.0 min. for the synergistic blend of the~e two additives in composition K. The use of MTBHQ

~3~

and TBTD singly in compositions H and J provide a corresponding +1.6 and +4.0 min. improvement in scorch time for a total of 5.6 min., as compared to 6.4 min.
for the synergistic blend of these two additives in composition L.

Thi~ example illu~trates the desirable increase in scorch tlme change, delta TS2, when using a synergistic blend of a hydroquinone such a~ mono-t-butylhydroquinone (M~BHQ)and a thiuram ~uch as tetrabutylthiuram disulfide (~BTD) as compared to the singular use of theqe additi~es in a 2,5-Dimethyl-2,5-di(t-butylperoxy) hexane cure of ~VA (U.S.I EY901). Five peroxide compo~itions were ev~lu~ted (A-E).
~9CeQ3~D~a A B C D E
(Quantities in parts by weight) 2,5-Dlmethyl-2,5-dilO0 100 lO0 lO0 100 (t-butylperoxy)hexane MTB~Q 0 2.0 0 0 2.0 TBTD 0 0 2.0 4.0 2.0 In order to accurately compare change in qcorch time, delta TS2 for each peroxide composition on the curing of EVA, the phr use level of each ~ 7~8 blend (A-E) was ad~u~ted to provide the same magnitude of cure (MH) for the EVA compositions (F-J~ below.
EvA CoMposl~lQ~
part~ of (A-E) F G H I J
S peroxide compositions per 100 part~ of EVA 1.24A 1.30B 1.29C 1.36D 1.35E
MH = 50 in.-lb. for all samples Mon~anto ODR at 360F, ~3 arc The use levels of MTBHQ and/or TBTD preqent in each composition i9 provided below, alonq with the resulting change in worch time, delta TS2~ obtained at equivalent degree of cure as indicated above.
~Qm~Q$~$~ F G H I J
(Quantitie~ in part~ by weight) lS 2,S-Dimethyl-2,5-dl 1.24 1.27 1.26 1.30 1.29 (t-butylperoxy) hexane TBTD 0 0 0.03 0.06 0.03 T82~min) 4.9 7.9 7.5 9.3 11.8 ~\Ts2(min) _ +3.0 +2.6 +4.4 +6.9 ~on~anto ODR at 290F, i3arc The equ~l weight u~age of MTBHQ and TBTD ~ingly in compo~ltion~ G and H provlde a +3.0 and +2.6 min.
improvement in ~corch time for a total of + 5.6 min. a~
compared to + 6.9 min. for the synergistic blend of the~e two additive~ in composition J.

.

2 ~

This example illustrates the desirable increase in scorch time change, delta Ts2, when using a synergistic blend of a hydroquinone such as hydroquinone monomethyl ether and a dithiocarbamate such as zinc diamyldithiocarbamate ~ZnDADTC) as compared to the use of these additives singly in a l,l-bi~-(t-butylperoxy)-3,3,5-trimethyl-cyclohexane cure of Nordel 1040 EPDM.
In order to accurately compare change in scorch time, delta TS2~ for each composition on the curing of EPDM, the phr u~e level of the peroxide was ad~usted to provlde the same magnitude of cure (MH) for the EPDM
compo~ltlon~ ted below. The additive~ included in the ~y~tem~ were kept at con~tant levels.

2 ~ 7. 8 EPDM COMPOSITIONS
Ingredient A B C D E
~Quantity in parts by weight) Nordel 1040 (DuPont~ 100 100 100 100 100 N660 Black 25 25 25 25 25 1,1-bi~-(t-butylperoxy)- 2.2 2.7 2.3 2.5 2.7 3,3,5-trimethyl-cyclo-hexane HQMM~ 0 .063 0 0 .063 ZnDADTC(pure basi~) 0 0 .032 .095 .032 Tc90(min) 9.5 9.5 9.5 9.5 9.5 MH(i~-lb) 63 63 63 63 63 Mon~anto ODR at 300F, +3arc Ts2(mLn) 6.3 9.6 6.4 7.7 11.3 ~\TS2(min) - +3.3 +0.1 +1.4 +5.0 Mon~anto ODR st 250F,~3arc The ~um of the delta TS2 ~ingular contribution~ from the HQMME ~nd ZnDADTC i~ +3.4 min (B and C).
Unexpectedly, combination E added 5.0 minutes of scorch ti~e protection to the control (A). The same amount of ZnDADTC (D) added only 1.4 minuteq. At levels ~uch as (D) HQMME i~ not ~oluble in the peroxide.
Therefore, E ~how~ a synergi~tic effect with a signlficant lncrease in scorch t~me of 793 at 250F
which can not be obtained by use of HQMME or ZnDADTC used alone.

2 ~

This example illustrates the increase in scorch time protection with hydroquinone-monomethyl ether (HQMME) and zinc dibutyl dithiocarbamate (ZnDBDTC), which are solids, dissolved in a blend of peroxides, dicumyl peroxide and l,l-di[(t-butylperoxy)-isopropyl]benzene (DTBPIPB) in the curing of EVA (UE637).

Components A B C D
(Quantities in part~ by weight) Dicumyl peroxide 60 60 60 60 l,1-di[(t-butylperoxy)-ieopropyl]benzene 40 40 40 40 Zn DBDTC O 2.5 0 2.5 HQMME O 0 5.0 5.0 EVA Com~positions In~redient~ E F G H
(Quantities in parts by weight) ZnO 4.0 4.0 4.0 4.0 antioxidant* 0.5 0.5 0.5 0.5 Component A 2.0 .20 .25 .35 B 0 2.05 0 0 C . 0 0 2.10 0 D 0 0 0 2.15 Monsanto ODR result3 at 360F, +3arc show all cures to be equal. MH wa~ 51 ln.lb. and Tcgo waq 8.0 min.
~polymer~zed 1,2-dihydro-2,2,4-trimethylquinollne (R. T .
Vanderbilt) Final use level~ and change in scorch time are 3hown below. Mon~anto ODR at 290F, +3 arc.
In~L~dlent E F ~ H
(Quantity in parts by weight) dlcumyl peroxide1.2 1.32 1.35 1.41 a,a-di[(t-butylperoxy)-~sopropyl]benzene .8 .88 .90 .94 ZnDBDTC 0 .05 0 .05 HQMME 0 0 .10 .10 TS2 (min.)9.0 9.8 16.0 17.7 /\TS2 ~ +.8 +7.0 +8.7 ZnDBDTC and HQMME u~ed individually improve TS2 by .8 min. and 7.0 min. for a total of 7.8 min. The actual ~ 35 ~ ~ ~3~

blend in composition (H) adds 8.7 min. to the original scorch time with no retarder additive (E).
The u~efulness of this ~ystem in a peroxide blend can be seen in this Table with all samples cured the ~ame, (Sl in.lb.) and arranged according to cure time, and hslf life.
Dicumyl Peroxide Comp. E Comp~ _~ DTBPIPB
Tcgo 0 360F (min.) 6.2 8.0 8.0 10.2 TS2 @ 290F (min.) 7.1 9.0 17.7 13.2 A common practice to increase scorch time is to blend or totally substitute a peroxide with a higher half life, for example the use of DTBPIPB to replace dicumyl peroxide. A disadvantage to this practlce i~ that a ~igniflcant improvement in scorch time 1~ obtained at the expen~e of decreased productlvity, e.g. longer cure time~. A blend of these two peroxides (composition E) provide~ intermediate cure and 4corch times. In the practice of this invention (compo~ition H) one unexpectedly obtains a significantly longer ~corch time not obtainable with the higher half life initiator DTBPIPB when used alone, without the disadvantage of a longer cure tlme.

Thi~ example illustrates that the hydroquinone compound and 4ulfur accelerator may be incorporated into a masterbatch to be added to the polymer to be crosslinked, separate from the peroxide. An EvA (UE634 U . S . I .) was used as the carrier for the scorch retarders which are used with and without a monomeric cocuring agent. Free flowing pellets are the final form.
Maqterbatch components A B
(Quantities in parts by weight) ZnDADTC (50%) 4 2 TAIC~ 0 6 ~trlallylisocyanurate Dlcumyl peroxlde, with these masterbatche~, was u~ed to cro~llnk the ~sme EVA u~ed at equal weight~ to peroxide ~olution~ contalning scorch retarders used to prepare compo~itlons (D) and (F). Thuq the final EVA
formulation~ ~E) and (G) prepared using the above (A), and (B) ma6terbatches are equivalent in composition to (D) and (F) re~pectively.

~ 37 ~ 2~ 7'~

C D E F G H
(Quantities in parts by weight) EVA 100100 97.5 100 95.0 100 S Batch A O0 2 . 7 0 0 0 Batch B O O O O S . 5 0 HQMME 0 .1 0 .1 0 .1 ZnDADTC 0 .1 0 .1 0 .1 Dlcumyl Peroxide 2.02.0 2.0 2.0 2.0 2.3 Mon8anto ODR at 360F, +3F

C __ E _ F G H
MH (in.lb.) 68.1 60.0 60.8 69.2 68.6 66.0 Tcgo min. 5.1 5.3 5.3 4.9 4.9 5.2 ~on~anto ODR at 290F
C ~_ E F G H
T82 mln. 3.6 10.0 9.7 9.5 9~2 8.9 The masterbatch procedure has more chances for weight loss and i8 the only reason for the slight difference in re~ults between (D) and (E). TAIC i9 well known for increasing the state of the cure while having little effect on cure and scorch time~. On a weight basis, it~ use is slightly better than additional dicumyl peroxide in this formulation, (F) and (G) v8. (H) as it 7 ~

restores the MH with only a small amount compared to normal use levels and has little effect on TS2.
Masterbatch (B), thus, allows variation of scorch retarder level without changing peroxide level or S affecting MH. When using the masterbatch approach, there are al~o no solubility or long term homogeneity concerns for the peroxide used.

These examples show that the composition may be added dispersed on a filler for use in the rubber indu~try where powders or solids are preferred. Di-t-amyl hydroquinone (DTAHQ) and a sulfur accelerator blend from U.S. patent number 4,632,950 ~hows a synergi~tic effect ln ~corch time~ when combined along with advantage~ in cure ln Nordel 1040 EPDM cured wlth 1,1-bis(t-butylperoxy)-3,3,5-trimethyl cyclohexane, 40~ on a filler.

~ 39 ~ ~$~ 7$

Composition A B C BhC D E
(Quantities in parts by weight) Nordel 1040 100 100 100 - 100 100 N550 black 60 60 60 - 60 60 Sunpar 2280 oil 10 10 10 - 10 10 1,1-bis-(t-butylperoxy)-3,3,5-tri-methylcyclo-hexane (40~) 6.0 6.0 6.0 - 6.0 6.0 di-t-amyl hydroquinone 0 .45 0 - .45 .516 Zinc dimethyl-dithio carbamate 0 0 .06 - .06 0 Copper dimethyl-dithiocarbamate 0 0 .006 - .006 0 Monsanto ODR at 300F at ~3arc MH (in.lb8.) 48 51 44 - 50 51 Tcgo (min-) 7.4 7,5 7.1 _ 6.6 8.2 Tv (min.) 6.1 6.0 5.7 - 4.9 6.5 Monsanto ODR at 250F
TS2 (min-) 6.6 9.1 7.1 _11.6 9.9 AMH - +3 _4 -1 +2 +3 ~TCgo ~ +.1 -.3 -.2 -.8 +.8 ~Tv ~ -.1 -.4 _.5-1.2 +.4 TS2 ~ +2.5 +.5 +3.0~5.0 +3.3 B and C are prior art scorch inhibitor systems which if combined additively as in column (B & C) would increase TS2 at 250 by 3.0 min. with slight change~ to 2~`~3~

the state and rate of cure. The sulfur accelerators lower the ~tate of cure and di-t-amyl hydroguinone at low levels act3 a3 a coagent in thi~ polymer and peroxide as a bensoquinone derivative works in EP~. The actual composition (D) increase3 TS2 over (A) by 5.0 min. at higher MH at a 20% fa~ter vulcanization time. Simply adding more DTAHQ cau~es a ~lightly longer TS2 but Tv i.e., vulcanlzation time, in (E) i3 one-third longer than (D).

Thi~ example al~o illu~trate~ the advantage of a hydroquinone and ~ulfur accelerator blend when added with a flller extended pexoxide for an ela~tomer cure.
2,5-dimethyl-2,5-di(t-butylperoxy)hexane 45~ on a CaC03 and ~lllca filler, when blended wlth 4 ~mall amount of dl-t-amyl hydroqulnone and tetramethylthiuram mono~ulfide results in better scorch time and cure time than these compound~ used alone at equal weight in curing a fluoroela~tomer.

2~3~7~

Compo~ition A B_ __ C _D
(Quantities in parts by weight) FC2480* 100 100 100 100 N774 black 20 20 20 20 Ca(OH)2 3.0 3.0 3.0 3.0 TAIC 2.5 2.5 2.5 2.5 2,5-dimethyl-2,5-di(t-butylperoxy)-hexane (45%) 2.5 2.5 2.5 2.5 di-t-amyl hydroquinone 0 .05 .10 .05 tetramethylthiuram monosulfide 0 0 0 .05 *FC2480 - fluoroelastomer from 3M
Monsanto ODR at 350F ~3 arc MH (ln-lb.) 96 99 99 98 Tcgo (min-) 7.6 8.4 9.4 7.7 Mon~anto ODR at 300F
TS2 (min.) 4.9 7.0 8.7 10.8 The first two additLons of .05 parts of the hydroquinone increase scorch time by only 2 minute~ each and cure time by one minute each. Sulfur accelerators or accelerator blend~ will increase TS2 at 300 by only .8 to 1.6 minutes at this level without changing the cure time. Higher sulfur levels would not be preferred because of odor and a negative effect on aglng. In sample D, adding tetramethyl thiuram monosulfide instead of additional di-t-amyl hydroquinone, scorch time i9 2 0 $ ~ fl ~ ~

improved by 5.9 minutes over the control A, instead of the 3.8 minutes improvement in C, while the cure time (Tcgo) is reduced back to the desirable original value.
This balance is not possible with either compound used individually.
Changing to a hiqher temperature half life peroxide such as 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 to increase scorch safety (as well as cure time) results in a TS2 at 300F of 9.8 min., or an improvement of 4.9 minutes at a lower state of cure.

This example show~ storage stability of scorch retarded peroxide ~olutionq. Varlous formulations and a control were aged three tlmes at three different temperature8 ~llghtly over normal storage temperatures And a~ayed for percent peroxide.

~L~CDentg A B C D
~parts by weight) dicumyl peroxlde 100 96.0 96.0 88.0 mono-t-butyl hydroquinone 0 2.0 2.0 0 hydroquinone monomethyl ether 0 0 0 6.0 Zn dlamyl dithiocsrbamate (50~) 0 2.0 0 6.0 tetrabutyl thiuram disulfide 0 0 2.0 0 - 43 - 2~ 7 Peroxide a~ay after aging conditions (%) Temperature30C 40C 50C
(time in weeks) Start 2 4 8 2 4 8 2 4 8 Peroxide for~ula~ion A 92.0 90.9 92.2 92.0 89.3 92.2 91.8 92.0 91.7 92.7 B 88.6 89.8 90.0 87.4 88.0 88.3 87.2 87.3 87.7 86.5 C 87.3 86.7 85.9 86.7 85.7 86.3 86.2 86.3 87.6 87.2 D 87.8* 86.5 87.6 89.3 86.3 87.2 89.3 86.4 87.1 88.7 Peroxide assayq (+2%) show no pattern of degradatlon, thereore they are stable at normal ~torage temperature~.

~Sample D WaJ made with a higher assay dlcumyl peroxide so the 1nal unaqed as~ay was simllar to B and C.

2 ~ 7 ~ ~

Solubility of some additives varies in different classes of peroxides and also over time. This can be improved by adding a liquid or solid co-curing agent.
The normal application of such co-curing agent (coagent) in lmproving the state of cure is useful here, but such agents appear to unexpectedly improve solubility and more importantly stability of additives, sometimes lowering melting point, and to increase ease of preparation of the peroxide solution without adding inert extenders. The table in this example shows two peroxide solutions with a ~mall portlon of the peroxide replaced with a coagent and a compari~on of visual changes over time.

Formulation A B C D
Ingredient (parts by weight) dicumyl peroxide 50 50 0 0 n-butyl-4,4-bis(t-butyl-peroxy)valerate 50 25 0 0 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 0 0 100 85 hydroquinone monomethyl ether 4.0 4.0 5.0 5.0 Zn diamyl dithiocarbamate (50%) 2.0 2.0 0 0 tetramethyl thiuram mono-sulfide 0 0 0.5 0.5 triallyl trimellitate 0 25 0 0 triallyl cyanurate 0 0 0 15 Age - ~ime (2 month~) (1 month) Color brown none slight slight In~olubles yes none, ~light none h ~ 7 8 Solutions A and B were originally clear and C and D
were clear and slightly yellow but A and C showed a change in solubility of additives. The coagents suprisingly facilitated the rate and amount of solubility of the acorch retarders with an active ingredient and more importantly unexpectedly stabilized mixtures such as B and D.

This example shows the activity of solutions from the last example in a crosslinking reaction. The ~olutions were compared to a single peroxide control in cro~sllnking the same polymer before and after aging.
Mlxing and curing condition~ in the Monsanto Rheometer were held con~tsnt at all time~.

~3~78 Formulation A B C D
Ingredient (parts by weight) dicumyl peroxide 53 100 0 0 n-butyl-4,4-bis(t-butyl-peroxy)valerate 25 0 0 0 2,5-dimethyl-2,5-di(t-butylperoxy)hexyne-3 0 0 85 100 hydroquinone monomethyl ether 0 0 5.0 0 di-t-amyl hydroquinone 2.0 0 0 0 Zn diamyl dithiocarbamate (50%) 1.0 0 tetramethyl thiuram mono-sulfide 0 0 0.5 0 triallyl cyanurate 22 0 15 0 Original cure properties crosslinking EVA (~3 arc) Solution ln EVA ~phr) 1.50 1.502.11 2.00 Rheometer temperature 360P .3~0F
MH ln. lb. 51.1 51.271.6 71.8 Tcgo min. 4.7 5.3 7.7 8.1 Rheometer temperature 290F 320F
TS2 min. 8.4 7.3 9.9 2.7 A and C aged 1 month at 32C, cure properties in same EVA
Rheometer temperature ~Q~E 380F
MH in. lb. 51.4 51.472.7 71.8 Tcgo min. 4.5 5.2 7.9 7.7 Rheometer temperature 290F 320F
TS2 min. 8.5 7.310.2 2.8 2~3~ 7~

There is no change in crosslinking efficiency as measured by MH and no loss of scorch retardation which is meaqured by TS2 after ageing one month at an average temperature of 32C. The solutions retain solubility and efficiency with the TAC coagent without dilution with inert ingredients. Unexpectedly we found that the order of addition of the various additives and peroxide can greatly affect the speed and ea~e of preparing a homogenous solution. A formulation such as C, in this example, is prepared more quickly by adding peroxide l~st. HQMME (melting point of 54C) and TMTM (105C) ~re very ~oluble in TAC (27C) resulting in a mixture whlch melt~ at about 15C and then blend3 quickly with DMDBPH-3. Mlxlng in the order of formulatlon (C) a~
llsted could take up to ten times longer. Samples A and B have equal crosslinking efficiency at equal weight.
Sllghtly more of solution C is used to equal D although extra peroxlde or co-agent alone could be used as relative efficlency varle~ with the polymer u~ed.
Varying the level of C has the least effect on ~corch time.

2 ~ 7 8 CROSSLINKING HIGH DENSITY POLYETHYLENE (HDPE) Resin: High density polyethylene having melt flow index (MFI) 38 g/10 min. at 190C and Sp.
Gr. 0.941-.98g/cc This Example illustrates the improvement in scorch time with minimal effect on cure time obtainable when crosslinking HDPE with a typical Rcorch retarding crosslinking composition of the invention.
Fe~oxide Solution~: A B C D E
(Quantitie3 in parts by weight) In~redien~.a 2,5-dimethyl-2,5-di(t-butylperoxy)0.75 0.75 0.75 0.75 0.75 hexyne-3 Triallylcyanurate0.15 0.15 0.15 0.15 0.15 Hydroquinone Monomethyl ether - 0.08 - 0.08 0.08 Tetramethyl Thiuram Mono~ulflde - - 0.01 0.01 0.02 Solutions Mixed Into HDPE Resin Batch F G H I J
(ouan~ s by weigh~
Resin 100 100 100 100 100 SGlution A 0.5 - - - _ Solution B - 0.8 Solution C - - 0.5 Solution D - - - 0.8 Solution E - - - - 0.8 2~3~7~

Monsanto ODR R-100 Cures at t3 arc.
F _ G H _ I ~
MH (in-lbs) at 400F30.4 2~.830.4 32.2 33.2 Tcgo (min-) at 400F 6.8 7.0 6.1 7.0 7.0 TS2 (min.) at 350F 9.1 10.58.5 12.1 12.4 TS2 (min.) at 350F --- +1.4-0.6 +3.0 +3.3 A Qolution of 2,5-dimethyl 2,5-di(t-butyl peroxy) hexyne-3 with triallylcyanurate (TAC) and hydroquinone monomethyl ether (HQMME) represented by formulation ~G~
provides a slight improvement in scorch time as compared to the control (formulation "F"). Using a Qmall amount of tetramethylthiuram mono~ulfide, formulation "H", actually re~ults in an adverse effect on scorch time (a decrease ln TS2 ver~us the control). Qulte unexpectedly, a blend of these addltlves "I" results ln a -Qlqnlflcant lmprovement ln scorch tlme which cannot be attained by the additlve effect of the materials used separately.
U~lng more qulnone to enhance scorch protection will continue to adversely reduce the final cure (MH). The 2 ~

unique composition of this invention ~ I" also provides an unexpected increased level of HDPE crosslinking as compared to G~ and even the control "F". To further support this unexpected synergism, increasing the amount of thiuram in formulation ~J shows continued improvement in crosslinking and scorch time protection.
EXAMP~E 13 This example describe~ the synergistic increase in ~corch time protection that can be obtained when a sulfur accelerator of the thiazole sulfenamide cla~3 is uqed in combination with a hydroquinone type compound. Thus an BVA containing two antioxidants is crosslinked with a ~corch retarding cro~linking composition consi~ting of a homogeneou~ ~olutlon of dlcumyl peroxide, N-cyclohexyl-2-benzothlazole ~ul~enamide and hydroqulnone monomethylether.
The two antloxldants used were supplied by R . T .
Vanderbilt and are llsted below.
Agerite MA~ polymerized trimethyl dihydroquinoline Vanox ZMTII Zn 2-mercaptotoluimidazole In the compo~ltion~ listed below, the level of peroxlde (dlcumyl peroxlde) was ad~u~ted in order to provlde equivalent ~tate of cure as mea~ured by the Mon~anto ODR.

- 52 ~ 3 ~ ~ 8 FINAL ~OLYMER COMPOSITION: A B C D
EVA UE637 ~USI) 100 100 100 100 Agerite MA 0.5 0.5 0.5 0.5 Vanox ZNTI 0.5 0.5 0-5 0-5 dicumyl peroxide 2.00 2.14 2.12 2.12 N-cyclohexyl-2-benzothiazole 0 0.04 0 0.04 sulfenamide hydroquinone monomethyl ether 0 0 0.06 0.06 MONSANTO ODR CURE AT 360, 3 arc MH (in-lbs) 34 34 34 33 TC90 (min) 6.4 6.2 6.3 6.4 MONSANTO ODR SCORCH EVALUATION AT 290F, 3arc TS2 ~min) 7.9 10.1 13.2 16.0 DELTA TS2 (min) - 2.2 5.3 8.1 Using the scorch retarder additives N-cyclohexy1-2-benzothiazole sulfenamide, in system ~'B" and the hydroquinone monomethyl ether, in system "C" separately provided a corresponding improvement in scorch protection of 2.2 and 5.3 respectively, versus the control "A".
U~ing both of these in combination, one would expect an improvement of about 2.2 + 5.3 = 7.5 minute~. However a~
contemplated by this invention, the synergi~tic combination of these additives in system ~D~ provides a significantly higher improved scorch protection of 8.1 ~3~ $

minutes, with no significant loss in the degree of crosslinking or cure rate performance.
ADDITIONAL FREE RADICAL INITIATORS
An addition preferred class of dialkyl peroxides included among the free radical initiators contemplated by the invention are those having the Formula:

C,H3 C,H3 ~_o_~

whereln R4 and R5 may Lndependently be in the meta or para po~itlon~ and may be the same or different and are ~elected from hydrogen, or straigh~ or branched chain lower alkyl of from 1 to about 3ix carbon atom~.

Claims

1. A scorch retarding composition comprising a hydroquinone and a sulfur accelerator.

2. A scorch retarding composition as defined in claim 1 comprising a hydroquinone and a sulfur accelerator selected from the group consisting of dithiocarbamates, thiurams, thiazoles, sulfenamides and mixtures thereof.

3. A composition as defined in claim 1 wherein the sulfur accelerator is selected from compounds represented by the structure:

wherein X is an ion derived from a metal selected from the group consisting of nickel, cobalt, iron, chromium, tin, zinc, copper, lead, bismuth, cadmium, selenium and tellurium, n may vary from 1 to 6 and is equal to the formal valence of the metal ion, R1 and R2 are independently alkyl of 1 to 7 carbon atoms.

4. A composition as defined in claim 1 wherein the sulfur accelerator is selected from the group consisting of: bismuth dimethyldithiocarbamate, cadmium diamyldithiocarbamate, cadmium diethyldithiocarbamate, copper dimethyldithiocarbamate, lead diamyldithiocarbamate, lead dimethyldithiocarbamate, selenium dimethyldithiocarbamate, tellurium diethyldithiocarbamate, zinc diamyldithiocarbamate, zinc diethyldithiocarbamate, and selenium dimethyldithiocarbamate.

5. A composition as defined in claim 1 wherein the sulfur accelerator is selected from compounds represented by the formula:

wherein R3 is an alkyl group of 1 to 7 carbon atoms and n may have a positive value from greater than zero up to about 6.

6. A composition as defined in claim 1 wherein the sulfur accelerator is selected from the group consisting of tetrabutyl-thiuram disulfide, tetramethylthiuram disulfide and tetramethylthiuram monosulfide or mixtures thereof.

7. A composition as defined in claim 1 wherein the hydroquinone is selected from the group consisting of hydroquinone, hydroquinone di(betahydroxyethyl) ether, hydroquinone monomethyl ether, mono-t-butyl -hydroquinone, di-t-butylhydroquinone, and di-t-amylhydroquinone or mixtures thereof.

8. A scorch retarding composition as defined in claim 1 additionally comprising a coagent.

9. A composition as defined in claim 8 wherein the coagent is selected from monofunctional vinyl monomers, monofunctional allyl monomers, difunctional vinyl monomers, difunctional allyl monomers, polyfunctional vinyl monomers, poly functional allyl monomers, or mixtures thereof.

10. A composition as defined in claim 8, wherein the coagent is selected from the group consisting of allyldiglycol carbonate, triallylcyanurate, triallylisocyanurate, allylmethacrylate, trimethylolpropane trimethacrylate, diallyladipate, diallyloxalate, diallylfumarate, triallylphosphate, tetraallyloxyethane, triallyltrimellitate and liquid 1,2-polybutadiene, and mixtures thereof.

11. A scorch retarding, crosslinking composition comprising a composition as defined in claim 1 and a free radical initiator selected from the group consisting of organic peroxides, azo compounds and mixtures thereof.

12. A composition as defined in claim 11 wherein the free radical initiator consists of at least one organic peroxide.

13. A composition as defined in claim 12 wherein the organic peroxide is selected from the group consisting of dialkyl peroxides, diperoxyketals and mixtures thereof.

14. A scorch retarding, crosslinking composition comprising a scorch retarding composition as defined in claim 8 and a free radical initiator selected from the group consisting of organic peroxide, azo compounds and mixtures thereof.

15. A composition as defined in claim 14 wherein the free radical initiator consists of at least one organic peroxide.

16. A composition as defined in claim 15 wherein the organic peroxide is selected from the group consisting of dialkyl peroxides, diperoxyketals and mixtures thereof.

17. A composition as defined in claim 13 wherein the dialkyl peroxides are selected from dicumylperoxide;
alpha, alpha-bis (t-butyl peroxy) diisopropylbenzene;
t-butyl cumyl peroxide; 2,5-dimethyl-2,5-di(t-butylperoxy)-hexane; 2,5-dimethyl-2,5-di(t-amylperoxy)-hexane; 2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3; 2,5-dimethyl-2,5-di(t-amylperoxy)-hexyne-3; di-t-amylperoxide; 1,3,5-tri[(t-butylperoxy)-isopropyl]-benzene; 1,3-dimethyl-3-(t-butylperoxy)butanol; and mixtures thereof.

18. A composition as defined in claim 13 wherein the diperoxyketal initiators are selected from the group consisting of: 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane; 1,1-di(t-butylperoxy) cyclohexane;
n-butyl-4,4-di(t-amylperoxy) valerate; ethyl-3,3-di(t-butylperoxy)-butyrate; 2,2-di(t-amylperoxy)-propane; 3,6,6,9,9-pentamethyl-3-ethoxy carbonyl-methyl-1,2,4,5-tetraoxacyclononane; n-butyl-4,4-bis (t-butylperoxy)-valerate; ethyl -3,3-di(t-amylperoxy)-butyrate and mixtures thereof.

19. A composition as defined in claim 16 wherein the dialkyl peroxides are selected from dicumylperoxide;
alpha, alpha-bis (t-butyl peroxy) diisopropylbenzene; t-butyl cumyl peroxide; 2,5-dimethyl-2,5-di(t-butylperoxy)-hexane; 2, 5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3;
2,5-dimethyl-2,5-di(t-Amylperoxy)-hexyne-3; di-t-amylperoxide; 1,3,5-tri[(t-butylperoxy)-isopropyl]-benzene; 1,3-dimethyl-3-(t-butylperoxy)butanol; and mixtures thereof.

20. A composition as defined in claim 16 wherein the diperoxyketal initiators are selected from the group consisting of: 1,1-di(t-butylperoxy) cyclohexane; n-butyl-4,4-di(t-amylperoxy) valerate; ethyl-3,3-di(t-butylperoxy)-butyrate; 2,2-di(t-amylperoxy)-propane; 3, 6,6,9,9-pentamethyl-3-ethoxy carbonylmethyl-1,2,4,5-tetraoxacyclonane; n-butyl-4,4-bis(t-butylperoxy)-valerate; ethyl-3,3-di(t-amylperoxy)-butyrate and mixtures thereof.

21. A composition as defined in claim 11 wherein the sulfur accelerator is selected from compounds represented by the structure:

wherein x is an ion derived from a metal selected from the group consisting of nickel, cobalt, iron, chromium, tin, zinc, copper, lead, bismuth, cadmium, selenium and tellurium, n may vary from 1 to 6 and is equal to the formal valence of the metal ion, and R1 and R2 are independently alkyl of 1 to 7 carbon atoms.

22. A composition as defined in claim 11 wherein the sulfur accelerator is selected from compounds represented by the formula wherein R3 is an alkyl group of 1 to 7 carbon atoms and n may have a positive value from greater than zero up to about 6.

23. A crosslinkable composition comprising a composition as defined in claim 11 and a thermoplastic and elastomeric polymer crosslinkable by peroxide or azo compounds.

24. A crosslinkable composition comprising a composition as defined in claim 11 and a thermoplastic polymer crosslinkable by a peroxide or an azo compound.

25. A crosslinkable composition comprising a composition as defined in claim 11 and an elastomeric polymer crosslinkable by a peroxide or an azo compound.

26. A composition as defined in claim 14 wherein the sulfur accelerator is selected from compounds represented by the structure:

wherein X is an ion derived from a metal selected from the group consisting of nickel, cobalt, iron, chromium, tin, zinc, copper, lead, bismuth, cadmium, selenium and tellurium, n may vary from 1 to 6 and is equal to the formal valence of the metal ion, and R1 and R2 are independently alkyl of 1 to 7 carbon atoms.

27. A composition as defined in claim 14 wherein the sulfur accelerator is selected from compounds represented by the formula wherein R3 is an alkyl group of 1 to 7 carbon atoms and n may have a positive value from greater than zero up to about 6.

28. A crosslinkable composition comprising a composition as defined in claim 14 and a thermoplastic and elastomeric polymer crosslinkable by peroxide or azo compounds.

29. A crosslinkable composition comprising a composition as defined in claim 14 and a thermoplastic polymer crosslinkable by a peroxide or an azo compound.

30. A crosslinkable composition comprising a composition as defined in claim 14 and an elastomeric polymer crosslinkable by peroxide or azo compounds.

31. A composition as defined in claim 1 wherein the hydroquinone is hydroquinone monomethylether, and the sulfur accelerator is zinc diamyldithiocarbamate.

32. A composition as defined in claim 11 wherein the hydroquinone is hydroquinone monomethyl ether, the sulfur accelerator is zinc diamyldithiocarbamate and the free radical initiator is dicumyl peroxide.

33. A composition as defined in claim 8 wherein the hydroquinone is hydroquinone monomethylether, and the sulfur accelerator is zinc diamyldithiocarbamate.

34. A composition as defined in claim 14 wherein the hydroquinone is hydroquinone monomethyl ether, the sulfur accelerator is zinc diamyldithiocarbamate, and the free radical initiator is dicumyl peroxide.

35. A crosslinkable composition as defined in claim 24 wherein the hydroquinone is hydroquinone monomethyl ether, the sulfur accelerator is zinc diamyldithiocarbamate, the free radical initiator is dicumyl peroxide and the thermoplastic polymer is linear low density polyethylene.

36. A composition as defined in claim 1 wherein the hydroquinone is mono-t-butylhydroquinone, and the sulfur accelerator is tetrabutylthiuram disulfide.

37. A composition as defined in claim 11 wherein the hydroquinone is mono-t-butylhydroquinone, the sulfur accelerator is tetrabutylthiuram disulfide and the free radical initiator is dicumyl peroxide.

38. A crosslinkable composition as defined in claim 24 wherein the hydroquinone is mono-t-butylhydroquinone, the sulfur accelerator is tetrabutylthiuram disulfide, the free radical initiator is dicumyl peroxide and the thermoplastic polymer is ethylene-vinylacetate.

39. A composition as defined in claim 11 wherein the hydroquinone is mono-t-butylhydroquinone, the sulfur accelerator is tetrabutylthiuram disulfide and the free radical initiator is 2,5-dimethyl-2,5-di(t-butylperoxy) hexane.

40. A crosslinkable composition as defined in claim 24 wherein the hydroquinone is mono-t-butylhydroquinone, the sulfur accelerator is tetrabutylthiuram disulfide, and the elastomeric polymer is ethylene-vinylacetate.

41. A composition as defined in claim 11 wherein the hydroquinone is hydroquinone monomethyl ether, the sulfur accelerator is zinc diamyldithiocarbamate, the free radical inltiator is 1, 1-bis-(t-butylperoxy)-3,3,5-trimethyl-cyclohexane.

42. A crosslinkable composition as defined in claim 24 wherein the hydroquinone is hydroquinone monomethylether, the sulfur accelerator is zinc diamyl-dithiocarbamate, the free radical initiator is 1,1-bis-(t-butylperoxy)-3,3,5-trimethyl-cyclohexane and the thermoplastic polymer is an ethylene-propylene-diene monomers terpolymer.

43. A composition as defined in claim 11 wherein the hydroquinone is hydroquinone monomethyl ether, the sulfur accelerator is zinc dibutyldithiocarbamate and the free radical initiator is a mixture of dicumyl peroxide and 1,1-di[(t-butylperoxy)isopropyl]-benzene.

44. A crosslinkable composition as defined in claim 29 wherein the hydroquinone is hydroquinone monomethyl ether,the sulfur accelerator is zinc diamyldithiocarbamate, the free radical initiator is dicumyl peroxide and the thermoplastic polymer is linear low density polyethylene.

45. A composition as defined in claim 8 wherein the hydroquinone is mono-t-butylhydroquinone, and the sulfur accelerator is tetrabutylthiuram disulfide.

46. A composition as defined in claim 14 wherein the hydroquinone is mono-t-butylhydroquinone, the sulfur accelerator is tetrabutylthiuram disulfide and the free radical initiator is dicumyl peroxide.

47. A crosslinkable composition as defined in claim 29 wherein the hydroquinone is mono-t-butylhydroquinone, the sulfur accelerator is tetrabutylthiuram disulfide, the free radlcal initiator is dicumyl peroxide and the thermoplastic polymer is ethylene-vinylacetate.

48. A composition as defined in claim 14 wherein the hydroquinone is mono-t-butylhydroquinone, the sulfur accelerator is tetrabutylthiuram disulfide and the free radical initiator is 2,5-dimethyl-2,5-di(t-butylperoxy) hexane.

49. A crosslinkable composltion as defined in claim 29 wherein the hydroquinone is mono-t-butylhydroquinone, the sulfur accelerator is tetrabutylthiuram disulfide, and the thermoplastic polymer is ethylene-vinylacetate.

50. A composition as defined in claim 14 wherein the hydroquinone is hydroquinone monomethyl ether, the sulfur accelerator is zinc diamyldithiocarbamate, the free radical initiator is 1,1-bis-(t-butylperoxy)-3,3,5-trimethyl-cyclohexane.

51. A crosslinkable composition as defined in claim 29 wherein the hydroquinone is hydroquinone monomethylether, the sulfur accelerator is zinc diamyl-dithiocarbamate,the free radical initiator is 1,1-bis-(t-butylperoxy)-3-3-5-trimethyl-cyclohexane and the elastomeric polymer is an ethylene-propylene-diene monomers terpolymer.

52. A composition as defined in claim 14 wherein the hydroquinone is hydroquinone monomethyl ether, the sulfur accelerator is zinc dibutyldithiocarbamate and the free radical initiator is a mixture of dicumyl peroxide and 1, 1-di[(t-butylperoxy) isopropyl]-benzene.

53. A composition as defined in claim 8 wherein the coagent is triallycyanurate.

54. A composition as defined in claim 14 wherein the coagent is triallylcyanurate.

55. A composition as defined in claim 8 wherein the coagent is triallyltrimellitate.

56. A composition as defined in claim 14 wherein the coagent is triallyltrimellitate.

57. A composition as defined in claim 56 wherein the hydroquinone is hydroquinone monomethylether, the sulfur accelerator is zinc diamyldithio carbamate and the free radical initiator is a mixture of dicumylperoxide and n-butyl-4,4-bis(t-butylperoxy) valerate.

58. A composition as defined in claim 54 wherein the hydroquinone is mono-t-butyl hydroquinone, the sulfur accelerator is zinc diamyldithio carbamate, and the free radical initiator is a mixture of dicumyl peroxide and ethyl-3,3-di-(t-butylperoxy) butyrate.

59. A composition as defined in claim 54 wherein the hydroquinone is hydroquinone monomethyl ether, the sulfur accelerator is tetramethylthiuram monosulfide and the free radical initiator is 2,5 dimethyl-2,5-di(t-butylperoxy)-hexyne-3.

60. A composition as defined in claim 29 wherein the polymer is high density polyethylene.

61. A composition as defined in claim 60 wherein the hydroquinone is hydroquinone monomethylether, the sulfur accelerator is tetramethylthiuram monosulfide, the peroxide is 2,5-dimethyl-2,5-di(t-butyl-peroxy)hexyne-3, and the coagent is triallylcyanurate.

62. A composition as defined in claim 60 wherein the hydroquinone is hydroquinone monomethylether, the sulfur accelerator is tetrabutyl thiuram disulfide, the peroxide is 2,5-dimethyl-2,5-di(t-butylperoxy)-hexyne-3, and the coagent is triallylcyanurate.

63. A composition as defined in claim 60 wherein the hydroquinone is hydroquinone monomethyl ether and the sulfur accelerator is tetrabutylthiuram disulfide, the peroxide is a mixture of 2,5 dimethyl-2,5-di(t-butylperoxy)-hexane and 1,1-di[(t-butyl-peroxy)-isopropyl]-benzene and the coagent is triallylcyanurate.

64. A composition as defined in claim 54 wherein the hydroquinone is hydroquinone monomethyl ether, the sulfur accelerator is tetrabutylthiuram disulfide and the free radical initiator is a mixture of dicumyl peroxide and ethyl 3,3-di-(t-butylperoxy)butyrate.

65. In a process for the preparation of a crosslinkable composition comprising a polymer selected from the group peroxide or azo compound crosslinkable thermoplastic polymers, elastomeric polymers, or mixtures thereof and a free radical initiator selected from peroxides, azo compounds, or mixtures thereof wherein said polymer is compounded with said free radical initiator, the improvement comprising performing said compounding in the presence of a scorch retarding composition as defined in claim 1.

66. A process as defined in claim 65 wherein the scorch retarding composition additionally comprises a coagent.

67. A composition as defined in claim 54 wherein the hydroquinone is hydroquinone monomethyl ether, the sulfur accelerator is tetrabutyl-thiuram disulfide and the free radical initiator is dicumyl peroxide.

68. A composition as defined in claim 1 wherein the sulfur accelerator is N-cyclohexyl-2-benzothiazole sulfenamide.

69. A composition as defined in claim 68 additionally comprising a coagent.

70. A composition as defined in claim 11 wherein the sulfur accelerator is N-cyclohexyl-2-benzothiazole sulfenamide.