CA1065531A - Stabilization of vinyl chloride polymers - Google Patents

Abstract

Abstract of the Disclosure - The heat stability imparted to plasticized vinyl chloride polymers by di- or triesters of phosphorous acid is significantly increased by the addition of 0.1 - 1% by weight of specified organotin compounds to the polymer composition. The concentration of organotin compound is between 3 and 45%, based on the combined weight of the phosphorous acid ester and organotin compound.

Description

10655 ~1 NOVEL PRODUCTS
BACKGROUND
This invention relates to plastisols containing vinyl chloride polymers which are st~bilized a~ainst heat-induced discoloration and degradation.
This invention ~urther relates to a method ~or .
S enhancing the heat stability imparted to plasticized vinyl chloride polymer compositions by organic esters of phosphorous acid.
It is weLl known that triorganophosphites of the general ~ormula P(OR)3 wherein ea~h R is an alkyl or aryl radical impart use~ul levels of heat stability to vinyl chloride polymers. U0 S. Patent 2,867,~94 to Floyd R. Hansen et al. discLoses that mixed alkyl-aryl phosphites are particularly suitable for this purpose. The patent further ~ teaches that mixtur2s containing the pho~phite~ and an organic acid salt o~ an alkali metal or alkaline earth metal can be employed in combination with other known stabilizers, including organic salts of cadmium 9 zinc or tin.
Using combinations of organophosphites or other auxiliary stabiLizers with specified reaction products of ~tannoic acids to improve the heat stabilization imparted to : vinyl chloride poLymers is discLosed in U. S, Patent 3,413,284.
~: A n~mber of patents, including British Patent 1,180,398 teach the desirability of adding organophosphites to organotin . mercaptides or organotin mercaptoacid esters to increase the heat stability o~ vinyl chloride polymers. The resultant ' ~ .

~. . ... .

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mixture of polymer and stabilizers together with other additives including plasticizeræ, impact modifiers, lubricants and pigments i~ blended to form a homogeneous composition.
In many instances the blending is accompLished u~ing ~ roller miLl or extruder. This is t~ue ~or the polymer samples disclosed in Ganadian Patent 910,538, which teaches that certain organophosphites enhance the heat stabilization imparted to vinyl chloride polymers by monoorganotin ~ derivatives of mercaptoacid estersO Experimental data contained in the aforementioned Canadian patent demonstrate that the beneficial effect of the phosphite is Limited to monoorganotin compounds. PoLymer compositions containing the corresponding diorganotin compounds such as dibutyltin~S,S' bis(isooctyl mercaptoacetate) exhibit a decrease rather than an increase in heat stabiLity when a phosphite is added~ , ~.
: Surprisingly it has now been found that if a : plasticized vinyL chloride polymer composition containing a phosphite as the primary stabiLizer i8 not subjected to a . signi~icant amount of shear while in the moLten state, the addition of between 0~1 and L%, based on the weight of the composition, of certain organotin compounds significantly increa~es re~istance to discoloration at temperatures of : 150~C. and higher. The concentr~tion of organotin compound : ~5 is between,3 and 45%, based on the combined weight of : pho~phit md organotin oompound.
. . .

. -2 . _ .. _ .. ..

l()~;SS3~

The invention provi~es a method for improving the heat sta-bility exhibited by shaped articles, films or coatings prepared using plasti-cized vinyl chloride polymer compositions consisting essentially o~ a) a vinyl chloride homopolymer or a copolymer wherein at least ';0% of ~he repeatlng units are derived from vinyl chloride, the remaining repeating units being derived from one or more ethylenically unsaturated compounds which are copolymerizable with vinyl chloride; b) between 5 and 60%, based on the weight of said composi-t1on of a plast.icizer for vinyl chloride polymers; c) between 0.5 and 5%, based on the weight of said composition, of an organic ester of phosphorous acid, said ester exhibiting the general formula P~ORl)3, Pt0Rl)2(0R2) or (R10)2PoR3 -OP~ORI)2 wherein Rl and R2 are each selected from the group consisting of alXyl radicals containing bet~een 1 and 20 carbon atoms, cycloalkyl, aralkyl, aryl, alkaryl radicals and hydrogen atoms with the proviso that the number of hydro-gen atoms is 0 or 1, and R is the residue obtained by removing the two termin-al hydrogen atoms of a polypropylene glycol, the method comprising (1) adding to said polymer composition between 0.1 and 1%, based on the weight of said composition, of an organotin compound corresponding to the general formula R}354Y4 ~ ' ; 4 ~ R ~(SR I~OR ) S--R
R2 Sn / C=0 wherein m represents the integer 1, 2 or 3 and Y represents a radical exhibi-ting a formula selected from the group conslsting of ~,~., ~55~

SR4 o ll R4 -SR5C ~ , R403CH2CH-CoR
oR4 S-O O O O O O
-ocR6COR , -OeCH=CHCOR and -OCCH=CHCO-; R and R are each in-dividually selected from the group consisting of alkyl radicals containing between 1 and 20 carbon atoms, cycloalkyl, aralkyl, aryl and alkaryl radicals and R5 is a methylene or ethylene radical and R6 is an alkylene radical containing between 1 and 8 carbon atoms, inclusive, with the pro-viso that the organotin compound constitutes between 3 and 45% of the combined weight of the organotin compound and the organic ester of phos-phorous acid, and ~2) subsequently converting said composition into a product selected from the group consisting of shaped articles, films and coatings, wherein the conversion is accomplished in the absence of sig-nificant amounts of shear.
The stabilizer compositions employed in accordance with the method of this invention enhance the resistance to heat-induced degradation of plasticized vinyl chloride polymers~

1~5S3~
which are not subjected to the high levels of shear ~ncountered when the poly~ers are processed using calender rolls or are ~orced under high pres-sure through the relatively small orifices present in conventional extruders and injection molding machines. Preferred plastici~e~rs are those selected rom the group consisting of esters of carboxylic acids wherein the acid and alcohol residues of the carboxylic acid esters contain between 2 and 20 carbon atoms, trialkyl, triaryl and mixed aryl-alkyl triesters of phos-phoric acid, esters derived from benzoic acid and oligomers of alkylene diols containing from 2 to 5 repeating units, epoxidized esters of unsaturat-ed fatty acids, esters of trimellitic acid, chlorinated paraffinic hydro-carbons and liquid polyesters derived from aliphatic dicarboxylic acids and diols.
The phosphites, or esters of phosphorous acid, which are prefer-red for use in the present stabili~er compositions exhibit the general formula tR10)3P or ~R10)2(R20)P wherein Rl and R2 are individually selected from among alkyl radicals c~ntaining between 1 and 20 carbon atoms, unsub-stltuted phenyl radicals and phenyl radicals bearing one or two alkyl radicals as substituents wherein the aIkyl radicals each contain between 1 and 20 carbon atoms, inclusive. ~ither Rl, R2 or both may contain ~ hydroxyl or alkoxy group as a substituent.
Suitable phosphites include:
Triphenyl phosphite Diphenyl isodecyl phosphite Bistp-nonylphenyl~ phenyl phosphite Phenyl diisodecyl phosphite (p-methoxyphenyl) ~iisodecyl phosphite p-hydroxyphenyl diisodecyl phosphite p-n~nylphenyl bis~hydrogenated bis phenol A) phosphite 106553~L

Tetrakis(p-nonylphenyl) polypropyLene glycol (PPG) 42 5 diphosphi te Bis(p-nonyLphenyl~ PPG 425 phosphite l-naph thyl diisodecyl phosphite .

2-naphthyl diisodecyl pho~phite p~ycLohexylphenyl diisodecyl phosphite - Bis(isooc~yl) p-nonylphenyl pho~phite Triphenyl phosphite, diphenyl isodeoyl phosphite, trii~odecy~ phosphite and diisod~.cyL pherlyl pho~phite are .
particularly preferred for use in the present stabilizer compositions .
me phosphite is the major stabilizing component o:E
the present compositions and constitute~ be~7een 0.2 and 5%, based on the weight of said composition~ The degree of heat stabiliæation is considerably enhanced when ~he phosphite i8 combined with certain mono-9 di~ and triorganotin compounds : ~n such lo~ concentrations as are usually considered ineffective in tha~ t~ey do not impart significant heat stabilîty in the ab~ence o~ the phosphite. Be~ween O.L and 1~ o~ the organotin compou~d, baæed on the weight of the poL~mer composition, is useful~ Little i~ any beneficial effect : results from employing more than about 1% o~ the organotin compound. Concentrations of between 0~1 an~ 0~5% are preferredO me organotin compound extends the period of time during which thP polymer composition can he exposed to el~vated temperatures without di~co~oring to the extent that the compo~ition i~ no longer commercially u~efulO
., ~ 065531 Organotin compounds that are suitable or use with phosphite to orm the pre~ent ~;tabilizer composition~
S - R
exhibit the general ormula RmSnY~I, RzSn I 9 \o/' ` ' O O
[R2SnSR ( ]S or R SnS~ C wherein R , R , Y

R Sn(SR C \ )2 and m have been defined in the preceding section o~ this specifica~ion. One class of suitabLe compounds can be broadly de~ined as mono-, di- and triorganotin derivatives of mercapt~ns, mercaptoacids and mercaptoacid esters, the : : organotin compound having been ~ormed ~y replacement of a :~ 10 hydrogen-sulfur or hydrogen-oxygen bond with a tin-sul~ur or tin-oxygen bond. A ~econ~ class of ~uitable organotin :~ com~o~nds includes m~no~, di- and triorganotin carboxylates wherein the acid re~idue îs derived ~rom monocarbox~lic acîds containing between 2 and 20 carbon atom~. Alternatively the acid portion of the molecule can be the re~idue o~ a dicarboxylic acid such as maleic, fumaric or adipic acid or a half ester of a dicarboxylic acid. Residue~ derived ~ O O
: ~rom ha~ ester~ o~ maleic acid, ;.e~ ~OCCH=CHCOCgHl7 are particularLy pre~erred.
me ~olLowing radical~ are among those which can be represented by R and Y in the foregoing fonmula ~mSnY4_m a .' '106 '53i 1) alkyl radicals - methyl, ethyl9 n-propyl, isopropyl, the isomeric butyL, hexyl, 2-ethyL hexyL, octyl9 decyl, dodecyl and eico9anyl radicaLs;
2) aryl radicals ~ phenyl, naphthyl;

3) cycloalk~l radicals - cyclopenty:L, cyclohexylt cyclooctyl;

4) aralkyl radicaLs - benzyl, ~-phetlylethyl;

5) alkaryl radicals - tolyl~ o-9 m- or p~ xylyl.
Y
1) a mercaptan residue ~SR wherein R i~ selected ~rom the same group as R ;

2) a mercaptoacid ester re~idue - SR C~ 4 or a mercaptoacid re~idue -OCR S- wherein R is a~ de~;ned hereinabove and ~ i8 a methyLene or ethylene radical. m is class includes alkyl and aryl esters of mercaptoacetic acid .
and mQ~captopropionic acid in addition to the free acids;
O
3? a residue of a monocarboxylic acid -OCR wherein R is selested fran the same group as R , e.g. a residue o acetic, propionic, stearic~ lauric, benzoic, haphthoic or phenylacetic acid, one of the isomeric methylbenzoic acids, or the mixture of f~tty acids present in tall oil ~a ~y~product of the paper-making process from wood pulp~;

' .
.

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4) a residue of a half ester of a ~turated or ethylenically unsaturated dicarboxyLic acid1 ~.g. maleic or adipic acid wherein the alcohoL residue of the ester contains between 1 and 20 ¢arbons atom~; representative haL~ esters include isopropyl maleateg iso-oc~yl maleate9 lauryl maleate, .
stearyl maleate~ benzyl maleate, cyclohexyl maleate and lauryL adipate; 0 Q
5) a residue o~ a diester o~ thiomalic acid, R OC-CH-CH2COR
bonded to the sulfur atom; 0 0 .. ..

6 ) a residue of maleic acid~ -VC-CH=CH-C0- or other dicarboxylic acid.
Th2 stab`ilizer compositions of this invention are suitable for use with plastisol~ c~ntaining vinyl chLoride polymers. As used herein the term "~inyL chlorlde pol~mers"
incLudes both homopolymers of vinyl chloride and copolymers wherein the major portion of the repeating units i8 derived : ~rom vinyl chloride7 the remaining units being derived from : one or more et~ylenically unsaturated monomers which can be copolymerized with vin~l ohloride. Suitable comonomers include vinyLidene chloride, olefinic hydrocarbons such as ethylene and propylene, esters o~ unsatura~ed acids such as the lower alkyl esters o~ acrylic, methacrylic and maleic :~ acid~ a~d vinyl esters of saturated acids such as vinyl acetate.
In addition to vinyl chloride polymer and stabilizers the present compositions alæo contain a plasticizer for the polymer in an amount of between 5 and 607o based on the weight of the composition. VinyL chLoride polymers of æuitable inherent Yi~Co3ity (be~ween 0.5 and 1.60, measured as a 002%

1~6S531 solution in cyclohexane at ~O~C.) are inherentLy rigid, brittle materials. By combining the poLymer with a suitable pLasticizer it is pos~ible to obtain a plastisol which is solid, semi-solid or liquid at ambient temperatures.
Alt~rnatively, an organic solvent can be added to the plasticized polymer to form an organosol. The resultant plastisoL or organosol can readily be converted to shaped articles ~y casting or molding. Plasticized vinyl chloride polymers are employed as coating or encapsulating m~terials for a wide variety o~ metallic and non-metallic substrates.
Coatings for fabrics is only one of the many uses $or these materials. The plasticized polymers are applied to the ~abric in liquid ~orm by dipping~ spread ~oating or ~praying.
Plasticized polymers in a finely di~ided solid form known as powder coatings can be appLied by suspending the polym~r particles in an air stream and dipping a heated substrate into the suspended particles. Some o the particle~ contact and are melted by the heated surface to form a coherent coating.
Other ~nown techniques for applying powder coa~ings, including electro~tatic spraying, can also be employed. Regardless of the application method, ~he coated substrate is usually heated to melt the polymer particles and form a coherent film.
Among the classes of know~ plasticiæers ~or vinyl chloride polymcrs are esters derived from aromatic or aliphatic dicarboxylic acids and monohydric alcohol~9 both of which contain between 6 and 20 carbon atoms. Repres~ntative plasticizers include dioctyl phthalate, dioctyl adipate and dioctyL sebacate. Other plasticizers include alkyl, aryl and mixed alkyl-aryl triesters of phosphoric aeid such a~

106553~L

triphenyL phosphate; esters o~ benzoic acid with oligomers of alkyLene diols~ such as dipropylene gLycol dibenzoate, epoxidized esters of unsaturated acilds such as butyl epoxy stear~te, lower alkyl esters of trimellitic acid9 chlorinated paraff~nic hydrocarbons containing between 30 and 70% by weight of chlorine and liquid poLyesters derived from aliphatic dicarboxylic acids and diols~
m e stabilized compositions o~ this invention may optionalLy eontain one or more materials selected from volatile organic solvents (inc7uding ketonest primary alcohols, and liquid hydrvcarbons containing between 1 and L2 carbon atoms), pigments such as titanium dioxide, antioxidants such as hindered phenols, lubricating agents, which include paraffin waxe~, fillers such as calcium oarbonate or kaolin and viscosity control agents ~uch as fused silica or polymeric glycols containing an average o~ be~ween 2 and 5 repeating units per molecule. m e antioxidant prevents or lnhibit~
degradation of the vinyl chloride poly~er or other component by oxidizing agents, such as the oxygen present in ~he air.
Polyethylene glycols and polypropylene glycols are particularly preferred for use as visco~ity control agents.
The heat stability imparted to plasticized vinyl chloride poLylEers by ~he present combinations of an organo-phosphite and an organotin compound is further ~hanced when a hea~y metal æalt, particularly a zinc cadmium or bariuun salt o~ a monocarboxylic acid containing between 6 and 12 carbon atoms~ is included in the polymer composition at a concentration of between 005 and lO~, based on the weight of the ~tabilizer component, ` .

106~531 The ~ollowing examples demonstrate pre~erred embodiments o~ the present stabilizer compositions, and shouLd not be interpreted as limiting the scope o~ the invention as de~ined in the acco~panying claims. In the S examples all parts and percentages are by weight.

The stabilizers were evaluated using plasticized vinyl chloride polymer compositions containing the following ingredients:
Vinyl chloride homopolymer L00 parts DioctyL phthalate 60 parts Epoxidized soybean oiL5 parts StabiLizer as specified me formulations were prepared by gradually adding all o the polymer to 45 parts o~ dioctyl phthalate with stirring. me remaining 15 part~ of pht~alate ester was then blended into the resultant thick paste, ~ollowed by the epoxidized soybe~n oil~ Depending upon the number of samples needed, the desired amount of the resultant mi~ture wa~
weighed out and combin~d with the required amount of stabilizer using high speed agitation. me compo~ition was then dearated under reduced pre~sure and ca~t into a ~ilm u~ing a draw-down blade. The thickness of the film thus produced was between 0.02 and 0.03 inch (0.05 and 0008 cm.)~ Ihe ~ilm was heated to a tempe~ature of 190~ . for 5 minutes to fuse together the individual polymer particles~ After cooling, the film was cut into æquare sample~ measuring 2.5~ cm~ along each side.

... ,~_ . ...... .

,~ 1~6553^~l The samples were placed in a circulating air oven heated to 205C. for 25 minutes. Samples were withdrawn from the oven at S minute intervals a~d rated for color using the Gardner Color Scla~ by visuaLly comparing the color of the sample with a s~t o~ Gar~ner standar~ color disks which were numbered according to depth o shade ~rom 1 ~water-white) to 18 (dark brown). m e color ratings for compositions containing combina~ions of diphenyl isodecyl phosphite and an organotin compound or the phosphite alone appear in Table lo The ratings obtained ~or samples containing the organotin co~pound as the sole stabilizer are summarized in Table 2.
m e organotin compounds are repre6ented by Letters as follows:
A ~ di-n-butyltin-S,S'-~is(isooctyL mercaptoacetate);
used alone at 2.0 parts R - di-n-butyltin dilaurate; used aLone at 2.0 parts and 0025 part C = triphenyltin lauryl mercaptide; used aLone at 2~5 parts D = monobutyltin tris~2-ethyl hexoate); used alone at 2.5, LoO and 0~25 parts E = di-~-butyLtin bis~i~ooctyl maleate); used alone at 0~25 part F = di-n-butyLtin-S,S'-bis(lauryl mercaptopropionate~;
used alone at 0~25 part G = di-n~butyltin-S9S'-bis(diisooctyl thiomaleate);
used alone at 0.25 part : H - butyltin tri~ talLate (derived from tall oil fatty acids); used alone at 2.S parts ~ .

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~g o ~ C`1 .

. '3~-1 r~ _1 4.C C~ ~ Q c~l O ~ O_~ O o O O

~'~ _l _l O O O O o O O o o O
C!~ X O O O O O O O O .0 0 0 0 0 `

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'$~ ~ P' ^ ~ t ^ ^^ ^ ^ ^ '' ^
P J ~d ~ ~o ~ O C~
~ Q. h P O O O O O _~ O O O O
h O ~8 0 o o ~ ~ a a) ~ ~
~ p~'~
~C Oq ~ ~ u~ U~ u~ u'~ ~ ~ ~1 ~ ~ P~ ~ o ~ o U-c~ C`l tQ S~ ~ ~ O
,s ~ao,l , I

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C~l ~ ~
C~
o O ~ J ~
N N ,~ I .

a~ ~ c'- N ~ ;~ ~ ~ C`~I~ O~ U') .~
.C O 1-l J N N r~l ~ N C'') ~~
~:: 0 ~1, Oh ~ u~ O O ,1 _I O _I ,1 ~1 _I ~1 _I
.~
~ ~X O O O O O O O O O O O O

_, _ ~ ~ ~ . .
:~ ~ ~ 0,~
. :~ ~ Q. u~
.:. ~ ~ O O c~ ~ O. C~l ~ C~l ~ U~
' ~ C~ O ~ I O o o 0 a~
: ~ .CO , . .
N . ~

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~ 5531 ___ This example demonstrates that the improved stabilization imparted by the present organotin compounds is obtained using a variety of phosphites. The samples employed to evaluate heat stability were prepared and tested as described in ExampLe 1. Each o~ the phosphites were tested aLone and in combination with 0025 partæ of monobutyLtin-S,S',S'I-tris(isooctyl mercaptoacetate) per 100 parts of polymer. The amount of each phosphite empLoyed was equivaLent to a phosphorus content of 0.2 part per 100 parts of vinyl chloride polymer.
The results of the evaluation are swmmarized in th- f louing Table 3.

;:

:
~:
~:

~ 6S531 I ,_ ' ~ o~ ~ o~
0,~ ~ ~.P
~ ~o ` ~ o ~ o ~ o P ~ ." ~ $ ~ '~
O bO ~ bO ~ O b~
~:: h P h 1~ h P h ~d O c~ O I:d O ~ C) ~0 b~ ~0 bO
O ~ O ~ O ~ O
.C: ,¢ S ,1: ~ S ~ .
.~ .~ '3 '~ '~3 '~e .~ .~
~ _, ~ ~, ~, ~ ~_ .
In ~ ~ c~ ,1 ~ ~o u~ ~o I ~ ~1 ~1 ~1 _ C.~
Xc) o ~ _~ oo _~
.~ . , rl ~ W
O ~ O cr~ O ~ O ~ ~
i~ ~::
I h~d 0 ~$ ~ O ~ O c~ O 1-1 O ~1 0 04~
X VO
~ O ~1 O ~ O ~ O ~
' ~ ~ . h ~ ~ ~ ~
.'~ ~ . ,_._ ._ ___ 0 ~ ~ S~
: ~ ~ g~
: ~ ~:~ ,, $ u~ u~ u~ u~
: a) ~ ~c~ ~o ~D O OX 00 ~ O ~ a~
~ ~~ O C~ e~l C`l e~ ~1 ~1 ' "~ ~tD 0 ~
:~: : ~ ~ ~ . 0 P~ ~ ~

o o ~ ,,~ ~ ~ ~ .
~ ~'~ _I-S ~ ~
o ~ ~ a) ~ ~ ~ CD
Q~ al co d~ ~: ~q ~ q ~ C~
q~ rl O ~ O ~ O ~ rl O C) ~ a ~ ~ E~ ~ ~ ~
:~

EXAMP~E 3 The evaluation described in Example 2 was repeated using 0.25 part o dibutyltin bis(isooctyl maleate) as the organotin compound. m e results of the e~aluation are summarized in Table 4.

Effect o Various Phosphite~ on Heat Stability Using Dibutyltin bis(isooctyl maLeate).
Parts per 100 Gardner Color FolLowing x Phosphite parts of polymer Minutes o~ Heating at 205C.
X=0 5 L0 15 20 25 , , ~
Triphenyl l~85 0 l 4 8 12 14 phosphite Trii~odecyl 3.00 0 L 2 5 11 15 phosphite Phenyl diiæodecyL 2.60 0 l 2 5 ~ 12 phosphite Diphosphite ~ 4,20 0 l 3 6 ll 14 None 0 l 3 12 L6 17 (organotin compound alone at 0.25 part) Diphosphite=Tetrakis (nonylphenyl) polypropylene glycol 425 diphosphite (contains 4~5~ phosphorus).

The data in the foregoing examples demonstrate the impro~ed resistance to initial discoloration ;mparted by the organo~in compound.

~6SS3~

. _ _ Thi~ example demonstrates that no improvement or a decrease rather than an increa~e in heat stabiLity is obtained when the weight ratio of phosphite to organotin compound is less than 1:1.
The samples were prepared and tested as described in Exampl~ 1. The organotin compounds employed were dibutyltin-S,Sl-bis(isooctyL mercaptoacetate) (A) and dibutyltin di(isooctyL maleate) (B). The phosphite was diphenyl iæodecyl phosphite. me concentrations of the two stabilizer components together with the Gard~er coLor values observed during the test are summarized in the following Table 5, wherein all parts are by weight based on 100 parts of vinyl chloride polymer~

TABLE 5 .

Heat Stability for Compo~itions Wherein Phosphite:Organotin i8 le~s ~han 1:1 Organo~in Gardner Color Value Followi.ng x Compo~nd Parts of minutes of heating at 205C.
(parts) Phosphite X~0_ 5_10 15 20 , A (2.25) 0.25 0 0 0 1 2 A (1.5) 1.0 0 0 0 1 2 A ~2.5) Q 0 0 0 B ~2 o25) 0.25 0 1 1 2 12 . . .

IL06553 ~

This exampLe demonstrates that the heat stabiLity imparted to vi.nyl chLoride polymers by the present stabiLizer compositions is not observed when the polymers are ~ubjected to high leveLs of shear such as are encountered during extrusion or i~jection molding.
The mixing bowl of a Brabender Plasticorder was charged wi~h a 55 gram sampLe exhibiting the following composition:
Vinyl chloride homopolymer - L00 parts Dio~tyL phthaLate (plasticizer)- 45 parts Epoxidized soybean oil - 5 parts Stabilizer (as specified) _ 1 part m e cvntents of the mixing bowl were hea$ed to 190C. and the speed of the rotors adju~ted to 200 r~volutions per minute. The amount of torque r~quired to maintain a constant motor speed o~ 200 revolutions per minu~e was recorded a~ a ~Imction of ~ime. As the polymer melted the torque decreaæed to ~ value wh;ch remained fairLy constant umtil the polymer began to decompose and undergo crosslinking, a~
: which~time the sLope of the r~corder plot abruptly increased.
The time which had elapsed when the slope of the curve increased due to polymer decomposition is recorded as the time to f ailure in the ~ollowing tabLe .
The phosphite and organo~in compound empLoyed were diphenyL isodecyl phosph;te and dibutyltin-S ,S' -'bi6 ( isoocty ercaptoaceta te~ respec tiveLy .

~20 10~i55;~i Parts of Parts of Time to Phosphite Organotin Compound Yailure (minutes) 0~25 0.75 38 0.75 0.25 26 o~g 0.1 30 Parts per 100 parts by weight of polymer.
.

The results of this test demonstrate that the stability imparted by the phosphite is ad~ersely af~ected by the addition of an organotin compound in an amount within the scope of the present inventionO

-21~

Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method for improving the heat stability exhibited by shaped articles, films or coatings, prepared using plasticized vinyl chloride polymer compositions, consisting essentially of (a) a vinyl chloride homopolymer or a copolymer wherein at least 50% of the repeating units are derived from vinyl chloride, the remain-ing repeating units being derived from one or more ethylenically unsaturated compounds which are copolymerizable with vinyl chloride;
(b) between 5 and 60%, based on the weight of said compo-sition of a plasticizer for vinyl chloride polymers;
(c) between 0.5 and 5%, based on the weight of said compo-sition of an organic ester of phosphorous acid, said ester exhibiting the gen-eral formula P(OR1)3,P(OR1)2(OR2) or (R1O)2POR3OP(OR1)2 wherein R1 and R2 are each selected from the group consisting of alkyl radicals containing between 1 and 20 carbon atoms, cycloalkyl, aralkyl, aryl, alkaryl radicals and hydrogen atoms with the proviso that the number of hydrogen atoms is 0 or 1, and R3 is the residue obtained by removing the two terminal hydrogen atoms of a poly-propylene glycol, the method comprising (1) adding to said polymer composition between 0.1 and 1%, based on the weight of said composition, of an organotin compound corresponding to the general formula Rm3SnY4-m, , or wherein m represents the integer 1, 2 or 3 and Y represents a radical exhibi-ting a formula selected from the group consisting of , , , , and ;
R3 and R4 are each individually selected from the group consisting of alkyl radicals containing between 1 and 20 carbon atoms, cycloalkyl, aralkyl, aryl and alkaryl radicals and R5 is a methylene or ethylene radical and R6 is an alkylene radical containing between 1 and 8 carbon atoms, inclusive, with the proviso that the organotin compound constitutes between 3 and 45% of the com-bined weight of the organotin compound and the organic ester of phosphorous acid, and (2) subsequently converting said composition into a product selected from the group consisting of shaped articles films and coatings, wherein the conversion is accomplished in the absence of significant amounts of shear.

2. The method of claim 1 wherein the phosphite is selected from the group consisting of triphenyl phosphite, diphenyl isodecyl phosphite, triso-decyl phosphite, phenyl diisodecyl phosphite and tetrakis(nonylphenyl) poly-propylene glycol 425 diphosphite.

3. The method of claim 1 wherein the vinyl chloride polymer is a homopolymer.

4. The method of claim 1, 2 or 3 wherein the combined concentration of ester and organotin compound is between 1.5 and 2.5%.

5. The method of claim 1, 2 or 3 wherein the organotin compound is se-lected from the group consisting of butyltin-S,S',S"-tris(isooctyl mercapto-acetate), dibutyltin-S,S'-bis(isooctyl mercaptoacetate), dibutyltin dilaurate, dibutyltin bis(2-ethyl hexoate) dibutyltin bis(isooctyl maleate), dibutyltin-S,S'-bis(isooctyl mercaptopropionate), dibutyltin-S,S'-bis(thiomaleate) and triphenyltin S-lauryl mercaptide.

6. The method of claim 1, 2 or 3 wherein the plasticizer is an alkyl, aryl or a mixed alkyl-aryl triester of phosphoric acid.