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Publication numberCA2068116 A1
Publication typeApplication
Application numberCA 2068116
Publication date10 Nov 1992
Filing date7 May 1992
Priority date9 May 1991
Also published asDE69202919D1, DE69202919T2, EP0512955A1, EP0512955B1, US5128397
Publication numberCA 2068116, CA 2068116 A1, CA 2068116A1, CA-A1-2068116, CA2068116 A1, CA2068116A1
InventorsDouglas W. Horsey, Ambelal R. Patel
ApplicantNovartis Ag, Ciba Specialty Chemicals Holding Inc., Douglas W. Horsey, Ambelal R. Patel, Ciba-Geigy Ag
Export CitationBiBTeX, EndNote, RefMan
External Links: CIPO, Espacenet
Stabilized hot melt adhesive systems
CA 2068116 A1
Abstract
STABILIZED HOT MELT ADHESIVE SYSTEMS

Abstract of the Disclosure Hot melt adhesive compositions stabilized against thermal degradation, discoloration, skin formation and substantial viscosity changes, said adhesives being based on ethylene-vinyl acetate copolymer and a hydrocarbon tackifying resin and containing a stabilizer system of a hindered phenol antioxidant, a phosphite costabilizer and an acid scavenger.
Claims(14)
1. A stabilized hot melt adhesive composition comprising (a) ethylene-vinyl acetate copolymer, (b) a hydrocarbon tackifying resin; and (c) a stabilizer composition comprising (1) a phenolic antioxidant;
(2) a phosphite co-stabilizer; and (3) an acid scavenger selected from the group consisting of epoxidized oils, alkali metal salts of higher fatty acids, alkaline earth metal salts of higher fatty acids and amines.
2. The composition of claim 1, wherein components (a) and (b) are present in a weight ratio of 10:90 to 90:10, especially 25:75 to 75:25.
3. The composition of claim 1, which additionally contains (d) up to 50% by weight of a petroleum derived wax, based on components (a) and (b).
4. The composition of claim 1, wherein said hindered phenolic antioxidant corresponds to the formula R1X-(CaH2a)-Q (I) wherein R1 is a group of the formula Ia, (Ia) X is oxygen or sulfur, a is an integer from 6 to 30, b is an integer from O to 6, R2 and R3 are independently C1-C18alkyl, C5-C12cycloalkyl, phenyl or C7-C9aralkyl, and R2 is also hydrogen, Q is hydrogen or -A-(CH2y)-R4, A is oxygen, sulfur or , y is an integer from 2 to 20, B is C1-C4alkyl or C1-C4alkanoyl, and R4 is hydrogen, hydroxy, C1-C4alkanoyloxy or a group of the formula Ib, (Ib);

(II) wherein R2, R3 and b are as defined above, r is 1, d is an integer from 2 to 6, and Q1 is a divalent aliphatic hydrocarbon of 1 to 18 carbon atoms, a divalent aromatic or aromatic aliphatic hydrocarbon of 6 to 20 carbon atoms or a group of the formula IIa when r is also 0 (IIa) wherein f is an integer from 1 to 4;

(III) wherein R2, R3 and b are as defined above, and Q2 is C1-C18alkylene;

R1X-[(CzH2z)-Y]e-R5 (IV) wherein R1 and X are as defined above, z is an integer from 2 to 6, e is an integer from 3 to 40, Y is oxygen or sulfur, and R5 is hydrogen, C1-C4alkyl or a group of the formula Ia;

(V);

wherein R6 and R7 are independently C1-C18alkyl, C5-C12cycloalkyl, phenyl or C7-C9aralkyl, and R6 is also hydrogen, and A1 is a group wherein R8 and R9 are independently hydrogen or C1-C6alkyl;

(VII) wherein R3 is as defined above, p is 1 or 2 and Q3 is C2-C10alkylene; or (VIII) wherein R10 is C1-C10alkyl or C5-C12cycloalkyl, R11 independently is C1-C18alkyl, phenyl or benzyl and R12 is hydrogen or methyl.
5. The composition of claim 4, wherein the hindered phenolic antioxidant corresponds to formula I and X is oxygen, b is an integer from 0 to 2, R2 and R3 are alkyl of 1 to 8 carbon atoms, A is oxygen, y is 2 and R4 is hydrogen or a group of the formula Ia.
6. The composition of claim 4, wherein the hindered phenolic antioxidant corresponds to formula II and r is 1, R2 and R3 are C1-C8alkyl, b is 2, d is 2 or 4 and Q1 is C2-C10alkylene or pentaerythritol.
7. The composition of claim 4, wherein the hindered phenolic antioxidant corresponds to formula m and R2 and R3 are C1-C8 alkyl, b is 2 and Q2 is C2-C6 alkylene.
8. The composition of claim 4, wherein the hindered phenolic antioxidant corresponds to formula IV and X and Y are oxygen, b is 0-2, R2 and R3 are C1-C8 alkyl, z is 2, e is 3-20 and R5 is a group of formula Ia.
9. The composition of claim 1, wherein said phosphite co-stabilizer corresponds to the formulae (IX) wherein R14 is tert.butyl, 1,1-dimethylpropyl, cyclohexyl or phenyl, and one of R15 and R16 is hydrogen and the other is hydrogen, methyl, tert.butyl, 1,1-dimethylpropyl, cyclohexyl or phenyl;

(X) *indicates an isomeric mixture of nonyl;

(XI) wherein R17 is n-C18H37, or phenyl, R18, R19 and R20 independently are C1-C8alkyl, R20 is also hydrogen andR19 is also D-COOR21 wherein D is a direct bond, methylene or ethylene and R21 is C1-C18alkyl; or (XII).
10. The composition of claim 9, wherein the phosphite corresponds to formula IX, X or XI.
11. The composition of claim 1, wherein said acid scavenger is epoxidized soy bean oil, epoxidized castor oil, epoxidized linseed oil, epoxidized sunflower oil or calcium stearate.
12. The composition of claim 1, wherein component (c) is present in a concentration of 0.1-2.5%, preferably 0.5-1,0% by weight based on the total adhesive composition.
13. The composition of claim 1, which additionally contains (e) a (mixed alkylated) diphenylamine antioxidant.
14. A method for stabilizing a hot melt adhesive composition comprising an ethylene-vinyl acetate copolymer and an effective tackifying amount of a hydrocarbon tackifying resin against oxidative and thermal degradation which comprises incorporating into said hot melt adhesive composition (1) a phenolic andoxidant, (2) a phosphite co-stabilizer and (3) an acid scavenger selected from the group consisting of epoxidized oils, alkali metal salts of higher fatty acids and alkaline earth metal salts of higher fatty acids and amines.
Description  (OCR text may contain errors)

206811~

STABILlZED HOT MELT ADHESIVE SYSTEMS

Hot melt adhesives, including those based on ethylene vinyl acetate copolymer, are especially susceptible to oxidation due to high temperature (180C) compounding, storage, handling and application. As the perfoTmance requirements for such adhesives increased, the use of antioxidants evolved to prevent discoloration, undesirable viscosity changes and skin formation on the surface of the adhesive. Hindered phenols were the primary antioxidant of choice for stabilization of the adhesive systems.

A further approach to achieving stabilization beyond that provided by the hindered phenols involved the use of secondary antioxidants such as thiosynergists or phosphite stabilizers including triarylphosphites. The combination of primary and secondary antioxidants provided stabilization performance beyond that which could be expected based on the sum of the performance of the individual components.

A complication was, however, encountered by the frequent use of white or light colored hydrocarbon tackifying resins in adhesive formulations where good color stability is ~equired.
Thus, negative interactions were experienced with such hydrocarbon tacldfiers as evidenced by way of gray-black discoloration upon heating. Since it was hypothesized that the interactions involved the phosphite costabilizer, the applicability of the latter has been substantially reduced. Accordingly, solutions to this problem are required which eliminate the discoloration effect while still preserving the effective properties provided by the presence of the tackifler and the phosphite costabilizer.

Background material on these issues are provided by the following: US-A-4,360,617 which discloses blends of phenols and symmetrical triarylphosphites for stabilizing a broad range of organic polymers including elastomers and ethylene-vinyl acetate copolymers;
US-A-3,658,743 which discloses synergistic combinations of phenols, an organic sulfide or thioester and an epoxide or phosphite ester for the stabilization of hydrocarbon elastomers;
US-A-4,835,200 which discloses stabilizer systems of a thio compound, a phenolic 2068~16 antioxidant, a tris(nonylated phenyl)phosphite and an aliphatic compatible epoxy compound for use in various tackified block copolymer resin systems; and US-A4,857,572 which discloses (alkylthioaUcyl) phenols with optional addidon of phosphites for use in stabilizing various elastomers.

It has now been surprisingly discovered that a unique combination of primary and secondary antioxidants and of an acid scavenger substandaUy eliminates the aforemendoned difficuldes encountered in the stabilizadon of ethylene-vinyl acetate hot melt adhesives containing hydrocarbon tackifying resins. Thus, the blend of hindered phenol, phosphite and acid scavenger provides color stability while m~nimizing viscosity changes, heat degradadon and skin forrnadon. By facilitadng the use of phosphite costabilizers, the combinadon provides stabilization properties which additionaUy exceed the performance of the individual state of the art andoxidants.

The invention pertains to a stabilized hot melt adhesive composition comprising (a) ethylene-vinyl acetate copolymer;
(b) a hydrocarbon tackifying resin; and (c) a stabilizer composition comprising (1) a phenolic antioxidant;

(2) a phosphite c~stabilizer, and (3) an acid scavenger selected from the group consisting of epoxidized oils, alkali metal salts of higher fatty acids, alkaline earth metal salts of higher fatty acids and amines.

The primary components of the hot melt adhesive system are ethylene-vinyl acetate copolymer, a hydrocarbon tackifying resin and, opdonally, petroleum derived waxes and various plasticizing oils.

The applicable tackifying resins may be described as hydrogenated and non-hydrogenated aliphatic petroleum hydrocarbon resins (preferably hydrogenated varieties) resulting from the polymerization of monomers consisting primarily of mono- and diolefins, hydrogenated and non-hydrogenated aromatic petroleum hydrocarbon resins and hydrogenated and non-hydrogenated alicyclic petroleum hydrocarbon resins. Additionally, hydrogenated and non-hydrogenated polyteIpene hydrocarbon resins may be used as the tackifying resin.
Mixtures of the above are also applicable. Such tackifying resins for example are present in concentrations ranging from 10 to 90%, by weight, and preferably 2S to 50%, by weight. The particular resin is selected on the basis of compatibility with the adhesive system, with 20~811~

colorless or white tacldfiers being paTticularly preferred. (~)ARKON P-90 from Arakawa Chemical, (~)ESCOREZ 5300 from Exxon Chemical and ~\REGALREZ 1094 from Hercules,for example, are typical commercial tacldfying resins.

Preferred composidons are those, wherein said hydrocarbon tackifying resin is selected from the group consisting of aliphatic petroleum hydrocarbon resins and hydrogenated derivatives thereof, aromadc petroleum hydrocarbon resins and hydrogenated deIivatives thereof and alicyclic petroleum hydrocarbon resins and hydrogenated derivatives thereof, polyterpene hydrocarbon resins and hydrogenated derivatdves thereof, and mixtures thereof. Pardcularly preferred are those, wherein said hydrocarbon tackifying resin is hydrogenated.

The petroleum derived waxes are optionally present in concentrations ranging from 0 to 50%, by weight, and serve to impart greater fluidity to the molten mateAal, flexibility to the set adhesive and wefflng characteristics. Paraffin and microcrystalline waxes with melting points of 55-110C as well as polyethylene or Fischer-Tropsch waxes are illustrative of this component.

The composition described above may additionally contain (d) up to 50% by weight of a petroleum derived wax, based on components (a) and (b). In these compositions components (a), (b) and (d) are preferably present in a weight ratio of 1:1:1.

These plasticizing or extending oils are also present in order to provide wetting action and viscosity control. Concentrations from 1 to 50%, by weight, are applicable. Typical oils include ole~m oligomers, vegetable and animal oils and naphthenic oils.

In the compositions of the present invention components (a) and (b) are present in a weight ratio of 10:90 to 90:10, especially 25:75 to 75:25.

The combination of stabilizers which substantially eliminates heat degradation, color formation, undesirable viscosity changes and sldn formation comprise (1~ a hindered phenolic antioxidant;
(2) a phosphite co-stabilizer; and (3) an acid scavenger.

206811 ~

Hindered phenols are well known to those skilled in the art.
The composition of the present invention comprises hindered phenolic antioxidants corresponding to the formulae RlX~(CIlH2a)~Q (1) wherein Rl is a group of the formula Ia, H~}(CbH2b)-- I-- (Ia) X is oxygen or sulfur, a is an integer from 6 to 30, preferably 6 to 18, b is an integer from 0 to 6, R2 and R3 are independently Cl-Cl8aL~cyl, Cs-Cl2cycloaL~yl, phenyl or CrC9aralkyl, and R2 is also hydrogen, Q is hydrogen or -A-(C~H2y)~R4~ A is oxygen, sulfur or--Nl--, y iS an integer from 2 to 20, I3 is Cl-C4aL~cyl or Cl-C4alkanoyl, and R4 is hydrogen, hydroxy, Cl-C4alkanoyloxy or a group of the formula Ib, H~(CbH2b)--C---- (Ib);

u~(CbH2b)--C--o~Ql wherein R2, R3 and b are as defined above, r is 1, d is an integer from 2 to 6, and Ql is a divalent aliphatic hydrocarbon of 1 to 18 carbon atoms, a divalent aromatic or aromatic aliphatic hydrocarbon of 6 to 20 carbon atoms or a group of the formula Ila when r is also 0 206~116 (H2C)f N N--(CH2)~

O~N~o (IIa) (Cl H2~f wherein f is an integer from 1 to 4;

L ~ (CbH2b)--C--1 ~ Q2 wherein R2, R3 and b are as defined above, and Q2 iS Cl-C18alkylene;

RlX-[(CzH2~)~Ye~R5 aV) wherein Rl and X are as defined above, z is an integer ~om 2 to 6, e is an integer from 3 to 40, preferably 3 to 10, Y is oxygen or sul~r, and Rs is hydrogen, Cl-C4aLlcyl or a group of the formula Ia;

2 ~

(H3C)3C C(CH3)3 HO~CHH~OH

CH3 ¦ H3C
CHCH3 (V);
H3C~p~

~\C(CH3)3 OH

OH OH
R6~ ~R6 R~ Al~R7 (VI) wherein R6 and R7 are independendy Cl-Cl8alkyl, Cs-C~2cycloaL~cyl, phenyl or C7-C9araL~cyl, and R6 is also hydrogen, and Al is a group ~C(Rg)Rg wherein R8 and Rg are independently hydrogen or Cl-C6aLIcyl;

OH

R3~ l H3C--C--(CpH2p)--C--O- -3 (VII) OH

wherein R3 iS as defined above, p is 1 or 2 and Q3 iS C2-CIOalkylene; and OH
Rl~CHz--S--Rll CH2~ S--Rl 1 wherein Rlo is Cl-ClOallyl or Cs-CI2cycloaL~cyl, Rll independently is Cl-C18alkyl, phenyl or benzyl and R12 iS hydrogen or methyl.

ALkyl is straight chain or branched as for example methyl, ethyl, propyl, n-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 1,1,3,3-tetramethylbutyl, nonyl, decyl, undecyl, dodecyl or octadecyl.

Cl-CI8alkyloxy is for example methoxy, ethoxy, propoxy, n-butoxy, tert-butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, nonyloxy, decyloxy, undecyloxy, dodecyloxy or octadecyloxy.

Cl-C4alkanoyl is for example acetyl, propionyl or butyryl.

Cl-C4aL~canoyloxy is for example acetyloxy, propionyloxy or butyryloxy.
C5-Cl2cycloaL~cyl is for example cyclopentyl, cyclohexyl or cyclooctyl. Cyclohexyl is preferred.

CTCgarallyl is in particular C7-CgphenylaL~cyl~ for example benzyl, a-methylbenzyl, a,a-dimethylbenzyl orphenylethyl. Benzyl is preferred.

Cl-CI8alkylene is for exa nple methylene, dimethylene, trimethylene, tetramethylene, pentamethylene, hexamethylene, heptamethylene, octamethylene, decamethylene, dodecamethylene or octadecamethylene.

For compounds of forrnula II when r is 1, Ql as a divalent hydrocarbon is e.g. straight-chain or branched C2-Cl8aL~tylene, preferably C2-CIOallcylene, or C2-C6aL~ylidene such as, for example, ethylene, ethylidene, tIimethylene, tetramethylene, pentamethylene, 2,2~imethylpropane-1,3-diyl, hexamethylene, heptamethylene, octarnethylene, 206~

decamethylene, 2,2-pentamethylene-propane-1,3-diyl, and cyclohexylene or Ql as a divalent aromatic or aliphatic aromatic hydrocarbon of 6 to 20 carbon atoms is e.g. unsubstituted or substituted C6-ClOarylene such as, for example, phenylene, phenylene substituted by one or more, for example 1 to 3 Cl-C4aL~cyl, naphthylene or ~ C~

Ql as a trivalent, tetravalent or pentavalent hydrocarbon is, for exarnple, a group of the following formulae b ~ ~ ~,~

alkanetriyl of 3 to 6 carbon atoms, such as e.g. glyceryl or trimethylylpropane or alkanetetrayl of 4 to 6 carbon atoms such as e.g. pentaerythrityl.

Formula Ia represents preferably one of the following groups:

(H3C)3C (H3C)3C

H~ CH2CH2--C-- ~ H~ CH2CHz--C--(H3c)3c H3C

Formula Ib is in particular one of the groups (H3C)3C (H3C)3C

H~ CH2CHz--~C--O-- ~Id H(~ CH2CH2--C--O--.
~d (H3C)3C H3C

In the group of the fonnula lIa when r is 0, f is preferably 1 or 2.

2~8~6 Those composidons are preferred, wherein component (1) is a compound of the formula I, II, m, IV, V or VI, in particular I, II, m or IV.

Preferred compositions are those, wherein the hindered phenolic antioxidant corresponds to formula I and X is oxygen, b is an integer from 0 to 2, R2 and R3 are alkyl of 1 to B carbon atoms, A is oxygen, y is 2, R4 is hydrogen or a group of the formula la. Particularly preferred are those compounds wherein R2 and R3 are tert-butyl posidoned ortho to the hydroxyl group and b is 2. Compounds of preference are octadecyl 3-(3',5'-di-tert-butyl-4'-hydroxyphenyl) propionate and 2-ethylhexyl 3-(3',5',-di-tert butyl-~hydroxyphenyl)propionate.

Further prefeIred compositions are those, wherein the phenolic antioxidant corresponds to formula II and R2 and R3 are Cl-C8aL~cyl, in particular tert-butyl posidoned ortho to the hydroxyl group, b is 2, d is 2 or 4 and Q1 is C2-ClOaLtcylene or pentaerythritol. Specific compounds of preference are l,~hexamethylene bis[3',5'-di-tert-butyl-4'-hydroxyhydrocinnamate] and tetralds[methylene 3-(3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate]methane.
Other preferred composidons contain compounds of formula II are those, wherein the hindered phenolic andoxidant corresponds to fo~mula lI, r is 0 and Q1 is formula IIa. A preferred compound of formula II when Ql is forrnula IIa is tris(3,5-di-tert.butyl-4-hydroxybenzyl)isocyanurate.

Preferred composidons are those, wherein dle hindered phenolic andoxidant corresponds to formula I~ and R2 and R3 are Cl-C8alkyl and preferably tert-butyl posidoned ortho to the hydroxyl group, b is 2 and Q2 is C2-C6alkylene. The specific compound of preference is N,N'-hexamethylene bis[3,5-di-tert-butyl-4-hydroxyhydrocinna nide].

Further, composidons containing compounds of for nula IV, wherein X and Y are oxygen, b is an integer from 0 to 2, R2 and R3 are allcyl of 1 to 8 carbon atoms, z is 2, e is an integer from 3 to 20, and R5 is a group of the formula Ia are preferred. Pardcularly prefeIred are those compounds, whereinR2 and R3 are tert-butyl posidoned ortho to the hydroxyl group. A
specific compound of preference is triethylene glycol bis[3-(3'-tert-butyl-S'-methyl4'-hydroxyphenyl)-propionate].

In preferred compositions containing compounds of formula VI R6 and R7 are methyl or 2~811~

tert-butyl and R8 and R9 are hydrogen or methyl. Specific compounds of preference are bis[2-hydroxy-3-tert-butyl-S-methylphenyl]methane and 1, 1-bis[2'-hydroxy-3',5 '~i-tert-butylphenyl]ethane.

A preferred compound of formula VII is OH OH
~C(CH3)3 (H3C)3C~¢I

¢I\C(CH3)3 (H3C)3C~
OH OH

A preferred composition contains a compound of formula vm, wherein Rlo is Cl-C4alkyl and most preferably methyl, Rll is C8-Cl2alkyl and most preferably n-octyl, and R13 is hydrogen.

Exarnples for hindered phenolic antioxidants are tetrakis[methylene-3-(3'-S'-di-tert.butyl-4'-hydroxyphenyl)propionate]methane, thiodiethylene bis(3,5-di-tert.butyl-4-hydroxy)hydrocinnamate, octadecyl 3-(3',5'-di-tert.butyl-4'-hydroxyphenyl)propionate, triethylene glycol bis-[3-(3'-tert.butyl-5'-methyl-4'-hydroxyphenyl)propionate], 1,3,5-trimethyl-2,4,~tris-(3',5'-di-tert.butyl4'-hydroxybenzyl)benzene, 2,~di-tert butyl-p-cresol, tris(3,5-di-tert.butyl-4-hydroxybenzyl)isocyanurate, I,~hexamethylene bis(3,5~i-tert butyl-4-hydroxy-hydrociMamate, and 2,4-bis(n-octylthiomethyl)-~methylphenol.

Applicable phosphites correspond to the formulae 2~6~

~5~o~r ~

wherein Rl4 is tert.butyl, l,l-dimethylpropyl, cyclohexyl or phenyl, and one of Rls and Rl6 is hydrogen and the other is hydrogen, methyl, tert.butyl, 1,1-dimethylpropyl, cyclohexyl or phenyl;

[C9H19~ 3--P (X) *meaning isomer mixture of nonyl;

f--H2C~ ~CH2--0~
R170--P C P--OR17 (XI) \0--H2C CH2--0 Rl8 wherein Rl7 is n-Cl8H37, ~}Rlg or phenyl, Rl8, Rlg and R20 independently are Cl-CI8alkyl, R20 is also hydrogen and Rl9 is also D-COOR2l wherein D is a direct bond, methylene oq ethylene and R2l is Cl-Cl8alkyl and 206811~

C(CH3)3 o~ C(CU3h C(CH3)3 2 Preferred compositions contain compounds of formulae IX, X and XI.
A preferred compound of formula lX is tris(2,~di-tert.butylphenyl)phosphite. A preferred compound of formula XI is bis(2,4-di-teTt.butylphenyl)pentaary~ritol diphosphite.

Applicable phosphite co-stabilięrs include tris(2,4-di-tert.butylphenyl)phosphite, bis(2,4-di-tert.butylphenyl)pentaerythritol diphosphite, and tris~4-nonylphenyl)phosphite.

Applicable acid scavengers include epoxidięd oils and alkali metal and aL~aline ear~ metal salts of higher fatty acids. The epoxidięd oil is readily miscible in the adhesive fo~mulation.
Typical oils include epoxidized soy bean oil, epoxidized castor oil, epoxidięd linseed oil and epoxidized sunflower oil, preferably epoxidized soy bean oil. Typical salts include calcium stearate, zinc stearate, magnesium stearate, sodium ricinoleate, potassium palmitate, antimony pyrocatecholate or tin pyrocatecholate, preferably calcium stearate. Amines a~e also applicable including aLkanolamines such as triethanolamine and sterically hindered amines such as bis-(2,2,6,6-tetramethylpiperidyl)-sebacate, bis-(1,2,2,6,6-pentamethylpiperidyl)-sebacate, n-butyl-3,5 di-tert.butyl-4-hydroxybenzyl malonic acid, bis-(1,2,2,6,6-pentamethylpiperidyl)ester, condensation product of l-hydroxyethyl-2,2,6,6-tetra~nethyl-4-hydroxypiperidine and succinic acid, condensation product of N,N'-(2,2,6,6-tetramethylpiperidyl)-hexamethylenediamine and 4-tert.octylamin~
2,6-dichloro-1,3,5-s-triazine, tris-(2,2,6,~tetramethylpiperidyl)-nitrilotriacetate, tetrakis-(2,2,6,6-tetramethyl4-piperidyl)-1,2,3,4-butane-tetrac ar~onic acid and1,1,'-(1,2-ethanediyl)-bis-(3,3,5,5-tetramethylpiperazinone).

In preferred compositions the acid scavenger is epoxidized soy bean oil, epoxidized castor oil, epoxidized linseed oil, epoxidized sunflower oil or calcium stearate.

206811~

The concentrations (by weight) of the respecdve components in the stabilizer system are as follows: from 25 to 74% of hindered phenol (c 1): and preferably 47.5%; from 5 to 74% of phosphite co-stabilizer (c 2), and preferably 25 to 74% and most preferably 47.5%; and from 2 to 50% of acid scavenger (c 3), preferably 2 to 10% and most preferably 5%.
The total amount of stabilizer system (c) added to the adhesive component is from 0.1-2.5%, preferably preferably 0.5-1.0% by weight based on the total adhesive formuladon.
Additional stabilizers may be opdonally incorpo¢ated into the adhesive compositions. Such additives include other antioxidants, light stabilizers and the like. Compositions containing (e) (mixed alkylated) diphenylamine antioxidants are particularly preferred. Typical alkyl groups include C4-CI8 alkyls.

The adhesive compositions of the present invention a~e typically prepared by blending the components at an elevated temperature, for example between 100C and 250C, preferably between 130C and 200C, until a homogeneous blend is obtained, usually less than 3 hours.
Various methods of blending are known to the art and any method that produces a homogeneous blend is satisfacto~y. The resultant adhesives may then preferably be used in a wide variety of product assembly applications.

The invention also pertains to a method for stabilizing a hot melt adhesive composition comprising an ethylene-vinyl acetate copolyrner and an effective tackifying amount of a hydrocarbon tackifying resin against oxidadve and thermal degradation which comprises incorporating into said hot melt adhesive composition (1) a phenolic antioxidant, (2) a phosphite co-stabilizer and (3) an acid scavenger se}ected from the group consisting of epoxidized oils, alkali metal salts of higher fatty acids and allcaline earth metal salts of higher fatty acids and amines.

The following examples illustrate the preferred embodiments of the invention. In these examples, all parts and percentages given are by weight unless other vise noted.
The following materials are employed in these examples:

"Adhesive" - 1:1:1 weight ratio of ethylene-vinyl acetate copolymer ((~LVAX 250 from DuPont): hydrogenated hydrocarbon tacldfier (~ARKON P-90 from Arakawa Chemical):microcrystalline wax (Bareco BE Square 195 from Petrolite).

2~S~1~ 6 A. tetrakis[methylene 3-(3',5'-di-tert butyl-4'-hydroxyphenyl)propionate]methaneB. thiodiethylene bis(3,5-di-tert.butyl-4-hydroxy)hydrocinnamate C. octadecyl3-(3',5'-di-tert.butyl-4'-hydroxyphenyl)propionate D. triethylene glycol bis[3-(3'-tert.butyl-S'-methyl-4'-hydroxyphenyl)propionate]
E. 1,3,5-trimethyl-2,4,~tris(3',5'-di-tert.butyl-4'-hydroxybenzyl)benęne F. 2,6-di-tert.butyl-p-cresol G. tris(3,5~i-tert.butyl-4-hydroxybenzyl)isocyanurate H. 1,6-hexamethylene bis(3,5-di-tert butyl~hydroxy-hydrocinnamate I. 2,4-bis(n-octylthiomethyl)-6~methylphenol J. tris(2,4-di-tert.butylphenyl)phosphite K. bis~2,4-di-tert butylphenyl)pentaerythritol diphosphite L. tris(4-nonylphenyl)phosphite M. epoxidized soy bean oil (Drapex 6.8 from Witco Chemical) N. epoxidized soy bean oil (Flexol from Union Carbide) P. (aL~cylatedmixture)diphenylamine Q. calcium stearate Example l This Example illustrates the improved performance characteristics provided by the compositions of this invention.

The a&esive composition ("A&esive") and additives are blended until homogeneous.Samples are then maintained in an oven at 177C and measured for color at periodic intenals utilizing a Gardner Color Scale.
The results are given below.

g = gray coloration b = black coloration Additive Conc. % Gardner Color I. 024 48 72 96 A 0.5 12 3 5 6 A 1.0 12 3 4 6 A/J 0.5/0.5 13 g A/J/M 0.5/0.510.05 1 1 2 3 4 A/J/N 0.5/0.5/0.05 1 2 2 3 4 II.
A/J 0.5/0.5 13 g A/J/M .49/.49/.021 2 3 4 5 A/J/~ .485/.485/.03 1 2 3 3 4 A/J/~ .48/.48/.041 2 3 3 4 A/J/M .475/.475/.05 1 2 3 3 4 m.*

A 1.0 0 2 5 6 7 A/J 0.5/0.5 0 3 g A/J/~ .475/.475/.05 0 1 2 2 3 A/J/M .49/.49/.0~ 0 0 1 2 3 * contains hydrogenated hydrocarbon tackfier (tg)ESCOREZ 5300 from Exxon) 2 ~

IV.
120 hrs A 0.5 0 33 4 4 6 A 1.0 0 33 4 4 6 J 0.5 0 2 g g g g A/M .5/.025 0 33 4 4 6 A/Q .5/.025 0 34 7 7 8 A/J .5/.5 0 48 b b b J/M .5/.025 0 26 10 11 12 J/Q .5/.025 0 36 9 11 12 A/J/M .5/.5/.05 0 11 2 3 5 A/J/Q .5/.5/.05 0 11 3 4 5 Example 3 The procedures of Example 1 are repeated wi~ a series of addi~onal hindered phenols.

Additive Conc. (%) Gardner Color J 1.0 0 g b A 1.0 0 3 5 5 5 A/J O.S/0.5 0 4 b A/J/M .nsl.ns/.os o 3 3 4 6 B 1.0 0 4S 10 11 B/J 0.5/0.5 0 gb B~ .475/.475/.05 03 3 4 6 C 1.0 0 45 5 6 Cl~ 0.5/0.5 0 5b C/J/M .475/.475/.05 o3 4 4 4 20681~ ~

D 1.0 0 5 6 7 7 D/~ 0.5/0.5 0 g b - -D/J/M .475/.475/.05 0 3 5 6 6 E 1.0 0 6 6 7 7 E/J 0.5/0.5 0 g b E/J/~I .475/.475/.05 0 3 4 5 6 F 1.0 0 6 910 10 F/J 0.5/0.5 0 4 b ~/J/M .475/.475/.05 0 3 3 4 6 G 1.0 0 5 6 7 7 G/J 0.5/0.5 0 g b G/J/M .475/.475/.05 0 3 3 3 4 H 1.0 0 4 6 6 7 HlJ 0.5/0.5 0 g b - -H/J/M .475/.475/.05 0 2 3 3 4 1.0 0 4 610 12 VJ 0.5/0.5 0 g b - -VJ~M .475/.475/.05 0 3 611 11 P/A 0.5/0.5 0 4 5 6 7 P/A/J .25/.25/.5 0 5 b - -P/A/J/M 24/.24/.47/.05 0 1 2 3 4 The data in Examples 1 and 2 clearly illustrate the significandy improved stabilization characteristics provided to the ethylene-vinyl acetate hot melt adhesive formulations.

Summarizing, it is seen that this invention provi~es improved stabilization systems ~or use in ethylene-vinyl acetate hot melt adhesive compositions containing hydrogenated hydrocarbon tackifying resins. Vatiations may be made in procedures, proportions and materials without departing from the scope of the invention as defined by the following claims.

Classifications
International ClassificationC09J131/04, C09J123/08, C08K5/00
Cooperative ClassificationC09J123/08, C08K5/005
European ClassificationC08K5/00P6, C09J123/08
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DateCodeEventDescription
16 Apr 1999EEERExamination request
7 May 2001FZDEDead