CA2026088A1 - Dihydropyridines as costabilizers for moulding compositions based on polymers of vinyl chloride - Google Patents

Abstract

ABSTRACT
A stabilized thermoplastic moulding composition based on halogen-containing polymers, in particular polyvinyl chloride or copolymers thereof, comprising as primary heat stabilizers zinc compounds and polymeric stabilizers from the group of polyoxazo-lines. The composition comprises as costabilizers compounds of the formula I

Description

2 ~ 2 ~ 8 HULS AKTIENGESELLSCHAFT O.Z. 4422- PATENTABTEILUNG -Dihydropyridines as costabilizers for mouldinq composi-- tions based on polymers of vinyl chloride The invention relates to rigid or plasticized, stabilized thermoplastic moulding compositions based on halogen-containing polymers, in particular polyvinyl chloride or polymers containing esRentially vinyl chloride.
It i8 known that chloride-containing polymers are readily degraded by the action of heat, for example during processing, this degradation leading to undesired dis-colorations and to an impairment of the mechanical properties. Consequently, this degradation i8 avoided by adding stabilizers to the polymers before processin~. In ; 15 the case of polyvinyl chloride and copolymers containing essentially vinyl chloride, particular use is made of organotin compounds, inorganic and organic lead salts, ~; organic antimony compounds or combinations of cadmium carboxylates and barium carboxylates and also of a mixture of zinc soaps and polyoxazolines. These so-called primary stabilizers are frequently supplemented with costabilizers to improve their effectiveness. The mode of action of primary or co-stabilizers and their combined action (synergism) are described in the relevant litera-ture, for example in the publication by L. I. Nass, ~HeatStabilizers~, Rirk-Othmer Encyclopedia of Chemical Technolo~y,~volum 12, 3rd edition, page 225, published y~John Wll~y and Sons, 1980.

E~sentially, these are costabilizers which improve the 'initial colour and the ultimate stability. For instance, epoxy compounds, polyols, organic phosphites, substituted dihydropyridines, 1,3-diketones or else combinations of these compoundsi are uJed.

At the pre~ènt time, no highly effective costabilizers are available for primary stabilizers based on polymers.
Therefore, there is a need for substances or mixtures of ~ 2 - 2 ~ 3 ~ 8 substances which support or reinforce the heat- ` ~-stabilizing action of polymeric primary stabilizers.~ ~
~ , Surprisingly, it has now been found that costabilizers of the formula Rl00C C00R

H3C i CH3 (I)~

H
in which Rl is Cg-C22-alkyl, alkenyl, cyclohexyl, phenyl or substituted phenyl, greatly improve the stabilization.

Preference is given to the use of dihydropyridines in ~; which R1 are C9-Cl~-alkyl groups. The dihydropyridines are generally prepared by the process published in Chem.
Reviews, 72, 1 (1972), in which an acetoacetate of the genera} formula in which R = linear or~ branched Cg-C~-alkyl, alkenyl, 15~ ~ cyclohexyl, phenyl or substituted phenyl, i8 ~reacted ~with formaldehyde and ammonia which are optionally generated in situ.

Be-ldes the~co~tabilizer, th- stabilizer systems accord-ing to the invention contain primary stabilizers based on 's~zinc compound and polyoxazolines. The zinc compound i~
characterized in that it contains one or more compounds of zinc of the formula~
; R2O - Zn - oR3 (II) in which R2 and R3 may~ b~e identical or different and repre~ent straight-chain or branched, optionally hydroxyl-substituted aliphatic acyl group~ having 8 to 21 .;~:

2 ~

carbon atoms or aryl groups which are optionally sub-stituted by alkyl groups having 1 to 22 carbon atoms. The C~-C21-carboxylic acids are for example benzoic acid, p-tert-butylbenzoic acid or aliphatic carboxylic acids, in particular octanoic acid, dodecanoic acid, stearic acid or oleic acid.
.
Preferred examples of zinc compounds are zinc soaps of fatty acids having 8 to 36, preferably 8 to 22 carbon atoms. Suitable examples of these are caprylates, caprates, laurates, myristates, palmitates, stearates and behenates. It is also possible to use the salts of branched fatty acids such as 2-ethylhexanoic acid, 2-octyldecanoic acid or tetradecyloctadecanoic acid or else hydroxy-fatty acids such as 9(10)-hydroxystearic acid or 9,10-dihydroxystearic acid. The zinc soaps may be composed of the salts of individual fatty acids or else from fatty acid mixtures such as are obtained from natural fats. Suitable sa}ts of aromatic carboxylic acid~
are in particular the zinc salts of benzoic acid and of substituted benzoic esters, in particular of alkyl-substituted~ benzoic acid. Suitable phenolates are:
~;` methylphenolates, tert-butylphenolate~, nonylphenolates, dodecylphenolates or naphthenates of zinc.
~ ,~ r '~ ~
The polyoxazolines used are represented by the following formula:
_CH2 CH2 C=0 (III) I i R4 n in which R~ are optionaliy different, straight-chain or branched alkyl radicals having 1 to 22 carbon atoms or optionally substituted ~cycloalkyl or aryl radicals, preferably alkyl radical~ having 1 to 12 carbon atoms ;~ while n represent~ integers from 10 to 10,000 (cf.
DE-C-0,253,985). Examples of compounds of the formula III

` - 4 _ 2Q2 are polymethyloxazoline, polyethyloxazoline, poly-n-propyloxazoline, polyisopropyloxazoline, polyundecyl-oxazoline and polyphenyloxazoline. Other primary stabi-li~ers which can be used are copolymers of two different alkyl- or aryl-oxazolines each being present in a pro-portion of between 5% and 95 %. It i8 also possible to use terpolymers of three different oxazolines, each being present in a proportion of 5 to 95 %.

Other highly suitable materials are those stabilized moulding compositions which, in addition to the above~
mentioned primary stabilizers (II) and (III), contain compounds of tin, lead or antimony or combinations of compounds of cadmium, barium, calcium and zinc. -~

The stabilizer mixture according to the invention is used for chlorine-containing polymers. These are preferably ;~
vinyl chloride homopolymers or vinyl chloride copolymers.
Preference is furthermore given to suspension polymers and mass polymers and al80 to emulsion polymers. Suitabls comonomers for the copolymers are for example: vinyl acetate, vinylidene chloride, trans-dichloroethane, ethylene, propylene, butylene, maleic acid, acrylic acid, fumaric acid and itaconic acid. Other suitable chlorine-containing polymers are post-chlorinated PVC and chlorin-ated polyolefins, and also graft copolymers of PVC with ethylene-vinyl acetate (EVA), acrylonitrile-butadiene-styrene (ABS) and methacrylate-butadiene-styrene (MBS).

The stabilized moulding compositions contain the primary ~stabilizers of the formula II and III, advantageously in ~; amounts of 0.02 to 2.0 per cent by weight, in particular in amounts of 0.05 to 1.0 per cent by weight each, ~; relative to chlorino-containing polymer.

The costabilizer according to the invention of the formula I is advantageously used in amounts of 0.01 to 2.0 per cent by weight, preferably in amounts of 0.05 to 0.1 per cent by weight, relative to chlorine-containing 2~2~3`~i3~

polymer.

The stabilized moulding compositions according to the invention may additionally contain commercially available costabilizers. These are, for example, epoxy compounds, preferably epoxidized fatty acids such as epoxidized soya bean oil, phosphites, in particular mixed aryl-alkyl phosphites and phenolic antioxidants, which are prefer-ably incorporated in amounts from 0.05 to 5.0, in parti-cular 0.1 to 3.0, per cent by weight relative to chlor-ine-containing polymer.

Suitable prior-art phosphites are phosphites of the general formulae IV and V

R60_p (R80)2P

(IV) (V) in which R5, R6 and R7 are identical or different and denote C6-Cl8-alkyl, a phenyl radical which may be unsub-stituted or substituted by Cl-C9-alkyl or Cl-Cg-alkoxy, or denote C5-C,-cycloalkyl, and in which Ra is C5-Cl8-alkyl.

If R5, R6, R7 and R8 denote C6-Cl8-alkyl, this i8 for example n-hexyl, n-octyl, n-nonyl, decyl, dodecyl, tetradecyl, hexadecyl or octadecyl. Preference is given to alkyl groups having 8 to 12 carbon atoms.

R5, R6 and R7, as substituted phenyl, are for example, tolyl, ethylphenyl, xylyl, nonyl, cumyl, cresyl, 4-~ethoxyphenyl, 2,4-dimethoxyphenyl, ethoxyphenyl, butoxy-phenyl, p-n-octylphenyl or p-n-nonylphenyl.

Most particularly suitable phosphites are trioctyl, - ,.. , . ~ . . . .. . .... ..

2~

tridecyl, tridodecyl, tritetradecyl, tristearyl, tri-oleyl, triphenyl, tricresyl, tris-p-nonylphenyl and tricyclohexyl phosphite and particular preference is given to the aryl dialkyl phosphites and also to the alkyl diaryl phosphites such as for example phenyl didecyl phosphite, nonylphenyl didecyl phosphite, (2,4-di-tert-butylphenyl) didodecyl phosphite and (2,6-di-tert-butylphenyl) didodecyl phosphite.

Examples of antioxidants are alkylated monophenols and hydroquinones, hydroxylated thiodiphenyl ethers, 1,4-alkylidene-bis-phenols, benzyl compounds, acylamino-phenols, esters or amides of ~-(3~5-di-tert-butyl-4-hydroxyphenyl)propionic acid and esters of ~-(5-tert-butyl-4-hydroxy-3-methylphenyl)propionic acid.

Preferred antioxidants are alkylated monophenols, alkyli-dene-bisphenols and phenyl-substituted propionic esters, in particular, however, 2,6-di-tert-butyl-p-cresol, 2,2-bis(4'-hydroxyphenyl)propane and n-octadecyl ~-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate.

The compound of the formula I can also be used with other nitrogen-containing organic stabilizers. Examples of these are cyanamide, dicyandiamide, guanamines such as benzoguanamine, indoles such as phenylindole, paryzoles (for example as described in GB-B-866,936), ureas and thioureas such as monophenylurea and diphenylthiourea, and aminocrotonic esters; al~o, ~-diketones such as stearylbenzoylmethane, and polyols such as pentaerythri-tol.

It was observed, with the stabilized moulding composi-;~ 30 tions according to the invention based on polymers of vinyl chloride which contain a compound of the formula I
as costabilizer, that this compound reinforces the stabilizing action of a primary stabilizer mixture of zinc compounds and polymers from the group of polyoxazolines to an extent which could not have been _ 7 _ 2~
foreseen. The positive effect of this costabilizer is seen in an improvement in the initial colour and in a prolongation of the ultimate stability. Although DE-A-2,844,130 employs dihydropyridines as stabilizers for vinyl chloride polymers, the stabilizer mixtures employed in the above-cited document differ from the stabilizer mixtures according to the present invention with regard to the primary stabilizers.

It is possible to prepare the stabilized moulding com-positions according to the invention by customary methods, for example by simple mechanical mixinq of the components in conventional mixers. This mixing operation may be used to incorporate other customary processing auxiliaries such as for example lubricants (montan waxes or polyol partial esters), plasticizers, fillers, light stabilizers, pigments or other costabilizers such as for example epoxidized fatty acid esters.

It is possible to achieve a homogeneous distribution of the stabilizers in PVC, for example with the aid of a two-roll mill at 150 to 200C.
i Preparation and testing of milled sheet The action of the stabilizer combinations was tested by determining the static heat stability of milled sheet.
For this purpose, the stabilizer combinations and option-ally plasticizers and processing auxiliaries were mixed with polyvinyl chloride for 30 seconds on a laboratory mill and then processed on a two-roll mill at a roll temperature of 170-C, with co-rotation, in the course of 5 minutes to form 1 mm thick milled sheets. Strips of dimensions 14 x 250 mm were cut from the milled ~heets and these strips were then sub~ected to heat stress in a special oven (Metrastat, type Sigma) at 180C. Under the test conditions, the test strips were continuously discharged from the heating zone and show the effect of the stabilizers from the colour variation.

`J i~

The colour variations were assessed ob~ectively and the test strips compared with each other by determining the yellowness indices (YI; ASTM Method E 313-73 ) using a colorimeter (LabScan 5100 plus) from Dr. Slevogt ~ Ca.
S and plotting the yellowness indices against the duration of heat stress. High YI values indicate strong discolor-ation and thus low stability.

The following stabilizers were used:
Zn = zinc stearate Ba = barium stearate PX = polyethyloxazoline PC = copolymer of methyl- and isopropyl-oxazoline TMP = trimethylolpropane DHP = dihydro-dimethyl-bis(dodecyloxycarbonyl)pyridine Formulations were prepared from the following ingredients (part~ = parts by weight):

Formulation A
- 100 parts of suspension-polyvinyl chloride (R-value 70; VESTOLIT S 7054;
Huls AG, Marl) ;~ - 30 parts of dioctyl phthalate (VESTINOL AH;
Huls AG, Marl) - 0.3 part of montan wax Formulation B t - 100 parts of suspension-polyvinyl chloride (K-value 70; VESTOLIT S 7054;
Huls AG, Marl) - 30 parts of dioctyl phthalate (VESTINOL AH;
Huls AG, Marl) - 0.3 part of zinc stearate - 0.6 part of barium stearate ~ ' ~

9 2~$~

Formulation C:
- 100 parts of suspension~polyvinyl chloride (K-value ~0; VESTOLIT S 7054;
Huls AG, Marl) - 1.0 part of stearic acid Formulation D:
- 100 parts of suspension-polyvinyl chloride ~R-value 60; VESTOLIT S 6058;
H~ls AG, Marl) - 1.0 part of stearic acid Formulation E:
- 100 parts of suspension-polyvinyl chloride (K-value 58; VESTOhIT M 5867;
Huls AG, Marl) - 5.0 parts of epoxidized soyabean oil (Reoplast 39, Ciba-Geigy AG, Bensheimf) f~he invention is further explained and the surprising technical advance is confirmed by the examples which are described below.

The polyvinyl chloride moulding compositions were pre-pared by adding stabilizers from the given tables to the formulations A to E and these mixes were processed in the manner described-above to form test strips.
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Comparison of the results of the heat test, with and without costabilizer Stabilizer composition: Zinc stearate (Zn) Polyethyloxazoline (PX) Copolymer of methyl-oxazoline and iso-propyloxazoline (PC) Trimethylolpropane (TMP) and costabilizer: Dihydropyridine (DHP) _ Formulation Zn~PX/DHP/ Zn/PC/DHP/
without with without with TMP TMP . TMP TMP
. _ S 7054 better better Stearic acid '': ~: , :~ S 70S4 better better VESTINOL AH
~: Zn stearate ;
: 20 Ba stearate .......
S 705;4 better better -VESTINOL AH .
~montan wax (corr. to~Wax~E) S 6058 better better Stearic acid ~ :
:
M 5867 better bet~er Reoplast 39 : . : ~ ;

~ .
~:

3 J ~3 Constituents of the stabilizer compositions in parts by weight 6tabilizer mixtures Zn PX PC T~P DHP

Zn/PX 0.2 0.2 Zn/PC 0.2 0.2 Zn/PX/TMP 0.2 0.2 0.5 Zn/PC/TMP 0.2 0.2 0.5 Zn/PX/DHP 0.2 0.2 0.07 Zn/PC/DHP 0.2 0.2 0.07 Zn/PX/TMP/DHP 0.2 0.2 0.5 0.07 Zn/PC/TMP/DHP 0.2 0.2 0.5 0.07 ;

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Claims (5)

1. A stabilized thermoplastic moulding composition based on halogen-containing polymers comprising primary stabilizers and costabilizers, wherein the costabilizers are dihydropyridines of the formula I
(I) in which R1 is C9-C22-alkyl or alkenyl, cyclohexyl, phenyl or substituted phenyl, and the primary stabilizers are compounds of zinc of the formula R2O - Zn - OR3 (II) in which R2 and R3 may be identical or different and represent straight-chain or branched, optionally hydroxyl-substituted aliphatic acyl groups having 8 to 21 carbon atoms or represent aryl groups optionally substituted by alkyl groups having 1 to 22 carbon atoms, which composition further comprises at least one polymeric primary stabilizer from the group of polyoxazolines of the formula (III) in which R4 are optionally different, straight-chain or branched alkyl radicals having 1 to 22 carbon atoms or optionally substituted cycloalkyl or aryl radicals, while n represents integers from 10 to 10,000.

2. A stabilized moulding composition according to claim 1, wherein the halogen-containing polymers are polyvinyl chloride or polymers containing essentially vinyl chloride.

3. A stabilized moulding composition according to claim 1, wherein R4 represents alkyl radicals having 1 to 12 carbon atoms.

4. A stabilized moulding composition according to claim 1, 2 or 3, said composition containing compounds of the formula II and III, as defined in claim 1, each in amounts of 0.02 to 2.0 per cent by weight and also the compounds of the formula I as defined in claim 1 in amounts of 0.01 to 2.0 per cent by weight, relative to halogen-containing polymer.

5. A stabilized moulding composition according to claim 1, 2, or 3, wherein the compounds of the formulae I to III as defined in claim 1 may additionally contain stabilizers in the form of compounds of tin, lead or antimony or in the form of combinations of compounds of cadmium, barium, calcium and zinc and also addi-tional costabilizers in the form of compounds of the substance categories phosphites, 1,3-diketones, polyols, alkylated phenols, cyanamides, dicyandiamides, guanamines, indoles, pyrazoles, ureas, thioureas, monophenylureas, diphenyl thiourea and aminocrotonic esters.