WO1992001017A1

WO1992001017A1 - Pvc stabilizer composition and process for manufacture of the composition

Info

Publication number: WO1992001017A1
Application number: PCT/AU1991/000289
Authority: WO
Inventors: Andrew Geoffrey Swincer; Stephen Kenneth Duplock; Alexander Joseph Hruza
Original assignee: Ferro Corporation
Priority date: 1990-07-03
Filing date: 1991-07-02
Publication date: 1992-01-23

Abstract

A primary heat stabilizer for vinyl halide polymers, particularly polyvinyl chloride is disclosed comprising the product formed from mixing an oxide or hydroxide of a Group 2B or 3A metal of the Periodic Table and a polyol. The preferred oxide is zinc oxide while the preferred polyol is pentaerythritol. As well as the stabilizer, compositions of polyvinyl chloride containing the stabilizer and methods of preparing the stabilizer, such as by mixing at elevated temperature are disclosed.

Description

PVC STABILIZER COMPOSITION AND PROCESS FOR MANUFACTURE OF THE COMPOSITION

Background of the Invention

The present invention relates to primary stabilizer compositions for vinyl halide polymers.

During the production of articles from vinyl halide polymers, the polymers are normally exposed to heat. Typical of such processing steps are the compounding of vinyl halide polymers with additives such as plasticisers, ultra violet light stabilizers and lubricants, and the extrusion and/or moulding of the polymers to form useful articles. When vinyl halide polymers are exposed to heat for extended periods of time they tend to decompose by loss of hydrohalide molecules from the polymer chain. Such degradation results initially in discolouration and ultimately in embrittlement of the polymer and its loss of utility.

In order to overcome the heat instability of vinyl halide polymers, heat stabilizers have been incorporated into the polymers at an early stage of processing - for example during compounding. The stabilizers hitherto employed fall into three main categories. These are compounds of lead, organo tin compounds and mixed metal compounds. According to the Encyclopedia of PVC, Second

Edition edited by Leonard L. Nass and Charles A. Heiberger, lead stabilizers are the most cost effective means of stablizing PVC and have hitherto been unequalled in electrical properties especially in applications in which the vinyl halide polymer requires good electrical insulation properties. Three basic reasons have been advanced for the stablizing properties exhibited by lead compounds. These are: (i) lead oxide is an excellent hydrohalide scavenger because of its basicity and extremely fine particle size; (ii) lead halide is not a strong Lewis acid and therefore does not catalyse the dehydrohalogenation of vinyl halide polymers; and (iii) lead halides are some of the few halides that are not water soluble or ionizable.

According to the Encyclopedia of PVC, lead stabilizers which when incorporated into polyvinylchloride "generate lead chloride which is neither ionizable or water soluble. As a result, lead stabilizers provide PVC wire and cable with long term ageing and insulating properties that are unachievable with all other stabilizer classes. "

While the United States changed to organo tin stabilizers for potable water pipe and most other rigid applications during the late 1950's, lead stabilizers remained entrenched in North America for the stabilization of PVC insulation for electrical and telecommunication cables due in combination to the low cost of the lead compounds and to their superior electrical and heat stabilizing properties, and this is consistent with the practice in all other countries.

According to the Encyclopedia of PVC "the historical connotation of the term mixed metal stabilizers refers to a .class of non-lead containing, non-organo tin containing stabilizers based on cadmium or zinc compounds, functioning as primary stabilizers, and augmented by the inclusion of alkali or alkaline earth metal compounds to prevent the premature formation of the strong Lewis acids cadmium and zinc halide especially cadmium and zinc chloride" . Such strong Lewis acids catalyse the dehydrohalogenation of vinyl halide polymers.

The mixed metal stabilizers gained popularity because of their flexibility in use, especially in end use applications such as flooring, upholstery, floor coverings and roofing. Normally the mixed metal stabilizers were used in the form of soaps because the soaps provided a lubricating function as well as a stabilizing function. Combinations that found particular popularity were combinations of barium and cadmium soap in a typical weight ratio lying in the range between 2:1 and 1:2.

The mixed metals dominated flexible PVC applications in spite of the evolution of greatly improved lead and organo tin products. The principal reason for this has been the discovery of organic synergists or secondary stabilizers that greatly extend the stability of the primary stabilizer. The greatest synergistic effect for mixed metal stabilizers was provided by epoxy derivatives of oils and esters. In addition, organo phosphites were also found to be another important group of organic synergists. However, it was also discovered that the performance of powdered mixed metal stabilizers with a high cadmium or zinc content could also be improved by incorporation of polyhydric alcohols in combination with the soaps. Preferred polyhydric alcohols for use as secondary stabilizers for mixed metals included glycerol, sorbitol, mannitol, trimethylol propane and pentaerythritol.

Today, mixed metal stabilizer systems are comprised of a number of combinations of active metal components. These combinations include (a) barium, cadmium and zinc, (b) barium and cadmium, (c) barium and zinc, and (d) calcium and zinc. Of these, only calcium/zinc systems have been classified as non-toxic. For food contact use, specific compounds of calcium and zinc (as well as other costabilizers and additives) are allowed and these are listed in appropriate legislation (e.g., the Code of Federal Regulations of the Food and Drug Administration of the United States of America) . The disadvantage of calcium/zinc systems as a whole is their poor heat stability even when costabilizing additives are used. This is attributed to the reactivity of the zinc compounds and in particular, to the formation of zinc chloride, which further catalyses the degradation of PVC, as described earlier. It is this deficiency in heat stability coupled with inferior colour and electrical properties that have prevented calcium/zinc stabilizers from replacing lead stabilizers and barium/cadmium stabilizers in most applications.

The specification of United States patent No. 3948833 describes the inclusion of metal derivatives of polyols as part of the stabilizer system for asbestos vinyl chloride polymer compositions. In particular the specification exemplifies the use of "calcium zinc derivatives of pentaerythritol together with conventional stabilizers such as organo tin, barium/cadmium and co- stabilizers such as epoxy compounds and polyols".

The specification of United States patent No. 4501840 describes and claims a process for producing a co- stabilizer suitable for the stabilization of polyvinylchloride. The process comprises heating pentaerythritol at a temperature of about 180 to 220°C with a strongly alkaline acting material (e.g. calcium oxide). This patent exemplifies the use of calcium oxide as the preferred strongly alkaline acting material and claims specifically only the use of alkali metal or alkaline earth metal oxides or hydroxides as the strongly alkaline acting materials useful in preparing the products of the invention. The specification states that pentaerythritol treated in this way can be homogeneously worked into the polyvinylchloride and other vinylhalide resins without difficulty to perform its function as a co-stabilizer.

The specification of examined Japanese patent publication No. 62-24453 in the name of Sakai Chemical Industry Company Limited discloses a vinyl chloride resin composition containing as stabilizer a ternary composition comprising a zinc salt of an organic acid, dipentaerythritol having an average particle diameter of at most 50 micron and at least one compound selected from the group consisting of oxides, hydroxides, carbonates, sulphates, phosphates, phosphites, silicates, borates and titanates of an alkali metal or alkaline earth metal.

The specification of Japanese examined patent publication No. 51-18453 in the name of Matsushita Electric Works Limited discloses a vinyl chloride resin composition containing as heat stabilizer a mixture of calcium and/or barium stearate, zinc stearate and zinc oxide. Examples contained in the specification exemplify the use of pentaerythritol as a co-stabilizer together with dibutyl tin maleate. All of the preceding patents have claimed the use of their inventions as co-stabilizers to be used in conjunction with other conventional PVC stabilizers (e.g. organo tin stabilizers, barium/cadium stabilizers, etc.). None of the foregoing disclosures have contemplated the use of a polyhydric alcohol in combination with a Group 2B or Group 3A metal .oxide or hydroxide as a primary stabilizer, useful in stabilizing PVC without the co-use of other conventional PVC stabilizers. It has now been discovered that polyols when mixed with certain metal oxides can be used as primary heat stabilizers in vinyl halide polymer compositions. Summary of the Invention

According to the present invention there is provided a primary heat stabilizer for vinyl halide polymers, the stabilizer being formed from an oxide or hydroxide of a group 2B or 3A metal and a polyol.

Preferably, the oxide is zinc oxide, although mixtures of zinc oxide and aluminium hydroxide have also exhibited useful properties. Other inorganic oxides may also be mixed with the oxide or hydroxide of the group 2B or 3A metal oxide or hydroxide.

The polyol may be pentaerythritol, dipentaerythritol, trimethylol propane, di-trimethylol propane, tris-2-hydroxyethyl iso-cyanurate, mannitol, sorbitol or mixtures thereof. Pentaerythritol is preferred.

The proportion of oxide or hydroxide to polyol may lie in the range from 0.5% to 70% and preferably lies in the range from 0.5% to 40% by weight of the stabilizer composition. At levels outside this range the synergistic effect of the combination reduces. Detailed Description of the Invention

The compositions of this invention may be formed by mixing the polyol with the oxide at elevated temperatures, preferably at least about 200*C, more preferably 150° to 260°C. In compositions derived from zinc oxide and pentaerythritol, the pentaerythritol is preferably melted and the zinc oxide is mixed into the molten pentaerythritol whilst maintaining the temperature above 200°C. The heat stabilizer compositions of the present invention have shown excellent heat stabilizing characteristics in a range of applications including rigid PVC pressure pipe and injection moulded fittings for potable water and other rigid applications, electrical cable, calendering, automotive applications, refrigerator gaskets, flooring and general flexible and semi-rigid^' applications. PVC/asbestos systems have not been examined and are excluded.

Even though polyols such as pentaerythritol are highly water soluble, test results indicate that the volume resistivity for cable formulations containing the stabilizer compositions of the present invention are comparable with those for lead stabilizers.

Up to 10% by weight of the stabilizer compositions of the present invention may be incorporated into vinyl halide polymer compositions depending on cost and performance.

The primary stabilizer composition of the present invention may be used in conjunction with a secondary stabilizer. Suitable secondary stabilizers include alkaline earth metal soaps and carboxylates such as calcium benzoate, calcium octoate and calcium naphthenate.

The heat stabilizer compositions of the present invention also display benefits in PVC pipe formulations. In particular there is an absence of plate-out during extrusion, which is normally associated with systems containing pentaerythritol.

Preferred embodiments of the invention are illustrated in the following examples and comparative examples and with reference to accompanying Figure 1 which is a graph of Congo Red heat stability and colour stability in a polyvinyl chloride composition measured in units of time and units of colour, respectively both as a function of the respective amounts of each of the two components. Example 1

100 grams of pentaerythritol was heated above its melting point (255 to 259°C) whilst being stirred mechanically in a glass flask using a heating mantle. Small portions of pentaerythritol were added thereafter until 400 grams had been melted. 118 grams of zinc oxide was added in 3 to 4 gram portions. After approximately 15 to 20 grams of zinc oxide had been added the mixture had begun to foam vigorously and some pentaerythritol was lost due to sublimation. 20 minutes after all the zinc oxide had been added, the foaming subsided. Heating was then stopped and the mixture poured onto a metal plate to 'cool. The resulting mixture had a 1:2 molar ratio of zinc oxide to pentaerythritol. Example 2 The above procedure was repeated to produce a 1:1 molar composition of zinc oxide and pentaerythritol.

It is to be noted that the scope of the present invention includes the product or result of mixing together the oxide or hydroxide and the polyol irrespective of the precise nature of the product either chemically or physically. The result of the mixing may include such things as a internate mixture, a complex, a compound, including a co-ordination compound, an adduct, a reaction product or the like or any such similar product. It is preferred that the product be a mixture or a complex. It is also be be noted that at present there appears to be evidence that the product may be either a mixture or a complex or a combination of both which is to say that the product exhibits some characteristics of a mixture and some of a complex among other characteristics. Example 3

400 grams of pentaerythritol and 118 grams of zinc oxide were blended in a glass beaker by hand mixing with a spatula and then charged to a round bottom glass flask equipped with an anchor-blade agitator and immersed in an oil bath at 150^β . The mixture was then stirred for 40 minutes and any material that built up on the sides of the vessel was scraped back into the bulk of the mix. Melting of the material was not observed. The resulting product was then removed, allowed to cool and ground in a laboratory ball-mill. Particles greater than 150 microns were removed by screening. Example 4

The above procedure as described in Example 3 was repeated at a temperature of 175°C. In this example, a small amount of melting was observed in the mixture mainly near the bottom of the vessel. The resulting product was then ground and screened as described in Example 3. Example 5 A sample of the product of Example 1 was formulated into a stabilizer/lubricant system suitable for the extrusion of rigid PVC pressure pipe for potable water and was compared to a lead system and a typical calcium/zinc system exemplifying current technology as found in Europe and Australia. The performance of a stabilizer system using zinc oxide and pentaetythritol, as a simple admixture not prepared by the process of Example 1 but at the equivalent levels as detailed in the process for the manufacture of product of Example 1, was also included. Tests were also performed on the products of Example 3 and Example 4. The evaluations were carried out firstly in laboratory tests for dynamic thermal stability and then subsequently in a production situation by running extrusion trials. Example 5 Part A - Laboratory Evaluations Dynamic Thermal Stability

The dynamic thermal stability was performed on a pre-mixed sample in a Brabender torque rheometer at 196*C and 60 rpm. The pre-mixed sample was prepared by mixing all ingredients as listed below in a Henschel mixer to 120*C and then cooling to 50*C; the dry blend was then allowed to stand for 24 hours before testing.

The test procedure used was to remove small specimens from the rheometer head every two minutes and then assess these for colour stability. The thermal stability was also determined by measuring the time interval before cross-linking due to degradation which was observed by the increase in torque.

The compositions of the six stabilizer formulations have been listed below. Formulation A - Lead System

Components

Tribasic lead sulphate

Lead stearate Calcium stearate^*

Pentaerythritol tetrastearate

Sasolwax HI

Paraffin wax

melting point approx. 65*C Total parts by weight 2.47

Formulation B - Typical calcium/zinc system - current technology

Components Parts b Wei ht

Calcium stearate Zinc stearate

Dipentaerythritol

Trimethylol propane

Paraffin wax,

melting point approx. 65*C Total parts by weight 3.50

Formulation C - Calcium zinc system based on product of

Example 1

Components Parts by Weight

Product from Example 1 0.52 Calcium stearate 1. 3

Bisphenol A 0.10

Stearic acid 0.21

Sasolwax HI 0.21

Paraffin wax, 0.83 melting point approx. 65*C

Total parts by weight 2.90

Formulation D- Formulation C but using zinc oxide and pentaetythritol as individual ingredients

Components Parts by Weight Zinc oxide 0.12

Pentaetythritol 0.40

Calcium stearate 1.03

Bisphenol A 0.10

Stearic acid 0.21 Sasolwax HI 0.21 Paraffin wax-, 0. 83 melting point approx. 65*C Total parts by weight 2.90

Formulation E - Formulation C using product of Exam le 3

melting point approx. 65*C Total parts by weight 2.90

Note:

In Example 1, the quantities of zinc oxide and pentaerythritol used to form the product are 118 grams of zinc oxide and 400 grams of pentaerythritol and this corresponds to a ratio of 22.8 of zinc oxide to 77.2 of pentaerythritol. Consequently, in Formulation D, when zinc oxide and pentaerythritol are added directly, the equivalent amounts of zinc oxide and pentaerythritol are respectively 0.12 and 0.40 parts by weight to compare to product of Example 1 at 0.52 parts by weight.

Each of these six stabilizer formulations was evaluated in a PVC compound of the composition listed below. Stabilizer Formulation: A B C D PVC Compound Component Parts by Weight Resin, 67K 100 100 100 100 100 100

Calcium carbonate filler 2.0 2.0 2.0 2.0 2.0 2.0 Titanium dioxide 2.0 2.0 2.0 2.0 2.0 2.0 Stabilizer 2.47 3.5 2.9 2.9 2.9 2.9

RESULTS OF DYNAMIC THERMAL STABILITY FORMULATION

Formulation A White in colour with a steady deterioration to a strong brown colour at the degradation point at 10.5 minutes. Formulation B Off-white in colour developing more intensely at 4 minutes and increasing to a green-beige colour at 8.0 minutes. Formulation C Off-white colour developing more intensely at 4 minutes but then remaining constant to the degradation point at 12.5 minutes. Formulation D Off-white in colour developing more intensely at 4 minutes but then remaining constant to the degradation point at 12.5 minutes. Formulation E Off-white in colour developing more intensely at 4 minutes but then remaining constant to the degradation point at 12.5 minutes. Formulation F Off-white in colour developing more intensely at 4 minutes but then remaining constant to the degradation point at 12.5 minutes.

These tests show that the product of Example 1 in Formulation C functions as a primary heat stabilizer.

Formulation C exhibits far superior heat stability than Formulation B (current calcium/zinc technology) and, at the levels used, is better than Formulation A (the lead system) .

Formulations D, E and F show the same performance as Formulation C. Example 5 Part B - Production Trials

Formulation C was run on production extruders to manufacture pressure pipe up to 150 mm diameter and some fifty tonnes of pipe were produced over several days. When the dies were changed, there was no evidence of plate-out on the internal metal surfaces such as normally found with formulations containing dipentaerythritol such as Formulation B, the current calcium/zinc technology cited above. This absence of plate-out is especially significant as previous trials with formulations containing pentaerythritol and without zinc oxide or other oxides and hydroxides as embodied in this invention, resulted in uncontrollable plate-out within 4 hours, necessitating the stopping of extrusion and the stripping down of the extruder and die.

The pipe produced passed all physical tests such as impact test and, in particular, the 1,000 hour pressure test at 60*C (Australian Standard AS 1462.6) indicating that the product from Example 1 is resistant to water. This confirms the suitability of Formulation C and the product of Example 1 for the production of PVC pressure pipe.

Formulation D was also run on a production extruder; however, the pipe manufactured on this stabilizer system showed inferior colour to that produced on

Formulation C. This result illustrates the superior performance of the invention when prepared in accordance with the process described in Example 1 compared to that obtained when zinc oxide and pentaerythritol are used without pretreatment by the process described in Example 1.

Example 6

A sample of the product of Example 1 was formulated into a stabilizer/lubricant system for the PVC insulation of electrical cable and was compared to a commercial lead stabilizer/lubricant system in a typical formulation for heat stability and electrical properties.

The test procedure used was to prepare a PVC sheet by mixing all the components in a planetary mixer and then placing the blend onto a 2-roll mill at 170*C where the material was melted and banded together, with frequent mixing. Residence time on the mill was five minutes after full-banding to form a PVC sheet.

For heat stability, the Congo Red test was used and in this test, small pieces of the prepared PVC sheet were cut and placed into a test tube. A piece of Congo Red paper was then fastened near the top. The evolution of hydrocholoric acid (due to the degradation of PVC) is detected by the red paper turning blue and the time taken for this to occur is the heat stability.

Electrical properties were tested by taking the prepared PVC sheet and pressing a flat sheet at 170*C and 2,000 psig for 5 minutes. The pressed sheet was then immersed in deionised water at 20*C for 24 hours after which it was wiped dry and then the volume resistivity measured on a suitable high resistance meter and the insulation constant, Ki, calculated.

The PVC sheets prepared from the lead system (Formulation A) and the zinc system based on the product of Example 1 (Formulation B) were also tested for U.V. stability by placing samples of each in a QUV Accelerated Weathering Tester for 300 hours under UVA-340 lamps with 4 hours condensation cycle and 4 hours ultra-violet cycle, the temperatures being respectively 50*C and 60*C The colour measurements were made on an ACS colour computer using CIE L, a, b colour option. Lower delta E values signify better resistance to U.V.

Three stabilizer formulations were tested and these have been detailed below.

Formulation A - Lead S stem - Control

Formulation B - S stem Based on Product of Example 1 '

melting point approx 65*C Total parts by weight 5.58

Formulation C - System Based on Product of Example 1 and Boosted for V.R.

Components Parts by Weight Formulation B 5.58

Proprietary Booster for V.R. 1.00

Total parts by weight 6.58

Each of these three stabilizer formulations was evaluated in a PVC compound of the composition listed below.

C

.58

Formulation A 235

Formulation B 170

Formulation C 270 U.V. STABILITY EXPRESSED AS DELTA E Formulation A 14.7

Formulation B 8.1

These examples show that the product of Example 1 functions as a primary stabilizer, imparting superior heat stability to the two zinc systems compared to the lead control.

The electrical resistivity of PVC is not adversely affected, as the Ki values of the zinc system easily exceed the minimum required by the Australian

Standards. The minimum Ki value is 36.7 gjgohm metre at 20*C as defined in Australian Standards 3147 - 1981 and 3191 - 1981. Consequently, the product of Example 1 is suitable for the stabilization of PVC insulation for electrical applications.

The lower delta E value for Formulation B, containing the product of Example 1, shows that this stabilizer system is performing as a U.V. stabilizer. Example 7 A series to investigate the effect of different levels of zinc oxide (and pentaerythritol) on heat stability was carried out in a semi-rigid formulation. The performance of another zinc compound, zinc benzoate, in combination with pentaerythritol was included in these tests at a level of 52:48 parts by weight (or 1:2 molar ratio) to determine if it exhibited the same synergism with pentaerythritol as zinc oxide. Congo Red heat stability tests as described in Example 6 were run, the PVC sheet being prepared as detailed in Example 6. Although the colour of the PVC specimen is not usually recorded in Congo Red tests, significant variations in colour stability were observed. These were considered important to the application of the invention and, consequently, have been recorded. The formulations have been listed below and are preceded by a table of abbreviations.

FORMULATION 1 2 3 4 5 6 7 ^" 8

PVC compound Parts by weight component

71K 100 100 100 100 100 100 100 100 CaC0₃ 30 30 30 30 30 30 30 30

DIOP 25 25 25 25 25 25 25 25

StH 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15

Wx65 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15

CaBnZ 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 BPA 0.13 0.13 0.13 0.13 0.13 0.13 0.13 0.13

DLTDP 0.13 0.13 0.13 0.13 0.13 0.13 0.13 0.13

Exl 4.17 —

PE ~ 3.21 3.21 4.15 3.96 2.09 2.00 —

ZnO — 0.96 — 0.02 0.21 2.08 — 0.96 ZnBnz — — — — — — 2.17 —

RESULTS

CONGO RED HEAT STABILITY IN MINUTES

1. Product of Example 1 (ZnO 22.8:PE 77.2) 135 minutes

2. ZnO:PE untreated (22.8:77.2 parts by weight) 145 minutes 3. PE only 69 minutes

4. ZnO + PE (0.5:99.5 parts by weight) 110 minutes

5. ZnO + PE (6.0:95.0 parts by weight 160 minutes

6. ZnO + PE (50.0:50.0 parts by weight) 65 minutes

7. ZnBnz + PE (52:48 parts by weight) 45 minutes 8. ZnO only 15 minutes

COLOUR AND COLOUR STABILITY

A colour scale of 1 to 10 has been used to rate the overall colour of the specimens of PVC. On this scale, 1 has the least colour development and 10 has the most.

1. Product of Example 1 Gradual increase in

(ZnO 22.8 : PE 77.2) colour to the degradation point colour still fawn. Colour rating 3. .2. • ZnO + PE untreated Same as 1.

.(22.8 : 77.2 parts b- weight) Colour rating 3 3. PE only Colour began to develop at 10 minutes, rapidly intensifying to a dark red brown; however, hydrochloric acid not evolved until 69 minutes. Colour rating 8..

4. ZnO + PE Colour development

(0.5 :99.5 parts by weight) much stronger than 1 and 2, and brown at degradation. Colour rating 6.

ZnO + PE Colour and colour

(5.0 :95.0 parts by weight) development in between 1 and 4, medium brown at degradation. Colour rating 4.

6. ZnO +PE Good light colour and

(50.0 :50.0 parts by weight) colour stability up to degradation. Colour rating 1.

7. ZnBnz + PE Colour and colour

(52 : 48 parts by weight) stability as in 6. Colour rating 1. 8. ZnO only Colour development at 10 minutes with degradation at 15 minutes. Colour rating 10.

The important feature of these tests is that the zinc oxide acts synergistically with pentaerythritol at a level as low as 0.5 part by weight and shows significant improvement in heat stability and in colour stability over zinc oxide alone and pentaerythritol alone. At higher zinc oxide levels (i.e. greater than 23.8 parts by weight)", the zinc exerts the dominating effect and the Congo Red heat stability is decreased progressively. However, the colour is superior at these higher levels and consequently, formulations based on the higher zinc oxide levels (e.g. 70%) may be suitable for applications requiring good early colour and where a lower heat stability (e.g. 40 minutes) is adequate.

The graph of Figure 1 illustrates the effect of different levels of zinc oxide and pentaerythritol on Congo Red heat stability and on colour stability.

However, zinc benzoate does not show the same synergistic improvement in heat stability with pentaerythritol as does zinc oxide. Example 8

Pentaerythritol and combinations of zinc oxide/magnesium hydroxide and zinc oxide/aluminium hydroxide were tested for static oven heat stability in the semi-rigid formulation as detailed in Example 7. The static oven heat stability test was carried out by placing specimens of the PVC sheet as prepared in Example 6 into an air circulating oven at 180*C at ten minute intervals. The time taken to reach degradation (blackening) of these samples was assessed by visual observation. The additional abbreviations used in these formulations are:

Magnesium hydroxide MgHy

Aluminium hydroxide AlHy

AlHy 0.35 RESULTS

STATIC OVEN STABILITY IN MINUTES

1. Product of Example 1 slight colour development at

20 10 minutes, .black edging at 100 minutes, and full burn out at 150 minutes

ZnO/MgHy/PE colour development slightly worse than 1, black edging at 140

25 minutes with full burn out at 180 minutes

ZnO/AlHy/PE colour development worse than 1 and 2, black edging at 150 minutes, full burn out not

30 attained at 250 minutes when test terminated. When used in conjunction with zinc oxide, both magnesium hydroxide and aluminium hydroxide have shown synergistic improvement in heat stabilizing performance

35 with pentaerythritol in plasticised PVC. Example 9

The performance of various polyols, metal oxides and hydroxides and combinations thereof were investigated in rigid PVC to determine if any synergistic effects in heat stability could be obtained. These formulations were compared to the product of Example 1. The performance of a stabilizer system using zinc oxide and pentaerythritol, as a simple admixture, not prepared by the process of Example 1 but at the equivalent levels detailed in the procedure for the manufacture of the product of Example 1, was also carried out. Systems were also investigated in which (a) zinc oxide only was used and (b) pentaerythritol only was used and the levels of use corresponded to the amounts used when untreated zinc oxide and pentaerythritol together were added directly to the PVC mix. This was done to demonstrate the inherent degree of stability of each of these compounds when acting independently and to serve as a basis of comparison to measure synergistic improvements.

The laboratory trails consisted of evaluating the dynamic heat stability in a Brabender torque rheometer as described earlier in Example 5.

The test formulations have been set out in table form; due to the number of tests, abbreviations have been used and a table of abbreviations precedes the formulations.

TABLE OF ABBREVIATIONS

Resin, 67k 67k

Calcium Carbonate filler CaCo₃

Titanium dioxide Tiθ2 Calcium stearate CaSt

Bisphenol A BPA

Paraffin wax, melting pt approx 65*C Wx65 Pentaerythritol tetrastearate PESt Sasolwax HI HI Polyethylene wax PEWx

Product of Example 1 Exl

Zinc oxide ZnO

Pentaerythritol PE

Dipentaerythritol DPE Tri ethylol propane TMP Ditrimethylol propane DTMP

Tris-2-hydroxyethyl iso-cyanurate THEIC

Mannitol ^" MANN

Sorbitol SORB

Zinc sulphide ZnS

Strontium oxide SrO

Magnesium hydroxide MgHy

Calcium hydroxide CaHy

Aluminium hydroxide AlHy

FORMULATION: 1 2 3 4

PVC compound Parts by weight component

67K 100 100 100 100 100 100 100 100

CaC0₃ 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0

Ti0₂ 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0

CaSt 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2

BPA 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

Wx65 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7

PESt 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

PEWx 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

HI 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

Exl 0.52

ZnO 0.12 0.12 — 0.12 0.12 0.12 0.12

PE 0.4 ~ 0.4

DPE 0.4

TMP 0.4

DTMP 0.4

THEIC 0.4

MANN

SORB

ZnS

SrO

MgHy

CaHy

AlHy FORMULATION: 9 10 11 12 13 14 15 ^" 16.

PVC compound Parts by weight component

67K 100 100 100 100 100 100 100 100 CaC0₃ 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0

Ti0₂ 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0

CaSt 1.2 1.2 1.2 1.2 1.2 1.2 1.2 1.2

BPA 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

Wx65 0.7 0.7 0.7 0.7 0.7 0.7 0.7 0.7 PESt 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

PEWx 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1

HI 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

Eχl

ZnO ^' 0.12 0.12 0.12 0.12 0.07 — PE — — 0.2 0.2 0.45 0.4

D E

TMP — — 0.2 — — — 0.4

DTMP

THEIC -- — — — ^' -- MANN 0.4 -- — 0.2 — -- — 0.4

SORB — 0.4

ZnS — — — — — 0.12 0.12 0.12

SrO

MgHy CaHy

AlHy - 25

FORMULATION: 17 18 19 20 21 22 23 24

RESULTS

In these laboratory tests no difference could be found between the performance of product of Example 1 and untreated zinc oxide and pentaerythritol directly added to the PVC blend. All combinations show an improvement in heat stability over pentaerythritol or zinc oxide alone and this demonstrates that these combinations are acting synergistically to increase heat stability. Although mannitol and mannitol/pentaerythritol show an improvement in heat stability over the product of Example 1, these combinations were found to be inferior in colour compared to that of Example 1. The best early colour was obtained with the product of Example 1 and untreated zinc oxide/pentaerythritol added directly. ZnO/trimethylol propane, ZnO/tris-2-hydroxyethyl iso-cyanurate and ZnO/PE/ trimethylol propane were found to be slightly inferior.

Claims

THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

I. A primary heat stabilizer for vinyl halide polymers, the stabilizer being formed from an oxide or hydroxide of a group 2B or 3A metal and a polyol.

2. A primary heat stabilizer according to Claim 1 wherein the oxide is zinc oxide.

3. A primary heat stabilizer according to Claim 1 or 2 wherein the polyol is pentaerythritol, dipentaerythritol, trimethylol propane, di-trimethylol propane, tris-2- hydroxyethyl iso-cyanurate, mannitol, sorbitol or mixtures thereof.

4. A primary heat stabilizer according to Claim 3 wherein the polyol is pentaerythritol.

5. A primary heat stabilizer according to any one of Claims 1 to 4 in which the molar ratio of the oxide or hydroxide to polyol is from 1:1 to 1:2.

6. A primary heat stabilizer according to any one of Claims 1 to 4 wherein the oxide or hydroxide comprises from 0.5% to 70% by weight of the composition.

7. A primary heat stabilizer according to any one of Claims 1 to 5 wherein the oxide or hydroxide is a mixture of zinc oxide and aluminium hydroxide.

8. A polyvinyl chloride composition comprising polyvinyl chloride and primary heat stabilizer formed by mixing an oxide or hydroxide of a group 2B or 3A metal with a polyol.

9. A polyvinyl chloride composition according to Claim 8 wherein the oxide is zinc oxide.

10. A polyvinyl chloride composition according to Claim 8 or 9 wherein the polyol is pentaerythritol.

II. A polyvinyl chloride composition according to any one of Claims 8 to 10 wherein the amount of primary heat stabilizer is up to about 10% by weight of the polyvinyl chloride composition.

12. A method of preparing a primary heat stabilizer according to any one of Claims 1 to 7 comprising fusing the oxide or hydroxide with the polyol.

13. A method of preparing a primary heat stabilizer according to Claim 12 in which the oxide or hydroxide is fused with the polyol at an elevated temperature.

14. A method of preparing a primary heat stabilizer according to Claim 13 in which the temperature is about 200°C or greater.

15. A method of preparing a primary heat stabilizer according to Claim 13 in which the temperature is in the range from 150°C to 260*C

16. A material formed from a polyol and an oxide or hydroxide of a group 2B or 3A metal.

17. A material according to Claim 16 wherein the oxide or hydroxide is zinc oxide.

18. A material according to Claim 16 or 17 wherein the polyol is pentaerythritol.

19. A material according to any one of Claims 16 to 18 in which the material is a mixture, a compound, an adduct, a complex, a reaction product or a combination of one or more of these.

20. A primary heat stabilizer according to any one of Claims 1 to 7 which is also an ultra violet stabilizer for polyvinyl chloride.

21. An article of manufacture made from a polyvinyl chloride composition including the primary heat stabilizer of any one of Claims 1 to 7.

22. An article of manufacture according to Claim 21 being a polyvinyl chloride pipe, polyvinyl chloride insulation of an electrical conductor, or a rigid polyvinyl chloride sheet.

23. A primary heat stabilizer substantially as hereinbefore described with reference to any one of the foregoing examples.

24. A polyvinyl chloride composition comprising a primary heat stabilizer substantially as hereinbefore described with reference to any one of the foregoing examples.

25. A method of preparing a primary heat stabilizer substantially as hereinbefore described with reference to any one of the foregoing examples.