GB1575305A - Polyvinylchloride compositions - Google Patents

Description

(54) IMPROVEMENTS RELATING TO POLYVINYLCHLORIDE COMPOSITIONS (71) We, THE BRITISH PETROLEUM COMPANY LIMITED, of Britannic House, Moor Lane, London, EC2Y 9BU, a British Company, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to rigid polyvinylchloride compositions suitable for use in the production of thermoplastic pipes for gutters drain pipes etc. or for injection moulded components.

In the manufacture of polyvinylchloride compositions, it is normal to add other materials e.g. extenders and fillers to reduce costs and also to add materials e.g. impact modifiers and plasticisers to modify the characteristics of the product. Any added materials must, of course, be compatible with the PVC and provide the necessary balance between quality and cost.

One potential extender for rigid PVC is hardened extract but it has poor compatibility with PVC giving products with inferior properties. It has now been found that the addition of a relatively small amount of a particular polymer counteracts the adverse effect of the addition of hardened extract giving an acceptable product which is cheaper than PVC alone.

According to the present invention a rigid polyvinylchloride composition comprises from 20-70% wt of polyvinylchloride, from 20-70% wt of hardened extract and from 10-30% of a styrene-acrylonitrile co-polymer, all percentages being by total weight of the three components.

Preferred proportions are as follows: Polyvinyl chloride % wt 30 - 55 Hardened extract % wt 35 - 55 Styrene-acrylonitrile copolymer % wt 10 - 20 The polyvinylchloride may be a mass or suspension grade resin which is a free flowing powder with bulk density in the range 0.5 - 0.7 g/cm3, porosity 0.2 - 0.3 cm3/g and viscosity average mol wt of 50,000 - 80,000. Suitable materials are e.g. Breon (Registered Trade Mark) S110/10 or M110/50 marketed by B.P. Chemicals Ltd.

In a preferred modification, up to 50% of the PVC resin may be replaced by a vinyl chloride-vinyl-acetate copolymer containing up to 15% vinyl acetate. The inclusion of this resin improves the quality of extruded pipes and increases its impact strength. Breon AS70/42 is a suitable vinyl chloride-vinyl acetate copolymer.

Throughout this specification 'hardened extract' means a material obtained by blowing a gas containing free oxygen into a petroleum extract at elevated temperatures, the petroleum extract having been obtained by the solvent extraction of a product of petroleum refining which is a distillate petroleum fraction or a de-asphalted petroleum residue, which product boils above 350"C at atmospheric pressure and which contains a major proportion of aromatic hydrocarbons.

The product of petroleum refining subjected to solvent extraction may be for example a vacuum distillate obtained by vacuum distillation of a residue from an atmospheric pressure distillation. Alternatively the product of petroleum refining may be obtained from vacuum residue (the residue of the vacuum distillation referred to above) after asphaltenes have been removed by precipitation with liquid propane. The solvent extraction to give a product containing a major proportion of aromatic hydrocarbons may be carried out on mixtures of distillates and residues.

-The blowing of the extract is believed to cause condensation of the aromatics giving a hardened product with a high proportion of asphaltenes, cyclics, and insolubles and a relatively low proportion of saturates. The hardened extracts may have penetrations of from 0.1 to 6 at 250C and softening points (Ring and Ball) of from 80 to 1700C.

Hardened extract blended with bitumen may also be used, providing that the softening point of the mixture remains within the above limits.

The styrene-acrylonitrile co-polymer may have a styrene content of from 70 to 80% by weight and an acrylonitrile content of from 20 to 30% by weight and a number average molecular weight of from 20,000 to 100,000. Suitable materials are sold by the B.F.

Goodrich Company under the name Hycar 2301 and by the Dow Chemical Co. under the name Dow Tyril SAN 790T.

Adding hardened extract to PVC lowers the overall cost but, as will be shown in more detail hereafter, adversely affects the quality of the material. A very rigid but extremely brittle material with substantially reduced tensile and impact strength is produced. Adding the styrene-acrylonitrile co-polymer counteracts these tendencies and although it is more costly than either the PVC or the hardened extract, it gives a large improvement relative to the quantity required, and so gives an overall cost saving.

Other known components of PVC compositions may also be added. Thus the composition may contain from 3 - 15% wt, by weight of total composition, of an impact modifier, which acts to improve impact strength. Examples of suitable impact modifiers are styrene-butadiene-acrylonitrile co-polymers and methyl methacrylate-butadiene-styrene co-polymers. Materials of this type which may'be used are Blendex 401 manufactured by the Borg Warner Corporation or Paraloid (Registered Trade Mark) KM607A, manufactured by Rohm and Haas. Preferred impact modifiers are materials of the ABS type containing 40-55% butadiene, 30-40% styrene and 10-20% acrylonitrile.

A filler may also be desirable to decrease cost and modify product quality and may be used in an amount of from 5 to 30% wt, by weight of total composition. Suitable fillers include powdered limestone, pulverised fuel ash, carbon black, finely divided clay or silica, chopped glass fibre or asbestos, or wood flour.

Conventional stabilisers and lubricants for PVC should preferably be incorporated into the compositions at levels normally used in rigid PVC compounds. Typical examples of such materials include lead compounds such as tribasic lead sulphate, dibasic lead stearate, calcium or lead stearate and organo tin compounds e.g. dibutyl tin dilaurate and organothiotin compounds.

Since the primary object of the invention is to produce rigid PVC compositions, the presence of plasticisers in large amounts would be undesirable. However, a plasticiser may be present to improve impact strength if there is an adequate margin on rigidity, the amount used being preferably 1 to 20% wt by weight of total composition and more particularly 1 to 10% wt. Suitable plasticisers include chlorinated n-paraffins and dialkyl phthalates.

The components may be formed into a powder blend by blending in a high speed mixer, e.g. a Papenmeier Universal High Speed Mixer. Typically, a blend may be prepared by mixing for 5 to 10 minutes at 500 rpm. The temperature of the mix should not be allowed to exceed 100"C. Suitable blends may be fabricated into sheets or pipes by extrusion through conventional single or twin screwed extruders.

The compositions may also be used for preparing moulded articles, e.g. by compression, transfer or injection moulding, in which case the composition is better prepared in the form of a granulated compound. The compound may be prepared by mixing in a Banbury mixer at 140-160"C, discharging the mix into a two roll mill and rolling the product until a suitable hide is formed, and then granulating the product. Typically, the mill should be used with the back roller temperature set at 1600C and the front roller set at 140"C.

The invention is illustrated by the following comparative Examples.

Examples 1 - 5 Examples of compositions with their physical properties which illustrate this invention are quoted in Table 1 below. The compositions were prepared by mixing in a Brabender Plasticorder Type 100 fitted with a roller mixing measuring head Type 50. About 66 gms of the mixture were charged to the mixing head chamber which had been preheated to 1500C.

Mixing was carried out for 20 minutes at 60 rpm. The composition was then removed from the mixing head, and milled on a two roller mill (roll dimensions 10" x 6") heated to 1200C for 5 minutes using a friction ratio of 1:1 (relative speed of rollers).

Physical properties of the compositions were measured on compression moulded test specimens, and were determined according to the methods cited below.

The Vicat softening points were determined according to British Standard Specification 2782 method 102D or J with the following minor differences: A. A truncated cone specimen was used instead of the specified square specimen.

B. A graphical plot of temperature vs. millimetre indentation was used to determine the Vicat temperature which is taken as that temperature at which a penetration of 1 mm is observed.

Impact strengths were determined by the Charpy method using notched bars nominally by British Standard 2782 method 306 E but mm standard dimensions 0.15" x 0.15" x 1.5" notched to 0.050" and 0.010 inches notch rip radius were used.

The tensile strength and elongation were measured at 220C according to ASTM 638 using a non standard specimen width of 0.212" and nominal thickness of 0.050".

Flexural moduli were determined at 220C according to ASTM 0790 method for measurement of tangent modulus of elasticity (3rd section 10.11.1). The initial straight line portion of the curve was used for the calculation. The flexural strength was measured at the breaking point of the specimen (Section 10.5).

TABLE 1 Composition % wt Physical Properties Hardened Elongn Tensile Flexural Flexural Impact Vicat Extract at strength strength Modulus Strength Soft Example a. b. c. d. e. f. (150 C break MNm-2 MNm-2 MNm-2 KJm-2 Pt.

softening % C NO. point) 1. 98 - - - - 2 - 5.5 53 80 2730 4.8 85 2. 49.5 - - - - 1 49.5 1.4 18.5 26 1876 0.4 61 3. 29.8 9.9 - 19.9 0.6 - 39.8 5.0 25.7 83 2846 2.5 89.7 4. 31.9 16.0 - 19.2 1.0 - 31.9 6.0 38.7 55 3208 1.8 93.2 5. 31.2 9.8 5.9 19.5 2.0 0.5 31.2 5 28.0 47 2799 4.8 92.2 a. PVC used = Breon (Registered Trade Mark) S110/10 e. TBLS = tribasic lead sulphate b. SAN used = Hycar (Registered Trade Mark) 2301 f.PbSt = lead stearate c. ABS = BLENDEX (Registered Trade Mark) 401 d. Calcium carbonate filler = SNOWCAL (Registered Trade Mark) 7ML In the table, Examples 1 and 2 clearly demonstrate that 50% substitution of PVC resin by hardened extract has a deleterious effect on tensile strength, impact strength and softening point.The incorporation of 10% SAN and 20% calcium carbonate filler (Examples 3 and 4) restored softening point and flexural modulus to a similar level as PVC alone and improved impact and tensile strength to greater than 50% of unmodified PVC. The incorporation of 6% ABS impact modifier restored impact strength to the level of unmodified PVC (see Example 5) without otherwise reducing the other physical properties significantly.

Example 6 Composition Parts by weight PVC suspension resin 26.6 Hardened extract 140 26.6 Styrene acrylonitrile polymer (Hycar 2301) 8.7 Acrylonitrile/Butadiene/Styrene impact 5.3 modifier (Blendex 401) Vinyl chloride-vinyl acetate copolymer 13.3 containing 12-14% of vinyl acetate Calcium carbonate filler (Snowcal 7ML) 17.7 Tribasic lead sulphate 1.8 The above ingredients were dry blended in a Papenmeier high speed mixer at 50 rpm for 5 mins at 200C. The bulk density of the product was 820 Kg/m3.

Pipe of 1" internal diameter, 1/8" wall thickness was extruded on a single screw Reifenhauser extruder at a rate of 3.4 Kg per hr. Good quality pipe with a shiny surface finish was obtained.

WHAT WE CLAIM IS: 1. A rigid polyvinylchloride composition comprising from 20 - 70% wt of polyvinylchloride, from 20 - 70% wt of hardened extract (as hereinbefore defined) and from 10 - 30% wt of a styrene-acrylonitrile co-polymer, all percentages being by total weight of the three components.

2. A rigid polyvinylchloride composition as claimed in claim 1 wherein the proportions of the three components are: Polyvinylchloride 30 - 55% wt Hardened extract 35 - 55% wt Styrene-acrylonitrile copolymer 10 - 20% wt 3. A modification of the rigid polyvinylchloride composition as claimed in claim 1 or 2 wherein up to 50% wt of the polyvinylchloride is replaced by a vinylchloride-vinylacetate copolymer containing up to 15% wt of vinylacetate.

4. A rigid polyvinylchloride composition as claimed in claim 1, 2 or 3 wherein the styrene-acrylonitrile copolymer has a styrene content of 70 - 80% wt, an acrylonitrile content of 20 - 30% wt and a number average molecular weight of from 20,000 - 100,000.

5. A rigid polyvinylchloride composition as claimed in any of claims 1 to 4 which contains also from 3 - 15% wt of an impact modifier and from 5 - 30% wt of a filler, both by weight of total composition.

6. A rigid polyvinylchloride composition as claimed in claim 1 substantially as described in the Examples.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. In the table, Examples 1 and 2 clearly demonstrate that 50% substitution of PVC resin by hardened extract has a deleterious effect on tensile strength, impact strength and softening point. The incorporation of 10% SAN and 20% calcium carbonate filler (Examples 3 and 4) restored softening point and flexural modulus to a similar level as PVC alone and improved impact and tensile strength to greater than 50% of unmodified PVC. The incorporation of 6% ABS impact modifier restored impact strength to the level of unmodified PVC (see Example 5) without otherwise reducing the other physical properties significantly. Example 6 Composition Parts by weight PVC suspension resin 26.6 Hardened extract 140 26.6 Styrene acrylonitrile polymer (Hycar 2301) 8.7 Acrylonitrile/Butadiene/Styrene impact 5.3 modifier (Blendex 401) Vinyl chloride-vinyl acetate copolymer 13.3 containing 12-14% of vinyl acetate Calcium carbonate filler (Snowcal 7ML) 17.7 Tribasic lead sulphate 1.8 The above ingredients were dry blended in a Papenmeier high speed mixer at 50 rpm for 5 mins at 200C. The bulk density of the product was 820 Kg/m3. Pipe of 1" internal diameter, 1/8" wall thickness was extruded on a single screw Reifenhauser extruder at a rate of 3.4 Kg per hr. Good quality pipe with a shiny surface finish was obtained. WHAT WE CLAIM IS:

1. A rigid polyvinylchloride composition comprising from 20 - 70% wt of polyvinylchloride, from 20 - 70% wt of hardened extract (as hereinbefore defined) and from 10 - 30% wt of a styrene-acrylonitrile co-polymer, all percentages being by total weight of the three components.

2. A rigid polyvinylchloride composition as claimed in claim 1 wherein the proportions of the three components are: Polyvinylchloride 30 - 55% wt Hardened extract 35 - 55% wt Styrene-acrylonitrile copolymer 10 - 20% wt

3. A modification of the rigid polyvinylchloride composition as claimed in claim 1 or 2 wherein up to 50% wt of the polyvinylchloride is replaced by a vinylchloride-vinylacetate copolymer containing up to 15% wt of vinylacetate.

4. A rigid polyvinylchloride composition as claimed in claim 1, 2 or 3 wherein the styrene-acrylonitrile copolymer has a styrene content of 70 - 80% wt, an acrylonitrile content of 20 - 30% wt and a number average molecular weight of from 20,000 - 100,000.

5. A rigid polyvinylchloride composition as claimed in any of claims 1 to 4 which contains also from 3 - 15% wt of an impact modifier and from 5 - 30% wt of a filler, both by weight of total composition.

6. A rigid polyvinylchloride composition as claimed in claim 1 substantially as described in the Examples.