GB Patent 606936 - Improvements in and relating to moulding polyvinyl chloride pastes

Description

PATENT SPECIFICATION

^. Application Date: Jan. 22, 1946. No. 2124/46.

Complete Specification Left: July 12, 1946.

E E E / Complete Specification Accepted: Aug. 23, 1948.

Index at acceptance:-Class 2(iii), R4c(8: 9:12: 13), R4d(l: 7), R4t2.

P1ROVISIONAL SPECIFICATION

Improvements in and relating to Moulding Polyvinyl Chloride Pastes We, B.X. PLASTICS LImITED, a British Company, of Branthain Works, near Manningtree, Essex, and JOHN Aitm.uit HETHERINGTON, a British subject, of Brantham Works, near Manningtree, Essex, do hereby declare the nature of this invention to be as follows:The present invention is concerned with improvements in and relating to moulding polyvinyl chloride pastes and is more particularly concerned with the production of rigid or semi rigid products by the paste moulding technique.

It is well known that polyvinyl chloride can be dispersed in suitable plasticising agents comprising liquids of low volatility, which are practically nonsolvents for the polymer at room temperature but which dissolve the polymer rapidly at elevated temperatures, to give paste-like products which are admirably adapted for moulding by filling into suitable moulds, applying- heat until the mass becomes completely gelatinised and then cooling before removal from the mould.

It is found, however, that the quantity of plasticiser necessary to give a smooth, flowable paste is always such as to impart a considerable amount of rubber-like elasticity to the finished gelatinised product and, hitherto, it has not been possible to produce rigid or semi-rigid products by the aforementioned technique.

It is an object of the present invention to provide a method of manufacturing rigid or semi rigid mouldings from a pourable polyvinyl chloride paste, which mouldings are harder than those prepared by methods previously proposed.

We have found that if one or more easily polymerisable monomeric liquids as hereinafter defined are intimately mixed with the polyvinyl chloride paste, gelatinisation can be made to take place at a lower temperature than is the case with the paste alone. We have further T, -, found that products moulded from the said intimate mixture are harder than those moulded from the paste alone. 50 According to the present invention therefore there is provided a method of manufacturing rigid or semi-rigid mouldings from polyvinyl chloride pastes in which the said paste is intimately mixed 55 with one or more easily polymerisable monomeric liquids prior to moulding and is then moulded under such conditions of temperature, pressure and time as will cause complete gelatinisation of the paste 60 and at the same time substantially comiplete polymerisation of said monomeric liquid or liquids.

The expression " easily polymerisable monomeric liquid " may be defined as 65 including any monomeric liquid which is soluble in the plasticiser used for dispersing the polyvinyl chloride and which polymerises to give a rigid product.

There are many monomeric liquids which 70 are suitable for use according to the invention, and it will be understood that whilst we prefer to employ methyl methacrylate because it polymerises quickly and gives a tough product we do 75 not intend the scope of the invention to be limited thereto.

-It is preferred, in making up the paste, to use the minimum quantity of plasticiser or plasticisers which will impart 80 smooth, paste-like properties to the dispersion and to select a grade of polyvinyl chloride which readily forms a paste when mixed with the plasticiser. The quantity of plasticiser required will 85 depend on its chemical nature and on the nature and solubility of the polymer particles.

We have found that polyvinyl chloride sold under the Registered Trade Mark 90 " Corvic " may advantageously be employed to make up the initial paste, although the process according to the invention is in no way limited to the use V ,936 on C) 606,9:36 of such a substance. Furthermore as plasticisers there may for example be used trieresyl phosphate and/or dioctyl phtlhalate. In adding the monomeric 6 liquid to the paste. prior to moulding, care must be taken to.mix the ingredients without trapping any air and mixing must be continued until the mass is uniformly blended. This operation is preferably conducted immediately prior to moulding and, generally, it is unsatisfactory to add the monomier 'during the manufacture of the paste as this leads to premature gelatinisation. The quantity of monomer added may be adjusted according to the degree of extra rigidity it is desired to impart to the finished moulding and the greater the amount of monomer added, the more rigid will be the finished moulding. In general, it is found convenient to add up to about;505.

of monomer on the initial weight of the polyvinyl chloride paste without encountering any undue difficulty due to void 26 formation during the moulding operation. If desired also a polymerisation catalyst may be employed which will enable the operation to be carried out' more quickly and it is usually convenient to add i to 1% of an organic peroxide catalyst, such for instance as benzoyl peroxide, to the monomner prior to mixing with the paste.

On adding methyl methacrylate monomer to a polyvinyl chloride paste. there is, first of all, a decrease in viscosity as would be expected by the addition of any mobile liquid. In a short time, however, the polymer grains begin to swell, due to the increased solvent action of the plasticiser when fortified with methacrylate monomer, the latter being. at room temperature, a powerful swelling agent for the polymer. This -swelling gives rise to a progressive increase in viscosity on standing and may result in the formation of undesirable clots if allowed to proceed too far. It may often be- convenient, however, to allow the viscosity to increase slightly before packing the treated paste into the mould, as this minimises the risk of void formation and when external pressure is applied during the moulding the extra stiffness provides a desirable added resistance to the applied pressure. It is found, moreover, that the increased solvent powder of the liquid phase enables the gelatinisation to be completed at a lower temperature than has hitherto been possible when using the known, untreated polyvinyl chloride pastes as moulding materials.

The optimum heating and cooling periods as well as the conditions of temnperature and pressure will depend on the thickness of mouldingo on the quantity of monomer present and, to a lesser extent, on the composition of the initial polyvinyl chloride paste but, in general, this can easily be ascertained by trial. A 70 wide choice of moulds may be used in practising the invention, depending on the particular type of article it is desired to produce. In order that the invention may be well understood the following 75 examples in which the polyvinyl chloride employed is the type known under the Registered Trade Mark- " Corvic " are given by way of illustration only.

EXAMPLE 1. 80

Parts of a paste consistin' of 1(JU parts of finely divided polyvinyl chloride and 60 parts of di(ethyl hexvl)phtlhalate is prepared by intimately mixing the ingredients and passing through a triplebowl paint mill until of smooth and flowable consistency.

Parts of methyl metitacrylate mnonomier containing 1'9 benzoyl peroxide is then added and uniformly blended with 90 the paste in a pestle and mortar.

The mixture is allowed to stand for about 10 minutes at room temperature and then packed into a positive "l' platemould and heated to 120 C. under a 95 pressure of:300 lbs. per sq. inch for 20 minutes. At the end of this time the mould is cooled and the moulding removed.

The moulding is found to be tough and 100 almost rigid, having an indentation hardness figure 13, as compared with 63 for a similar moulding prepared from the original untreated paste moulded at 15(310 C. The hardness figures are measuired by 105 the method given in British Standards Specification No. 903.

EXAMPLE 2.

Parts of a paste c'onisistilng i'f 1(0 parts of finely divided polyvinyl chlomide 110 and 70 parts tricresyl phosphate is prepared by intimately mixing the ingredlients and passing' through a triplebowl paint mill until of simooth and flowsable consistency. 115 8.5 Parts of methyl methacrylate monomer containing 1% of benzovl peroxide is then added and uniformly blended witl the paste by means of a palate knife.

The mixture is allowed to stand for 120 about 1.5 minutes at room temperature and a slight excess is then packed into a semii-positive 1" plate-miould and heated to 12.50 C. under slight pressure for:30 minutes. At the end of this time the 125 mould is cooled and the moulding removed.

The finished moulding' is found to be tough and almost rigid with an indentation hardness figure, measured as in 130 606,936 Example 1, of 17, as compared with (68 for a similar moulding prepared from the original untreated paste moulded at 150 C.

Dated this 22nd day of January, 1946.

For the Applicants, FRANK B. DIEHN & CO., Chartered Patent Agents, Kingsway House, 103, Kingsway, London, W.C.2.

COMPLETE SPECIFICA1TON Improvements in and relating to Moulding Polyvinyl Chloride Pastes We, B.X. PLASTICS LimiTnm, a British Company, of Brantham Works, near Manningtree, Essex, and JOHN ARTnrut IIETHERINGTON, a British subject, of Brantham Works, near Manningtree, Essex, do hereby declare the nature of lthis invention, and in what -manner the same is to be performed, to be particularly described and ascertained in and by the following statement:-

The present invention is concerned with improvements in and relating to moulding polvinyl chloride pastes and is more particularly concerned with the production of rigid or semi rigid products by the paste moulding technique.

It is well known that polyvinyl chloride can be dispersed in suitable plasticising agents comprising liquids of low volatility, which are practically nonsolvents for the polymer at room temperature but which dissolve the polymer rapidly at elevated temperatures, to give paste-like products which are admirably adapted for moulding by filling into suitable moulds, applying heat until the mass becomes completely gelatinised and then cooling before removal from the mould.

It is found, however, that the quantity of plasticiser necessary to give a smooth, fiowable paste is always such as to impart a considerable amount of rubber-like elasticity to the finished gelatinised product, and hitherto, it has not been possible to produce rigid or semi-rigid products by the aforementioned technique. The term " polyvinyl chloride paste " as used herein means a paste-like product of the kind described above.

It is an object of the present invention to provide a method of manufacturing rigid or semi-rigid mouldings from polyvinyl chloride paste, preferably such as is readily pourable, which mouldings are harder than those prepared by methods previously proposed.

We have found that if one or more easily polymerisable monomeric liquids as hereinafter defined are intimately mixed with the -polyvinyl chloride paste.

5.5 gelatinisation can be made to take place at a lower temperature than is the case with the paste alone. We have further found that products moulded from the said intimate mixture are harder than those moulded from the paste alone. 60 According to the present invention therefore there is provided a method of manufacturing rigid or semi-rigid mouldings from polyvinyl chloride pastes in which the said paste is intimately mixed 635 with one or more easily polymetisable monomeric liquids prior to moulding and is then moulded under such conditions of temperature, pressure and time as will cause complete gelatinisation of the paste 70 and at the same time substantially complete polymerisation of said monomeric liquid or liquids. U The expression " easily polymerisable monomeric liquid " is defined as including any monomeric organic liquid having ethylenic unsaturation which is soluble in the plasticiser used for dispersing the polyvinyl chloride and which polymerises to give a rigid product. There are many 80 monomeric liquids which are suitable for use according to the invention, and it will be understood that whilst we prefer to employ methyl methacrylate because it polymerises quickly and gives a tough 85 product we do not intend the scope of the invention to be limited thereto.

It is preferred, in making up the paste, to use the minimum quantity of plasticiser or plasticisers which will impart 9() smooth, paste-like properties to the dispersion and to select a grade of polyvinyl chloride which readily forms a paste when mixed with the plasticiser. The quantity of plasticiser required will depend on its chemical nature and on the nature and solubility of the polymer particles.

We have found that polyvinyl chloride sold under the Registered Trade Mark 100 " Corvic " may advantageously be employed to make up the initial paste, although the process according to the invention is in no way limited to the use of such a substance. Furthermore as 105 plasticisers there may for example be used tricresyl phosphate andlor dioctyl phthalate. In adding the monomeric liquid to the paste, prior to molding, care must be taken to mix the ingredients without trapping any air and mixing must be continued until the mass is uniformly blended. This operation is preferably conducted immediately prior to moulding and, generally, it is unsatisfactory to add the monomer during the manufacture of the paste as this leads to premature gelatinisation. The quantity of monomer added may be adjusted according to the degree of extra rigidity it is desired to impart to the finished moulding and the greater the amount of monomer added, the more rigid will be the finished moulding. In general, it is found convenient to add up to about 5Q00', of monomer on-the initial weight of the polyvinyl chloride paste without encountering any undue difficulty due to void formation during the moulding operation. If desired also a polymerisation 25catalyst may be employed which will enable the operation to be carried out more quickly and it is usually convenient to add _, to 1,' of an organic peroxide catalyst, such for instance as beizoyl peroxide, to the monomer prior to mixing with the paste.; On adding methyl nlethacrylate monomer to a polyvinyl chloride paste, there is. first of all, a decrease in viscosity as would be expected by the addition of any mobile liquid. In a short time, however, the polymer grains begin to swell, due to the increase solvent action of the plasticiser when fortified with methacrylate monomer, the latter being, at room temperature, a powerful swelling agent for the polymer. This swelling gives rise to a progressive increase in viscosity on standing and may result in the formation of undesirable clots if allowed to proceed too far. It may often be convenient, however. to allow the viscosity to increase slightly before packing- the treated paste into the mould, as this minimises the risk of void formation and when external pressure is applied during the moulding the extra stiffness provides a desirable added resistance to the applied pressure. It is found, moreover, that the increased solvent power of the liquid phase enables the gelatinisation to be completed at a lower temperature than has hitherto been possible when using the known, untreated polyvinyl chloride pastes as moulding materials.

The optimum heating and cooling periods as well as the conditions of temperature and pressure will depend on the thickness of moulding. on the quantity of nlonoiier present and, to a lesser extent, on the composition of the initial polyvinyl chloride paste but, in general, this can easily be ascertained by trial. A wide choice of moulds may be used in 70 practising the invention, depending on the particular type of article it is desired to produce. In order that the invention mav be well understood the following examples in which the polyvinyl chloride 75 employed is the type known under the Registered Trade Mark ' Corvic " are given by way of illustration only.

The. parts referred to in the examples are parts by weight. so EXAMPLE 1.

Parts of at paste consisting of 100 parts of finely divided polyvinvy chloride and (60 parts of di (ethyl llexyl) phthalate is prepared by intimately mixing the inrredients and passing through a triplebowl paint mill until of smooth and flowable consistency.

Parts of methyl metlhacrylate mon0oomer containing 1% benzoyl peroxide are 90 then added and uniformly blended with the paste in a pestle and mortar.

The mixture is allowed to stand for about 10 minutes at room temperature and then packed into a positive 1" platemould and heated to 1200 C. under a pressure of 300- lbs. per sq. inch for 20 minutes. At the end of this time the mould is cooled and the moulding removed. 100 The moulding is found to be tourhl and almost rigid, having an indentation hardness figure 1: as compared with (13 for a similar moulding prepared from the original untreated paste moulded at 150)0 105 (C. The hardness figures are measured by the method given in British Standards Specification No. 90)3.

EXAMPLF, 2.

Parts of a paste consisting, of 100 110 parts of finely divided polyvinyl chloride anmd 70 parts tricresyl phlosphate is prepared by intimately mixing the ingredients and passing through a triplebowl paint mill until of smooth and flowable consistency.

8O5 Parts of methyl methacrylate monomner containing 1% of benzoyl peroxide is then added and uniformly blended with the paste by means of a palate knife. 120 The mixture is allowed to stand for about 15 minutes at room temperature and a slight excess is then packed into a semi-positive {" plate-mould and heated to 12?5 C. under slight pressure for 30 125 minutes. At the end of this time the mould is cooled and the moulding removed.

TThe finished moulding is found to be tough and almost rigid with an indenta6065,9:36 tion hardness figure, measured as in Example 1, of 17, as compared with 68 for a similar moulding prepared from the original untreated paste moulded at 1-500 Specification No. 574,804 claims a plastic compound comprising a polyvinyl resin, which is either polyvinyl chloride or a co-polymer of vinyl chloride and vinyl acetate with from 90% to 95.% of chloride, a temporary plasticiser and a permanent plasticiser in a quantity equal to or greater than the temporary plasticiser, the total plasticiser content of the mix being within the range 55:%-80% by weight, the temporary plasticiser being a liquid ester of an aliphatic monohydric alcohol with an acrylic acid, either unsubstituted or substituted in the e-position by an alkyl or halogen group, and being polymerisable by heat, so that the compound has plasticity and tackiness similar to unvulcanised rubber compounds and is convertible by heat treatment in which the said liquid is polymerised to a non-plasticising resinous substance, the final product being a material resembling, in flexibility, toughness and elasticity, vulcanised rubber. In a further claim the said specification claims a method of covering wire with such a compound.

We make no claim to a plastic compound as claimed in Specification No.

574,804, or to any compound prepared from a mix in which the amount of perinanent plasticiser exceeds the amount of polyvinyl resin.

Rlaving now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we