WO2013092363A1

WO2013092363A1 - Process for manufacturing articles by rotational moulding of a composition based on vinyl chloride polymer

Info

Publication number: WO2013092363A1
Application number: PCT/EP2012/075339
Authority: WO
Inventors: Joël FUMIRE
Original assignee: Solvay Sa
Priority date: 2011-12-19
Filing date: 2012-12-13
Publication date: 2013-06-27
Also published as: FR2984341B1; FR2984341A1

Abstract

Process for manufacturing articles, characterized in that it comprises a step of rotational moulding of a composition (C) comprising at least one vinyl chloride polymer (P) and at least one heat stabilizer (S), according to which - the said polymer (P) is a rigid polymer chosen from copolymers (P1) containing monomer units derived from vinyl chloride and monomer units derived from at least vinyl acetate and mixtures (M) comprising at least 30% by weight, relative to the total weight of polymers in the mixture (M), of at least one copolymer (P1) and at most 70% by weight, relative to the total weight of polymers in the mixture (M) of at least one vinyl chloride homopolymer (P2), the molecular mass of the polymer (P) being such that its K value, measured according to standard ISO 1628-2, is between 45 and 60, and - the stabilizer (S) is chosen from liquid organotins. Composition, use thereof and manufactured articles.

Description

Process for manufacturing articles by rotational moulding of a composition based on vinyl chloride polymer

This application claims priority to French application No. 1161865 filed on December 19, 2011, the whole content of this application being incorporated herein by reference for all purposes

The present invention relates to a process for manufacturing articles by rotational moulding of a composition based on vinyl chloride polymer. The invention also relates to a particular composition based on vinyl chloride polymer, advantageously for use by rotational moulding. The invention also relates to the use of this composition for the manufacture of articles by rotational moulding. Finally, the invention relates to the articles manufactured by the rotational moulding of this composition.

To manufacture moulded particles of complex shapes, the plastics industry generally uses injection moulding. However, the complex injection moulding machines operate at high pressures and the moulds are very expensive since they must withstand high shear forces and these high pressures. The injection moulding of plastics thus proves to be difficult and non- viable when it is a matter of producing large items in small runs.

Another moulding technique, which is less complex and less expensive, but which may be more suitable for this purpose, is rotational moulding (also known as rotary moulding). According to this moulding technique, the heating, the forming and the cooling of the plastic are all performed in the mould, without applying pressure. The technique of rotational moulding is based on the property of a material to gel (i.e. to pass from a heterogeneous phase to a homogeneous phase (free of a grain structure)) only under the action of heat and without shear or with a very low shear. Details regarding rotational moulding (rotary moulding) and the plastics that may be fashioned via this moulding technique are found in the article Rotational Molding published in the Encyclopedia of

Polymer Science and Engineering published by John Wiley & Sons Inc., 1988, volume 14, pages 659 to 670. This article is incorporated by reference in the present description for everything that it discloses.

Thus, according to the rotational moulding technique, a certain amount of plastic in powder or paste form is introduced into a mould, which is placed in an oven and rotated about different axes in order to uniformly distribute the plastic in the mould. The heat melts the plastic in contact with the surface of the mould. At the end of the moulding cycle, the mould is cooled and then opened to remove the moulded article.

Rotational moulding especially offers the following advantages over other plastics transformation processes:

- a more uniform thickness of the single or double walls of the moulded articles;

- the easy inclusion of protruding parts, ribs and inserts;

- virtually unlimited variety of models and structures of the articles;

- simple, inexpensive tooling.

Many plastics are entirely suitable for rotational moulding. Among these plastics, the article indicated above especially mentions polyethylene and, to a lesser extent, poly( vinyl chloride) (PVC). The latter polymer, however, can only be fashioned by rotational moulding in the form of plastisols, which may melt merely by the action of the heat and without shear, and produce flexible or semirigid articles. Specifically, hitherto, it has not been possible to achieve the gelation of rigid PVC without substantial shear of the material, and,

consequently, it has not been possible to apply the technique of rotational moulding to rigid PVC. It has therefore not been possible hitherto to

successfully apply the technique of rotational moulding to the fashioning of rigid PVC articles.

The present invention is directed towards solving this problem by providing a process for manufacturing articles by rotational moulding of a composition based on rigid vinyl chloride polymer.

To this end, a main subject of the invention is a process for manufacturing articles, characterized in that it comprises a step of rotational moulding of a composition (C) comprising at least one vinyl chloride polymer (P) and at least one heat stabilizer (S), according to which

- the said polymer (P) is a rigid polymer chosen from copolymers (PI)

containing monomer units derived from vinyl chloride and monomer units derived from at least vinyl acetate and mixtures (M) comprising at least 30% by weight, relative to the total weight of polymers in the mixture (M), of at least one copolymer (PI) and at most 70% by weight, relative to the total weight of polymers in the mixture (M) of at least one vinyl chloride homopolymer (P2), the molecular mass of the polymer (P) being such that its K value, measured according to standard ISO 1628-2, is between 45 and 60, and

- the stabilizer (S) is chosen from liquid organotins.

In the present description, the terms "rotational moulding" and "rotary moulding" will be used indiscriminantly to qualify the technique of rotational moulding, which may be defined, for the purposes of the present invention, by the sequence of operations in which a certain amount of composition (C) is introduced into a mould placed in an oven and rotated about different axes in order to uniformly distribute the composition in the mould before heat melts the composition in contact with the surface of the mould, and at the end of the moulding cycle, the mould is cooled and then opened to remove the moulded article.

When applied to the process according to the invention, this moulding technique thus advantageously comprises at least:

- the introduction of a certain amount of the composition (C) into a mould, which is placed in an oven and rotated about different axes in order to uniformly distribute the composition in the mould;

- the melting of the composition in contact with the surface of the mould via the action of heat;

- at the end of the moulding cycle, the cooling and opening of the mould to remove the moulded article therefrom.

The expression "composition (C) comprising at least one polymer" is intended to denote, in the present description, that the composition (C) may comprise one polymer or a mixture of several distinct polymers; it preferably comprises one polymer or a mixture of two distinct polymers. In the rest of the present description, the term "polymer" is used indistinctly in the singular and in the plural. This is likewise the case for the terms "homopolymers" and

"copolymers" mentioned below.

According to the invention, the polymer (P) is a rigid polymer. The term "rigid polymer" is intended to denote, in the present description, a polymer or a mixture of polymers in which the content of plasticizer(s) is less than or equal to 10% by weight, preferably less than or equal to 5% by weight and particularly preferably less than or equal to 2.5% by weight, relative to the weight of polymer(s). Polymers or mixtures of polymers free of plasticizer (in other words not containing any plasticizer at all) are most particularly preferred. The copolymers (PI) that may be used in the process according to the invention are copolymers containing monomer units derived from vinyl chloride and monomer units derived from at least vinyl acetate (as comonomer that is copolymerizable with vinyl chloride). According to the invention, the term "at least" is intended to denote that the copolymer (PI) must comprise monomer units derived from vinyl acetate, but may optionally also comprise monomer units derived from other comonomers that are copolymerizable with vinyl chloride. Among the other comonomers, non-limiting examples that may be mentioned include vinyl alcohol, ethylene and acrylic esters. Preferably, however, the copolymers (PI) contain monomer units derived from vinyl chloride and monomer units derived from vinyl acetate. In other words, they preferably contain only these monomer units.

According to the invention, vinyl chloride is advantageously present in predominant amounts in the copolymer (PI). The expression "in predominant amounts" is intended to denote that the copolymer (PI) contains at least 50% by weight, preferably at least 60%> by weight, particularly preferably at least 70%> by weight and most particularly preferably at least 80% by weight of monomer units derived from vinyl chloride.

In the case where the copolymers (PI) contain monomer units derived from vinyl chloride and monomer units derived from vinyl acetate, the content of vinyl chloride in the copolymers (PI) is advantageously between 75% and 95%, preferably between 82% and 92% and particularly preferably between 85% and 90% by weight.

The copolymers (PI) that may be used in the process according to the invention are advantageously copolymers whose molecular mass is such that their K value, measured according to standard ISO 1628-2, is greater than or equal to 45. This K value is advantageously less than or equal to 60, preferably less than or equal to 59 and particularly preferably less than or equal to 57.

Excellent results have been obtained with copolymers (PI) with a K value of between 45 and 57.

According to the invention, the polymer (P) is chosen from the copolymers (PI), with the characteristics and preferences defined above, and mixtures (M) comprising at least 30% by weight, relative to the total weight of polymers in the mixture (M), of at least one copolymer (PI) and at most 70% by weight, relative to the total weight of polymers in the mixture (M), of at least one vinyl chloride homopolymer (P2). In the present description, the expression "mixtures (M) comprising at least 30% by weight, relative to the total weight of polymers in the mixture (M), of at least one copolymer (PI)" is intended to denote that the mixtures (M) may comprise one copolymer (PI) or several copolymers (PI). They preferably comprise one copolymer (PI).

In the present description, the expression "mixtures (M) comprising at most 70% by weight, relative to the total weight of polymers in the mixture (M), of at least one homopolymer (P2)" is intended to denote that the mixtures (M) may comprise one homopolymer (P2) or several homopolymers (P2). They preferably comprise one vinyl chloride homopolymer (P2).

The mixtures (M) thus preferably comprise at least 30% by weight, relative to the total weight of polymers in the mixture (M), of one copolymer (PI) and at most 70% by weight, relative to the total weight of polymers in the mixture (M), of one vinyl chloride homopolymer (P2).

The polymer (P) is thus preferably chosen from the copolymers (PI), with the characteristics and preferences defined above, and mixtures (M) comprising at least 30% by weight, relative to the total weight of polymers in the mixture (M), of one copolymer (PI) and at most 70% by weight, relative to the total weight of polymers in the mixture (M), of one vinyl chloride homopolymer (P2).

The vinyl chloride homopolymers (P2) that may be used in the process according to the invention are advantageously homopolymers whose molecular mass is such that their K value, measured according to standard ISO 1628-2, is greater than or equal to 45, preferably greater than or equal to 47 and particularly preferably greater than or equal to 48. This K value is advantageously less than or equal to 60, preferably less than or equal to 55 and particularly preferably less than or equal to 52. Excellent results have been recorded with mixtures (M) comprising at least one vinyl chloride homopolymer (P2) whose K value is about 50.

According to the invention, the molecular mass of the polymer (P) is such that its K value, measured according to standard ISO 1628-2, is between 45 and 60.

For the purposes of the present description, the expression "molecular mass of the polymer (P)" is intended to denote the molecular mass of the copolymer (PI) when the polymer (P) is chosen from the copolymers (PI) and the molecular mass of the mixture (M), when the polymer (P) is chosen from the mixtures (M), which is then the weight average of the individual molecular masses of the polymers constituting the mixture (M).

The polymers (P) (copolymers (PI) and homopolymers (P2)) may be synthesized according to any known process. Advantageously, they are obtained by aqueous suspension polymerization.

The synthesis in aqueous suspension of the polymers (P) may be performed in a manner that is well known to those skilled in the art,

advantageously in the presence of conventional ingredients such as:

- protective colloids, for instance partially saponified polyvinyl alcohol and cellulose ethers;

- initiators that are soluble in the monomers, such as peroxides, for example dilauryl peroxide, di-t-butyl peroxide and dibenzoyl peroxide;

hydroperoxides, for example t-butyl hydroperoxide; peresters, for example t- butyl perpivalate, t-butyl 2-ethylhexanoate and t-butyl perneodecanoate; percarbonates, for example diethyl peroxydicarbonate and diisopropyl peroxydicarbonate and di-n-butyl peroxydicarbonate; azo compounds, for example azobisisobutyronitrile;

- pH regulators, such as buffer salts, for example sodium phosphate, sodium polyphosphate and sodium hydrogen carbonate.

The (co)polymerization temperature is generally adjusted so as to obtain the K value desired for the polymer (P). Usually, this temperature is between 50 and 100°C, preferably between 55 and 95°C and more particularly between 57 and 90°C. The polymerization is generally carried out at a pressure of between 9 and 20 bar and preferably between 10 and 19 bar.

Composition (C) subjected to the rotational moulding according to the invention also contains at least one heat stabilizer (S) chosen from liquid organotins. Specifically, it has been found that when solid-state organotins are used, they cannot be uniformly distributed in the composition (C), and sufficient gelation of this composition cannot be obtained.

In the present description, the expression "composition (C) containing at least one heat stabilizer (S)" is intended to denote that composition (C) may comprise one heat stabilizer or a mixture of several distinct heat stabilizers. In the present description, the terms "heat stabilizer" and "organotin" are used indiscriminantly in the singular and in the plural.

In the present description, the term "liquid organotin" is intended to denote compounds that contain at least one carbon-tin bond in their molecule and that are in liquid form under standard temperature (25°C) and pressure (1013 hPa) conditions. The terms "liquid" and "in liquid form" are used to define both pure organotins that are in liquid form and organotins that are in the form of a liquid after they have been dissolved in a suitable organic solvent.

Advantageously, the heat stabilizer (S) is chosen from (1) organotins containing at least one tin-sulfur bond (also known as organotin mercaptides) and (2) organotin carboxylates.

Examples of organotins (1) that can be used as heat stabilizers (S) are:

- alkyltin thioglycolates (mercaptoacetates), such as methyl-, butyl- or octyl tin 2-ethylhexyl (or isooctyl) thioglycolates, and more particularly dimethyltin bis(2-ethylhexyl (or isooctyl) thioglycolate), monomethyltin tris(2-ethylhexyl (or isooctyl) thioglycolate), dioctyltin bis(2-ethylhexyl (or isooctyl) thioglycolate), monooctyltin trace(2-ethylhexyl (or isooctyl) thioglycolate), and mixtures thereof;

- alkyltin mercaptopropionates, such as methyl-, butyl- or octyltin

isooctylmercaptopropionates, and more particularly mono- or dimethyltin isooctylmercaptopropionates;

- alkyltin (ethanol)mercaptides (or mercaptoethanol), such as mono- or dimethyltin (ethano l)mercaptides;

- alkyltin alkylmercaptides, such as methyl-, butyl- or octyltin

isooctylmercaptides, and more particularly mono- or dimethyltin

isooctylmercaptides;

- alkyltin sulfides, such as methyl-, butyl- or octyltin sulfides, and more particularly mono- or dimethyltin sulfides.

Examples of organotin carboxylates (2) that can be used as heat stabilizers (S) are:

- dialkyltin bis(acetates), such as dibutyl- and dioctyltin bis(acetates);

- dialkyltin bis(alkylmaleates), such as dibutyl- and dioctyltin

bis(methy lmaleates) .

Mixtures of two or more organotins (1), of two or more organotin carboxylates (2) and of organotins (1) and organotin carboxylates (2) together may be used in the process according to the invention.

Preferably, the heat stabilizer (S) is chosen from organotins (1) and particularly preferably from alkyltin thioglycolates. Heat stabilizers (S) that are most particularly preferred are dimethyltin bis(2-ethylhexyl thioglycolate), monomethyltin tris(2-ethylhexyl thioglycolate) and mixtures thereof (such as the commercial product ADVASTAB™ TM-181FS sold by Dow) and also dioctyltin bis(2-ethylhexyl thioglycolate) and mixtures comprising the same (such as the commercial product MARK^® 17 MOK sold by Galata).

The heat stabilizers (S) are advantageously present in conventional amounts in composition (C); these amounts are advantageously between 0.1% and 10% by weight, preferably between 0.2%> and 6%> by weight and more particularly between 1% and 4.5% by weight relative to the weight of polymer

(P).

Preferably, composition (C) also contains a non-stick agent. In the present description, the term "non-stick agent" is intended to denote any substance that contributes to assure a correct demoulding of the articles manufactured via the process according to the invention.

Non-stick agents that may be used are the agents that are well known for the demoulding of PVC. Examples of non-stick agents are:

- silicone oils,

- metal stearates,

- lignite wax,

- non-functionalized paraffins, and

- oxidized polyethylene waxes.

A preferred non-stick agent comprises an oxidized polyethylene wax. The non-stick agent may thus be, for example, a mixture of an oxidized polyethylene wax with a non-functionalized paraffin or an oxidized polyethylene wax alone.

The non-stick agent is advantageously present in the composition (C) in amounts of between 0.05%> and 5%> by weight, preferably between 0.1%> and 3%> by weight and more particularly between 0.2% and 1% by weight relative to the weight of polymer (P).

Composition (C) may also optionally contain other compounds that promote its gelation during the rotary moulding. These compounds are advantageously chosen from additives that promote the gelation of PVC and preferably from additives that can exert a lubricant and/or stabilizing action. Examples of additives that exert a lubricant action are especially esters of dicarboxylic acids and of saturated fatty alcohols, including, inter alia, dioctyl phthalate, diisononyl phthalate, distearyl phthalate and dioctyl sebacate, and also hydrogenated castor oil and tricresyl phosphate. Examples of additives that exert a stabilizing action are epoxidized fatty acid esters, and, among these, the products of epoxidation of the fatty acid esters present in natural oils, such as epoxidized cotton oil, epoxidized linseed oil, epoxidized olive oil and epoxidized soybean oil. The latter agent is particularly preferred as an additive that exerts a stabilizing action in composition (C).

When these additives that exert a lubricant and/or stabilizing action are incorporated into composition (C), they are advantageously present in amounts of between 0.3% and 15% by weight relative to the weight of polymer (P).

Other additives that are usually used in PVC-based compositions may also be incorporated into composition (C). Among these, mention may be made of conventional heat stabilizers other than liquid organotins, pigments or dyes, UV stabilizers, mineral fillers, processing aids, antistatic agents, flame retardants, antioxidants and chlorine or oxygen scavengers. These additives are then advantageously introduced in conventional amounts.

The preparation and use of composition (C) may be performed according to any method that enables its gelation in the mould solely by the action of heat and without exerting significant shear forces.

In the present description, the expression "gelation of the composition" is intended to denote that the composition passes from a heterogeneous phase to a homogeneous phase (free of grain structure).

Thus, according to a first embodiment (first variant), a premix of at least some, and preferably of all, of the polymer (P) with at least some, and preferably all, of the heat stabilizer (S) may be prepared before they are subjected to the rotary moulding, i.e. before introducing them into the rotary mould placed in an oven. The other optional constituents (non-stick agent, other additives, etc.) may also be added, partially or totally, during this premixing.

The term "premixing" is understood to denote any operation that includes the use of a mixer and that makes it possible to mix the various constituents of composition (C) according to the process of the invention.

This premixing is advantageously performed without heating or at a temperature of between 30 and 130°C, preferably between 40 and 110°C and more particularly between 50 and 100°C to obtain composition (C) in the form of a powder.

According to one particular embodiment of this first variant, pregelation of the powder resulting from the premixing is performed. This pregelation may be performed in any known device that is capable of exerting on the powdered composition (C) shear forces that are strong enough to bring it from an at least partially heterogeneous phase to a homogeneous phase (free of grain structure). This device may be, for example, a batch blender or a continuous blender. Extruders are preferred as continuous blenders. The term "extruder" is understood to mean any continuous blender comprising at least one feed zone and, at its outlet, a discharge zone preceded by a compression zone, the latter forcing the pregelled composition (C) to pass through the discharge zone. The discharge zone may also be followed by a granulation device which gives the pregelled composition (C) a homogeneous form that is particularly suited to the final gelation in the rotary moulding mould. Advantageously, use is made of known extruders based on the work of a single screw or of two screws which, in the latter case, may cooperate in a co-rotating or counter-rotating manner (same direction of rotation or opposite directions of rotation).

According to a second embodiment (second variant), the polymer (P), the heat stabilizer (S) and the other optional constituents are mixed together directly in the rotary mould placed in an oven.

It may occasionally be difficult to adjust the amount of heat stabilizer (S) in order for it to be neither too little, not enabling sufficient gelation of the mixture, nor excessive to the point of causing problems of agglomeration of the mixture. The preparation and use of composition (C) may then be performed according to a third embodiment (third variant) involving the use of a masterbatch based on vinyl chloride polymer, rich in stabilizer (S). The vinyl chloride polymer present in the masterbatch may be chosen from vinyl chloride homopolymers and from copolymers derived from vinyl chloride and vinyl acetate. In the case where the vinyl chloride polymer present in the masterbatch is a copolymer, it may be a copolymer that is identical to or different from the copolymer (PI). It is preferable for the vinyl chloride polymer present in the masterbatch to be a homopolymer prepared by aqueous suspension

polymerization and to have a K value of between 50 and 75 and preferably between 58 and 70.

In the present description, the expression "masterbatch... rich in stabilizer (S)" is intended to denote a mixture into which has been incorporated from 1.5 to 10 times more and preferably from 2 to 5 times more stabilizer (S) than in the composition itself. The masterbatch powder thus constituted may contain agglomerates that are then removed by subjecting it to a compounding operation (for example in an extruder, preferably a single-screw extruder), followed by milling. The masterbatch is then incorporated into an additional amount of polymer (P), in proportions advantageously equivalent to 20% to 70% by weight of the polymer (P) and preferably from 30% to 50% by weight of the polymer (P) and the whole subjected to rotary moulding.

The first and third variants of preparation and implementation of composition (C) are preferred, more particularly the first.

Whatever the variant selected, the residence time of composition (C) during the rotational moulding step is advantageously between 1 and 60 minutes, preferably between 5 and 45 minutes and more particularly between 10 and 30 minutes. The temperature during the rotational moulding step is advantageously between 150 and 270°C, preferably between 170 and 260°C and more particularly between 190 and 250°C. The spin speed during the rotational moulding step is advantageously between 5 and 100 rpm, preferably between 7 and 80 rpm and particularly preferably between 10 and 70 rpm.

The gelation, optionally preceded by a pregelation, of composition (C) during the rotary moulding advantageously gives the manufactured article a smooth and translucent appearance.

A subject of the present invention is also a composition (C) comprising at least one vinyl chloride polymer (P) and at least one heat stabilizer (S), characterized in that the polymer (P) is a rigid polymer chosen from copolymers (PI) containing monomer units derived from vinyl chloride and monomer units derived from at least vinyl acetate and mixtures (M) comprising at least 30% by weight, relative to the total weight of polymers in the mixture (M), of at least one copolymer (PI) and at most 70% by weight, relative to the total weight of polymers in the mixture (M) of at least one vinyl chloride homopolymer (P2), the molecular mass of the polymer (P) being such that its K value, measured according to standard ISO 1628-2, is between 45 and 60, and in that the stabilizer (S) is chosen from liquid organotins.

Composition (C) according to the invention is advantageously a composition for use by rotational moulding, preferably via the process according to the invention.

All the definitions and limitations stated and described above in relation with the process according to the invention are applicable, mutatis mutandis, to composition (C) itself.

Composition (C) according to the invention can however also be used for other purposes and in particular for the manufacture of composite plates based on PVC and a network of fibers by a method such as that defined in patent application WO 2008/065061 incorporated herein by reference, which comprises the following steps: - dispersing the composition (C) in powder form in said network;

- subjecting the dispersion to an alternating electrostatic field with a sufficient intensity and for a sufficient time to distribute the powder in the network;

- heating the dispersion under pressure until the powder forms a continuous matrix.

The concerned fibers may be any commercially available fibers. It can be organic fibers (from natural products such as hemp and flax for example, or from synthetic products such as polymeric fibers) and/or mineral fibers (glass fibers for example). These fibers can be short or long, woven or nonwoven and the fiber network can be ordered or not.

A subject of the present invention is also the use of a composition (C) according to the invention for the manufacture of articles by rotational moulding.

All the definitions and limitations stated and described above in relation with the process according to the invention are applicable, mutatis mutandis, to the use of composition (C) itself.

Finally, a subject of the present invention is articles manufactured by the rotational moulding of a composition (C) according to the invention or manufactured via the process according to the invention.

All the definitions and limitations stated and described above in relation with the process according to the invention are applicable, mutatis mutandis, to the manufactured articles.

Taking into account the fact that the technique of rotary moulding has fewer practical limitations than the other techniques for processing plastics, very varied articles (objects and parts of objects) may be manufactured by rotary moulding. Among the articles that may be manufactured by rotary moulding of compositions (C) according to the invention, mention may be made of decorative articles; furniture components; electrical connection cases; components for fat separators in water treatment plants; reservoirs and containers in the fields of agriculture, chemistry, packaging and transportation; portable toilets; battery cases; lighting globes; vacuum cleaner bodies; toys; waste containers; kayaks and canoes; sporting equipment, etc.

The process according to the invention allows the successful manufacture of rotary-moulded articles made of rigid PVC. The process thus makes it possible to exploit the rigidity properties of PVC while at the same time avoiding the heavy investment associated with the injection moulding technique. Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence."

The following examples are intended to illustrate the invention without however limiting the scope thereof.

Determination of the K value

The K value was measured according to standard ISO 1628-2.

Determination of the degree of gelation

The degree of gelation was estimated via a visual method by observing the appearance of the sample (smooth and translucent if the sample is correctly gelled - granular and white if the sample is not gelled) and/or by measuring the heat of fusion (AHa) of the polymer crystallites present in the sample according to a protocol similar to that described in standard ISO 18373-2 and detailed below.

According to this protocol, differential scanning calorimetry (DSC) measurements were taken using a Mettler-Toledo DSC 823e analyser, and the evaluation of the results was made with version 9.10 of the Mettler-Toledo STARe software. Indium was used for calibrating the temperature and the enthalpy.

A piece of about 20 mg was cut from the thickness of each sample using a tool (razor blade or cutting pliers) not inducing any heating or tension in the sample. The piece cut off was inserted into an aluminium crucible closed with a lid made of this metal. After sealing the assembly, three holes were made in the lid to allow better circulation of nitrogen and evacuation of the volatile fractions.

The temperature programme was as follows: maintenance for 5 minutes at a chosen temperature markedly below the glass transition temperature of the polymer of the sample (typically -20°C) and then uniform rise at a rate of 20°C per minute up to 220°C. The measurements were taken under a 50 ml/minute stream of nitrogen.

The degree of gelation of the sample was assessed by measuring the enthalpy of the first melting endotherm (AHa) expressed in J/g. This enthalpy was calculated by integration of the area of the peak between the following two limits: the lower limit was located after the end of the glass transition (and of the enthalpy of endotherm relaxation that may be associated therewith), typically between 90 and 120°C, such that the baseline does not pass through the DSC trace; the upper limit was the working temperature to which the sample is subjected. This temperature was generally located between the two melting endotherms, due, respectively, to the primary and secondary crystallites of the polymer of the sample. In the case where the upper endotherm was not observed, the upper integration limit was set either at the place where the baseline deviated again in the endothermic direction, or, if this deviation was not observed, at the final temperature of the temperature programme (220°C). For the integration, a straight baseline was used, without correction. The

measurement was repeated twice.

An enthalpy of fusion of the crystallites of the polymer of less than 4 J/g was linked to insufficient gelation; an enthalpy of between 4 and 6 J/g to acceptable gelation, and an enthalpy of greater than 6 J/g to very good gelation. Examples 1 to 13

To determine the capacity for processing by the rotary moulding of compositions, a first series of examples was performed by placing compositions in powder form in a metal channel subjected statically to heating at 200°C for a duration of between 0 and 30 minutes in an oven, and sliding slowly from the oven. The oven used was a Metrastat IR 5 oven manufactured by the company Dr. Stapfer GmbH, Dusseldorf.

The heat stability of the composition was evaluated at the same time. It corresponds to the time in minutes at which degradation of the composition is observed when it is exposed to 200°C.

The compositions tested in Examples 1 to 13 are detailed below and Table 1 below relates the results obtained.

Example 1 (according to the invention)

A composition comprising

- 100 parts by weight of the rigid copolymer, with a K value equal to 50, containing 87% by weight of vinyl chloride monomer units and 13% by weight of vinyl acetate monomer units, sold under the name Solvin^®550GA by SolVin,

- 0.5 part by weight of oxidized polyethylene wax sold under the name

A-C^®316 by Honeywell,

- 0.7 part by weight of the dicarboxylic acid ester of saturated fatty alcohols sold under the name Loxiol^®G60 by Cognis, and

- as liquid organotin, 3.5 parts by weight of the mixture of dimethyltin bis(2- ethylhexyl thioglycolate) and of monomethyltin tris(2-ethylhexyl thioglycolate) sold under the name Advastab™ TM-181 FS by Dow, was prepared by mixing these various compounds in a Brabender P600 blender (planetary mixer); the solids were introduced before the liquids. The nominal temperature of the thermostat was 95°C and mixing was performed for 10 minutes.

Example 2 (in accordance with the invention)

Example 1 was repeated, replacing in the composition the copolymer Solvin^®550GA by the rigid copolymer, with a K value equal to 45, containing 85% by weight of vinyl chloride monomer units and 15% by weight of vinyl acetate monomer units, sold under the name Lacovyl^®GA6015 by Arkema.

Example 3 (in accordance with the invention)

Example 1 was repeated, with a composition comprising

- 100 parts by weight of a mixture of polymers comprising 70%> by weight, relative to the total weight of polymers in the mixture, of the copolymer Solvin^®550GA and 30%> by weight, relative to the total weight of polymers in the mixture, of the vinyl chloride homopolymer with a K value equal to 50, sold under the name Solvin^®250SB by Solvin,

- 0.5 part by weight of oxidized polyethylene wax A-C^®316,

- 0.7 part by weight of the dicarboxylic acid ester of saturated fatty alcohols sold under the name Loxiol^®G60,

- as liquid organotin, 3.5 parts by weight of dioctyltin bis(2-ethylhexyl

thioglycolate) sold under the name Mark^® 17 MOK by Galata, and

- 0.5 part by weight of the silica Sipernat 310 sold by Evonik Degussa GmbH. Example 4 (according to the invention)

Example 3 was repeated, except that the mixture of polymers was replaced in the composition with another mixture of polymers comprising 50% by weight, relative to the total weight of polymers in the mixture of the copolymer

Solvin^®550GA and 50%> by weight, relative to the total weight of polymers in the mixture, of the vinyl chloride homopolymer Solvin^®250SB, and that the powder composition was subjected to pregelation.

This pregelation was performed in an extruder using a Coperion ZSK 25 twin-screw gelling machine, the four temperature zones being set at: 110°C- 120°C- 130°C- 130°C and the spin speed of the screw at 150 rpm, which led to a flow rate of 5 kg/hour. The compounding head was performed so as to extrude two rods 4 mm in diameter. The granulator chopped granules 2-3 mm thick.

The granules obtained had a degree of gelation characterized by a AHa of 6.4 J/g. After this pregelation, the granules were ground to regain a sufficiently fine granulometry, i.e. grain diameters < 500 μιη, using a Kolloplex 160Z mill, before being introduced into the metal channel.

Example 5 (according to the invention)

Example 1 was repeated, with a composition comprising

- 100 parts by weight of a mixture of polymers comprising 50% by weight, relative to the total weight of polymers in the mixture, of the rigid copolymer, with a K value equal to 57, containing 90%> by weight of vinyl chloride monomer units and 10% by weight of vinyl acetate monomer units, sold under the name Solvin^®557 RB by SolVin, and 50% by weight, relative to the total weight of polymers in the mixture, of the vinyl chloride homopolymer Solvin ^®250SB,

- 0.3 part by weight of oxidized polyethylene wax A-C^®316,

- 3.5 parts by weight of the liquid organotin Advastab™ TM- 181 FS, and

- 0.2 part by weight of the silica Sipernat 310.

Example 6 (according to the invention)

Example 3 was repeated, except that the mixture of polymers was replaced in the composition with another mixture of polymers comprising 30% by weight, relative to the total weight of polymers in the mixture of the copolymer

Solvin^®550GA and 70%> by weight, relative to the total weight of polymers in the mixture, of the vinyl chloride homopolymer Solvin^®250SB.

Example 7 (comparative)

Example 1 was repeated, replacing in the composition the copolymer

Solvin^®550GA by the vinyl chloride homopolymer Solvin^®250SB and adding to the composition 0.5 part by weight of the silica Sipernat 310.

Example 8 (according to the invention)

Example 1 was repeated, reducing the amount of oxidized polyethylene wax A-C^®316 to 0.3 part by weight and adding 0.2 part by weight of the silica

Sipernat 310.

Example 9 (comparative)

Example 1 was repeated, reducing the amount of oxidized polyethylene wax A-C^® 316 to 0.3 part by weight, adding 0.2 part by weight of the silica Sipernat 310 and replacing the liquid organotin Advastab™ TM- 181 FS with the liquid calcium-zinc heat stabilizer Mark^®CZ 108 sold by Galata. Example 10 (comparative)

Example 1 was repeated, reducing the amount of oxidized polyethylene wax A-C^® 316 to 0.3 part by weight, adding 0.2 part by weight of the silica Sipernat 310 and replacing the liquid organotin Advastab™ TM-181 FS with the solid tin heat stabilizer Thermolite^® 8000 sold by Arkema.

Example 11 (comparative)

Example 1 was repeated, reducing the amount of oxidized polyethylene wax A-C^®316 to 0.3 part by weight, adding 0.2 part by weight of the silica Sipernat 310 and replacing the liquid organotin Advastab™ TM-181 FS with the liquid barium- zinc heat stabilizer Lankromark^®LZB 770 sold by Akcros Chemicals.

Example 12 (according to the invention)

Example 3 was repeated, replacing the mixture of polymers with another mixture of polymers comprising 50% by weight, relative to the total weight of polymers in the mixture, of the copolymer Solvin^® 550GA and 50%> by weight, relative to the total weight of polymers in the mixture, of the vinyl chloride homopolymer Solvin^®250SB, and adding 5 parts by weight of the acrylic impact modifier Kane Ace FM™ 22 sold by Kaneka.

Example 13 (in accordance with the invention)

Example 12 was repeated, increasing the amount of liquid organotin

Mark^® 17 MOK to 5 parts by weight.

Table 1

n.d. not determined

Examples 14 to 17

To simulate the operating conditions prevailing in a plant comprising a rotary moulding mould placed in an oven, compositions in powder form were placed in an oven equipped with a system enabling elementary rotary moulding by rotation about a single axis. The mould was a steel cylinder 80 mm in diameter and 120 mm long rotating at 70 rpm. The oven was maintained at 200°C and the exposure time was set at 20 minutes. The compositions tested in Examples 14 to 17 are detailed below and Table 2 below collates the results obtained.

Example 14

A composition identical to that of Example 5 except that the mixture of polymers was replaced with the copolymer Solvin^®550GA and prepared as described in Example 1 was used.

Example 15

A composition identical to that of Example 4 but not having undergone pregelation, and prepared as described in Example 1 , was used. After the rotary moulding operation, cooling and removing from the mould, a cylinder whose wall thickness was about 2 mm was obtained.

Example 16

A composition identical to that of Example 4 having also undergone pregelation, and prepared as described in Example 1, was used. The granules obtained had a degree of gelation characterized by a AHa of 6.8 J/g.

After this pregelation, the granules were ground to regain a sufficiently fine granulometry, i.e. grain diameters < 500 μιη, using a Kolloplex 160Z mill, before being introduced into the rotary moulding oven.

After the rotary moulding operation, cooling and removing from the mould, a cylinder whose wall thickness was about 2 mm was obtained.

Example 17

A composition identical to that of Example 7 and prepared as described in Example 1 was used. After the rotary moulding operation, cooling and removing from the mould, a cylinder whose wall thickness was about 2 mm was obtained. Table 2

n.d. not determined

Examples 18 and 19

Finally, compositions were subjected to moulding in an industrial rotary moulding oven for the manufacture of balls.

After filling the cold mould, it was rotated about the two axes at 10 rpm. After 25 seconds of heating at 245°C, the curing was continued for 18 minutes and the rotary-moulded balls, weighing 140 g, with a diameter of 9.5 cm and a density of 1.3, were then cooled outside the oven for 10 minutes.

The compositions tested in Examples 18 and 19 are detailed below.

Example 18

A composition comprising:

- 100 parts by weight of the copolymer Solvin^®550GA,

- 0.3 part by weight of the oxidized polyethylene wax A-C^®316,

- 1 part by weight of the acrylic processing aid sold under the name Paraloid™ K-175 by Dow,

- 3 parts by weight of the liquid organotin Advastab™ TM- 181 FS, and

- 15 parts by weight of epoxidized soybean oil.

The rotary-moulded balls, which are satisfactorily gelled (AHa = 6.9 J/g - smooth and translucent) and which have a thickness of 1 mm, withstood a drop of at least 1 metre. Example 19

A composition comprising:

- 100 parts by weight of a mixture of polymers comprising 50% by weight, relative to the total weight of polymers in the mixture, of the copolymer Solvin^®550GA and 50% by weight, relative to the total weight of polymers in the mixture, of the vinyl chloride homopolymer Solvin^®250SB,

- 0.4 part by weight of the oxidized polyethylene wax A-C^®316,

- 2 parts by weight of hydrogenated castor oil sold under the name Loxiol^®G15 by Cognis,

- 0.4 part by weight of the acrylic processing aid sold under the name

Paraloid™K-175,

- 3.5 parts by weight of the liquid organotin Advastab™ TM- 181 FS,

- 4 parts by weight of epoxidized soybean oil,

- 5 parts by weight of diisononyl phthalate,

- 0.1 part by weight of the non-functionalized paraffin Vestowax^®SH 105 sold by Degussa,

- 0.5 part by weight of the silica Sipernat 310, and

- 0.01 part by weight of ultramarine blue.

The rotary-moulded balls, which are satisfactorily gelled (AHa = 6.7 J/g - smooth and translucent) and which have a thickness of 1 mm, withstood a drop of at least 1 metre.

Claims

C L A I M S

1. Process for manufacturing articles, characterized in that it comprises a step of rotational moulding of a composition (C) comprising at least one vinyl chloride polymer (P) and at least one heat stabilizer (S), according to which - the said polymer (P) is a rigid polymer chosen from copolymers (PI)

- the stabilizer (S) is chosen from liquid organotins.

2. Process according to Claim 1, characterized in that the copolymers

(PI) contain monomer units derived from vinyl chloride and monomer units derived from vinyl acetate.

3. Process according to Claim 2, characterized in that the content of vinyl chloride in the copolymers (PI) is between 85% and 90% by weight.

4. Process according to any one of Claims 1 to 3, characterized in that the mixtures (M) comprise at least 30% by weight, relative to the total weight of polymers in the mixture (M), of one copolymer (PI) and at most 70% by weight, relative to the total weight of polymers in the mixture (M), of one vinyl chloride homopolymer (P2).

5. Process according to any one of Claims 1 to 4, characterized in that the heat stabilizer (S) is chosen from (1) organotins containing at least one tin-sulfur bond and (2) organotin carboxylates.

6. Process according to Claim 5, characterized in that the heat stabilizer (S) is chosen from alkyltin thioglycolates.

7. Process according to any one of Claims 1 to 6, characterized in that composition (C) contains a non-stick agent.

8. Process according to Claim 7, characterized in that the non-stick agent comprises an oxidized polyethylene wax.

9. Process according to any one of Claims 1 to 8, characterized in that the residence time of composition (C) during the rotational moulding step is between 1 and 60 minutes.

10. Process according to any one of Claims 1 to 9, characterized in that the temperature during the rotational moulding step is between 150 and 270°C.

11. Process according to any one of Claims 1 to 10, characterized in that the spin speed during the rotational moulding step is between 5 and 100 rpm.

12. Composition (C) comprising at least one vinyl chloride polymer (P) and at least one heat stabilizer (S), characterized in that the polymer (P) is a rigid polymer chosen from copolymers (PI) containing monomer units derived from vinyl chloride and monomer units derived from at least vinyl acetate and mixtures (M) comprising at least 30% by weight, relative to the total weight of polymers in the mixture (M), of at least one copolymer (PI) and at most 70% by weight, relative to the total weight of polymers in the mixture (M) of at least one vinyl chloride homopolymer (P2), the molecular mass of the polymer (P) being such that its K value, measured according to standard ISO 1628-2, is between 45 and 60, and in that the stabilizer (S) is chosen from liquid organotins.

13. Use of a composition (C) according to Claim 12, for the manufacture of articles by rotational moulding.

14. Articles manufactured by the rotational moulding of a composition (C) according to Claim 12 or manufactured via the process according to any one of

Claims 1 to 11.