Improved popyester for extrusion molding

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In blow molding processes, molten resins must be formed into stable blanks for a period of time long enough to allow a mold to enclose the blank. SL these molten polymers do not have sufficient mechanical strength in the molten state or viscosity in the molten state, the extruded tube will tend to elongate or stretch under its own weight, so that the article resulting obtained by blow molding will have non-uniform thicknesses of its walls, a low surface gloss and a shape which reproduces only slightly that of the control article.

When split, polymers such as polyesters, polyamides, polyethers and polyamines generally form fluid liquids having low melt viscosities. These low viscosity melt materials are unsuitable or only poorly suited for manufacture. extruded articles, tubes, articles obtained by deep drawing and large articles obtained by blow molding. In order to overcome these disadvantages and transform these polymers into. a suitable form, better for the aforementioned manufacturing techniques, it is known to add to plastics compounds or compositions which will increase its viscosity in the molten state. The materials which are added to increase the viscosity of the plastics in the molten state are generally crosslinking agents as described, for example, in United States Patent No. 3,378,532. Such crosslinking agents can be added during the condensation reaction allowing the formation of plastics and / or plastics after their formation (before or during their melting).

Examples of crosslinking agents which can be added to plastics after their formation and before or after their melting, in order to increase the viscosity in the molten state, include compounds containing at least two epoxy or isocyanato groups in their molecule, organic phosphorus compounds, peroxides, bis-haloalkylaryl compounds, and polyesters derived from carbonic acid.

These known crosslinking agents, which are added to increase the viscosity of the polymer in the molten state, are not entirely satisfactory. For example, they can cause an excessively rapid and large increase in viscosity or

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they can form reaction products having an adverse influence on the quality of plastics. Furthermore, the results obtained by using these known crosslinking agents are not always uniform or reproducible.

For example, when polyesters derived from carbonic acid are used to increase the viscosity in the molten state, the degree of increase in viscosity generally depends not only on the amount of additive used but also its molecular weight and the stage of the polycondensation reaction at which the addition takes place.

In addition to having sufficient melt viscosity or sufficient melt strength, polymers that are intended for use in blow molding and related applications must also have sufficient swelling after passing through a die. , that is, the molten polymer must expand as soon as it leaves the extrusion die and is released from it. This swelling after passing the die is important for blow molding applications since (a) it is all the easier to inject air into the polymer melt as the diameter of the extruded polymer. tall ; and (b) the expansion of the molten polymer, to adjust and correspond to the particular mold, is all the greater as the swelling after passage of the die is more pronounced.

Polyesters with low intrinsic viscosities are particularly difficult to blow mold. Although the prior art illustrates the use of numerous additives in order to modify various properties of polyesters, research has continued to find improved methods for increasing the mechanical strength of polyesters in the split state, so that these Polyesters with greater mechanical strength in the molten state can be used for blow molding and related applications.

Carbodiimides have been used as additives to stabilize polyesters (see, for example, U.S. Patents 3,193,522, 3,193,523 and 3,193,524). For example, in the aforementioned United States Patent No. 3,193,522, a method is proposed for stabilizing polyester compositions against hydrolytic degradation by the use, as additives, of highly substituted polycarbodiimides having molecular masses at least equal to approximately 500 and comprising in their molecule more than 3 carbodiimide groups. Likewise, the aforementioned U.S. Patent Nos. 3,193,523 and

No. 3,193,524 describe the use of mono-carbodiimides to stabilize polyesters. However, none of these previous attempts to stabilize polyesters by adding carbodiimides has given polyesters having characteristics of mechanical strength in the molten state or of swelling after passing through the die allowing these polyesters to be useful Π for extrusion applications.

Therefore, a general aim of the present invention consists in avoiding or substantially solving the aforementioned problems of the prior art.

A more particular object of the present invention is to provide a process for preparing improved polyester compositions having greater mechanical strength in the molten state or having a higher rate of mechanical strength in the molten state.

Another object of the present invention is to provide a process for preparing better polyester compositions useful for extrusion applications. _s

Another object of the present invention consists in proposing. a process for preparing polyester compositions having better swelling characteristics after passing the die.

Yet another object of the present invention is to provide the improved polyester compositions prepared by this process. \

The present invention also aims to provide an improved process for the extrusion of polyesters which uses these improved polyesters.

Other objects and advantages of the invention will appear on examining the brief summary which follows and the description of the preferred aspects of the present invention.

In one aspect, the present invention provides a process for preparing thermoplastic polyesters modified with polycarbodiimide, having better mechanical strength in the faith state, and which are suitable for extrusion applications. This process consists in reacting a saturated thermoplastic polyester, while it is in the molten state, with at least one polycarbodiimide which (a) comes from at least one unsubstituted aromatic diisocyanate or which contains up to one substituent. methyl

5- on each aromatic ring, and which (b) also contains at least 3 carbodiimide units per molecule of the polycarbodiimide.

According to another aspect, the present invention provides thermoplastic polyester modified with polycarbodiimide and which is produced by this process.

According to yet another aspect, the invention provides an improved molding process which consists in giving a melt of thermoplastic polyester modified with polycarbodiimide and described above in the form of a desired article and in cooling the thermopiastic polyester modified with imide and melted polycarbodi15.

The essential part of the present invention lies in the discovery that a limited group of polycarbodimides' reacts with saturated thermoplastic polyesters by causing the attachment of side branches on the saturated thermoplastic polyesters; it follows that the products of these reactions have greater mechanical strength in the molten state and greater intrinsic viscosity, and that they contain a lower number of carboxylic acid groups; terminal, the thermoplastic polyesters modified with polycarbodiimide and prepared according to the process of the present invention also have better characteristics of swelling after passage of the die; that is to say that after extrusion of the molten polyesters through an orifice having a particular diameter, the diameter of the extruded polyesters. can increase until it reaches approximately 2 or 3 times the diameter of the extrusion orifice.

As indicated above, the process of the present invention consists in reacting saturated thermoplastic polyesters, while they are in the molten state, with a polycarbodi35 imide to form improved polyesters having a greater mechanical resistance to melted state.

Any thermoplastic saturated polyester which is capable of reacting in the molten state can be used in the process of the present invention. The term saturated polyester is intended to include all polyesters which do not contain ethylenic unsaturation in the polymer chain. The term saturated includes. thus saturated aliphatic / aromatic polyesters and fully aromatic polyesters. Likewise, these polyesters can be halogenated, that is to say that they can contain halogen (for example bromine and / or chlorine) attached as substituents in the polymer chain. It is particularly desirable to thus use halogenated polyesters when it is desired to obtain products having a lower flammability.

The term thermoplastic polyester is intended to include all polyesters which soften when exposed to sufficient heat and which return to their original state when cooled to room temperature.

The thermoplastic saturated polyesters useful in the process of the present invention can be obtained or formed in a multitude of ways which are well known to experts in this field.

Typical thermoplastic saturated polyesters which are used in the present invention can be prepared from dialcohols or dihydroxy compounds, on the one hand, and dicarboxylic acids, on the other hand. Typical dialhydric or dihydroxy compounds include aromatic dihydroxy compounds such as bisphenol A (i.e. 2,2-bis (4-hydroxyphenol) -propane, phenolphthalein, 4,4'-sulfonyl diphenol , resorcinols, hydroquinone, 'catechol, naphthalene-diols, stilbene-bisphenol, 1' (ether-oxide of 4.4 '_x diphenyl) -diphenol, and mixtures thereof, as well as aliphatic dialcohols such as saturated dialcohols having 2 to 4 carbon atoms and mixtures thereof.

Dihydroxy compounds or halogenated dialcohols can also be used. Such dihydroxy compounds or such halogenated dialcohols include, for example, tetrabromobisphenol A, tetrachloro-bisphenol A, 2,2 '- (isopropylidenebis (2,6-dichloro-p-phenylene)) and 2,2 -bis (3,5-dibromo-4- (235 hydroxyethoxy) phenyl) propane.

Typical aromatic carboxylic aids include, for example, phthalic acid (which includes isophthalic acid and terephthalic acid), hydroxybenzoic acid and mixtures thereof.

Fully aromatic and typical thermoplastic polyesters include the reaction product of bisphenol A, isophthalic or terephthalic acid or mixtures (50 mole e / ojy) mole% or 60 mole% / 40 mole%) of isophthalic acid that and terephthalic acid. Such polyesters may further contain minor amounts of a saturated aliphatic dialcohol having 2 to 4 carbon atoms. Fully aromatic and halogenated thermoplastic polyesters include, for example, the reaction product of tetrabromobisphenol A and a mixture (in a molar ratio of 50/50) of isophthalic acid and terephthalic acid (and, optionally , of a small amount of ethylene glycol).

Preferred polyesters include the reaction products of a saturated aliphatic dialcohol having 2 to 4 carbon atoms and terephthalic acid. Thus, polyethylene terephthalate, polypropylene terephthalate and polyethylene terephthalate are preferred polyesters in the present invention.

The polycarbodiimides which can be used in the present invention are chosen from a group defined in a particular way. When reacted with polyester, not all polycarbodiimides will increase the mechanical strength of molten polyesters so that the resulting polyester can usefully be used for extrusion applications. It has been found that only polycarbodiimides which achieve (a) both come from at least one unsubstituted or aromatic diisocyanate containing up to a methyl substituent on, achieve the desired result. each aromatic nucleus, and (b) contain at least 3 units because bodiimides per molecule of pûlycarbodiimide.

The aromatic diisocyanates which are more highly substituted give polycarbodiimides which are not reactive enough to ensure the desired rate of reaction with the polyester Polycarbodiimides having less than 3 carbodiimide units per molecule of the polyoarbodiimide do not succeed, when put at the contact with polyester, only with an extension of the polyester chain without achieving a significant degree of ramifications. Branching by attaching side chains is necessary to obtain better mechanical strength in the molten state ”

The polycarbodiimide must be miscible with polyester which is in the molten state. The polycarbodiimides useful in the present invention can have number average molecular weights generally comprised between approximately 450 and approximately 10,000, typically between approximately 800 and approximately 8,000 and preferably between about 1,000 and about 6,500, polycarbodiimides having

- “molecular weights greater than about 10,000 may not dissolve in the mass of the split polyester and thus they may not be useful in the present invention®

Specific examples of polycarbodiimides which are useful in the present invention include poly (tolyl ~ carbodiimide), poly (4,4'-diphenylmethane-carbodiimide), poly (3,3'-dimethyl-4,4 * -biphenyImethane -carbodiimide), poly (p-phenylene-carbodiimide), poly (m-phenylene-carbodiimide), poly (3,3'-dimethyl-4,4'-diphenyIméthane-carbodiimide) and their

15.mixtures® Preferred polycarbodiimides include poly (tolylcarbodiimide), poly (4,4'-dipheny1-methane-carbodiimide) and mixtures thereof.

Polycarbodiimides can be formed in any manner known to those skilled in the art, for example by heating

20 ′ the aromatic diisocyanates defined above in the presence or in the absence of a solvent. The formation of polycarbodiimide • is accompanied by the evolution of carbon dioxide. '

The polycarbodiimides useful in the present invention can be prepared without the use of a catalyst, but much higher temperatures (about 300 ° C) are required when operating in the absence of a catalyst. For some polycarbodi, imideb, the use of such high temperatures can lead to the formation of large quantities of secondary products and colored products. ^ Thus, poly30 carbodiimides can typically be prepared by heating isocyanates in the presence of a catalyst, such as the phosphorus-containing catalysts which have been described in US Pat. Nos. 2,853,473,

N ° 2 663 737 and N ° 3 755 242, and also in Monagle J, Org. Chem. 22, 3851 (1962), Phospholine oxides, such as those described in the article, by Campbell et al., J, Amer. Chem. Soc 84. 3-673 (1962) are preferred catalysts. A particularly preferred catalyst is 1-ethyl-3-methyl3-phospholine 1-oxide "

The poly \ carbodiimide formation reaction is preferably carried out in an argon or other inert and dry gas atmosphere in order to minimize the amount of water that is likely to be in contact with the reacted bodies, since isocyanates tend to react quickly with water at high temperatures.

Aromatic diisocyanates which can be used to prepare the desired polycarbodiimides include, for example, toluene diisoeyanate, diphenylmethane 4,4'-diisoeyanate, 3,3'-dimethyl diphenylene 4,4'-diisoeyanate , phenylene p-diisocyanate, phenylene m-diisocyanate, 4,4'-diisoeyanate of 3.3^,-dimethyl-diphenylmethane, and mixtures thereof. Preferred aromatic diisocyanates are toluene diisocyanate, diphenylmethane 4,4'-diisoeyanate and mixtures thereof.

Aromatic diisocyanates are preferably used in an essentially pure state, but may contain minor amounts (i.e., less than about 2% by weight) of other compounds such as ureas, amines and traces water and / or acids. The term toluene diisoeyanate is intended to include toluene 2,4-diisocyanate, toluene 2,6-diisocyanate or any combination of these isomers. Mixtures of the 2,4 and 2,6 isomers typically contain 80 parts by weight of toluene 2,4-diisocyanate and 20 parts by weight of toluene 2,6diisocyanate or 65 parts by weight of toluene 2,4diisocyanate and 35 parts by weight of tolueneo 2,6-diisocyanate

Small amounts (i.e., amounts less than or equal to 50% by weight) of aromatic monoisocyanates can also be used with the aromatic diisocyanates for the preparation of the polycarbodiimides which are used in the process of the present invention. These mono-isocyanates help to regulate the molecular weight and viscosity of the resulting polycarbodiimides. The amount of the aromatic mono-isocyanate which is used depends on the particular diisoeyanate employed, but generally about 20 to about 50% by weight can be employed, typically about 25 to about 45% by weight and preferably about 30 to about 40 % by weight of the mono-isocyanate and, correspondingly, generally about 50 to. about 80% by weight, typical ο

about 55 to about 75 and preferably about 60 to about 70% by weight of the diisocyanate relative to the total weight of the isocyanates

Aromatic mono-isocyanates which can be used in this way include, for example, chlorophenyl p-isocyanate, chlorophenyl m-isocyanate, phenyl isocyanate, methoxyphenyl p-isocyanate, m- methoxyphenyl isocyanate, tolyl p-isocyanate, tolyl m-isocyanate, tolyl o-isocyanate, nitrophenyl p-isocyanate, nitrophenyl m-isocyanate, 2,6-diethyl isocyanate - the?

phenyl and mixtures thereof.

Phenyl isocyanate, chlorophenyl p-isocyanate, chlorophenyl m-isocyanate and mixtures thereof are the preferred mono-isocyanates for use in the present invention.

One cannot use mono-isocyanates alone to prepare the polycarbodiimides, since polymeric carbodiimides cannot come from the heating of mono-isocyanates alone.

The amount of the saturated thermoplastic polyester and the polycarbodiimide which is used to obtain the desired product is generally between approximately 95 and approximately 99% by weight, typically between approximately 96 and approximately 98.5 and preferably between approximately 97 and approximately 98.5% by weight of the saturated thermoplastic polyester and, correspondingly, generally between approximately 1 and approximately 5% by weight, typically between about 1.5 and about 4% and preferably between about 1.5 and about 3 by weight of the polycarbodiimide. The percentages thus indicated are by weight relative to the total reaction mixture (that is to say the total weight of the polyester and of the polycarbodiimide).

Amounts of the polycarbodiimide exceeding about 5% of the weight of the total reaction mixture can result in polyesters having an extremely high viscosity. Amounts less than about 1% of the weight of the total reaction mixture may not be effective in increasing the mechanical strength of the molten polyesters sufficiently, so that the resulting product may not be useful for extrusion applications.

Other additives, both polymeric and non-polymeric, can be used, such as flame retardants, lubricants, colorants, antioxidants, and mineral fillers (such as glass) as long as these additives do not do not interfere with the reaction between polycarbodiimides and polyesters "Such additives can generally be present in proportions of up to about 10% of the weight of the total reaction mixture"

The polyester and the polycarbodiimide to be reacted can be kneaded or mixed in any way, as long as the polycarbodiimide is in contact with the. polyester while it is in the molten state, for a period of time sufficient for a chemical reaction to take place. dry the polycarbodiimide, a solid sprayed additive, with pieces of the solid polyester and then introduce this mixture into a screw extruder (such as a 2-screw WernerPfleiderer ZSK extruder) which is at a temperature high enough to cause the polyester to melt. The polycarbodiimide dissolves in the bulk of the molten polyester and, thus, a reaction can occur between the polyester and the polycarbodiimide. Alternatively, polyesters can be ground until completely melted in a plastograph (such as a CX Brabender Pasti-Corder) at temperatures high enough to · cause the polyester to melt. The solid polycarbodiimide can then be dissolved directly in the molten polyester until a torque level generally between approximately 200 and approximately 1600 gm is typically obtained between approximately 250 and approximately 1500 gm and preferably between approximately 270 and approximately 1400 gm "

By torque level is meant the work carried out during the processing of the materials in a plastograph, such as a Rolle type plastograph by CW Brabender. The torque level is measured using a recording graph in units which are gram-meters. The magnitude of the torque level depends on the amount and kind of polycarbodiimide used, the intrinsic viscosity, the number of terminal carboxylic acid groups and the level or. moisture content of the particular polyester that is used. A low level of torque can be achieved by decreasing the intrinsic viscosity, increasing the number of terminal carboxylic acid groups and / or increasing the percentage of the moisture content of the polymer, assuming a fixed amount or proportion of polycarbodiimide, a fixed grinding time and a fixed amount of the total charge. It is also possible to obtain a low level of torque by using smaller amounts of

P-Olycarhodiimide .. Higher levels of torque can be obtained by using larger amounts of the polycarbodiimide or by using a particular polyester having higher intrinsic viscosity, lower moisture content and / or lower amounts of carboxylic acid groups only terminal.

The present process can be carried out at any temperature such that the polyester remains in the molten state for a period of time sufficient to allow the reaction between the polyester and the polycarbodiimide to occur.

The reaction temperature should be high enough for the polyester to be in the molten state, but it should not be so high as to decompose the polyester or polycarbodiimide. At atmospheric pressure, the reaction can be carried out at temperatures of between about 200 ° and 350 ° C, typically between about 225 ° and about 290 ° C, and preferably between about 235 ° and about 265 ° vs. . \

Although the pressures can vary widely, and pressures below, equal to, or greater than atmospheric pressure can be used, preference is given to a substantially atmospheric pressure.

..- The molten polyester and the polycarbodiimide must be in contact for a period of time sufficient for one. chemical reaction occurs. The progress of the reaction can be followed by observing the decrease in the terminal carboxylic acid groups (GACT) over time. When there is no further decrease in GACT, the reaction has stopped. Of course, the reaction time is a function of the temperature but, in the present process, a reaction time generally between about one and about 7 min, typically between about

1.25 and approximately 6.8 min and preferably between approximately 1.5 and approximately 6.5 min (screw extruder) is usually sufficient to obtain the desired product. Since mixing does not occur to a degree, as large in a plastograph as in a screw extruder,^xreaction times are generally one. slightly longer in the plastograph.

Of course, the materials can be reacted, as desired, discontinuously, continuously or semi-continuously.

It should be noted that in the process of the present invention, a chemical reaction actually occurs between the polyester and the polycarbodiimide. This reaction is demonstrated by an increase in mechanical strength in the molten state as well as by the simultaneous decrease in the level of GACT and by an increase in intrinsic viscosity (IV).

The increase in mechanical strength in the molten state and the simultaneous increase in IV as well as the decrease in GACT result from the branching of polyester, which occurs during the reaction of polyester and polycarbodiimide.

As indicated above, the present process gives thermoplastic polyesters modified with polycarbocLiimide and which have greater mechanical strength in the molten state. These new polyesters are useful for extrusion applications. Such applications include the manufacture of pipes, films and the implementation of blow molding techniques for hollow articles, such as for example blow molding of bottles.

The mechanical strength in the molten state or the rate of mechanical resistance in the molten state (EM) can be defined by the following ratio:

RM = —-.

where T.] is the time necessary to extrude the first 7.5 cm from a continuous 15 cm rod of molten polyester, and is the time necessary to extrude the following 7.5 cm from the continuous 15 cm rod or rod. The mechanical strength in the molten state can be measured by extruding the 15 cm rod in a device (at constant speed) for determining the melt flow index, comprising a piston with constant speed (6, 35 mm / min) at a temperature high enough to keep the polyester melted (generally around 235 ° C). A value of the rate of mechanical resistance to. the molten state of between about 1.0 and about 2.0 is desirable when the material is to be used for extrusion applications. In the ideal case, we would like a value of 1.0 for this ratio since this would mean that the second portion of 7.5 cir will be extruded at the same speed as the first portion.

For polyesters having poor or poor mechanical strength in the molten state, the second segment is extruded much faster than the first segment, which results in a ratio significantly greater than 1.0.

Thus, polyesters having poor or very low mechanical strengths in the molten state have rather large values ​​of the ratio T ^ / Tp. when it is indicated that certain poly10 esters have no mechanical strength in the molten state, we mean that the second segment of the 15 cm rod is extruded so quickly that it cannot be measured.

The expression polyesters with high mechanical strength in the molten state denotes polyesters having a ratio of T ^ / T?

approaching the ideal value of 1.0, and the expressions polyester with poor mechanical strength in the molten state or polyester with poor mechanical strength at. the molten state denotes polyesters having relatively large ratios, the polyesters having no mechanical strength in the molten state have such a low value that one cannot measure the mechanical strength in the molten state.

the improved polyesters of the present invention have mechanical strengths in the melt generally less than about .2.0, typically less than 1.6, and preferably less than about 1.55 at 235 ° C.

. the polyesters of the present invention, which have better_v their melt strength, also have better swelling characteristics after passing a die. Swelling after passing through a die can be described as the increase in diameter which occurs when molten polyester is released or leaves an extrusion die. When the polymer crosses, the die, the tangles and the crosslinks of the polymer chains are deformed or displaced relative to their equilibrium positions. This represents a storage of elastic energy, when the polymer is released from the die, this energy is regained by a return of the tangles and reticulations to their equilibrium positions. This results in swelling after passing the die.

The diameter of the polyesters of the present invention, which have better melt strength, can increase to about 2 or 3 times the diameter of the extrusion orifice. The swelling after passing the die is important for blow molding applications since (a) it will be easier to inject air into the melt as the diameter of the extruded polymer is larger, and ( b) the expansion of the polyester to correspond to a particular mold will be greater the greater the swelling after passing through the die.

The polyesters of the present invention, which have better mechanical strength in the molten state, also have increased intrinsic viscosities. The intrinsic viscosity of the polyesters of the present invention can be conveniently determined by the equation

IV = log c * ohc where ^ r is the relative viscosity obtained by dividing the viscosity of a dilute polyester solution by the viscosity of the solvent used (measured at the same temperature), and c is the concentration of the polymer in the solution , expressed in grams per 100 ml. The intrinsic viscosity of the improved polyesters of the present invention is generally between about 1.1 and about 2.5, typically between about 1.2 and about 2.3 and preferably between about 1.3 and about 2.2.

By terminal carboxylic acid groups is meant the number of terminal carboxylic acid groups present in the polymer, measured in micro-equivalents per gram of the polymer.

We can measure the number of acid groups. ' carboxylic terminals by dissolving the polymer in a 70/30 mixture of o-cresol and chloroform (solvent) and titrating potentiometrically this solution with tetra butylammonium hydroxide.

The improved polyesters of the present invention may generally contain less than about 10 micro-equivalents, typically less than about 8 micro-equivalents, and preferably less than about 6 micro-equivalents of terminal carboxylic acid groups per gram of the polyester. ..... ·

The present invention is further illustrated by the examples ^:following non-limiting magpies. In the examples, as well as in the description, all parts and percentages are by weight unless otherwise indicated.

Example 1

The present example illustrates the preparation of the thermoplastic polyesters modified with polycarbodiimide according to the present invention. Tests 1 and 2 illustrate the effect of the various concentrations of po3.y (4,4'-diphenylmethane-carbodiiroiâe) on the improved polyesters. Tests 1 and 4 illustrate the effect of the various polycarbodiimides on the improved polyesters. Tests 2 and 3 illustrate the effect of different lengths of stay in the extruder on the improved polyesters. Tests 4 and 5 illustrate the effect of different blending or kneading techniques on the final improved polyesters.

Here are the reaction details for tests 1 to 4 ί

The sprayed and dried polycarbodiimide is mixed with approximately 1.36 kg of polybutylene terephthalate pellets. Polybutylene terephthalate tablets have an initial intrinsic viscosity of 0.75 and contain approximately 50 to 55 micro-equivalents of terminal carboxylic acid groups per gram of polybutylene terephthalate. The flow of molten unmodified polybutylene terephthalate is too rapid to allow a precise measurement of the initial mechanical strength of the melt. The mixture of polybutylene terephthalate and polycarbodiimide is introduced into a 2-screw WernerPfleiderer ZSK extruder comprising a screw configuration with kneading blocks for intense kneading.

The temperature of the melt is approximately 250 ° C. and the reaction is carried out substantially under atmospheric pressure.

Test 5 is carried out under the same conditions as tests 1 to 4, except that 50 g of polybutylene terephthalate are ground in a CW Brabender plastograph at 260 ° C. until complete fusion, then the the polycarbodiimide is added directly to the melt and the grinding of the mixture is continued.

The results of these tests are shown in Table I below. In this table I, unmodified, denotes polybutylene terephthalate which has not been reacted with polycarbodiimide, and modified denotes polybutylene terephthalate which l^s.we reacted with polycarbodiimide.

r.

'TABLE I

<td>Test No</td><td> 1</td><td> 2</td><td> 3'</td><td> 4</td><td> 5</td>

<td>Polycarbodiimide</td><td>AT</td><td>AT</td><td>AT</td><td>B</td><td>B</td>

<td>derived from</td><td>VS</td><td>VS</td><td>VS</td><td>D</td><td>D</td>

<td>quantity (% by weight)</td><td> 2</td><td> 3</td><td> 3</td><td> 2</td><td> 2</td>

<td>Mixing techniques</td><td>E</td><td>E</td><td>E</td><td>E</td><td>P</td>

<td>length of stay in The extruder (seconds)</td><td> 290</td><td> 380</td><td> 90</td><td> 90</td><td> ——</td>

<td>Mechanical strength rate of the melt</td><td></td><td></td><td></td><td></td><td></td>

<td>unmodified polymer</td><td></td><td></td><td></td><td></td><td></td>

<td>amended</td><td> 1,25</td><td> 1,05</td><td> 1,01</td><td> 1,5</td><td> 1,!</td>

<td>Intrinsic viscosity</td><td></td><td></td><td></td><td></td><td></td>

<td>unmodified polymer</td><td> 0,84</td><td> 0,84</td><td> 0,84</td><td> . 0,75</td><td>0, i</td>

<td>amended</td><td> 1,76</td><td> 1,96</td><td> 2,03</td><td> 1,4</td><td>b:</td>

<td>Terminal carboxylic acid groups</td><td></td><td></td><td></td><td></td><td></td>

<td>unmodified polymer</td><td> 55</td><td> 55</td><td> 55</td><td> 50</td><td> 50</td>

<td>modified polymer Torque (kgm)</td><td> &lt;2</td><td> &lt; 2</td><td> &lt;2</td><td> &lt; 2</td><td> &lt; 2</td>

<td>unmodified polymer</td><td> —</td><td> —</td><td> —</td><td> —</td><td> 3,·</td>

<td>amended</td><td> —</td><td> —</td><td> —</td><td> —</td><td> 69</td>

A: poly (4,4'-diphenylmethane-carbodiimide)

B: poly (tolyl-carbodiimide)

C: 4,4'-diphenylmethane diisocyanate

D: toluene diisocyanate

E: dry mixing of the solid polyester and of the polycarbodiimide, then introduction of this mixture into an extruder at high temperatures so that the polyester melts and a chemical reaction takes place between the polyester and the polycarbodiimide

E: mixing of the polycarbodiimide by direct introduction into molten polyester in a plastograph

G: The flow of the molten mass is too fast to allow a precise measurement of the initial rate of mechanical resistance in the molten state.

Comparative example

This example illustrates the effect of incorporating a mono-carbodiimide (test 6) and a strong polycarbodiimide₁₇ 2304635 ment substituted (test 7) ​​in polybutylene terephta-late „the quantities, the reaction and apparatus conditions are the same as in test 5 of example 1, but instead of using one gram poly (tolyl-carbodiimide), one uses in test 6 a gram of p-chlorophenyl-carbodiimide (which is a mono-carbodiimide) and one uses in test 7 a gram of poly (2,6- diisopropyl-1,3-phenylene-carbodii.nide), which is a highly substituted polycarbodiimide ,,

Table II below gives the results of these tests.

<td rowspan="2">10 Test No</td><td colspan="2">TABLE II</td>

<td> 6</td><td> 7</td>

<td>Carbodiimide</td><td>H</td><td>I</td>

<td>derived from</td><td>J</td><td>K</td>

<td>quantity (% by weight)</td><td> 2</td><td> 2</td>

Mechanical strength rate in the molten state

<td>\ G- unmodified polymer</td><td> —</td><td> —</td>

<td>modified polymer</td><td> —</td><td> —</td>

<td>Intrinsic viscosity</td><td></td><td></td>

<td>20 unmodified polymer</td><td> 0,81</td><td> 0,81</td>

<td>modified polymer</td><td> 0,81</td><td> 0,88</td>

<td>Terminal carboxyl group</td><td></td><td></td>

<td>unmodified polymer</td><td> 50</td><td> 50</td>

<td>modified polymer</td><td> 30</td><td> 7</td>

<td>25 Torque (kgm)</td><td></td><td></td>

<td>unmodified polymer</td><td> 10,35</td><td> 5,52</td>

<td>modified polymer \</td><td> 10,35</td><td> 6,9</td>

<td>G: the flow cfe the mass</td><td>fondue is too</td><td>quick to allow</td>

be a precise measurement of the mechanical resistance rate of the melt.

H: p-chlorophenyl-carbodiimide

I: poly (2,6-diisopropyl-1,3-phenylene-carbodiimide)

J: chlorophenyl p-isocyanate

K: 2,6-diisopropyl-1,3-phenylene diisocyanate.

Thus, the polyesters of the present invention (tests at 5) have greater mechanical strengths in the molten state (that is to say lower rates or ratios T ^ / Tg), greater intrinsic viscosities and they contain smaller amounts of the terminal carboxylic acid groups than the polyesters which are modified by mono-carbodiimides (test 6) or by polycarbodiimides carrying larger substituents (test 7). As noted above, the improved polyesters of the present invention are particularly useful for extrusion applications such as the manufacture of pipes, films and blow molding applications.

Example 2

The present example illustrates the preparation of a polycarbodiimide which is used for the preparation of a thermoplastic polyester, modified with polycarbodiimide, of the present invention. The particular polycarbodiimide which is used is the product of the reaction of an aromatic diisocyanate and an aromatic monoisocyanate.

To a 500 ml reaction flask for the production of a resin, a gas inlet tube, a magnetic stir bar and a condenser (G-raham spiral loop) are fitted at the top of which the gas inlet leads to a bubbler allowing the observation of gas evolution. 105 g of toluene diisocyanate, 62.1 g of chlorophenyl pisocyanate and 13 g of bis (beta-chloroethyl) vinyl phosphonate are introduced into the flask. Bis (beta-chloroethyl) vinyl phosphonate is commercially available from the Stauffer Chemical 0θά under the trademark Fyrol Bis beta, and it serves as a catalyst in the present reaction.

A large quantity of argon is passed over the surface of the reacted bodies. The flask containing the bodies to be reacted is lowered in an oil bath at approximately 190 ° C. (the internal temperature of the reaction mixture is between approximately 170 ° and 180 ° C.). Argon is continuously passed over the reacting bodies at a low speed while this reaction continues.

In the few minutes following the immersion, one can observe bubbles of carbon dioxide disturbing a lime water solution. The reaction is continued for about 4 hours until a foam is formed in the flask. Heating is continued for an additional period of time until the foam almost completely fills the balloon. Argon is quickly passed to the surface during this period.

The heating is then stopped and the flask is allowed to cool in an argon atmosphere. The reactor containing the product is then weighed and a loss of about 20% is observed. The foam is completely crumbly and it is easily removed in pieces "You can also remove in pieces the deep red material that remains or you can remove it by softening it with acetone" The product shows a small ridge in the infrared corresponding to isocyanate (4.4 microns), a large ridge corresponding to carbodiimide (4.7 microns) and a large supporting ridge which probably corresponds to polymerized carbodiimide (6.0 microns ). Carbodiimide and polymerized carbodiimide together made up about 90-95% of the product.

This product is further purified by heating it under vacuum in an oil bath at 205 ° 0 for 2.5 hours. Weight loss is variable and about 15% of the material is lost. The final product does not show infrared absorption corresponding to isocyanate. A purification seems to equal remove almost all of the catalyst, since the proportions of phosphorus are less than 0.1%.

The polycarbodiimide thus produced is reacted with polybutylene terephthalate in a similar manner to that of test 1 of Example 1, and similar results are obtained.

Example 5

The polyesters formed in tests 1 and 7 of the example

1t as well as polybutylene terephthalate with intrinsic viscosity. high (1.40), which was reacted with 2% by weight. polycarbodiimide used in test 7 (poly. (2,6-diisopropylV, „.servent

1,3-phenylene-carbodiimide) / for blow molding an aerosol container in the form of a cylinder 5.59 cm in diameter and 8.3 et cm in height.

The blow molding of the modified polybutylene terephthalate compositions is carried out by introducing the polymer into a 6.35 cm multi-station rotary blow molding machine and treating the polymer under the following conditions:

screw rotation speed - 45 back pressure. , 11.2 bars blowing pressure 8.4 bars compression ratio - 3.5 / 1.

Γ.

The modified polybutylene terephthalate from Test 7, which has a relatively low intrinsic viscosity (0.88), cannot be molded into an aerosol container due to the low mechanical strength of the modified and melted polyester.

The blow molded article, which is formed from the improved polyester produced in Test 1 of Example 1, is well formed, has a uniform thickness and a high gloss, and has no pits. The blow molded article formed from relatively high intrinsic viscosity polyethylene terephthalate (1.40), which was modified by the polycarbodiimide used in test 7, can also be blow molded. However, the molten resin does not have sufficient mechanical strength, in the molten state, for the^sblank hangs from the extrusion die long enough for the injected air to evenly expand the molten resin. Consequently, the container has a poor shape and has non-uniform walls. Table III below summarizes the results obtained when using polybutylene terephthalate modified with polycarbodiimide according to test 1 (TPB) and the results obtained when using polybutylene terephthalate with relatively high intrinsic viscosity ( 1.40) (TPB) modified with poly (2,6-diisopropyl-1,3-phenylene-carbodiimide):

<td></td><td colspan="2">TABLE III</td>

<td>Properties</td><td>TPB with increased mechanical strength in the molten state. (test 1)</td><td>TPB of the comparative example *</td>

<td>Wall thickness</td><td>uniform</td><td>variable</td>

Soldering or pinching

<td>the bottom</td><td>good.</td><td>poor</td>

<td>Samples of the sample</td><td>well defined</td><td>poorly</td>

* Polybutylene terephthalate (intrinsic viscosity: 1.40) modified with polycarbodiimide containing large substituents.

It goes without saying that the invention has only been described by way of illustration, but not limitation, and that it is capable of receiving various variants coming within its scope and in its spirit, -.