FR2459120A1 - Heat treating appts. for blow moulded articles - having a cavity defined by members differentially heatable along their length to impose different crystallinity modifications - Google Patents

Abstract

A blow moulded plastics article, e.g. of polyethylene terepthalate, is heat teated differentially over its surface to modify the crystallinity in different ways in different areas in a cavity defined by members split into sections each of which can be heated differentially, or even cooled. In the illustrated embodiment, the members may define the blowing mould or a separate heat treating cavity. Each member comprises portions sepd. by insulating layers, each position contg. independently operable fluid heat exchange channels. Various sections of a blown article can be given a desired crystallinity to modify the strength, clarity, etc. of the article. A blown bottle may be so treated, the neck and base regions being cooled to prevent crystal growth, whilst the body and heel portions are heated to induce crystal growth.

Description

The invention relates to a method and an apparatus for gentering crystallization in an article made of blown thermoplastic material
More particularly, it relates to the thermal conditioning of a blown article of polyethylene terephthalate, such that only the molecularly oriented portions of the article are heated, so as to obtain a clear article whose physical properties are improved.

 Methods have been proposed by various patents for forming a biaxially oriented polyethylene terephthalate film which it undergoes heat treatment to cause crystallization. Examples are, for example, US Pat. Nos. 3,177,277, 2,995,779, 3,107,139 and 2,823,421, as well as British Pat. Nos. 851,874, 915,805 and 1,803,665. US Patent 3,733,309, more recent, discloses a bottle of polyethylene terephthalate blown that can be heat treated.

 However, prior processes have not considered that a blown polyethylene terephthalate bottle may have varying degrees of molecular orientation along its axial dimension. Heat treatment of the entire bottle, without discrimination, will result in spherulitic crystal growth in the non-molecularly oriented portions of the bottle. Moreover, the prior methods do not suggest any method for thermally treating a blown bottle by preventing it from deforming by removal of the material during the treatment.

 It can therefore be considered that, up to then, the potential problems and undesirable effects of heat treatment of blown thermoplastic bottles have been neglected, and no solution has been proposed to solve these problems.

 The object of the invention is to solve the problems posed by the heat treatment of blown thermoplastic bottles.

The apparatus according to the invention can be made in one, or two or more forms. In particular, the desired heat treatment can be carried out by combining heating means with the blow molds themselves, or with separate mold-shaped members. Whatever the version, the device has two separable organs that cooperate to define an inner cavity having the dimensions and shape of the ar
desired blown article. Each separable organ has thermic portions
isolated along the axis of the cavity, and means are provided for
selectively heat the parts of each separable organ, to treat
thermally corresponding parts of the blown articles.
ence, means are provided for exerting hydraulic pressure at
the interior of the blown article, during its heat treatment, to improve the heat transfer and to avoid shrinkage of the thermoplastic material. In addition, means may be provided to cause axial tension to the parison during the blowing phase or before.

 According to the process according to the invention, a parison of amorphous material, having less than about 5% of crystals, is thermally conditioned at a temperature in a range for which molecular orientation occurs. For polyethylene terephthalate, this temperature range is between 750C and 110oC approximately. The parison is then blown into a blow mold while the material is in the appropriate temperature range; we obtain a blown article with parts whose molecular orientations are different.

For example, during blowing, the body of a bottle is stretched and oriented more strongly than the bottom and the end. The blowing speed of the material may be chosen within certain ranges; but, preferably, it is such that it initiates crystallization by internal tension. After being blown, the article is subjected to a heat treatment during which the parts of this article, which are strongly molecularly oriented, are heated to a temperature capable of leading to crystal growth. The other, less strongly oriented portions of the article, the end and the bottom of the bottle, can be either cooled or heat treated at a lower temperature to limit the extent of crystal growth in these areas.

 The article blown and heat treated according to this method, and with the aid of this apparatus, has crystallized zones differently, depending on the nature of the orientation and the heat treatment they have undergone. For example, the part that has been most strongly molecularly oriented during blowing will be the one that will be the most highly crystallized after heat treatment. The crystalline structure obtained in this particular zone by the described method will have a crystalline texture formed by internal tension, in contrast to a thermally formed spherulitic crystalline texture, since it has been oriented molecularly before heat treatment. The other less strongly oriented portions of the article will be less crystallized, and will even be substantially amorphous, even after blowing and thermal conditioning. For example, the thermoplastic material of the neck of the bottle will be practically not stretched during the course of the operation. blowing and will not, therefore, molecularly oriented. It is recommended to cool this part of the article during heat treatment, to avoid the development or formation of spherulitic crystals that can lead to an opaque and brittle structure. Other parts of the article, for example the bottom, may have a moderately developed orientation and will only undergo a mild heat treatment to limit the formation of undesirable spherulitic crystals. Of course, the temperatures and times of the heat treatments are a function of the nature of the thermoplastic material, the importance of the molecular orientation and the crystalline properties that it is desired to give the material through these treatments.

The invention therefore has the following advantages over what is known
first of all, it makes it possible to obtain thermoplastic materials with a number of improved properties; for example, yield strength, density, impermeability, insulation resistance, creep resistance, dimensional stability and thermal resistance.

And these properties are improved without sacrificing to a significant extent the clarity of the material.

 many advantages result from the improvement of the properties of the material. For example, a bottle made according to the invention, and of the same thickness as a bottle made so far from the same parison, will have greater strength and better crystalline characteristics. This latter feature is extremely important in reducing the carbon dioxide permeability of containers used for the packaging of carbon dioxide-containing beverages.

 Moreover, with regard to the characteristics that certain packages must have, the invention makes it possible to use thinner bottles, which is advantageous since (a) the quantity of material is lower, (b) the formation of the parison is simplified, and (c) the parison is reheated to a lesser extent before blowing.

The remainder of the description refers to the attached drawings which represent
Figures 1 to 3, a parison in the cavity of a blow mold, being drawn and blown,
4, a blown bottle, between the parts of the mold separated, the scales being modified to highlight the various thermally insulated portions of the mold that allow a correct thermal conditioning of the article,
Figures 5 and 6, schematically, an arrangement in which an article is blown into a first mold, and transferred to one of a plurality of separable member devices for thermal conditioning.

 The invention therefore relates to a method and an apparatus for the heat treatment of an article of thermoplastic material, after this article has been blow molded. The heat treatment can be done in the mold itself, as illustrated in FIGS. 1 to 4, or in a separate device, as illustrated in FIGS. 5 to 7.

According to the version illustrated in FIGS. 1 to 4, the article is heat-treated in the mold parts which are more clearly shown in FIG. 4. The two mold parts bear the references 12 and 16, and each comprise four thermally insulated sections, 12A to 12D for one, 16A to 16D for the other. The insulation is provided by a suitable material that has been designated by the references 13A, 13B, 13C, on the one hand, and 17A, 17B, 17C, on the other hand. Glass ceramics sold by Corning
Glass Works, under the brand name Macor, is a suitable material. Alternatively, the mold can be mounted on molding blocks, with air gaps where there is shown an insulation material. Of course, the mold parts 12 and 16 are of a suitable metallic material and can be mounted on molding blocks and presses (not shown).

 Each section formed in the mold portions may include means suitable for thermal conditioning of the blow molded article. Such thermal conditioning means are shown by internal fluid conduits 14A to 14D and 18A to 18D. A thermal conditioning fluid can be fed into these conduits by appropriate means (not shown) and via feed ports as is conventional.

 In accordance with the selected application example, sections 12A and 16A define a neck-forming zone for the parison, while sections 12B and 163. define the formation cavity or imprint of the tubular body portion of In the puffed article, the sections 12C and 16C define the annular bead portion of the article which connects the body of this base member formed in sections 12D and 16D. As will be discussed in the following, a cooling fluid is preferably circulated in the conduits 14A and 18A to reduce the temperature of the plastic material at the level of the bottle. The fluid flowing in the conduits 14B, 14C, 18B and 18C is preferably a high temperature silicone oil for heat treating the corresponding parts of the bottle. As for the conduits 14D and 18D, they can receive a cooled fluid or a fluid heated, according to the "morphology" of the plastic material in this area of the blow molded article.

Referring now to Figures 1 to 3. The blowing parison 10, illustrated in Figure 1, is mounted on the core 21 of the mechanism of a blowpipe 20, within the cavity defined by the mold portions 12 and 16. Before being placed inside the mold, the parison is brought to a temperature within the temperature range
molecular orientation. If it is polyethylene terephthalate, it
It is recommended to heat the parison at a temperature between 750C and 1100C, the exact temperature depending on the viscosity inherent in the material. Prior to the initial heat treatment, the thermoplastic material is substantially amorphous with less than about 5% crystallinity. Of course, thermoplastic materials other than polyethylene terephthalate can be treated according to the invention.

 According to the example chosen, the parison 10 is initially stretched by an axially movable blowing rod 22, as can be seen in FIG. 2. The drawing speed can be chosen at will to establish a molecular orientation and, preferably, initiating a crystallization by deformation or crystallization by internal tension, the speed being a function of the chosen thermoplastic material, the temperature of the material, the desired crystallization and the importance of the molecular orientation.

For example, for polyethylene terephthalate, the drawing speed can range from about 10% per second to about 500% per second; a speed of about 100% per second is preferably selected. At a speed of 100% per second, a parison of initial length equal to 5 cm will have a length of 10 cm after one second. Other thermoplastic materials can be stretched at a rate of the order of 1000% per second.

 As is known, the initial axial stretching of the material leads to an axial molecular alignment and initiates internal tension crystallization, in those of those materials that are likely to take such "morphology". Axial stretching can be done either before or at the same time that the blowing fluid is introduced into the interior of the parison.

To complete the molding operation, a pressurized fluid is introduced into the parison via radial orifices 23 formed in the drawing and blowing rod 22. The pressure may be chosen within a certain range. for various thermoplastic materials. For polyethylene terephthalate, the fluid pressure is preferably from about 20 to about 40 kg / cm when the fluid is introduced into the parison prior to any expansion; it is preferably between 20 and 35 kg / cm. Alternatively, the fluid can be supplied at a pressure of between about 7 and 14 kg / cm 2 at the beginning of the blowing operation, which pressure is then brought to about 20 to 35 kg / cm 2.
just before the material is pressed against the walls of the mold.
blow molding completes the molecular orientation and develops more
before crystallization by before crystallization by internal tension.

 In the version described here, the blown article is left in the mold cavity for heat treatment. Because of the configuration of the bottle, and because the material has been dilated in different measures during the drawing and blowing operations, this material has different "morphologies" depending on the part of the bottle considered. In particular, the material in the vicinity of the neck of the bottle remains substantially amorphous, having been-if it is as it is-that very weakly crystallized and molecularly oriented during the initial thermal conditioning and molding operation. The tubular body of the article is the part which has the highest degree of molecular orientation, since it is in this part that the parison has undergone the strongest stretching. The annular bottom part of the bottle will present some molecular orientation, less however than in the tubular part of this bottle. As for the bottom of the bottle, it will present a very weak molecular orientation. The invention proposes to subject the different parts of the blown article to different thermal treatments, in order to reinforce the "morphology" of a crystallization by internal tension in the body of the bottle, and to avoid, by cooling, spherulitic "morphology" in other parts of the bottle.

 For example, for a polyethylene terephthalate bottle, the neck of the bottle is cooled by circulation of a cooling fluid in the inner conduits 14A and 18A, in order to keep the material in the substantially amorphous state. The tubular body of the bottle undergoes a heat treatment, at a temperature between 150 and 2200C approximately; preferably, this portion of the bottle is heated to about 1800 ° C, at which temperature the crystallization rate is maximum. The annular bead of the bottle can be heated to a temperature between about 1000 ° C and about 2000 ° C, depending on the importance of the molecular orientation given to it by stretching and molding operations; but lower temperatures will be preferable if the orientation is weak. The bottom of the bottle will be cooled in the case where the molecular orientation is very low, but it is possible to envisage, if necessary, a heat treatment at a temperature between 1000C and 200C.

 The duration of the heat treatment can be chosen according to certain variables such as the inherent viscosity of the material, its thickness and the desired crystalline character. For polyethylene terephthalate, the heat treatment cycle can be selected in a range from about 10 seconds to about 10 minutes, taking into account, first, the desired degree of crystallinity and the progress of crystallization in the process. thickness of the walls. For example, the surface of the blown article can be heated rapidly to cause crystallization only in the vicinity of the surface, to enhance the properties of the material. it is recommended to carry out the heat treatment so that the tubular body of the bottle has a crystallinity of between 10% and 50% approximately.

Reference is made to US Pat. No. 2,823,241, already cited, for defining the treatment times necessary to obtain various degrees of crystallinity.

The equipment illustrated in FIGS. 1 to 4 is preferably used for short-term thermal treatments. For longer heat treatments, it may be desirable to cool the bottle after blowing inside its mold, and then to transfer it into a separate cavity formed by separable members in accordance with those shown in Figure 4, in order to perform the heat treatment.

 In the embodiment of FIGS. 1 to 4, it is preferable to maintain the blowing pressure inside the blown article, in order to avoid any removal of the material during the heat treatment and to maintain this material against walls of the cavity for reasons of shape and heat transfer. When the material has been suitably heat treated, the mold parts are separated and the bottle ejected. As a result of the heat treatment followed by cooling, the material of the different parts of the bottle will be sufficiently self-supporting, that is to say sufficiently rigid to ensure its own support itself. A cooling fluid can, of course, be circulated in the conduits 14B, 14C, 18B and 18C, to cool the bottle after heat treatment and give the material the appropriate rigidity.

 The article obtained by this method will not present spherulitic crystals, but will be crystallized in the parts which had a significant molecular orientation, to have a "morphology" of crystallization by internal tension.

 With the equipment illustrated in FIGS. 5 and 7, the article is first blown into a cavity defined by two mold parts 110 and 120.

These mold parts are substantially identical to those shown in FIG. 4, but they do not consist of thermally insulated sections and their internal ducts are intended to receive a cooling fluid. When such equipment is used, a substantially amorphous thermoplastic parison is first thermally conditioned at a temperature in a molecular orientation development range. Then, the parison is placed in the cavity formed by the parts 110 and 120, a fluid under blowing pressure then being introduced into the parison to form the container. The material is finally cooled in the mold until it is self-supporting.

 When the article is sufficiently cooled, it is transferred, using a cane 130, from the blow molding station to a position where it is between two mounted members, at the periphery of the body. a drum 140, with other pairs of members which, like the first, define a cavity in the manner of a mold. These pseudo-molds have the references 141 to 148 Figure 6; they preferably have the shape of the mold illustrated in FIG. 4. An appropriate transfer structure (not shown) can be used for the transfer of the articles, using rods 130, between the molding station and the drum; such a structure is illustrated in US Patent 3,599,280 already cited.

 When the blown article and the cane 130 are in the position shown in FIG. 7, the two parts of the member 141 are closed on the article to initiate the heat treatment. Almost simultaneously, the parts of the member 148 are open to allow the ejection of a heat-treated article. The rod associated with the member 148 can then be moved to the molding station to receive a new parison to blow. The drum 140 is driven in the anti-clockwise direction, the member 141 being brought into the position previously occupied by the member 142. The member 148 is then aligned with the mold parts 110 and 120 and can receive the The article in the member 141 is then heat-treated as the reel is rotated. it is strongly recommended to introduce pressurized fluid from a source (not shown) and through the rod 130 into the interior of the article, to avoid the removal of the material during the heat treatment. it therefore appears that with equipment as illustrated in FIGS. 5 and 7, it is possible to heat-treat articles that are desired with greater crystallinity, and therefore require longer heat treatment times.

 The bottle obtained has, in its tubular part, a crystallization morphology by internal tension which allows it to have, in this part, a thickness that would otherwise make it permeable to carbon dioxide in the case of use for the packaging of beverages containing it. In other words, a thinner bottle can be formed while being impervious to carbon dioxide.

 it is understood that the description has been made by way of non-limiting example and that variants may be envisaged within the scope of the invention. Other materials than polyethylene terephthalate can be used with different cycle times; it is not necessary to stretch the material before blowing; and the parison can be conditioned thermally to the correct blowing temperature by cooling it after injection molding.

Claims (25)

REVFNI) lCATlONS  1. Method for crystallizing an article formed by blowing a thermoplastic material capable of crystallising at elevated temperature, characterized in that, following a blow molding operation, a blown article of thermoplastic material molecularly oriented is enclosed in an impression or cavity whose dimensions and shape correspond to those of the article, and, simultaneously (a) pressurizing the inside of the article to maintain the thermoplastic material against the walls of the cavity and to avoid its (b) heating only those portions of the article having undergone significant molecular orientation to a temperature capable of favoring crystallization, in order to give these parts a "morphology" resulting from crystallization by internal tension.  2. Method according to claim 1, characterized in that, for carrying out the pressurizing and heating operations, the blown article is held enclosed in the mold cavity after the blow molding operation.  3. Method according to claim 1, characterized in that the article is molded by blowing into a first cavity, the article is cooled while it is held in this first cavity, to a temperature for which the material Thermoplastic essentially provides its own support, and then the blown article is transferred into a second cavity to effect the operation of the pressurized and heat-treated ions.  4. A method according to claim 1, characterized in that simultaneously cooling the article portions that have not undergone significant molecular orientation during the heating of the other sections of the article.  5. Method according to claim 1, the article being a bottle comprising a neck, a convex bottom connected to an annular heel, and a tubular body connecting the collar and the annular heel, characterized by the fact that the body is heated. tubular at a temperature T1 and the heel to a temperature T2 ~ T1 and the neck is cooled.  6. Process according to claim 5, characterized in that the convex bottom of the bottle is cooled.  7. Process according to claim 5, characterized in that the convex bottom of the bottle is heated.  8. A method according to claim 5, the thermoplastic material being terephthalate polyethylene, characterized in that the body of the bottle is heated to a temperature between 450 C and 200 C approximately, the heel is heated up to a temperature included  between 100 C and 200 C approximately, and one applies, inside the article,  a pressure of between 21 and 35 kgfcm approximately.  9. Blow molding process involving screaming  by internal tension, characterized in that  (a) the parts of a blow mold are closed on a  blowing parison of substantially amorphous polyethylene terephthalate  (b) while the parison is at temperature  favoring a molecular orientation, (i) axially stretching this  are there to induce axial molecular alignment and prime a crystal  by internal tension and (ii) blowing air is introduced under  pressure in the drawn bead, in order to radially expand the tereplitalate  polyethylene in the form of a blown article to induce an orien  bi-axial reaction and enhance the development of crystallisation by  internal voltage, and  (c) heating only portions of the blown article in which there is a significant amount of bi-axially oriented crystals to establish temperature-induced growth in the oriented crystals.  10. The method of claim 9, characterized in that ltereration heating in the blow mold while simultaneously maintaining a fluid pressure of between 21 and 35 kg / cm inside the article.  11. Process according to claim 9, characterized in that the blown article is cooled in the impression of the mold until it  to be able to support itself, then, one withdraws the article of the mold  blowing and then encloses the cooled article in a cavity whose shape  corresponds to the external form of the article and in which  heating while simultaneously maintaining a pressure inside this article through a gaseous fluid.  the parts having substantially no molecular orientatfon being cooled.  crystalline material, the non-high molecular weight portions being heat treated at lower temperatures, and  at a high temperature in a growth-promoting range  the article with the highest molecular orientation being submitted  parts distilleles and separated from the blown article while it is enclosed in a cavity or cavity under internal pressure, the parts of  (c) heating. and cool, in different proportions.  formed, areas of different molecular orientations, then  different parts of the parison to establish, in the article  (b) during phase (a), it is dilated, in proportion  blown article having the shape and dimensions of said imprint  that it is in a blow mold cavity at a temperature favoring a molecular orientation, so as to obtain a  12. A method of differential heat treatment of a blown article, said method involving internal tension crystallization and being characterized by: (a) expanding a blowable thermoplastic parison;  thermally polyethylene terephthalate.  pressure inside the bottle, (li) the body is heated to treat  the shape and dimensions of the article, and simultaneously (i) we put under  (c) enclosing the blown article in a cavity having  no molecular orientation, and  in the body that coatis the bottom and: the heel and the collar not having practic  and a cervix, dilation promoting: stronger molecular orientation  tubular as a whole, a heel connecting the bottom to the tubular body  at a temperature promoting a molecular orientation, the parison is dilated in the impression to form a bottle having a bottom, a body  (b) while polyethylene terephthalate is  mold in the form of a neck and so as to enclose the bulk of the parison in a bottle-shaped impression  folds, so as to grip one end of the wall in an impression  (a) closing the Inarties of a blow mold on a paraison blow blowing of essentially amorphous polyethylene terephthalate  13. Process for forming a hot-rolled article of polyethylene terephthalate, which method involves crystallization by internal tension and being characterized in that  The method of claim 13, characterized in that  what is heated the body of the bottle to a temperature between  150 C and 200 C approximately, the heel is heated up to a temperature of  between 100 C and 200 C, and the neck is cooled.  15. The method of claim 14, characterized in  what is kept the bottle founded by blowing inside the  parts of the blow mold during the heat treatment.  16. The method of claim 13, characterized in that  during operation (b), the parison is stretched axially first,  then it is expanded radially with a pressure blowing fluid.  17. Thermo-thermoplastic blown thermoplastic container  a neck, a body and a bottom, characterized in that the body has a  "morphology" resulting from crystallization by internal tension obtained  (a) by expanding the material during a blow molding operation to promote molar orientation and initiating internal tension crystallization, and then (b) treating the material to develop the crystallization by internal material, the material of the neck being essentially amorplic and that of the bottom having a "morphology" lying between that of a substantially amorphous material and the "morphology" of crystallization by internal tension of the body.  18. Polyethylene terephthalate bottle obtained by a process involving internal crystallization and comprising a neck, a body, a heel and a bottom, characterized in that the different parts of this bottle do not essentially comprise spherulitic crystals, the material of the wherein the neck is essentially amorphous, the body material being molecularly oriented and having enhanced crystallinity of at least about 107 up to a maximum of 50%, the heel and the bottom being less crystalline than the body.  19. polyethylene tereplitalate container having a neck, a body and a bottom, characterized in that these different parts do not contain essentially spherulitic crystals, the material of the neck being essentially amorphous and thicker than the material of the body and that of the in order to prevent C021 penetration therein, the body material being substantially oriented and having an internal tension crystallization "norphology", with a crystallization of at least about 10%, and the thickness of the body material being that it would allow a large penetration of C02 if the "morphology" of this body was not that of a crystallization by internal tension.  20. Apparatus for the heat treatment with crystallization by internal tension of an article of blown thermoplastic material, characterized in that  - - it comprises separable members cooperating to define a cavity or internal cavity with a longitudinal axis which essentially has the shape and dimensions of the article,  said separable organ has thermally separated portions along the longitudinal axis of the cavity, and  - It comprises means for heating at least a corresponding part in claque separable member, to treat tiiermiquement annular section of a blown article maintained in said rectification.  21. Apparatus according to claim 20, characterized in that it further comprises means for applying the pressure of a fluid inside the article during the heat treatment of this article.  22. Apparatus according to claim 21, characterized in that the separable members serve as a blow mold for the formation of the blown article.  23. Apparatus according to claim 21, characterized in that the separable members are (separate and spaced from the blow mold in which the blast item is formed.  24. Apparatus according to claim 21, characterized in that the separable members define an interior cavity or cavity corresponding to the dimensions and the shape of a bottle provided with a neck, a body, a bottom and a an annular bead connecting the bottom to the body, said separable members having four thermally separated portions corresponding to the aforesaid parts of the bottle, and internal fluid conduit heating means being mounted in the parts corresponding to the body and at the heel of the bottle, means being provided for sending a heated fluid into said inner ducts.  25. Apparatus according to claim 24, characterized in that the parts of the separable members which correspond to the neck and bottom of the bottle comprise internal fluid conduits, means being provided for sending a cooling fluid into the internal ducts of the container. part corresponding to the collar.