WO2014183791A1

WO2014183791A1 - Method of manufacturing a pet bottle with improved resistance to environmental stress cracking

Info

Publication number: WO2014183791A1
Application number: PCT/EP2013/060149
Authority: WO
Inventors: Matthias Stolp; Marion Nagel; Volkmar Voerckel; Rolf Eckert
Original assignee: Equipolymers Gmbh
Priority date: 2013-05-16
Filing date: 2013-05-16
Publication date: 2014-11-20
Also published as: TW201444665A; WO2014183812A1; TW201444666A

Abstract

The present invention relates to a PET bottle having improved resistance to environmental stress cracking when the inner or outer surface of the bottle is treated with stress cracking causing chemical substances and to a method of manufacturing such a bottle. The invention also relates to a preform of such a bottle, the preform being modified to obtain a PET bottle having said improved resistance to environmental stress cracking. The invention further relates to the use of specific organic solvents for treating a PET bottle or a PET preform of such a bottle in order to obtain a bottle having said improved resistance to environmental stress cracking.

Description

Method of Manufacturing a PET Bottle

with Improved Resistance to Environmental Stress Cracking

The present invention relates to a bottle made of polyethylene terephthalate (PET) having improved resistance to environmental stress cracking when the inner or outer surface of the bottle is treated with stress cracking causing chemical substances and to a method of manufacturing such a bottle. The invention also relates to a preform of such a bottle, the preform being modified to obtain a PET bottle having said improved resistance to environmental stress cracking. The invention further relates to the use of specific organic solvents for treating a PET bottle or a PET preform of such a bottle in order to obtain a bottle having said improved resistance to environmental stress cracking.

PET bottles are widely known to be used for filling of mineral water, juices soft drinks and alcoholic or non-alcoholic beverages, each of which being carbonated or uncarbonated. The advantage of PET as material for the bottles is its gas barrier property, good transparency, heat resistance, and mechanical strength. PET bottles are manufactured by stretch blow molding a preform made of PET to obtain the PET bottle.

However, regarding the mechanical strength of stretch blow molded PET bottles it is known that there exists a problem with a so-called environmental stress cracking. The environmental stress cracking can be provoked by various chemical substances if at the same time the PET material is under tension force. Environmental stress cracking may occur at those areas of a PET bottle where the PET material is amorphous or has a very low degree of crystallinity. Parts of PET bottles are amorphous or have a low degree of crystallinity if they are unstretched or just slightly stretched like at the bottom area and at the neck area. The reason for this phenomenon is that stretching of PET leads to a partial crystallization of the previously amorphous PET material, by so-called "strain induced crystallization".

At present and due to the great market success of PET bottles there are

considerations and attempts to introduce these PET bottles into the market also as containers for consumer compositions, like hair spray, shaving foam, and other products containing various chemical substances. To date these consumer products are normally filled in pressurized dispensers, e.g. made of aiuminum. As

pressurized dispensers of aluminum becomes more and more unpopular because of their assumed environmental impact there is a demand of alternative containers having a better acceptability by the consumers.

However, the use of PET bottles as containers for the above mentioned consumer products is problematic since many chemical substances included in the consumer compositions are known to cause the above discussed environmental stress cracks, particularly at unstretched portions or just slightly stretched portions of PET bottles. Such portions are known to exist in the bottom area of PET bottles as well as in its neck area. In case of pressurized and chemical substances containing consumer products being filled in the containers there is a high risk of break or burst of the containers if being made of PET.

It is therefore an object of the present invention to provide a PET bottle and a method of manufacturing thereof, where the bottle has an improved resistance against environmental stress cracking and, as a consequence, against breaking or bursting which could be caused by filling the bottle with pressurized and chemical substances containing consumer products.

Now, it has surprisingly been found by the present inventors that the above object can be achieved by a method of manufacturing a treated stretch blow molded PET bottle having an improved resistance to environmental stress cracking, wherein the method comprises the steps of: a) providing a stretch blow molded PET bottle, and b) treating at least those parts of the stretch blow molded PET bottle where its PET materia! is amorphous or has an insufficient degree of crystallinity, the crystallinity being typically but not necessarily solely generated by strain induced crystallization, with an organic solvent or an aqueous solution of the organic solvent, wherein the treatment is carried out for a time in the range of 1 second to less than 1 hour, preferably in the range of 3 seconds to less than 20 minutes, more preferably in the range of 5 seconds to less than 10 minutes, most preferably in the range of 10 second to less than 5 minutes.

The crystallinity of the PET material of a stretch blow molded PET bottle is typically generated by strain induced crystallization. However, crystallinity in PET bottles can also, or in addition, be generated by other methods like so-called heat set. For example, if a preform is stretch blow molded and the mold is heated to a certain temperature the resulting bottle will comprise crystallinity formed by strain induced crystallization as well as crystallinity formed by thermally induced crystallization. Both kinds of crystallinity can at least partially overlay or interfere with each other.

The "parts of the stretch blow molded PET bottle where its PET material is amorphous or has an insufficient degree of crystallinity" as herein referred to means a) those parts of the bottle where the degree of crystallinity of the PET material compared to the maximum degree of crystallinity present at any part of the bottle is less than 20%, preferably less than 30%, more preferably less than 40%, or b) those parts of the bottle where the absolute degree of crystallinity of the PET materia! is less than 6%, preferably less than 9%, more preferably less than 12%, determined by the density method as described in the Examples section.

An insufficient degree of crystallinity - in context of the problem to be solved underlying the invention - typically appears at those parts of a bottle where its PET material is unstretched or only slightly stretched, i.e. where the strain induced crystallization has not reached a degree for imparting the bottle with a sufficient resistance to environmental stress cracking. Typical parts of a PET bottle having an insufficient degree of crystallinity are at the bottom area and at the neck area of a PET bottle. As only these parts need to be treated with the organic solvent or the aqueous solution of the organic solvent mentioned above these parts have been defined as above. Both definitions under a) and b) characterize more or less the same parts of a bottle since a typical maximum absolute degree of crystallinity present at any part of such a bottle is about 30% determinable by the mentioned density method. So, the invention is carried out if at least those parts of a PET bottle are treated falling under one of the definitions mentioned under a) or b). For determining the relative degree of crystallinity defined under a) any appropriate method for determining a degree of crystallinity can be used if for every

measurement the same method is used. However, also for alternative a) the density method as mentioned above is preferred.

The bottle manufactured according to this method has an improved resistance to environmental stress cracking at its treated parts, including those parts of the bottle where its PET material was amorphous or had an insufficient degree of crystallinity before treating.

"A stretch blow molded PET bottle" or simply a "PET bottle" as herein referred to means a PET bottle which has been manufactured by a method comprising the step of stretch blow molding a PET preform to obtain the PET bottle. The manufacturing process of stretch blow molding a preform under obtaining a bottle is well known to a person skilled in the art and needs not to be described in detail here.

"The bottom area of a bottle" as herein referred to means those parts of a stretch blow molded PET bottle where its PET material is amorphous or has an insufficient degree of crystallinity near the injection gate of the former preform used for making the bottle.

"The neck area of a bottle" as herein referred to means those parts of a stretch blow molded PET bottle where its PET material is amorphous or has an insufficient degree of crystallinity near the threaded closure of the bottle.

The method of manufacturing a stretch blow molded PET bottle according to the invention also comprise, as an alternative to the step of treating the stretch blow molded PET bottle with the organic solvent or the aqueous solution of the organic solvent, the steps of treating the PET preform of the bottle and stretch blow molding this preform to obtain the stretch blow molded PET bottle, wherein at least parts of the preform are treated with the above described organic solvent or the aqueous solution of the organic solvent, namely those parts which result after stretch blow molding in parts of the bottle where its PET materia! would be amorphous or would have an insufficient degree of crystallinity if the preform would not be treated.

Also the bottle manufactured according to this method has an improved resistance to environmental stress cracking at its unstretched parts or slightly stretched parts when the inner or outer surface of the bottle is treated with one or more of the chemical substances known to cause environmental stress cracking.

A "preform" as herein referred to means an injection molded item that is meant to be stretch blow molded into a bottle, the material the preform and the bottle are made of is preferably PET.

"Improved resistance to environmental stress cracking" as herein referred to means fewer and/or less distinctive microscopic and/or macroscopic stress cracks at unstretched or just slightly stretched parts of a PET bottle having been treated with the organic solvent or the aqueous solution of the organic solvent prior to the application of a stress cracking provoking chemical substance compared to the number and/or distinctness of stress cracks of an equal PET bottle having not been treated with the organic solvent or the aqueous solution of the organic solvent.

The organic solvent used to treat the preform or the bottle as described above is preferably selected from the group consisting of acetone, ethyl acetate, methyl propyl ketone, toluene, 2-propanol, pentane, methanol, and mixtures thereof.

Preferred is acetone or ethyl acetate or mixtures thereof.

Correspondingly, the aqueous solution of the organic solvent used to treat the preform or the bottle is preferably a mixture of water with an organic solvent selected from the group consisting of acetone, ethyl acetate, methyl propyl ketone, toluene, 2-propanol, pentane, methanol, and mixtures thereof.

In a preferred embodiment of the inventive method the organic solvent or the aqueous solution of the organic solvent is acetone with a volume ratio of acetone to water in the range of 40:60 to 100:0. In general, using undiluted acetone is most efficient in improving the resistance to environmental stress cracking. However, due to the flammability of acetone and possible negative health effects it is preferred to dilute the acetone as much as possible. Therefore, the volume ratio of acetone to water is preferably in the range of 50:50 to 90:10, more preferably in the range of 60:40 to 80:20, most preferably in the range of 60:40 to 70:30.

In a further preferred embodiment of the inventive method the organic solvent or the aqueous solution of the organic solvent comprises ethyl acetate in an amount of 0.5 to 98.5 % by weight and acetone in an amount of 1.5 to 99.5 % by weight and water in an amount of 0 to 98 % by weight, each based on the total weight of the organic solvent or the aqueous solution.

In an even more preferred embodiment the organic solvent or the aqueous solution of the organic solvent comprises ethyl acetate in an amount of 5 to 85 % by weight and acetone in an amount of 15 to 95 % by weight and water in an amount of 0 to 80 % by weight, each based on the total weight of the organic solvent or the aqueous solution.

In general and as in the case of pure acetone, using an undiluted mixture of ethyl acetate and acetone is most efficient in improving the resistance to environmental stress cracking. However, due to the flammability of acetone and ethyl acetate and possible negative health effects it is preferred to dilute the mixture of ethyl acetate and acetone as much as possible. Therefore, in a preferred embodiment the organic solvent or the aqueous solution of the organic solvent comprises ethyl acetate in an amount of 5 to 75 % by weight and acetone in an amount of 15 to 85 % by weight and water in an amount of 10 to 80 % by weight, each based on the total weight of the organic solvent or the aqueous solution.

In a particularly preferred embodiment the organic solvent or the aqueous solution of the organic solvent comprises ethyl acetate in an amount of 7.5 to 77.5 % by weight and acetone in an amount of 22.5 to 92.5 % by weight and water in an amount of 0 to 70 % by weight, each based on the total weight of the organic solvent or the aqueous solution. In another preferred embodiment, for the reasons mentioned above with respect to the diluted mixtures, the organic solvent or the aqueous solution of the organic solvent comprises ethyl acetate in an amount of 7.5 to 57.5 % by weight and acetone in an amount of 22.5 to 72.5 % by weight and water in an amount of 20 to 70 % by weight, each based on the total weight of the organic solvent or the aqueous solution

In a most preferred embodiment the organic solvent or the aqueous solution of the organic solvent comprises ethyl acetate in an amount of 10 to 70 % by weight and acetone in an amount of 30 to 90 % by weight and water in an amount of 0 to 60 % by weight, each based on the total weight of the organic solvent or the aqueous solution. In another preferred embodiment, for the reasons mentioned above with respect to the diluted mixtures, the organic solvent or the aqueous solution of the organic solvent comprises ethyl acetate in an amount of 10 to 40 % by weight and acetone in an amount of 30 to 60 % by weight and water in an amount of 30 to 60 % by weight, each based on the total weight of the organic solvent or the aqueous solution.

Regarding the step of treating at least those parts of the stretch blow molded PET bottle where its PET material is amorphous or has an insufficient degree of crystallinity or at least those parts of the preform which result after stretch blow molding in parts of the bottle where its PET material would be amorphous or would have an insufficient degree of crystallinity if the preform would not be treated many different treating methods can be performed. One preferred method is that at least that parts of the preform that will not be stretched or will just slightly be stretched during blow molding the bottle or at least the unstretched or just slightly stretched parts of the bottle, i.e. those parts as defined in the claims, are immerged in a bath of the organic solvent or the aqueous solution of the organic solvent. The immerging is carried out for a time in the range of 1 second to less than 1 hour or a preferred time as already mentioned above. The time of immerging can be less than 1 second if the time of remaining on the surface of the preform or the bottle prior to evaporation of the solvent or the aqueous solution of the solvent is in the range of 1 second to less than 1 hour or a preferred time as already mentioned above.

In general, the time of remaining on the surface of the preform or the bottle prior to evaporation of the solvent or the aqueous solution of the solvent is defined as the time of treating.

Another preferred method is that the parts of the preform or of the bottle as defined above are wetted with a sponge or textile soaked with the organic solvent or the aqueous solution of the organic solvent. The wetting is carried out for a time in the range of 1 second to less than 1 hour or a preferred time as already mentioned above. The time of wetting can be less than 1 second if the time of remaining on the surface of the preform or the bottle prior to evaporation of the solvent or the aqueous solution of the solvent is in the range of 1 second to less than 1 hour or a preferred time as already mentioned above.

A further preferred method is that the organic solvent or the aqueous solution of the organic solvent is sprayed onto the parts of the preform or of the bottle as defined above. The time of spraying can be less than 1 second if the time of remaining on the surface of the preform or the bottle prior to evaporation of the solvent or the aqueous solution of the solvent is in the range of 1 second to less than 1 hour or a preferred time as already mentioned above.

The temperature of the organic solvent or the aqueous solution of the organic solvent applied to for treating the preform or the bottle can vary within broad ranges, i.e. above the melting point up to below the boiling point of the respective organic solvent or the aqueous solution of the organic solvent. However, a preferred temperature is in the range of 5 to 40 °C, more preferably in the range of 10 to 30 °C, most preferably in the range of 15 to 25 °C. Also the temperature of the preform or of the bottle or of that parts of the preform or the bottle which are treated can vary within broad ranges during treatment. Preferably, the temperature of the preform or of the bottle or of that parts of the preform or the bottle which are treated during treatment is in the range of 5 to 40 °C, more preferably in the range of 10 to 30 °C, most preferably in the range of 15 to 25 °C.

A further aspect of the invention is a PET bottle having a complete outer layer of solvent induced crystallized PET, wherein the outer layer of solvent induced crystallized PET has a thickness in the range of 3 to 200 μιη, preferably in the range of 5 to 160 pm, more preferably in the range of 10 to 120 μιη, most preferably in the range of 15 to 80 m, measured under a microscope at a cross section of the bottle wail or the preform wall in polarized light. The PET bottle can be, preferably, manufactured by the above described method.

Preferably, the complete outer layer of solvent induced crystallized PET is at least at that parts where the PET bottle comprises amorphous PET material or where the PET material has an insufficient degree of crysta!linity over the whole thickness of the PET material.

"A complete outer layer" means here a surface area which is completely covered by the solvent induced crystallized PET. Preferably, the complete outer layer is at every position of the parts with amorphous PET material or parts where the PET material has an insufficient degree of crystallinity, like at the bottom area and the neck area.

The measuring method under a microscope at a cross section of the bottom area in polarized light is described in more detail in the Examples section. In a preferred embodiment the bottle according to the invention is at a pressure above 1 bar at least in part filled with a chemical substance or a composition comprising the chemical substance, the chemical substance being selected from the group consisting of alcohols, ketons, aldehydes, esters, natural flavor enhancers, or mixtures thereof.

In context of the present invention the following substances are of particular relevance as they represent typical substances which can be present in containers for consumer compositions and/or as they are known to be able to cause stress cracking: Alcohols like C₂-Ci₂ saturated and unsaturated aliphatic, cyclic and/or aromatic alcohols, ethoxylated alcohols, particularly ethanol, isopropanol, propylene glycol, dimethyl octenol, 1-phenyl-2-ethanol; ketons like C3-C5 aliphatic linear and/or cyclic ketones, particularly acetone, methy ethyl ketone, methyl propyl ketone;

aldehydes like C7-C10 aliphatic saturated and unsaturated aldehydes, particularly heptanal, decanal, octenal; esters based on C1-C10 saturated and unsaturated linear and/or cyclic alcohols and C2-C4 acids, particularly ethylacetate, amylacetate, butyl cyctohexyl acetate, acetic acid pheny!methyl ester, benzylacetate; and natural flavor enhancers like mono terpene alcohols, particularly eugenol, eugenolacetate, geraniol, geranyl ester, citronellol, citral, !inalyl acetate, jasmonates, salicylates, and derivatives thereof.

It should be mentioned that in context of the present invention PET bottles are of interest having a filling volume in the range of 10 to 1500 ml, preferably 20 to 1000 ml, and most preferably in the range of 50 to 750 ml. At least PET bottles having these sizes benefits from the inventive treatment described herein. Nonetheless, also PET bottles of smaller or greater size should benefit from the present invention if the treatment conditions are adapted accordingly. In a preferred embodiment of the invention the bottle is at least in part filled with the chemical substance or the composition mentioned above at a pressure above 1.5 bar, more preferably in the range of 3 to 20 bar, most preferably in the range of 5 to 15 bar, measured at a temperature of 50 °C. A still further aspect of the invention is a PET preform, the preform being suitable for the manufacture of a bottle by stretch blow molding the preform, the preform having at least in part a complete outer layer of solvent induced crystallized PET, wherein the outer layer of the solvent induced crystallized PET has a thickness in the range of 3 to 200 μη% preferably in the range of 5 to 160 μιη, more preferably in the range of 10 to 120 μιη, most preferably in the range of 15 to 80 pm, measured under a microscope at a cross section of the treated part of the preform in polarized light. The preform has parts which will be formed - after stretch blow molding to a bottle - to parts of the bottle where its PET material is unstretched or just slightly stretched. Preferably, the complete outer layer of solvent induced crystallized PET is at least at that parts of the preform where - after stretch blow molding to a bottle - the PET material of the bottle is unstretched or just slightly stretched, i.e. where its PET material would be amorphous or would have an insufficient degree of crystallinity if the preform would not be treated.

"A complete outer layer" means here a surface area which is completely covered by the outer layer of the solvent induced crystallized PET. Preferably, the complete outer layer is at every position of the parts of the preform which will be formed - after stretch blow molding to a bottle - to parts of the bottle where its PET material is unstretched or just slightly stretched, i.e. where its PET material would be

amorphous or would have an insufficient degree of crystallinity if the preform would not be treated.

A further aspect of the invention is the use of an organic solvent or an aqueous solution of the organic solvent, the solvent being selected from the group consisting of acetone, ethyl acetate, methyl propyl ketone, toluene, 2-propanol, pentane, methanol, and mixtures thereof, for treating at least those parts of a stretch blow molded PET bottle where its PET material is amorphous or has an insufficient degree of crystallinity, when the bottle is destined for being at least in part filled at a pressure above 1 bar with a chemical substance or a composition comprising the chemical substance, the chemical substance being selected from the group consisting of alcohols, ketons, aldehydes, esters, natural flavor enhancers, or mixtures thereof. The chemical substances of particular relevance already have been described in more detail above.

In a preferred embodiment of the invention the bottle is destined for being at least in part filled with the chemical substance or the composition mentioned above at a pressure above 1.5 bar, more preferably in the range of 3 to 20 bar, most preferably in the range of 5 to 15 bar, measured at a temperature of 50 °C. Finally, a further aspect of the invention is the use of an organic solvent or an aqueous solution of the organic solvent, the solvent being selected from the group consisting of acetone, ethyl acetate, methyl propyl ketone, toluene, 2-propanol, pentane, methanol, and mixtures thereof, for treating at least parts of a PET preform. Preferably, the preform is destined for the manufacture of a bottle by stretch blow molding the preform.

In a preferred embodiment of the inventive uses the treatment of the bottle or of the preform is carried out for a time in the range of 1 second to less than 1 hour, preferably in the range of 3 seconds to less than 20 minutes, more preferably in the range of 5 seconds to less than 10 minutes, most preferably in the range of 10 second to less than 5 minutes

The figures 1 to 4 are given to further illustrate the invention:

Figure 1a shows a photomicrograph taken in polarized light of a thin slice {20 μιτι) of part of the cross-section of a tensile bone after acetone treatment for 5 seconds

Figure 1b shows a photomicrograph taken in polarized light of a thin slice (20 m) of part of the cross-section of a tensile bone after acetone treatment for 30 minutes.

Figure 1c shows a photomicrograph taken in polarized light of a thin slice (20 μηι) of part of the cross-section of a tensile bone after acetone treatment for 60 minutes. Figure 2 shows two graphs of the thickness of the crystalline layer on the outside of tensile bones (made of PET Lighter S98 from Equipolymers) after treating them for different periods of time in ethyl acetate or acetone, respectively.

Figure 3 shows five tensile bones (top-down 1 to 5) made of PET Lighter S98 after treating them in mixtures of acetone and water for 5 seconds followed by bending and applying acetone as stress cracking provoking chemical substance ( : without treatment, 2: acetone/water 50:50 vol%, 3: acetone/water 60:40 vol%, 4:

acetone/water 70:30 vol%, 5: acetone/water 80:20 vol%). Figure 4 shows eight tensile bones (top-down M8 to M1) made of PET Lighter S98 after treating them in mixtures of acetone, ethyl acetate and water for 5 seconds followed by bending and applying acetone as stress cracking provoking chemical substance (M8: acetone/ethylacetate/water 0.5:1.5:98 wt%, M7:

acetone/ethy!acetate/water 2.5:7.5:90 wt%, 6: acetone/ethylacetate/water 5:15:80 wt%, M5: acetone/ethylacetate/water 7.5:22.5:70 wt%, M4:

acetone/ethylacetate/water 10:30:60 wt%, M3: acetone/ethylacetate/water 55:35:10 wt%, M2: acetone acetone/ethylacetate/water 25:37.5:37.5 wt%, M1 :

acetone/ethylacetate/water 35:40:25 wt%).

Examples Measuring layer thickness of solvent induced crystallized PET

Thin slices (20 pm thick) of the cross-section of tensile bones were taken by using a microtom HM 355 S from Microm. The thin slices were embedded in Canada balsam between a microscope slide and a cover glass. The determination of the thickness of the solvent induced crystalline layer was done using the digital microscope system VHX-1000 from Keyence and the zoom lens VH-Z250R in polarized light.

Determining the absolute degree of crystallization (density method)

Starting from the completely amorphous material having a density of 1.331 g/cm³ and the 100 % crystalline material having a density of 1.445 g/cm³ the crystallinity of the respective part of the bottle is interpolated from the measured values of the density. The density was determined by using a density gradient column according to ISO 1183-2:2004. Example 1

The birefringent outer layer shown in Figure 1a was made by immerging a tensile bone in a bath of acetone for 5 seconds. Example 2

The birefringent outer layer shown in Figure 1 b was made by immerging a tensile bone in a bath of acetone for 30 minutes. Example 3

The birefringent outer layer shown in Figure 1c was made by immerging a tensile bone in a bath of acetone for 60 minutes.

Example 4

Comparison of the impact of treating tensile bones with either ethyl acetate or acetone (see Figure 2):

Tensile bones made of PET (Lighter S98 from Equipolymers) were immerged for different periods of time in a bath of ethyl acetate or acetone. Thin slices (20 pm thick) of the cross-section of these tensile bones were taken by using a microtom HM 355 S from Microm. The thin slices were embedded in Canada balsam between a microscope slide and a cover glass. The determination of the thickness of the solvent induced crystalline layer was done using the digital microscope system VHX-1000 from Keyence and the zoom lens VH-Z250R in polarized light.

Example 5

Comparison of the impact of treating tensile bones with different mixtures of acetone and water (see Figure 3):

Each of five tensile bones made of PET (Lighter S98 from Equipolymers) were immerged in a different mixture of acetone and water for 5 seconds followed by bending and subsequently pouring 1 ml acetone as stress cracking provoking chemical substance over each bended tensile bone. Shortly after relaxing each tensile bone each of the pictures shown in figure 3 was made.

The different mixtures were: Tensile bone 1 : without acetone/water treatment,

Tensile bone 2: acetone/water 50:50 vol%,

Tensile bone 3: acetone/water 60:40 vol%,

Tensile bone 4: acetone/water 70:30 vol%, and

Tensile bone 5: acetone/water 80:20 vol%.

Example 6

Comparison of the impact of treating tensile bones with different mixtures of acetone, ethyl acetate and water (see Figure 4):

Each of eight tensile bones made of PET (Lighter S98 from Equipolymers) were immerged in a different mixture of acetone, ethyl acetate and water for 5 seconds followed by bending and subsequently pouring 1 mi acetone as stress cracking provoking chemical substance over each bended tensile bone. Shortly after relaxing each tensile bone each of the pictures shown in figure 4 was made.

The different mixtures were:

Tensile bone M8: acetone/ethylacetate/water 0.5:1.5:98 wt%,

Tensile bone M7: acetone/ethylacetate/water 2.5:7.5:90 wt%,

Tensile bone M6: acetone/ethylacetate/water 5:15:80 wt%,

Tensile bone M5: acetone/ethylacetate/water 7.5:22.5:70 wt%,

Tensile bone 4: acetone/ethylacetate/water 10:30:60 wt%,

Tensile bone 3: acetone/ethylacetate/water 55:35:10 wt%,

Tensile bone M2: acetone acetone/ethylacetate/water 25:37.5:37.5 wt%, and

Tensile bone M1 : acetone/ethylacetate/water 35:40:25 wt%.

Claims

A method of manufacturing a treated stretch blow molded PET bottle having an improved resistance to environmental stress cracking, the method comprises the steps of:

a) providing a stretch blow molded PET bottle, and

b) treating at least those parts of the stretch blow molded PET bottle where its PET material is amorphous or has an insufficient degree of crystallinity with an organic solvent or an aqueous solution of the organic solvent,

wherein the treatment is carried out for a time in the range of 1 second to less than 1 hour.

Method according to claim 1 , wherein the parts of the PET bottle having amorphous PET material or an insufficient degree of crystallinity are those parts where the degree of crystallinity of the PET material of the bottle compared to the maximum degree of crystallinity present at any part of the bottle is less than 20%, or where the absolute degree of crystallinity of the PET material is less than 6%.

Method according to claim 1 to 2, wherein the organic solvent is selected from the group consisting of acetone, ethyl acetate, methyl propyl ketone, toluene, 2-propanol, pentane, methanol, and mixtures thereof. Preferred is acetone or ethyl acetate or mixtures thereof.

Method according to claim 1 to 2, wherein the aqueous solution of the organic solvent is a mixture of water with an organic solvent selected from the group consisting of acetone, ethyl acetate, methyl propyl ketone, toluene, 2-propano!, pentane, methanol, and mixtures thereof. Preferred is acetone or ethyl acetate or mixtures thereof.

5. Method according to one or more of claims 1 to 4, wherein the organic solvent is acetone and the volume ratio of acetone to water is in the range of 40:60 to 100:0.

Method according to one or more of claims 1 to 4, wherein the organic solvent or the aqueous solution of the organic solvent comprises ethyl acetate in an amount of 0.5 to 98.5 % by weight and acetone in an amount of .5 to 99.5 % by weight and water in an amount of 0 to 98 % by weight, each based on the total weight of the organic solvent or the aqueous solution.

Method according to one or more of the preceding claims, wherein the step of treating is performed by immerging the parts of the PET bottle having the amorphous PET material or the insufficient degree of crystallinity in a bath of the organic solvent or the aqueous solution of the organic solvent, or wherein the step of treating is performed by wetting the parts of the PET bottle having the amorphous PET material or the insufficient degree of crystallinity with a sponge or textile soaked with the organic solvent or the aqueous solution of the organic solvent, or wherein the step of treating is performed by spraying the organic solvent or the aqueous solution of the organic solvent onto the parts of the PET bottle having the amorphous PET material or the insufficient degree of crystallinity.

A PET bottle manufactured by the method according to one or more of the claims 1 to 7.

9. A PET bottle having at least in part a complete outer layer of solvent

induced crystallized PET, wherein the outer layer of the solvent induced crystallized PET has a thickness in the range of 3 to 200 m.

10. Bottle according to claim 9, wherein the complete outer layer of solvent induced crystallized PET is at least at that parts where the PET bottle comprises amorphous PET material or where the PET material has an insufficient degree of crystallinity over the whole thickness of the PET material. 1. Bottle according to claim 9 or 10, wherein the bottle is at a pressure above 1 bar at least in part filled with a chemical substance or a composition comprising the chemical substance, the chemical substance being selected from the group consisting of alcohols, ketons, aldehydes, esters, natural flavor enhancers, or mixtures thereof. 12. A preform made of PET, the preform being suitable for the manufacture of a bottle by stretch blow molding the preform, the preform having at least in part a complete outer layer of solvent induced crystallized PET, wherein the outer layer of the solvent induced crystallized PET has a thickness in the range of 3 to 200 μητι.

13. The preform according to claim 12, wherein the complete outer layer of solvent induced crystallized PET is at least at that parts of the preform which will be formed - after stretch blow molding to a bottle - to parts of the bottle where its PET material would be amorphous or would have an insufficient degree of crystallinity if the preform would not be treated.

14. Use of an organic solvent or an aqueous solution of the organic solvent, the solvent being selected from the group consisting of acetone, ethyl acetate, methyl propyl ketone, toluene, 2-propanol, pentane, methanol, and mixtures thereof, for treating at least those parts of a stretch blow molded PET bottle where its PET material is amorphous or has an insufficient degree of crystallinity, when the bottle is destined for being at least in part filled at a pressure above 1 bar with a chemical substance or a composition comprising the chemical substance, the chemical substance being selected from the group consisting of alcohols, ketons, aldehydes, esters, natural flavor enhancers, or mixtures thereof. Use of an organic solvent or an aqueous solution of the organic solvent, the solvent being selected from the group consisting of acetone, ethyl acetate, methyl propyl ketone, toluene, 2-propanol, pentane, methanol, and mixtures thereof, for treating at least parts of a PET preform, the preform being destined for the manufacture of a bottle by stretch blow molding the preform.