Method for producing preform and method for producing bottle

Abstract

The invention relates to a method of manufacturing a preform and a method of manufacturing a bottle. The invention discloses a method for manufacturing a preform (11) of an injection molded aerosol or pump bottle made of PET, the article having at least one crystalline portion (3), the method comprising the steps of: a) producing an injection molded article by injecting a crystallizable polymer into a mold, b) crystallizing the portion (3) of the injection-molded article by heating and then cooling the injection-molded article wherein, in the process, between step a) and step b), the injection-molded article is maintained under storage conditions for a sufficient duration to subject it to a moisture absorption of from 1% to 3% by weight, the injection molded article is stored in a large bag during moisture absorption, with a relative humidity during storage of at least 60%, a storage duration of at least one month, and a storage temperature of from 5 DEG C to 35 DEG C.

Description

[0001] This application is a divisional application of the Chinese patent application with the application date of June 10, 2020, application number 202080043875.3, and invention name “Method for manufacturing injection molded articles, especially bottle preforms”. Technical Field

[0002] The present invention relates to finished and semi-finished products, in particular bottles, more particularly aerosol bottles (ie pressurized bottles for containing a composition and a propellant gas, in particular a liquefied propellant gas). The invention also relates to pump-action bottles, ie those bottles equipped with a pump. Background Art

[0003] It has already been proposed to produce aerosol bottles from thermoplastic materials.

[0004] To this end, a preform is produced by injection molding of a thermoplastic material (e.g. PET), in which the neck is used to fasten the dispensing head. In order to increase the mechanical strength of the neck, the plastic material undergoes a crystallization heat treatment in the neck region. Next, the preform is transferred to a blow molding station to give the bottle its final shape. Crystallization can make the bottle lighter while increasing the mechanical strength.

[0005] Plastic aerosol bottles should comply with the regulations. Testing of plastic aerosol bottles containing liquefied gases is generally more difficult to meet than the tests associated with plastic aerosol bottles containing compressed gases.

[0006] This test verifies that a plastic pressurized bottle can withstand operating pressures of typically several bars, due to the presence of pressurized gas inside the bottle, in particular pressurized liquefied gas. This resistance must be verified at relatively high temperatures to ensure safety in use. Furthermore, since the bottle can be filled under vacuum, this ensures crushing resistance at maximum reduced pressure before starting filling. The bottle must also be shock-resistant, especially when dropped at different temperatures.

[0007] JP 2003 053826 discloses an apparatus for producing a preform with a crystallized neck portion, comprising a preform molding apparatus for injection molding the preform, a neck portion crystallization apparatus for crystallizing the neck portion of the preform, and a first conveying line for conveying the preform from the molding apparatus to the crystallization apparatus, wherein the conveying line comprises a humidity controller for allowing the preform to absorb moisture. Summary of the invention

[0008] Conducted in-house tests have shown that heat treatments, for example by means of lamps emitting infrared radiation, do not always produce the desired mechanical properties, in particular those desired for bottles for containing liquefied propellant gases, in a completely reproducible manner. SUMMARY OF THE INVENTION

[0010] The present invention aims to solve this problem. According to a first aspect of the invention, the subject of the invention is a method for producing an injection-molded article made of a crystallizable polymer material, preferably a preform for a bottle, in particular a preform for an aerosol bottle, the article, in particular the preform, having a crystallized portion and a tubular body, preferably closed at one end, the method comprising the following steps:

[0011] a) producing an injection-molded article, in particular an injection-molded preform, by injecting a crystallizable polymer into a mold,

[0012] b) crystallizing said part by heating and then cooling the injection-molded article, in particular the injection-molded preform,

[0013] Therein, in the method, between step a) and step b), the injection molded article, in particular the injection molded preform, is kept under storage conditions for a sufficient duration to allow it to undergo a moisture absorption of at least 0.4% by weight, better at least 0.8% by weight, even better at least 1% by weight, preferably less than 3% by weight.

[0014] Although the present invention is preferably applicable to injection molded articles constituting preforms, the present invention may also be applicable to other injection molded articles constituting finished or semi-finished products. Therefore, although the following description most specifically relates to preforms, the features of the present invention may be applicable to other injection molded articles.

[0015] The crystallized portion may be a neck portion of the preform.

[0016] During the injection molding of articles, in particular preforms, the moisture content of the plastic material is relatively low, typically about 100 ppm. The invention is based on the discovery that this moisture absorption improves the thermal conductivity of the material of the article, in particular the preform, thereby promoting the effect of the crystallization heat treatment, whereby the crystallization heat treatment can be carried out under conditions that produce satisfactory and reproducible results. The presence of moisture makes it easier to obtain the desired crystallinity gradient in the crystallized part, in particular the neck.

[0017] Thermoplastic materials used during injection molding of articles, in particular preforms, are usually dehydrated. Therefore, when the articles, in particular preforms, leave the mold in which they have been injection molded, the water content of the plastic material is zero or almost zero.

[0018] The moisture absorption of the thermoplastic material is then dependent on its storage conditions until the subsequent heat treatment step of the part to be crystallized, in particular the neck.

[0019] The higher the relative humidity and the longer the storage duration, the greater the moisture absorption.

[0020] Moisture absorption can therefore be promoted by placing the article, in particular the preform, in an environment having a relatively high relative humidity.

[0021] The relative humidity during storage is therefore preferably at least 30%, better at least 60%, or even better at least 80%. The desired relative humidity level can be achieved by humidifying the environment around the preforms, for example with the aid of a suitable air conditioning system. In a variant, the relative humidity is caused by the atmospheric conditions outside the storage location; in this case, the storage duration can be variable so as to allow time to obtain the desired moisture absorption level. In the case of dry weather, this duration can be extended compared to storage during humid weather.

[0022] The storage duration is selected depending on the relative humidity during storage and may be at least 7 days, or even at least 15 days, 1 month, 3 months or 1 year.

[0023] The storage temperature is preferably 5°C to 35°C, more preferably 15°C to 25°C.

[0024] Injection-moulded articles, in particular injection-moulded preforms, can be stored during moisture absorption in big bags, optionally provided with holes to promote exchange with ambient air.

[0025] Preferably, the crystallizable polymer material is PET, but the invention is not limited to this polymer. Thus, the plastic material used may comprise at least one polymer selected from the group consisting of: PET or PETP (polyethylene terephthalate); PEN (polyethylene naphthalate); PCT (polyethylene cyclohexyl dimethyl terephthalate); recycled polymers, in particular polymers called PCR (post-consumer recycled), in particular recycled PET; bioPET (biopolyethylene terephthalate); PP (polypropylene); PE (polyethylene); PEF (polyethylene furandicarboxylate); furanoate); PET-G / PCT-G (glycolated polyethylene terephthalate / glycolated polycyclohexyl dimethyl terephthalate); PET with mineral fillers, such as calcium carbonate or glass fibers; PC (polycarbonate); POM (polyoxymethylene); SMMA (styrene methyl methacrylate); PMMA (polymethyl methacrylate); SAN (styrene acrylonitrile); PBT (polybutylene terephthalate); PA6 (polyamide 6); PA12 (polyamide 12); PEEK (polyetheretherketone); PPO (polyphenylene oxide); PSU (polysulfone); filled polymers, in particular filled polymers with mineral fillers and / or glass fibers; and mixtures thereof, including organic or inorganic pigments or colorants.

[0026] The crystallization step, in particular the crystallization step of the neck, can be carried out by means of a heating device having at least one infrared radiation lamp or any other energy input means.

[0027] The heating device is preferably adjusted to apply a temperature gradient to obtain the desired crystallinity. The heating temperature may be non-uniform. The distance between the heating device and the preform may be adjusted to this effect.

[0028] The heating device is preferably arranged in such a way as to prevent crystallization of the tubular body of the preform which will later be heated and then subjected to the blow-moulding operation.

[0029] While heating, at least one cooling rod can be brought close to the preform from the inside or outside of the preform. In a variant or in addition, while heating, at least one cooling rod can be introduced into the preform, in particular through an opening in the neck of the preform. Such a cooling rod serves to cool areas that are not intended to crystallize and also to achieve a gradient between heated areas where the maximum crystallinity is obtained and unheated areas where the crystallinity is minimal. Without departing from the scope of the invention, another cooling system other than cooling rods can be provided for the same purpose.

[0030] The bottle may hold cosmetics or other products.

[0031] The bottle may contain liquefied or compressed gas having a pressure of 1 bar to 13 bar (10 5 Pahe 13.10 5 The bottle may also accommodate a pump which is crimped to the neck and is not pressurized.

[0032] The bottle may have a dispensing system for dispensing the cosmetic product contained therein, provided with an actuating member that the user can press to dispense the product, for example in the form of a spray, foam, gel or cream, through at least one outlet opening. The dispensing system has, for example, a button fastened to the container and a cup with a valve with a hollow control stem that is controlled by pressing or tilting.

[0033] The bottle may also have a Bag-on-Valve (BoV) type system with an aerosol valve with a welded bag. In this case, the composition is placed in the bag while the propellant fills the space around the bag in the bottle. The composition is dispensed by the propellant simply by squeezing the bag. When the actuating member is depressed, the composition is extracted from the bag by the pressure of the propellant, which results in the composition being dispensed in particular in the form of a spray, cream or gel.

[0034] Another subject of the invention is a method for manufacturing bottles, in particular aerosol bottles, in which the bottles are formed by stretch blow moulding of preforms having a crystalline neck obtained by the method as defined above.

[0035] Another subject of the invention is a bottle, in particular an aerosol bottle, obtained by implementing this method.

[0036] The invention may be better understood by reading the following detailed description of non-limiting illustrative embodiments of the invention and by studying the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS

[0037] [ Figure 1 ] Figure 1 An example of an aerosol bottle according to the present invention is shown;

[0038] [ Figure 2 ] Figure 2 The preform itself is shown;

[0039] [ Figure 3 ] Figure 3 The bottle body itself is shown after the preform has been blown;

[0040] [ Figure 4 ] Figure 4 is a block diagram of a manufacturing method according to the present invention;

[0041] [ Figure 5 ] Figure 5 is a schematic diagram of a partial cross section of a prefabricated component;

[0042] [ Figure 6 ] Figure 6 An example showing the variation of crystallinity in the longitudinal direction within a preform;

[0043] [ Figure 7 ] Figure 7 An example showing the variation of crystallinity in the radial direction;

[0044] [ Figure 8 ] Figure 8 schematically illustrates an example of an apparatus for heat treatment of preforms; and

[0045] [ Fig. 9 ] Fig. 9 is with Figure 8 A diagram of a variation of a similar heat treatment apparatus. DETAILED DESCRIPTION

[0046] Figure 1 An example of an aerosol bottle 1 produced by implementing the method according to the invention is shown.

[0047] The aerosol bottle 1 has a body 2 made of thermoplastic material ( Figure 3 ), which has a neck 3 on which is mounted a dispensing head 5 having a button 4 equipped with a dispensing nozzle 6, which a user can press to cause the contents of the bottle to be dispensed.

[0048] The dispensing head 5 has a cup with a valve, which may be fastened to the neck 3 by snapping, crimping or in any other way and has a dip tube (not visible) extending down to the bottom of the bottle.

[0049] In the example discussed, the bottle contains a composition to be dispensed (eg a cosmetic composition) and a liquefied propellant gas (eg butane).

[0050] The bottle is made from PET, but other thermoplastic materials may also be suitable.

[0051] The neck 3 is at least partially crystalline, whereas the remainder of the body 2 is in amorphous form. In the case of PET, the amorphous nature makes the material transparent, whereas the crystallinity makes it white and opaque.

[0052] Crystallization of the neck 3 can improve its mechanical properties.

[0053] We will now refer specifically to Figure 4 The manufacture of the bottle body 2 is described.

[0054] First, in step 10, if Figure 2 The schematically shown preform 11 is produced by injection molding.

[0055] This preform 11 already has a neck 3 in its final shape and a tubular body 14 closed at one end 16. The neck 3 may have a flange 22 at its base, which is useful for blow-molding, which enables the formation of a stop on the blow-molding mold, and is also useful for transporting the preform 11 or the bottle 2 after blow-molding during the preheating of the preform and / or during the blow-molding and / or during the cooling phase. The neck 3 has an annular protrusion 24 in its upper part for connecting a dispensing system.

[0056] According to the invention, the preform 11 is subjected to a moisture absorption step 13 under conditions selected so that the moisture absorption is at least 0.4% by weight.

[0057] Therefore, the weight of the preform after moisture absorption is at least 1.04 times greater than the weight of the preform before moisture absorption.

[0058] In order to obtain the desired moisture absorption, a large number of preforms 11 can be stored in large bags in an air-conditioned warehouse, the temperature and humidity of which are regulated so that the temperature is between 15° C. and 25° C. and the relative humidity is at least 30% RH, better at least 60% RH, and even better at least 80% RH. The storage duration is selected according to the storage conditions to produce the desired moisture absorption. For example, the storage duration is at least 7 days, better at least 15 days.

[0059] Next, the preform 11 is subjected to a crystallization heat treatment 15 of the neck 3 by exposing the neck 3 of the preform 11 to heating means using, for example, infrared radiation. Examples of heating means that can be used to achieve this heat treatment are described below.

[0060] The crystallization step is preferably carried out in such a way that Figure 5 As shown, a first region 30 and a second region 31 (the middle part between the first region 30 and the tubular body 14) are obtained in the neck 3, the crystallinity of the second region 31 is lower than that of the first region, and the second region axially extends over a height of at least 0.5 mm; and the polymer material of the tubular body 14 remains in an amorphous state.

[0061] The first region 20 is located between the upper end 18 of the neck 3 and the lower end at the boundary with the upper end of the second region 31. The boundary between the first region 30 and the second region 31 is Figure 5 1 , the second region 31 is delimited at the top by this line L1 and at the bottom by a line L2, which is a virtual line constituted by the boundary surface between the second region 31 and the tubular body 14. Although the second region 21 belongs to the neck 3 of the preform 11, the second region 21 constitutes an intermediate region between the neck 3 and the tubular body 14. As can be seen, the boundary surfaces L1 and L2 are not perpendicular to the longitudinal axis X of the preform 11, but form conical surfaces having a semi-cone angle α equal to about 60° with the axis X.

[0062] In this example, the two boundary surfaces have the same angle α, but this could be otherwise without departing from the scope of the present invention.

[0063] The mass fraction crystallinity of the second region 31 is lower than that of the first region 30, and preferably the mass fraction crystallinity is not uniform in the second region 31. The mass fraction crystallinity of the tubular body 14 is close to zero, and the polymer material is in an amorphous state in this part of the preform 11, or in a semi-crystalline state if the preform is made of PP or PE.

[0064] The first area 30 of the neck is white, the part of the tubular body 14 remains substantially transparent, while the second area 31 in the middle of the neck 3 has a milky appearance, a beige gray hue, and its visual appearance is potentially uneven. The light transmittance percentage in the area of ​​the tubular body 14 is higher than the light transmittance percentage in the second area 31, which itself is higher than the light transmittance percentage in the first area 30, especially at 973 cm -1 This is related to the fact that the higher the crystallinity, the lower the light transmittance percentage.

[0065] Thus, the second region 31 forms not only an intermediate region between the first region 30 and the tubular body 14, but also a transition region in terms of crystallinity, since the crystallinity has a maximum in the first region 30 and a minimum in the tubular body 14. The presence of this transition region makes it possible to improve the mechanical properties of the bottle, in particular the mechanical strength. Thus, the bottle produced from the preform 11 can withstand a temperature of 75°C.

[0066] The crystallinity in the second region 31 is preferably inhomogeneous, varying linearly or non-linearly in the radial and / or axial direction within the region.

[0067] In the example shown, the crystallinity in the second region 31 decreases substantially linearly in the axial direction from line L1 towards line L2. Similarly, in the example shown, the crystallinity in the second region 21 decreases substantially linearly in the radial direction from outer surface 27 towards inner surface 26.

[0068] Thus, in this example, the crystallinity varies axially and radially in the second region 31, as shown in FIG. Figure 6 and Figure 7 shown.

[0069] The crystallinity can be expressed as T c (x, r). The crystallinity can show rotational symmetry, which means that T c (x, r) is constant regardless of the azimuth angle θ about the longitudinal axis X. Alternatively, T c (x, r) varies with angle θ.

[0070] For a given r, the transition between the first region 30 and the second region 31 can be considered by definition to be at 0.9T c最大 and 1.1T c最小 The axial extension between c最大 Indicates the highest crystallinity in the first region, T c最小 Indicates the lowest crystallinity of the tubular body.

[0071] Thus, we can obtain a boundary surface defined by the point

[0072] When r changes, T c (x) = 0.9T c最大 ,

[0073] and another boundary surface defined by the point at which

[0074] When r changes, T c (x) = 1.1T c最小 .

[0075] Each of these boundary surfaces may be substantially conical with a top half-angle α relative to the axis X.

[0076] The flange 22 may be formed on the circumference of the neck 3 in the lower portion of the first region 30 , particularly at the lower end of the first region 30 , in which case it may define a boundary with the second region 31 .

[0077] The mass fraction crystallinity of the neck 3 in the first region 30 is preferably 20% to 80%, in particular 25% to 50%, preferably 25% to 40%, and the mass fraction crystallinity of the neck in the first region 30 is preferably substantially uniform in the axial and radial directions. The crystallinity can be substantially uniform over the entire height of the first region, which can be 7 mm to 11 mm, for example, equal to 9 mm.

[0078] The mass fraction crystallinity in the second region 31 of the neck 3 is, for example, 8% to 20%. As described above, the crystallinity preferably presents an axial gradient within the second region, and the crystallinity preferably decreases from the first end where the second region contacts the first region toward the second end where the second region contacts the tubular body. In this case, the crystallinity may vary linearly from the first end to the second end according to the position on the longitudinal axis in the second region. Alternatively, the crystallinity varies nonlinearly in the axial direction.

[0079] The crystallinity may present a radial gradient in the second region, the crystallinity preferably decreasing from the outer surface 27 of the preform towards the inner surface 26 of the preform. In this case, the crystallinity may vary substantially linearly in the second region in the radial direction between the inner surface of the preform and the outer surface of the preform. Alternatively, the crystallinity varies nonlinearly in the radial direction.

[0080] This variation of crystallinity within the thickness starting from the outer highest crystallinity is controlled by heat diffusion through the material.During step 15, the presence of water in the plastic material of the neck 11 resulting from moisture absorption improves the thermal conductivity of the neck 3 in a reproducible manner and obtains the desired crystallinity.

[0081] Figure 8 An example of a heating device 100 is shown which may be used in a heat treatment step of a preform to heat the first region 30 and partially heat the second region 31 in order to induce at least partial crystallization of the polymer.

[0082] The heating device 100 has a plurality of mirrors 42 which make it possible to limit the heating achieved by the infrared radiation lamps 43 to the desired zones. The preform 11 is covered by an oven mandrel 44 which is inserted into the opening in the neck 3 and extends inside the neck 3 to the lower limit of the first zone 30. In a variant, one or more of the mirrors have an indentation in order to promote a crystallinity gradient in the second zone 31.

[0083] Already in Fig. 91 shows another example of a heating device 100. In this example, an infrared radiation lamp 43 is arranged outside the preform 11 in the area around the neck 3. A cooling rod 47 approaches the preform from the outside, below the flange 22. In this example, a rod 46 has been inserted through the opening in the neck 3 along the longitudinal axis X and is present inside the tubular body 14. The rod 46 turns the preform itself in such a way that uniform heating and uniform cooling are achieved over the entire periphery.

[0084] During heating, an axial heating temperature gradient is created in the space around the preform due to the cooling rods 47, so as to limit the diffusion of heat into the material.

[0085] Cooling of the preform after heating may be carried out using natural convection, ie relatively slowly, to complete crystallization.

[0086] The cooling time is, for example, longer than 30 seconds, in particular 30 seconds to 10 minutes. The cooling is therefore slow at ambient temperature.

[0087] Once the crystallization heat treatment has been carried out, the preform is transferred to a stretch blow molding station in order to form the bottle body 2 having the final shape in a stretch blow molding step 17, such as Figure 3 The bottle body 2 has a shape that flares downwards to a circular base 7, for example as shown in the figure, and is provided with an indentation 9 on its lower surface 8. If necessary, a preliminary step of heating the preform is performed before blow molding.

[0088] Finally, in step 19 , the bottle can be equipped with a dispensing head 5 and filled.

[0089] Of course, the invention is not limited to the examples just given.

[0090] For example, moisture absorption can be achieved by utilizing the natural humidity of the air rather than through the use of air-conditioned facilities.

[0091] The present invention is applicable to unpressurized bottles. In this case, crystallization, particularly in the neck, can stiffen certain areas of the bottle, thereby reducing the amount of material used to produce the bottle while having the desired mechanical properties.

[0092] The crystallization may exhibit other forms than those described above, such as non-uniform crystallization around the longitudinal axis of the neck.

Claims

1. A method for producing a preform (11) for an injection-molded aerosol bottle or a pump bottle made of PET, the preform having at least one crystallized portion (3), the method comprising the following steps: a) producing an injection-moulded article by injecting a crystallizable polymer into a mould, b) crystallizing said portion (3) by heating and then cooling said injection molded article, Wherein, in the method, between step a) and step b), the injection molded article is maintained under storage conditions for a sufficient duration to subject it to moisture absorption of 1 wt % to 3 wt %, the injection molded article being stored in a large bag during moisture absorption, the relative humidity during storage being at least 60%, the storage duration being at least 1 month, and the storage temperature being 5° C. to 35° C.

2. The method according to claim 1, wherein: The relative humidity during storage is at least 80%.

3. The method according to claim 1, wherein: The storage temperature is 15°C to 25°C.

4. The method according to claim 1, wherein: The crystallization step is carried out with the aid of a heating device.

5. The method according to claim 1, wherein: The crystallized part is the neck (3) of the bottle.

6. The method according to claim 1, wherein: The article has a tubular body (14) which is closed at one end (16).

7. A method for manufacturing a bottle, wherein: The bottle is formed by stretch blow molding a preform (11) having a crystallized portion (3) obtained by the method according to claim 1.

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