FR2781210A1 - Dispenser piston for container of cream product, e.g. food stuff, has cylindrical wall with rounded projection at one end and annular groove for seal at other - Google Patents

Abstract

The piston (1) has a domed top (2) and a cylindrical side wall (3) with a rounded projection (4) at one end and an annular groove (5) for a seal at the other. It is made by stamping and drawing a varnished aluminum alloy sheet less than 1 mm thick, and has a recess (7) in its cylindrical wall between the projection and groove.

Description

DISPENSER OF CREAMY PRODUCTS UNDER PRESSURE PROVIDED WITH A

WATERPROOF PISTON

TECHNICAL AREA

  The invention relates to housings dispensing pressurized products of high viscosity with or without emulsifying gas, to be separated from the propellant gas. These are, for example, dispenser boxes for pasty or creamy products,

especially food creams.

  The boxes targeted more particularly must meet a binding specification: a) they must have a large capacity, while respecting the national regulations in force concerning pressure vessels. In this case, the

  European regulations limit the maximum volume of such boxes to one liter.

  b) there must be a separation between the product and the propellant. This is particularly important when the product is intimately mixed with an emulsifying gas under a pressure of several atmospheres: the injection of the emulsifying gas must be carried out very gradually so that the mixing acquires a characteristic consistency which gives the product smoothness. and the sought-after sweetness. The emulsifying gas used cannot be used as propellant gas. A sudden injection at a higher pressure at the end of packaging would cause a sudden change in the structure of the product and would make the dispenser totally ineffective, in any event would distort the desired oiliness of the product. A second gas is therefore required, used as a propellant gas and perfectly separated from the product intimately mixed with the emulsifying gas. When it comes to distributing pasty or creamy products

  food, nitrogen is chosen as the propellant.

  c) the product, optionally mixed with an emulsifying gas, is in the form of a paste or a highly viscous cream, the viscosity being between 100 and 100,000 centipoises in the temperature range targeted. It is therefore necessary to exert a sufficient propulsion force to remove this particularly viscous product from the housing and allow it to flow through the dispensing valve. d) To distribute the viscous product, the propellant is introduced under a

  pressure between 6 and 20 atmospheres at room temperature.

  The tightness of the separation must make it possible to maintain, throughout the use of the housing and when the valve is actuated, a pressure difference

  sufficient between the chamber containing the product and the chamber of the propellant gas.

  If an emulsifying gas has been introduced into the product, the separation must allow

  also to respect the specificities of the two gases.

  e) In the case of food products, the packaging may impose a sterilization phase before filling the product, the housing being cleaned for example with hydrogen peroxide, and a phase succeeding filling and pressurizing, o the housing can be brought to very low temperatures, especially when it comes to ice cream dispenser boxes. Typically, the housing must be able to ensure good separation between product and propellant in the

  temperature range: -40 C, +120 C.

  f) It is envisaged for these boxes, in the case of their use by professionals of the food circuit, that they are rechargeable, that is to say

  reusable after sterilization and refilling.

STATE OF THE ART

  Two solutions are envisaged to achieve a separation between the product and the gas

  propellant: either a pocket case or a piston case is produced.

  As regards the pocket case, one can choose either a metal pocket or a plastic pocket. Due to the dimensions relating to large capacity boxes (diameter close to 80 mm, height close to 300 mm), it is not economically advantageous to choose metal bags: either they are conventionally produced by impact spinning and in this case they are thick, imperfectly transmit the pressure exerted by the propellant gas and greatly increase the total weight of the housing, or they are manufactured by stamping-stretching -3- according to the process described in French application FR 98 06560 filed by the applicant but the cost of developing the process and tools is not

  compatible with the limited market corresponding to this type of housing.

  Regarding the plastic bag, it is necessary to find a polymeric material which can resist the particular thermal conditions of the specifications described above. Low Density Polyethylene has the advantage of being an inexpensive polymer with good resistance to cracking at low temperatures but it

  has the drawback of creeping under a low load - of the order of MPa - at 100 C.

  But the pocket to be produced has such a diameter (typically 40 mm to 80 mm) that it is not possible to make it separately and then to thread it into the already conified case (opening diameter of one inch): it is necessary either to carry it out in situ, or to thread a cylindrical blank into the cylindrical housing blank and then to conify the assembly, for example by following the process described in patent EP 0 547 982 of the applicant. In addition to these technical and economic difficulties, the bag is not very tight due to the high gas permeability of polyethylene. With respect to piston housings, although many of them have been described

  for many years, no convincing industrial solution has been found.

  Indeed, no piston known to date can, during the entire use of the housing, that is to say for at least 6 months after packaging, slide freely inside the housing while maintaining effective separation between the product and the propellant, due to the high mechanical and thermal stresses imposed

  by the specifications set out above.

  US Patent 3,255,936 describes a housing intended in particular for the distribution of shaving creams, whipped creams and sugar icings, provided with a piston in the form of an inverted bowl, the periphery of which is extended by a cylindrical skirt

  covered with a hydrogel which allows it to slide in the housing.

  The patent GB 2 015 655 also reveals the difficulties encountered in obtaining a piston which can slide perfectly inside the housing while maintaining a certain seal between product and propellant gas. It offers a piston also in the form of an inverted bowl extended by a rigid cylindrical skirt provided at its two ends with annular bosses and, in the middle, with two flanges surrounding a foam ring. The first boss, located at the periphery of the bottom, scrapes the internal wall of the housing. The assembly of the flanges and the foam ring is intended to maintain a separation as tight as possible between the chamber containing the product and the chamber containing the propellant gas, subjected to a

  1o pressure less than 9 atmospheres.

  Such boxes cannot guarantee a tight separation of the product and the propellant under the extreme conditions of stress and temperature of the specifications. To illustrate the technical difficulty, we can evoke the fact that at the present time, it is not uncommon to encounter boxes, initially intended for dispensing shaving gel, which in fact dispense a foam, said foam being the result of the propellant leaking into the gel. These boxes are however significantly less thermally and mechanically stressed than the boxes targeted in the context of the

present invention.

PROBLEM

  The Applicant has sought to overcome these difficulties and to produce, under economically satisfactory industrial conditions, a housing which makes it possible to dispense under pressure a product whose viscosity is greater than 100 centipoise (or 0.1 Pa.s) - in particular pastry creams. and coolers with a viscosity of between 20,000 and 100,000 centipoises - while keeping the product and the propellant gas separated under an initial pressure of between 6 and 20 atmospheres at ambient temperature, said separation having to remain effective for at least 6 months, said housing being able to be subjected several times to

  temperatures in the range (-40 C; +120 C).

-5-

OBJECT OF THE INVENTION

  The distributor housing according to the invention is a metal piston housing in the form of a bowl extended by a generally cylindrical wall, characterized in that said generally cylindrical wall is provided with a boss at one of its ends and an annular groove, intended to collect a seal at its other end. The piston is metallic, which provides an effective barrier to the diffusion of the propellant gas 1 towards the product. It includes a bottom and a generally cylindrical wall. The shape of the bottom of the piston is an inverted bowl. In order to increase the rate of return of the product, it is possible to choose a shape matching that of the dome which supports the valve, by providing a cavity making it possible to accommodate the lower part of the valve and radial channels making it possible to supply this cavity with

produced at the end of the piston stroke.

  The height of the generally cylindrical wall of the piston is such that it favors the axial guidance of the piston in the housing. This generally cylindrical wall does not come into contact with the internal wall of the housing over this entire height, since contact is ensured at the level of the boss and of the O-ring, each located at one end of said cylindrical wall. This configuration can be accentuated by providing a recess between the boss and the seal, the diameter at this level being less than the diameter of the bottom of the piston (hereinafter called the diameter of the piston). This not only makes it possible to reduce the friction forces but also to evacuate, by trapping them, the roughness or particles encountered on the internal wall and

  likely to hinder the smooth sliding of the piston.

  The boss can be located at the bottom in the shape of an inverted bowl and the

  seal can be located at the open end of the cylindrical wall of the piston.

  However, the Applicant has found that the opposite configuration - seal located at the bottom and boss at the open end of the cylindrical wall of the piston - is more advantageous. The seal, in direct contact with the product, does not act as a doctor blade on the internal wall of the housing but advances by leaving a "shirt", that is to say, taking up the vocabulary of profile spinners metal, a thin film of product adhering to the wall of the housing. When the product is particularly viscous (consistency greater than 20,000 centipoise), this jacket, by its presence, contributes to the good sealing of the assembly. The boss is located on the open end and essentially serves as an axial guide, its maximum diameter preferably being slightly smaller than the diameter of the piston, so that the boss is not in contact with the tank wall on its entire surface. circumference. The main role of the boss is to guide the piston axially, preventing any jamming of said piston by untimely pivoting. In order to ensure good axial guidance, the distance between the boss and the groove is

  preferably greater than the radius of the housing.

  The cylindrical wall of the piston is provided, preferably at the junction with the bottom, with a groove capable of receiving an O-ring. The section of the O-ring is arbitrary, the simplest form being the circle. The integrity of the seal, therefore the quality of the seal, also depends on the shape of the groove. It is particularly necessary to avoid the jamming of the seal during the sliding of the piston by "extrusion" between the internal wall of the housing and the cylindrical wall of the piston, because this jamming risks quickly tearing the seal. For this, the groove must have a depth greater than the radius of the seal and a width such that the surface of the section of the groove is greater than that of the section of the O-ring. In this way, the bottom of the annular groove has a straight cylindrical vertical part. In addition, the side walls must have a geometry unfavorable for the extrusion of the seal between housing and piston during its movement, that is to say be perpendicular to the internal wall of the housing over a sufficient length, for example in making the leaves of connection of these walls with the generally cylindrical wall of the piston also

weak as possible.

  An additional precaution to prevent the seal from coming out of the groove during its movement and from getting caught between the internal wall of the housing and the external wall of the piston, consists in giving the O-ring a section with a specific profile: - the active part in contact with the internal wall of the housing retains a circular shape, the non-active part in contact with the groove of the piston follows the profile of the groove

  the surface of the assembly must not exceed the section of the groove.

  The quality of the contact between the seal and the internal wall of the housing depends on the differences in hardness, or rather rigidity, between the seal and the piston on the one hand and between the seal and the housing on the other hand. Whether it is the piston or the casing, the Applicant has found that it is above all a question of seeking the best circumferential rigidity: the orthogonal sections of the casing and of the piston may possibly deform elastically, it suffices that the perimeters are retained, provided that the main axes of deformation of the piston and of the housing remain approximately identical. So preferably choose a housing and a piston in a material of the same kind. The housing is preferably metallic,

like the piston.

  Aluminum alloys are well suited materials for both the housing and the piston. They are possibly different for the piston and the housing. The alloys chosen for the piston are preferably part of the group comprising the

  alloys designated 5182, 5052, 3104, 3105, 3003 and 8011 by the Aluminum Association.

  The piston is obtained for example by stamping or by stamping and then knurling, which makes it possible to obtain, under satisfactory economic conditions, a thin cylindrical wall, of the order of 0.2 to 1 mm. Such a wall is

  easily elastically deformable but remains rigid circumferentially.

  The O-ring has a section such that it compensates for the respective dimensional variations of the housing and the piston. The metal case is in

  general made by impact spinning, or by stamping or stamping-

  drawing. The piston is preferably produced by stamping or stamping-

  -8- stretching. In this way, the cumulative manufacturing tolerances can reach, for the geometries concerned (diameters close to 80 mm), a difference of 0.6 mm, which the O-ring must be able to "absorb" without loss of efficiency in terms of the tight separation between the propellant and the product and without risk of pinching between the piston groove and the internal wall of the housing. For this purpose, with the targeted geometries, the external leaves of the groove of the piston intended to receive the seal must not be greater than 1.5 mm. So that the seal is not too compressed when the piston is manufactured with a maximum diameter 1o and the housing with a minimum internal diameter, it is preferable to choose an O-ring whose circumscribed diameter of the section is greater than five times, preferably 8 times, the allowable play between the diameter of the piston and the diameter of the inner wall of the housing. Thus for a maximum clearance of 0.6 mm, the circumscribed diameter of the section of the joint must be greater than 3 mm and preferably it will be chosen greater than

4.8 mm.

  The seal must remain housed at the bottom of the piston groove, held between the horizontal side walls of the groove so that it does not roll on itself locally as this would cause significant twists and weaken it. On the other hand, the external part of the seal must be able to deform easily under the effect of contact with the internal wall of the housing. The section of the seal has a rounded tip, projecting from the diameter of the piston when the seal is placed in the groove. This rounded point shape facilitates radial compression of the joint and the material of the joint can move freely towards the empty part of the groove. In order to avoid pinching of the seal between piston and wall, the volume occupied by the groove must

be greater than that of the joint.

  Although these materials generally have adhesion properties which do not a priori facilitate the sliding of the piston, the Applicant recommends for the O-ring an elastomeric plastic or a silicone. The elastomeric plastic material can be chosen from nitriles, butyls, hydrogenated nitriles, terpolymers (ethylene, propylene, diene), fluoroelastomers, etc., or their alloys -S- or their mixtures. The seal can also be made of silicone or of silicone mixed with the preceding elastomeric materials. To facilitate the formation of the jacket, the joint must have a minimum hardness, greater than 45 Shore A., preferably between 45 and 85 Shore A, depending on the viscosity of the product to be packaged. In fact, to maintain good flexibility allowing the separation to be maintained despite the variable clearance between housing and piston, it is desirable that the hardness of the seal does not exceed 85 Shore A. To facilitate sliding, additives such as stearins, stearates , erucamides, etc ... can possibly be used but they are generally not necessary. With regard to distributors of food creams, the material

  the seal must also be adapted to the required food hygiene conditions.

  Such a configuration has been developed for large capacity boxes but remains entirely suitable for smaller capacity boxes (less than 1 liter), having to dispense high viscosity products under pressure and having to be protected from propellant gas. Likewise, these boxes can also be quite suitable for uses associated with less restrictive thermal and mechanical stresses.

  MODES FOR CARRYING OUT THE INVENTION - EXAMPLE

  The method according to the invention will be better understood by the detailed description of a

  pastry cream dispenser, the latter having a viscosity close to

  000 centipoises, exposed here by way of nonlimiting example.

  Figure 1 shows the piston used for a distributor housing according to the invention.

  FIG. 2 illustrates the distributor box provided with the metal piston of FIG. 1 and

a seal.

  3o Figures 3 to 5 show sections of joints according to the invention. The latter are at rest, juxtaposed with the detail drawing of the piston groove and the wall of the

  case, the rounded tip superimposed on a part of the case.

  - 10- The piston I illustrated in FIG. 1 comprises a bottom 2 in the form of an inverted bowl and a generally cylindrical wall 3. The ends of this wall are provided with a boss 4 on the side of the open end 6 and, at the junction with the bottom 2, an annular groove 5. Intended to receive an O-ring (marked 10 in FIG. 2 ), this annular groove 5 has a radial depth of approximately 4.6 mm and a width L equal to that of the seal 10. The surface of the section of the groove is greater than that of the section of the O-ring 10. The side walls 9 of the groove 5 are straight and horizontal over a sufficient length, thanks to fillets 11 for connection with the cylindrical wall 3 of several tenths of a millimeter. They keep the internal part of the seal 10 stable at the bottom of the groove 5, that is to say that it does not

  no risk of rolling over locally and twisting.

  The diameter of the bottom D1 is greater than the diameter D2 of the outer wall of the recess 7 located between the boss 4 and the O-ring 10. The boss 4 has a maximum diameter D3 slightly less than the diameter D1 of the bottom, called the diameter of the piston . The housing 20, illustrated in FIG. 2, has a capacity of 1.25 liters. First, a shock spinning blank is produced. The housing 20 is made of 1050 alloy, has a diameter of 80 mm and a final height of 280 mm. The thickness of the cylindrical wall is close

  0.46 mm. Its internal wall is covered with an epoxy varnish.

  A piston I identical to that illustrated in FIG. 1 is placed in the housing blank which is then conified to obtain an orifice 21 delimited by a rolled edge 22, on which

  a valve cup (not shown) is crimped.

  The piston divides the internal volume of the housing into two chambers: the lower chamber 26 intended to receive the propellant gas and the upper chamber 23, intended to collect the product to be dispensed. The cream is poured into the chamber 23, while the piston rests on the bottom 24 of the housing. The cup fitted with the dispensing valve

- 11 -

  is crimped on the rolled edge 22 then the propellant gas is injected under a pressure of 15 atmospheres into the lower chamber 26 via the hole provided

  in the bottom 24 of the housing, then plugged with a gas cap 25.

  The piston was obtained by stamping a sheet painted in 8011. Its thickness is close to 35 hundredths of a millimeter. The final shape is obtained by stretching and then molding to obtain the desired profile. Thanks to this shape matching those of the neck of the housing and the bottom of the valve, the bottom 2 allows a very high product restitution rate, greater than 95%. The height of the cylindrical wall of the piston, imposing the distance between the seal and the boss, is close to the radius of the housing, which allows a

good axial guidance.

  The boss has a radial height of 2 mm relative to the surface of the recess 7.

  The diameters D1, D2 and D3 are respectively 78.6 mm, 74 mm and 78 mm.

  The boss has a diameter D3 slightly smaller than the diameter of the piston Dl: it is not

  not in continuous contact over the entire periphery with the internal wall of the housing.

  The seal is made of silicone and has a Shore 60 A hardness. Three types of seal, shown in FIGS. 3, 4 and 5, have been produced in the context of the invention. The joint of Figure 3 has a large section with an outer part with a rounded point, the radius being equal to 2 mm. This seal resists wear well and makes it possible to make up for significant piston-housing clearances. Its seat in the groove gives it good stability and prevents the risks of kinking and pinching of the joint. However, its cost is quite high due to the material used. The joint of Figure 5 has a significantly smaller section, with an outer part also in a rounded point, the radius of the rounding being equal to 1 mm. It is more economical and makes it possible to make up for such a large piston-housing clearance (0.6 mm). The diameter of its internal part, equal to the

  width L of the groove, is equal to 4 mm. Its circumscribed diameter is close to 5.0 mm.

  The seal of Figure 4 has a geometry also well suited to the conditions

  binding use of the housing according to the invention.

  - 12- The separation between product and propellant gas is maintained under satisfactory conditions over time. One month after conditioning, the pressure in chamber 26 only decreased by 0.05 atmosphere. After 6 months, the pressure has

  dropped by 0.5 atmospheres and the pastry cream is not altered.

BENEFITS

  ò The height of the cylindrical wall of the piston is such that it allows the piston to rest on the bottom of the housing in a stable position when filling

  of the product and the injection of the emulsifying gas.

  The large section O-ring ensures good separation between the product and

  the propellant, whatever the play due to manufacturing tolerances.

  * The large surface occupied by the metal bottom of the piston and the small surface occupied by the O-ring make it possible to respect the specific characteristics of the propellant gas and of the emulsifying gas throughout the use of the housing, that is to say

for at least 6 months.

- 13-

Claims (11)

  1. Piston (1) for distributor housing (20) under pressure of viscous products, comprising a bottom (2) in the form of an inverted bowl extended by a cylindrical wall (3), characterized in that said cylindrical wall (3) is provided a boss (4) at one of its ends (6) and an annular groove (5), intended for   collect a seal (10) at its other end.   2. Piston according to claim 1, characterized in that it is metallic.   3. Piston according to claim 1 or 2, characterized in that it is made of an aluminum alloy belonging to the group grouping alloys 5182, 5052, 3104, 3105,   3003 and 8011 according to the standardized designation of the Aluminum Association.   4. Piston according to any one of claims 1 to 3, characterized in that it   exists on the cylindrical wall (3) a recess (7) between said boss (4) and said seal sealing (10).   5. Piston according to any one of claims 1 to 4, characterized in that the   seal (10) is located at the junction between said bottom (2) and said cylindrical wall (3) and   that the boss (4) is located on the open end (6) of said cylindrical wall.   6. Piston according to any one of claims 1 to 5, characterized in that the   groove (5) intended to receive said O-ring (10) has straight and horizontal side walls (9) making it possible to keep the internal part of the seal (10) stable at the bottom of the throat (5).   7. Piston according to any one of claims 1 to 6, characterized in that the   wall of the piston has a thickness of less than 1 mm.   8. Piston according to claim 7, characterized in that it is obtained by stamping   or stamping-drawing of a painted thin sheet then knurling.   - 14- 9. Housing (20) pressure distributor of high viscosity products, characterized in   that it is provided with a piston (1) according to any one of claims I to 8 and with a   O-ring (10) made of a material belonging to the group grouping elastomeric plastics and silicones, as well as their mixtures. 10. Distributor housing according to claim 9, characterized in that said O-ring (10) has a section whose external part is in the form of a rounded point projecting from the diameter of the piston, the diameter of the circumscribed circle of said section being greater than 5 times, preferably 8 times, the allowable play between   the diameter of the piston and the diameter of the housing.   11. Dispenser box according to claim 9 or 10, characterized in that said seal (10) has a hardness greater than 45 Shore A.