EP3579979B2 - Spray head for a fluid product and use of such a head - Google Patents

Description

The present invention relates to a fluid product spray head which comprises a body forming a housing in which a core extends. The head also comprises a nozzle engaged in the housing around the core so as to form between them several swirl channels as well as a swirl chamber into which the swirl channels open. The nozzle also comprises a dispensing orifice which forms the outlet of the swirl chamber. Such a spray head design is entirely conventional in the fields of cosmetics, pharmacy or perfumery. The spray head is generally mounted on the free end of the valve stem of a pump or a valve. In general, the spray head forms a push button on which the user can press axially using a finger, typically the index finger.

It exists in the prior art, see for example the document WO 97/13584 , all kinds of fluid product spray heads with various characteristics, in particular related to the configuration, orientation, formation, proportions, of the swirl channels, the swirl chamber and the dispensing orifice, to achieve various purposes, such as easy assembly, easy molding, a particular type of spray, an extended or reduced spray duration, etc. The aim of the present invention is to produce swirl channels, a swirl chamber and a spray orifice which make it possible to obtain a spray of optimum quality for a particular type of fluid product, namely rheofluidifying fluid products. However, the spray head of the present invention can also be implemented with other types of fluid product while always obtaining a spray of admissible, or even optimum, quality.

Shear thinning refers to the fact that a fluid product "becomes more fluid" when the flow rate increases. More precisely, it refers to the fact that the dynamic viscosity decreases when the shear rate increases. It is also referred to as shear thinning or pseudo-plasticity. Shear thinning should not be confused with thixotropy, which refers to the decrease in viscosity under the effect of shear stress.

The behavior of a fluid product is shear thinning or "pseudoplastic" (old name sometimes encountered) in the shear thinning domain, located after the 1st Newtonian plateau. The viscosity of the fluid decreases (thinning) with the increase in the speed gradient. The structure of the material is oriented/deformed by shear (example: alignment of the chains of a polymer following the direction of the stress). At high shear rates (corresponding to the second Newtonian plateau), there is destructuring of the material. A structure that does not flow requires a greater effort to be destructurized. Most samples containing large objects compared to the atomic scale are shear thinning. The majority (about 90%) of substances are shear thinning: polymers, lightly filled emulsions, suspensions, shampoo, etc.

The needs of the cosmetic market require the use of increasingly viscous formulations in order to ensure their stability. This viscosity reaches a critical limit to be aspirated with conventional manual pumps. Xanthan gel or gum has been identified as a new base to solve this problem. An excellent stabilizer, this low-viscosity liquid has rheofluidifying characteristics.

To obtain a spray, it is necessary to optimize the nozzle passage sections, so that the speed of the fluid product is as high as possible to generate fine droplets at the nozzle outlet.

Thus, the present invention aims to optimize the characteristics of the swirl channels, the swirl chamber and/or the dispensing orifice to obtain a homogeneous and balanced spray, both in space and in terms of droplet sizes. Concerning the spray shape, the minimum spray angle must be greater than 30°. The droplets at a distance of 20 cm must be sufficiently distributed so as not to form drips.

To achieve this goal, the present invention provides a fluid product spray head according to claim 1. Thus, according to the invention, the dispensing orifice is cylindrical and has an axial length L3 which is less than approximately 30% of D3. It is thus possible for the dispensing orifice to be formed by an annular edge, so that L3 is zero.

Indeed, it has been noticed that the length of the swirl channels must be correlated with the diameter of the swirl chamber to obtain an optimal spray quality.

Furthermore, there is another advantageous characteristic of the invention, namely that 30% of S2 ≤ S3 ≤ 55% of S2, and preferably S3 is equal to approximately 42% of S2, so that 54% of D2 ≤ D3 ≤ 74% of D2, and preferably D3 is equal to approximately 65% of D2.

Compared to a conventional nozzle suitable for spraying alcoholic solutions, the outlet section S3 of the dispensing orifice is considerably larger. This is because xanthan gel has elastic properties: when it is constrained, it absorbs energy to "expand" when released. This is the effect that occurs when passing through the dispensing orifice of conventional nozzles (≈0.3 mm in diameter). During this "expansion", the droplets being formed stick together to form a jet.

Indeed: 0.2 mm ² ≤ S3 ≤ 0.38 mm ² , and preferably S3 is equal to approximately 0.33 mm ² , so that 0.5 mm ≤ D3 ≤ 0.7 mm, and preferably D3 is equal to approximately 0.65 mm. On the other hand: 0.5 mm ² ≤ S2 ≤ 1.13 mm ² , and preferably S2 is equal to approximately 0.785 mm ² , so that 0.8 mm ≤ D2 ≤ 1.2 mm, and preferably D2 is equal to approximately 1 mm.

According to another advantageous characteristic of the invention: L2 ≥ 80% of D2, and preferably L2 is equal to approximately 0.88 mm.

According to an advantageous embodiment, the swirl chamber comprises a truncated portion whose maximum diameter is equal to D2 and which has an axial length L23 which is between 30% and 60% of D2, and preferably approximately half of D2. Preferably, the swirl chamber also comprises a cylindrical portion at which the swirl channels open, this cylindrical portion having an axial length L22 which is equal to approximately 40% of D2. Thus, the swirl chamber defines, from upstream to downstream, first a cylindrical portion of diameter D2, then a truncated portion at which the diameter changes from D2 to D3.

Without departing from the scope of the invention, it is also possible to produce a swirl chamber that does not include a truncated cone-shaped portion. In this case, the swirl chamber consists solely of a cylindrical portion that connects to the dispensing orifice by a shoulder.

For the swirl channels, S1 ≤ 50% of S0, and preferably S1 = 33% of S0. Advantageously, S1 is equal to about 0.07 mm ² and S0 is equal to about 0.21 mm ² . This means that the channels have a more or less triangular overall configuration with a large inlet and a small outlet.

When correlating the output of the swirl channels to the swirl chamber, the following relationship is obtained: S1 ≤ 10% of S2.

According to another advantageous aspect of the invention, the channel inlet forms a rounded wall. This allows the fluid product flowing in the connecting passages to be deflected into the swirl channels by sliding along the rounded wall, so as to reduce disturbances and maintain a laminar flow as much as possible. This rounded wall is of particular advantage with shear-thinning fluid products that are sensitive to high pressure losses and disturbances. With this rounded wall, the fluid product can enter the swirl channels substantially without disturbances and without pressure losses due to the change in orientation. The fluid product in the swirl channels is then accelerated, since the cross-section S1 is smaller than the cross-section S0.

According to another advantageous aspect of the invention, the core side wall is cylindrical and the core front wall is planar. Thus, the core has no orientation, and the nozzle can be engaged around the core without paying attention to its orientation. Easier assembly is thus achieved.

The present invention thus defines a spray head having a very particular configuration, which finds a preferred use with rheofluidifying fluid products, which contain for example xanthan gum with a content of the order of 1% or less.

The spirit of the invention lies in the fact that the fluid product which circulates through the nozzle undergoes the least possible variation in pressure losses, in order to avoid too great an absorption of energy which then induces too great an expansion which disrupts the formation of the droplets which then tend to stick together to form a jet. This is particularly the case for rheofluidifying fluid products, but also for other types of fluid product. The cross-section (or diameter) ratio of the distribution orifice and the swirl chamber and/or the length of the swirl channels relative to the diameter of the swirl chamber constitute characteristics which can be considered as directly influential for the formation of a spray of optimum quality. Of course, the other characteristics of the nozzle allow for further improvement of the spray quality.

The invention will now be described in more detail with reference to the accompanying drawings, giving, as non-limiting examples, two embodiments of the invention.

• La figure 1 est une vue en coupe transversale verticale à travers une tête de distribution selon un premier mode de réalisation de l'invention,
• La figure 2 est une vue agrandie d'une partie de la figure 1,
• La figure 3 est une vue encore plus agrandie du gicleur des figures 1 et 2,
• La figure 4 est une vue en perspective de derrière montrant l'intérieur du gicleur de la figure 3,
• La figure 5 représente la veine de produit fluide à l'intérieur du gicleur,
• Les figures 6a et 6b sont des représentations en transparence de la veine de produit fluide de la figure 5 sous deux angles de vue différents, et
• La figure 7 est une vue similaire à la figure 3 pour un second mode de réalisation de l'invention.

In the figures:

• There figure 1 is a vertical cross-sectional view through a dispensing head according to a first embodiment of the invention,
• There figure 2 is an enlarged view of part of the figure 1 ,
• There figure 3 is an even larger view of the nozzle of the Figures 1 and 2 ,
• There figure 4 is a perspective view from behind showing the interior of the nozzle of the figure 3 ,
• There figure 5 represents the fluid product vein inside the nozzle,
• THE Figures 6a and 6b are transparent representations of the fluid product vein of the figure 5 from two different angles of view, and
• There figure 7 is a view similar to the figure 3 for a second embodiment of the invention.

We will first refer to the Figures 1 and 2 to generally describe the structure of a fluid product spray head according to a first embodiment of the invention. On the figure 1 , it can be seen that the dispensing head comprises a head body 1 which forms a connection sleeve 11 in which is engaged the free end of a valve stem P1 of a dispensing unit P, which may be a pump or a valve. Preferably, it is a standard pump which delivers fluid product through its valve stem P1 with a pressure of the order of 3 to 6 bars. Above the connection sleeve 11, the body 1 forms an axial space 12 which extends substantially in the extension of the valve stem P1. The body 1 then forms a supply duct 13 which extends horizontally, that is to say perpendicular to the connection sleeve 11. This supply duct 13 opens into an annular housing 14 in which extends a core 16 which defines a core side wall 16a and a core front wall 16b. Housing 14 opens laterally into body 1. This is a completely classic design for a head body in the fields of cosmetics, perfumery or even pharmacy.

The head also comprises a nozzle 2 which is forcibly engaged in the housing 14 around the core 16. The nozzle 2 has a general cup shape with a distribution wall 21 into which a spray orifice O opens. The distribution wall 21 comes into abutting contact with the core front wall 16b. The nozzle 2 also comprises a fixing side wall 22 which is engaged around the core 16. Thus, there remains in the housing 14 an annular space 15 located between the outlet of the supply channel 13 and the free end edge of the fixing side wall 22. The fixing side wall 22 can also form one or more harpoon notches 23 to ensure the fixing of the nozzle in the housing 14.

The distribution wall 21 forms upstream of the distribution orifice O a swirl chamber C which is supplied by several swirl channels T, themselves supplied by several connecting passages P, all formed between the core 16 and the nozzle 2. The connecting passages P are supplied by the annular space 15. This is a completely conventional design for a nozzle in the fields of perfumery, cosmetics or even pharmacy.

The spray head also comprises a covering band 3 which is in the form of a hood in which the core 1 is engaged. The covering band 3 comprises a side skirt 31 which is pierced with a window 32 facing the distribution wall 21 of the nozzle 2. The upper wall 30 of the covering band 3 forms a support surface for a finger of a user. Again, this is a completely conventional design for a covering band in the field of perfumery, cosmetics or even pharmacy.

We will now refer to the Figures 3 and 4 to describe in detail the fine characteristics of the nozzle 2. The distribution orifice O has a chamber outlet diameter D3 which defines a chamber outlet section S3, as well as an axial depth or length L3 measured along the X axis of the figure 3 .

The swirl chamber C is centered on the distribution orifice O along the longitudinal axis of revolution X. The swirl chamber C has a maximum chamber inlet diameter D2 defining a maximum chamber inlet section S2. The chamber outlet is formed by the distribution orifice O, such that the minimum chamber outlet diameter is equal to D3. In more detail, it can be seen that the swirl chamber C comprises a cylindrical portion C2 whose diameter is D2 and a frustoconical portion C3 arranged between the cylindrical portion C2 and the distribution orifice O, such that the maximum diameter of the cylindrical portion C3 is equal to D2 and its minimum diameter is equal to D3. The axial length or depth of the cylindrical portion C2 is L22 and the axial length or depth of the frustoconical portion C3 is L23. It can thus be said that L2 = L22 + L23.

Furthermore, we can see on the figure 4 that the nozzle 2 comprises three swirl channels T which have a generally triangular configuration. The three swirl channels T are arranged equiangularly around the swirl chamber C. Each swirl channel T comprises a channel inlet T0 defining a section channel input S0 and a channel output T1 defining a channel output section S1. Each swirl channel T also defines a length L1, as seen in the figure 4 . Each swirl channel T comprises two walls T2 and T3 which extend substantially tangentially to the swirl chamber C. As a result, the two walls T2 and T3 are not parallel, but on the contrary convergent towards the swirl chamber, where they form between them the channel outlet T1 of section S1. Consequently, S0 is greater than S1. The two other walls (not referenced) of the swirl channel T are identical, parallel and respectively formed by the front wall 16b of the core 16 and the distribution wall 21.

It may also be noted that the fixing side wall 22 internally forms three reinforcements 24 which are arranged between the three channel inlets T0. These three reinforcements 24 have the function of coming into contact with the side wall 16a of the core 16. Between the reinforcements 24, the nozzle 2 forms with the core 16 the three connecting passages P. These connecting passages P are in fluid communication with the channel inlets T0. It may be noted for this purpose that the channel inlets T0 comprise a rounded wall Ta, such that the fluid product which travels in the connecting passages P is progressively deflected along the rounded walls Ta in the respective swirl channels T. These rounded walls Ta thus form gentle ramps which respectively connect each connecting passage P to a swirl channel T. They make it possible to pass without break from an axial orientation (that of the connecting passages P) to a radial orientation (that of the swirl channels).

Sections S0, S1, S2 and S3 are more clearly visible on the Figures 5, 6a and 6b , which represent fluid veins, that is, the volume occupied by the fluid product between the core 16 and the nozzle 2. In other words, the fluid vein corresponds to the volumes of the swirl channels, the swirl chamber and the distribution orifice O.

The sections S2 and S3 extend perpendicular to the X axis and are arranged parallel to each axial end of the swirl chamber C. The outlet section S1 of the channels extends parallel to the X axis substantially tangentially to the swirl chamber C. Finally, the inlet section S0 extends parallel to the sections S2 and S3, but eccentrically relative to the swirl chamber C. It can even be said that the section S0 extends in the same plane as the section S3, since they are defined at the front wall 16b of the core 16. It can also be said that the sections S0 and S1 extend in respective planes arranged perpendicular to each other.

• S0 : section de l'entrée T0 du canal de tourbillonnement T,
• S1 : section de la sortie T1 du canal de tourbillonnement T,
• S2 : section d'entrée de la chambre de tourbillonnement C,
• S3 : section de l'orifice de distribution O correspondant à la section de sortie de la chambre de tourbillonnement C,
• D2 : diamètre d'entrée de la chambre tourbillonnement C,
• D3 : diamètre de l'orifice de distribution O correspondant au diamètre de sortie de la chambre tourbillonnement C,
• L1 : longueur du canal de tourbillonnement T,
• L2 : longueur de la chambre tourbillonnement C,
• L22 : longueur de la partie cylindrique C2 de la chambre tourbillonnement C,
• L23 : longueur de la partie tronconique C3 de la chambre tourbillonnement C,
• L3 : longueur de l'orifice de distribution O.

The different lengths, sections and diameters are now defined:

• S0: section of the inlet T0 of the swirl channel T,
• S1: section of the outlet T1 of the swirl channel T,
• S2: inlet section of the swirl chamber C,
• S3: section of the distribution orifice O corresponding to the outlet section of the swirl chamber C,
• D2: inlet diameter of the swirl chamber C,
• D3: diameter of the distribution orifice O corresponding to the outlet diameter of the swirl chamber C,
• L1: length of the swirl channel T,
• L2: length of the swirl chamber C,
• L22: length of the cylindrical part C2 of the swirl chamber C,
• L23: length of the truncated cone part C3 of the swirl chamber C,
• L3: length of the distribution orifice O.

The term "section" should be understood as the maximum section, the term "diameter" should be understood as the maximum diameter, the term "length" should be understood as the maximum length. The term "approximately" means ± 5% when it is a percentage and ± 10% when it is a magnitude.

• R1 : 30% de S2 ≤ S3 ≤ 55% de S2, et de préférence S3 est égale à environ 42% de S2, ce qui correspond en terme de diamètre à : 54% de D2 ≤ D3 ≤ 74% de D2, et de préférence D3 est égale à environ 65% de D2.
• R2 : L1 ≥ 110 % de D2, et de préférence L1 est égale à environ 150% de D2,
• R3 : S1 ≤ 50% de S0, et de préférence S1 = 33% de S0,
• R4 : L2 ≥ 80% de D2,
• R5 : 30% de D2 ≤ L23 ≤ 60% de D2, et de préférence L23 est égale à environ la moitié de D2,
• R6 : 30% de D2 ≤ L22 ≤ 50% de D2, et de préférence L22 est égale à environ 40% de D2,
• R7 : L3 < 30% de D3.
• R8 : S1 ≤ 10% de S2,

According to the invention, these different lengths, sections and diameters correspond to the following relationships R1 to R8:

• R1: 30% of S2 ≤ S3 ≤ 55% of S2, and preferably S3 is equal to approximately 42% of S2, which corresponds in terms of diameter to: 54% of D2 ≤ D3 ≤ 74% of D2, and preferably D3 is equal to approximately 65% of D2.
• R2: L1 ≥ 110% of D2, and preferably L1 is equal to approximately 150% of D2,
• R3: S1 ≤ 50% of S0, and preferably S1 = 33% of S0,
• R4: L2 ≥ 80% of D2,
• R5: 30% of D2 ≤ L23 ≤ 60% of D2, and preferably L23 is equal to approximately half of D2,
• R6: 30% of D2 ≤ L22 ≤ 50% of D2, and preferably L22 is equal to approximately 40% of D2,
• R7: L3 < 30% of D3.
• R8: S1 ≤ 10% of S2,

To achieve optimum spray quality, it has been found that the relationships R1 and R2, considered individually or cumulatively, are often predominant, without neglecting the other relationships, which also have an effect on spray quality. In some cases, R1 is more influential than R2, and in other cases, it is the opposite, and in some applications R1 and R2 are equal.

Relationship R3 turned out to be the third most influential relationship in most cases. The conjunction of the relationships R1 + R3 or R2 + R3 can therefore also be considered particularly influential on the quality of the spray.

The same is true for R4 in some applications, so that the conjunction of the relationships R1 + R4 or R2 + R4 can therefore also be considered as particularly influential on the quality of the spray.

Relations R5 and R6 correspond to a preferred embodiment which gives the best results in terms of spray quality. It is however possible to produce a swirl chamber C' without a truncated part, as can be seen in the figure 7 . In this case, the swirl chamber C' is connected to the distribution orifice by a shoulder C4.

Relation R7 implies that L3 can be zero, so that the distribution orifice O can be formed by an annular edge.

It cannot be excluded that in certain applications one or other of the relationships R1 to R9 proves to be the most influential or preponderant, so that protection could be sought for each of the 9 relationships taken individually.

• S0 = 0,21 mm²,
• S1 = 0,07 mm²,
• S2 = 0,785 mm², soit D2 = 1 mm,
• S3 = 0,33 mm², soit D3 = 0,65 mm,
• L1 = 1,46 mm,
• L2 = 0,88 mm,
• L22 = 0,38 mm,
• L23 = 0,5 mm, et
• L3 = 0.025 mm.

A nozzle particularly well suited to spraying a fluid product containing approximately 0.5% xanthan gel or gum has been produced with the following dimensions (with a tolerance of 10%):

• S0 = 0.21 mm ² ,
• S1 = 0.07 mm ² ,
• S2 = 0.785 mm ² , i.e. D2 = 1 mm,
• S3 = 0.33 mm ² , or D3 = 0.65 mm,
• L1 = 1.46 mm,
• L2 = 0.88 mm,
• L22 = 0.38 mm,
• L23 = 0.5 mm, and
• L3 = 0.025 mm.

These values also take into account the standard dimensions for the housing 14 and the core 16 of a conventional head in perfumery or cosmetics, which are generally 4.5 mm in diameter for the housing and 2.8 mm for the core.

• 0,15 mm² ≤ S0 ≤ 0,28 mm²,
• 0,05 mm² ≤ S1 ≤ 0,1 mm²,
• 0.5 mm² ≤ S2 ≤ 1.13 mm², de sorte que 0,8 mm ≤ D2 ≤ 1,2 mm,
• 0,2 mm² ≤ S3 ≤ 0.38 mm², de sorte que 0,5 mm ≤ D3 ≤ 0,7 mm,
• 1,4 mm ≤ L1 ≤ 1,8 mm,
• 0,7 mm ≤ L2 ≤ 1,1 mm,
• 0,3 mm ≤ L22 ≤ 0,5 mm,
• 0,3 mm ≤ L23 ≤ 0,6 mm, et
• 0 mm ≤ L3 ≤ 0,3 mm, sous réserve que L3 est inférieure à environ 30% de D3.

Several nozzle versions were tested to determine the ranges of values for S0, S1, S2, S3, L1, L2, L22, L23 and L3 that would produce an acceptable spray quality. The results are as follows:

• 0.15 mm ² ≤ S0 ≤ 0.28 mm ² ,
• 0.05 mm ² ≤ S1 ≤ 0.1 mm ² ,
• 0.5 mm ² ≤ S2 ≤ 1.13 mm ² , so that 0.8 mm ≤ D2 ≤ 1.2 mm,
• 0.2 mm ² ≤ S3 ≤ 0.38 mm ² , so that 0.5 mm ≤ D3 ≤ 0.7 mm,
• 1.4 mm ≤ L1 ≤ 1.8 mm,
• 0.7 mm ≤ L2 ≤ 1.1 mm,
• 0.3 mm ≤ L22 ≤ 0.5 mm,
• 0.3 mm ≤ L23 ≤ 0.6 mm, and
• 0 mm ≤ L3 ≤ 0.3 mm, provided that L3 is less than approximately 30% of D3.

Concerning D2 and D3 in particular, the following ratios of D2/D3 were tested: 1/0.4 - 1/0.5 - 1/0.6 - 1/0.65, 1/0.7. The best spray was obtained with D2/D3 = 1/0.65. The ratio 1/0.4 proved insufficient and the ratios 1/0.5, 1/0.6 and 1/0.7 proved satisfactory.

Several L2 lengths ranging from 0.4 mm to 1 mm were also tested with D2 = 1 mm: when L2 < 0.8 mm, the spray degrades. The optimal value was 0.88 mm.

It is clear that it is not possible to determine in a general and universal manner which of the characteristics S0, S1, S2 (D2), S3 (D3), L1, L2, L22, L23 and L3 and/or which of the relationships R1 to R8 is essential in relation to the others, and this in any situation, case or application, and regardless of the type of fluid product. Nevertheless, with a shear-thinning fluid product containing for example xanthan gum, with a content of less than 1%, and preferably less than 0.5%, the influence of S2/S3 and/or L1/S2 often proves to be decisive.

Claims (13)

1. A fluid spray head comprising:

   ▪ a body (1) forming a connection sleeve (11) that is adapted to receive a valve rod of a dispenser member, such as a pump or a valve, the connection sleeve (11) being connected via a feed duct (13), to a housing (14) in which there extends a core (16) that defines a core side wall (16a) and a core front wall (16b),

   ▪ a nozzle (2; 2') engaged in the housing (14) around the core (16), the nozzle (2; 2') forming a spray orifice (O) through which the fluid leaves the spray head in the form of a spray, the spray orifice (O) presenting a chamber outlet diameter D3 and a chamber outlet section S3,

   ▪ the core (16) and the nozzle (2; 2') defining between them, from upstream to downstream:

   • a plurality of connection passages (P) in fluid communication with the feed duct (13),

   • a plurality of swirl channels (T) respectively connected to the connection passages (P), each swirl channel (T) presenting a channel length L1, a channel inlet (T0) having a channel inlet section S0 and a channel outlet (T1) having a channel outlet section S1,

   • a swirl chamber (C) into which the swirl channels (T) open out, the swirl chamber (C) defining a longitudinal axis of revolution X and presenting an axial length L2, a chamber inlet diameter D2 and a chamber inlet section S2 where the swirl channels (T) open out, the spray orifice (O) forming an outlet for the swirl chamber (C),

   wherein L1 ≥ 110% of D2, and preferably L1 is equal to approximately 150% of D2,
   the spray head being characterized in that the dispenser orifice (O) is cylindrical and presents an axial length L3 that is less than approximately 30% of D3.
2. A spray head according to claim 1, wherein 30% of S2 ≤ S3 ≤ 55% of S2, and preferably S3 is equal to approximately 42% of S2, such that 54% of D2 ≤ D3 ≤ 74% of D2, and preferably D3 is equal to approximately 65% of D2.
3. A spray head according to claim 1 or claim 2, wherein 0.5 mm² ≤ S2 ≤ 1.13 mm², and preferably S2 is equal to approximately 0.785 mm², such that 0.8 mm ≤ D2 ≤ 1.2 mm, and preferably D2 is equal to approximately 1 mm.
4. A spray head according to any preceding claim, wherein 0.2 mm² ≤ S3 ≤ 0.38 mm², and preferably S3 is equal to approximately 0.33 mm², such that 0.5 mm ≤ D3 ≤ 0.7 mm, and preferably D3 is equal to approximately 0.65 mm.
5. A spray head according to any preceding claim, wherein L2 ≥ 80% of D2, and preferably L2 is equal to approximately 0.88 mm.
6. A spray head according to any preceding claim, wherein the swirl chamber (C) includes a frustoconical portion (C3) having a maximum diameter that is equal to D2 and that presents an axial length L23 that lies in the range 30% to 60% of D2, and preferably is approximately half of D2.
7. A spray head according to claim 7, wherein the swirl chamber (C) also includes a cylindrical portion (C2) into which the swirl channels (T) open out, the cylindrical portion (C2) presenting an axial length L22 that is equal to approximately 40% of D2.
8. A spray head according to any preceding claim, wherein S1 ≤ 50% of S0, and preferably S1 = 33% of S0.
9. A spray head according to any preceding claim, wherein S1 is equal to approximately 0.07 mm² and S0 is equal to approximately 0.21 mm².
10. A spray head according to any preceding claim, wherein S1 ≤ 10% of S2.
11. A spray head according to any preceding claim, wherein the channel inlet (T0) forms a rounded wall (Ta), so that the fluid passing through the connection passages (P) is deflected in progressive manner along the rounded walls (Ta) into the respective swirl channels (T).
12. A spray head according to any preceding claim, wherein the core side wall (16a) is cylindrical and the core front wall (16b) is plane.
13. The use of a spray head according to any preceding claim, so as to spray a shear thinning fluid that, by way of example contains xanthan gum.

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