BE1026110B1 - PRODUCTION OF HOLLOW BODIES MONO OR MULTICOLORES AND TRANSPARENT BY ROTOMOULAGE - Google Patents

Abstract

A method of manufacturing hollow articles having both transparent areas and mono or multicolored areas, obtained by rotational molding in a single step.

Description

PRODUCTION OF MONO OR MULTICOLORED AND TRANSPARENT _HOLLOW BODIES§ _E2O 18/0033

BY ROTOMOLDING

FIELD OF THE INVENTION

The present invention relates to a process for the production of mono or multicolored hollow articles having both transparent zones and translucent or transparent colored zones, these articles being obtained by rotational molding from thermoplastic polymers.

In particular, the present invention relates to a process for the production of mono or multicolored hollow articles, in a single step of rotational molding of a mixture comprising (i) a polyethylene made transparent when it is rotomolded with (ii) a polymer or more colored polymers; however, it is not beyond the scope of the process of the invention if this second polymer is not colored and remains transparent or translucent; these polymers are chosen in particular from polylactide (PLA), polypropylene and in the latter case preferably random propylene-ethylene copolymers or else amorphous and transparent thermoplastics such as polycarbonate, polyamides, polystyrene.

I read in particular the process of the invention relates to hollow mono or multicolored illuminated articles obtained by rotational molding and provided with a lighting system installed inside the object.

The rotational molding process, also called rotational molding, has been known for a very long time and allows the production of hollow plastic articles. This process involves placing the plastic in a mold and rotating the mold so that all the points on the internal surface of the mold are brought into contact with the molten plastic on the internal surface of the mold. Thereafter a cooling step allows the solidification of the part which is then removed from the mold.

Rotational molding is appreciated because it avoids the induction in the plastic of tensions like those that can be found in injection molded parts.

Indeed, the plastic does not undergo kneading or compaction as far as in an extruder or in an injection device. Rotational molding allows the production of large hollow articles and / or design and complex shapes. It is also known that the most widely used convenience thermoplastic polymer in rotational molding is polyethylene; unfortunately this polymer when it is rotomolded, does not retain any property of transparency and therefore of no use for the desired objective.

Q / HHQQ

At the present time when one wants to obtain multicolored hollow articles by rotational molding, one can use PE, but without obtaining transparency because the PE is translucent which is practically without effect when one uses these hollow objects like luminaries .

When you want to use the hollow object as a luminaire and you have used PE, you are not only confronted with the loss of luminosity due to the translucency but you are also confronted with the opalescence which gives this milky appearance to the PE luminaire.

In order to give a colored appearance to hollow objects, it has already been imagined to use at least two polymers, one of which is a colored polyester as described in WO92 / 13921 or also in EP215322 but the same problem of transparency arises in addition completely random and uncontrolled distribution of colored polymers.

The use of the powder combination of a polymer with pellets of the same polymer, or respectively a polymer, has also been described in the case of a colored appearance, in particular in US Pat. No. 4,238,537 or in US Pat. rubbery synthetic like EVA, or more simply LLDPE, however with powder / pellets ratio <1 and desired objectives such as maintaining tensile strength or even to improve the rebound of the objects thus prepared.

It was also noted that in US Pat. No. 4,533,696, it was recommended to mix a powder whose particle size is between 50 μm and 250 μm with pellets, colored or not, whose average size is 1 mm and this in order to avoid performing 2 stages of rotational molding.

Also, in the field of luminaires obtained by rotational molding of PE and if one wishes more transparency, more brightness, more brilliance there is not yet in the state of the art a simple and valid solution to this problem. .

There is therefore a need to produce articles by rotational molding which meet the criteria of gloss, coloring, transparency and luminosity.

An object of the present invention is a method of manufacturing hollow mono or multi-colored objects while presenting areas of transparency, in a single rotational molding step, and without migration from one area to the other.

Another object of the present invention is to provide a one-step rotational molding process for obtaining mono or multicolored hollow objects while preserving transparent parts and transparent or translucent parts colored when they are rotomoulded. the invention is to provide a method for obtaining fixtures to be placed or suspended from these hollow bodies which are both transparent and mono or multi-colored.

At least one of the above objects is achieved with the present invention

BE2018 / 0033

DESCRIPTION

The Applicant has now found that it was possible, in a single rotational molding step, to manufacture a mono or multicolored hollow body comprising transparent areas and transparent or translucent colored areas by introducing into the mold subjected to rotational molding a mixture of polymers at least one of which is natural and used in powder form while the other polymer (s), which can be colored, are necessarily used in the form of pellets, this mixture being used so that the weight ratio between the powder of the natural coloring polymer and the pellets of the colored polymer (s) either> 1, and preferably> 1.5 depending on the desired color range.

The Applicant has also found that to achieve the objectives of the process of the invention, it is necessary that the size ratio between the pellets and the powder is such that the ratio between the average length of the pellets and the average size of the particles of the powder should be 5 or more.

The invention relates to a method for manufacturing transparent, mono or multicolored hollow articles, optionally provided with an electric lighting device placed inside the hollow article; these hollow articles are prepared from a polymer chosen from PLA, Polypropylene, preferably including propylene-ethylene copolymers with random distribution of ethylene.

The present invention relates to a process for manufacturing multicolored hollow articles having transparency zones from a mixture of powder and pellets of polymers chosen from PLA, PP, preferably statistical propyleneethylene copolymers or mixtures thereof, consisting in a single rotational molding step and comprising the following sequence:

Mix (i) a polymer (A) taken in the form of a powder, of natural coloring, chosen from PLA, PP, including preferably propyleneethylene random copolymers, said powder having particles of dimensions between 200 μm and 600 μm, with (ii ) one or more mono or multicolored polymers (B), identical or different from the first, taken in the form of pellets of dimensions between 2 and 6 mm, so that the polymer (A) / polymer (B) weight ratio is> 1 and preferably greater than 1.5

- Introduce this mixture of powder and pellets into a rotational molding mold

Submit this mixture to a rotational molding which includes heating to a temperature ^{E2018 / 0033} between 150 ° C and 240 ° C depending on the polymer treated.

Cool the mold and or the object obtained in a relatively short time between min and several tens of minutes

- Demou 1st 1 ’obj and

Among the polymers which can be used in the process of the invention as polymer (A), there is the PLA, which is a lactic acid polymer, and which in order to obtain transparency is quenched during its crystallization;

It generally has a molecular weight of between 70,000 and 150,000

The process for producing PLA is well known to those skilled in the art and is described in particular in US patents 5053522 and US5117008.

Other suitable examples of polymer (A) that may also be mentioned are polypropylene and in particular random propylene-ethylene copolymers.

The polymers used must be additive, either directly at the outlet of the polymerization reactor during the extrusion phase or by compounding of the pellets obtained during the extrusion, with an antioxidant formulation allowing them not to undergo degradation during of their high temperature processing.

If these objects are likely to be exposed outside, they must also contain an anti-UV formulation in order to avoid their degradation. These formulations and their quantity are well known to those skilled in the art.

The polymer (A) is obtained in the form of pellets by extrusion at the outlet of the polymerization reactor or by compounding, and must be ground in the form of powder having the adequate size comprised between 100 and 100 pm, preferably between 200 and 600 pm and more preferably between 300 and 500pm.

The grinding can be carried out in the form of cryogenic grinding or by any other type of grinding of pellets compatible with the properties of the PLA itself such as its low Tg (of the order of 55 ° C.) when the latter is used or compatible. with the properties of easily oxidizable PP when heated) when it is used.

The polymers (B) can be of the same nature as the polymers (A) with the appropriate additives identical or different from those used for the polymer (A).

For example in the case of Polypropylenes, they can be added with a certain amount of EPR (Ethylene-Propylene Rubber) phase in order to improve their impact resistance; this EPR phase is chosen from materials which do not disturb the transparency of the pellets colored with transparent dyes; they can also contain natural fibers (flax, hemp, ...) or mineral fibers (glass fibers, base, ...) which will strengthen their

BE2018 / 0033 structures.

As regards the dyes added to the pellets, they can be solid pigments which disturb the transparency of the pellets or additive transparent dyes in liquid form or in the form of masterbatch during the manufacture of the colored pellets. With transparent colored pellets, the addition of the various additives (anti-oxidant, anti-UV, etc.) must be optimized to keep a certain transparency to the colored pellets during rotational molding in order to obtain a multicolored object having transparent zones. resulting from the PP or PLA powder and the transparent colored zones originating from the pellets of the polymer (B) used.

It is also possible to obtain a colored polymer as described in US Pat. No. 3,157,663 according to which a polyalkyleneoxy group is coupled with a chromophore group. This dye is then introduced into a thermoplastic polymer chosen from polyolefins such as PE, PP, preferably including random propylene-ethylene copolymers or also polyesters such as PLA. This colored pigment can be incorporated into the thermoplastic resin by any of the methods known to those skilled in the art, but the polymer pellets (B) can also be directly colored by a known method.

Polypropylenes and random PP-PE copolymers have Fluidity Indices (MFR) (230 ° C / 2.16 kg) between 7 and 30 g / 10 'and preferably between 10 and 15 g / 10', density included between 0.900 g / cm3 and 0.905 g / cm3; the melting points will be above 130 ° C.

Polypropylenes and random PP-PE copolymers can be produced by Ziegler-Natta catalysis or by metallocene catalysis. The latter is preferred because it brings more transparency to rotomolded objects.

It is also well known that to maintain their transparency, the PP-PE random copolymers must contain a clarifying agent, which will be the case for the PP-PE random copolymers used in the process of the present invention.

The PLA will have a melt index (MFR 190 ° C / 2.16 kg) between 10 and 20 g / 10 ’, a density around 1.24 g / cm3 and a melting point close to 180 ° C.

According to the process of the invention, the natural polymer (A) must be in the form of a powder, the particles of which have a size of between 100 and 100 μm, preferably between 200 and 600 μm and more preferably between 300 and 500 μm; the polymer (B) whether or not colored must be in the form of pellets; these have dimensions

ΒΕ2Ω18 / ΩΩ33 averages between 1 and 10mm, preferably between 2 and 6mm for the length for about 1 to 6mm and preferably from 3 to 4mm in diameter.

In addition, the Applicant has now unexpectedly found that, in order to obtain better properties such as the glassy appearance or the gloss, the ratio between the average length of the pellets and the average size of the powder particles must be greater than or equal to

5.

According to the process of the invention, the polymer powder (A) of natural coloring is introduced into the mold and then the pellets of polymers (B) colored or not; the powder and the pellets can also be mixed beforehand before their introduction into the rotational molding mold.

The rotation involved in rotational molding will induce segregation between the powder and the pellets, in particular due to the difference in fluidity, the powder being found first on the walls of the mold, while the pellets will be distributed randomly on the wall of this same mold while obscuring or reducing the transparency of this part.

During the rotation of the mold, the temperature is brought to a value between 150 and 240 ° C. for a period of 30 to 45 minutes.

When the powder / pellets mixture is introduced into the mold and the latter is rotated, by difference in fluidity the powder will be placed first on the walls of the mold and the pellets will then be distributed in the already fixed powder and during melting on the mold wall, the thin layer of powder initially deposited on the wall will give a shiny and transparent appearance to the final object; through this transparent layer we will see the colored pellets melted and distributed in the powder layer.

Therefore if you want there to be transparent areas which are not disturbed by the presence of molten colored pellets at the level of the final object, you must adjust the amount of powder relative to that of the pellets of such so that it is greater than that of the quantity of colored pellets in a mass ratio greater than 1, and preferably> 1.2. If we want to further increase the surface area of the transparent areas of the final object, we must further increase this weight ratio powder / colored pellets and a ratio of 1.5 is recommended. Then begins the rotation of the mold while bringing the temperature thereof to a temperature between 150 and 240 ° C, preferably between 180 and 240 ° C.

This temperature can vary depending on the polymer used; thus when PLA is used as Polymer (A) the temperature of the mold will be brought to a temperature less than or equal to 225 ° C. while if polypropylene or clarified statistical PP-PE copolymers are used, the temperature at l the interior of the mold will be equal to or greater than 210 ° C. It is understood that the temperatures indicated above may vary depending on whether ^ 2018/0033 whether or not a slight overpressure (<or = at 1 bar) is imposed in the mold.

The mold is then allowed to cool before unmolding the object. In the case where the polymer (A) is PLA, the cooling must be very rapid to obtain good transparency of the object and is generally between 1 minute and 10 minutes to go from 220 ° C to 50 ° C. The transparency of the PP is also influenced by the speed of cooling.

According to the process of the invention, migration of the colored areas towards the transparent areas is avoided, which is probably due to the fact that the pellets are colored in the mass by extrusion of the solid pigment and the pellets; the pigment is introduced in the form of a masterbatch during the compounding phase. there is no migration from a colored area to a transparent area because the coloring is given by the colored pellets which are melted during rotational molding and the transparency by grains of powder which are also melted during the rotational molding process; there is no migration from one area to the other.

The articles thus obtained by rotational molding are hollow hollow parts such as, for example, tanks, bins, flasks, boxes, truncated-conical objects, boxes or even tanks and the like.

The great advantage of the process of the present invention is that one does not have to perform several successive rotational molding to obtain the multicolored objects.

The process of the present invention is also described using the examples below, but without limiting its scope.

Example 1

A mixture of a random copolymer of natural coloring (Lumicene TRC-0023 from TOTAL) in powder form, the average particle size of which is 400 μm, was introduced into a mold, intended for producing objects by rotational molding. TRC-0023 but taken this time in the form of colored pellets whose diameter is 4 mm and the length of between 2 and 4 mm.,

The weight ratio between the powder and the pellets is 1.6 while the ratio between the average length of the pellets and the average size of the powder particles is 7.5. This mixture was subjected to a rotational molding process according to the conditions. following operations:

- Mold heating up to 230 ° C in 17 minutes

Maintaining the maximum temperature for 6 minutes

Cooling the mold to a temperature between 25 and 80 ° C in 20 minutes

BE2018 / 0033

- Total cycle time: 43 minutes

The rotomolded object is a multicolored object in the shape of a football

Example 2

Same thing with ratio 1.67. We introduced into a mold, intended to produce objects by rotational molding, a mixture of a polypropylene of natural coloring (Lumicene TRC0023 of TOTAL) in the form of powder whose average particle size is 303pm with the same resin TR.C-0023 but taken this time in the form of colored pellets whose diameter is 3.8 mm and the length between 2 and 4 mm.,

The weight ratio of the powder to the pellets is 1.67 while the ratio of the average length of the pellets to the average size of the powder particles is 9.9 This mixture was subjected to a rotational molding process according to the conditions following operations:

Mold heating to 238 ° C in 19 minutes

Maintaining the maximum temperature for 5 minutes

- Cooling of the mold to a temperature between 25 and 80 ° C in 18 minutes

- Total cycle time: 42 minutes

The rotational molded object is a multicolored object in the shape of a soccer ball into which a light device has been inserted.

Example 3 (comparative)

A weight ratio of 1.67 is also used, as in Example 2, with the natural statistical copolymer (Lumicene TRC-0023 from TOTAL) in powder form, the average size of which is 303 μm and this same copolymer TRC-0023 in form colored pellets with an average diameter of 3.9 mm and an average length of 3 mm.

The ratio of the average length of the pellets to the average size of the powder particles is 9.9.

This mixture was subjected to a rotational molding process according to the following operating conditions:

- Mold heating to 203 ° C in 14 minutes including a 5-minute tray at maximum temperature.

Cooling time: 20 minutes

BE2018 / 0033

- Total cycle time: 34 minutes

The rotomolded object is a multicolored object with transparent areas but with a significant amount of air bubbles.

Example 4

A mixture comprising (i) a PLA having a low content of D isomer (Ingeo 3100 HP from Nature Works) has been introduced into a spherical mold capable of giving rise to objects in the shape of a football. having an MI2 of 24g / 10 minutes (at 210 ° C; 2.16kg) and taken in the form of powder obtained by cryogenic grinding and having particles whose average size is 350 μm and (ii) colored pellets of the same PLA (Ingeo 3100 HP) having the following dimensions: length between 2 and 4mm; diameter 3mm. The weight ratio between the powder and the pellets is 1.7 while the ratio between the average length of the pellets and the average size of the powder particles is 8.

This mixture was subjected to a rotational molding process according to the following operating conditions:

Heating the mold to 222 ° C in 9 minutes and maintaining this maximum temperature for 4 minutes

- Rotation ratio is 2.5

- Cooling of the mold from 222 ° C to 55 ° C in 5 minutes

The rotational molded object is a multi-colored object with a shiny surface and transparent areas.

Claims (9)

BE2018 / 0033 1. A method of manufacturing hollow articles having both transparent zones and transparent or translucent mono or multicolored zones, characterized in that it consists of a single rotational molding step comprising the following sequence: o Mix (i) a polymer, (A) in the form of a powder, of natural coloring, chosen from PLA, PP, preferably including random propylene-ethylene copolymers, the powder having particles of dimensions between 200 μm and 600 μm with ( il) a second mono or multicolored colored polymer (B), identical or different from the first, taken in the form of pellets of dimensions between 2 and 6 mm, so that the polymer weight ratio (A) Zpolymer (B) is> 1 and preferably greater than 1.5 o Introduce this mixture of powder and pellets into a rotational molding mold o Submit this mixture to a rotational molding which includes heating to a temperature between 150 ° C to 240 ° C. o Cool the mold and or the object obtained in a relatively short time between 1 minute and a few tens of minutes. o Unmold the object 2. Method according to claim 1 characterized in that the ratio between the average length of the pellets and the average size of the particles is equal to or greater than 5 3. Method according to claims 1 and 2 characterized in that the polymer weight ratio (A) Z polymer (B) is greater than 1.5 4. Method according to any one of claims 1 to 3 characterized in that the rotational molding temperature is between 150 and 225 ° C when the polymer (A) is PLzA 5. Method according to any one of claims 1 to 3 characterized in that the rotational molding temperature is between 210 and 240 ° C when the polymer (A) is polypropylene or the clarified statistical PP-PE copolymers. 6. Multicolored hollow article obtained in a single rotational molding step according to the method described in any one of claims 1 to 5. 7. Multicolored hollow article according to claim 6, characterized in that it is spherical in shape _t RF9Û1 ft / ΠΠ ^ 8. multicolor hollow article according to claim 6 characterized in that it is ⁵ .muni an internal lighting device. 9. Multicolored hollow object provided with an internal lighting device and presented in the form of a soccer ball, obtained according to the method described in one 5 any of claims 1 to 8.