AU2011264077B2 - Enhanced process for the production of expanded PVC and plastic materials based on expanded PVC obtained therewith - Google Patents

Description

ENHANCED PROCESS FOR THE PRODUCTION OF EXPANDED PVC AND PLASTIC MATERIALS BASED ON EXPANDED PVC OBTAINED THEREWITH

The present invention relates to an enhanced process for the production of expanded PVC, in particular IPN (Inter Penetrating Network) polymeric foams consisting of polyamide, polyimide, polyvinylchloride , polyisocyanurate and polyurea .

The invention is also extended to the plastic materi- als based on expanded PVC obtained by means of this process .

The field of the invention is that of processes used for preparing expanded PVC which comprise heating a starting mixture in a mould having a constant volume, closed by a lid, and the subsequent expansion of the embryo obtained.

In particular, in the field of the production of IPN polymeric foams consisting of polyamide-polyimide- polyvinylchloride-polyisocyanurate-polyurea (see descrip- tion of the IPN concept in "Interpenetrating Polymer Networks" , D. Klempner, L.H. Sperling, L.A. Utracki; vol. 239; American Chemical Society; Ed. 1994) , the initial mixture of polymers, surfactants, chemical blowing agents, isocyanates, etc., is introduced into the mould. Once the latter has been closed by means of a suitable lid, the mixture is heated, thus causing the generation of blowing gas, the gelation of the polymer and the desired cross-linking reactions, with the incorporation of the gas inside the molecules of cross-linked IPN thus obtained. This part of the process is, in particular, effected in a closed mould and at a constant reaction volume, the pressure inside the mould being generated by the formation of gas and by the thermal expansion.

The known art described herein, however, has the drawback that, due to the expansion induced by the formation of blowing gas and by the heating of the plastic material, the mass of molten polymer and reagents tends to expand, in contrast with the action exerted by the lid which closes the mould. This compressed molten mass therefore tends to expand, leaking through the closed areas of the lid on the mould. Consequently, in traditional production processes which follow this moulding technique, considerable quantities of waste material are formed, which are responsible for an undesired increase in the general production costs, in addition to maintenance problems relating to the machine and environmental impact .

In addition to these disadvantages, there is also the degradation of the microcellular structure of the fin- ished product, particularly in correspondence with the leakage of plastic material from the mould.

A further drawback of the present methods for the production of expanded PVC lies in the high amounts of chemical blowing agents used, which, in addition to being harmful for the environment, are also expensive due to the complexity of the production, transportation and storage of these products.

The publication EP 2039496 Al discloses a process for the production of rubber, using microspheres suitable for being crushed under the action of the volume increase of the starting mixture inside the vulcanization mould. According to this known technique, which does not relate to the field of expanded plastic materials, the moulded product incorporates the microspheres in their final and definitive crushed or collapsed state, which is that of the final product based on rubber.

A main objective of the present invention is therefore to provide a new process for the production of expanded PVC, in particular IPN polymeric foams wherein, in addition to avoiding losses of molten product during the moulding process, an expanded PVC, having the desired density value, can be obtained, even with much lower quantities of chemical blowing agents than those used in the known art .

A further objective of the invention is to provide a process of the type mentioned above, which is capable of considerably reducing product waste at the outlet of the moulding phase, thus minimizing both the overall plant management costs and the environmental impact of the pro- duction of plastic material.

The invention also has the objective of contributing to enhancing the quality of the final product, by avoiding strong degradation of the microcellular structure of plastic material in correspondence with the mould closing areas.

These and other objectives are achieved with the process, the polymeric mixture and expanded plastic material of claims 1, 7 and 8, respectively. Preferred embodiments of the inventions are indicated in the remain- ing claims.

With respect to the known technology for the production of expanded plastic materials, the process of the invention not only avoids the loss of molten product during the moulding process, but also allows an expanded PVC having the desired density value to be obtained, even using a much lower quantity of chemical blowing agents with respect to those used in current processes of this type.

In particular, thanks to the significant reduction in the amount of chemical blowing agents used in the process of the invention, the latter not only reduces the envi- ronmental damage caused by these products, but also the production costs of the expanded plastic material on which the production, transportation and storage costs of the chemical blowing agents have a considerable impact.

A further advantage of the invention is represented by the enhanced quality of the plastic material obtained due to the substantial absence of degradation in the mi- crocellular structure, also in that formed in correspondence with the closing of the mould.

The process of the invention also offers the advantage that, thanks to the volumetric compensation induced by the temporary contraction of the microparticles inside the compressed polymer mass, the process can be carried out at pressures lower than the normal values used with the mould, with consequent advantages also with respect to the operating conditions of the same.

Furthermore, thanks to the substantial absence of losses of plastic material from the mould, both the recovery and disposal costs of the waste products and the effect of the latter on the environment, are greatly reduced .

These and other objectives, advantages and characteristics are evident from the following description of a preferred embodiment of the process and the expanded plastic material of the invention, shown, for illustra- tive and non-limiting purposes, in the figures of the enclosed drawings .

In which:

- figure 1 schematically illustrates the structure of a polymeric IPN foam;

- figure 2 illustrates a scheme of a processing example in a closed mould, of an expanded plastic material according to the known art ;

- figure 3 illustrates the detail of an example of a microparticle of compressible material as used in the process of the invention;

- figure 4 illustrates a schematic view of the process of the invention.

The polymeric IPN foam produced with the process of the invention, as shown in figure 1 above, is obtained by the penetration of the linear chains C of PVC with a reticular structure R of polyamide, polyimide, polyiso- cyanurate and polyurea .

According to the process of the known art illustrated in figure 2, a mass of starting polymeric mixture 13a (PVC resin, anhydride, isocyanates, chemical blowing agents, surfactants and catalyst) is injected into a mould 10, closed by a lid 11 activated by a press plate 12, said mixture, when subjected to heating by the heating plates 14, 15 and compressed as a result of the con- trast action exerted by the plate 12 against the expansion caused by the process reactions (in particular by the formation of microcells 20 of blowing gas) tends to expand energetically, until it overcomes the closing ac- tion of the lid 11 on the body of the mould 10. As a consequence, part of the polymeric material forming the mass 13b of moulded product, tends to exit in correspondence with the closing rebates of the lid 11 on the body of the mould 10 (arrows F of figure 2) .

The final product 13c, in turn, has the density conferred by the sole microcells 20 of blowing gas, which must consequently be present in the mass 13a of the starting mixture, in the high dosages necessary for this purpose .

According to the invention, in order to avoid the described loss of polymeric mixture from the mould 10, and to significantly reduce the quantities of chemical blowing agents used for generating the mentioned microcells of gas 20 inside the mass of expanded polymer, hollow mi- croparticles 16 are added to the starting mixture, together with material elastically or reversibly compressible under the process conditions. In the example illustrated in figure 3, these microparticles consist of microspheres formed by an outer casing 17 of material elas- tically deformable under the process conditions, prefera- bly polyacrylonitrile (PAN) or polymethacrylonitrile (PMAN) , inside which a cavity 19 filled with a gas 18 (preferably isopentane) , is defined. The use of the described elastically deformable materials, forming the mi- croparticles 16 has the particular advantage of making them reversibly compressible, so as to allow them to return to their initial configuration, once the hot moulding process of the starting polymeric mixture has been completed. In this way, the microparticles 16 help to in- crease, in their expanded or highest volume conformation, inside the expanded plastic material, both the density and the mechanical characteristics of the final manufactured product .

Thanks to the elastically deformable nature of the outer casing 17 and to the intrinsic compressibility of the gas 18 collected in the cavity 19, of the microparticles 16, the above microparticles 16 can be temporarily contracted, under the action of an external pressure, from the initial form A having larger dimensions to the form B with smaller dimensions, with the recovery of their initial configuration A by heating the moulded IPN mass under humidity, once extracted from the mould 10 (fig. 3) . In particular the mentioned microparticles 16 are in the form of microspheres preferably having a di- ameter of 35-55 μπι even if, for the applications of the invention, microspheres having a diameter of 10-110 μιη can be advantageously used.

As better illustrated in figure 4, the initial mass 13 of polymeric mixture is introduced or cast into the mould together with the compressible microparticles, in their initial configuration 16A having a larger volume. Said microparticles are, in particular, homogeneously dispersed inside the mentioned mass 13 of starting polymeric mixture, together with the other components of the same.

Starting from this initial configuration, the mass 13 injected inside the mould 10, in an environment having a constant volume by closing the lid 11, is then subjected to heating thus creating the gas microcells 20, obtained by decomposition of the chemical blowing agents, and also by means of the gelation and cross-linking reactions of the IPN polymer.

The expansion, thus effected on the mass 13, in contrast with the closing action of the lid 11 on the mould 10 having a constant volume, causes an increase in the pressure which causes the temporary contraction of the above microparticles 16 dispersed inside the initial mass 13 of figure 4.

Thanks to the contraction phenomenon of the micropar- tides 16 described above, in response to the increase in pressure¹ in the polymeric mass 13 collected in the mould 10 having a constant volume, these turn from their initial configuration 16A having a larger volume, to that 16B with a reduced volume, the latter referring to the polymer mass 13b (also called "embryo 13b") extracted from the mould 10.

At this point the embryo 13b is heated under humidity conditions (in the presence of water vapour, inside an oven 21, or by immersion in a boiling water bath), until a mass 13c having the desired density of the IPN polymer is obtained, by recovering the initial volume A of the microparticles 16, in combination with the chemical expansion due to the formation of the microcells 20 of blowing gas (figure 4) .

According to a preferred embodiment, a starting mixture for the production of IPN polymeric foams of the invention, consists of (the percentages are by weight) :

PVC 35-60%

Anhydride 1-20%

Isocyanates 20-50%

Chemical blowing agents 0.5-7%

Surfactant 0.08-0.8%

Catalyst 0.02-0.2% wherein 0.05-0.5% of microspheres 16 are added.

As a comparison with the known art, a starting mix ture having the following composition:

PVC 45%

Anhydride 9%

Isocyanates 45%

Surfactant 0.5%

Catalyst 0.13%

is treated once with only 5.5% of blowing agents (known art of figure 2) and a second time with 2.5% of chemical blowing agents, in the presence of 0.2% of microspheres (process of the invention, figure 4) . In both cases an expanded IPN polymeric foam 13c was obtained, having a density of 45 kg/m³. The process of the invention consequently allowed an expanded material to be obtained (13c of figure 4) having the desired density degree, with the use of chemical blowing agents in quantities which are a half of those used in current methods (expanded product 13c of figure 2) , maintaining however the mechanical properties of the final product unchanged, with a more homogeneous distribution of the same inside the mass of the manufactured product.

Claims (10)

1. A process for the production of expanded PVC of the type which comprises heating a mass of polymeric mixture (13) inside a closed mould, characterized in that it comprises :

(a) control of the expansion of said mass (13) due to the hot moulding process in the environment having a constant volume defined by the mentioned closed mould (10) , said control being obtained by the presence, in the mentioned mass of polymeric mixture (13) , of microparticles (16) of compressible material, suitable for being contracted, under the action of the pressure generated by the formation and expansion of microcells (20) of blowing gas in the same mass (13) , from an initial form (A) having a larger volume, to a form (B) having a smaller volume ; and

(b) expansion of the mentioned microparticles (16) contained in the mass of moulded expanded material, from their configuration (B) to the initial configuration (A) having a larger volume, the density of said expanded material thus obtained being determined by the contemporary presence, in the mass (13c) of the latter, of both micro- cells (20) of blowing gas and the mentioned microparti- cles (16) in their configuration (A) having a greater ume .

2. The process according to claim 1, characterized in that said expansion phase (b) is carried out under humid conditions .

3. The process according to claim 1, characterized in that said microparticles (16) are in the form of microspheres, consisting of an outer casing (17) of deformable plastic material, inside which a cavity (19) containing a gas (18) is defined.

4. The process according to claim 3, characterized in that the outer casing (17) of said microparticles (16) consists of polyacrylonitrile or polymethacrylonitrile , said cavities (19) being filled with isopentane.

5. The process according to claim 3 or 4 , characterized in that said microspheres have a diameter of 10-110 μπι.

6. The process according to one or more of the previous claims, characterized in that said polymeric mixture is a mixture for the production of IPN polymeric foams having the following starting composition (w %) :

PVC 35-60%

Anhydride 1-20%

Isocyanates 20-50%

Blowing agents 0.5-7%

Surfactant 0.08-0.8%

Catalyst 0.02-0.2% in the presence of 0.05-0.5% of microspheres (16).

7. A starting polymeric mixture for the production of expanded PVC inside a closed and heated mould, characterized in that it comprises microparticles (16) of cora- pressible material, as used in the process according to one or more of the previous claims 1 to 6.

8. Expanded plastic material based on PVC, characterized in that it is obtained by means of the process according to one or more of the claims from 1 to 6 and with the polymeric mixture of claim 7.

9. A product made of expanded PVC, characterized in that it is produced using the plastic material of claim 8.

10. The product according to claim 9, characterized in that said expanded plastic material consists of IPN polymeric foams, containing said microparticles (16) in their state (A) having a larger volume .