BE1019920A5 - METHOD FOR THE CONTINUOUS MANUFACTURE OF POLYSTYRENE PROFILES - Google Patents

Abstract

Method for manufacturing profiles comprising polystyrene-based edges with a maximum radius of 1 mm, which profiles have a density of 50-290 g / l, which comprises the following steps: dosing of polymers comprising polystyrene to obtain of a composition, plasticizing the composition in a single extruder with a single screw to obtain a mixture, and injecting CO 2 OR N 2 under pressure, characterized in that the concentration of the gas is 0.5 and 3.0 wt. % is based on the polymers comprising the polystyrene.

Description

Method for the continuous manufacture of polystyrene profiles

Description

FIELD OF THE INVENTION

The present invention relates to a method for manufacturing solid, hollow and open profiles, in particular those which have sharp edges (such as with a maximum radius of 1 mm (e.g. between 0.5 and 1 mm)) based on polystyrene.

State of the art

For many years, profiles of polystyrene with a density greater than 290 kg / m have been produced for use in the interior or exterior decoration of houses. Profiles themselves can have different shapes and furthermore have a distinct decorative aspect. They are used, for example, to replace or imitate decorations such as that of stucco ceilings. Moreover, they find application in, for example, vehicles such as automobiles in absorbing collisions, among other things due to their relatively high density and flexibility. Polystyrene can also be used at ground level, because it absorbs virtually no water.

It is preferred that profiles have a regular structure, that is to say have fine and uniform cells. This makes it possible to use complex, high-quality decors with an acceptable surface aspect. After all, surface errors will be visible if these cells are irregular and as a result, the profiles cannot be commercialized.

EP 1,628,818 B1 discloses a method for manufacturing solid, hollow or open profiles, in particular those with sharp edges based on polystyrene. The profiles thus produced have a density of 295-344 kg / m3.

The manufacture includes the use of 0.2-0.4% by weight of CO2 as a blowing agent.

EP 0,461,298 discloses foam films (not profiles) with densities in the range of 160-330 kg / m3. However, the amount of CO2 used is very high for a given density. EP 995,273 A2 discloses a process for the manufacture of solid, hollow-or-open-profiles based on polystyrene and which have sharp edges and have a density of 160. 240 g / l. The manufacture includes use of pentane as a blowing agent.

The object of the present invention is therefore a new preparation method for manufacturing profiles which overcome one or more of the aforementioned problems and which contain a polystyrene foam with a density lower than 290 kg / m3. This foam preferably contains fine cells.

Summary of the invention

The object is achieved with a preparation method according to claim 1.

An advantage of embodiments according to the present invention is that these densities can be obtained with a low amount of gas (CO2 or N2).

This method makes it possible to realize foams based on polystyrene with a density between 50 kg / m3 and 290 kg / m3 that have a smooth surface aspect and without obvious errors.

Detailed description of the invention

According to a first embodiment, the polymer used is selected from the group consisting of polystyrene, Styrene-Ethylene-Butadiene-Styrene (SEBS), Acrylonitrile-Butadiene-Styrene (ABS), Styrene-Butadiene-Styrene (SBS), acrylonitrile-styrene (ASA styrene acrylonitrile (SAN), styrene-butadiene and acrylonitrile-styrene-acrylic acid ester and their mixtures. Various types of polystyrene can also be used, as further indicated below.

The foaming gas used may be N2 or CO2, but is preferably CO2.

The detailed description below shows details and features of the invention. ^

Description of the drawings

FIG. 1 shows a graph of density of foams obtained versus the CO2 content used in an embodiment according to the present invention (wybertjes) and those obtained according to the prior art (triangles and squares).

1. Manufacturing method 1.1. Dosage of the components: ---------------------------------------- —.- ------------- - --------------

The desired composition can be accurately realized by a dosing station of, for example, the volumetric or gravimetric type. Components of the formulation can be dosed separately. Raw materials are preferably in the form of regular granules, with, if possible and preferably the same or substantially the same size and the same or substantially the same shape, for a component. Preferably indicate that an apparent density of a raw material and / or component is in a narrow and mutually comparable range, to prevent premature demixing.

t.

1.2. Extrusion device:

The dosed components are fed to the feed of a plasticizing extruder. The extruder preferably comprises a single screw. The method according to the present invention is advantageous because it makes it possible to manufacture solid, hollow and open profiles, in particular those which have sharp edges (e.g. with a maximum radius of 1 mm) based on polystyrene, which have a density of 50- 290 g / l, with a single extruder with a single screw. The extruder may also contain two screws, which may be co-rotating or counter-rotating, and may or may not be self-cleaning. In one example, the cylinder contains more than one heating zone. In order to plasticize solid components dosed with the feed, a first part of the cylinder is heated to a high temperature in an example. Like this. it is homogenized for the whole. In one example, CO2 or N2 is injected under pressure through an injection port drilled into the cylinder, for example to improve viscosity and pressure in the cylinder. In particular in a liquid state in the case of CO2, the gas in an example will be maintained in a condensed phase. In order to obtain good homogeneity and optimum solution of the gas in a molten mixture, a mixture of the constituents and the gas is kneaded and pressurized to obtain a single phase. In order to maintain the necessary pressure in the liquefaction of the gas, zones of the cylinders then gradually become colder.

* 1.3, Cooling down - --------------------------------------------- ------------- ----------------------

An example of a device is a "Dynamic" heat exchanger "by using, for example, a configuration of long screws: a first part of the cylinder that served for plasticizing and homogenizing the solid components with the gas described in the preceding point b) a second part of the propeller, the zones of which are cooled by circulation of a heat-bearing fluid, which allows the cooling of the single-phase mixture. of this last part is particularly adapted, thereby increasing a potential cooling capacity and therefore favoring productivity.In an example, to obtain an optimum temperature at the mouth of the nozzle, a design of the cooling section of the screw will be adjusted. homogeneity in a perpendicular section at the outflow will allow an advantageous combination of n to obtain density and cell size, as described in, inter alia, claim 1.

1.4. Foam nozzle:

A stream of the mixture is, for example, passed into a forming tool consisting of a nozzle that directs the stream to the desired foam form.

It is preferably homogeneous in composition and temperature, with a phase of the plasticizing components and of the gas. A separate second phase is formed At a time when the pressure falls below a critical threshold whereby gas that has been solubilized in advance starts to saturate the mixture and gas bubbles will then arise as a result. Preferably, formation of these primary bubbles does not occur too much, otherwise a pre-foaming follows, which produces a deformed and unstable foam with a little attractive surface. A number of parameters are important in this connection, such as flow rate of the extruder, temperature of the tool, quantity of gas, viscosity of the components, shape of the workpiece, etc. All these parameters must be optimized for a foam profile to be realized.

1.5. Formation:

The foam goes in a high-temperature process from a container and its - outside to the atmosphere - expands therein-free-under-cooling-and-migration when gas in the cells takes the viscosity from cell walls to the stiffening of the cell structure. However, this process takes some time and, among other things, the shape of a foam obtained is not immediately stable. For example by passing through a calibration system, such as by means of a motorized draw table at an end of an extrusion line, dimensions of the foam can be controlled. Calibrators charge progressively a definitive shape of the foam mass.

This is optionally also regulated in temperature for a more efficient control of the shape, in particular at the beginning when the foam is still the warmest.

1.6. Pulling and cutting:

A foam can be drawn with a motorized pulling device. This can be done according to a number of profiles extruded in parallel, such as single or double. In this way a profile with a good perpendicular cut is obtained in a longitudinal direction, for example cut with a saw.

1.7. Any decoration:

It is possible to print decorative motifs or patterns onto a selected portion of the cut-out profile, such as with a printing system that continues with the profile or is pressed by a heated roller against the locally pre-heated foam or by any other method known to those skilled in the art.

1.8. Any in-line decoration:

It is possible to print decorative motifs or patterns on a selected part of the profile, such as with a printing system that continues with the profile or is pressed by a heated roller against the locally pre-heated foam or by any other method known to the skilled person.

1.9. Homogenization:

In order to make the temperature profile of a perpendicular section of the stream as flat as possible, a stream of the cooled mixture is, for example, possibly re-homogenized; -Asidoor-feed-through: a: static: mixer ^ This ~ can: the ~~ r - - ---- - divide stream into several "channels", which channels are crossed and redistributed in an example.

2. Raw materials: 2.1. Polymers:

Polystyrene is used as the base polymer. As a function of the foam profile, viscosity of a polystyrene, for example for obtaining good quality, at a pressure required for this, and desirable extrusion flow rate, can be adjusted. Different types of polystyrenes can be used alone or in admixture. For example, they can differ in viscosity and therefore in molecular weight, and in flow index ("Melt Flow Rate" MFR), measured according to ASTM 2 D1238 (measured at 200 ° C and a load of 5.0 kg from 1 to 2 g / 10 minutes ). Copolymerization with a better impact resistance and a better elasticity can also be used, such as that. of styrene and a diene monomer. Other examples are: polystyrene, styrene-ethylene-butadiene-styrene (SEBS), acrylonitrile-butadiene-styrene (ABS), styrene-butadiene-styrene (SBS), acrylonitrile-styrene (ASA), styrene-acrylonitrile (SAN), styrene -butadiene and acrylonitrile-styrene-acrylic acid ester and their mixtures, preferably with a variable flow index ("Melt Flow Rate" MFR), suitable for a foam to be obtained.

Reuse of material is possible. This material may need to be treated. It must be compatible with a set of components.

In general, the materials must be selected to form a sufficient cohesive bond with a base foam. This may concern thermoplastic, thermosetting materials.

2.2. Additions: a. Additives:

Additives can be added in the present process. This concerns, for example, lubricating compounds that facilitate extrusion. An example is a low molecular weight molecule such as C 1 -C 4 alcohols, styrene waxes, polyethylene waxes, fatty acid amides, esters of C 4 -C 20 monoalcohols, - polysiloxane compounds. polyethylene oxide waxes, etc., for example, substantially and regularly covering a flow channel of a nozzle for the purpose of forming a layer of very low coefficient of friction. to the mixture at the entrance of the extruder in the form of a polystyrene-based parent mixture. This can be done, for example, by injection with regularity and precision at a suitable location of the extrusion tool via a distribution ring and in liquid form by injection into the extruder. b. Nucleating agent:

In one example, the size of cells of a foam can be regulated by using a homogenizer, with the aim of achieving a homogeneous distribution of the cells in the foam. It can be a product that does not react chemically, such as silicon dioxide, calcium carbonate, clay, talc, etc. It can be a product that decomposes under heat, whereby a gas phase is developed. This promotes, among other things, homogeneous nucleation and the presence of finely divided gas regions. Well-known combinations are those of citric acid and sodium hydrogen carbonate, azodicarbonamide, OBSH, etc. d. Further additions:

Additives can be provided to the present foams.

Such additives are well known per se. Examples of this include: • Reinforcing fibers (cellulose, glass, etc.); • UV inhibitors or blockers; • Fire retardants (halogenated [brominated, chlorinated, fluorinated]) or non-flameproof [hydroxides, phosphates, expandable graphite, etc.]; • Fillers, such as mineral fillers; • Antioxidants; • Viscosity enhancers, such as those for a molten state (such as polymers with a high molecular weight).

2.3. Gas:

The gas used is preferably CO2. In one example, it is CO2 under pressure and at a temperature below boiling point. Under no circumstances should the CO2 be supercritical - such as at a temperature higher than 31.1 ° C. The density of this must be - ~ - - higher than the liquid used, which makes pumping safe. The CO2 is pumped below the critical temperature, for example, into cooled pipes, in order to maintain the liquid state, such as up to an injection flow control device. The flow meter can function according to the Coriolis effect, as a result of which the mass of metered gas can connect per unit of time with a difference of vibration speed generated by the passage of a fluid in a line in vibration. For the present method it is therefore extremely important that the CO2 remains in this state because the flow meter only functions for liquids. The liquid CO2 is then fed into the cylinder of the extruder via an injection opening, which is provided with an anti-return valve.

3. Implementation examples:

In the following table, obtained densities are summarized as a function of the amount of CO2 injected in the manufacture of polystyrene profiles.

The theoretical density is calculated by dividing the total weight of the whole of polymers comprising the polystyrene and the gas used, by the total volume of the whole of polymers comprising the polystyrene and the

gas used, the volume of gas used being recorded at 15 ° C and 1 atm. The density of CO2 at 15 ° C and 1 atm is 1,874 g / L

The current version of the IUPAC standard is a temperature of 0 0 C (273.15 K) and an absolute pressure of 100 kPa (0.986 atm), while NIST's version is a temperature of 20 ° C (293.15 K) and a absolute pressure of 101.325 kPa (1 atm). International standard metric conditions for natural gas and similar liquids is 15 ° C (288.15 K) and 101.325 kPa (1 atm).

The obtained profiles with 0.5; 0.61 and 0.72 wt. % CO2 are manufactured using the same tools. They are immediately comparable as a result. The profiles obtained with 2.23-2.84 wt. % CO2 has been obtained using different extrusion profiles and forms thereof. This partly explains a less good correlation between wt. % CO2 and density.

In figure 1 obtained values (wybertjes) are compared with values found in EP 1,628,818 B1 (triangles) and in EP 0,461,298 (squares).

It has surprisingly been found that for densities of 150-290 kg / m3 the concentration of CO2 in wt. % from (330 g / l of the density) / 170 g / l to (385 g / l of the density) / 200 g / l. Such values for the concentration of CO2 are significantly lower than values reported in EP 0,461,298. This is advantageous because less greenhouse gas is required to achieve a comparable density. to achieve. Moreover, these values were obtained for sharp-edged profiles with a maximum radius of 1 mm, whereas in EP 0,461,298 only foam films were produced.

Claims (10)

Process for producing solid, hollow or open profiles, which have sharp edges based on polystyrene, which profiles have a density of 50-290 g / l, comprising the following steps: dosing: - polymers containing polystyrene - at least one nucleating agent, and - optionally other additives, resulting in a formulation with specific composition, plasticizing the composition in a single extruder with a single screw to obtain a homogeneous mixture, injecting CO2. or N 2 under pressure and in the liquid state through an injection port, kneading and pressurizing the metered components and the gas, gradually cooling the mixture in a single phase to maintain the pressure necessary to solubilize the gas to a temperature above 135 ° C, the passage of the single-phase mixture into a molding tool to form a foam, the passage of the foam thus formed through a calibration system that is optionally temperature-controlled, the motorized drawing of the calibrated foam, characterized in that the concentration of the gas is 0.5 to 3.0 wt. % is based on the polymers comprising the polystyrene, and where the profiles have a density that is within 10% of the theoretical density, the theoretical density being calculated by dividing the total weight of the whole of polymers comprising the polystyrene and the gas used, by the total volume of the whole of polymers comprising the polystyrene and the gas used, the volume of the gas used being taken up at 15 ° C and 1 ahn. • 1 Method according to claim 1, characterized in that the gradual cooling to the foaming temperature is controlled to ensure a homogeneous temperature profile in a straight section perpendicular to the flow. Process according to claim 1 or 2, characterized in that the polymer used is selected from the group consisting of polystyrene, acrylonitrile-butadiene-styrene, styrene-butadiene-styrene, styrene-ethylene-butadiene-styrene and their mixtures. Process according to claim 1, 2 or 3, characterized in that various types of polystyrenes are used, which differ in viscosity, alone or in admixture with copolymers of styrene and a diene monomer. Process according to claim 4, characterized in that the copolymers are selected from the group consisting of acrylonitrile-butadiene-styrene, styrene-butadiene-styrene, styrene-ethylene-butadiene-styrene and their mixtures. Process according to one of the preceding claims, characterized in that compounds are added which facilitate the extrusion of the polystyrene mixture selected from the group consisting of esters of C 4 -C 20 monoalcohols, fatty acid amides, polyethylene waxes, polyethylene oxide waxes, styrene waxes, C2 -C4 alcohols, polysiloxane compounds and their mixtures. Method according to claim 6, characterized in that the compounds facilitating the extrusion of the polystyrene mixture are injected with regularity and precision at a suitable location of an extrusion tool through a distribution ring, to exclusively and regularly feed the flow channel of a nozzle to dress. A method according to any one of the preceding claims, wherein the density is from 200-290 g / l, preferably from 200-250 g / l. The method of claim 8, wherein the concentration of the CO2 in wt. % from

is. Method according to one of the preceding claims, characterized in that the sharp edges have a maximum radius of 1 mm.