Process for molding a thermoplastic part

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DESCRIPTION

Procedure for molding a thermoplastic part.

The invention relates to a process for producing a thermoplastic molding, comprising the following steps:

a) dispersing reinforcing fibers in a melt of a polyolefin or in a polycondensation polymer.

b) injecting the polymer composition thus obtained into a closed mold by means of an extruder or an injection molding machine.

Such a procedure is known from JP-A-5-17631. JP-A-5-17631 describes a process for injection molding a fiber reinforced polypropylene flat plate.

JP-A-7-16933 describes a method according to the preamble of the method of claim 1.

A drawback of the method described in JP-A-5-17631 is that the fiber-reinforced polypropylene described therein gives rise to a specific modulus and a specific mechanical strength that are lower than desired.

The object of the invention is to eliminate this drawback.

This object is achieved by the method of claim 1.

The molding surprisingly expands during the opening of the mold and a thermoplastic molding with a porous center is obtained. The expanded molded part, obtained by the process according to claim 1, has better specific modulus and mechanical strength than the known molded part.

The term "partially opening the mold" in this specification is understood to refer to the opening of the mold over a certain length of travel until the distance between both halves of the mold is equal to the desired thickness of the molding.

In the case of molded parts, the requirements regarding rigidity and mechanical strength determine the thickness of the molded part and therefore also its price. So-called specific strength and modulus are used to facilitate comparison of the strength and modulus of materials for molded parts. They are indicator numbers, which are measures of the resistance offered by a molded part to deformation and failure, respectively, under the influence of a bending load per unit density. Specific modulus and strength are especially used to compare the modulus and strength of materials having different densities, when looking for the lightest material that offers the highest stiffness or strength for a particular shape. A detailed description of these indicator numbers is presented in "Materials Selector: guidelines for minimum weight design", Chapman & Hall, London.

Preferably, a converging nozzle is used in the process according to the invention, because this surprisingly causes better expansion of the molded part during the opening of the mold. The use of a convergent nozzle is known from WO-A-94/11177, but here, a convergent nozzle is used to obtain the orientation of the plastic and / or the fiber reinforcement in the molding, as a result of the which, it can possess superior rigidity and mechanical resistance in a particular direction. WO-A-94/11177 does not mention anywhere the fact that a converging nozzle would lead to expansion of the molded part, while the process according to the invention causes virtually no or no anisotropy in the molded part.

A converging nozzle can be obtained with a nozzle ending in a conical shape, but also, for example, by placing a breaker plate (a plate with a number of holes) in front of the nozzle.

The merits of the invention become very clear if the process according to the invention is used for the production of plate-shaped moldings.

Such a molded part has two surfaces of the plate, which in this description it is understood that the two surfaces are usually almost parallel, that are opposite each other, and whose length and width are greater than the thickness of the molded part that is between them. surfaces. The plate surfaces need not only be flat, but can also be, for example, curved or double curved.

Partially opening the mold only when at least one surface of the plate has cooled below the softening temperature of the polyolefin or polycondensation polymer, results in a molded part with at least one surface of the plate that is not porous. , that is, with at least one surface free of pores. The presence of at least one surface of the plate that is not porous results in a specific modulus and strength improvement over an unexpanded molding. In addition, such a surface can be properly painted.

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Preferably, the mold is only partially opened when both surfaces of the plate have cooled down.

As a result, both surfaces of the plate are non-porous so that a molding with a sandwich structure is obtained. A sandwich structure gives a plate-shaped molding extra high rigidity and strength. A weak point in sandwich structures is often the adhesion between the center and the surface of the plate. In known sandwich structures this adhesion is often improved by using a so-called 3D fabric, which is understood to be a three-dimensional fiber structure in the form of a fabric. A characteristic of a 3D fabric is that some of the fibers that reinforce the center continue on the surface of the plate, which promotes adhesion between the center and the surface of the plate. 3D fabrics and composite materials made from them are described by A. Schrauwers in "Kunststof Magazine", 1933, p. 16. Disadvantages of using a 3D fabric are that it has to be made to measure beforehand and that it must be placed separately in the mold for each injection. Furthermore, a 3D fabric can only be used in combination with thermosetting plastics with a very low viscosity. Surprisingly it has been found that with the process according to the invention, at least a portion of the reinforcing fibers is present partially in the center and partially on the non-porous surface of the plate, as a result of which it is not necessary to use a fabric of 3D. It has also been discovered that the fibers in the center of the molding form a three-dimensional network and are parallel to the surface on the molding plate surface. With this, the process according to the invention for the first time offers the possibility of using the injection molding technique to produce (half) a fiber-reinforced sandwich from a fiber-reinforced thermoplastic plastic, in which the fibers of the center are prolonged on the surface. This structure contributes to the excellent modulus and specific mechanical strengths, even if only one surface of the platter is non-porous.

Melt index (IF) in this description is understood to be the melt index measured in accordance with ISO

1133. For polypropylene, the melt index is measured at 230 ° C, under the action of a weight of 2.16 kg.

The melt index of the polyolefin to be used in the process according to the invention is preferably greater than 30 g / 10 min, and even more preferably greater than 50 g / 10 min. It has been found that with such a flow rate, better expansion of the molded part occurs when the mold is opened. Preferably, the melt index is less than 700 g / 10 min.

The number average molecular mass (Mn) of the polycondensation polymers to be used in the process according to the invention is preferably greater than 5,000 g / mol. The procedure turns out to be effective for all polycondensation polymers available to date. With current polymerization technologies approximately 90,000 g / mol is the upper limit of the molecular mass of available polycondensation polymers. It is to be expected that polycondensation polymers with higher molecular masses, if they become available, can be processed with the process according to the invention, up to a molecular mass of approximately 200,000 g / mol.

The "average fiber length" in this description is understood to be the number average length of the fibers.

This can be determined in the molding by measuring the length of the fibers with the aid of an optical microscope, after the polymer matrix has been separated, for example by burning the polymer.

If the polymer composition contains glass fibers as reinforcing fibers, the polymer composition preferably contains 5-60%, by weight, and more preferably 10-60%, by weight, of glass fibers. If the polymer composition contains carbon fibers as reinforcing fibers, the polymer composition preferably contains 110%, by weight, and preferably 2-7%, by weight, of carbon fibers.

Such mixtures have been found to expand very well.

The molded part has been found to be easily expandable to twenty times its original thickness. This results in a molded part with a porosity of 95%. The porosity (P) of a molded part is understood to be here and below:

P = [d (0) - d (p)] / d (0) * 100 (%)

In which:

d (0) is the density before expansion, and d (p) is the density after expansion.

An advantage of the process according to the invention is also that a porous molding can be obtained without having to use a physical or chemical foaming agent. A high porosity of the molding is advantageous with respect to achieving specific high modulus and strength, since these indicator numbers are inversely proportional to density.

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Preferably, the speed at which the mold opens is chosen depending on the viscosity of the polyolefin or the Mn of the polycondensation polymers. At a high value of viscosity / Mn preferably a lower speed is chosen than at a low value of viscosity / Mn. Best results are obtained by adjusting the speed, to the rate of expansion of the molded part, so that, when the mold is opened, the molded part continues to be compressed against the two halves of the mold as a result of the expansion of the molded part. and the two surfaces of the plate accurately reflect the adjacent surfaces of the mold.

The mold is opened at the speed that is between 0.05 and 10 mm / s, as this results in a molded part having a high porosity and a non-porous surface.

The amount of moisture in the dispersion is less than 5,000 ppm. In this way, the appearance of scratches on the surface is avoided.

The invention also relates to a plate-shaped thermoplastic molding comprising at least one polyolefin or polycondensation polymer and reinforcing fibers.

Such molded parts are described in JP-A-5-17631. The moldings described in JP-A-17631 contain a polyolefin with a melt index of 30 g / 10 min or greater and more than 20%, by weight, of reinforcing fibers with a length of 5 mm or more.

A drawback of the moldings described in JP-A-5-17631 is that they have a specific modulus and a specific mechanical strength which are too low for the fiber-reinforced polyolefins employed.

The molded part produced by the method of claim 1 has a porous center and at least one non-porous plate surface, 1 to 60%, by weight, of the molded part consists of reinforcing fibers with an average length between 0 , 8 and 15 mm, at least a portion of which is present partially in the center and partially on the non-porous surface of the plate, and the molded part has a porosity between 5 and 95%, by volume, preferably between 10 and 90%, and more preferably between 20 and 85%. The expanded molding according to the invention has higher specific stiffness and strength than unexpanded molded parts, which, for example, are described in JP-A-5-17631.

In the case of molded parts with a porosity of more than 20% by weight, the anisotropy turns out to be very low, while molded parts with a porosity of less than 95% by volume have a non-porous plate surface.

The polyolefin preferably has a melt index of at least 30 g / 10 min.

The polyolefin can be chosen from the group comprising polyethylene or polypropylene or copolymers of ethylene and propylene. Preferably, the polyolefin contains polypropylene. The advantage of polypropylene is its high melting point, as a result of which the molded part has a higher heat bending temperature and a relatively low cost price.

Suitable polycondensation polymers are polycarbonate, polyester, polyamides, polyarylate, polyketone, polyimide, polyaramide, liquid crystal polymer (LCP), polyurethane, and copolymers of such polycondensates. Preferably, polycondensation polymers are selected from the group comprising polyamide 6, polyamide 6,6, polyamide 11, polyamide 12, poly (ethylene terephthalate), poly (butylene terephthalate) or their copolymers. The advantage of the last group is the relatively low cost price.

The reinforcing fibers can be chosen from the group comprising carbon fibers, aramid fibers, metal fibers, glass fibers, ceramic fibers, or mixtures thereof. Preferably, the molding according to the invention comprises glass fibers or carbon fibers as reinforcing fibers. Glass fibers have the advantage that they are cheap. Carbon fibers have the advantage that they have high tensile strength.

Although the advantages of the invention are already achieved when at least one surface of the plate is non-porous, preferably both surfaces of the plate are non-porous. The molded part, then, has a sandwich structure. The advantage of a sandwich structure is that the specific properties of the material are better than those of a molded part that does not have this sandwich structure. As a result of this sandwich structure and the fact that a portion of the reinforcing fibers is partially in the center and partially on the non-porous surface of the plate, the molding according to the invention preferably has a specific flexural modulus of at minus 10.

Molded parts obtainable by the invention are preferably used in building panels, element / body panels for the automobile industry, white goods and building industry; splash fenders, noise fenders, firewalls, parcel shelves, fenders, hoods, dashboards, panels for washing machines, tumble dryers, caravans and airplanes, bumper bars, car doors, cargo platforms, helmets, Shielding plates, heat and noise insulation walls, containers, loading pallets, acoustic screens, roof linings, and transport containers. The

ES 2 201 325 T3 molded parts according to the invention can also be used in bicycle parts, scooter parts, and motorcycle parts. Especially in applications where sound insulation is important, the molded parts according to the invention have an important advantage. In particular, the use of the molding according to the invention has advantages in products that have to meet acoustic insulation requirements. Differences in density between the pore-free plate surface and the interior of the molded parts according to the invention have been found to have a favorable effect on their sound insulation properties.

The invention will be further elucidated with reference to the following examples.

The reinforcing fibers can be dispersed in a melt of a polyolefin or in a condensation polymer using as a starting material a chopped filament of continuous fibers that have been made by pultrusion or coated with the thermoplastic in question.

In pultrusion, a bundle of continuous fibers is separated into individual fibers and passed through an impregnating matrix, into which the molten thermoplastic is injected. As the fibers have been separated, each filament is wetted and totally impregnated by the molten thermoplastic. A smooth filament, with a diameter of about 3mm, is pulled out of the die and then cooled. Finally, the filament is cut into granules of the desired length (eg 10-12 mm). Generally, the fibers are parallel to each other in the granulate, each fiber being separately surrounded by thermoplastic. Pultrusion fibers are available, for example, from

Hochst / PCI (Compec®, Celstran®), Borealis (Nepol®) LNP / Kawasaki Steel (Verton®).

Coating continuous reinforcing fibers with thermoplastic without the individual fibers being wetted is referred to in this description as Continuous Glass Coating (RVC). The advantage over pultrusion is the higher production rate (and therefore lower costs). In the case of RVC granulate, moreover, the length of the glass is the same as the length of the granule and the fibers are parallel to each other.

Coated pultrusion fibers are easily dispersed in the melt of a thermoplastic in the melt zone of an extruder.

The melt index was measured according to ISO 1133, for polypropylene at 230 ° C and a weight of 2.16 kg.

Flexural modulus and flexural strength were determined according to ISO 178, with an L / D ratio of 16.

The resistance of molded parts to bending under the influence of a force is expressed in the specific modulus and the breaking strength in the specific resistance. These specific amounts depend on the shape of the object in question. The specific modulus and strength of a plate-shaped molding are closest to that of a flat plate. The specific modulus of a flat plate is the quotient of the cubic root of the flexural modulus and the density, obtaining the indicator number when the flexural modulus is expressed in kg / mm² and the density in g / cm³. The specific mechanical resistance of a plate is given by the quotient between the square root of the flexural strength and the density, obtaining the indicator number when the flexural stress is expressed in kg / mm² and the density in g / cm³. A description of these indicator numbers is given in "Materials Selector: guidelines for minimum weight design", Chapman & Hall, London.

A Stork injection molding machine of the type SX-3000-2100 was used in the test. The screw used was a general purpose screw with a diameter of 72 mm, a length of 22D (feeding / compression / dosing: 12D / 6D / 4D). The depth of the thread pitch in the feed zone is 9.75 mm and that of the dosing zone is 5 mm. The compression ratio is 1.95.

The screw end is a standard screw end for PVC fabrication combined with a streamlined annular valve. The forelimb is a standard forelimb with a length of 117mm and an internal diameter of 19mm, which converges along a length of 10mm to an ultimate diameter of 4mm.

The material was injected into a flat plate mold (510 x 310 mm) through a central sprue.

Example I

A molded part was produced using as a material a mixture consisting of a fiberglass wick coated with PP. The fiberglass wick is mixed with PP fibers. Glass / PP mixed fiber was obtained from Vetrotex (Twintex®, R PP75 630-02); the IF (230 ° C, 2.16 kg) of the PP fiber is 20 g / 10 min. The PP liner was obtained from DSM (Stamylan^® P 112MN40). The IF of the PP coating is 47 g / 10 min. The glass content of the mixture is 37.5% by weight, the weight ratio of PPIF = 100 to PPIF = 20 is 4: 1. The IF of PP in the mixture is therefore 40 g / 10 min. The length of the granulate is 12 mm.

The Stork injection molding machine described above was used as an injection molding machine, with the following conditions: The temperatures of the injection cylinder in the hopper / zone 1 / zone 2 / zone 3 / zone 4 / zone 5 / zone front are successively: 40/280/290/300/320/320/320 ° C; mold temperature:

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110 ° C; screw speed: 20 rpm; dosing travel: 180 mm; back pressure = 0.3 MPa; holding pressure: nothing; cooling time: 105-150 s, which depends on the thickness of the article; injection speed:

mm / s; dosing time: 35 s; load degree: 100%.

The material was dispersed in the injection molding machine and injected into the plate mold, which had a thickness of 4 mm, through a converging nozzle. Immediately after injection, the mold was opened at the linear speed of 0.08 mm / s, in a path length of 3.1 mm. After the cooling time, in which the entire molding was cooled below the softening temperature of PP, the mold was opened further and the part was removed from the mold.

It was found that the molded part had expanded homogeneously and had a thickness of 7.1 mm, a density of 602 kg / m³ and a porosity of 51%. The flexural modulus (E) is 2.325 MPa, the flexural strength 44.3 MPa, and the elongation at break (eroture) is 3.3%. The specific modulus (Eespec) is 10.2 and the specific resistance (Respec) is 3.5. The surface is free of pores and is smooth on one side and porous on the other side. This represents that, at IF = 40 g / 10 min, the expansion takes place so slowly that, at the chosen opening speed, only one surface of the molded part has sufficient contact with the mold to form a surface of the plate that does not it is porous.

Example II

A molded part was produced using as a material a mixture comprising a PP coated fiberglass wick. The fiberglass wick is mixed with PP fibers. The fiberglass / PP blended was obtained from Vetrotex (Twintex^®, R PP75 630-02): the IF of the PP fiber is 20 g / min. The PP liner was obtained from BASF (Novolen^® 1100VC). The IF of the PP coating is 100 g / 10 min. The mixture comprises 37.5% by weight of glass, the weight ratio of PPIF = 100 to PPIF = 20 is 4: 1. The IF of the PP in the mixture is therefore 70 g / 10 min. The length of the granulate is 12 mm.

The material was dispersed in the Stork injection molding machine, under the same conditions as in Example I, and was injected into the plate mold, which had a thickness of 4 mm, through a convergent nozzle. Immediately after injection, the mold was opened at a linear speed of 0.08 mm / s in a path length of 3.1 mm. After the cooling time, the mold was opened further and the molded part was removed.

The molded part was found to have expanded homogeneously and had a thickness of 7.1 mm, a density of 567 kg / m³ and a porosity of 54%. The flexural modulus (E) is 2,555 MPa, the flexural strength 46.9 MPa and the elongation at the breaking point (e_break) is 3.1. The specific properties are: E_spec= 11.2 and ^. ^ = 4.0. The surface is completely smooth and free of pores on both sides.

Example III

The material, conditions in the injection molding machine and the procedure, including injection, were the same as in Example II. However, the mold was 3mm thick instead of 4mm.

Immediately after injection, the mold opens at the linear speed of 0.08 mm / s in a stroke length of 1.9 mm. After the cooling time the mold was opened further and the molded part was removed.

It was found that the molded part had expanded homogeneously and had a thickness of 4.9 mm, a density of 610 kg / m³ and a porosity of 51%. The flexural modulus is 2,689 MPa, the flexural strength 55.5 MPa and the elongation at break is 3.4%. The specific properties are: E_spec= 10.6 and σ ^ = 3.9. The surface is completely free of pores and is smooth on both sides.

Comparative experiment A

The material, the conditions of the injection molding machine and the procedure are the same as in Example I, although now the entire molded part is cooled immediately after injection below the softening temperature of PP, without being the mold partially open. After the cooling time, the mold is fully opened and the molded part is removed.

The molded part has a thickness of 4.0 mm, a density of 1,028 kg / m³ and a porosity of 16%. The flexural modulus of the plate is 4.266 MPa, the flexural strength 110.9 MPa and the elongation at the breaking point is 4.0%. The specific properties are: E_spec= 7.4 and CT-_spec= 3.1. The surface is completely free of pores and is smooth on both sides. The molding was found not to expand and to have poor specific properties. The porosity of 16% is a consequence of the cavities formed, due to the fact that maintenance pressure was not used.

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Comparative experiment B

The material, injection molding machine conditions and procedure are the same as in Experiment A, only now a holding pressure of 3.5 MPa was applied for 10 s immediately after injection. After the cooling time, the mold is fully opened and the molded part is removed.

The unexpanded molding has a thickness of 4.0 mm, a density of 1,225 kg / m³ and the porosity is 0%.

The flexural modulus is 6,720 MPa, the flexural strength 178.3 MPa and the elongation at the breaking point is

4.0%. The specific properties are: E_spec= 7.2 and σ ^_ριχ= 3.4. The surface is completely free of pores and is smooth on both sides. This experiment demonstrates that the porosity of the molding from Experiment A is a consequence of the absence of holding pressure.

Comparative experiment C

The material, the conditions of the injection molding machine and the procedure are the same as in Example I, although only now a holding pressure of 3.5 MPa is applied for 10 s, immediately after injection. Immediately after this, the mold is partially opened at the linear speed of 0.08 mm / s over a distance of 3.1 mm. After the cooling time, the mold is fully opened and the molded part is removed.

On both sides, the molding has rough and porous plate surfaces, from which glass fibers protrude. The thickness varies from 4 to 7.1 mm. Density is less than 1,000 kg / m³. This shows that the use of a holding pressure does not promote homogeneous expansion of the molded part. In the 10 s during which the holding pressure was applied, the molded part has already cooled to such an extent that there is no longer a mixture with a temperature above the softening temperature of the PP between the two surfaces of the plate. Comparative experiment D

The conditions of the injection molding machine and the procedure are the same as in Example I, only now a different material is used: Stamylan^® P 112MN40, with an IF of 47 g / 10 min and 40%, by weight, of short glass fibers (length 0.1 - 0.3 mm).

Immediately after injection, the mold opens at a linear speed of 0.08 mm / s, in a path length of 3.1 mm. After the cooling time, the mold was opened further and the molded part was removed. The molded part has not expanded and has not taken the shape of the mold and has a porosity of 12%. This shows that a 0.1-0.3mm fiberglass length is too short to allow the molded part to expand. Example IV

The procedure and the conditions of the injection molding machine are the same as in Example II, only now the conditions of the temperature of the injection cylinder in the hopper / zone 1 / zone 2 / zone 3 / zone 4 / zone 5 / front end are successively: 40/280/290/310/325/325/325 ° C.

The material used in this example is Fiberstran^® G1 / 40 available from DSM; Engineering Plastics USA (pultrusion granulate comprising polyamide with a Mn of 25,000 g / mol, containing 40% by weight of fiberglass).

Immediately after injection, the mold opens at a linear speed of 0.55 mm / s over a path length of 3.1 mm. After the cooling time, the mold is opened further and the molded part is removed.

The molded part has been found to have expanded homogeneously and has a thickness of 6.1 mm, a density of 625 kg / m³ and a porosity of 57%. The mechanical properties were measured using dry samples. The flexural modulus of the plate is 4,400 MPa, the flexural strength 85 MPa and the elongation at the breaking point is 3.2%. The specific properties are E_spec= 12.2 and = 4.7. The surface is free of pores and smooth on both sides.

Example V

The conditions of the injection molding machine and the procedure are the same as in Example IV.

The material used in this example is Celstran^® N66C40-01-04, which is a pultrusion material available from PCI / Hochst-Celanese, comprising PA 6.6 with an M_n of more than 5,000 g / mol and containing 40%, by weight, of carbon fiber.

Immediately after injection, the mold opens at a linear speed of 0.55 mm / s over a stroke length of 2.7 mm. After the cooling time, the mold is opened further and the molded part is removed.

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It is found that the molded part has expanded homogeneously and has a thickness of 5.7 mm, a density of 671 kg / m³ and a porosity of 50%. The mechanical properties were measured using dry samples. The flexural modulus of the plate is 8,600 MPa, the flexural strength 110 MPa and the elongation at the breaking point is 2.9%. The specific properties are: E_spec= 14.2 and σ ^_ριχ= 4.9. The surface is free of pores and smooth on both sides. Example VI

A molded part was produced using as a material a blend comprising PP coated glass fiber roving. The fiber of the glass fiber roving was available from Vetrotex and continuous fibers from PP (Twintex^®, R PP75 630-02) have been added in addition to glass fibers. The IF of the PP fibers is 20 g / 10 min. The PP liner was available from Montell (Valtec^® HH442-H). The IF of the coating is 700 g / 10 min. The mixture contains 37.5% by weight of glass, the weight ratio of PPIF = 700 = 700 to PPIF = 20 is 4: 1. The IF of the PP in the mixture is therefore 340 g / 10 min . The length of the granulate is 12 mm. The moisture content of the mixture, measured via the Karl-Fischer method, is less than 100 ppm.

As injection molding machine, the Stork injection molding machine described above was used, with the following conditions: the temperatures of the injection cylinder for the hopper / zone 1 / zone 2 / zone 3 / zone 4 / zone 5 / front end are successively: 40, 190, 210, 230, 270, 285, 285 ° C; mold temperature: 85 ° C; screw speed: 40 rpm; dosing length: 110 mm; back pressure: 0.1 MPa; holding pressure: none; cooling time: 60-80 s; injection speed: 100 mm / min; dosing time: 25 s; load degree: 100%.

The material was dispersed in the injection molding machine and injected into the plate mold, which had a thickness of 2 mm, by means of a converging nozzle.

Immediately after injection, the mold was opened at the linear speed of 0.1 mm / s in a stroke length of 1.8 mm. After the cooling time, in which the entire molding was cooled below the PP processing temperature, the mold was opened further and the molding was removed. It was found that the molded part had expanded homogeneously and had a thickness of 3.8 mm, a density of 645 kg / m³and a porosity of 40%. The flexural modulus is 3.015 MPa, the flexural strength 54.5 MPa and the elongation at the breaking point 3.9%. The specific properties are: E_spec= 10.5 and 3.6. The surface is completely free of pores and is smooth on both sides.

Example VII

The operating conditions of the injection molding machine are the same as in Example VI, except for the stroke length over which the mold opens immediately after injection. The material is also the same as in the previous example. Immediately after injection, the mold was opened at the linear speed of 0.1 mm / s in a stroke length of 2.9 mm. After the cooling time, in which the entire molding was cooled further below the PP processing temperature, the mold was opened and the molding was removed. The surface of the molding was not completely free of pores on both sides. Example VIII

The operating conditions of the injection molding machine are the same as in Example VI, except for the stroke length with which the mold opens immediately after injection. The material is also the same as in the first example, except for the measured moisture content, which was 2,732 ppm. Immediately after injection, the mold was opened at the linear speed of 0.1 mm / s with a stroke length of 2.9 mm. After the cooling time, in which the entire molding was further cooled below the PP processing temperature, the mold was further opened and the molding removed.

It was found that the molded part had expanded homogeneously and had a thickness of 4.9 mm, a density of 490 kg / m³and a porosity of 60%. The flexural modulus is 1.869 MPa, the flexural strength 31.5 MPa and the elongation at the breaking point is 3.7%. The specific properties are: E_spec= 11.7 and = 3.6. The surface is completely free of pores and smooth on both sides.

Comparative experiment E

The operating conditions of the injection molding machine are the same as in Example VI, except for the stroke length with which the mold opens immediately after injection. The material is also the same as in the first example, except for the measured moisture content, which was 5,600 ppm. Immediately after injection, the mold was opened at the linear speed of 0.1 mm / s in a stroke length of 2.9 mm. After the cooling time, in which the entire molding was cooled further below the PP processing temperature, the mold was opened further and the molding was removed. The surface is completely free of pores on both sides and exhibits a substantial number of scratch marks caused by entrained and undissolved moisture.