SK48599A3 - Rod-shaped pellets - Google Patents

Abstract

Rod-shaped pellets containing a thermoplastic polymer and glass fibres, with the glass fibres extending in the longitudinal direction of the pellet and having the length of the pellet, wherein the pellets have a core and a sleeve, with the core containing a mixture of glass fibres and polypropylene fibres, with the polypropylene of the fibres being a homopolymer or a random copolymer of propylene and less than 10 wt.% of one or more olefins from the group ethylene, 1-olefins with 4-10 C-atoms and dienes with 4-10 C-atoms, the polypropylene of the fibres having a melt index (230 DEG C/2.16 kg) of 5 - 500 dg/min. and a density of at least 900 kg/m<3>, with at least 50 wt.% of the sleeve consisting of a polypropylene homopolymer, random copolymer of propylene and less than 10 wt.% of one or more olefins from the group ethylene, 1-olefins with 4-10 C-atoms and dienes with 4-10 C-atoms or a block copolymer of propylene and at most 27 wt.% of one or more olefins from the group ethylene and butene and at most 8 wt.% of one or more olefins from the group 1-olefins with 3-10 C-atoms and dienes with 4-10 C-atoms and the propylene contained in the sleeve having a melt index of 1 - 200 dg/min. (230 DEG C/2.16 kg) and a density of at least 900 kg/m<3>.

Description

PELLETS IN THE FORM OF RODS AND METHOD OF THEIR PRODUCTION

Field of the invention

The invention relates to pellet-shaped rods comprising a thermoplastic polymer and glass fibers, with glass fibers oriented along the longitudinal axis of the pellets and having a pellet length.

BACKGROUND OF THE INVENTION

Pellets of this type are known from EP-A-170245. The above patent describes a granulate comprising a thermoplastic polymer with a very low viscosity. The granulate was produced by drawing the glass fiber bundle with the molten polymer so that the glass fiber bundle is impregnated with the melt, further cooling the resulting glass fiber strand and the thermoplastic polymer and processing it into a granulate.

Due to the low viscosity of the polymer, the melt of the polymer penetrates into the glass fiber bundle during the manufacture of the granulate so that each or virtually each individual glass fiber is surrounded by the polymer. Since the glass fibers are surrounded by a polymer, the strand has a very high strength and the shaped articles made of granulate have very good mechanical properties. The reason for this is that during the shaping of the granulate into the shaped articles, the glass fibers are very well dispersed and their breakdown occurs only to a small extent.

However, the production of pellets according to EP-A-170425 is very cumbersome, especially since the glass fiber bundle can be drawn by the melt at only a low speed.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION It is an object of the present invention to provide rod-shaped pellets that are easier to manufacture but which can provide shaped articles with good

31194 T mechanical properties.

Surprisingly, this object has been achieved by producing pellets having a core and a shell and prepared from a core comprising a mixture of glass fibers and polypropylene fibers. The polypropylene of fibers is a homopolymer or random copolymer of propylene and less than 10 weight percent of one or more olefins selected from the group consisting of ethylene, 1-olefins of 4 to 10 carbon atoms and dienes of 4 to 10 carbon atoms. Polypropylene for fibers has a melt index (230 ° C / 2.16 kg) ranging from 5 to 500 dg / min and a density of at least 900 kg / m ³ . The coating consists of at least 50% by weight of a polypropylene homopolymer, a random copolymer of propylene and less than 10% by weight of one or more olefins selected from the group consisting of ethylene, 1 to 10 carbon atoms and 4 to 10 carbon dienes or propylene block copolymers. and not more than 27% by weight of one or more olefins selected from the group consisting of ethylene and butene and not more than 8% by weight of one or more olefins from the group consisting of 1-olefins of 3 to 10 carbon atoms and dienes of 4 to 10 carbon atoms. The propylene contained in the package has a melt index in the range of 1 to 200 dg / min (230 ° C / 2.16 kg) and a density of at least 900 kg / m ³ .

A granulate of this type can be easily produced, for example, by drawing a bundle comprising glass fibers and polypropylene fibers with the aid of a cable coating device, cooling the resulting strand and processing into a granulate. It has been found that in this way a very high process performance can be achieved, which means that the pellets can be produced on an industrial scale.

In addition, it has been found that if the granulate is processed into a shaped product by melting the pellets in an extruder, followed by extrusion onto the article, the article is placed in the form of a melt in an open mold and closed and molded. mechanical properties. In particular, shaped articles have a very high impact resistance. That is, these pellets

31194 T are very suitable for the production of structural shaped articles.

The fact that good mechanical properties are achieved with the aid of the pellets produced according to the invention is very surprising, since the glass fibers in the pellets are not completely surrounded by the polymer, and EPA-170245 explicitly states that this is necessary.

EP-A-170245 discloses a flexible rod-shaped composite comprising a core of reinforcing fibers and polymer fibers and a thin thermoplastic polymer shell. This composite can be processed into pellets. Carbon fibers are recommended as reinforcing fibers. However, the pellets according to the invention are not described in EP-A-226420 nor can it be inferred from this document that the granulate according to the invention is easy to manufacture and that pellet-shaped articles have these good mechanical properties.

Preferably, the melt index value of the polypropylene fibers is higher than the melt index value of the sheathing polymer composition. This allows for very homogeneous shaping with even better mechanical properties.

For glass fibers in pellets, conventional fibers may be used, usually having a thickness of between 8 and 25 μηη. The glass fibers should preferably have a thickness of between 15 and 20 μηη.

The polypropylene fibers may have a thickness customary for polypropylene fibers, for example in the range of 5 to 35 μηη, more preferably in the range of 10 to 30 μηη. The polypropylene fibers preferably have a melt flow index in the range between 10 to 300 dg / min (230 ° C / 2.16 kg), even more preferably in the range of 20 to 100 dg / min. The fibers may contain, in addition to polypropylene, conventional additives such as stabilizers, processing aids, nucleating agents and pigments. The polypropylene used is more preferably a homopolymer.

The glass and polypropylene fibers according to the invention may be present in separate bundles, for example in the range of 400 to 4000 fibers of each type in pellets. However, the fibers should be distributed as much as possible

31194 T homogeneous such that the glass fibers are present as single fibers and / or in groups with a maximum of 300 fibers, more preferably a maximum of 100 fibers, more preferably a maximum of 50 fibers. More preferably, the fibers should be spaced such that a maximum of 50% of the fibers are completely surrounded by glass fibers. The glass fiber is completely surrounded by the glass fibers as long as all the fibers directly adjacent to the glass fiber are also glass fibers.

The pellet core according to the invention preferably comprises glass fibers in an amount of 50 to 95% by weight and polypropylene fibers in an amount of 50 to 5% by weight. Even more preferably, the core comprises glass fibers in an amount of 60 to 85% by weight and polypropylene fibers in a range of 40 to 15% by weight.

Preferably, the wrapper comprises polypropylene in the range of 75 to 100% by weight, even more preferably the wrapper comprises polypropylene in the range of 85 to 100% by weight.

Preferably, the package comprises a polypropylene homopolymer or block copolymer consisting of a block comprising 94 to 100% by weight of polypropylene monomer units and 6 to 0% by weight of ethylene monomer unit and 20 to 80% by weight of ethylene monomer block and propylene monomer unit units in the range of 80 to 20% by weight, wherein the block copolymer comprises a total of in the range of 1 to 25% by weight of ethylene.

It is also possible for the coating to contain, in addition to polypropylene, an elastomer, for example a copolymer of ethylene with a 1-olefin having 3 to 10 carbon atoms, or for example a polymer of ethylene, propylene and one or more dienes, for example EPDM.

The pellets comprise glass fibers preferably in an amount of 10 to 50% by weight and polypropylene and elastomer in an amount of up to 30% by weight, even more preferably glass fibers in an amount of 30 to 50% by weight and polypropylene in an amount of 50 to 50% by weight.

31194 T weight% and elastomer.

In a special embodiment, the pellets comprise industrial carbon black in the range of 0.01 to 4.0% by weight. The pellets contain industrial carbon black preferably in the range of 0.1 to 1.0% by weight. More preferably, the sheath and polypropylene core fibers contain carbon black. Glass fiber pellets must also contain carbon black for many applications, as shaped articles are often required to have a black color. A disadvantage, however, is that the mechanical properties of the shaped articles have a lower value compared to the shaped articles made of glass fiber-free granulate which does not contain carbon black. However, it is very surprising that this disadvantage arises to a much lesser extent in shaped articles made of carbon black containing pellets according to the invention.

Any commonly used type of carbon black for polypropylene may be used. Preferably, carbon black with a specific surface area of at least 150 m ² / g, more preferably at least 200 m ² / g (as measured by the BET method using N ₂ absorption) should be used.

It is also possible for the pellets to contain a filler. The filler is preferably incorporated into the pellet shell. This will ensure that in addition to the presence of the filler, a high production rate is achieved. For example, the pellets may contain a filler in the range of 10 to 30% by weight. If the pellets contain a filler, the total percentage of filler and glass fibers is preferably in the range of 25 to 80% by weight and even more preferably in the range of 35 to 50% by weight.

Examples of suitable fillers are talc, wolastonic, chalk, barium sulfate, mica, clay, and the like. Preferably talc is used.

The use of a filler in the pellets according to the invention opens up further application possibilities.

In another suitable embodiment, the pellets according to the invention comprise one or more binders which improve the bond between the glass fibers and the polypropylene matrix in the shaped articles that can be produced

31194 T of pellets. Examples of suitable binders are propylene polymers grafted with maleic anhydride. More preferably, the binder has a lower viscosity than the fiber polymer. The amount of binder contained in the pellets is usually in the range between 0.2 and 5% by weight and depends, for example, on the type of binder and on the amount and type of glass fibers. The binder is more preferably incorporated into the polypropylene fibers of the pellet core. This ensures that the binder is highly effective.

The fiber bundle used may consist, for example, of a bundle of parallel-oriented fibers with several turns per linear meter. The bundle is preferably made by spinning several glass fibers and several polypropylene fibers in a conventional manner, splitting the fibers and then joining them. Examples of suitable fiber distribution techniques are described in patents EP-A-616055, EP-A-59969 and EP-A-505275.

For the production of pellets, the fiber bundle may be provided with a wrapper using a known cable coating device. The cable sheathing device usually consists of an extruder for melting the polymeric composition that forms the sheath and an extruder head which is bundles of fibers forming the core of the center of gravity. The polymeric coating composition is extruded around or close to the core in the extruder head. Further, the extrudate may be cooled by drawing the resulting strand through a water bath and the cooled strand may be processed into pellets, for example by cutting the strand using a granulator.

The fiber bundles constituting the core are preferably pulled by the extruder head of the coating device at a speed of at least 100 m / min, even more preferably at a speed of at least 200 m / min.

The strand is preferably processed into pellets after cooling to a temperature in the range of 50 to 100 ° C. The length of the granulate is more preferably in the range of 5 to 50 millimeters, even more preferably in the range of 10 to 30 millimeters. The strand is preferably cut into granules by means of a rotary knife granulator and a stator without a gap between the knife and the stator. This can be achieved, for example, by supporting the blade with a spring. The advantage is that the strand can be

31194 T cut well without, for example, pulling core fibers out of the package.

The pellets according to the invention can be processed into shaped articles by conventional methods, for example by molding and injection molding and extrusion.

The invention also relates to a process for processing the pellets according to the invention into shaped articles

- melting the pellets in an extruder

- extruding the resulting melt into one or more objects

- placing the article or articles of the open mold on the shaped articles still in the molten state

- closing the mold to form the shaped article.

The result of this process is that the shaped articles have very good mechanical properties. In addition, the shaped article has a homogeneous composition.

More preferably, a single-screw extruder is used for melting the pellets. The single-screw extruder preferably has a screw size such that the granulate melts mainly under the influence of heat from the extruder walls. The length of the screw is more preferably in the range of 15 D to 40 D (D is the diameter of the screw), even more preferably in the range of 20 D to 30 D. in the pumping zone of the screw, it is more preferably in the range of 0.08 D to 0.15 D.

On the head side, the exruder preferably has a valve that can be closed during melting of the granulate. Here is a buffer space between the valve and the end of the screw in which an adequate amount of melt can accumulate to be extruded onto the desired article. During melting of the granulate in an amount sufficient to form the article, the screw preferably converts the melt in such a way that the buffer volume increases as a function of the amount of molten granulate and the melt accumulates in the buffer space at a pressure greater than atmospheric but more preferably no greater than 3.0 MPa. (30 bar), much more preferably not more than 1.5 MPa

31194 T (15 bar). In this way, it is achieved that the granulate is well melted and the glass fibers are impregnated with the polypropylene melt, but the breaking of the glass fibers occurs only to a small extent.

Then the valve can be opened and the article can be extruded using a screw connected in the opposite direction and then the valve is closed again. Preferably, the slot cross-sectional area in the extruder head is at least 50% of the cross-section of the extruder barrel. Even more preferably, the cross-sectional area of the slot corresponds to between 75 and 100% of the cross-section of the cylinder. The slot may have any shape. For example, the slot may have a circular, square or rectangular shape depending on the desired shape of the object.

The article or articles are preferably placed in the mold immediately after extrusion. The mold is preferably closed as soon as possible after extrusion of the article or articles to form the shaped article.

It is also possible to produce shaped articles from a mixture of pellets according to the invention and polypropylene pellets which do not contain glass fibers.

The invention also relates to moldings made from pellets. Examples of such shaped articles are covers of electronic and electromechanical devices, machine parts and car parts such as bumper frames, dashboards, shelves, profiles and seat constructions.

DETAILED DESCRIPTION OF THE INVENTION

Example I

The fiber bundle of glass fibers and polypropylene fibers were covered with a polypropylene sheath by means of an extruder with an extruder head fitted to cover the surface of the cables.

The fiber bundle was composed of five "straight strands" of 630 Tex each containing 75 weight percent glass fibers and 25 weight percent polypropylene fibers. The fibers were split in such a way that they were present in the fiber bundle as individual fibers and in

31194 T groups of fibers of not more than 50 fibers. The polypropylene used for the polypropylene fibers was a homopolymer with a melt flow index (230 ° C / 2.16 kg) of 21 dg / min and a density of 904 kg / m ³ .

The polypropylene of the shell was a homopolymer with a melt index of 45 dg / min and a density of 904 kg / m ³ . Polypropylene fibers contained 2 weight percent binder and the wrapper contained 1 weight percent binder. That is, the granulate contained 1.2 weight percent binder. Polybond (TM) 3150, maleic anhydride modified polypropylene manufactured by Uniroyal, UK, was used as a binder.

The extruder used was a single-screw extruder supplied by Schwabenthan (TM), Germany and had a screw diameter of 30 millimeters. The cable coating heads were of tubular type and the diameter of the nozzle of the fiber bundling head was 2.4 millimeters. The melting temperature of the polypropylene shell was 240 ° C. The fiber bundle was pulled through the head at a speed of 100 m / min (line speed) and deposited. After coating, the glass fiber content of the pellets was 30 weight percent.

The strand thus formed was passed through a water bath and thus cooled to 50 ° C and cut into granules of 12.5 millimeters in length.

The pellets were later fed into a single-screw extruder from Kannegiesser from Germany, whose diameter was 80 millimeters and length 26 D, the processing depth in the feed zone was 15 mm, and the processing depth in the pumping zone was 9 millimeters. On the end of the screw, the cylinder is lockable by a hydraulic valve. The pellets were melted and accumulated in the stabilization space at the threaded end of the extruder while the screw was created by maintaining a pressure of 1.5 MPa (15 bar) in the stabilization space. Approximately 600 grams of molten granulate was recovered in the stabilization space in about 27 seconds.

Then, the article was extruded for about 2.7 seconds with the valve open, and the screw was lowered in the opposite direction to empty the stabilization space. The object had a cylindrical shape with a diameter of 85 millimeters and a length of 140

31194 T millimeters.

Immediately after extrusion, the article was placed in the center of the square mold cavity, the longitudinal direction of the article parallel to one side of the mold cavity. Then a plate having a length and width of 400 millimeters and a thickness of 3.2 millimeters was pressed. The mold had a temperature of 50 ° C.

Test plates were cut from the plate, perpendicular and parallel to the direction coinciding with the longitudinal direction of the article as it was placed in the mold cavity before the plate was pressed.

E-modulus (Emod), rupture stress (σ stress) and rupture elongation (ε elongation) in accordance with ISO R 527-1 B, and Izod impact strength in accordance with ISO 180-4A were determined.

The results are shown in Table I. This table lists the values in the perpendicular direction (JL) and in the parallel direction (//) and the mean of these values.

Comparative experiment

A granulate containing 30 weight percent glass fibers was prepared by impregnating a 2400 Tex glass fiber bundle through a melting impregnation process using a polypropylene homopolymer having a viscosity of 150 Pa * s, measured at a shear rate of 1 s ^-1 and at 240 ° C, cutting the resulting strands of glass. fibers and a polymer to a granulate length of 12.5 millimeters as described in EP-A-170245. During the impregnation the line speed was 10 m / min. The pellets contained 1.2 weight percent Polybond (TM) 3150.

The pellets were melted, the material was extruded into an article, and pressed to obtain a plate as described in Example 1. The mechanical properties were then measured as described in Example I. The results are also shown in Table 1.

31194 T

Table 1

Mechanical properties of shaped articles of granulate according to the invention and of granulate of impregnated glass fibers.

Example I Attempt A // 1 · average // 1 average E module (MPa) 7500 3200 5350 5930 3930 4930 Breaking stress (Mpa) 136 45 91 101 65 83 Elongation at break (%) 2.4 2.7 2.6 2.2 2.7 2.5 Izod impact strength (KJ.m ² ) 62 42 53 54 34 44

Example II

Example II was carried out in the same manner as Example I, except that the pellets contained 0.12 weight percent carbon black. Carbon black sold under the trade name Elftex (TM) by Cabot of the USA having a specific surface area of 74 m ² / g (BET, N ₂ absorption) was used. The carbon black was incorporated into the pellet shell.

The results are shown in Table 2.

31194 T

Comparative experiment

Comparative Experiment B was carried out in the same manner as Comparative Experiment A except that the pellets contained 0.12 weight percent carbon black. Carbon black sold under the trade name Elftex (TM) was used.

The results are shown in Table 2.

A comparison of the results of Tables 1 and 2 shows that the addition of carbon black deteriorates the mechanical properties, but that this deterioration is less pronounced in the pellets of the present invention.

Table 2

Mechanical properties of granular articles according to the invention and of carbon black impregnated glass fibers.

Example II Attempt B // 1 average // 1 average E module (Mpa) 5900 3700 4800 5400 3700 4550 Breaking stress (Mpa) 87 50 69 88 47 68 Elongation at break (%) 1.8 2.2 2.0 1.7 1.8 1.8 Izod impact strength (KJ.m ² ) 38 17 28 30 16 23

31194 T

Example III

Example III was performed in the same manner as Example II, except that carbon black sold under the tradename Black Pearls (TM) 800 from Cabot, USA, having a specific surface area of 210 m ² / g was used. The carbon black was incorporated into the pellet shell.

The results are shown in Table 3.

Comparisons of the results of Examples II and III show that the mechanical properties are better when the carbon black has a higher specific surface area.

Table 3

Mechanical properties of the shaped pellet articles according to the invention with carbon blacks having a high specific surface area.

Example III // 1 average E module (Mpa) 7200 3400 5300 Breaking stress (Mpa) 130 42 86 Elongation at break (%) 2.3 2.2 2.3 Izod impact strength (KJ.m ² ) 56 32 44

31194 T

Claims (11)

A bar-shaped pellet comprising a thermoplastic polymer and glass fibers, with glass fibers oriented in the longitudinal direction of the pellet and having a pellet length, characterized in that the pellets have a core and a shell, the core comprising a mixture of glass fibers and polypropylene fibers. a random copolymer of propylene and less than 10% by weight of one or more olefins selected from the group consisting of ethylene, 1-olefins of 4 to 10 carbon atoms and dienes of 4 to 10 carbon atoms, the polypropylene fibers having a melt index (230 ° C / 2.16) kg) in the range of 5 to 500 dg / min and a density of at least 900 kg / m ³ , the casing consisting of at least 50% by weight of a polypropylene homopolymer, a random copolymer of propylene and less than 10% by weight of one or more olefins of ethylene; olefins of 4 to 10 carbon atoms and dienes of 4 to 10 carbon atoms carbon or propylene block copolymer and not more than 27% by weight of one or more olefins selected from the group consisting of ethylene and butene and not more than 8% by weight of one or more olefins from the group consisting of 1-olefins of 3 to 10 carbon atoms and dienes of 4 to 10 carbon atoms; The propylene contained in the packaging has a melt index in the range of 1 to 200 dg / min (230 ° C / 2.16 kg) and a density of at least 900 kg / m ³ . Pellets according to claim 1, characterized in that the value of the melt index of the polypropylene for the fibers is higher than the value of the polymer flow index for the package. Pellets according to claim 1 or 2, characterized in that the glass fibers are single fibers and / or fiber bundles with a maximum of 300 fibers. Pellets according to claim 3, characterized in that the glass fibers and propylene fibers are present as single fibers and / or bundles of fibers 31194 T with a maximum of 100 fibers. Pellets according to claims 3 and 4, characterized in that at most 50% of the glass fibers are completely surrounded by glass fibers. Pellets according to claims 1-5, characterized in that the package comprises 75-100% by weight of polypropylene. Pellets according to claims 1-6, characterized in that the pellets contain 0.01-4.0% by weight of carbon black. Pellets according to claim 7, characterized in that carbon black with a specific surface area of at least 150 m ² / g is used. Process for preparing rod-shaped pellets according to any one of the preceding claims 1-8, characterized in that the strand is cut into pellets by means of a rotary knife and a stator, without a gap between the knife and the stator. A granulate treatment process according to any one of the preceding claims 1-8, characterized in that molded materials are prepared by melting the pellets in an extruder, extruding the resulting melt into one or more articles, placing the article or articles in an open mold for the molded article in the molten state. and closing the mold to form the article. A shaped article made of pellets according to any one of claims 18.