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PELLET TRANSPORTATION SYSTEM AND METHODS FOR USE THEREOF

20220016803 · 2022-01-20

    Inventors

    Cpc classification

    International classification

    Abstract

    The present invention relates to a method for reducing an amount of glass filaments separating from pellets comprising a thermoplastic polymer sheath intimately surrounding the glass filaments. The method can include transporting the pellets through a piping system and/or by a vibrating conveyor means. The pellets have a length of at least 13 mm. The amount of glass filaments separating from the pellets when such pellets are subjected to repetitive mechanical loads in transportation is reduced as compared other pellets subjected to the same repetitive mechanical load, such that blocking caused by the glass filaments within the pellet transport system is reduced or eliminated as compared to transporting pellets having a length of less than or equal to 12.1 mm.

    Claims

    1. A method for reducing an amount of glass filaments separating from pellets comprising a thermoplastic polymer sheath intimately surrounding the glass filaments, which glass filaments are covered at least in part with an impregnating agent and extend in a longitudinal direction of said pellets, when such pellets are subjected to repetitive mechanical loads in or on a pellet transport system comprising at least one of a piping system and a vibrating conveyor belt, the method comprising: a) providing at least one continuous strand of glass filaments containing at most 2 wt % of a sizing composition based on the total weight of the glass filaments, and b) applying from 0.5 to 20 wt %, based on the weight of the glass filaments in the pellets, of an impregnating agent to said strand, c) applying a sheath of thermoplastic polymer around the strand of step b) to form a sheathed continuous strand of glass filaments covered at least in part with said impregnating agent; and d) cutting the sheathed continuous strand of glass filaments covered at least in part with said impregnating agent to pellets having a length of at least 13 mm.

    2. The method according to claim 1, wherein the impregnating agent is non-volatile, has a melting point of at least 20° C. below the melting point of the thermoplastic polymer sheath, has a viscosity of from 2.5 to 100 cS at application temperature, and is compatible with the thermoplastic polymer.

    3. The method according to claim 1, wherein the pellets are cut to a length of from 13 to 20 mm.

    4. The method according to claim 1, wherein the pellets contain from 10 to 70 wt % of glass filaments based on the pellets.

    5. The method according to claim 1, wherein the glass filaments have a thickness of from 5 to 50 μm.

    6. The method according to claim 1, wherein the at least one continuous strand of glass filaments has a linear density of from 1000 to 5000 tex.

    7. The method of claim 1, wherein the pellets have a length of from 13 to 20 mm; the pellets contain from 10 to 70 wt % of glass filaments based on the weight of the pellets; and the glass filaments have a thickness of from 5 to 50 μm.

    8. The method of claim 1, wherein the pellets have a length of from 14 to 18 mm; the pellets contain from 20 to 60 wt % of glass filaments based on the weight of the pellets; and the glass filaments have a thickness of from 10 to 30 μm.

    9. The method of claim 1, wherein the pellets have a length of from 15 to 17 mm; the pellets contain from 20 to 60 wt % of glass filaments based on the weight of the pellets; and the glass filaments have a thickness of from 15 to 25 μm.

    10. The method of claim 1 further comprising transporting the pellets through a piping system, transporting the pellets by a vibrating conveyor means or both.

    11. The method of claim 10 further comprising, after the transporting, placing the pellets in a container.

    12. A method comprising: providing pellets having a length of at least 13 mm wherein the pellets comprise a thermoplastic polymer sheath intimately surrounding glass filaments, which glass filaments are covered at least in part with an impregnating agent and extend in a longitudinal direction of said pellets; and transporting the pellets through a piping system, transporting the pellets by a vibrating conveyor means or both.

    13. The method of claim 12 further comprising, after the transporting, placing the pellets in a container.

    Description

    EXAMPLES 1-5

    [0041] A sheathed continuous strand of glass filaments, which glass filaments are covered at least in part with an impregnating agent was manufactured in accordance with the method of WO 2009/080281 on a pilot line.

    [0042] The continuous strand of glass filaments had a linear density of 3000 Tex and comprised 0.35 wt % of a sizing composition. The glass filaments had an average diameter of 19 μm. The strand was provided with 8.7 wt % of an impregnating agent as defined in WO 2009/080281 having a drop melting point of 77° C. (ASTM D127) and a viscosity at 100° C. of 50 mPa.Math.s. Following the application of the impregnating agent a propylene homopolymer sheath comprising SABIC PP 579 S, having an MFI of 47 g/10 min (ISO 11330, 2.16 kg @ 230° C.) was provided around the continuous strand of glass filaments in such a manner that the propylene homopolymer intimately surrounded the continuous strand. The sheathed strand was cooled in a water bath after which it was cut into pellets having a length as indicated in

    [0043] Table 1 below. The pellets comprised 30 wt % of glass filaments.

    [0044] The tendency for glass filaments separating the pellets was measured using two different methods.

    [0045] The first method actually measures the amount of glass filaments separating from the pellets. To that extent 1 kg of pellets is fed to a first container and then, by means of air drag, transported to a second container through a (curved) flexible pipe of about 2.5 m long. The air is filtered through a device filter with sufficient pore size to capture any glass filament separating from the pellets. The pellets are then transported to the first container again and the procedure is repeated for four additional times. The weight of the device filter is measured before and after the test so that it can be established how much glass filaments have separated from the kilo of pellets. In an alternative manner the device filter is vacuum cleaned and the amount of glass filaments is separated and weighed. Both methods yield the same results.

    [0046] The second method involves the manual testing of 100 pellets randomly selected from a batch of pellets. An operator uses a needle having a blunt tip with a surface area slightly smaller than the surface area of the core of the pellet, i.e. the surface area occupied by the glass filaments. The operator then tries to push out the glass filaments using this needle. The amount of successful push outs per 100 pellets is reported. Although this method is more subjective than the first method, for reason that the outcome of the test may depend on the force that the operator uses when trying to push out the glass filaments, it can also be used to show the effect of the present invention.

    [0047] Table 1 below shows the normalized results of both tests. Example 1 is regarded as the reference example and is not according to the present invention.

    [0048] The table clearly shows that the “free glass” reduces significantly when the pellet length is increased from 12.1 to 17.9. The same advantageous effect is observed for the “push out”.

    TABLE-US-00001 TABLE 1 Pellet length Free glass Push out [mm] [−] [−] Ex. 1 12.1 1 1 Ex. 2 13.7 0.71 0.61 Ex. 3 14.6 0.34 0.46 Ex. 4 16.4 0.17 0.36 Ex. 5 17.9 0.12 0.25

    [0049] FIG. 1 shows the same results, i.e. the normalized values of “free glass” and “push out”, in a graph are plotted against the pellet length. The FIGURE clearly shows that the tendency for glass filaments separating from the pellets is significantly reduced compared to Example 1 when the pellet length is increased to at least 13 mm. The graph shows that there is a significant improvement of the free glass in the range of 12 to about 14 mm pellet length.

    EXAMPLES 6-7

    [0050] A sheathed continuous strand of glass filaments, which glass filaments are covered at least in part with an impregnating agent was manufactured in accordance with the method of WO 2009/080281 on a production line.

    [0051] The continuous strand of glass filaments had a linear density of 3000 Tex and comprised 0.6 wt % of a sizing composition. The strand was provided with 8 wt % of impregnating agent. The impregnating agent for Examples 6-7 was the same as the impregnating agent in Examples 1-5.

    [0052] Following the application of the impregnating agent a propylene sheath was provided around the continuous strand of glass filaments in such a manner that the propylene polymer intimately surrounded the continuous strand. The sheathed strand was cooled in a water bath after which it was cut into pellets having a length as indicated in

    [0053] Table 2 below. The pellets comprised 60 wt % of glass filaments.

    [0054] Table 2 below shows the normalized results of both tests. The examples with pellet length of 12.5 mm were regarded as the reference example.

    [0055] It is clear that the “free glass” reduces significantly when the pellet length is increased from 12.5 to 15. The same advantageous effect is observed for the “push out”.

    TABLE-US-00002 TABLE 2 Pellet lengh Free glass Push out Polypropylene [mm] [−] [−] Ex. 6 PP homopolymer 12.5 1 1 SABIC PP 579 S 15 0.59 0.60 MFI = 47 g/10 min (ISO 1133, 2.16 kg @ 230° C.) Ex. 7 PP copolymer 12.5 1 1 SABIC PP 513 MNK 10 15 0.70 0.50 MFI = 70 g/10 min (ISO 1133, 2.16 kg @ 230° C.)