Screw combined structure produced by halogen-free flame-retardant reinforced PA6 material and production process

Abstract

The invention discloses a screw combined structure for producing a halogen-free flame-retardant reinforced PA6 (polyamide 6) material, which comprises a pair of double screws inclined relative to the horizontal plane, and a plurality of dispersedly arranged through holes for a flame retardant and / or glass fiber to pass through are formed in blades of each screw in a penetrating manner. The invention also discloses a production process of the halogen-free flame-retardant reinforced PA6 material, which comprises the following steps: uniformly mixing the flame retardant and PA6, then intermittently adding into a twin-screw extruder, adding the glass fiber from a lateral feeding port, carrying out extrusion molding, then pelletizing, and then carrying out injection molding to obtain the halogen-free flame-retardant reinforced PA6 material. The flame retardant has sufficient dispersing and mixing performance on materials, and also has the temperature resistance of the flame retardant. According to the present invention, the full dispersion of the glass fiber material in the material system is considered so as to provide the smooth surface and no floating fiber generation of the finished product prepared from the material by the final user, and the glass fiber cannot be cut excessively and finely during the production so as to ensure the mechanical property of the prepared material;

Description

Technical Field

[0001] The invention relates to a screw assembly structure and a production process for producing a halogen-free flame-retardant reinforced PA6 material. Background Art

[0002] Kong Wei mentioned in the paper "Preparation and Performance of UV-resistant Halogen-free Flame Retardant Toughened PA66" published in "Engineering Plastics Applications" Vol. 49, No. 7, July 2021: PA66, flame retardant, toughening agent, antioxidant and UV-resistant aging additive are weighed according to the corresponding formula, mixed in a high-speed mixer for 5-6 minutes, discharged, and the mixture is extruded through a twin-screw extruder at 260°C, cooled and pelletized. The material is dried at 120°C for 1 hour, and then injection molded into the corresponding standard specimen at 270°C. Tan Yilun mentioned in the paper "Preparation and Performance of Halogen-free Flame-retardant Glass Fiber Reinforced PA6" published in "Plastics Industry" Vol. 42, No. 1, January 2014: The flame retardant and PA6 were mixed evenly and added to the feed port of TSE-30A twin-screw extruder (Nanjing Ruiya Polymer Equipment Co., Ltd.), and the glass fiber was added from the side feed port. After pelletizing, it was injected into standard combustion, tensile and impact specimens by CJ80E injection molding machine (Foshan Zhende Plastic Machinery Co., Ltd.). The temperature of each zone of the twin-screw extruder was 205~235℃, the screw speed was 150r / min; the injection molding temperature of the injection molding machine was 230~240℃. In the paper "Research and Development of Halogen-free Flame-retardant and Permanently Antistatic Glass Fiber Reinforced Polyamide 6 Materials" published by Lv Qiang in "China Plastics" Volume 35, Issue 7, July 2021, it is mentioned: PA6, flame retardant LX-15, permanent antistatic agent MH-2030, GF and additives are added to the high-speed mixer according to the ratio in Table 1, and mixed evenly; the same-rotating twin-screw extruder is used for extrusion granulation (the temperature of each section is controlled at 210~230℃, and the head temperature is 220℃) to obtain halogen-free flame-retardant and permanently antistatic PA6 / GF composite material particles; the pellets are dried at 120℃ for 4h and injection molded into standard test specimens. The temperature of each section of the injection molding machine is controlled at 220~250℃, and the injection molding pressure is 100MPa. It can be seen that the existing technologies are all halogen-free flame-retardant reinforced PA6 materials prepared by extrusion, pelletizing and injection molding of screw extruders, and the existing technologies have few improvements to the screw combination. The aspects that need to be considered at present are: 1. The screw combination is designed with full consideration of the characteristics of PA6 reinforced halogen-free flame retardant materials.

[0003] 2. The overall idea is to consider the structure of the screw assembly to have sufficient dispersion and mixing properties for the material, and also to consider the temperature resistance of the flame retardant; The screw combination process must take into account the full dispersion of the glass fiber material in the material system, so that the surface of the finished product made by the end user using the material is smooth and free of floating fibers, and at the same time, it must prevent the glass fiber from being sheared too finely during production, which would lead to a decrease in the mechanical properties of the material. Summary of the invention

[0004] The purpose of the present invention is to overcome the defects existing in the prior art and provide a screw assembly structure for the production of halogen-free flame-retardant reinforced PA6 material, which not only has sufficient dispersion and mixing properties for the material, but also takes into account the temperature resistance of the flame retardant. It not only takes into account the sufficient dispersion of the glass fiber material in the material system, so that the surface of the finished product made by the end user using the material is smooth and free of floating fibers, but also prevents the glass fiber from being sheared excessively during production, thereby ensuring the mechanical properties of the obtained material.

[0005] To achieve the above-mentioned purpose, the technical solution of the present invention is to design a screw combination structure for producing halogen-free flame-retardant reinforced PA6 material, including a pair of twin screws arranged obliquely to the horizontal plane, and a plurality of dispersed through holes for the passage of flame retardants and / or glass fibers are penetrated on the blades of each screw.

[0006] A further technical solution is that the through holes include glass fiber through holes and flame retardant through holes; a plurality of dispersed glass fiber through holes are provided on the blades of the screw from the glass fiber side feed to the end of the material extrusion, and the aperture of the glass fiber through holes is 40~50μm; a plurality of dispersed flame retardant through holes are provided on the blades of the screw, and the aperture of the flame retardant through holes is 50~100μm. Since the particle size range of PA6 is usually 2.5×3mm; the diameter of the single fiber of glass fiber is usually between a few microns and more than twenty microns; the particle size of the flame retardant is generally at the micron level, such as the particle size of melamine phosphate is between 10μm and 50μm; after such a setting, some of the glass fiber added by the side feed directly passes through the glass fiber through holes on the blades of the screw, reducing the residence time of the glass fiber and also reducing the excessive crushing of the glass fiber. Some of the added flame retardant directly passes through the flame retardant through holes on the screw blades, which reduces the residence time of the flame retardant and takes into account the temperature resistance of the flame retardant.

[0007] Another technical solution is that the aperture of the through hole is 50-100 μm; the through holes on the blades of the screw from the glass fiber side feeding to the end of the material extrusion are arranged more than the through holes on the blades of the screw at other positions. Through holes are set so that both the glass fiber and the flame retardant can pass through or pass through. In this way, through holes of the same specification are set to facilitate processing, but more through holes are set on the blade part of the screw after the glass fiber side feeding to ensure that a certain amount of glass fiber and flame retardant can pass quickly, reduce retention, and avoid the reduction of the rapid passing of flame retardant and glass fiber after the glass fiber is added.

[0008] A further technical solution is that the number of through holes on the blades of the screws of the inclined twin screws increases along the extrusion direction. This can prevent too much glass fiber or flame retardant from passing through the through holes and gathering at the end of the extruder body at the inclined twin screws, ensure the dispersion of the flame retardant and glass fiber in the system, and also take into account the temperature resistance of the flame retardant (due to faster passing) and avoid excessive crushing of the glass fiber.

[0009] A further technical solution is that a pair of horizontally arranged twin screws are arranged behind a pair of inclined twin screws along the material extrusion direction. A pair of horizontally arranged twin screws are arranged behind the inclined twin screws, which can take into account the fast passing property of glass fiber or flame retardant {that is, taking into account the temperature resistance of flame retardant and avoiding excessive crushing of glass fiber} and sufficient dispersion in the material system.

[0010] The technical solution also provided by the present invention is a production process of halogen-free flame retardant reinforced PA6 material, using a screw extruder containing a screw combination structure for producing the halogen-free flame retardant reinforced PA6 material, after the flame retardant and PA6 are evenly mixed, they are intermittently added to the twin-screw extruder, and the glass fiber is added from the side feed port, pelletized after extrusion molding, and then injection molded. On the one hand, the inclined twin screws ensure that the residence time of the glass fiber is short after addition, avoiding excessive shearing of the glass fiber during production. On the other hand, intermittent addition can ensure sufficient dispersion, avoiding too much glass fiber being located at the lower end of the body due to the inclined screw combination structure. The halogen-free flame retardant is an organic hypophosphite and / or polyphosphate melamine; or the halogen-free flame retardant is a composite flame retardant of organic hypophosphite aluminum and polydimelamine dihydrogen phosphate aluminum salt.

[0011] The advantages and beneficial effects of the present invention are: it not only has sufficient dispersion and mixing properties for the material, but also takes into account the temperature resistance of the flame retardant. It not only takes into account the sufficient dispersion of the glass fiber material in the material system, so that the surface of the finished product made by the end user using the material is smooth and free of floating fibers, but also prevents the glass fiber from being sheared excessively during production, thereby ensuring the mechanical properties of the obtained material.

[0012] Since the particle size of PA6 is usually 2.5×3mm; the diameter of the single fiber of glass fiber is usually between a few microns and more than 20 microns; the particle size of flame retardants is generally at the micron level, such as the particle size of melamine phosphate is between 10μm and 50μm; after this setting, some of the glass fiber added by side feeding directly passes through the glass fiber through-holes on the blades of the screw, reducing the residence time of the glass fiber and also reducing the excessive crushing of the glass fiber. Some of the added flame retardant directly passes through the flame retardant through-holes on the blades of the screw, reducing the residence time of the flame retardant and taking into account the temperature resistance of the flame retardant.

[0013] Through holes are set so that both glass fiber and flame retardant can pass through. Through holes of the same specification are used for easy processing. Only more through holes are set on the blade part of the screw after the glass fiber side feeding to ensure that a certain amount of glass fiber and flame retardant can pass through quickly and reduce retention, so as to avoid the reduction of rapid passability of flame retardant and glass fiber after the glass fiber is added.

[0014] It can prevent too much glass fiber or flame retardant from passing through the through hole and gathering at the end of the extruder body at the inclined twin screw, ensuring the dispersion of flame retardant and glass fiber in the system, and also taking into account the temperature resistance of flame retardant and avoiding excessive crushing of glass fiber (due to faster passing). A pair of horizontally arranged twin screws is arranged behind the inclined twin screws, which can take into account the fast passing property of glass fiber or flame retardant {that is, taking into account the temperature resistance of flame retardant and avoiding excessive crushing of glass fiber} and sufficient dispersion in the material system.

[0015] On the one hand, the tilted twin screws ensure that the glass fiber stays for a short time after being added, avoiding excessive shearing of the glass fiber during production. On the other hand, intermittent addition can ensure sufficient dispersion, avoiding too much glass fiber being located at the lower end of the machine body due to the tilted screw combination structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a schematic diagram of a twin-screw extruder including a screw assembly structure embodiment 1 for producing a halogen-free flame-retardant reinforced PA6 material of the present invention; Figure 2 yes Figure 1 Side view of Figure 3 yes Figure 2 AA section view; Figure 4 yes Figure 1 Schematic diagram of the twin screw in; Figure 5 is a schematic diagram of a twin-screw extruder in Embodiment 2 of the present invention; Figure 6 is a schematic diagram of a twin-screw extruder in Embodiment 3 of the present invention; Figure 7 yes Figure 6 an enlarged schematic diagram of the upper end portion of; Figure 8 is a schematic diagram of a twin-screw extruder in Embodiment 5 of the present invention; Fig. 9 yes Figure 8 Side view of Fig.10 is a schematic diagram of a twin-screw extruder in Embodiment 6 of the present invention; Fig.11 yes Fig.10A partial enlarged schematic diagram of the middle part of the blade.

[0017] In the figure: 1. Side feed port; 2. Blade; 3. Glass fiber through hole; 4. Flame retardant through hole; 5. Twin-screw extruder; 6. Screw; 7. Through hole; 8. Channel; 9. Water-proof and breathable membrane; 10. Liquid; 11. Hole; 12. Fan blade. DETAILED DESCRIPTION

[0018] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and embodiments. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0019] Embodiment 1: Figures 1 to 4 As shown (for ease of illustration, Figure 1 , Figure 3 The screw, the side feed port and the side feed weight loss scale at the side feed port are not shown). The present invention is a screw assembly structure for producing halogen-free flame-retardant reinforced PA6 material, in which a pair of twin screws in the screw assembly structure are tilted; the screw assembly structure is arranged in a twin-screw extruder 5; A plurality of dispersed glass fiber through holes 3 are provided on the blade 2 of the screw from the glass fiber side feeding port 1 to the material extrusion end, and the aperture of the glass fiber through holes 3 is 40-50 μm; a side feeding loss-in-weight scale is provided at the side feeding port; A plurality of dispersed flame retardant through holes 4 are provided through the blades of the screw, and the aperture of the flame retardant through holes is 50-100 μm.

[0020] Embodiment 2: The difference from Embodiment 1 is that Figure 5 As shown, a plurality of dispersed through holes 7 are provided through the blades 2 of the screw 6, and the aperture of the through holes is 50-100 μm; the through holes 7 on the blades of the screw from the glass fiber side feed port 1 to the end of material extrusion are arranged more than the through holes on the blades of the screw at other positions.

[0021] Embodiment 3: The difference from Embodiment 1 or 2 is that Figure 6 , Figure 7As shown, along the material extrusion direction, a pair of horizontally arranged twin screws 6 are provided behind a pair of inclined twin screws 6; such a combination can be repeatedly provided (that is, another pair of inclined twin screws and a horizontally arranged twin screw arranged behind the twin screws are provided, which is specifically determined according to the length of the machine body and the length of the screws. In this embodiment, two pairs of inclined twin screws and a pair of horizontal twin screws located between the two pairs of inclined twin screws are provided; the length of the entire extrusion screw machine is slightly longer than that of an extruder of the same specification, but due to the inclined twin screws, the time the material stays in the extruder is slightly shorter than that of an extruder of the same specification; the inclined twin screws and the horizontally arranged twin screws are rotatably provided relative to the machine body through bearings provided in the machine body of the twin screw extruder; the screws adjacent to each other in the front and rear along the extrusion direction can realize the transmission of rotational motion of different axes through a soft shaft) to ensure the dispersion of the glass fiber in the material system, while taking into account that the glass fiber is not sheared excessively during production.

[0022] Embodiment 4: The difference from Embodiment 1 is that the number of through holes on the blades of the screws of the inclined twin-screws increases along the extrusion direction.

[0023] Embodiment 5: The difference from Embodiment 2 is that Figure 8 , Fig. 9 As shown, the interior of the blade 2 is provided with a channel 8 that penetrates the blade and is connected to the through hole 7. The size of the channel 8 is smaller than the through hole. There are several channels and a part of each channel is located inside the blade and the other part is located inside the screw. The channel forms a ring with a notch, and the notch of the annular channel is the through hole. Water-proof and breathable membranes 9 are fixed at both ends of the annular channel. A liquid 10 (such as water) with half the volume of the channel is set in the channel. After such a setting, as the screw rotates, there is a certain amount of time for each rotation of the screw when the air in the channel is squeezed into the through hole and the other end of the channel by the liquid (the liquid moves rapidly toward the outer edge of the rotating channel due to centrifugal force). In this way, due to Bernoulli's principle, the air outside the through hole will form a certain airflow to pass through the through hole. Therefore, when the flame retardant passes through the through hole, it is blown by the wind, so that the flame retardant can be cooled to a certain extent when passing through (but the flame retardant will not enter the channel when passing through the through hole 7, because the size of the channel is smaller than the size of the through hole and can be set to be much smaller than the particle size of the flame retardant). Taking into account the temperature resistance of the flame retardant, it is well known that during the extrusion of flame retardant reinforced PA, due to the high temperature, the temperature resistance of the flame retardant generally cannot withstand the long-term high temperature in the high temperature zone of the extruder, which can easily lead to the failure of the flame retardant, and ultimately lead to poor flame retardant effect of the finished product. Therefore, during extrusion, we try our best to avoid the problem of flame retardant failure caused by high temperature and long-term extrusion.

[0024] Embodiment 6: The difference from Embodiment 5 is that Fig.10 , Fig.11As shown, a hole 11 penetrating the blade and connected to the through hole 7 is arranged in the blade 2, and the rotation axis of the hole is arranged obliquely to the rotation axis of the through hole, and a fan blade 12 is fixedly arranged at the starting end of the screw. After such arrangement, the fan blade blows air to the blade when the screw rotates. In addition, due to the arrangement of the hole that is inclined but connected to the through hole 7 when the screw rotates, air flow is also generated when the screw rotates, which helps the flame retardant to play a certain cooling effect when passing through the through hole on the blade, and takes into account the temperature resistance of the flame retardant.

[0025] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. The screw assembly structure produced by halogen-free flame retardant reinforced PA6 material is characterized by: The invention comprises a pair of twin screws which are arranged obliquely with respect to the horizontal plane, and a plurality of dispersed through holes for passing the flame retardant and / or the glass fiber are penetrated on the blade of each screw.

2. The screw assembly structure produced by the halogen-free flame-retardant reinforced PA6 material according to claim 1 is characterized in that: The through holes include glass fiber through holes and flame retardant through holes; a plurality of dispersed glass fiber through holes are provided on the blades of the screw from the glass fiber side feed to the material extrusion end, and the aperture of the glass fiber through holes is 40-50 μm; a plurality of dispersed flame retardant through holes are provided on the blades of the screw, and the aperture of the flame retardant through holes is 50-100 μm.

3. The screw assembly structure produced by the halogen-free flame retardant reinforced PA6 material according to claim 1 is characterized in that: The aperture of the through hole is 50-100 μm; the through holes on the blades of the screw from the glass fiber side feeding to the material extrusion end are arranged more than the through holes on the blades of the screw at other positions.

4. The screw assembly structure produced by the halogen-free flame-retardant reinforced PA6 material according to claim 2 or 3, characterized in that: The number of through holes on the blades of the screws of the inclined twin-screws increases along the extrusion direction.

5. The screw assembly structure produced by the halogen-free flame retardant reinforced PA6 material according to claim 4 is characterized in that: Along the material extrusion direction, a pair of horizontally arranged twin screws are arranged behind a pair of inclinedly arranged twin screws.

6. The production process of halogen-free flame retardant reinforced PA6 material is characterized by: A screw extruder with a screw combination structure comprising the halogen-free flame-retardant reinforced PA6 material as described in claim 5 is used, characterized in that the flame retardant and PA6 are mixed evenly and then intermittently added to the twin-screw extruder, the glass fiber is added from the side feeding port, pelletized after extrusion molding, and then injection molded.

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