Apparatus and method for pelletizing polyethylene

Abstract

The present invention relates to an apparatus for pelletizing polyethylene including: a molten polymer separation unit that separates a polyethylene solution into a polymer melt and a solvent; a viscosity control unit that controls a viscosity of the separated polymer melt; a first measuring unit that measures a temperature and a viscosity through a temperature and viscosity indicator at a front end of the viscosity control unit; a second measuring unit that measures a temperature and a viscosity through a temperature and viscosity indicator at a rear end of the viscosity control unit; a control unit that receives information from the first measuring unit and the second measuring unit and controls the viscosity control unit; and a pelletization unit that processes the polymer melt having the controlled viscosity into a pellet shape.

Description

APPARATUS AND METHOD FOR PELLETIZING POLYETHYLENE

[0001] The present invention relates to an apparatus and method for pelletizing polyethylene having a wide range of a molecular weights with a melt index of 0.5 to 1,000 g / 10 min.

[0002]

[0003] A hot melt adhesive (HMA) uses a 100 % thermoplastic resin without using water or a solvent, and is used by turning it into a liquid state using heat when bonding solid materials at room temperature. The hot melt adhesive exerts adhesive strength while quickly hardening after being applied to an adherend in a melted liquid state, and has a characteristic of a fast adhesion speed because it does not require a drying process compared to other adhesives.

[0004] Polyethylene (PE) is a representative resin most commonly used as a hot melt adhesive, and is a polymer obtained by polymerizing ethylene as a monomer. Polyethylene is one of the synthetic polymers called a polyolefin, and, along with polypropylene, is the most widely produced product in the world. Polyethylene is a general-purpose plastic used in many aspects of life, from industrial materials to daily necessities, and is widely used in various containers, packaging films, fibers, pipes, packing, and paints.

[0005] Since the physical properties of the hot melt adhesive are greatly affected by cohesiveness and adhesive strength of a base resin (base polymer), a high molecular weight resin has been used as a base resin in the related art to increase cohesiveness and adhesive strength. However, the use of the high molecular weight resin results in a high increase in viscosity, and the high viscosity requires a high processing temperature which may cause the adhesive to decompose, carbonize, gel, or lose adhesive strength. Accordingly, problems such as a reduction in productivity of the hot melt adhesive, the occurrence of stability risks, and deformation and discoloration of attachments or substrates occured.

[0006] Therefore, a low-viscosity polyethylene (density of 0.880 to 0.860) having a melt index (MI) in a range of 500 to 1,000 g / 10 min was intended to be used for a hot melt adhesive. However, in a polyethylene process of the related art, typically, only polyethylene having an MI of 0.5 to 30 g / 10 min was produced in the form of pellets and commercialized. Polyethylene having an MI of 500 to 1,000 g / 10 min has a low crystallinity and a significantly low viscosity under normal operating conditions, which makes it difficult to make polyethylene into a pellet shape. In addition, when a dedicated process is created to pelletize polyethylene having an MI of 500 g / 10 min or more, there is a disadvantage in that it requires a lot of investment costs.

[0007]

[0008] The present invention provides an apparatus and method capable of producing polyethylene having an MI of 0.5 to 30 g / 10 min as well as polyethylene having an MI of 500 to 1,000 g / 10 min into pellets without a loss of production amount by controlling a pressure, temperature and viscosity of polyethylene in a molten state.

[0009]

[0010] In one general aspect, an apparatus for pelletizing polyethylene includes: a molten polymer separation unit that separates a polyethylene solution into a polymer melt and a solvent; a viscosity control unit that controls a viscosity of the separated polymer melt; a first measuring unit that measures a temperature and a viscosity through a temperature and viscosity indicator at a front end of the viscosity control unit; a second measuring unit that measures a temperature and a viscosity through a temperature and viscosity indicator at a rear end of the viscosity control unit; a control unit that receives information from the first measuring unit and the second measuring unit and controls the viscosity control unit; and a pelletization unit that processes the polymer melt having the controlled viscosity into a pellet shape.

[0011] The viscosity control in the viscosity control unit may be performed by the control unit in consideration of the temperature and the viscosity measured in the first measuring unit.

[0012] The viscosity control in the viscosity control unit may be performed by the control unit by feeding back the temperature and the viscosity measured in the second measuring unit.

[0013] The viscosity control unit may control the viscosity measured in the second measuring unit to be 40 to 5,000 Pa·s.

[0014] The viscosity control unit may control the temperature measured in the second measuring unit to be 280 ℃ or lower.

[0015] When the viscosity measured in the first measuring unit or the viscosity measured in the second measuring unit is higher than 5,000 Pa·s, a heat medium may be supplied to the viscosity control unit by the control unit to heat the separated polymer melt.

[0016] The heat medium may be heated to a high temperature by a furnace.

[0017] When the viscosity measured in the first measuring unit or the viscosity measured in the second measuring unit is lower than 40 Pa·s, a heat medium may be supplied to the viscosity control unit by the control unit to cool the separated polymer melt.

[0018] The heat medium may be cooled to a low temperature by a cooler.

[0019] The heat medium supplied to the viscosity control unit may be recovered and recycled by a circulation pump connected to the viscosity control unit.

[0020] A melt index of the separated polymer melt may be 0.5 to 1,000 g / 10 min.

[0021] A temperature of the separated polymer melt in the molten polymer separation unit may be 220 to 280 ℃.

[0022] The molten polymer separation unit may additionally include a feed pump at a lower end.

[0023] The first measuring unit may additionally include a pressure indicator.

[0024] The second measuring unit may additionally include a pressure indicator.

[0025] In the pelletization unit, the polymer melt having the controlled viscosity may be processed into a pellet shape through a cutter rotating in a chamber containing a refrigerant after passing through a die plate.

[0026] The pelletization unit may additionally include a pressurizing pump and / or a melt filter at a front end.

[0027] In another general aspect, a method for pelletizing polyethylene includes: a step S1) of separating a polyethylene solution into a polymer melt and a solvent; a step S2) of measuring a temperature and a viscosity of the separated polymer melt; a step S3) of heating or cooling the separated polymer melt to control the viscosity of the separated polymer melt; and a step S4) of processing the polymer melt having the controlled viscosity into a pellet shape.

[0028] A melt index of the separated polymer melt may be 0.5 to 1,000 g / 10 min.

[0029] In the step S1), a temperature of the separated polymer melt may be 220 to 280 ℃.

[0030] In the step S2), a pressure of the separated polymer melt may be additionally measured.

[0031] In the step S3), the viscosity of the separated polymer melt may be controlled to be 40 to 5,000 Pa·s.

[0032] In the step S3), the temperature of the separated polymer melt may be controlled to be 280 ℃ or lower.

[0033] When the viscosity measured in the step S2) is higher than 5,000 Pa·s, the separated polymer melt may be heated.

[0034] When the viscosity measured in the step S2) is lower than 40 Pa·s, the separated polymer melt may be cooled.

[0035]

[0036] According to the present invention, polyethylene having a wide range of a molecular weights with a melt index (MI) of 0.5 to 1,000 g / 10 min may be pelletized in a single line by adding several devices such as a heat exchanger and control structures to a polyethylene process of the related art. Accordingly, it is possible to produce products having various molecular weights and supply necessary products at low production costs depending on market conditions.

[0037] In addition, products having a low viscosity with an MI of 500 to 1,000 g / 10 min corresponding to high-value-added hot melt adhesives may be produced in the polyethylene process of the related art without creating a dedicated process, such that investment and production costs are saved.

[0038]

[0039] FIG. 1 illustrates an apparatus for pelletizing polyethylene according to the present invention.

[0040] FIG. 2 illustrates the results of pelletizing polyethylene having an MI of 1,000 according to the present invention.

[0041]

[0042] Embodiments disclosed in the present specification may be modified into various different forms and the technology according to an embodiment is not limited to the embodiments described below. In addition, an implementation of an embodiment is provided in order to further completely describe the present disclosure to those skilled in the art. Technical terms and scientific terms used herein have the general meanings understood by those skilled in the art to which the present invention pertains unless otherwise defined, and a description for the known function and configuration unnecessarily obscuring the gist of the present invention will be omitted in the following description and the accompanying drawings.

[0043] In addition, unless the context clearly indicates otherwise, singular forms used in the present specification and the scope of the appended claims are intended to include plural forms.

[0044] In addition, the terms "first", "second", and the like in the present specification and the scope of the appended claims are not used as limiting meanings, but are used to distinguish one component from another component.

[0045] In addition, in the present specification and the appended claims, when a film (layer), a region, or a component is positioned "above", "on an upper portion", "on an upper end", "below", "on a lower portion", or "on a lower end" another part, this includes not only a case where one part is in contact with another part, but also a case where another part exists between the two parts.

[0046] In addition, the terms "about" and "substantially" used in the present specification and the appended claims are used with a numerical value or in the vicinity of the numerical value in the meanings mentioned when inherent manufacturing and material allowable errors are presented, and are used to prevent unconscious infringers from illegally using the accurate or absolute numbers disclosed in the present invention to help understanding of the present specification and the appended claims.

[0047] In addition, a numerical range used in the present specification includes upper and lower limits and all values within these limits, increments logically derived from a form and span of a defined range, all double limited values, and all possible combinations of the upper and lower limits in the numerical range defined in different forms.

[0048] Furthermore, the terms "comprise(s)", "include(s)", "have (has)", and the like used in the present specification and the scope of the appended claims indicate the presence of features or components described in the specification, and do not preclude the presence or addition of one or more other features or components, unless specifically limited.

[0049] Hereinafter, an apparatus and method for pelletizing polyethylene of the present invention will be described in detail with reference to the accompanying drawings.

[0050]

[0051] A hot melt adhesive (HMA) uses a 100 % thermoplastic resin without using water or a solvent, and is used by turning it into a liquid state using heat when bonding solid materials at room temperature. The hot melt adhesive exerts adhesive strength while quickly hardening after being applied to an adherend in a melted liquid state, and has a characteristic of a fast adhesion speed because it does not require a drying process compared to other adhesives.

[0052] Since the physical properties of the hot melt adhesive are greatly affected by cohesiveness and adhesive strength of a base resin (base polymer), a high molecular weight resin has been used as a base resin in the related art to increase cohesiveness and adhesive strength. However, the use of the high molecular weight resin results in a high increase in viscosity, and the high viscosity requires a high processing temperature which may cause the adhesive to decompose, carbonize, gel, or lose adhesive strength. Accordingly, problems such as a reduction in productivity of the hot melt adhesive, the occurrence of stability risks, and deformation and discoloration of attachments or substrates occured.

[0053] Therefore, a low-viscosity polyethylene (density of 0.880 to 0.860) having a melt index (MI) in a range of 500 to 1,000 g / 10 min was intended to be used for a hot melt adhesive. However, in a polyethylene process of the related art, typically, only polyethylene having an MI of 0.5 to 30 g / 10 min was produced in the form of pellets and commercialized. Polyethylene having an MI of 500 to 1,000 g / 10 min has a low crystallinity and a significantly low viscosity under normal operating conditions, which makes it difficult to make polyethylene into a pellet shape. In addition, when a dedicated process is created to pelletize polyethylene having an MI of 500 g / 10 min or more, there is a disadvantage in that it requires a lot of investment costs.

[0054] Therefore, the present invention provides an apparatus and method capable of producing polyethylene having an MI of 0.5 to 30 g / 10 min as well as polyethylene having an MI of 500 to 1,000 g / 10 min into pellets without a loss of production amount by controlling a pressure, temperature and viscosity of polyethylene in a molten state.

[0055] In the present specification, the "pellet" means a small piece formed by compressing a material into a sphere, cylinder, or prismatic shape with a diameter or side length of about 2 to 5 mm.

[0056] FIG. 1 illustrates an apparatus for pelletizing polyethylene according to the present invention.

[0057] An apparatus for pelletizing polyethylene of the present invention may include: a molten polymer separation unit that separates a polyethylene solution into a polymer melt and a solvent; a viscosity control unit that controls a viscosity of the separated polymer melt; a first measuring unit that measures a temperature and a viscosity through a temperature and viscosity indicator at a front end of the viscosity control unit; a second measuring unit that measures a temperature and a viscosity through a temperature and viscosity indicator at a rear end of the viscosity control unit; a control unit that receives information from the first measuring unit and the second measuring unit and controls the viscosity control unit; and a pelletization unit that processes the polymer melt having the controlled viscosity into a pellet shape.

[0058] A melt index (MI) indicates the fluidity of a resin, and a higher melt index indicates preferable fluidity. Therefore, as the MI increases, a molecular weight of a polymer decreases. In general, since a relationship between a molecular weight and a melt index is inversely proportional, a high molecular weight has a low melt index value, and conversely, a low molecular weight has a high melt index value.

[0059] In the present invention, the melt index (MI) of polyethylene is not particularly limited, and the polymer may be, for example, a low-density polyethylene elastomer (polyolefin elastomer, POE) having an MI of 0.5 to 30 g / 10 min, linear low-density polyethylene (LLDPE) having an MI of 0.5 to 5 g / 10 min, a polyolefin plastomer (POP) having an MI of 1.0 to 5.0 g / 10 min, or a hot melt adhesive (HMA) having an MI of 500 to 1,000 g / 10 min corresponding to the POE density through a process change, but the present invention is not limited thereto.

[0060] In the molten polymer separation unit, a polyethylene solution is separated into a polymer melt and a solvent, and the separated polymer melt is heated to a processable temperature range. The molten polymer separation unit is not particularly limited, and may be performed using, for example, a heating hopper, a heating silo, a heating feeder, or the like, but is not limited thereto.

[0061] In the molten polymer separation unit, the polymer melt and the solvent are separated by lowering the pressure to a vacuum and evaporating the solvent through a flash process, such that the solvent may be separated from the polymer melt at a level of several hundred to several thousand ppm.

[0062] An MI of the separated polymer melt may be 0.5 to 1,000 g / 10 min.

[0063] A temperature of the separated polymer melt is not particularly limited, and may be 220 to 280 ℃, 230 to 280 ℃, or 230 to 250 ℃. When the temperature of the separated polymer melt is lower than 220 ℃, the temperature is too low, which makes it difficult to separate the solvent, and the viscosity increases, which increases the pressure loss within the process and reduces the production amount, and when the temperature of the separated polymer melt is higher than 280 ℃, the temperature is too high, which increases the possibility of thermal decomposition of the polymer.

[0064] The separated solvent may be a C3-C20 hydrocarbon, and preferably includes one or more selected from butane, isobutane, pentane, hexane, heptane, octane, isooctane, nonane, decane, dodecane, cyclohexane, methylcyclohexane, benzene, toluene, and xylene. In addition, the separated solvent may be recovered and recycled for process cost-effectiveness.

[0065] As an embodiment, in the present invention, a polyethylene solution is injected into the molten polymer separation unit and pelletized, and solid polyethylene may also be injected, melted, and pelletized.

[0066] The molten polymer separation unit may additionally include a feed pump at a rear end to move the separated polymer melt to a line connected to the pelletization unit. The feed pump is not particularly limited, and any general feed pump may be used without limitations.

[0067] The viscosity control unit controls a viscosity of the separated polymer melt flowing from the molten polymer separation unit. In general, a viscosity of a fluid changes depending on a temperature; as the temperature increases, the viscosity decreases, and conversely, as the temperature decreases, the viscosity increases. The viscosity control in the viscosity control unit is not particularly limited, but the viscosity of the separated polymer melt may be controlled through heat exchange with a heat medium in a heat exchanger. The heat medium is not particularly limited as long as it may be heated to a high temperature and operated at a low temperature, and may be preferably dibenzyl toluene (DBT), but is not limited thereto.

[0068] The viscosity control unit may be controlled by a control unit including a distributed control system (DCS). The control unit controls the viscosity control performed in the viscosity control unit so that pelletization may be performed smoothly.

[0069] The first measuring unit measures the temperature and the viscosity of the separated polymer melt flowing into the viscosity control unit through the temperature and viscosity indicator and transmits the measured temperature and viscosity to the control unit, thereby causing the control unit to control heating or cooling the separated polymer melt in the viscosity control unit.

[0070] Since the viscosity of the separated polymer melt changes depending on a temperature, the temperature indicator is used to determine an appropriate temperature control level for controlling the viscosity, and a conventional temperature measuring device may be used.

[0071] As the viscosity indicator, a conventional viscosity measuring device may be used, and the viscosity indicator may measure the viscosity online by using a degree of vibration damping according to the viscosity of the separated polymer melt. Alternatively, a pressure indicator may be additionally included in the viscosity measuring device to measure the viscosity by measuring the pressure loss while flowing the separated polymer melt at a constant flow rate.

[0072] The pressure indicator is intended to determine a degree of pressure loss and use the determined degree of pressure loss for viscosity control, and a conventional pressure measuring device may be used.

[0073] The second measuring unit measures the temperature and the viscosity of the polymer melt having the controlled viscosity discharged from the viscosity control unit through the temperature and viscosity indicator and transmits the measured temperature and viscosity to the control unit for feedback, thereby controlling the viscosity control and the flow rate of the heat medium in the viscosity control unit. In addition, the second measuring unit may additionally include a pressure indicator to measure the pressure of the polymer melt having the controlled viscosity discharged from the viscosity control unit.

[0074] Since the separated polymer melt flowing into the viscosity control unit has a large difference in viscosity depending on the melt index (MI), the viscosity should be controlled to 40 to 5,000 Pa·s in order to produce a polymer melt having an MI of 0.5 to 1,000 g / 10 min into pellets. The viscosity of the polymer melt should be 40 Pa·s or higher at a shear rate of 1,000 / s to be produced into pellets. When the viscosity is lower than 40 Pa·s, it is difficult to cut the polymer melt into a pellet shape at a desired production speed due to the low viscosity, and even when the polymer melt is cut, the pellets may have tails or may be produced into an abnormal shape. In addition, when the viscosity is higher than 5,000, a high pressure loss may occur during the process, which may cause problems such as a reduction in productivity due to the high pressure loss, the occurrence of safety risk, and deformation and discoloration of attachments or substrates.

[0075] When the temperature of the separated polymer melt is lower than 220 ℃, the temperature is too low, which makes it difficult to separate the solvent, and the viscosity increases, which increases the pressure loss within the process and reduces the production amount, and when the temperature of the separated polymer melt is higher than 280 ℃, the temperature is too high, and therefore, the temperature should be controlled to be 280 ℃ or lower.

[0076] The control unit controls the viscosity of the polymer melt discharged from the viscosity control unit based on the temperature, viscosity, and pressure data measured in the first measuring unit, and to this end, the control unit controls the temperature and flow rate of the heat medium by an input calculation formula or logic so that the polymer melt may be controlled to an appropriate temperature.

[0077] As an embodiment, when the viscosity measured in the first measuring unit or the viscosity measured in the second measuring unit is higher than 5,000 Pa·s, the heat medium heated to a high temperature by a furnace is supplied to the viscosity control unit, and the temperature of the separated polymer melt increases and the viscosity of the separated polymer melt decreases through heat exchange.

[0078] As another embodiment, when the viscosity measured in the first measuring unit or the viscosity measured in the second measuring unit is lower than 40 Pa·s, the heat medium cooled to a low temperature by a cooler is supplied to the viscosity control unit, and the temperature of the separated polymer melt decreases and the viscosity of the separated polymer melt increases through heat exchange.

[0079] The viscosity of the polymer melt having the controlled viscosity measured in the second measuring unit may have a viscosity of 40 to 5,000 Pa·s and a temperature of 280 ℃ or lower.

[0080] The heat medium supplied to the viscosity control unit and heat-exchanged with the separated polymer melt may be recovered and recycled by a circulation pump connected to the viscosity control unit. The circulation pump is not particularly limited, and any general feed pump may be used without limitations.

[0081] In the pelletization unit, the polymer melt having the controlled viscosity is processed into a pellet shape, and the processing may be performed using various molding units. For example, the processing may be performed using a general pelletizer, but is not limited thereto.

[0082] As an embodiment, the polymer melt having the controlled viscosity flowing into the pelletization unit may be discharged after passing through a die plate and may be cut into small pieces by a cutter rotating in a chamber containing a refrigerant to be produced into pellets. The refrigerant is not particularly limited as long as it may cool the polymer melt discharged from the die plate, and is preferably general water in consideration of harmlessness to the human body and ease of removal, but the present invention is not limited thereto.

[0083] The pelletization unit may additionally include a pressurizing pump and / or a melt filter at a front end. The pressurizing pump is used to move the polymer melt having the controlled viscosity to the pelletization unit, and any general pressurizing pump may be used without limitations. In addition, the melt filter is intended to remove foreign substances from the polymer melt having the controlled viscosity for homogenization, and may be, for example, a screen changer, but is not limited thereto.

[0084] The produced pellets are formed into a final product through an additional process, and to this end, the produced pellets should have a certain size and shape. Since the pellets produced according to the present invention have a wide range of a molecular weight, low-viscosity polyethylene may be pellets having an oval shape, and high-viscosity polyethylene may be pellets having a shape close to a cylinder.

[0085] A method for pelletizing polyethylene of the present invention may include: a step S1) of separating a polyethylene solution into a polymer melt and a solvent; a step S2) of measuring a temperature and a viscosity of the separated polymer melt; a step S3) of heating or cooling the separated polymer melt to control the viscosity of the separated polymer melt; and a step S4) of processing the polymer melt having the controlled viscosity into a pellet shape.

[0086] In the present invention, the melt index (MI) of polyethylene is not particularly limited, and the polymer may be, for example, a low-density polyethylene elastomer (polyolefin elastomer, POE) having an MI of 0.5 to 30 g / 10 min, linear low-density polyethylene (LLDPE) having an MI of 0.5 to 5 g / 10 min, a polyolefin plastomer (POP) having an MI of 1.0 to 5.0 g / 10 min, or a hot melt adhesive (HMA) having an MI of 500 to 1,000 g / 10 min corresponding to the POE density through a process change, but the present invention is not limited thereto.

[0087] In the step S1), a polyethylene solution is separated into a polymer melt and a solvent, and the separated polymer melt is heated to a processable temperature range. An MI of the separated polymer melt may be 0.5 to 1,000 g / 10 min.

[0088] In the step S1), a temperature of the separated polymer melt is not particularly limited, and may be 220 to 280 ℃, 230 to 280 ℃, or 230 to 250 ℃. When the temperature of the separated polymer melt is lower than 220 ℃, the temperature is too low, which makes it difficult to separate the solvent, and the viscosity increases, which increases the pressure loss within the process and reduces the production amount, and when the temperature of the separated polymer melt is higher than 280 ℃, the temperature is too high, which increases the possibility of thermal decomposition of the polymer.

[0089] The separated solvent may be a C3-C20 hydrocarbon, and preferably includes one or more selected from butane, isobutane, pentane, hexane, heptane, octane, isooctane, nonane, decane, dodecane, cyclohexane, methylcyclohexane, benzene, toluene, and xylene. In addition, the separated solvent may be recovered and recycled for process cost-effectiveness.

[0090] In the step S2), the temperature and the viscosity of the separated polymer melt are measured. The measurement method is not particularly limited, and any method may be used without limitations as long as it is a method for measuring a temperature and a viscosity in general. In addition, a pressure of the separated polymer melt may be additionally measured, and any method may be used without limitations as long as it is a method for measuring a pressure in general.

[0091] In the step S3), the polymer melt separated in the step S1) is cooled or heated according to the viscosity measured in the step S2) to control the viscosity to 40 to 5,000 Pa·s. When the viscosity is lower than 40 Pa·s, it is difficult to cut the polymer melt into a pellet shape due to the low viscosity, and even when the polymer melt is cut, the pellets may have tails or may be produced into an abnormal shape. In addition, when the viscosity is higher than 5,000, a high processing temperature is required, and such a high processing temperature may cause problems such as a reduction in productivity, the occurrence of safety risk, and deformation and discoloration of attachments or substrates.

[0092] When the temperature of the separated polymer melt is lower than 220 ℃, the temperature is too low, which makes it difficult to separate the solvent, and the viscosity increases, which increases the pressure loss within the process and reduces the production amount, and when the temperature of the separated polymer melt is higher than 280 ℃, the temperature is too high, and therefore, the temperature should be controlled to be 280 ℃ or lower.

[0093] Although not particularly limited, the step S3) may be performed using a heat exchanger, and the temperature and the viscosity may be controlled through heat exchange between the separated polymer melt and the heat medium.

[0094] As an embodiment, when the viscosity measured in the step S2) is higher than 5,000 Pa·s, the separated polymer melt is heated to increase the temperature of the separated polymer melt and decrease the viscosity of the separated polymer melt.

[0095] As another embodiment, when the viscosity measured in the step S2) is lower than 40 Pa·s, the separated polymer melt is cooled to decrease the temperature of the separated polymer melt and increase the viscosity of the separated polymer melt.

[0096] In the step S4), the polymer melt having the controlled viscosity may be processed into a pellet shape, and various molding units may be used. For example, the step S4) may be performed using a general pelletizer, but is not limited thereto.

[0097] As an embodiment, the polymer melt having the controlled viscosity may be cut into small pieces by a cutter rotating in a chamber containing a refrigerant to be produced into pellets.

[0098] According to the present invention, polyethylene having a wide range of a molecular weights with a melt index (MI) of 0.5 to 1,000 g / 10 min may be pelletized in a single line by adding several devices such as a heat exchanger and control structures to a polyethylene process of the related art. Accordingly, it is possible to produce products having various molecular weights and supply necessary products at low production costs depending on market conditions.

[0099] In addition, products having a low viscosity with an MI of 500 to 1,000 g / 10 min corresponding to high-value-added hot melt adhesives may be produced in the polyethylene process of the related art without creating a dedicated process, such that investment and production costs are saved.

[0100]

[0101] Hereinafter, Examples and Experimental Examples will be described in detail below. However, Examples and Experimental Examples to be described below are merely illustrative of a part of an embodiment, and the technology described in the present specification is not limited thereto.

[0102]

[0103] <Experimental Example 1>

[0104] A polyethylene polymer melt is a non-Newtonian fluid and exhibits a shear thinning phenomenon in which a viscosity decreases depending on an external force (shear rate). Table 1 shows the viscosity of the polyethylene polymer melt according to the shear rate. A shear rate of a general pelletizing line is approximately 1.0 / s, and a shear rate of a die plate has a value of 1,000 / s. Therefore, the shear rate was set to 0.1 to 1,000 / s.

[0105]

[0106] MITemp.(℃)Shear Rate ( / s)0.11.01010010000.52805,0003,8002,2001,0005102458,1005,6003,0001,2007002359,4006,3003,3001,30075012454,0003,3002,00090053052457006505503702802524512012012011010050011055100011038

[0107]

[0108] The viscosity of the polyethylene polymer melt having an MI of 0.5 to 25 decreased as the shear rate increased due to the shear thinning phenomenon, but the viscosity of the polyethylene polymer melt having an MI of 500 to 1,000 did not change because the shear thinning phenomenon according to the shear rate did not occur.

[0109]

[0110] <Experimental Example 2>

[0111] The pelletization results according to the temperature and the viscosity of polyethylene having an MI of 1,000 were confirmed. Table 2 shows the viscosity of polyethylene having an MI of 1,000 according to the temperature.

[0112]

[0113] Temperature (℃)90110120Viscosity (Pa·s)753830

[0114]

[0115] FIG. 2 illustrates the results of pelletizing polyethylene having an MI of 1,000 according to the present invention. At a temperature of 90 ℃, the viscosity was 75 Pa·s and pellets having a normal shape were produced. At a temperature of 110 ℃, the viscosity was 38 Pa·s and pellets having a normal shape were not produced. In addition, at a temperature of 120 ℃, the viscosity was 30 Pa·s and pellets having a normal shape were not produced. Accordingly, it was confirmed that the viscosity of polyethylene having an MI of 1,000 should be 50 Pa·s or higher to form a normal pellet shape.

[0116]

[0117] <Example 1>

[0118] Using a system for pelletizing polyethylene according to the present invention, a polyethylene solution having an MI of 1 g / 10 min was placed in a molten polymer separation unit at 250 ℃, and then a polymer melt separated from a solvent was supplied to a heat exchanger of a viscosity control unit through a feed pump. A pressure (P1), temperature (T1), and viscosity (AI1) at a front end of the heat exchanger were measured, the viscosity of the polymer melt was controlled by supplying a heat medium having a temperature of 250 ℃ to the heat exchanger, and then, a pressure (P2), temperature (T2), and viscosity (AI2) at a rear end of the heat exchanger were measured. The polymer melt having the controlled viscosity was produced into pellets using a pelletizer, and the production amount was measured.

[0119]

[0120] <Example 2>

[0121] Pellets were produced in the same manner as that of Example 1, except that the MI of polyethylene was 30 g / 10 min.

[0122]

[0123] <Example 3>

[0124] Pellets were produced in the same manner as that of Example 1, except that the MI of polyethylene was 0.5 g / 10 min and the temperature of the heat medium was 300 ℃.

[0125]

[0126] <Example 4>

[0127] Pellets were produced in the same manner as that of Example 1, except that the MI of polyethylene was 1,000 g / 10 min and the temperature of the heat medium was 90 ℃.

[0128]

[0129] <Example 5>

[0130] Pellets were produced in the same manner as that of Example 1, except that the MI of polyethylene was 1,000 g / 10 min and the temperature of the heat medium was 80 ℃.

[0131]

[0132] <Comparative Example 1>

[0133] Pellets were produced in the same manner as that of Example 1, except that the MI of polyethylene was 0.5 g / 10 min and the temperature of the heat medium was 250 ℃.

[0134]

[0135] <Comparative Example 2>

[0136] Pellets were produced in the same manner as that of Example 1, except that the MI of polyethylene was 1,000 g / 10 min and the temperature of the heat medium was 230 ℃.

[0137]

[0138] <Experimental Example 3>

[0139] Examples 1 to 3 and Comparative Examples 1 and 2 were compared, and the process conditions and the amount of pellets produced for each were shown in Table 3. A decrease in pressure is a change in pressure that occurs as the polymer melt passes through the heat exchanger, and is represented by P1-P2.

[0140]

[0141] Example 1Example 2Example 3Example 4Example 5Comparative Example 1Comparative Example 2MI (g / 10 min)1300.5100010000.51000P1 (kgf / cm2)8827.59014.119909T1 (℃)245245245225225245225A1 (Pa·s)380011080503380503P2 (kgf / cm2)5424521215508.5T2 (℃)24524528010590245225A2 (Pa·s)38001104870517580503Decrease in pressure(kgf / cm2)343.5382.14400.5Heat medium temperature (℃)2502503009080250230Production amount(kg / hr)505050365026Not available for production

[0142]

[0143] In Examples 1 and 2, as the molecular weight and the viscosity were in appropriate ranges, pellets were produced without changes in temperature and viscosity through a heat exchanger. In Example 3, as the molecular weight and the viscosity were high, pellets were produced by increasing the temperature and decreasing the viscosity through a heat exchanger. In addition, in Examples 4 and 5, as the molecular weight and the viscosity were low, pellets were produced by decreasing the temperature and increasing the viscosity through a heat exchanger.

[0144] However, in Comparative Example 1, the temperature and the viscosity were not changed through a heat exchanger, and the amount of pellets produced was low due to a high pressure loss. In Comparative Example 2, the molecular weight and the viscosity were low, and pellets were produced without changes in temperature and viscosity through a heat exchanger, but pelletization was not possible due to a low viscosity, and thus, no pellets were produced.

[0145] By controlling the temperature and the viscosity in the heat exchanger as in the examples described above, polyethylene having a wide range of a molecular weights with a MI of 0.5 to 1,000 g / 10 min was produced into pellets.

[0146]

[0147] Hereinabove, although the present invention has been described by specific matters and exemplary embodiments, they have been provided only for assisting in the entire understanding of the present invention. Therefore, the present invention is not limited to the exemplary embodiments. Various modifications and changes may be made by those skilled in the art to which the present invention pertains from this description. Therefore, the spirit described in the present specification should not be limited to the described embodiments, but the claims and all modifications equal or equivalent to the claims are intended to fall within the spirit described in the present specification.

Claims

An apparatus for pelletizing polyethylene, the apparatus comprising:a molten polymer separation unit that separates a polyethylene solution into a polymer melt and a solvent;a viscosity control unit that controls a viscosity of the separated polymer melt;a first measuring unit that measures a temperature and a viscosity through a temperature and viscosity indicator at a front end of the viscosity control unit;a second measuring unit that measures a temperature and a viscosity through a temperature and viscosity indicator at a rear end of the viscosity control unit;a control unit that receives information from the first measuring unit and the second measuring unit and controls the viscosity control unit; anda pelletization unit that processes the polymer melt having the controlled viscosity into a pellet shape.The apparatus of claim 1, wherein the viscosity control in the viscosity control unit is performed by the control unit in consideration of the temperature and the viscosity measured in the first measuring unit.The apparatus of claim 1, wherein the viscosity control in the viscosity control unit is performed by the control unit by feeding back the temperature and the viscosity measured in the second measuring unit.The apparatus of claim 1, wherein the viscosity control unit controls the viscosity measured in the second measuring unit to be 40 to 5,000 Pa·s.The apparatus of claim 1, wherein the viscosity control unit controls the temperature measured in the second measuring unit to be 280 ℃ or lower.The apparatus of any one of claims 2 to 5, wherein when the viscosity measured in the first measuring unit or the viscosity measured in the second measuring unit is higher than 5,000 Pa·s, a heat medium is supplied to the viscosity control unit by the control unit to heat the separated polymer melt.The apparatus of claim 6, wherein the heat medium is heated to a high temperature by a furnace.The apparatus of any one of claims 2 to 5, wherein when the viscosity measured in the first measuring unit or the viscosity measured in the second measuring unit is lower than 40 Pa·s, a heat medium is supplied to the viscosity control unit by the control unit to cool the separated polymer melt.The apparatus of claim 8, wherein the heat medium is cooled to a low temperature by a cooler.The apparatus of any one of claims 6 to 9, wherein the heat medium supplied to the viscosity control unit is recovered and recycled by a circulation pump connected to the viscosity control unit.The apparatus of claim 1, wherein a melt index of the separated polymer melt is 0.5 to 1,000 g / 10 min.The apparatus of claim 1, wherein a temperature of the separated polymer melt in the molten polymer separation unit is 220 to 280 ℃.The apparatus of claim 1, wherein the molten polymer separation unit additionally includes a feed pump at a lower end.The apparatus of claim 1, wherein the first measuring unit additionally includes a pressure indicator.The apparatus of claim 1, wherein the second measuring unit additionally includes a pressure indicator.The apparatus of claim 1, wherein in the pelletization unit, the polymer melt having the controlled viscosity is processed into a pellet shape through a cutter rotating in a chamber containing a refrigerant after passing through a die plate.The apparatus of claim 1, wherein the pelletization unit additionally includes a pressurizing pump and / or a melt filter at a front end.A method for pelletizing polyethylene, the method comprising:a step S1) of separating a polyethylene solution into a polymer melt and a solvent;a step S2) of measuring a temperature and a viscosity of the separated polymer melt;a step S3) of heating or cooling the separated polymer melt to control the viscosity of the separated polymer melt; anda step S4) of processing the polymer melt having the controlled viscosity into a pellet shape.The method of claim 18, wherein a melt index of the separated polymer melt is 0.5 to 1,000 g / 10 min.The method of claim 18, wherein in the step S1), a temperature of the separated polymer melt is 220 to 280 ℃.The method of claim 18, wherein in the step S2), a pressure of the separated polymer melt is additionally measured.The method of claim 18, wherein in the step S3), the viscosity of the separated polymer melt is controlled to be 40 to 5,000 Pa·s.The method of claim 18, wherein in the step S3), the temperature of the separated polymer melt is controlled to be 280 ℃ or lower.The method of claim 22 or 23, wherein when the viscosity measured in the step S2) is higher than 5,000 Pa·s, the separated polymer melt is heated.The method of claim 22 or 23, wherein when the viscosity measured in the step S2) is lower than 40 Pa·s, the separated polymer melt is cooled.

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