JP2006110949A - Viscosity calculating method for molten resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a viscosity calculating method for a molten resin capable of obtaining the viscosity of a molten resin according to change in set temperature of the resin used for molding. <P>SOLUTION: A numerical value X2 is calculated by subtracting a numerical value X1 obtained by adding a constant a to the glass transition temperature Tg of a resin from the standard molding temperature Ta of the resin. A numerical value X3 is calculated by dividing the value X2 by a constant b. A numerical value X4 is calculated by subtracting the numerical value X3 from a constanc c. The viscosity change rate Δη/°C accompanying change in temperature of the resin is calculated by dividing the numerical value X4 by the numerical value X2. A value Y2 is calculated by multiplying a numerical value Y1 obtained by subtracting the standard molding temperature Ta from the actual molding temperature Tc by the viscosity change rate Δη/°C. The viscosity η corresponding to the actual molding temperature Tc is calculated by subtracting the value Y2 from the standard viscosity ηd at the standard molding temperature Ta. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for calculating the viscosity of a molten resin used for molding such as injection molding, cast molding, and extrusion molding.

  In resin molding such as injection molding, cast molding, and extrusion molding, the resin is melted and supplied into the mold or extruded through the mold. Then, when simulating the flow state of the molten resin during the molding, it is important to determine the viscosity of the molten resin. In order to determine the viscosity of the molten resin, the supply pressure / speed of the molten resin, the shape of the cross section of the molten resin passage, and the temperature (molding temperature) of the molten resin are important factors. In particular, the temperature of the molten resin is closely related to the viscosity, and it is well known that the viscosity decreases as the temperature of the molten resin increases. However, even if the viscosity of the molten resin changes with temperature, the rate of change varies greatly depending on the type of resin. Therefore, conventionally, it has been desired to know the viscosity of the resin corresponding to the temperature of the molten resin by a simple method according to the type of the resin.

  As what calculates | requires the viscosity of the conventional molten resin, what was described in patent document 1, patent document 2, and patent document 3 is known. For a molten resin that is a non-Newtonian fluid, the formula for obtaining the viscosity obtained by dividing the shear stress by the strain rate cannot be applied as it is. Therefore, Patent Document 1 and Patent Document 2 describe that the viscosity of the molten resin is calculated or measured by actually measuring the injection pressure. In Patent Document 3, the pressure loss formula based on the viscosity of the viscous fluid, the passage length, the flow velocity, and the passage cross-sectional area includes the viscosity coefficient based on the shear rate, the viscosity coefficient based on the shear length, and the viscosity coefficient depending on the resin type. A method of multiplying to predict pressure loss is described. However, none of those described in Patent Documents 1 to 3 can determine the viscosity of the molten resin in accordance with the change in molding temperature of each resin.

JP 2004-142204 A (0018 to 0022, FIG. 9) JP 11-10893 A (0044, 0045) JP 10-80941 A (0005, 0006)

  The present invention has been made in view of the above problems, and provides a viscosity calculation method for a molten resin that can determine the viscosity of the molten resin in accordance with a change in the molding temperature of each resin used for molding. Is.

  The method for calculating the viscosity of a molten resin according to claim 1 of the present invention calculates a viscosity change rate accompanying a temperature change of the resin from the standard molding temperature of the resin and the glass transition temperature of the resin, and the viscosity change rate. Is used to calculate the viscosity corresponding to the molding temperature of the resin.

  In the method for calculating the viscosity of the molten resin according to claim 2 of the present invention, the numerical value X1 obtained by adding the constant a to the glass transition temperature Tg of the resin is subtracted from the standard molding temperature Ta of the resin to calculate the numerical value X2. X2 is divided by the constant b to calculate the numerical value X3, the numerical value X3 is subtracted from the constant c, the numerical value X4 is calculated, and the numerical value X4 is divided by the numerical value X2 to change the viscosity change rate accompanying the temperature change of the resin Δ η / ° C. is calculated, and a numerical value Y 2 is calculated by multiplying the numerical value Y 1 obtained by subtracting the standard molding temperature Ta from the actual molding temperature Tc by the viscosity change rate Δη / ° C. From the standard viscosity ηd at the standard molding temperature Ta. By subtracting the numerical value Y2, the viscosity η corresponding to the actual molding temperature Tc of the resin is calculated.

  A computer-readable recording medium according to a third aspect of the present invention stores the melt resin viscosity calculation method according to the first or second aspect.

  Since the viscosity calculation method of the molten resin of the present invention calculates the viscosity change rate of the resin from the standard molding temperature and glass transition temperature of the resin, the viscosity of the resin is calculated using the viscosity change rate. The viscosity corresponding to the molding temperature of the molten resin can be determined by a simple method. Then, by calculating the viscosity corresponding to the molding temperature of each resin, it can be used for selecting a molding machine, setting molding conditions in the molding machine, designing a mold cavity and a molten resin passage, and the like.

  An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a graph showing the viscosity change rate of each resin. FIG. 2 is an input screen diagram of calculation software in the viscosity calculation method of the present embodiment.

  When molding a molded product by injection molding, it is suitable for molding a molded product, a mold in which a molten resin introduction path is formed toward the cavity, and supplying molten resin to the mold. An injection molding machine is used (both not shown). The solid resin made of pellets or the like supplied to the injection molding machine is brought into a molten state in the heating cylinder of the injection molding machine, and is injected and filled into the cavity of the mold. At that time, the molding temperature of the molten resin (actually set in the molding machine is the heating cylinder temperature and the nozzle temperature), the injection pressure, and the injection speed are important molding conditions. Therefore, in this embodiment, paying attention to the relationship between the molding temperature of the molten resin and the viscosity of the molten resin, the viscosity of the molten resin is calculated from the molding temperature of the molten resin to be used for setting the molding conditions of the injection molding machine. It is what you do.

  Although the change of the viscosity accompanying the temperature change of the molten resin varies greatly depending on each resin, in this embodiment, the viscosity change rate can be obtained for each resin by the following formula 1.

  Explaining the above formula 1, the numerical value X1 obtained by adding 50 (the constant a) to the glass transition temperature Tg of the molten resin is subtracted from the standard molding temperature Ta of the resin to calculate the numerical value X2, and the numerical value X2 is set to 0. The numerical value X3 is calculated by dividing by .35 (constant number b), the numerical value X3 is subtracted from 1600 (constant number c) to calculate the numerical value X4, and the numerical value X4 is divided by the numerical value X2 to obtain the temperature of the resin. Viscosity change rate Δη / ° C. accompanying change is calculated. Note that the constant a, constant b, and constant c used in Equation 1 are not necessarily limited to these values, and may be approximate values. In addition, the calculation method and order may be changed in order to obtain the same result. Further, the viscosity change rate Δη / ° C. may be obtained by using Poise (P) as a unit.

  FIG. 1 shows the viscosity change rate [Delta] [eta] / [deg.] C. of each resin calculated by the equation 1. For example, in the case of polystyrene (PS), the standard molding temperature Ta = 220 ° C. and the glass transition temperature Tg = 100 ° C. Therefore, when the numerical values are substituted into the above equation 1, the viscosity change rate Δη / ° C. = 2 Pa · s. Is calculated. In the case of polypropylene (PP), the standard molding temperature Ta = 240 ° C. and the glass transition temperature Tg = −10 ° C. When the numerical values are substituted into the above equation 1, the viscosity change rate Δη / ° C. = 0. 5 Pa · s is calculated. Separately from Equation 1, the standard viscosity ηd of each resin at the standard molding temperature Ta is prepared in advance as a numerical value of the viscosity ηd on the assumption that the flow of the resin is extremely low.

  Next, when the actual molding temperature Tc is different from the standard molding temperature Ta, the corresponding viscosity η is calculated by the following formula 2.

  For example, in the case of polystyrene (PS), the standard molding temperature Ta = 220 ° C. and the standard viscosity ηd = 360 Pa · s, but when actually molding at 240 ° C., the numerical value and the above formula 1 were used. Calculation is performed by substituting the viscosity change rate Δη / ° C. = 2 Pa · s into Equation 2 above. Specifically, a numerical value Y2 is calculated by multiplying the numerical value Y1 obtained by subtracting the standard molding temperature Ta from the molding temperature Tc by the viscosity change rate Δη / ° C, and the numerical value Y2 is subtracted from the standard viscosity ηd at the standard molding temperature Ta. Then, the viscosity η corresponding to the actual molding temperature Tc of the resin is calculated, and the viscosity η corresponding to the actual molding temperature 240 ° C. is calculated as 320 Pa · s. The viscosity η in this case is also based on the assumption that the flow of the resin is extremely low. In the case of polypropylene (PP), the standard molding temperature Ta = 240 ° C. and the standard viscosity ηd = 260 Pa · s, but when actually molding at 260 ° C., the numerical value and the viscosity determined by the above formula 1 are used. By substituting the change rate Δη / ° C. = 0.5 Pa · s into Equation 2, the viscosity η corresponding to the actual molding temperature of 260 ° C. is calculated as 250 Pa · s.

  Next, the present embodiment will be described with reference to the calculation software input screen of FIG. 2. When a resin name is selected or directly input from the cell 1 corresponding to the upper resin name, the glass transition temperature Tg of the resin, standard molding The temperature Ta, the standard viscosity ηd, and the viscosity η are displayed in the respective cells 2, 3, 5, and 6. When only the standard molding temperature Ta is input, the same values are displayed for the standard viscosity ηd and the viscosity η. An actual molding temperature (molding temperature Tc) can be input to the cell 4 below the cell 3 that displays the resin temperature, and an actual set temperature of the heating cylinder can be input. When the actual molding temperature (molding temperature Tc) is input to the cell 4, the viscosity η at the actual molding temperature (molding temperature Tc) is corrected using Equation 2 using the viscosity change rate Δη / ° C. Calculated in cell 6. The viscosity change rate Δη / ° C. is not displayed in the cell on the calculation software input screen, but may be displayed separately.

  In the case of a resin not set in the calculation software in FIG. 2 or a grade different from the standard resin even if set, the cells 7, 8, 9 arranged on the right side of the cells 2, 3, 5 are used. From this, the glass transition temperature Tg, standard molding temperature Ta, and standard viscosity ηd of the resin can be input to determine the viscosity η of the resin. Furthermore, the molten resin is actually purged from the injection device, and the viscosity obtained from the injection speed, injection pressure, nozzle cross-sectional area and length, etc. at that time can be directly input to the cell 9. When the arbitrary viscosity is directly input to the cell 9 as described above, the value input to the cell 9 is directly displayed in the cell 6 as the viscosity η. The viscosity η at the actual molding temperature (molding temperature Tc) calculated in this way may be used as it is, and the viscosity during the flow and the resin in relation to the resin passage and the shear rate as described below. The pressure loss may be obtained and used for setting molding conditions and the like.

  Next, calculation of the viscosity during the flow of the resin passage made of a circular pipe using the viscosity η calculated as described above will be described. In cell 10 of “calculation of resin viscosity during circular pipe flow” in FIG. 2, the viscosity η of cell 6 is displayed as it is. The next cell 11 is inputted with L / D which is a ratio of the diameter d of the circular tube to the length L of the resin flowing in the flow passage. The next cell 12 is input with a shear rate γ. The shear rate γ can be obtained from the following formula 3.

  Next, the viscosity coefficient C according to the shear rate is calculated in the cell 13 by the following formula 4.

  Further, the value obtained by dividing the flow length L of the resin by the diameter d of the passage is defined as the shear length with the shear rate γ as a parameter, and the change in the viscosity decrease with respect to the shear length is obtained by the following equation 5; 14 is displayed.

  Note that the shear rate γ is an expression when the passage is a circular pipe, and therefore can be applied to the nozzle and the sprue as they are. However, in a runner having a trapezoidal or square passage cross section, it is necessary to apply a formula different from the above formula.

  Furthermore, the viscosity coefficient by the kind of resin was defined as C2. The C2 is a coefficient as an empirical value for correcting the viscosity that varies depending on the type of resin, and is 1.0 for a standard grade resin and 1.1 to 1.2 for a resin containing glass fiber. For flammability grades, the standard is 1.5 to 1.8. Then, the viscosity correction coefficient C3 is obtained by the following formula 6 using the viscosity coefficient C2 and displayed in the cell 15. When the values corresponding to the resin grade are input in the cells 7, 8, and 9, correction by C2 is not necessary here.

  Then, the resin viscosity ηv during the flow is obtained by the following formula 7 and displayed in the cell 16.

  Therefore, since the resin viscosity ηv during the flow is calculated by the formula 7, it can be used for the simulation of the flow of the molten resin that is a non-Newtonian fluid.

  Further, using the viscosity η, the viscosity coefficient C due to the shear rate, the viscosity coefficient C1 based on the shear length with the shear rate as a parameter, and the viscosity coefficient C2, the formula 8 (described below as Formula 8) is multiplied, Formula 9 which calculates | requires pressure loss (DELTA) p of molten resin can also be obtained.

  Then, using each resin, molding is carried out by applying it to a nozzle having various circular pipe passage diameters and resin flow lengths (or passage lengths), and in this case, the measured value of pressure loss and the calculated value As a result of comparing Δp, the difference between the actually measured value and the calculated value Δp was within ± 10%, and it was confirmed that the difference was within practical use. The pressure loss Δp determined above is used for calculation of molding conditions such as injection speed and injection pressure, verification of mold clamping pressure, and selection of injection molding machines and molds used for molding. Is possible.

  The above calculation software is generally stored and executed in a personal computer or the like independent from the injection molding machine, but since many recent injection molding machines are equipped with a control device by a microprocessor, it is assumed that the calculation is performed by the control device. Also good. In that case, when it is predicted that the pressure loss is large due to the calculation result and molding is impossible, an alarm can be issued or the set injection pressure can be automatically increased within the range of the maximum injection pressure.

  Further, the present invention is not enumerated one by one, but is not limited to the above-described embodiment, and it goes without saying that the present invention can be applied to those modified by a person skilled in the art based on the gist of the present invention. It is.

It is a graph which shows the viscosity change rate of each resin. It is an input screen figure of the calculation software in the calculation method of the viscosity of this embodiment.

Explanation of symbols

  1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16 cells

Claims (3)

  The viscosity change rate accompanying the temperature change of the resin is calculated from the standard molding temperature of the resin and the glass transition temperature of the resin, and the viscosity corresponding to the molding temperature of the resin is calculated using the viscosity change rate. A method for calculating the viscosity of a molten resin.   The numerical value X1 obtained by adding the constant a to the glass transition temperature Tg of the resin is subtracted from the standard molding temperature Ta of the resin to calculate the numerical value X2, and the numerical value X2 is divided by the constant b to calculate the numerical value X3. The numerical value X3 is subtracted from the constant c to calculate the numerical value X4, and the numerical value X4 is divided by the numerical value X2 to calculate the viscosity change rate Δη / ° C. accompanying the temperature change of the resin, and the actual molding A numerical value Y2 is calculated by multiplying the numerical value Y1 obtained by subtracting the standard molding temperature Ta from the temperature Tc by the viscosity change rate Δη / ° C., and the numerical value Y2 is subtracted from the standard viscosity ηd at the standard molding temperature Ta. A method for calculating a viscosity of a molten resin, which calculates a viscosity η corresponding to an actual molding temperature Tc.   A computer-readable recording medium storing the melt resin viscosity calculation method according to claim 1.

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