JPH0535665B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for monitoring and controlling the thickness in the width direction of a plastic film sheet formed by an extrusion molding machine using a T-die at the extrusion port. In particular, the present invention relates to a method for improving control accuracy by optimizing die bolt operation amount.

[Conventional technology]

Generally, as a method for controlling the average thickness of this type of film sheet, a profile control method is known in which the thickness is controlled in the width direction of the film sheet. In addition, in this type of film sheet forming process, one of the causes of uneven thickness of the extruded film sheet is that the film sheet extruded from the mold extrusion port (referred to as the T die lip exit) is transferred to the forming roll. The so-called net-in phenomenon is known, in which both ends of the film sheet shrink during the arrival. This net-in phenomenon is caused by the viscoelasticity of the plastic material, and the amount of net-in or its streamline pattern, which is the amount of shrinkage of the film sheet, depends on the type of material and molding conditions [e.g., resin temperature, draw ratio (take-up speed) and outflow velocity), air gap, roll temperature, etc.]. For this reason, in an extrusion molding machine for plastic film sheets, etc., a T-die that can adjust the thickness unevenness in the width direction of the film sheet has a fixed lip and a movable lip facing each other, which form an extrusion opening. By supporting the movable lip with a plurality of die bolts disposed in the width direction of the lip outlet and rotating the lip, the gap between both lips can be adjusted and the thickness of the film sheet in the width direction can be adjusted. There are known devices that allow adjustment. Therefore, in order to properly adjust the lip gap of such a T-die, a scanning thickness gauge is used to measure the thickness by moving the measuring head back and forth in the width direction of the film sheet to be extruded. An automatic profile control system is adopted in which the die bolt is operated by a servo motor or the like based on the profile data, which is the measured value, and the lip gap of the T-die is selected at an appropriate interval (Japanese Patent Publication Publication No. 1989-1999). Publication No. 50133).

However, when determining the amount of change in the lip gap of the T-die previously described, if the film sheet thickness t, the thickness deviation Δt, the lip gap C, and the change amount ΔC, the film sheet thickness, that is, the material Based on the idea that the discharge amount is proportional to the lip gap dimension, the following formula ΔC = C/t・Δt...(1) was held to hold, and the amount of change (operation amount) ΔC was determined from the above formula (1). . However, when forming a film sheet that causes the net-in phenomenon as described above, it is difficult to properly control the profile even if the motion amount is determined using the above general formula.

Therefore, when the material and its structural elements in the lip of the T-die are the material discharge amount per unit q, the material pressure p, and the lip length l, the following formula holds: p=l{2 ⁿ⁺¹ (n+2)/C ⁿ⁺²・μ・q} ⁿ⁺¹ …(2) However, n: Structural viscosity index μ: Pseudoplastic viscosity From the above formula (2), q=p ⁿ /2 ⁿ⁺¹ (n+2) μl・C ⁿ⁺² …(3) is derived. Here, to simplify equation (3),
If p, n, μ, and l are kept constant, the following equation (4) can be obtained.

q=a・C ⁿ⁺² …(4) However, a=p ⁿ /2 ⁿ⁺¹ (n+2)・μ・l If the above equation (4) is differentiated, the following equation is obtained.

dq/dc=a(n+2)C ⁿ⁺¹ =aC ⁿ⁺² ·n+2/C =q·n+2/C (5) The following equation is obtained from the above equation (5).

dq/q=(n+2)・dc/C...(6) In the above equation (6), if dc is small, dc≒ΔC
Therefore, the following formula holds true.

Δq/q=(n+2)·ΔC/C (7) In the above equation (7), if it is considered that the discharge amount q and the film sheet thickness t are proportional, the following equation can be obtained.

Δt/t=(n+2)・ΔC/C…(8) Therefore, the following equation can be obtained from the above equation (8).

ΔC=1/n+2・C/t・Δt (9) Here, a method has been proposed in which 1/n+2・C/t is set as a constant gain G in the above equation (9) to perform more appropriate profile control. (Japanese Unexamined Patent Publication No. 1989-89120).

[Problem that the invention seeks to solve]

However, when performing profile control based on the above-mentioned arithmetic expression, the following problem occurs if the gain G is constant in the width direction of the film sheet. For example, as shown in Figure 6,
Two representative bands where the netquin phenomenon occurs are selected. In this case, the band is ₁ /
2. For the band, the net-in ratio ε ₂ is set to 1 (no net-in). That is, it is expressed by the following equation.

ε ₁ = a ₁ ′/a ₁ = 1/2 ε ₂ = a ₂ ′/a ₂ = 1 …(10) However, a ₁ = a ₂ (die bolt pitch) Now, both the band and the profile deviation e ₁ , e ₂ are the same (e ₁ = e ₂ ). in this case,
The target gap changes ΔC ₁ and ΔC ₂ of the T-die extrusion port according to the conventional method are set to be the same (ΔC ₁ =ΔC ₂ ). As a result, the flow rate changes Δq ₁ and Δq ₂ in each band are also approximately the same (Δq ₁ =Δq ₂ ). However, the amount of change Δt ₁ and Δt ₂ in the thickness of the film sheet are not the same.
That is, Δt ₁ =2Δt ₂ . This is natural since the film sheet width differs depending on the netquin. Therefore, if the profile gain G is kept constant as in the past, highly accurate profile control cannot be achieved.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to control the profile gain involved in the change in sheet thickness at a corresponding position when changing the lip gap of a T-die in profile control of a film sheet.
By integrating the gains obtained for the material flow rate change process, net-in process, and draw process in the T-die, the optimum value of the target gap change amount at the T-die extrusion port can be determined from the profile data measured by the thickness gauge. An object of the present invention is to provide a method for controlling the profile of a film sheet, which can be set and achieve highly accurate profile control.

[Means for solving problems]

A method for controlling the profile of a film sheet according to the present invention is to continuously form a film sheet using an extrusion molding machine equipped with a plurality of die bolts that can adjust the opening gap of the mold extrusion port in the width direction of the mold extrusion port. The profile data of the film sheet is measured by reciprocating the measurement head of a scanning thickness gauge in the width direction of the film sheet, and the operation amount of the die bolt is determined based on this profile data. In the method for controlling the profile of a film sheet, the thickness of the film sheet is controlled by operating the die bolt based on the operation amount, and the amount of change in the opening gap of the mold extrusion port is determined based on the profile data. The average profile gain between the amount of change in film sheet thickness corresponding to this is set, and the net-in ratio in the band where net-in of the film sheet occurs is calculated. Set the profile gain, set the target amount of change in the opening gap of the mold extrusion port corresponding to each die bolt position from these average profile gains and individual profile gains, and take action based on each of the target amounts of change. The present invention is characterized in that the operating amount of each die bolt is calculated and each die bolt is controlled based on this operating amount.

In the above film sheet profile control method, the average profile gain _p is calculated using the following formula: _p = n + 2/r _d ... () where n: structural viscosity index r _d : draw ratio. Calculate the net-in ratio ε _i in the band and the following formula ε _i = a _i ′/a () where a _i ′: Bandwidth shrunk by net-in a: Calculate with Diebolt interval, and calculate the net-in ratio ε _i and the average. profile gain
Calculate and set the individual profile gain G _pi from G _p using the following formula G _pi = G _p / ε _i (), and further calculate the amount of change C _i in the thickness of the film sheet based on the profile data and the above set value. From this, the target change amount ΔC _i of the opening gap of the die extrusion port corresponding to each die bolt position can be calculated and set using the following formula ΔC _i =C _i /G _pi ().

[Effect]

According to the film sheet profile control method of the present invention, the amount of change in the opening gap of the die extrusion port and the corresponding amount of change in the film sheet thickness is determined based on the measured profile data of the film sheet. In relation to this, the average profile gain without considering netquin is calculated and set using a conventional method, and then the average netquin ratio in the band where netquin occurs is calculated, and from this netquin ratio and the average profile gain, the average profile gain in the band where netquin occurs is calculated. The individual profile gain is calculated and set, and the optimum value of the target change amount of the opening gap of the mold extrusion port is calculated and set from each of these set values and the change amount of the film sheet thickness. By appropriately determining the operating amount of the die bolt, profile control for highly accurate film sheet molding can be easily achieved.

〔Example〕

Next, an embodiment of the film sheet profile control method according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a system configuration diagram showing an example of a film sheet extrusion molding process that implements the profile control method of the present invention. In FIG. 1, reference number 10 is an extrusion molding machine, 12 is a mold (T
14 is an extrusion outlet (rip outlet), 16 is a forming roll unit, 18 is a film sheet, 20 is a scanning thickness gauge, 22 is a winder, 24 is a measuring head, and 26 is a die bolt. Film sheet 18 measured by the measuring head 24
The measurement signal 28 indicating the thickness is inputted to the CPU 32 via the input interface 30 as profile data. The CPU 32 includes a memory 34 as a storage means, a keyboard 36 as an input means, and a display device 3 as an output means.
8 and a printer 40 are connected and arranged. Said
The CPU 32 outputs an operation signal 42 related to the die bolt operation amount for controlling the profile that has been arithmetic processed based on the profile data, and inputs this to the control unit 44 . The control unit 44 is composed of, for example, a servo motor, and is driven by the operation signal 42 to control the plurality of die bolts 2 disposed on the mold 12.
6 to adjust the opening gap of the extrusion port 14 and control the thickness of the film sheet 18 to be extruded. The film sheet 18 passes through the forming roll unit 16, then between the measuring heads 24 of a scanning thickness gauge 20, and is wound onto a winder 22. The new measurement signal detected by the measurement head 24 is input again to the CPU 32 via the input interface 30 as new profile data. The thickness of the film sheet is controlled by a control method using such a feedback loop.

However, in the present invention, when calculating the target change amount ΔC of the lip gap due to the die bolt based on profile data measured by a thickness gauge, if the lip gap is changed to the target change amount ΔC. Since the amount of change (deviation) e in the sheet thickness at the corresponding position is obtained, a new profile gain G _p is set for the relationship between the target amount of change ΔC and the deviation e. That is,
This profile gain G _p is given by the following equation.

G _p ≡e/ΔC (11) Therefore, in the present invention, the profile gain G _p is divided into the following three elements in accordance with the film sheet forming process, and these are integrated. I can get it.

(1) Rheological element _G1 This relates to the change in flow rate during the extrusion process from the lip gap of the T-die.

(2) Neckin element G ₂ This relates to the change in netquin during the process in which the film sheet extruded from the lip gap of the T-die generates netquin at the beginning of its molding.

(3) Draw element G ₃ This relates to the speed change in the process of feeding the film sheet at the same time as the net-in change occurs.

The above relationship is shown in FIG. 2. In addition, in Fig. 2, Δy ₁ , Δy ₂ , Δy ₃ are
The sheet thickness deviation Δy ₁ when the rheological element G ₁ is the gain, respectively, and then the netquin element G ₂
It shows the sheet thickness deviation Δy ₂ when G is added as a gain, and the sheet thickness deviation Δy ₃ (=e) when the draw element G ₃ is added as a gain.

Next, each element of the profile gain G _p will be explained in detail with reference to FIG. 3.

●Flow rate change process (rheological process) The relationship between the lip gap change amount ΔC and the flow rate change Δq is shown by the conventional relational expression (7). However, since the dimensions of the lip gap and the flow rate are different, the above equation (7) is replaced by the following equation assuming a change amount Δy ₁ in the sheet thickness after exiting the lip.

Δq/q=Δy ₁ /y ₁ = (n+2)・ΔC/C...(12) In the above equation (12), since y ₁ and C are not currently managed in any way, they are assumed to be the same for convenience, and as a result, the rheological element The gain G ₁ of is defined by the following equation.

G ₁ = Δy ₁ / ΔC = n+2 …(13) ●Draw process In the draw process, there is no contraction of the sheet width, only the speed is different, and the following equation of continuity holds: Δy ₂・v ₂ = Δy ₃・v ₃ (14) Therefore, from equation (14) above, the gain of the draw element
G ₃ is defined by the following equation.

G ₃ = Δy ₃ / Δy ₂ = v ₂ / v ₃ = 1/r _d …(15) However, r _d : Draw ratio Select elements (bands). Here, the net-in ratio ε _i is defined by the following equation based on the relationship shown in FIG.

ε _i =a _2i /a _1i ...(16) The following continuity equation holds between the streamlines.

r ₁ a ₁ Δy ₁ v ₁ = r ₂ a ₂ Δy ₂ v ₂ …(17) In the above equation (17), from the definition on the model, v ₁ =
v ₂ , and although the melt (r ₁ ) and sheet (r ₂ ) have different specific gravity, this is the final correction coefficient (α)
Since it can be processed within , let r ₁ = r ₂ . Therefore,
From the above equation (17), the gain G ₂ of the netquin element is defined by the following equation.

G ₂ = Δy ₂ / Δy ₁ = a ₁ / a ₂ = 1/ε (18) where ε: net-in ratio Note that the net-in ratio ε varies depending on the position in the width direction of the sheet, so the formula (16 ), the gain G _2i for each sheet width is expressed by the following formula.

G _2i = 1/ε _i (19) From the gains G ₁ , G _2i , G ₃ of each of the three elements mentioned above,
The profile gain G _pi of the present invention is expressed by the following equation.

G _pi = G ₁・G _2i・G ₃ = n+2/r _d・ε _i (20) where n: Structural viscosity index Therefore, from the relationship in equation (11) above, the target change in lip gap for each die bolt is The quantity ΔC _i is determined by the following formula.

ΔC _i =e _i /G _pi =r _d ·ε _i /n+2·e _i (21) In this way, according to the present invention, in the film sheet process shown in FIG.
From the profile data (deviation in sheet thickness at each part) e _i measured by the thickness gauge, the optimum value of the target change amount ΔC _i of the lip gap is calculated using the relational expression defined as the profile gain G _pi . In addition, precision profile control can be easily achieved by calculating and executing the operation amount of each die bolt from this target change amount ΔC _i .

Further, such profile control according to the present invention can be executed by performing the arithmetic processing described above in the CPU 32 shown in FIG. An example of arithmetic processing operations in this case will be described in detail with reference to the flowchart shown in FIG.

First, at the beginning of the control operation, a scanning thickness gauge is moved back and forth in the width direction of the film sheet to be continuously formed to measure the required profile and store these profile data. It can be held and displayed on a display device as needed. In addition to these profile measurements, the sheet width is also measured. Next, after completing a predetermined number of scans, statistical calculations are performed on the profile data.
During this time, the amount of net-in is calculated from the dimensions of the T-die extrusion opening, the set position of the die bolt, and the measured width of the film sheet, and the net-in ratio is set, and the position of the die bolt corresponding to the width of the film sheet is set. Then, these data are stored and retained. Through the above operations, each profile deviation e _i in relation to the die bolt corresponding position can be calculated. Similarly, the average net-in ratio ε _i can also be calculated.

Thereafter, in the present invention, the average profile gain _p is calculated by the following formula based on the above formula (20) (in this case, the net-in ratio is set to 1).

_p = n+2/r _d (22) Then, based on the calculated value of the average net-in ratio ε _i in relation to the already calculated die bolt corresponding position, the individual profile gain G _pi is calculated using the following formula.

G _pi = _p / ε _i ...(23) Therefore, from these results, the target amount of change ΔC _i in the relationship between the lip gap and each die bolt corresponding position
is calculated by the following equation from the relationship between the already calculated profile deviation e _i and the above equation (23).

ΔC _i =e _i /G _pi …(24) Then, from the target change amount ΔC _i of the lip gap calculated in this way, each die bolt operation amount is calculated to obtain an automatic die operation output signal, which allows automatic die operation. Adjust the die bolt of the die.

By performing similar processing operations thereafter, optimal profile control can be achieved.

Although preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various design changes can be made without departing from the spirit of the present invention. .

〔Effect of the invention〕

As is clear from the embodiments described above, according to the present invention, the gains in the flow rate change process, net-in process, and draw process at the extrusion port of the T-die are determined by the rip gap, respectively, from the profile data measured with a thickness gauge. It is possible to set the target amount of change to the optimum value, especially in the band where the net-in phenomenon occurs, by converting it according to the position of the die bolt to be adjusted, and it is possible to perform profile control for all molding conditions in extrusion molding of this type of film sheet. It is possible to improve performance and achieve highly accurate film sheet molding.

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram showing an example of an extrusion molding process for implementing the film sheet profile control method according to the present invention, and FIG. Figure 3 is an explanatory diagram of the relationship between the profile gain shown in Figure 2 and the extrusion molding process of the film sheet. Figure 4 shows the profile gain in a band with a typical net-in process. FIG. 5 is a flowchart showing an example of the extrusion molding process when the profile control method of the present invention is implemented in the system configuration shown in FIG. 1; FIG. 6 is a model diagram showing the net-in phenomenon of an extrusion-molded film sheet. DESCRIPTION OF SYMBOLS 10... Extrusion molding machine, 12... Mold, 14... Extrusion opening, 16... Forming roll unit, 18... Film sheet, 20... Scanning thickness gauge, 22... Winding machine, 2
4...Measurement head, 26...Die bolt, 28...Measurement signal, 30...Input interface, 32...CPU,
34...Memory, 36...Keyboard, 38...Display device, 40...Printer, 42...Operation signal,
44...Control unit.

Claims (1)

[Claims] 1. A film sheet is continuously extruded by an extrusion molding machine equipped with a plurality of die bolts that can adjust the opening gap of the mold extrusion port in the width direction of the mold extrusion port, and the film sheet is The profile data of the film sheet is measured by reciprocating the measurement head of the scanning thickness gauge in the width direction of the sheet, and the operation amount of the die bolt is calculated based on this profile data. In the method for controlling the profile of a film sheet, the thickness of the film sheet is controlled by operating the die bolt, the amount of change in the opening gap of the mold extrusion port and the corresponding thickness of the film sheet based on the profile data. The average profile gain between the amount of change in thickness is set, the net-in ratio in the band where net-in of the film sheet occurs is calculated, and the individual profile gain is set from this net-in ratio and the average profile gain. , From these average profile gains and individual profile gains, set the target amount of change in the opening gap of the mold extrusion port corresponding to each die bolt position, and calculate the operation amount of the corresponding die bolt based on each of the target amounts of change. A method for controlling the profile of a film sheet, characterized in that each die bolt is controlled based on the calculated operation amount. 2. In the method for controlling the profile of a film sheet according to claim 1, the average profile gain _p is calculated using the following formula _p = n + 2/r _d ... () where n: structural viscosity index r _d : draw ratio The net-in ratio ε _i in the band where film sheet net-in occurs is calculated using the following formula: ε _i = a _i ′/a … () where a _i ′: Bandwidth contracted by net-in a: Die bolt interval and the net-in ratio ε _i and the average profile gain
Calculate and set the individual profile gain G _pi from G _p using the following formula G _pi = G _p / ε _i (), and further from the amount of change in film sheet thickness C _i based on the profile data and the above set value. A film sheet profile control method in which the target change amount ΔC _i of the opening gap of the mold extrusion port corresponding to each die bolt position is calculated and set using the following formula: ΔC _i =C _i /G _pi ().