阅读说明：本技术 吹膜成型装置 (Blown film forming device ) 是由 藤原一优 于 2020-03-23 设计创作，主要内容包括：本发明提供一种能够成型更高品质的管状且薄膜状的树脂的吹膜成型装置。吹膜成型装置具备：获取部,获取与从模具挤出的管状树脂相关的数据；及判定部(55),根据通过获取部获取的数据来推断在管状树脂中产生的应力,且在所推断的应力为规定的阈值以上的情况下,判定为存在管状树脂断裂的可能。(The invention provides a blown film forming apparatus capable of forming a tubular and film-like resin with higher quality. The blown film forming apparatus includes: an acquisition section that acquires data relating to a tubular resin extruded from a die; and a determination unit (55) that estimates the stress generated in the tubular resin from the data acquired by the acquisition unit, and determines that the tubular resin is likely to break when the estimated stress is equal to or greater than a predetermined threshold value.)

1. A blown film forming apparatus is characterized by comprising:

an acquisition section that acquires data relating to a tubular resin extruded from a die; and

and a determination unit that estimates stress generated in the tubular resin from the data acquired by the acquisition unit, and compares the estimated stress with a predetermined threshold value to determine whether or not there is a possibility of breakage of the tubular resin.

2. The blown film forming apparatus according to claim 1,

the determination unit estimates, based on a set value relating to molding, a stress generated in the tubular resin when molding is performed at the set value, and compares the estimated stress with a predetermined threshold value to determine whether or not there is a possibility of breakage of the tubular resin.

3. The blown film forming apparatus according to claim 1 or 2,

the threshold value is obtained based on information on stress generated in the tubular resin when the tubular resin is broken in the past molding.

4. A blown film forming apparatus is characterized by comprising:

the determination unit estimates, based on a set value relating to molding, a stress generated in the tubular resin extruded from the die when the molding is performed at the set value, and compares the estimated stress with a predetermined threshold value to determine whether or not there is a possibility of breakage of the tubular resin.

Technical Field

The present application claims priority based on japanese patent application No. 2019-060879, applied on 27/3/2019. The entire contents of this Japanese application are incorporated by reference into this specification.

The invention relates to a film blowing forming device.

Background

There is known a blown film molding in which a molten resin is extruded from a die into a tubular shape, and air is blown into the inside of the tubular shape to expand the resin and form a thin film. Conventionally, there has been proposed a technique for controlling the thickness of the resin within a target range by adjusting the lip width, the volume of cooling air, and the air temperature.

Patent document 1: japanese patent laid-open publication No. 2017-177348

Conventionally, resin fracture occurs during molding. In the case of a break, the blown film forming apparatus must be restarted, and the work efficiency is lowered. Also, resin is wasted.

Disclosure of Invention

The present invention has been made in view of such circumstances, and an exemplary object of one embodiment thereof is to provide a blown film forming apparatus capable of suppressing resin breakage.

In order to solve the above problem, a blown film forming apparatus according to an embodiment of the present invention includes: an acquisition section that acquires data relating to a tubular resin extruded from a die; and a determination unit that estimates stress generated in the tubular resin from the data acquired by the acquisition unit, and determines whether or not there is a possibility of breakage of the tubular resin by comparing the estimated stress with a predetermined threshold value.

Another embodiment of the present invention is also a blown film forming apparatus. The device is provided with: the determination unit estimates, based on a set value relating to molding, a stress generated in the tubular resin extruded from the die when the molding is performed at the set value, and compares the estimated stress with a predetermined threshold value to determine whether or not there is a possibility of breakage of the tubular resin.

In addition, any combination of the above-described constituent elements or any combination obtained by mutually replacing the constituent elements and expressions of the present invention among methods, apparatuses, systems and the like is also effective as an aspect of the present invention.

Effects of the invention

According to the present invention, a blown film forming apparatus capable of suppressing resin breakage can be provided.

Drawings

Fig. 1 is a diagram showing a basic configuration of a blown film forming apparatus according to an embodiment.

Fig. 2 is a block diagram schematically showing the function and configuration of the control device of fig. 1.

Fig. 3 is a flowchart showing an operation of determining the breakage of the bubble at the time of setting by the blown film forming apparatus of fig. 1.

Fig. 4 is a flowchart showing an operation of determining the breakage of the bubble at the time of molding by the blown film molding apparatus of fig. 1.

In the figure: 1-blown film forming device, 6-thickness obtaining part, 7-control device, 10-mould, 26-solidification line height obtaining part, 55-determination part, 56-1 st determination part, 58-2 nd determination part.

Detailed Description

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and overlapping description is omitted as appropriate.

In the blown film molding, the resin extruded from the die into a tubular shape may be broken. As a cause of the breakage, it is considered that a force applied to the resin is larger than the breaking strength of the resin. Therefore, in the present embodiment, for example, it is periodically determined whether or not a stress that may cause a fracture is generated in the tubular resin. Specifically, the stress generated in the resin is estimated from the data relating to the tubular resin acquired during molding, and it is determined that there is a possibility of resin fracture when the estimated stress is equal to or greater than a threshold value. Thus, the user can quickly detect the breakage of the bulb in the case where there is a possibility of the breakage, and can quickly take measures.

Fig. 1 shows a basic configuration of a blown film forming apparatus 1 according to an embodiment. The blown film forming apparatus 1 includes a mold 2, a cooling device 3, a pair of stabilizing plates 4, a tractor 5, a thickness acquiring unit 6, a width acquiring unit 22, a solidification line height acquiring unit 26, and a control device 7.

The molten resin supplied from an extruder (not shown) is extruded from an annular discharge port 2a formed in the die 2. At this time, air is blown out from air blowing ports 2b formed in the center of the die 2 toward the inside of the extruded resin, thereby forming a thin resin film (hereinafter, also referred to as "bubble") that is expanded into a tubular shape.

The cooling device 3 is disposed above the mold 2. The cooling device 3 blows cooling air to the bulb to cool the bulb.

The pair of stabilizer plates 4 is disposed above the cooling device 3, and guides the bulb to the tractor 5. The tractor 5 is disposed above the stabilizer plate 4. The tractor 5 includes a pair of pinch rollers 38. The pair of pinch rollers 38 is driven and rotated by a motor, not shown, and folds the guided bulb while pulling it up. The winder 20 winds the folded resin film to form a film roll 11.

The thickness acquisition unit 6 is disposed between the cooling device 3 and the stabilizing plate 4. The thickness acquiring section 6 acquires (measures) the thickness of the bulb at each position in the circumferential direction while surrounding the circumference of the bulb. The thickness data acquired by the thickness acquiring unit 6 is sent to the control device 7.

The width acquisition unit 22 is disposed between the tractor 5 and the winder 20. The width acquisition section 22 acquires (measures) the film width of the folded resin film. The width data acquired by the width acquisition unit 22 is sent to the control device 7.

The solidification line height obtaining portion 26 is disposed between the cooling device 3 and the stabilizing plate 4. The coagulation line height acquiring section 26 detects the coagulation line height at each position in the circumferential direction while surrounding the circumference of the bubble. The solidification line height is a height from the discharge port 2a of the die 2 to a position where the resin is solidified, that is, a solidification line. The structure of the solidification line height obtaining portion 26 is not particularly limited. For example, the coagulation line height obtaining portion 26 may be configured to include: a visible light camera for photographing the appearance of the film in a mode of comprising a discharge port 2a and a solidification line; and an image processing unit for determining the height of the solidification line by performing image processing on the captured image. For example, the coagulation line height obtaining portion 26 may include: an infrared sensor for taking a thermal image of the film; and an image processing unit for determining the height of the solidification line by performing image processing on the captured thermal image. The detection result by the coagulation line height obtaining section 26 is sent to the control device 7.

The control device 7 is a device for controlling the blown film forming device 1 in a unified manner.

Fig. 2 is a block diagram schematically showing the function and configuration of the control device 7. Each block shown here can be realized by an element or a mechanical device such as a CPU of a computer in hardware, or by a computer program or the like in software, and functional blocks realized by these cooperation are depicted here. Accordingly, those skilled in the art will appreciate that these functional blocks can be implemented in various forms by a combination of hardware and software.

The control device 7 includes: a communication unit 40 for performing communication processing with the thickness acquisition unit 6 and the solidification line height acquisition unit 26 in accordance with various communication protocols; a U/I unit 42 that receives an operation input by a user and displays various screens on the display unit; a data processing unit 46 for executing various data processing based on the data acquired from the communication unit 40 and the U/I unit 42; and a storage unit 48 for storing the data referred to and updated by the data processing unit 46.

The reservoir 48 includes a stress-at-break reservoir 64. The breaking stress storage unit 64 stores information on stress generated in the bulb when the bulb breaks in the past molding. The information related to the stress may be the stress itself, or may be information used to calculate the stress.

The data processing unit 46 includes a receiving unit 50, a registration unit 52, a display control unit 54, a 1 st determination unit 56, a 2 nd determination unit 58, and an operation control unit 60.

The receiving portion 50 receives the thickness of the bubble, the film width of the resin film, and the solidification line height from the thickness obtaining portion 6, the width obtaining portion 22, and the solidification line height obtaining portion 26, respectively.

The determination unit 55 determines whether or not there is a possibility of breakage of the bulb. The determination unit 55 includes a 1 st determination unit 56 and a 2 nd determination unit 58.

The 1 st determination unit 56 estimates, from the design values or set values of the blown film forming apparatus 1 related to the forming and the properties of the resin used, that stress is generated in the bubble when the blown film is formed with the design values, set values and resin. The method of estimating the stress by the 1 st determining unit 56 will be described later.

The 1 st determination unit 56 determines whether or not there is a possibility of breakage of the bulb based on the estimated stress. Specifically, the 1 st determining unit 56 compares the estimated stress with the 1 st threshold, determines that there is a possibility of the bubble breaking when the estimated stress is equal to or greater than the 1 st threshold, and determines that there is no possibility of the bubble breaking when the estimated stress is smaller than the 1 st threshold. The 1 st threshold may be, for example, the stress at the time of fracture itself determined based on the information on the stress stored in the stress-at-fracture storage unit 64, and may be, for example, a value obtained by multiplying the stress at the time of fracture by a safety factor. The 1 st threshold value may be determined, for example, according to the resin characteristics of the resin used.

When determining that the bubble breakage is likely, the 1 st determination unit 56 warns (notifies) the user of the fact, for example, by displaying the bubble breakage on a screen via the display control unit 54. The warning is not limited to the screen display, and may be performed by using a voice output or other method. In this case, the user may change various set values (for example, the extrusion amount of the resin, the blow-up ratio, the drawing speed, the die exit temperature, the atmospheric temperature, the lip width, the air temperature of the cooling air, and the like).

The 2 nd determination unit 58 estimates the stress generated in the bubble during molding from the data received by the receiving unit 50 and design values of the blown film molding apparatus 1 related to molding (for example, the radius of the discharge port 2a of the die 2, the radius of the pinch roll 38, and the like). The method of estimating the stress by the 2 nd determining unit 58 will be described later.

The 2 nd determination unit 58 determines whether or not there is a possibility of the bubble breakage based on the estimated stress. Specifically, the 2 nd determination unit 58 compares the estimated stress with the 2 nd threshold, determines that there is a possibility of the bubble breaking when the estimated stress is equal to or greater than the 2 nd threshold, and determines that there is no possibility of the bubble breaking when the estimated stress is smaller than the 2 nd threshold. The 2 nd threshold may be, for example, the stress at the time of fracture itself determined based on the information on the stress stored in the stress-at-fracture storage unit 64, and may be, for example, a value obtained by multiplying the stress at the time of fracture by a safety factor. The 2 nd threshold value may be determined, for example, according to the resin characteristics of the resin used. The 2 nd threshold may be the same value as the 1 st threshold or may be a different value.

When determining that the bubble breakage is likely, the 2 nd determination unit 58 warns (notifies) the user of the fact, for example, by displaying the bubble breakage on a screen via the display control unit 54. The warning is not limited to the screen display, and may be performed by using a voice output or other method. In this case, the user may simply readjust the various set values and change them appropriately before the bubble actually breaks.

The display control unit 54 controls screen display. For example, when the determination units 56 and 58 determine that the breakage of the bulb is possible, the display control unit 54 displays the content on the screen. Further, for example, the display control unit 54 displays an input screen for inputting various setting values.

When the bubble breaks, the registration unit 52 stores information relating to the stress generated in the bubble, for example, the stress estimated immediately before the bubble breaks, in the break-time stress storage unit 64, for example, upon an instruction from the user. When the information on the stress is stored in the fracture stress storage unit 64, the registration unit 52 may update the information on the stress stored in the fracture stress storage unit 64 when the stress is lower this time.

The operation control section 60 controls the operation of the blown film forming apparatus 1 in accordance with various set values determined by the user. For example, when the operation control unit 60 receives an instruction to start molding from the user, if it is determined that there is a possibility of breaking the bubble in the determination by the 1 st determination unit 56, the user is not started to be notified of the start of molding. That is, when it is determined that there is a risk of breakage of the bulb, the start of molding is prohibited. On the other hand, if it is determined in the determination by the 1 st determining unit 56 that there is no possibility of the bubble breakage, the operation control unit 60 controls the operation of the blown film forming apparatus 1 to start the forming. That is, in the case where it is determined that there is no possibility of breakage of the bulb, the start of molding is allowed. Specifically, the operation controller 60 controls operations such as the amount of resin extruded from an extruder, not shown, the flow rate of air blown from the air outlet 2b, the air temperature of cooling air blown into the tubular bubble from the cooling device 3, and a drive current flowing through a motor that drives the pinch roller 38. Further, the user may set and change various set values so that the thickness of the bulb acquired by the thickness acquiring unit 6 falls within a target range. The user may set and change various setting values with reference to the determination result of the 2 nd determining unit 58.

Next, a method of estimating the stress by the 1 st determining unit 56 will be described.

The stress (σ) generated in the bubble (particularly the solidification line) is calculated by the following formula (1).

σ＝4η……(1)

Wherein the content of the first and second substances,

eta: viscosity of the oil

: the strain rate.

Regarding the strain rate (), it is assumed that the following formula (2) holds in the present embodiment.

＝(v_f-v_d)/L……(2)

Wherein the content of the first and second substances,

v_f: the speed of the drawing bulb, i.e. the drawing speed

v_d: flow velocity of the resin in the discharge port 2a

L: the height of the solidification line.

Therefore, the formula (1) can be rewritten as the following formula (3).

σ＝4η×(v_f-v_d)/L……(3)

That is, the stress (σ) can be estimated from data relating to the bubble, specifically, from the viscosity (η) and the traction speed (v)_f) And the flow velocity (v) of the resin in the discharge port 2a_d) And a solidification line height (L).

The viscosity (η) may be estimated by a known technique. For example, the viscosity (η) may be estimated by measuring the viscosity of the resin used in advance and fitting the measured viscosity using a viscosity model formula. In the viscosity model formula, for example, a Power-law model can be used.

Traction speed (v)_f) Is a set value.

Flow velocity (v) of the resin in the discharge port 2a_d) Represented by the following formula (4).

v_d＝(m/ρ_melt)/(2πR₀H₀)……(4)

Wherein the content of the first and second substances,

m: extrusion amount (mass flow rate) of resin

ρ_melt: melt density of resin

R₀: radius of discharge port 2a of die 2

H₀: width of lip

Further, the extrusion amount (m) of the resin and the lip width (H)₀) The melt density (. rho.) of the resin is set_melt) The radius (R) of the discharge opening 2a of the die 2 is resin property₀) Is a design value.

The solidification line height (L) is represented by the following formula (5).

L＝mC_p/HTC×ln{-(T_die-T_air)/(-T_solid+T_air)}×1/(2πy)……(5)

Wherein the content of the first and second substances,

C_p: specific heat capacity of resin

HTC: heat transfer coefficient of resin

T_die: exit temperature of die 2

T_air: temperature of cooling air (ambient temperature)

T_solid: curing temperature of resin

y: average radius of the bulb

Further, the specific heat capacity (C) of the resin_p) And curing temperature (T) of the resin_solid) Is resin-specific and the exit temperature (T) of the mold 2_die) And ambient temperature (T)_air) Is a set value. The Heat Transfer Coefficient (HTC) may be determined in advance by experiments for each of the air volume and the air temperature of the cooling air from the cooling device 3.

In addition, in actual molding, the flow rate or the temperature of the cooling air is often adjusted so that the solidification line height becomes a height desired by a user. In this case, the solidification line height (L) may be set to a set value.

The average radius (y) of the bubble is represented by the following formula (6).

y＝(BUR+1)×R₀/2……(6)

Wherein the content of the first and second substances,

BUR: the blow-up ratio.

The blow-up ratio (BUR) is a set value, and the radius (R) of the discharge port 2a of the die 2 is set₀) Is a design value.

Next, a method of estimating the stress by the 2 nd determining unit 58 will be described.

As described above, the stress generated in the bubble (particularly the solidification line) is calculated by the equation (1).

Hereinafter, formula (1) is described again.

σ＝4η……(1)

The viscosity (η) is assumed to be satisfied by the following formula (7) in the present embodiment. That is, the viscosity (η) is simply calculated without considering the influence of the temperature.

η＝FL/{8πR_fH_f(v_f-v_d)}……(7)

Wherein the content of the first and second substances,

f: traction force

R_f: radius of bubble in solidification line

H_f: thickness of the bubble in the solidification line.

As described above, regarding the strain rate () it is assumed that equation (2) holds in the present embodiment. Hereinafter, the formula (2) is described again.

＝(v_f-v_d)/L……(2)

Therefore, the formula (1) can be rewritten from the formulae (2) and (7) to the formula (8).

σ＝F/{2πR_fH_f}……(8)

That is, the stress (σ) can be estimated from data on the bubble acquired during molding, specifically, from the traction force (F) and the radius (R) of the bubble in the solidification line_f) And the thickness (H) of the bubble in the solidification line_f) To make inferences.

The traction force (F) is represented by the following formula (9).

F＝T/Rr……(9)

Wherein, it is as follows:

t: torque moment

Rr: the radius of the pinch rollers 38.

The torque (T) can be determined by detecting a drive current flowing through a motor that drives the pinch roller 38. The radius (Rr) of the pinch roll 38 is a design value and can be determined by actual measurement.

Radius (R) of bubble in solidification line_f) Represented by the following formula (10).

R_f＝w/π……(10)

Wherein the content of the first and second substances,

w: film width [ m ].

The film width (w) is measured by the width acquisition unit 22.

Thickness of bubble in solidification line (H)_f) Is acquired by the thickness acquiring section 6.

The above is the structure of the blown film forming apparatus 1. Next, the operation will be described.

First, an operation of determining that the bulb is broken when setting is performed will be described. Fig. 3 is a flowchart showing the operation of determining the breakage of the bubble at the time of setting by the blown film forming apparatus 1. The flow of fig. 3 is executed every time the setting value is set and changed.

The control device 7 acquires a set value of the blown film forming apparatus 1 related to the forming, for example, the following set value, which is input to the input screen by the user (S10).

Extrusion amount (mass flow rate) of resin (m)

Blow-up ratio (BUR)

Traction speed (v)_f)

Exit temperature (T) of the die 2_die)

Temperature (T) of cooling air_air)

Lip Width (H)₀)

The control device 7 estimates the stress generated in the bulb at the time of molding from the design value of the blown film molding device 1, the set value input to the input screen, and the characteristics of the resin used (S12). The control device 7 compares the inferred stress with the 1 st threshold value (S14). If the estimated stress is equal to or greater than the 1 st threshold (yes in S14), the user is warned by screen display, audio output, or other means to change the set value (S16) and the flow ends, because there is a possibility of breakage. At this time, the start of molding is prohibited. If the inferred stress is less than the 1 st threshold (no in S14), the process of S16 is skipped and the flow ends. At this point, the molding is allowed to start.

Next, an operation of determining the breakage of the bulb at the time of molding will be described.

Fig. 4 is a flowchart showing the operation of determining the breakage of the bubble at the time of molding by the blown film molding apparatus 1. The flow of fig. 4 is executed at the start of molding.

The control device 7 receives the data on the bubble from each acquisition unit or the like (S20). The control device 7 infers the stress generated in the bubble during molding from the received data or the design value of the blown film molding device 1 (S22). The control device 7 compares the inferred stress with the 2 nd threshold value (S24). If the estimated stress is equal to or greater than the 2 nd threshold (yes in S24), the possibility of breakage exists, and therefore the user is warned by screen display, audio output, or other means to adjust various adjustment requirements (S26). If the inferred stress is less than the 2 nd threshold (no in S24), the process of S26 is skipped. When the molding is completed (yes in S28), the control device 7 ends the flow, and when the molding is not completed (no in S28), the control device returns to S20.

According to the present embodiment described above, it is determined whether or not a stress that may break is generated in the bulb. Thus, the user can quickly detect the breakage of the bulb in the case where there is a possibility of the breakage, and can quickly take measures.

Further, according to the present embodiment, it is determined whether or not there is a possibility that the bulb is broken when the bulb is molded with the inputted set value. This can suppress the setting of a set value that causes bubble breakage.

The structure and operation of the blown film forming apparatus according to the embodiment are explained above. Those skilled in the art will appreciate that these embodiments are illustrative, various modifications can be made to the combination of these respective constituent elements, and such modifications are also within the scope of the present invention.

(modification 1)

The method of estimating the stress by the 2 nd determination unit 58 is not limited to the method of the embodiment.

The stress (σ) generated in the bubble (particularly, the solidification line) can also be calculated by the following formula (11).

σ＝F/S……(11)

Wherein the content of the first and second substances,

s: cross-sectional area of the bulb.

The cross-sectional area (S) of the bulb is represented by the following formula (12).

S＝2πR₀H₀……(12)

Therefore, the formula (11) can be rewritten as the following formula (13).

σ＝F/(2πR₀H₀)……(13)

Lip Width (H) as described above₀) A set value, and a radius (R) of a discharge port 2a of the die 2₀) Is a design value.

Any combination of the above-described embodiments and modifications is useful as an embodiment of the present invention. The new embodiment which is produced by the combination has the effects of both the combined embodiment and the modified example.