WO2017049808A1

WO2017049808A1 - Film blowing production process

Info

Publication number: WO2017049808A1
Application number: PCT/CN2016/000418
Authority: WO
Inventors: 李子平; 林洁波; 林蔚
Original assignee: 广东金明精机股份有限公司
Priority date: 2015-09-25
Filing date: 2016-07-29
Publication date: 2017-03-30
Also published as: CN106553330A; CN106553330B

Abstract

A film blowing production process comprises the following steps: (1) a bubble thickness measuring device continuously measures initial thicknesses of various points on a bubble along a circumferential direction; (2) various initial bump thickness control mechanisms start to perform a bubble thickness reducing operation; (3) select some from all normal point thickness control mechanisms for performing a bubble thickening operation; (4) calculate an absolute value d of the difference between c and b, i.e., d = |c - b|, wherein c is an average value of actual thicknesses of all the normal points of the bubble, including the thickened ones, after the thickening operation, and b is an average value of the adjusted initial bump thicknesses of the various initial bumps of the bubble after the thickness reducing operation; (5) compare d with e, wherein e is the maximum allowable difference between c and b, and proceed to step (6); and (6) a full-circumference thickness control mechanism reduces the full-circumference thickness of the bubble according to the measurement result of the bubble thickness measuring device, to reduce the average full-circumference thickness of the bubble to a, wherein a is a designed value for the thickness of the bubble. After the produced bubble is rolled, the accumulative error of thicknesses of various points is evenly distributed along an axial direction of the roll, thereby avoiding winder wrinkles, and a traditional mechanical rotational traction process and apparatus are also omitted.

Description

Blown film production process

Technical field

The invention belongs to the technical field of plastic film production processes, and in particular relates to a blown film production process.

Background technique

The plastic film can be produced by a blown film device using a blown film process, the blown film device is provided with an extrusion die, the extrusion die is provided with a circular extrusion port, and a circular cooling air ring is arranged above the extrusion die. During production, the high-temperature molten resin material is extruded from an extrusion die and cooled by a cooling air ring to form a circular bubble. The annular bubble is flattened by a herringbone plate to form a double-layer film. After that, the wind can be wound in the middle of the conventional cooling air ring. The air guiding interlayer 3 has a circular shape on the horizontal projection, and the cooling airflow is from the air inlet of the periphery of the circular air guiding interlayer 3. 1 The radial air passage is directed to the annular air outlet 2 to cool the bubble 8, as shown in Figs.

In the above process, the bubble is filled with compressed air, and under the action of compressed air, radial (horizontal) inflation, that is, lateral stretching, thereby making the bubble thin; The bubble is directly pulled by the traction nip roller through the vertical direction, and the pulling speed is greater than the extrusion speed, thereby also making the bubble thin, that is, vertical stretching. In the above-mentioned transverse stretching and vertical stretching processes, the entire circumference of the bubble is simultaneously thinned in the same proportion, and thus the transverse stretching mechanism and the vertical stretching mechanism are collectively referred to as a full-thickness thickness control mechanism. The adjustment of the bubble thickness of the full-thickness thickness control mechanism is global, that is, when the thickness of a certain point in the circumferential direction is increased, other points in the circumferential direction must also be thickened, and vice versa. The full-thickness thickness control mechanism cannot perform independent differential adjustment on the circumferential local point thickness, and only equal-scale adjustment can be performed simultaneously for all points.

Later, a structure was designed which can adjust the thickness of the circumferential local position of the bubble. One of the structures is shown in FIG. 3, which is uniformly arranged with a plurality of electronic control elements 6 in the circumferential direction of the circular wind-guiding interlayer 3 (the number of electronic control elements is generally more than 72, even up to two or three hundred The electronic control component can be an electric heating component or an electric valve, and each electronic control component is independently controlled, and the circular air guiding interlayer is evenly divided into a plurality of radial channels 5 from the circumferential direction by using a plurality of partition plates 4, each The electronic control element 6 corresponds to the temperature or flow rate (flow rate) of the air flow of one radial channel 5. During operation, the cooling airflow passes from the annular air inlet 1 through the radial passages 5 to the annular air outlet 2, The temperature of each bubble is controlled to the temperature of each point of the bubble, and the electronic control elements of each radial channel are independently controlled, so that the cooling airflow of the radial channel of the corresponding azimuth is heated or controlled to different degrees to cool the corresponding azimuth. The temperature or flow rate of the airflow changes to different degrees, so that the temperature of the point in the corresponding azimuth of the bubble 8 changes to different degrees, so that when the bubble is inflated, the proportion of local point inflation and thinning is different with respect to other parts, so that The degree of inflating and thinning of the local point is different from that of other parts, thereby achieving differentially independent regulation of the thickness of a certain point or points in the circumferential direction. The above-described structure for differentially regulating the thickness of some locations in the circumferential direction is called a local thickness control mechanism. The local thickness control mechanism can simultaneously perform different ratios of thickness adjustments at different points in the circumferential direction. When the electronic control component of the local thickness control mechanism changes the operating parameters (for example, reducing the heating power or increasing the opening degree of the valve), when the local thickness control mechanism cools or accelerates the cooling airflow corresponding to the orientation, the bubble point temperature of the corresponding orientation The thickness of the bubble corresponding to the orientation is increased, and this process is called a bubble thickening operation. When the electronic control component of the local thickness control mechanism changes the operating parameters (for example, increasing the heating power or making the valve opening degree smaller), when the local thickness control mechanism heats up or decelerates the corresponding cooling airflow, the bubble point of the corresponding orientation When the temperature rises, the thickness of the bubble corresponding to the orientation becomes smaller, and this process is called a bubble thickening operation. The above air velocity can be reduced to zero, that is, the valve is completely closed. The operating parameters of the local thickness control mechanism refer to the power of the electric heating element for the mechanism that relies on the electric heating element; the opening size or the opening and closing state of the valve for the mechanism that operates by the valve.

In addition, the actual thickness of each point in the circumferential direction of the bubble must be continuously detected during the production process. The prior art can use the thickness measuring probe to continuously rotate around the annular bubble to perform the inspection. The above is responsible for detecting the actual thickness of each point in the circumferential direction of the bubble. The device is called a bubble thickness detector.

The accuracy of the above bubble thickness detector, local thickness control mechanism, and full-thickness thickness control mechanism are as follows:

The thickness measurement technology is very mature, so the detection result of the bubble thickness detector can be very accurate, the detection accuracy is high, and the detection precision can fully meet the accuracy of the winding quality requirement.

The control accuracy of the bubble thickness of the full-thickness control mechanism is also high, because the difference in traction speed is directly related to the degree of stretching, and the difference in traction speed can be precisely controlled, so the vertical stretching makes the bubble thinner. The ratio can be precisely controlled; for example, if the bubble is required to be thinned by 3%, the positive difference between the traction speed and the extrusion speed can be increased by 3%, and the positive difference between the traction speed and the extrusion speed is increased. After 3%, the thickness of the bubble may not be thinner by 4%, nor may it be thinner by 2%. It can only be accurately reduced by about 3%, so the process from control to reaction is very direct, sensitive, and precise. The correlation between control methods and control results is very high. Similarly, the pressure inside the bubble is directly related to the radial pull. The degree of extension and the difference in the pressure inside the bubble can be precisely controlled, and the thickness of the bubble can be precisely controlled by the difference in the pressure inside the bubble. In short, the full-thickness thickness control mechanism can accurately control the total thickness of the bubble, and the error of the control result is very small. Compared with the winding quality requirement, the error value can be neglected, so the control of the full-thickness thickness control mechanism can be considered. The result can be accurate to a specific target value.

The thickness control precision of the local thickness control mechanism of the bubble is relatively low, and can only be roughly controlled. For a specific control action, it can only be predicted according to experience that the control effect will be within a certain interval, and it is difficult to predict what the control result is. Point. This is because the temperature or flow rate of the cooling airflow cannot directly, uniquely and accurately determine the proportion of the local point thickness change of the bubble. It can only be controlled according to experience. Each specific control action can only be roughly predicted before the implementation. result. For example, if the bubble is required to be thinned by 5%, the temperature is not increased by 5%, but the operating parameter (ie, power) of the heating element can only be increased by a value according to experience. After the adjustment, the local point is likely to be changed. A thin 3% may also be 7% thinner. Similarly, depending on the operating parameters of the valve (ie, the size of the valve opening), the value of the local thickness of the bubble cannot be accurately determined. Therefore, although the local thickness control mechanism can control the local thickness of the bubble, the control precision is poor. Compared with the winding quality requirements, the error value can not be ignored, so the control result of the local thickness control mechanism of the bubble can only be predicted. It falls within a certain numerical interval, and it is difficult to expect its control result to be accurate to a specific target value.

On the other hand, due to mechanical design, mechanical structure, mechanical processing, etc., the thickness of the cylindrical bubble extruded from the annular extrusion port of the blow molding device is actually different, for example, corresponding to the orientation of the injection port. The thickness of the bubble will be significantly thicker, and the thickness deviation is a systematic error, that is, if the point of a certain direction of the bubble is thick, the subsequent bubble is continuously thick in the direction, so the above conventional method is wound up. If the film is not treated, the thick spots (or bumps) will gradually accumulate at the same position of the coil, so that the thickness of the film roll after winding is severely uneven, resulting in bursting phenomenon and poor winding quality.

In order to overcome the above shortcomings, a mechanical rotary traction device was designed to rotate the traction nip roller around the central axis of the machine head, that is, the traction nip roller rotates relative to the blow molding machine die (bubble), so that the film thickness is on the upper axis of the coil. The upward distribution position shows the waveform distribution state, along the axial direction of the coil Dispersed, thereby better solving the problem of winding accumulation caused by systematic errors of thick points (or bumps), so that the bumps of the film are evenly distributed in the axial direction of the coil, not in the same Accumulate the position, avoid bursting, and achieve the purpose of winding up. Rotating traction devices have appeared in many Chinese patents, such as CN201410774285.4, CN201320366814.8, CN02214546.X, CN200410015430.7, CN200920062191.9 and other Chinese patents.

However, although the above-mentioned rotary traction device solves the blasting phenomenon well, it pays a great price: the mechanical structure of the rotary traction device is complicated, the equipment is bulky, and when the film runs through the rotary traction mechanism, the surface of the film will be The surface of the movable guide roller is relatively slid and twisted, and the surface of the film may cause sliding friction with the surface of the movable guide roller, and the film is easily accidentally pulled.

At the same time, although the local thickness control mechanism of the bubble can control the thickness of the local point of the bubble, it cannot be directly used to replace the rotary traction device. This is because of the following two reasons: First, the thickness of the film caused by mechanical reasons Larger, can reach up to 8-11% of the film thickness, and relying on simple temperature adjustment can not reduce the film thickness to 8-11%, because if you increase the temperature, try to use the temperature increase will be 8 If the mechanical error factor of -11% is completely thinned and eliminated, the required temperature rise is too large, which will cause the bubble to not condense at this point. Even under the action of compressed air in the bubble, the bubble will break at this point. Loss of air pressure in the bubble, which in turn leads to serious problems of bubble collapse; Second, as mentioned above, even if the super-thickness of the bump generated by mechanical reasons is within the control ability of the local thickness control mechanism, it is also due to the local bubble The control precision of the thickness control mechanism is very low, so no matter how it is controlled, it is difficult to accurately eliminate the bumps and avoid the ribbing phenomenon simply by relying on the local thickness control mechanism of the bubble.

Summary of the invention

The object of the present invention is to overcome the above disadvantages and to provide a blown film production process. After the bubble is produced, the accumulated thickness error of each point is uniformly distributed along the axial direction of the coil to avoid the phenomenon of bursting, and the conventional Mechanical rotary traction technology and equipment.

The purpose can be achieved according to the following scheme: a blown film production process, the blown film device is provided with an extrusion die, the extrusion die is provided with a circular extrusion port, and the extrusion die is provided with a circular ring shape. The cooling air ring and the cooling air ring are formed with at least 72 partial thickness control mechanisms, and the respective partial thickness control mechanisms are evenly arranged along the circumferential direction of the cooling air ring; the blown film device is also provided with a full-thickness thickness control mechanism and bubble thickness detection. The following steps are included:

(1) The annular extrusion port of the extrusion die continuously extrude the annular film blank, and the film blank is extruded After inflating and cooling to form a bubble, each local thickness control mechanism works with the same working parameters. The working parameter is called the original working parameter, and the original working parameter is recorded; the bubble thickness detector continuously detects the bubble circumferential point. The initial thickness; when the initial thickness of a certain azimuth point in the bubble circumferential direction exceeds the bubble thickness design value a by more than the bubble thickness normal deviation value f, the point at which the bubble is in the orientation is regarded as the original bump, The points other than the original bump are regarded as normal points, and the local thickness control mechanism corresponding to the normal point is called the normal point thickness control mechanism; the local thickness control mechanism corresponding to the original bump is called the original bump thickness control mechanism;

(2) The original bump thickness control mechanism starts the bubble thinning operation, changes the working parameters, and reduces the thickness of the original bump of the bubble, and the estimated thickness h of the original bump after the control adjustment is in the following range: a +0.7f>h>a+0.2f; the bubble thickness detector continuously detects the thickness of each point of the bubble, and calculates the average value b of the original bump adjustment thickness of each original bump of the bubble after the thickness reduction operation, And record the working parameters of each original bump thickness control mechanism after the thickness reduction operation; f is the normal deviation value of the bubble thickness, which can be comprehensively determined according to the requirements of the winding quality level, film thickness, equipment precision and the like;

(3) In all the normal point thickness control mechanisms, select some of the normal point thickness control mechanisms to perform the bubble thickening operation, change the working parameters, and the normal point thickness control mechanism selected for the thickening operation is normal. The point is called the thickening point; the bubble thickness detector continues to continuously detect the thickness of each point of the bubble, and calculates the average actual thickness c of all the normal points of the bubble including the thickening point after the thickening operation; The normal point thickness control mechanism for performing the bubble thickening operation still maintains the original operating parameters;

(4) Calculate the absolute value d of the difference between c and b, where c is the actual thickness average of all bubble normal points including the thickening point after the thickening operation, and b is the original convex of the bubble The average value of the original bump adjustment thickness after the thickness reduction operation, d=|cb|;

(5), compare the size of d and e, where e is the maximum allowable difference between c and b; e is determined according to the quality requirements of the winding quality, film thickness, equipment accuracy and other factors, in advance, under normal circumstances e can be selected between 0.1f and 0.25f; if d≤e, it means that the difference between the average actual thickness of all the normal points of the bubble and the average actual thickness of the original bump after adjustment is affordable. The range of deviation, the number M of the normal point thickness control mechanisms for performing the thickening operation in this state, and the operating parameters of the normal point thickness control mechanism for each thickening operation, and starting the step (6);

If d>e, further compare the size of both c and b;

If c<b, the number of normal point thickness control mechanisms for performing the bubble thickening operation in step (3) is gradually increased, or the thickness of the individual normal point thickness control mechanism is gradually increased, and gradually adjusted. In the high process, repeat the average actual thickness of all normal points including the thickening point and calculate the new actual thickness average c, and repeatedly calculate the absolute value d of the new average values c and b, and repeat the comparison. The size of d and e up to d ≤ e, and record the number M of normal point thickness control mechanisms for thickening operation in this state, and the operating parameters of the normal point thickness control mechanism for each thickening operation, and then Start step (6);

If c>b, the number of normal point thickness control mechanisms for performing the bubble thickening operation in step (3) is gradually lowered, or the thickness of the individual normal point thickness control mechanism is gradually lowered, and gradually adjusted. In the low process, the average actual thickness of all normal points including the thickening point is repeatedly detected and a new average value c is calculated, and the new absolute value d of the new average values c and b is repeatedly calculated, and the comparison is repeated. The size of d and e up to d ≤ e, and record the number M of normal point thickness control mechanisms for thickening operation in this state, and the operating parameters of the normal point thickness control mechanism for each thickening operation, and then Start step (6);

(6) After the completion of the above step (5), the actual thickness average of each original bump is b, and the actual thickness average of all bubble normal points including the thickening point is also close to b (and b) The difference is less than e), that is, the average thickness of the full-circumferential bubble is close to b, and the full-thickness thickness control mechanism lowers the total thickness of the bubble according to the detection result of the bubble thickness detector, so that the total bubble is averaged. The thickness becomes smaller as a;

(7) In the subsequent production process, each original bump thickness control mechanism maintains the operating parameters recorded in step (2); and all normal point thickness control mechanisms alternately select one of them for thickening operation and maintain The total number of normal point thickness control mechanisms that perform the thickening operation at each time is the value M recorded in the step (5), and the operating parameters of the normal point thickness control mechanisms of the M thickening operations and the (5) The working parameters recorded in the step are the same one-to-one; at each moment, except for the M normal point thickness control mechanisms that perform the thickening operation, the normal point thickness control mechanism that does not perform the thickening operation is still performed with the original working parameters. The bubble thickness detector continuously detects the actual thickness of each point in the circumferential direction of the bubble, and the full-thickness thickness control mechanism maintains the average thickness of each point of the entire bubble at a.

In the above step (2), "the estimated thickness h of the original bump after the control adjustment is located in the following area The range is: a+0.7f>h>a+0.2f,”, this does not mean that a point is selected as the control target in the interval, but the expected thickness h falls within the range, because of this thickness reduction The target thickness is a relatively large range of ranges, and the existing local thickness control mechanism can achieve this rough control standard, so there is no difficulty and no special requirements.

The invention has the following advantages and effects:

1. After the bubble produced by the invention is wound, the partial thickness and the cumulative thickness of the film are uniformly distributed along the axial and circumferential directions of the coil to avoid the phenomenon of bursting, and the traditional mechanical rotating traction process can be omitted. And equipment.

2. The original bump of the present invention does not have to be excessively heated so that its thickness is completely flattened, thereby avoiding the problem of bubble collapse and bubble collapse.

3. Although the present invention, like the conventional process, can only roughly control the thickness of the specific local point of the bubble, it can precisely control the average actual thickness of all the normal points of the bubble (this is because a variation parameter is divided by about 100 samples). After the total number, the degree of influence of the variation parameter on all samples will be reduced by about 100 times than the degree of self-change, which means that the accuracy of the influence of the variation parameter on the average value is two orders of magnitude higher than the accuracy of the self-change, and therefore, the present invention can The average actual thickness of all the normal points of the bubble is accurately equal to the average thickness of each original bump adjusted, thereby making the overall thickness of the film roll uniform.

4. The present invention achieves the final bubble by thickening (shaving a part of the thickness of the bump), thickening (slightly thickening the normal point to be substantially equal to the thickness of the sharpened bump), and then thinning the whole. The overall average thickness meets the requirements of product quality and does not explode locally. Among them, although the normal point becomes a thickening point, since all normal points are balanced and thickened, there is no accumulation of thickening points and bursting. The problem.

DRAWINGS

Fig. 1 is a schematic view showing the structure of a cooling air ring for cooling a bubble.

FIG. 2 is a schematic diagram showing the horizontal projection position relationship of each main component in FIG. 1. FIG.

Figure 3 is a schematic diagram of the principle of a local thickness control mechanism.

detailed description

A blown film production process, the blown film equipment is similar to the structure shown in Fig. 1, Fig. 2, Fig. 3, which is provided with an extrusion die, the extrusion die is provided with a circular extrusion port, and an extrusion die An annular cooling air ring is arranged above the head, and the air guiding interlayer of the cooling air ring uses a plurality of partition plates to sandwich the circular air guiding layer It is evenly divided into 100 radial channels from the circumferential direction (the number of radial channels in Figure 3 is only schematic, and 100 are not accurately drawn for the sake of simplicity), each radial channel is provided with a local thickness control mechanism. There are 100 partial thickness control mechanisms, and the local thickness control mechanism specifically adopts electric heating elements, and each electric heating element is evenly arranged in the circumferential direction, and each electric heating element is located in a radial passage of a cooling air ring; and a full-thickness thickness control mechanism is also provided. The bubble thickness detector; the full-thickness thickness control mechanism specifically includes a vertical stretching mechanism led by the traction nip roller and a transverse stretching mechanism led by the air compressor.

Before the start of production, the target value of the bubble thickness is set to 100 μm, and the conditions for the identification of the original bump are determined according to the characteristics of the mechanical equipment, the production process, and the material: if the bubble thickness in a certain direction is greater than the bubble When the thickness target value is 100 micrometers and exceeds 10 micrometers (10 micrometers is the normal deviation value f of the bubble thickness, the value f is comprehensively determined according to the requirements of the winding quality grade, film thickness, equipment accuracy, etc., and is set in advance) The original bump caused by the mechanical problem is determined by the orientation, and the other azimuth points other than the original bump are regarded as normal points. According to the quality requirements of the winding quality, film thickness, equipment accuracy and other factors, the maximum allowable difference e is determined to be 1.5 microns, where e is the maximum allowable difference between c and b, and c is the thickening point. The actual thickness average of all bubble normal points, b is the average value of the original bump adjustment thickness after adjustment of each original bump of the bubble. The practical significance of the maximum allowable difference e is that as long as the average thickness of the final thickness of all the bubble normal points does not differ from the average thickness of the original bump adjustment by e (1.5 micrometers), it is considered to meet the requirements of the winding quality. .

The process comprises the following steps: (1), the annular extrusion port of the extrusion die continuously extrude the annular film blank, and after the film blank is extruded, the inflating and the cooling air ring are cooled to form a bubble, and the film begins. When the heating elements of the cooling air ring are all operated at the same heating power, the heating power is the original working parameter, and the original working parameters are recorded;

The bubble thickness detector continuously detects the initial thickness of each point in the circumferential direction of the bubble, and the initial thickness of a certain azimuth point in the bubble circumferential direction reaches 110 μm or more (above the target value of 100 μm of the bubble thickness exceeds the set value of 10 μm or more, When 10 micron is the normal deviation value f) of the bubble thickness, the point at which the bubble is in the azimuth is regarded as the original bump, and the other azimuth points other than the original bump are regarded as the normal point, and the local thickness control mechanism corresponding to the orientation of the normal point It is called a normal point thickness control mechanism; the local thickness control mechanism of the original bump corresponding orientation is called the original bump thickness control mechanism;

(2), each original bump thickness control machine component starts the bubble thinning operation, that is, the original The electric heating element corresponding to the azimuth of the bump increases the electric heating power, increases the bubble temperature at the original bump, and reduces the thickness of the original bump of the bubble, and the estimated thickness h of the original bump after the control adjustment is in the following range: a+ 0.7f>h>a+0.2f, that is, the estimated thickness h of the original bump after the control adjustment is less than 107 μm and larger than 102 μm; the bubble thickness detector continuously detects the actual thickness of each point of the bubble, and calculates each bubble. The original bump adjusted original bump adjusts the average value b of the thickness, and records the working parameters of each original bump thickness control mechanism after the thickness reduction operation, that is, records the original bump thickness control mechanism after performing the thickness reduction operation Electric heating power of the electric heating element;

(3) In all the normal point thickness control mechanisms, a part of the normal point thickness control mechanism is selected for the bubble thickening operation, and the way of the bubble thickening operation is to reduce the electric heating power of the corresponding electric heating element, so that the corresponding orientation The local temperature of the bubble decreases, and the normal point of the normal thickness control mechanism selected for the thickening operation is called the thickening point (the thickening point is still understood to be a component of the normal point); the bubble thickness detector Continue to continuously detect the actual thickness of each point of the bubble, calculate the average actual thickness c of all the normal points of the bubble including the thickening point; the normal point thickness control mechanism that is not selected for the bubble thickening operation still maintains the original work parameter;

(4) Calculate the absolute value d of the difference between c and b, d=|cb|; where c is the actual thickness average of all normal bubble points including the thickening point after the thickening operation, b Adjusting the average value of the thickness of the original bumps of the bubble before the thickness reduction operation;

(5) Comparing the sizes of d and e, where e is the maximum allowable difference between c and b;

If the comparison result is d ≤ e, it means that the difference between the average actual thickness of all normal points of the bubble and the average actual thickness of the original bump is not more than 1.5 μm, which is an acceptable tolerance range. Therefore, the thickening operation is achieved. Recording the number M of the normal point thickness control mechanisms for performing the thickening operation in this state, and the operating parameters (electrical heating power) of the normal thickness control mechanism (electric heating element) for each thickening operation, and starting the sixth (6) )step;

If the comparison result is d>e, it means that the difference between the average actual thickness of all normal points of the bubble and the average actual thickness of the original bump is greater than 1.5 micrometers, beyond the tolerance range, and the adjustment must be continued, then the c and b are further compared. Size

If the comparison result is b>c, the number of normal point thickness control mechanisms for performing the bubble thickening operation in step (3) is gradually increased, and the number of normal point thickness control mechanisms for each bubble thickening operation is adjusted. Higher one, although it is not possible to accurately predict the increase in bubble thickness corresponding to the local normal point A few microns, but it is expected that the average actual thickness of all normal points (100 points) including the thickening point will increase by less than 0.1 micron. This control accuracy is far beyond the need to gradually increase the bubble. During the process of increasing the number of normal point thickness control mechanisms of the operation, the average actual thickness of all normal points including the thickening point is repeatedly detected and a new average value c is calculated, and the new average values c and b are repeatedly calculated. The new absolute value of the difference d, repeatedly compares the size of d and e; until d ≤ e, when d ≤ e, means that the average actual thickness of all normal points of the bubble and the average actual thickness of the original bump are not more than 1.5 Micron, enters the range of tolerance that can be tolerated, therefore, indicates that the thickening operation achieves the purpose, records the number M of the normal point thickness control mechanism for thickening operation in this state, and the normal point thickness control for each thickening operation Operating parameters (electrical heating power) of the mechanism (electric heating element), and then starting step (6);

If the comparison result is c>b, the number of normal point thickness control mechanisms for performing the bubble thickening operation in step (3) is gradually lowered, and the number of normal point thickness control mechanisms for performing the bubble thickening operation is lowered. One (ie, restores the normal point thickness control mechanism for one of the bubble thickening operations to the original operating parameters), although it is not possible to accurately predict that the bubble thickness of the corresponding local point is reduced by a few microns, but it can be expected, including thickening points. The average actual thickness of all normal points (100 points) within the range will be reduced by less than 0.1 micron. This control accuracy is far beyond the need to gradually reduce the number of normal thickness control mechanisms for bubble thickening operations. Medium, repeatedly detecting the average actual thickness of all normal points including the thickening point and calculating a new average value c, repeatedly calculating the new absolute value d of the new average values c and b, repeating the comparison d and The size of e, until d ≤ e, when d ≤ e, means that the average actual thickness of all normal points of the bubble and the average actual thickness of the original bump are not more than 1.5 microns, into the tolerance range Therefore, it is explained that the thickening operation achieves the purpose, the number M of the normal point thickness control mechanisms for performing the thickening operation in this state, and the operation of the normal point thickness control mechanism (electric heating element) for each thickening operation are recorded. Parameter (electrical heating power), then start step (6);

(6) After the completion of the above step (5), the actual thickness average of each original bump is b, and the average actual thickness c of all bubble normal points including the thickening point is also close to b, after which, The circumferential thickness control mechanism lowers the total thickness of the bubble according to the detection result of the bubble thickness detector, specifically, increases the bubble pulling speed, so that the average thickness of the whole cell bubble becomes smaller a;

(7) In the subsequent production process, the local thickness control mechanism (electric heating element) corresponding to the orientation of each original bump maintains the operating parameter (electrical heating power) recorded in the step (2), And all the normal point thickness control mechanisms alternately select one of them to perform the bubble thickening operation, and maintain the normal point thickness control mechanism at each moment for the thickening operation, which is the M records recorded in the step (5), And the heating power of the electric heating elements of the M normal thickness control mechanisms for performing the thickening operation is the same as the heating power recorded in the step (5); at each moment, except for the M normal point thicknesses for performing the thickening operation In addition to the control mechanism, the remaining normal thickness control mechanism that does not perform the thickening operation still works with the original working parameters; the bubble thickness detector continuously detects the actual thickness of each point in the bubble circumferential direction, and the full-thickness thickness control mechanism (specifically The vertical stretching mechanism maintains the average thickness of each point of the entire circumference of the bubble to 100 microns, after which the bubble can be wound directly without mechanically rotating. Since in the above step (7), the chance that each bubble is normal as a thickening point is equal, that is, the thickening point is continuously and alternately rotated in the bubble circumferential direction, so after the winding, the thickening point is not Will cause the phenomenon of bursting.

In the above step (2), "the estimated thickness h of the original bump after the control adjustment is less than 107 micrometers and larger than 102 micrometers", since the target thickness after the thickness reduction is a relatively large interval range, the existing partial thickness control mechanism This rough control standard can be achieved, so there is no difficulty and no special requirements.

In the above embodiment, the full-thickness thickness control mechanism may also adopt a transverse stretching mechanism dominated by the air compressor, and the bubble pressure is used to control the total thickness of the bubble.

In the above embodiment, the partial thickness control mechanism can also adopt an electric valve installed in the radial passage, and the working parameter is the valve opening size or the valve switching state, and the thickening operation mode is to increase the valve opening degree, and the thickness is reduced. The mode of operation is to reduce the degree of valve opening.

In the above embodiment, the value of the local thickness control mechanism can be changed to 72, or can be changed to 144, or 288, or 360, and the like.

In the step (5) of the above embodiment, the sub-step of "gradually lowering the number of the normal point thickness control means for performing the bubble thickening operation" may also gradually reduce the bubble increase of a part of the thickening point. The magnitude of the thick operation, such as gradually increasing the power of a portion of the thickened electric heating element, results in a fine reduction in the "average actual thickness of all normal points including the thickening point".

In the step (5) of the above embodiment, the sub-step of "gradually increasing the number of normal point thickness control mechanisms for performing the bubble thickening operation" may also be carried out by gradually increasing the bubble growth of a part of the thickening points. The magnitude of the thick operation, such as the electric heating element that gradually reduces a part of the thickening point The power of the piece, the result also allows the "average actual thickness of all normal points including the thickening point" to be finely increased.

In the present invention and its embodiments, the target value a of the bubble thickness, the normal deviation value f of the bubble thickness, and the maximum allowable difference e may be specifically determined according to the actual winding volume and quality requirements, and the values of these values are mainly based on The product quality requirements are flexible and determined, and are not the problems to be solved by the present invention.

Claims

A blown film production process, the blown film device is provided with an extrusion die, the extrusion die is provided with a circular extrusion port, and a circular cooling air ring is arranged above the extrusion die, and a cooling air ring is formed. There are at least 72 partial thickness control mechanisms, and each partial thickness control mechanism is evenly arranged along the circumferential direction of the cooling air ring; the blown film device is further provided with a full-thickness thickness control mechanism and a bubble thickness detector; and the method includes the following steps :

(1) The annular extrusion port of the extrusion die continuously extrudes the annular film blank, and after the film blank is extruded, it is inflated and cooled to form a bubble, and each partial thickness control mechanism works with the same working parameters. The working parameter is called the original working parameter, and the original working parameter is recorded; the bubble thickness detector continuously detects the initial thickness of each point in the circumferential direction of the bubble; when the initial thickness of the azimuth point in the circumferential direction of the bubble is larger than the thickness of the bubble When the value a exceeds the normal deviation value f of the bubble thickness, the point at which the bubble is at the azimuth is regarded as the original bump, and the point other than the original bump is regarded as the normal point, and the local thickness of the normal point corresponds to the local thickness control. The mechanism is called a normal point thickness control mechanism; the local thickness control mechanism corresponding to the original bump is called the original bump thickness control mechanism;

(2) The original bump thickness control mechanism starts the bubble thinning operation, changes the working parameters, and reduces the thickness of the original bump of the bubble, and the estimated thickness h of the original bump after the control adjustment is in the following range: a +0.7f>h>a+0.2f; the bubble thickness detector continuously detects the thickness of each point of the bubble, and calculates the average value b of the original bump adjustment thickness of each original bump of the bubble after the thickness reduction operation, And record the working parameters of each original bump thickness control mechanism after the thickness reduction operation, and f is the normal deviation value of the bubble thickness;

(3) In all the normal point thickness control mechanisms, select some of the normal point thickness control mechanisms to perform the bubble thickening operation, change the working parameters, and the normal point thickness control mechanism selected for the thickening operation is normal. The point is called the thickening point; the bubble thickness detector continues to continuously detect the thickness of each point of the bubble, and calculates the average actual thickness c of all the normal points of the bubble including the thickening point after the thickening operation; The normal point thickness control mechanism for performing the bubble thickening operation still maintains the original operating parameters;

(4) Calculate the absolute value d of the difference between c and b, where c is the actual thickness average of all normal bubble points including the thickening point after the thickening operation, and b is the bubble original The average value of the original bump adjustment thickness of the starting bump after the thickness reduction operation, d=|c-b|;

(5) Comparing the sizes of d and e, where e is the maximum allowable difference between c and b; if d ≤ e, the number of normal point thickness control mechanisms for performing the thickening operation in this state is recorded M And the operating parameters of each normal thickness control mechanism for performing the thickening operation, and starting the step (6);

If d>e, further compare the size of both c and b;

If c<b, the number of normal point thickness control mechanisms for performing the bubble thickening operation in step (3) is gradually increased, or the thickness of the individual normal point thickness control mechanism is gradually increased, and gradually adjusted. In the high process, repeat the average actual thickness of all normal points including the thickening point and calculate the new actual thickness average c, and repeatedly calculate the absolute value d of the new average values c and b, and repeat the comparison. The size of d and e up to d ≤ e, and record the number M of normal point thickness control mechanisms for thickening operation in this state, and the operating parameters of the normal point thickness control mechanism for each thickening operation, and then Start step (6);

If c>b, the number of normal point thickness control mechanisms for performing the bubble thickening operation in step (3) is gradually lowered, or the thickness of the individual normal point thickness control mechanism is gradually lowered, and gradually adjusted. In the low process, the average actual thickness of all normal points including the thickening point is repeatedly detected and a new average value c is calculated, and the new absolute value d of the new average values c and b is repeatedly calculated, and the comparison is repeated. The size of d and e up to d ≤ e, and record the number M of normal point thickness control mechanisms for thickening operation in this state, and the operating parameters of the normal point thickness control mechanism for each thickening operation, and then Start step (6);

(6), after completion of the above step (5) is completed, the full-thickness thickness control mechanism according to the detection result of the bubble thickness detector to reduce the thickness of the entire bubble, so that the average thickness of the total bubble becomes smaller a;

(7) In the production process in the subsequent stage of production, each original bump thickness control mechanism maintains the working parameters recorded in step (2); and all normal point thickness control mechanisms alternately select one of them to perform thickening operation And maintaining the normal point thickness control mechanism at each time for the thickening operation is the value M recorded in the step (5), and the operating parameters of the normal thickness control mechanism of the M thickening operations and the (5) The working parameters recorded in the step are the same one-to-one; at each moment, except for the M normal point thickness control mechanisms that perform the thickening operation, the normal point thickness control mechanism that does not perform the thickening operation is still performed with the original working parameters. The bubble thickness detector continuously detects the actual thickness of each point in the circumferential direction of the bubble, and the full-thickness thickness control mechanism maintains the average thickness of each point of the entire bubble at a.