JPS6359855B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a film thickness control method that can be applied to a biaxially stretched film manufacturing apparatus.

Conventionally, in equipment for manufacturing biaxially stretched films from molten thermoplastic resin, when adjusting the uneven thickness in the width direction of films and sheets extruded from various die shapes, the adjustment work was conventionally done manually. was. However, this work requires a high degree of skill, and since it is done manually, there is a limit to the accuracy with which the uneven thickness can be adjusted in the end. In addition, since the working environment was poor, there was a strong desire to put an automatic thickness unevenness adjustment device into practical use.

Various automatic film thickness unevenness adjustment devices have been proposed in the past, but all of these devices are inadequate for practical use and are not used much. That is,
In order for an automatic thickness unevenness adjustment device to be adopted, it must be able to perform adjustment in a shorter time than conventional manual adjustment time, and must also have excellent final deviation accuracy.
To this end, the most important point is not only the automatic adjustment device, but also the establishment of a control method.

Conventionally, there has been no known method for determining the correspondence between the location where uneven thickness occurs in a film product and the position of the operating bolt. Also, when disassembling and reassembling the die, or when changing the thickness of the product (referred to as changing the number), adjusting the resin passage gap of the adjustment lip, or changing the extrusion amount per die width, etc. in some cases,
Since it was common to have to start with very poor thickness deviation accuracy, there was a demand for a highly accurate film thickness adjustment method.

The present invention was proposed to solve the above-mentioned conventional drawbacks, and after confirming that the profile in the width direction of the sheet before lateral stretching is within an allowable range, the lateral stretching magnification is adjusted. Based on the correspondence between the product width direction position and the film or sheet position before horizontal stretching, and from the correspondence between the operation bolt and the film or sheet position before horizontal stretching, the product width direction position and the operation bolt position are correlated. It is an object of the present invention to provide a film thickness control method that can perform highly accurate film thickness adjustment in a short time by finely adjusting the thickness distribution in the width direction of the film after transverse stretching.

Embodiments of the present invention will be described below with reference to the drawings. A molten thermoplastic resin is extruded through a slit in a die 1, and is formed into a sheet in a cooling and solidifying device 2. The cooling and solidifying device 2 is generally composed of a group of rolls. 3 is a formed sheet, which is stretched in the film traveling direction by a longitudinal stretching device 4 (longitudinal stretching). Further, the longitudinal stretching device 4 is also generally composed of a group of rolls.

The longitudinally stretched sheet 5 is stretched in a direction perpendicular to the film traveling direction by a horizontal stretching device 6 (transverse stretching).
The stretching method is generally 5 sheets with 7 clips.
Both ends are held and heated and stretched in the lateral stretching device 6. As shown in the figure, the laterally stretched film 8 has portions called edges 9, 9a which are not stretched at all at x ₁ and x ₂ from both ends. The widths of the ears 9, 9a are measured by ear width detection devices 10, 10a.

Since it is difficult to control the thickness of the stretched film near the edges to be uniform, the slit portion 11,
11a (width l ₁ , l ₂ ) is cut. The film 12 from which the slit portions 11 and 11a have been cut is the part that becomes the product, and the thickness distribution in the width direction is determined by the thickness gauge 1.
3, and the product film 1 is measured by the arithmetic and control unit 14.
2, and by associating the position of the deviation with each operating bolt 15, the operating amount of each operating bolt 15 is calculated using a predetermined formula based on the deviation of the product film 12 corresponding to each operating bolt 15. It is determined. Then, by operating each bolt 15 using the die bolt automatic adjustment device 16 and changing the mouth gap of the die 1 to control the amount of resin extruded in that part, the thickness of the product film 12 is controlled and the product film 12 is wound. It is wound up by machine 17.

Reference numeral 18 denotes a thickness measuring device, which measures the thickness in the width direction, calculates the thickness deviation from the set value corresponding to the die adjustment operating bolt 15 using the arithmetic and control device 14, and adjusts each operating bolt 1 based on the deviation.
5 is calculated using a predetermined method. In addition, the die bolt automatic adjustment device 16 rotates the operation bolt 15 by a predetermined amount, and as a result, the die adjustment lip 19 is deformed to adjust the extrusion amount corresponding to the bolt, thereby correcting the uneven thickness, and the result is measured using a thickness measuring device. 18, and the same operation is repeated to finally converge to the desired film width direction profile.

Next, to explain the operation, the operation bolts 15 attached to the die 1 are generally provided at equal intervals Wai, and the extruded molten resin is The width of sheet 3 is the width of the nozzle of die 1.
It is smaller than Wa and becomes Wb. However, the amount varies depending on the molding conditions. Further, the width of the sheet (strip width) corresponding to each bolt 15 is Wbi. this
Wbi varies depending on the location in the width direction of the sheet 3, and becomes smaller toward both ends of the sheet 3.

Evenly spaced pitch Wai of operation bolt 15 and strip width
The relationship between Wbi has reproducibility once the molding conditions are determined, and can be determined in advance through experiments. Furthermore, since there is a correlation between the width Wb of the sheet 3 and the strip width Wbi, it is convenient to find a correlation formula. On the other hand, longitudinal stretching also causes a netting phenomenon, and the width of the sheet becomes Wc, and the strip width Wci is also determined in advance through experiments.

Therefore, the correspondence between the width direction position of the sheet 5 after longitudinal stretching and the operating bolt 15 is obtained. Here, if the profile of the sheet 5 before lateral stretching is converged to a certain degree,
Focusing on the fact that the time for adjusting the thickness of the film 8 after the transverse stretching can be shortened, the profile of the sheet 5 before the transverse stretching is first converged to a certain tolerance range with respect to the set profile.

That is, the thickness in the width direction of the sheet 5 after longitudinal stretching is measured by the thickness measuring device 18, the thickness deviation with respect to the set profile of the sheet corresponding to the die operation bolt 15 is calculated by the arithmetic and control unit 14, and each The amount of operation of the operation bolt 15 is calculated using a predetermined method.

In addition, the automatic bolt adjustment device 16 rotates the operation bolt 15 by a predetermined amount, and as a result, the die adjustment lip 19 is deformed to adjust the extrusion amount corresponding to the bolt 15, thereby correcting the uneven thickness. Measurement is performed using the measuring device 18, and similar operations are repeated until the desired sheet width direction profile is finally converged within an allowable range.

The degree of convergence may be determined based on the standard deviation value, variance value, or maximum value of the deviation with respect to the set profile of the sheet corresponding to the die operating bolt 15. According to the experience of the inventors, if the standard deviation value for the set profile converges to 0.5%,
It has been found that the deviation of the film 12 after horizontal stretching is within ±3 to ±5%.

However, Pi: Setting profile corresponding to the i-th bolt Poi: Measurement profile corresponding to the i-th bolt The setting profile is the setting profile for the sheet 5 before horizontal stretching when the film 12 after the previous horizontal stretching is within the allowable range as a product. Just measure your profile. However, even if the profile before transverse stretching is strictly converged to the desired profile, the film 12 after transverse stretching may not necessarily fall within the permissible range as a product due to slight differences in the stretching conditions. After the pre-stretching profile converges, it is necessary to finely adjust the film 12 after the transverse stretching. Fine adjustment of the film 12 after horizontal stretching is performed by the method described below.

That is, the film 8 that has been laterally stretched in the transverse stretching device 6 has edges 9, 9a that are not laterally stretched, and the amounts x ₁ and x ₂ of the edges 9, 9a are determined depending on the conditions of the lateral stretching or in the vicinity of the edges 9, 9a. It changes depending on the thickness of the corresponding sheet 5.
However, since the ears 9 and 9a are not stretched laterally,
The positions of the ears 9 and 9a are the same as the positions of the ears of the sheet 5 after longitudinal stretching. Furthermore, the widths l ₁ and l ₂ of the slit portions 11 and 11a to be cut may be automatically measured, but since they are generally fixed values, they may be given as data for calculation.

The relationship between the width Wd of the product film 12, the position in the width direction, and the thickness is measured by the thickness meter 13, and the stretched portion (including the slit portions 11 and 11a) is determined by the thickness gauge 13.
The average lateral stretching ratio X is calculated by the following formula.

X=Wd+(l ₁ −x ₁ )+(l ₂ −x ₂ )/Wc−x ₁ −x ₂ Generally, the average lateral stretching ratio is 8 for polypropylene.
~10 times, and about 3-4 times for polyethylene terephthalate, polystyrene and nylon. Also, the position of the product film 12 in the width direction and the operation bolt 15
The correspondence relationship between the positions of can be estimated by the following method.

That is, the end point P of the product film 12 corresponds to the point (x ₁ +l ₁ -x ₁ /X) from the end Q on the longitudinally stretched sheet 5. Therefore, the sheet 5 after longitudinal stretching described above
The relative position of the end point P of the product film 12 and the operating bolt 15 is determined from the relationship between the strip width Wci and the operating bolt 15.

Also, the section y from point P is i of the operating bolt 15.
It is possible to calculate the value corresponding to the number. y ₂ ~ y ₁ from point P
The section corresponds to the i+1st operation bolt 15. In the same way, the product film 12 and the operating bolt 1 are
5 is calculated, and the average deviation of the product film 12 corresponding to each operating bolt 15 is calculated from the relationship between the position in the film width direction measured by the thickness meter 13 and the thickness deviation, and the average deviation of the product film 12 corresponding to each operating bolt 15 is calculated. By calculating the operating amount of each of the operating bolts 15 using a formula and operating the die bolt automatic adjustment device 16, the gap between the die 1 and the die 1 is adjusted, thereby controlling the amount of molten resin extruded from the die. All of these calculations are performed by the calculation control device 14.

The adjusted sheet is used as the ear width measuring device 10, 10a.
When reaching , measure the ear widths x ₁ and x ₂ , then measure the product thickness, and if the desired accuracy is not achieved, operate the operating bolt 15 again using the same method to ensure constant accuracy. Film can be obtained unattended. Controlled product film 1
2 is wound up by a winding machine 17.

In addition, if the widths x ₁ and x ₂ of the ears are stable and there is no need to measure them using the ear width measuring devices 10 and 10a,
The width may be measured artificially and input data to the arithmetic and control device 14. Furthermore, if the lateral stretching ratio of a specific portion differs due to the characteristics of the lateral stretching machine, etc., the lateral stretching ratio of that portion may be corrected and calculated.

In addition, in the case of rough adjustment, if the thickness in the width direction of the sheet 3 before longitudinal stretching is measured instead of measuring the thickness in the width direction of the sheet 5 after longitudinal stretching, the time required for rough adjustment before horizontal stretching can be can be further shortened.

Since the present invention is configured as described above in detail, it is possible to correlate the location where uneven thickness of the film or sheet occurs and the position of the operating bolt, and to adjust the profile of the sheet before horizontal stretching to an allowable range and after horizontal stretching. By performing fine adjustments, it is possible to always obtain products with highly accurate film thickness through short automatic adjustment operations, which eliminates the need for the conventional high level of skill, and also enables unmanned work in poor working environments. It has extremely excellent effects such as:

[Brief explanation of drawings]

Fig. 1 is a system diagram of an apparatus for carrying out the method of the present invention, Fig. 2 is a sectional view taken from A to A in Fig. 1, and Fig. 3 is a front sectional view of the bolt automatic adjustment device and die in Fig. 1. be. Explanation of the main parts of the figure, 1... Die, 3... Molded sheet, 4... Longitudinal stretching device, 5... Longitudinal stretched sheet, 6... Horizontal stretching device, 8... Laterally stretched sheet. Film, 13... Thickness gauge, 14... Arithmetic control device, 15... Operating bolt, 16... Die bolt operating device, 18... Thickness measuring device, 19... Die adjusting lip.

Claims (1)

[Claims] 1. When automatically controlling the thickness of a thermoplastic resin biaxially stretched film, find the correspondence between the position of the film or sheet and the position of the operating bolt, and first, after converging the profile of the sheet before horizontal stretching to an allowable range with respect to the set profile. . A film thickness control method, which comprises adjusting the thickness of a film or sheet by finely adjusting the film after transverse stretching.