JPS6359854B2 - - Google Patents

Description

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

Conventionally, biaxially stretched films of thermoplastic resins (polypropylene, polyethylene terephthalate,
In the method of adjusting the thickness distribution in the product width direction of the manufacturing equipment (polystyrene, etc.) using an automatic thickness control device, there is no way to determine the correspondence between the location of the thickness deviation of the product being measured and the die bolt position. Therefore, it was not possible to obtain a product with good thickness unevenness accuracy, so it was hardly used.

Previously, the measurement results of product thickness distribution were observed manually.
Through trial and error, they understood the relationship between the product and die bolt position and adjusted the die bolt. Moreover, this work required a high degree of skill and the working environment was poor. Additionally, in order to streamline the line and save labor, it was necessary to perfect a method for controlling product thickness using an automatic thickness control device.

The present invention has been proposed to solve the above-mentioned conventional drawbacks, and calculates the average stretching ratio from the width of the ear, the width of the slit, and the width of the product, and calculates the relationship between the die operating bolt and the sheet after longitudinal stretching. By associating the position of the product with the operating bolt,
The present invention aims to provide a film thickness control method that enables automatic thickness control of products.

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, the position of the deviation is associated with each operating bolt 15, and each operating bolt 15 is operated according to a predetermined formula based on the deviation of the product film 12 corresponding to each operating bolt 15. quantity is determined. Then, by operating each bolt 15 using the die bolt operating device 16 and changing the gap between the die 1 and the mouth gap, the thickness of the product film 12 is controlled by controlling the amount of resin extruded in that area. 17.

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 in the process of being molded by the cooling and solidifying device 2. The sheet 3 is reduced in the width direction (netking), and the width of the sheet 3 becomes Wb, which is smaller than the width Wa of the base of the die 1. 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 necking tendency, the width of the sheet is Wc, and the strip width Wci is also determined in advance through experiments.

The film 8 that has been laterally stretched in the lateral stretching device 6 has edges 9, 9a that are not laterally stretched, and the amount thereof is
x ₁ and x ₂ change depending on the conditions of lateral stretching or the thickness of the sheet 5 corresponding to the vicinity of the ears 9 and 9a. However, since the ears 9, 9a are not stretched laterally, the positions of the ears 9, 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 operating 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 12
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.

Since the present invention is structured as described above in detail, it is possible to correlate the position of the product film with the position of the operating bolt, and products with good film thickness accuracy can be obtained at all times. Moreover, it is an extremely useful invention that can solve all the conventional problems by unmanning work that requires a poor work environment.

[Brief explanation of drawings]

FIG. 1 is a system diagram of an apparatus for carrying out the method of the present invention, and FIG. 2 is a sectional view taken along line A--A in FIG. 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, 9, 9a... Ear part, 10, 10
a... Ear portion width detection device, 11, 11a... Slit portion, 12... Cut film, 13...
Thickness gauge, 14...Arithmetic control unit, 15...Operation bolt, _l1 , _l2 ...Width of slit portion, _x1 , _x2 ...Width of ear portion, Wc...Width of sheet before horizontal stretching , Wd…
...Product film width, X...Average lateral stretching ratio.

Claims (1)

[Claims] 1. When automatically controlling the thickness in the width direction of a biaxially stretched film made of thermoplastic resin, the lateral stretching ratio is calculated from the width of the edge portion that is not lateral stretched, the width before lateral stretching, the width to be slit, and the width of the product. In addition to correlating the position of the product in the width direction and the position of the sheet before lateral stretching, the correspondence between the position of the product in the width direction and the position of the operating bolt was determined from the correspondence between the operating bolt and the position of the sheet before lateral stretching, which was determined through a separate experiment. A film thickness control method characterized by automatically controlling the thickness of a product film in the width direction by attaching the film.