JPS5839649B2 - How to use the original film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for adjusting the thickness of a stretched thermoplastic resin film, and more particularly to a method for adjusting the thickness of an edge portion in the width direction.

Conventionally, the thickness adjustment of stretched films has generally been carried out by measuring the thickness distribution of the stretched film, and based on the measurement results,
This is done by adjusting the lip gap of the extrusion die, which allows the molten resin to flow out in the form of a film, using adjustment bolts.

However, in the conventional film thickness adjustment method, (1) the relationship between the thickness variation rate of the film before stretching and the film after stretching is not constant, which tends to result in more thickness adjustment than necessary; It takes a long time to obtain a desirable thickness distribution.

(2) When operating several adjustment bolts in close proximity at the same time, it is difficult to know the appropriate operating amount for each bolt due to mutual interference.

These drawbacks have caused problems in automatically controlling film thickness.

The inventors of the present invention previously proposed a film thickness adjustment method that solved these problems, but as a result of further investigation, further improvements were needed when adjusting the thickness of the edges of the film in the width direction. I acknowledged that I needed to add more.

In other words, at the start of film production, the thickness distribution at the edges of the film is often poor, but when the thickness of the edges of the film is adjusted, the effect may extend to the center of the film.
It is necessary to improve the thickness distribution at the edges first, and therefore it is extremely important to adjust the thickness at the edges of the film in a short time.

However, when adjusting the thickness of one end of the film,
A phenomenon in which the thickness distribution at the other end portions is disturbed is observed, resulting in the problem that it takes time to adjust both end portions to a good thickness distribution.

Therefore, in the present invention, if there is a thickness deviation exceeding the permissible range at the widthwise end of the film after stretching, (1) the thickness adjustment operation is performed at the other end as well, regardless of the size of the thickness deviation. (2) Correct the thickness deviation shape at both ends and convert it into the required adjustment amount for the film before stretching, (3) Select the corresponding number of films from the corrected deviation shape. (4) A thickness adjustment operation based on the calculated amount is applied to each end of the film before adjusting the thickness of the center portion of the film.

By combining these processes, the various problems mentioned above are solved.

The present invention will be explained in detail below.

FIG. 1 is a schematic diagram of a film manufacturing process explaining one embodiment of the present invention.

1 is an extrusion die for flowing out the molten resin in the form of a film, and is equipped with a large number of adjustment bolts 11.

The resin flowing out from the die 1 is cooled and solidified to obtain a film FA before stretching.

Next, this film FA is stretched by a lengthwise stretching device 2 and a widthwise stretching device 3 to obtain a stretched film (
A biaxially stretched film) Fs is obtained.

41 is a thickness measuring device for measuring the thickness distribution in the width direction of the film FA before stretching, and 42 is a thickness measuring device for measuring the thickness distribution in the width direction of the film Fs after stretching. .

For example, β-ray thickness measuring devices are used as these thickness measuring devices 41 and 42, and these devices scan in the width direction of the film to continuously measure the thickness distribution in the width direction of the film.

In carrying out the present invention, first, the thickness measuring devices 41 and 42 measure the thickness distribution in the width direction of the films FA and Fs, excluding the edges at both ends of the films.

The edges on both ends of the film are parts that are extremely thicker than the other parts caused by necking down when the molten resin flows out from die 1, but these edges are trimmed and discarded after stretching, so the thickness is Not subject to measurement.

The widthwise thicknesses of the films FA and F8 measured by the thickness measuring devices 41 and 42 are input to the calculator 5 and also recorded in the recorder 6.

This calculator 5 detects the position where the thickness deviation of the film Fs is large and the shape of the deviation (the cross-sectional shape of the film in the width direction at that part), and selects the bolt to be adjusted.

However, if the thickness is adjusted using the size of the thickness deviation measured for this film Fs as it is, the adjustment will be excessive and accurate adjustment will be difficult for the reasons described below. Therefore, this deviation should be corrected. It is necessary to use it.

That is, when there is a thickness deviation in the film before stretching, thinner parts are stretched more and thicker parts are less stretched.

To explain this relationship using FIG. 2, the average thickness of the film FA before stretching is tA, the deviation of the thick part is dA, and the average thickness of the film Fs after stretching is 18. If the deviation of the thick part is ds, then the film thickness variation rate AdS (CVA and CVs) before and after stretching is CVA-1 and CV8=-At
s, and the relationship between the two is d,<d.

tA tS Also, if the standard deviations in the width direction δA and δS of the thickness of the film before and after stretching are used instead of the deviations dA and ds, the same result is obtained.

tA ts Therefore, if the thickness of the film before stretching is adjusted using the ts and ds (or δS) measured for the stretched film as a guide, the adjustment will obviously be excessive.

CVs δS/δ, where m = −1 −, mCVA ts
tA indicates the rate at which the film thickness variation rate is increased by stretching.

(Hereinafter, m is referred to as the width increase rate. However, the width increase rate m varies greatly depending on the film manufacturing conditions (type of resin raw material, resin discharge amount, stretching ratio, stretching temperature, etc.), and even under the same manufacturing conditions. also varies depending on the size of the thickness deviation dA (or dA) of the film before stretching and the position of deflection, so when automatically controlling the film thickness,
If this is given as a simple coefficient, accurate thickness adjustment becomes difficult.

Therefore, the film FA is measured by the thickness measuring devices 41 and 42.
By measuring the thickness distribution in the width direction of the Correct the size of the thickness deviation.

These processes are performed by the computer 4. In other words, the thickness deviation shape of the film Fs (that part of the film F
The cross-sectional shape in the width direction of s) may be used as is, and the absolute value of its deviation may be corrected using the aforesaid amplification factor m.

The thus obtained corrected thickness deviation shape is converted into the thickness deviation shape to be corrected for the film FA before one stretching.

Therefore, if there is a thickness deviation exceeding the allowable range at the measured middle end of the film after stretching, the deviation shape of the measured middle end
is detected, and the deviation shape (2) is corrected by the amplification factor m near the end of the measurement peak to obtain a corrected deviation shape V'.

At the same time, the deviation shape W of the measuring end on the opposite side to the end with the thickness deviation is detected, and even if the deviation shape W does not exceed the tolerance range, the deviation shape W is used for thickness adjustment. Select as target.

Therefore, the deviation shape W is corrected by the amplification factor m1 near the end to obtain the corrected deviation shape W'.

Next, the corresponding bolts are operated in order to eliminate the deviation shapes I and W', and the amount of operation for each bolt is determined through the following process.

That is, as a result of examining the relationship between the amount of operation of the adjustment bolt and the movement of the lip due to the operation, the inventor found that the lip gap change shape hl per unit amount of operation of the adjustment bolt is as shown in FIG. a lj exp (-b 11 x2) =
It has been found that it can be approximated very well by (1) (where all, bA' is a constant, and X is the distance in the width direction from the center of the bolt).

FIG. 3 is a diagram illustrating the relationship between the amount of adjustment bolt operation and the lip gap change shape due to the operation, and the horizontal axis represents the width direction position on the die, and 111, 112, 113
indicates (positions of) three arbitrary adjustment bolts.

h A? 11 h −g2 + h A? 3 shows the lip gap change shape when each bolt 111.112113 is operated by a unit operation amount.As is clear from the figure, when the adjustment bolt is operated by a unit amount, the lip gap is the largest at the part corresponding to the center of the bolt. (al), and as the distance X moves away from the center of the bolt, the amount of lip gap change decreases according to equation (1).

Note that the constants al and bl are determined experimentally.

If the lip gap change shape hIl is obtained in this way,
This is expanded to the shape of the thickness change of the film F.

That is, h=a exp(-bx2)...
...(2).

Here, a and b are constants determined experimentally or by calculation, which are the same as a#, M? The value will be different from .

In this way, the shape of change in film thickness per unit operation amount of the adjustment bolt is determined and stored in the computer 4.

Then, a composite shape H of film thickness change when several adjacent bolts are operated simultaneously is given by adding the film thickness change shapes for each bolt.

For example, the composite shape H when the adjustment bolts 111, 112, and 113 are given operation amounts 2, 2, and 172, respectively, is:
As shown in FIG. 4A, the thickness change shape h1 for each bolt. h2. Add h3 and get H = 2 h, + 2
It is given in the form h2+ 1/2 h3.

Therefore, at the position corresponding to the poles Nll, 112° and 113 of the film F, the corrected thickness deviation shape v as shown in FIG. and each bolt 111, 112, 11 so that the difference between the composite shape H and this deviation shape V' is minimized.
The manipulated variables for each of 3 are calculated by the least squares method to obtain the manipulated variables 2, 2, and 1/2.

The adjustment operation amount for the deviation shape W is also calculated in the same manner.

In addition, as a rule, bolts located within the thickness measurement peak are selected as the bolts to be adjusted.

For example, if three adjacent bolts are to be operated as a set for one thickness deviation, and the bolt corresponding to the maximum thickness deviation is the bolt at the extreme end of the measurement width, Select a total of three bolts: the bolt at the end, one bolt inside, and two bolts inside, and also, the bolt corresponding to the maximum thickness deviation is 1 point larger than the bolt at the end of the measurement width. If it is a bolt on the inside of the book, select that bolt and the bolts on both sides of that bolt, a total of three.

In this way, once the operating amount of the adjustment bolt corresponding to the thickness deviation at the measured middle end of the stretched film Fs is calculated, the bolt drive device 7 is adjusted based on the calculated amount.
Add thickness adjustment operations to both ends of the film during measurement.

That is, when the thickness is adjusted (for example, made thicker) at one end of the film, the thickness distribution at the other end has the opposite tendency (becomes thinner).

Therefore, in the method of the present invention, if a thickness deviation exceeding the allowable range is detected at one end of the measurement width of the film, the other end of the measurement width is also subject to the thickness adjustment operation,
Thickness adjustment is applied to both ends of the film at the same time.

Thereby, while improving the thickness deviation at one end of the film, the thickness can be adjusted without causing a large disturbance in the thickness distribution at the other end, and the time required for adjustment can be greatly shortened.

In actual thickness adjustment, when calculating the operation amount of each bolt, add a coefficient k to correct the adjustment, and calculate by the formula h' = k a exp (-b x2) = (3), As the thickness distribution at the edge of the film improves, it is desirable to gradually shift from coarse adjustment to fine adjustment by changing the coefficient k in equation (3) from small to dog.

According to the method of the present invention, the thickness can be adjusted not only at the middle edge of the film where the thickness needs to be adjusted, but also at the other end of the measurement width at the same time. The thickness distribution of the film can be made uniform in a short time, and by adjusting the thickness of the film edges before the film center, the thickness of the film edges can be adjusted to the same thickness as the center of the film. can be prevented from affecting the distribution.

In addition, the thickness adjustment operation amount is automatically calculated based on the corrected thickness deviation shape by correcting the thickness deviation shape of the film after stretching by the amplification rate of the thickness variation rate due to stretching. Therefore, it is possible to perform accurate thickness adjustment operations within the shortest possible time without being affected by film manufacturing conditions or the size of film thickness deviation, and in particular, the adjustment time at the beginning of film manufacturing can be greatly shortened. Can be done.

[Brief explanation of drawings]

FIG. 1 is a film manufacturing process diagram showing an embodiment of the present invention,
Figure 2 is a perspective view of the film explaining the width increase rate m, Figure 3 is a diagram showing the relationship between the unit operation amount of the adjustment bolt and the lip gap change amount, and Figure 4 is the composite shape H of film thickness change. A diagram explaining. 1... Extrusion die, 11... Adjustment bolt, 2... Length direction stretching device, 3... Width direction stretching device, 41° 42... ...thickness measuring device,
FA...Film before stretching, Fs...
Film after stretching, ■t...Film thickness deviation shape after correction, h...Film thickness change shape per unit operation amount of adjustment bolt, H...Film Composite shape with thickness variation.

Claims (1)

[Scope of Claims] 1. In a method of adjusting the widthwise end thickness of a stretched film by operating a lip gap adjustment bolt of an extrusion die, the widthwise thickness distribution of the film before and after stretching is adjusted to the widthwise end thickness of the film at both ends of the film. If there is a thickness deviation that exceeds the allowable range at the middle end of the film after stretching, select the other end as the target of the thickness adjustment operation during the measurement, and (1) The thickness deviation shapes ■ and W are corrected by the amplification rate of the thickness variation rate of the film before and after stretching near the middle end of each measurement, and the thickness deviation shapes V′ and W after correction are obtained.
(2) On the other hand, the thickness change shape of the film before stretching per unit operation amount of the pre-adjusted bolt is calculated by the following formula % formula %) (In the formula, a and b are constants, and X is the center of the bolt. The composite shape H obtained by adding the shape of thickness change for each bolt when several adjacent bolts are operated simultaneously is obtained by approximating the width direction distance from (3) Based on the calculated amount, a thickness adjustment operation is applied to each end of the measurement width before adjusting the thickness of the central portion of the film. A method for adjusting the edge thickness of a stretched plastic resin film.