JP6242299B2 - Method for measuring puncture strength of stretched film - Google Patents

Description

  The present invention relates to a method for accurately measuring the puncture strength of a stretched film according to the thickness of the stretched film.

  Plastic films are processed into stretched films having various functions by being stretched, and are used in a wide range of fields such as optical applications and food packaging applications. By the way, when a plastic film is processed into a stretched film, the stretched film may tear and the product yield may be reduced.

  For example, a polarizing film used for optical applications is generally manufactured by uniaxially stretching a polyvinyl alcohol film (hereinafter, “polyvinyl alcohol” may be abbreviated as “PVA”). May tear in the stretching direction. One cause of this is thought to be the tension applied to the polarizing film. Specifically, when the polarizing film is transported, a conveying guide roll or the like is pressed against the polarizing film, and the polarizing film is perpendicular to the stretching direction. It is conceivable that tension is generated in any direction.

  Therefore, it is important to accurately and quantitatively evaluate the ease of tearing of a stretched film when developing plastic film materials or studying the production conditions of stretched films.

  The tear strength is known as a measure for evaluating the ease of tearing of a plastic film.For example, a cut is made parallel to the stretch direction of the stretched film, the stretched film is torn from the base point of the break, and the tear at that time A method of measuring the strength using a tensile tester is known (see, for example, Patent Document 1).

JP 2011-248293 A International Publication No. 2012/043192

  However, tearing of the stretched film often occurs from a state in which there is no break as a starting point or is unclear, and the actual tearability of the stretched film may not be sufficiently evaluated by the tear strength. On the other hand, a method for evaluating penetration resistance measured as the maximum load when a nail is pierced into a film is also known (see, for example, Patent Document 2), but a stretched film stretched at a particularly high stretch ratio. In this case, there was room for further improvement in the measurement accuracy. Then, an object of this invention is to provide the method which can measure the puncture strength of a stretched film accurately.

  As a result of intensive studies to achieve the above object, the inventors of the present invention measured the puncture strength by piercing the piercing tool into the stretched film to be measured. It was found that by setting the direction of the tip shape relative to the film to be specific, the puncture strength of the stretched film can be accurately measured, and the ease of tearing of the stretched film can be accurately and quantitatively evaluated. . Furthermore, according to the measurement method, it is possible to obtain a piercing strength highly dependent on the thickness of the stretched film. For example, when the thickness of the stretched film is changed, the piercing strength value before the change is changed. It has been found that it is easy to predict the value of the piercing strength. The present inventors have further studied based on these findings and completed the present invention.

That is, the present invention
[1] A method for measuring the piercing strength of a stretched film, the method of piercing a stretched film with a piercing tool having a rectangular tip shape so that the long side of the tip shape is substantially parallel to the stretching direction of the stretched film ;
[2] The method according to [1], wherein the stretched film is a polarizing film;
About.

  ADVANTAGE OF THE INVENTION According to this invention, the method which can measure the puncture intensity | strength of a stretched film accurately according to the thickness of a stretched film is provided.

It is the schematic which shows an example at the time of piercing a piercing tool in a stretched film according to the method of this invention.

The present invention is described in detail below.
The present invention is a method for measuring the puncture strength of a stretched film, and a puncture tool having a rectangular tip shape is stabbed into a stretched film so that the long side of the tip shape is substantially parallel to the stretching direction of the stretched film. Regarding the method. By adopting such a method, the puncture strength of the stretched film can be accurately measured according to the thickness of the stretched film, and the ease of tearing of the stretched film can be accurately and quantitatively evaluated.

  In the method of the present invention, a piercing tool having a rectangular tip shape is pierced into a stretched film. And the maximum load measured in this case can be made into the piercing strength of the stretched film used as the measuring object. In measuring the maximum load, the piercing tool may be pierced into the stretched film with the piercing tool attached to a device capable of measuring the maximum load such as a static material testing machine.

  In the method of the present invention, a piercing tool having a rectangular tip shape is used. Here, the tip shape refers to the shape of the tip portion when the piercing tool is viewed from the tip side. When measuring the piercing strength, the tip portion is opposed to the film surface to be measured and the piercing tool is pushed against the stretched film. Just stab it.

  The length of the long side in the rectangular tip shape is preferably in the range of 0.3 to 30 mm, since the effect of the present invention is more remarkably exhibited, and the length is 1 mm or more. Is more preferably 3 mm or more, more preferably 20 mm or less, and still more preferably 10 mm or less.

  The length of the short side in the rectangular tip shape is preferably in the range of 0.2 to 20 mm, since the effect of the present invention is more remarkably exhibited, and the length is 0.5 mm or more. More preferably, it is 0.8 mm or more, more preferably 10 mm or less, further preferably 3 mm or less, and particularly preferably 2 mm or less.

  The overall shape of the piercing tool can be, for example, a rod shape. Examples of the material of the piercing tool include metals such as iron, stainless steel, brass, bronze, and nickel steel; ceramics (such as silicon nitride), and the like. Metal is preferable, and stainless steel is more preferable.

  In the method of the present invention, when the piercing tool is pierced into the stretched film, the long side of the tip shape of the piercing tool is made substantially parallel to the stretching direction of the stretched film. If the direction of the long side is not substantially parallel to the stretching direction of the stretched film, it is difficult to obtain the puncture strength with high accuracy. In addition, the said long side becomes substantially parallel to the extending | stretching direction of a stretched film, for example, the angle (absolute value) which the said long side and the extending | stretching direction of a stretched film make is 30 degrees or less, Preferably it is 15 degrees or less, More preferably Includes the case of 10 ° or less, more preferably 5 ° or less, and the most preferable embodiment includes the case of 0 ° (parallel).

  The speed at the time of piercing the piercing tool into the stretched film is preferably 200 mm / min or less, more preferably 150 mm / min or less, and 120 mm / min or less because the piercing strength can be obtained with higher accuracy. More preferably it is. On the other hand, from the viewpoint of reducing the influence of disturbance, the speed is preferably 1 mm / min or more, more preferably 10 mm / min or more, and further preferably 50 mm / min or more.

  When the piercing tool is pierced into the stretched film, the stretched film to be measured is stabbed into the stretched film located at the hole in the state where the stretched film is sandwiched and fixed between the two plates with holes at the same position. It is preferable to pierce the tool because the piercing strength can be obtained with higher accuracy. Examples of the shape of the hole in the plate include a circle and a polygon, and a circle is preferable. The diameter of the circular hole can be set to 5 to 100 mm, for example.

  Although there is no restriction | limiting in particular in the kind of stretched film used as a measuring object in this invention, It is preferable that it is a film which has high orientation and is easy to produce the tear of an orientation direction, especially highly stretched, such as a polarizing film. A uniaxially stretched film is preferred. The polarizing film is generally a film having a function of transmitting only linearly polarized light having a specific vibration direction, and is a film dyed with iodine or a dichroic dye obtained by stretching a PVA film or the like. It is common.

  The stretch direction of the stretched film is the stretch direction when the stretched film is produced, and can be grasped by measuring the in-plane retardation value of the stretched film using, for example, a birefringence measuring apparatus. In addition, in this invention, although it is preferable to make a uniaxially stretched film into a measuring object, it can apply also to multiaxially stretched films, such as a biaxially stretched film. In this case, the direction in which the absolute value of the in-plane retardation value is maximized may be regarded as the stretching direction.

  Although there is no restriction | limiting in particular in the draw ratio (total draw ratio) at the time of manufacturing the stretched film used as a measuring object, The effect of this invention is more remarkable in the film which has high orientation and is easy to produce the tear of an orientation direction. Since it is played, the draw ratio is preferably 3 times or more, more preferably 4 times or more, and further preferably 5 times or more. An example of the upper limit of the draw ratio is 8 times.

  The thickness of the stretched film to be measured is preferably 1 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more, since the effects of the present invention are more remarkably exhibited. Moreover, it is preferable that it is 100 micrometers or less, It is more preferable that it is 50 micrometers or less, It is further more preferable that it is 40 micrometers or less.

  The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

[Production Example 1] Production of polarizing film having a thickness of 22 µm A PVA film having a thickness of 60 µm was uniaxially stretched twice in the length direction while being immersed in pure water at 30 ° C. Subsequently, while being immersed in an aqueous solution (dyeing bath) (temperature 32 ° C.) containing 0.04% by mass of iodine and 0.04% by mass of potassium iodide for 140 seconds, the length direction is increased 2.4 times. The film was uniaxially stretched to adsorb iodine. Next, the film was uniaxially stretched 2.6 times in the length direction while being immersed in an aqueous solution (crosslinking bath) (temperature 32 ° C.) containing 2.6% by mass of boric acid. Further, the film was uniaxially stretched in the length direction up to 6.3 times while being immersed in an aqueous solution (stretching bath) containing 2.8% by mass of boric acid and 5% by mass of potassium iodide (temperature 58 ° C.). . Then, it was immersed in an aqueous solution (cleaning bath) (temperature 22 ° C.) containing 1.5% by mass of boric acid and 5% by mass of potassium iodide for 13 seconds without stretching, and finally at 4 ° C. at 4 ° C. A polarizing film having a thickness of 22 μm was prepared by drying for 30 minutes. In addition, the draw ratio in each stage has shown the total draw ratio of the film until that time.

[Production Example 2] Production of polarizing film having a thickness of 12 μm A polarizing film having a thickness of 12 μm was produced in the same manner as in Production Example 1 except that a PVA film having a thickness of 30 μm was used.

[Example 1]
(1) Measurement of the puncture strength of a polarizing film having a thickness of 22 μm A polarizing film having a thickness of 22 μm produced in Production Example 1 is interposed between two 3 cm square stainless steel plates having a thickness of 1 mm with a circular hole having a diameter of 1 cm in the center. The polarizing film was fixed by sandwiching and overlapping the left and right sides of the overlapped stainless steel plate with clips to obtain a measurement sample. Next, the above measurement sample is fixed to the grip under the tabletop precision universal testing machine “Autograph AGS-J” manufactured by Shimadzu Corporation, and a rectangular shape with a tip shape of 1 mm wide and 5 mm long is attached to the upper grip. The metal piercing tool is fixed so that the long side of the tip shape is parallel to the stretching direction of the polarizing film, and the polarizing film located at the center of the hole in the stainless steel plate is pierced at a speed of 100 mm / min. The tool was stabbed and the maximum load at this time was determined. The same piercing test was performed 4 times in total, and the average value and standard deviation of the maximum load were calculated.
(2) Measurement of the puncture strength of a polarizing film having a thickness of 12 μm A puncture test similar to (1) was performed except that the polarizing film having a thickness of 12 μm prepared in Production Example 2 was used, and the average value and standard of the maximum load were measured. Deviation was calculated.
(3) Evaluation Table 1 shows the results of (1) and (2). It should be noted that a clear difference in the average value of the maximum load was confirmed between polarizing films having thicknesses of 22 μm and 12 μm, and any standard deviation was less than 0.4, and other than that, Were judged as “x”.

[Comparative Example 1]
The piercing test was performed in the same manner as in Example 1 except that the direction of the long side of the tip shape of the piercing tool was perpendicular to the stretching direction of the polarizing film, and the average value and standard deviation of the maximum load were calculated. . The results are shown in Table 1.

[Comparative Example 2]
A piercing test was performed in the same manner as in Example 1 except that a thick iron round nail CN65 (tip shape was spherical) defined in JIS A5508: 2009 was used as the piercing tool, and the average value and standard deviation of the maximum load were calculated. . The results are shown in Table 1.

1. Stretched film, 2. Piercing tool, 3. 3. Long side of the tip shape; 4. Static material testing machine Stainless steel plate, A. Tip of piercing tool, B. Stretch direction of stretched film, C.I. Piercing direction

Claims (2)

  A method for measuring the piercing strength of a stretched film, wherein a piercing tool having a rectangular tip shape is pierced into a stretched film so that the long side of the tip shape is substantially parallel to the stretching direction of the stretched film.   The method according to claim 1, wherein the stretched film is a polarizing film.

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