JP2003313314A - Method for evaluating fracture toughness of film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for evaluating fracture toughness of a film that has correlation with the practical use conditions and that enables quantitative evaluation. <P>SOLUTION: The method for evaluating fracture toughness of a film comprises subjecting a film with a thickness of 10-100 μm to a tensile test or a tearing test at a test speed of 5 m/min-300 m/min using a test specimen of the film in any of the forms as follows: (i) a form of the film having a specific location on which a stress is allowed to be concentrated when the film undergoes pulling or tearing and capable of observing the phenomenon of elongation or tearing selectively on the specific location; (ii) a form of No.2 dumbbell as described in JIS K7113; (iii) a form of an axial symmetry formed by symmetrically arranging two isosceles trapezoids with respect to the mating upper bases of the two isosceles trapezoids satisfying the condition: 2/5 ≤ a length of the upper base/a length of the lower base < 4/5; and (iv) a form of a notched strip as described in JIS K7128-A method and evaluating fracture toughness of the film by comparison of the elongation of the film at a low tensile speed with that of the film at a high tensile speed or by comparison of the tear strength of the film at a low tearing speed with that of the film at a high tearing speed. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaluation method which has a good correlation with the phenomenon of elongation or cracking when a film is stepped on in a practical state, and which has a quantitative property. More specifically, by pulling or tearing a test piece punched or cut into a specific shape in a speed range that cannot be controlled by conventional universal tensile testing machines, there is a "crack" in the film that could not be reproduced until now. The present invention relates to a novel film evaluation method capable of reproducing a phenomenon in good correlation with a practical state and capable of quantitative evaluation.

[0002]

2. Description of the Related Art Plastic materials have been in increasing demand since they were used as substitute materials for metal, wood, and paper due to their advantages of light weight, toughness, and ease of molding. There are various uses such as containers, sheets and films. For example, the container is required to have impact strength, transparency, gas permeability, etc., depending on its use. Further, as the applications and the shapes of products have become diverse, the required evaluation items and evaluation standards have become diverse. For example, in film applications, mechanical strength such as tensile strength / elongation, elastic modulus and tear strength, gas permeability of water vapor and carbon dioxide, light transmittance, transparency such as haze and turbidity are generally evaluated. These evaluation methods are standardized by JIS, ASTM and the like. For example, tensile strength / elongation is JISK-7113, and tear strength is JI.
SK-7128, gas permeation test is JIS K-712
6 is shown. However, these are methods for evaluating and comparing general physical properties, and are often insufficient in terms of practical and practical uses.

The tensile strength and elongation are generally defined by JIS K-7113, but in order to be applicable in many cases, the tensile strength and elongation are not always practically used in a stretched state or a slackened state. Not necessarily correlated with state. Also, the test speed is generally a constant speed test up to 1 m / min, which is far from the practical state. For example, when evaluated by the method according to JIS K-7113,
Even a film that stretches well may break when stepped on in the practical state, and a film that does not stretch very well may be difficult to crack in the practical state. That is, when a force is applied to the film, there are ones that "stretch without breaking" and ones that "crack without stretching". When put into practical use, it was not always necessary to collect cracks and cracks and to evaluate their tensile rupture elongations by the conventional method. Such an example is prominent in the field of agricultural mulch films, particularly in the field of biodegradable agricultural mulch films. As a result,
In addition to the existing tensile test method, a new film performance evaluation method has been required.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a film cracking evaluation method that correlates with a practical state and can be evaluated quantitatively.

[0005]

In order to solve these problems, the inventors of the present invention have earnestly studied, and as a result, first pay attention to the test speed of the film, and then optimize the test shape of the film. By examining the test speed range, it was found that the film can be evaluated in good correlation with the actual step of the film, and the present invention has been completed. This evaluation method can also be used for quantitative evaluation.

That is, the first aspect of the present invention is that the thickness is 10 μm.
A test piece obtained by molding a film having a thickness of 100 μm into any of the following shapes (i) to (iv): (i) When tensile or tearing, stress concentrates on a specific portion, and the portion selectively A test piece having a shape in which a phenomenon of elongation or tearing can be confirmed, (ii) No. 2 dumbbell-shaped test piece described in JIS K7113, (iii) 2/5 ≦ bottom length / bottom bottom length <4/5 A line-symmetrical shape test piece with two upper and lower isosceles trapezoids that meet, (iv) JIS
A strip-shaped test piece with a notch described in the K7128-A method,
The tensile test or the tear test is performed at a test speed of 5 m / min to 300 m / min using any of the following, and the elongation of the film at low speed and the elongation of the film at high speed are compared, or Provided is a film cracking evaluation method which is evaluated by comparing the film tear strength and the film tear strength at high speed. The second aspect of the present invention is that the test speed is 5
The film evaluation method according to claim 1, wherein the film is evaluated at a constant speed within the range of m / min to 300 m / min. The third aspect of the present invention is that the test speed is from 5 m / min to 300.
There is provided the film evaluation method according to the first aspect of the present invention, wherein the acceleration increases within the range of 0.1 to 2.0 m / s ² within the range of m / min. A fourth aspect of the present invention is the film according to any one of the first to third aspects of the present invention, characterized in that during one test, the acceleration is increased or decreased and / or becomes a constant velocity in a part of the section. Provide an evaluation method. Fifth of the present invention
Provides the film evaluation method according to any one of the first to fourth aspects of the present invention, wherein the film is a film obtained by inflation molding, T-die extrusion molding or calender molding. A sixth aspect of the present invention provides the film evaluation method according to any one of the first to fifth aspects of the present invention, in which a test speed is compared with a low speed value of 1 m / min or less and a high speed value of 5 m / min or more. To do. A seventh aspect of the present invention is that, when a tensile test is performed on a 20 μm thick aliphatic polyester film using a JIS K7113 No. 2 dumbbell-shaped test piece, the elongation of the film at a low speed is 500% or more and at a high speed. When the elongation of the film is 400% or more, it is evaluated as "difficult to crack", and when the elongation of the film at a high speed is 30% or less, it is evaluated as "easily cracked". The film cracking evaluation method described in 1.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Raw material resin The raw material resin for the film used in the present invention is not particularly limited, but is preferably a thermoplastic resin, a synthetic resin, a naturally produced resin; a crystalline resin, an amorphous resin; Any type of resin such as general-purpose resin, engineering resin; biodegradable resin, non-biodegradable resin may be used. As the thermoplastic resin, polyethylene (PE), polypropylene (PP),
Polystyrene (PS), AS resin, ABS resin, polyvinyl chloride (PVC), polyacrylonitrile (PA
N), (meth) acrylic resins, cellulosic resins, elastomers and the like. Examples of the engineering resin include various aliphatic polyamides such as nylon 6, 6, 6, 12 and 6, 12 or polyamides (PA) such as aromatic polyamides such as nylon 6T, polyethylene terephthalate (PET), Examples thereof include aromatic polyester resins such as polybutylene terephthalate (PBT), polycarbonate (PC), polyacetal, polyphenylene ether (PPO), polyphenylene sulfide (PPS), liquid crystal polyester, and fluorine resin. In addition, aliphatic hydroxycarboxylic acid (or its cyclic compound may be used, the same applies hereinafter) homopolymer, aliphatic hydroxycarboxylic acid copolymer, polymer of aliphatic dicarboxylic acid and aliphatic diol, aliphatic dicarboxylic acid and aliphatic It may be an aliphatic polyester such as a copolymer of a diol and an aliphatic hydroxycarboxylic acid, or a biodegradable resin such as an aliphatic polyester whose molecular weight is increased by diisocyanate. Further, these raw material resins include photodegradants, biodegradation promoters, inorganic additives, liquid lubricants, fine powder particles produced from paper, plasticizers, heat stabilizers, extenders, fillers, lubricants, colorants, Flame retardant, water resistance agent, autoxidizer, ultraviolet stabilizer, cross-linking agent, antibacterial agent, antifungal agent, herbicide, antioxidant, deodorant, nucleating agent, antiblocking agent, drip agent, antifogging agent, Antifog agents, antistatic agents or mixtures thereof can also be added.

Film The thickness of the film used in the present invention is not particularly limited, but is preferably 10 to 100 μm, more preferably 1
It is 5 to 50 μm. The method of molding the film used in the present invention is not particularly limited, but inflation molding, T-die extrusion molding, and calender molding are preferable. The film may be unstretched, uniaxially stretched or biaxially stretched. The uniaxial stretching ratio is 1.5 to 20 times, preferably 3
10 times. The biaxial stretching ratio is 1.5 to 20 times, preferably 3 to 10 times in each direction. (Stretching ratio measurement conditions) In the case of a crystalline resin film, the melting point + 10 ° C, and in the case of an amorphous resin film, the glass transition temperature + 10 ° C. The value obtained by dividing the initial length before immersion was taken as the draw ratio. Stretch ratio = initial length / length after immersion in oil bath

The film used in the present invention may be a monolayer film, a foamed film, a laminated film of resin films, a coextruded film, a coating film or the like.

Test Device The test device preferably used in the present invention is a high-speed tensile tester. A high-speed tensile tester used for a tensile or tear test has a tensile or tear test speed of 0.
For example, those of 01 to 300 m / min, preferably 0.1 to 100 m / min are exemplified. Further, constant velocity motion within the range of 0.01 to 300 m / min, uniform acceleration motion within the range of 0.01 to 300 m / min and within the range of 0.1 to 2.0 m / s ² , and the like. A device capable of changing the acceleration motion in multiple stages during the test is suitable.

Shape of Test Piece The shape of the test piece is exemplified by four types shown in FIG. However, since the elongation of the film varies greatly depending on the material, an optimum shape within the following range is selected for each material. (I) A test piece having a shape in which a stress is concentrated in a specific portion when it is pulled or torn, and a phenomenon that the portion is selectively stretched or torn can be confirmed. (Ii) No. 2 dumbbell-shaped test piece according to JIS K7113 ( Fig. 1-1) (iii) Length of upper bottom / length of lower bottom = 2/5 or more 4/5
A test piece with a line-symmetrical shape in which two upper and lower isosceles trapezoids are combined (Fig. 1-2) (iv) A strip-shaped test piece with a notch described in JIS K7128-A method (Fig. 1-3)

Test conditions The test speed is 5 m / min to 300 m / min, preferably 10 m / min.
~ 60 m / min. If the test speed is less than the above range, even a film that does not stretch in practical use and breaks, the test piece does not stretch well and the superior difference is not given as in the case of the tensile test at a normal low speed, and the test speed exceeds the above range. A film that stretches well without cracking during practical use or a film that cracks without stretching easily breaks, making it impossible to make a difference in advantage. The test speed may be an accelerating increasing speed within the range of 5 m / min to 300 m / min. The acceleration may be 0.1 to 2.0 m / s ² . Further, the acceleration may change in multiple stages during one test, and may include a constant velocity section during the test.

[0013]

EXAMPLES The present invention will now be described in detail with reference to examples, but the present invention is not limited thereto. The raw material resins used are shown below. The raw material resin was previously dried (5
(0 ° C. × 10 hours or more) was used. Bionore 1001: Polybutylene succinate type (manufactured by Showa Polymer Co., Ltd.) Bionole 3001: Polybutylene succinate adipate system (manufactured by Showa Polymer Co., Ltd.) Cellgreen PH7: Polycaprolactone system (manufactured by Daicel Chemical Industries Ltd.) ) Lacty 9400: Polylactic acid type (Shimadzu Corporation)
Made)

[Compound Pelletization] Using a tumbler, the resin blended in the following formulation was compounded and pelletized using a twin-screw extruder to form a film by an inflation molding apparatus.

[0015]

[Table 1]

<Compound pelletizing conditions> C1 (under hopper): 100 ° C C2: 180 ° C C3: 200 ° C C4: 200 ° C C5: 200 ° C C6: 210 ° C C7: 210 ° C AD: 210 ° C (adapter) D : 200 ° C. (die) The numbers 1 to 7 of C increase from the bottom of the hopper of C1 toward the die direction. The same applies to the numbering of the film forming process. The resin supplied from the hopper is extruded from C1 to D and then cut by a pelletizer.

[Filming] The above pellets were filmized by inflation molding. At this time, the pellets were also dried (50 ° C. × 10 hours or more) before inflation molding. <Inflation film molding conditions> C1 (under hopper): 100 ° C C2: 150 ° C C3: 170 ° C C4: 170 ° C C5: 170 ° C C: 170 ° C AD: 170 ° C (adapter) D1: 150 ° C (die) D2: The pellets supplied from the 150 ° C. hopper are extruded in the D direction from C1, and are extruded upward in the die D and expanded into a cylindrical shape by air pressure to form a film. Film take-up speed: 22.0 to 30.0 m / min Lip width: 2.0 mm Film folding diameter: 1350 mm Film thickness: 20 μm

Using the film thus obtained, the following various evaluations were carried out, and the results are shown in Table 2. [Evaluation Sample] As shown in 1-1 to 1-4 of FIG.
Using the tensile evaluation samples (five types), the crackability of each film was evaluated. In Examples 1 to 4, a test piece punched out with a No. 2 dumbbell described in JIS K7113 shown in FIG. 1-1 was used. In Examples 5 to 8, FIG.
An equilateral trapezoidal test piece having an upper base of 30 mm, a lower bottom of 50 mm, and a height of 60 mm, which was punched into a line-symmetrical shape by combining two upper bases, was used. In Comparative Examples 1 to 4, FIG.
-10 shown in -3, bottom 50mm, height 60mm
An isosceles trapezoidal test piece having a large iris drum shape punched into a line-symmetrical shape in which two upper bases are combined is used. In Comparative Examples 5-8,
Upper bottom 40 mm, lower bottom 50 mm, height 60 shown in FIGS.
A small-diameter drum-shaped test piece punched into a line-symmetrical shape in which two upper bases of an isosceles trapezoid of mm are combined. The test piece is 23
After conditioning the humidity for 24 hours with a constant temperature and humidity machine at ℃ × 50% RH,
It was subjected to measurement.

[Evaluation of Crackability] (Examples 1 to 8 and Comparative Example 1)
~ 8) The film obtained by the above-mentioned inflation molding was cut into each of the above shapes, and the film was evaluated for crackability with a high-speed tensile evaluation device. As the evaluation standard, the breaking elongation was used as a standard. Since there are various sample shapes, the elongation is indicated by the actual length of elongation (chuck movement distance, unit: cm). When the film does not crack, the breaking elongation shows several cm or more, but when the film cracks, the breaking elongation becomes almost zero. The evaluation criteria for crackability are as follows. ◯: Good elongation (breaking elongation) is maintained even if the tensile speed is high. Δ: A material that does not crack but has a lower elongation as the tensile speed increases. Poor: It stretches well when the pulling speed is slow, but cracks when the pulling speed becomes fast. The tensile measurement conditions are as follows. Equipment used: High-speed tensile tester Tensile conditions: Constant-speed tensile load cell: 10 kgf, 10% Crosshead speed: 0.5 m / min, 3 m / min,
20 m / min, 40 m / min, 60 m / min Distance between chucks: 8 cm Number of tests: n = 5 Table 2 shows the above measurement results.

[0020]

[Table 2]

[Foot-cracking property test] (Examples 9 to 12) A ridge was experimentally formed in a field, and the above film was spread by a film spreader. After that, the end of the ridge was intentionally stepped on with a foot, at which time it was evaluated whether the film actually cracked or cracked. With respect to each sample film, the number of tests was set to n = 20, and the ratio of no breakage at that time was shown in%. ((Number of times of no crack) / 20) × 100 (unit:%) The evaluation criteria for the stepping cracking resistance test are as follows. ◯: The rate of not breaking is 90% or more. Δ: The rate of not breaking is more than 80 and less than 90%. X: The rate of cracking is 80% or less. The above results are shown in Table 3. The tensile cracking resistance is listed in the bottom column of Table 3.

[0022]

[Table 3]

From the above results, it can be seen from the comparison between the tensile cracking properties of Examples 1 to 8 and the foot cracking properties of Examples 9 to 12 that the evaluation method of the present invention provides results that are correlated with the practical state. I understand. A film that breaks easily in a practical state has a test speed,
By making the shape of the test sample appropriate, it can be distinguished by a simple high-speed tensile test. With the sample shapes as in Comparative Examples 1 to 4, the films having the compositions described in the above examples cannot be easily differentiated because the films are easily broken even at a low tensile speed. On the contrary, Comparative Examples 5 to 5
In the sample shapes such as 8, all of them stretch well, and when they break, they break at the same time, so that no significant difference can be made. As a result, in the films described in the above Examples, the sample shapes as shown in Examples 1 to 8 were better able to give a significant difference between the samples, and the results evaluated with these samples showed correlation with the practical state. It can be said that there is something. Even if the composition of the film material changes, similar effects can be obtained by selecting the test speed and sample shape within the scope of the present invention.

From the above, by using the evaluation method shown in the present invention, it is possible to evaluate the cracking property of the film which is more correlated with the practical state.

[0025]

According to the present invention, the cracking property of a film can be evaluated with good correlation with the practical state of the film.

[Brief description of drawings]

FIG. 1 is a diagram showing a No. 2 dumbbell-shaped test piece according to an example. FIG. 1-2 is a diagram showing a medium-iris hourglass-shaped test piece according to the example. 1-3 is a figure which shows the large-diameter hourglass-shaped test piece which concerns on a comparative example. 1-4 is a diagram showing a small-iris hourglass-shaped test piece according to a comparative example.

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Claims (7)

[Claims] 1. A test piece obtained by molding a film having a thickness of 10 μm to 100 μm into any of the following shapes (i) to (iv): (i) When tensile or tearing, stress concentrates on a specific portion. However, a test piece having a shape in which the phenomenon of selective elongation or tearing can be confirmed at that portion, (ii) No. 2 dumbbell-shaped test piece described in JIS K7113, (iii) 2/5 ≦ bottom length / bottom bottom length A test piece with two symmetrical isosceles trapezoids that meet the condition of <4/5, (iv) JIS
A strip-shaped test piece with a notch described in the K7128-A method,
The tensile test or the tear test is performed at a test speed of 5 m / min to 300 m / min using any of the following, and the elongation of the film at low speed and the elongation of the film at high speed are compared, or A film cracking evaluation method, which is evaluated by comparing the film tear strength and the film tear strength at high speed. 2. The film evaluation method according to claim 1, wherein the test speed is a constant speed within a range of 5 m / min to 300 m / min. 3. The film evaluation according to claim 1, wherein the test speed increases within a range of 5 m / min to 300 m / min and the acceleration increases within a range of 0.1 to 2.0 m / s ^2. Method. 4. The film evaluation method according to claim 1, wherein the acceleration is increased or decreased and / or the speed is constant in a part of the section during one test. 5. The film evaluation method according to claim 1, wherein the film is a film obtained by inflation molding, T-die extrusion molding or calender molding. 6. A test speed of 1 m / min or less at a low speed and 5 m
The film evaluation method according to any one of claims 1 to 5, wherein the value is compared with a value at a high speed of not less than / minute. 7. A tensile test of an aliphatic polyester film having a thickness of 20 to 40 μm using a No. 2 dumbbell-shaped test piece of JIS K7113 shows that the elongation of the film at low speed is 500% or more and at high speed. The growth of the film is 4
The film of any one of claims 1 to 6 is evaluated as "difficult to break" when it is 00% or more, and "easy to break" when the elongation of the film at high speed is 30% or less. Crackability evaluation method.