JPH0720663B2 - Method for producing polyoxymethylene tape - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a polyoxymethylene tape. More specifically, it relates to a method for obtaining a stretched polyoxymethylene tape having a high elastic modulus and a high strength and having a small thickness unevenness in the width direction.

(Prior Art) When a tape-shaped unstretched body of polyoxymethylene obtained by melt molding is super-stretched, it becomes a polymer material having a high elastic modulus and high strength suitable for industrial materials. A method for producing a polyoxymethylene tape stretched body having such high physical properties by stretching is already known. For example, JP-A-60-
220730 discloses that a polyoxymethylene tape-shaped unstretched material is stretched 30 times or more.

In addition, on page 7,300 of the Proceedings of the 1987 IEICE General Conference, an unstretched polyoxymethylene tape with a width of 15 mm and a thickness of 0.5 mm was heated by the dielectric heating method to obtain a stretching ratio.
It is shown that a stretched body having a tensile elastic modulus of 50 GPa or more was obtained by stretching at 28 times.

(Problems to be solved by the invention) In order to use the stretched polyoxymethylene tape as an industrial material, not only excellent mechanical properties such as high elastic modulus and high strength but also uniformity in shape of the tape are obtained. Is required. In particular, the demand for uneven thickness in the width direction of the stretched tape is strict, and it is difficult to satisfy the thickness uniformity simply by increasing the stretching ratio in order to improve the mechanical properties. Further, if stretching is carried out in a state where the thickness unevenness is large, warping, cracking and other defects may occur, making it unusable as an industrial material. Further, when the tape stretched body is slit in a certain width and used, if the thickness unevenness is large, the utilization factor in the width direction is low, which is uneconomical.

An object of the present invention is to provide a method for obtaining a stretched polyoxymethylene tape which has excellent mechanical properties such as high elastic modulus and high strength and has small thickness unevenness in the width direction.

(Means for Solving the Problems) In order to achieve the above-mentioned object, the present inventors have described the mechanism when the tape-shaped unstretched body made of polyoxymethylene is super-stretched in multiple stages, the stretching ratio and the stretching stress. As a result of diligent research and study from both sides, polyoxymethylene has excellent mechanical properties such as high elastic modulus and high strength when stretched to satisfy a specific relationship, and has small thickness unevenness in the width direction. It was found that a stretched tape body can be obtained, and the present invention was achieved.

That is, the present invention is a method for producing a tape by stretching a tape-shaped unstretched body made of polyoxymethylene in multiple stages, wherein the stretching stress (σ _D ) in the second and subsequent stages is relative to the stretching ratio (λ), A method for producing a polyoxymethylene tape is characterized in that stretching is performed that satisfies the following formula.

σ _D > 0.78λ + 10.1 However, λ = λ ₁ × λ ₂ × ... × λ _n λ _n : draw ratio of the nth stage σ _n : Stretching stress at the nth stage (Kg / mm ² ) The stretching ratio (λ) and stretching stress (σ _D ) are calculated by the following equations.

L _n : sample length (cm), W _n : sample weight (g), ρ _n : sample density obtained from the density gradient tube method (g / cm ³ ). T _n : Nth Stage Stretching Stress (Kg) The present invention will be described in detail with reference to the drawings.

FIG. 1 is an explanatory view showing an example of a stretching device in the case of two-stage stretching. The apparatus shown in FIG. 1 uses a speed ratio between a feeding device 3 composed of a pair of nip rolls a and a ′ and a first take-up device 6 composed of a pair of nip rolls b and b ′ to utilize the speed ratio of the two. Between the first draw zone for carrying out the first draw and the second take-up machine 10 consisting of the first take-up machine 6 and the nickel rolls c, c ', the speed ratio of the two is used for the second step. The second stage drawing zone for carrying out the drawing. The first take-up device 6 corresponds to a tension separating device, and the tension of the stretched body is independently controlled on both sides thereof. In FIG. 1, the polyoxymethylene tape-shaped unstretched body 2 wound around the unstretched body winding drum 1 is fed to a first stage stretching zone by a feeding machine 3 and then in a first stage dielectric heating furnace 5. After the temperature is raised, the first stage drawing, that is, the net drawing is immediately performed, and the film is taken up by the first take-up machine which is a tension separating device and, at the same time, sent out to the second-step drawing zone. The temperature is raised in the second-stage dielectric heating furnace 7 and the external heating furnace 8, and the second-stage drawing is performed. Subsequently, the stretched body 11 is taken up by the second take-up machine 10 and then taken up by the take-up machine 12. It should be noted that reference numerals 4 and 9 in the figure denote first-stage and second-stage tension detectors, respectively.

In the stretching in the present invention, the stretching stress (σ _D ) after the second stage is σ _D > 0.78λ + 1 with respect to the stretching ratio (λ).
The stretching must satisfy 0.1. In super-stretching, which stretches from a stretch ratio of 7 to 30 times, there is a two-stage stretching mechanism, the first stage of which is a net stretching mechanism in which the cross-sectional area of the unstretched body sharply decreases. Is a mechanism by which the cross-sectional area of the net stretched body gradually decreases. When the tape-shaped unstretched body is stretched with a neck, a phenomenon called a so-called neck-in occurs, and the both ends of the tape have a thick edge height. In neck stretching, it is extremely difficult to eliminate this edge height by the stretching stress and the stretching ratio. When the stretching stress and the stretching ratio are reduced, the height of the ear height becomes remarkable,
On the contrary, if the both are increased, the height of the ear height is slightly reduced, but the stretchability is lowered in the second stage stretching. However, in the case of multi-stage super stretching, by performing the second stage stretching after the second stage and applying a stretching stress of a certain value or more at a predetermined stretching ratio, the edge height generated in the neck stretching is increased. Can be gradually reduced to reduce thickness unevenness. Further, since stretching is performed with a stretching stress of a certain value or more with respect to the stretching ratio, mechanical properties such as tensile elastic modulus and tensile strength can be increased at the same time. In addition, when the stretching stress is set to be equal to or more than a certain value represented by the above equation,
If the stretching stress is too high, it will break, so it is natural that there is a certain limit. In the case of a non-stretched polyoxymethylene tape, it may break if σ _D > 0.78λ + 30.

The stretching stress may be adjusted by adjusting the stretching temperature.
Further, the number of stretching stages is particularly preferably two-stage stretching or three-stage stretching, considering the cost and operability of equipment.

The heating means used during stretching is not limited, and external heating,
For example, in addition to the method of hot air, heat medium exposure type, hot plate, hot roll contact type, infrared irradiation type, etc., a dielectric heating method can be used.

The polyoxymethylene used in the present invention is a homopolymer or copolymer of polyoxymethylene, and various additives for modifying polyoxymethylene such as a heat stabilizer, a weather resistance improver and an antistatic agent are included in the polyoxymethylene. , A plasticizer, etc. can be added.

(Examples) Hereinafter, the present invention will be described in more detail with reference to Examples.
The measuring methods used in the examples are as follows.

Thickness measurement: Using a thickness measuring device, the thickness is measured at 10 points in the width direction of the sample at equal intervals. The average of the 10 measured values is taken as the sample thickness. In addition, the thickness unevenness is expressed as a percentage according to the following formula.

Tensile elastic modulus: Measured with a Tensilon type tensile tester that also uses a differential transformer type elongation detector, and obtain the initial elastic modulus in the range from the elongation-load curve to the elongation of 0.4% (pulling speed 5 mm / min).

Sectional area of the sample, the sample weight (W _S g) and length (25c
m) and the value calculated from the following equation from the density (ρ _S g / cm ³ ) obtained by the density gradient tube method.

Tensile strength: Measure the load at tensile break with the same tester used to measure the tensile modulus. (Pulling speed 100 mm / min). The cross-sectional area of the stretched body is the same as above.

Example 1 A tape-shaped unstretched body of polyoxymethylene (Tenatsk (registered trademark) 3010 manufactured by Asahi Kasei Kogyo Co., Ltd.) having a width of 50 mm and a thickness of 1 mm was used in Table 1 by using a two-stage stretching apparatus shown in FIG. It was stretched under the conditions shown. Hot air at 175 ° C. and 170 ° C. was circulated in the first-stage dielectric heating furnace and the second-stage dielectric heating furnace, respectively. Also,
The draw ratio in the first drawing zone was 10 times. FIG. 2 shows the relationship between the draw ratio and the draw stress, which satisfies the constituent requirement σ _D > 0.78λ + 10.1 of the present invention. The mechanical properties and thickness of the obtained stretched product are shown in Table 2. It can be seen that each stretched body has small thickness unevenness and is excellent in mechanical properties.

Comparative Example 1 The same polyoxymethylene tape-shaped unstretched body as in Example 1,
Using a stretching apparatus, hot air in the second stage dielectric heating furnace was circulated at 180 ° C, and stretching was performed under the same conditions except that the temperature of the external heating furnace was set at 170 ° C. The results are shown in Table 3. In addition, as shown in the results of FIG. 2, σ _D > 0.
Since 78λ + 10.1 is not satisfied, it can be seen from Table 3 that the thickness unevenness is remarkable.

Example 2 A tape-shaped unstretched body made of the same polyoxymethylene as in Example 1 with a width of 50 mm and a thickness of 1.2 mm was stretched using the same stretching device as in Example 1 under the conditions shown in Table 4. Hot air at 175 ° C and 170 ° C was circulated in the first-stage dielectric furnace and the second-stage dielectric furnace, respectively. As shown in FIG. 2, which shows the relationship between the draw ratio and the draw stress at that time, it is understood that σ _D > 0.78λ + 10.1 is satisfied. The mechanical properties and thickness of the obtained stretched product are shown in Table 5, and it can be seen that the thickness unevenness is small and the mechanical properties are excellent.

Comparative Example 2 Using the same polyoxymethylene tape-shaped unstretched body and stretching apparatus as in Example 2, hot air in the second stage dielectric heating furnace was circulated at 180 ° C, and the temperature of the external heating furnace was set to 170 ° C. All were stretched under the same conditions except the above. The results are shown in Table 6. Moreover, as shown in FIG. 2, the result is σ _D > 0.
It does not satisfy 78λ + 10.1, and it can be seen from Table 6 that the thickness unevenness is remarkable.

(Effect of the Invention) According to the present invention, it is possible to obtain a stretched polyoxymethylene tape having excellent mechanical properties such as high elastic modulus and high strength and having small thickness unevenness in the width direction.

[Brief description of drawings]

FIG. 1 is an explanatory view of a stretching device showing an embodiment of the present invention,
FIG. 2 is a diagram showing a relationship between a draw ratio λ and a draw stress σ _D when a polyoxymethylene tape-shaped unstretched body having a width of 50 mm and a thickness of 1.0 mm and 1.2 mm is drawn. 1: unstretched body winding drum, 2: unstretched body, 3: feeding machine, 4: first
Stage tension detector, 5: 1st stage dielectric heating furnace, 6: 1st take-off machine, 7:
Second stage dielectric heating furnace, 8: External heating furnace, 9: Second stage tension detector, 10: Second take-up machine, 11: Stretching body, 12: Winding machine

Claims (1)

[Claims] 1. A method for producing a tape by stretching a tape-shaped unstretched body made of polyoxymethylene in multiple stages,
A method for producing a polyoxymethylene tape characterized in that the stretching stress (σ _D ) after the second step satisfies the following formula with respect to the stretching ratio (λ): σ _D > 0.78λ + 10.1 , Λ = λ ₁ × λ ₂ × ... × λ _n λ _n : draw ratio of the nth stage, σ _n : Stretching stress at the nth stage (Kg / mm ² )