JPH10272687A - Method for producing polyolefin sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method capable of stably stretching at a high magnification even if the thickness is large and obtaining a polyolefin sheet having a high strength and a high elastic modulus. SOLUTION: In rolling and stretching a sheet mainly composed of a high-density polyolefin, a sheet is heat-treated at a temperature higher than a sheet forming temperature before stretching.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyolefin having excellent strength and elastic modulus, and more particularly, to rolling a sheet containing a polyolefin as a main component,
The present invention relates to an improvement in a method for producing a polyolefin sheet that enables high-magnification stretching by stretching.

[0002]

2. Description of the Related Art A crystalline resin such as polyolefin or polyfluorinated olefin is melt-extruded and crystallized under pressure with a set of calender rolls at a specific take-off speed or less to obtain a film, which is then heat-treated and stretched. Japanese Patent Application Laid-Open No. 2-47031 discloses a method for continuously producing a microporous film by sequentially performing each step of heat setting and heat setting.

[0003] Here, since the oriented lamellar structure can be formed at a relatively low speed, the steps from extrusion to stretching can be performed continuously, and the production cost can be reduced. It is said that forcible crystallization has an effect that the control width of the pore size is widened and that the thickness is easily controlled.

However, according to the method disclosed in Japanese Patent Application Laid-Open No. 2-47031, the stretching ratio is 1.1 to 4 times.
Since it was considerably low, about twice, the effect of orientation crystallization by stretching could not be expected so much. Therefore, the mechanical strength such as tensile strength and elastic modulus of the obtained microporous film did not increase so much. Also, when the thickness of the film increases,
In a normal stretching method such as tensile stretching or roll stretching, there is a problem that the film is cut during the stretching and the stretching becomes substantially impossible.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to stably stretch a high-magnification sheet even with a thick sheet and to produce a polyolefin sheet having a high strength and a high elastic modulus. It is to provide a method.

[0006]

According to the present invention, there is provided a method for producing a polyolefin sheet, comprising: a step of rolling a sheet mainly composed of polyolefin; a step of stretching the sheet; and a step of heat-treating the sheet before stretching. And characterized in that:

That is, in the production method according to the present invention, a sheet mainly comprising a polyolefin obtained by molding is rolled and further stretched, thereby enabling high-magnification stretching, and furthermore, by heat treatment before stretching, By increasing the degree of conversion in advance, it is possible to stretch even higher magnification,
The feature is that the strength and the elastic modulus are thereby improved.

Hereinafter, the present invention will be described in detail. As the polyolefin used in the present invention, a high-density polyolefin resin suitable for obtaining a polyolefin sheet having a high strength and a high elastic modulus is suitably used.

The high-density polyolefin resin is not particularly limited as long as it has high crystallinity. For example, polyethylene; polypropylene; a homopolymer such as 1-butene or 1-pentene; 10% by weight of copolymerized copolymer component
What consists of the following these copolymers is mentioned. Examples of the copolymerization components copolymerized at 10% by weight or less include, for example, vinyl monomers such as vinyl acetate, vinyl alcohol and vinyl chloride, and unsaturated carboxylic acids such as (meth) acrylic acid. can do.

Among the above-mentioned polyolefin resins, in the present invention, high-density polyethylene is preferably used because the effect of improving the strength and elastic modulus in the present invention is great.
When high density polyethylene is used, its density is 0.94
g / cm ³ or more is preferable. In the case of polyethylene having a lower density, improvement in strength and elastic modulus may not be expected much even after stretching.

When using high-density polyethylene,
Its melt index (MI) is preferably 0.
1 to 20, more preferably 0.1 to 10 is desirable. If the melt index is smaller than 0.1, a molding machine such as an extruder may be overloaded, and if it is larger than 20, molding may be difficult.

The polyolefin-based sheet used in the present invention may be composed of only polyethylene, but other polyolefin resins such as polypropylene, low-density polyethylene, ethylene-vinyl acetate copolymer, Polyvinyl acetate, polyvinyl alcohol and the like, preferably 10% by weight or less, may be mixed.

Further, in addition to the above-mentioned polyolefin, known plasticizers and the like may be added to the sheet containing polyolefin as a main component, as long as the object of the present invention is not impaired. In the following, a high-density polyethylene, which is a preferred example of the polyolefin, will be described as an example for ease of explanation and understanding.

When high-density polyethylene is melt-molded with an extruder or the like, the melting temperature is usually 130 ° C. or higher, preferably 140 ° C. or higher. When the melting temperature is lower than 130 ° C., the melting of the high-density polyethylene resin becomes incomplete, and a load may be imposed on a molding machine such as an extruder.

Further, if melt molding is performed at an excessively high temperature, the polyethylene may be decomposed to cause discoloration or a decrease in the strength due to a decrease in the molecular weight. Therefore, it is desirable that the melting temperature be substantially 300 ° C. or less.

The molten high-density polyethylene or a composition containing high-density polyethylene as a main component is formed into a raw sheet. The forming method is not particularly limited, and a usual roll forming method, calendar forming method, or the like can be used.

Further, the thickness of the raw sheet greatly affects a rolling step performed later. That is, if the thickness of the raw sheet becomes too large, the force required for the rolling roll to crush the sheet, the so-called rolling force, increases, the deflection of the rolling roll increases, and uniform rolling is performed in the width direction. Can not be done. Conversely, when the thickness of the raw sheet is too thin, not only the thickness of the sheet after rolling becomes too thin, but also the rolling rolls come into contact with each other to shorten the life of the rolls. Therefore, the thickness of the raw sheet is 0.5 to 4
mm.

In the present invention, the polyolefin-based sheet obtained as described above is first rolled. Rolling is a normal rolling method, i.e., the clearance of a pair of rolling rolls rotating in opposite directions is made smaller than the thickness of the raw sheet, and the raw sheet is inserted between the rolling rolls to reduce the thickness of the sheet. This is done by reducing and elongating in the longitudinal direction.

If the temperature of the rolling roll in the rolling step is too low, the rolling force is large, so that uniform rolling may be difficult. If the temperature is too high, the sheet may melt and break during rolling. Therefore, the temperature of the rolling roll in the rolling step is preferably 70 to 125 ° C, more preferably 90 to 120 ° C.

On the other hand, if the rolling ratio is too low, not only the effect of rolling cannot be expected, but also the burden on the subsequent stretching step. Conversely, if the rolling ratio is too large, the rolling force increases, and not only uniform rolling becomes difficult, but also
The thickness of the sheet after rolling becomes too thin, and the sheet may be cut in a subsequent stretching step. Therefore, the rolling ratio is preferably 2 to 10 times, more preferably 4 times.
９9 times.

The above-mentioned rolling ratio is a value defined by the following equation (1).

[0022]

(Equation 1)

Next, the rolled sheet is stretched. The stretching method is not particularly limited, and a usual roll stretching method or zone stretching method can be used. Preferably, a roll stretching method which is excellent in productivity is suitably used because a special device is not required and the stretching ratio can be easily controlled.

Various methods such as hot air heating, hot water heating, infrared heating, microwave heating and the like can be used for heating the sheet at the time of stretching. Among them, the apparatus is simple and the temperature control is also easy. Hot air heating, which is easy, is preferably used.

The number of times of stretching is not particularly limited, but a multistage stretching method in which stretching at a low stretching ratio is performed a plurality of times is preferred because stretching is hardly caused and stable stretching is possible. However, if the number of times of stretching is too large, the stability can be increased and the stretching ratio can be increased, but the apparatus becomes large. Therefore, it is preferable that the number of stretching is substantially five times or less.

The stretching temperature is 70 ° C. or more,
It is preferable to set the temperature to the range up to the melting point of the high-density polyethylene used, and more preferable to set the temperature to 80 ° C. or higher and a temperature lower by 10 ° C. than the melting point of the high-density polyethylene used.

In the present specification, the melting point of the high-density polyolefin refers to the maximum point of an endothermic peak accompanying melting of a crystal, which is observed when subjected to a thermal analysis such as a differential scanning calorimeter (DSC). Shall be.

If the sheet is stretched at a temperature lower than 70 ° C., the sheet may be whitened. At a temperature higher than the melting point, the effect of improving the strength by stretching may not be obtained,
In addition, the sheet may be stretched and cut.

The stretching ratio is preferably at least 5 times, more preferably at least 7 times. If the stretching ratio is less than 5 times, the effect of increasing the strength and the elastic modulus may not be sufficiently obtained. The stretching ratio is a value defined by the following equation (2), and in the case of multi-stage stretching, is represented by the ratio of the sheet cross-sectional area before and after the entire stretching step.

[0030]

(Equation 2)

In the method for producing a polyolefin sheet according to the present invention, heat treatment is performed before the stretching step. This heat treatment is performed before the stretching step, preferably at a temperature lower than or equal to 50 ° C. lower than the melting point of the high-density polyethylene used and lower than or equal to the melting point, unlike the heating at the time of stretching. Specifically, in the case of high density polyethylene, preferably 80
° C or higher, 140 ° C or lower, more preferably 100 ° C or higher,
Heat treatment is performed at a temperature of 135 ° C. or less. If the heat treatment temperature is lower than 80 ° C., the effect of enabling high magnification stretching by the heat treatment may not be sufficiently obtained, and if the temperature exceeds 140 ° C., the sheet is melted.

The above heat treatment may be performed at any stage before stretching. However, in the case where heat treatment is performed after performing the above-described rolling step, it is preferable to perform heat treatment in a state where the sheet is stretched after rolling in order to prevent the sheet from contracting due to heating during rolling.

If heat treatment is performed both before and after the rolling step, additives such as a plasticizer in the sheet may bleed out to the sheet surface, and conversely, the stretchability may be reduced. There is.

Action High-density polyolefins, especially high-density polyethylene, can significantly increase their strength and elastic modulus by stretching at high magnification. However, a sheet mainly composed of a thick high-density polyolefin cannot be stretched at a high magnification as it is. Therefore, in the present invention, a high-density drawing of a thick high-density polyolefin sheet can be performed by performing the rolling step prior to the drawing as described above.

In addition, in the present invention, by performing the above-mentioned heat treatment before the stretching, it is possible to perform the stretching at a higher magnification more stably, whereby the strength and elastic modulus of the polyolefin sheet are remarkably increased. ing.

It is to be noted that, by performing the heat treatment, the stretching at a higher magnification can be performed because a large number of long molecular chains are entangled in the amorphous portion of the high-density polyolefin. Is thought to be due to the reduction of

[0037]

The present invention will be clarified by the following non-limiting examples and comparative examples.

(Experimental Method) (1) Preparation of Raw Material High-density polyethylene having a weight-average molecular weight of 3.3 × 10 ⁵ , a melt index (MI) of 1.0, and a melting point of 135 ° C. (manufactured by Mitsubishi Chemical Corporation, grade: HY540) ) In the same direction 2
The resin was melted at a resin temperature of about 200 ° C. using a shaft kneading extruder (trade name: PCM30, manufactured by Ikegai Iron and Steel Company), and the roll temperature was 80 ° C.
60mm width and 1.5m thickness by calender molding machine
m.

(2) Rolling Step The sheet was rolled eight times in the longitudinal direction using a hot roll (made by Kodaira Seisakusho, roll diameter 6 inches) heated to 120 ° C.

(3) Stretching Step The sheet was stretched in a longitudinal direction at a stretching temperature of 95 ° C. at a preset stretching ratio of 1.8 times (excluding Comparative Example 3) using a hot-air heating roll stretching machine. The second stretching was performed at the individual magnifications described in 1. Note that the second stretching magnification is the maximum stretching magnification at which the sheet is not cut, and has been grasped through preliminary experiments in advance.

(4) Heat treatment step After winding the sheet around an iron core, the sheet is heated to 110 ° C. or 130 ° C.
For 14 hours.

(Example 1) In Example 1, the above (1) preparation of the raw material, (4) heat treatment step (however, the heat treatment temperature is 1
The sheet was processed in this order of (10 ° C.), (2) rolling step, and (3) stretching step.

(Example 2) A sheet was processed in the order of (1) preparation of a raw material, (4) heat treatment step (the heat treatment temperature was 130 ° C), (2) rolling step, and (3) stretching step.

Example 3 (1) Preparation of raw material, (2) Rolling step, (4) Heat treatment step (however, heat treatment temperature is 11
0 ° C.) and (3) the sheet was processed in the order of the stretching step.

(Example 4) (1) Preparation of raw material, (2) Rolling step, (4) Heat treatment step (however, the heat treatment temperature is 13
0 ° C.) and (3) the sheet was processed in the order of the stretching step.

(Comparative Example 1) A sheet was processed without performing (4) heat treatment, (1) preparation of a raw material, (2) rolling, and (3) stretching.

(Comparative Example 2) (1) Preparation of raw material, (2) rolling step and (3) stretching step were performed in this order, and (4) the sheet was processed without performing the heat treatment step.

(Comparative Example 3) As a raw sheet, (1) the high-density polyethylene used in the preparation of the raw material was melted in the same manner as in (1) the preparation of the raw material, except that the thickness was 190 μm.
(Corresponding to the sheet thickness after rolling when a 1.5 mm-thick raw sheet is rolled 8 times), and using the formed 190 μm-thick raw sheet, the rolling process of (2) , And only the stretching step was performed.

(Evaluation of Examples and Comparative Examples) Examples 1-4
For the sheets obtained in Comparative Examples 1 to 3, the total stretching ratio (the product of the rolling ratio and each stretching ratio) is shown in Table 1 below. For each sheet obtained in Examples and Comparative Examples, a test piece was prepared using a No. 2 dumbbell, and a tensile tester (manufactured by Orientic, model: Tensilon) was used.
A tensile test was performed in accordance with JIS K 7113, and a tensile strength and a tensile modulus were measured. Table 1 shows the results.

The crystallinity of the sheets obtained in Examples 1 to 4 and Comparative Examples 1 to 3 was measured as follows, and the results are shown in Table 1. Measurement of crystallinity: The heat of fusion of the sheet was measured using a differential scanning calorimeter (DSC220C, manufactured by Seiko Instruments Inc.), and the crystallinity was determined by the following equation.

[0051]

(Equation 3)

The measurement conditions were as follows: measurement temperature = 20 ° C. → 1
0 ° C./min→200° C., atmosphere: nitrogen gas flow (flow rate 5
0 ml / min), sample container: Al pan crimp.

[0053]

[Table 1]

In Comparative Example 1 in which no heat treatment was performed before the stretching step, the measured stretch ratio was low in the second stretching. Therefore, compared to Examples 1-4, the total stretching ratio is also:
In Comparative Example 1, the value was about 10% lower, and the mechanical properties were also low.

Further, the sheet of Comparative Example 1 had a crystallinity of 7
In contrast to 3.9%, in Example 1, 75.7%,
The crystallinity of Example 2 was 82.7%, that of Example 3 was 77.7%, and that of Example 4 was 80.8%.

The second stretching ratio was set to 1 in Comparative Example 1.
In Comparative Example 2, which was increased from 4 times to 1.6 times, the sheet was cut in the second stretching, and stretching was impossible. Therefore, by comparing Comparative Examples 1 and 2 and Examples 1 to 4, by performing a heat treatment before stretching, the degree of crystallinity of the sheet was increased, probably because the entanglement of the molecular chains in the amorphous portion was reduced,
It can be seen that the stretchability is enhanced.

Further, in Comparative Example 3, the raw sheet having a small thickness was stretched without being subjected to rolling. However, in the first stretching, it was possible to stretch to the natural stretching ratio of 8 times, but in the second and subsequent times. In the stretching of, cutting was performed when the set stretching ratio was doubled. Therefore, when the second stretching was performed with the set stretch ratio set to 1.8 times, and then the third stretch was performed at the set stretch ratio of 1.5 times, only the actually measured stretch ratio of 1.38 times was obtained. I couldn't. Therefore, the total stretching ratio is also 19.8.
It was twice as low and the mechanical properties were not improved. Therefore, it is understood that high-magnification stretching is impossible unless rolling is performed before stretching.

[0058]

As described above, according to the method for producing a polyolefin sheet according to the present invention, high-magnification stretching can be performed by rolling and stretching a sheet containing polyolefin as a main component. Since the sheet is heat-treated before stretching, the sheet can be stretched at a higher magnification. In addition, as described above, since the rolling, stretching and heat treatment are performed, even a relatively thick sheet or film can be stably stretched at a high magnification.

Therefore, according to the present invention, it is possible to provide a polyolefin sheet which is excellent in strength and elastic modulus as compared with the conventional method because it can be stretched stably at a high magnification.

Claims (1)

[Claims] 1. A method for producing a polyolefin sheet, comprising: a step of rolling a sheet mainly containing polyolefin; a step of stretching the sheet; and a step of heat-treating the sheet before stretching.