JPH11207813A - Manufacture of polyolefin sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a mechanism strength and an elastic modulus by drawing to a high magnifying ratio by a simple process by a method wherein after adding an irregular pattern to a surface of a sheet having a polyolefin as a main component, the sheet is drawn. SOLUTION: After adding preliminarily an irregular pattern on the surface of a sheet having a polyolefin as a main component, the sheet is drawn. As the polyolefin, a high density polyethylene is especially appropriate, its density is preferably 0.94 g/cm<3> or higher, and its melt index is preferably 0.1 to 10 g/min. This polyethylene may be singly used, or one mixed with another polyolefin based resin at a ratio of 10 wt.% or under may be also used. Further, in the case where melt molding is executed by an extruding machine or the like, a melt temperature is preferably 130 deg.C or higher. Furthermore, as a transfer method for the irregular pattern, a uniform irregular pattern can be formed at a high transfer rate by a method of transferring the irregularity on the surface of a heated metallic roll. As the heating method for the sheet in drawing, a hot air heating is suitable.

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 sheet having enhanced mechanical strength and elastic modulus by stretching, and more particularly, to a method for producing a polyolefin sheet capable of further increasing mechanical strength and elastic modulus. About.

[0002]

2. Description of the Related Art Japanese Patent Application Laid-Open No. 5-230732 discloses a method for stretching a polyolefin sheet in which a plurality of stretching tanks having different temperatures are arranged in series, and the stretching ratio in each tank is controlled by the temperature. A multi-stage stretching method is disclosed.

In the multi-stage stretching method described in the above prior art, if the overall stretching ratio is determined by a feeding roll and a take-off roll, the stretching ratio in each stretching tank can be adjusted by temperature. There is no need to control. Further, since it is hard to be affected by the rotation unevenness of the driving roll, which causes the stretching unevenness, it is possible to enhance the stability in the multi-stage stretching.

However, in order to accurately control the temperature of each stretching tank, it is necessary to use a liquid as a medium, and it is necessary to store the liquid in each stretching tank and to allow the polyolefin sheet to pass through the liquid. In addition, the manufacturing process was very complicated.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the disadvantages of the prior art described above and to provide a simpler process.
It is an object of the present invention to provide a production method capable of obtaining a polyolefin sheet which has been stretched at a high magnification and thus has excellent mechanical strength and elastic modulus.

[0006]

The invention according to claim 1 is characterized in that an uneven pattern is provided on the surface of a sheet containing polyolefin as a main component, and then the polyolefin sheet is stretched.

According to a second aspect of the present invention, the step of providing the concavo-convex pattern is performed by pressing a metal roll against a surface of a sheet containing polyolefin as a main component.

[0008] The invention described in claim 3 is characterized in that the step of imparting the concavo-convex pattern is performed simultaneously with or after the rolling of the sheet mainly composed of polyolefin.

The invention according to a fourth aspect is characterized by further comprising a step of heating and compressing the obtained stretched sheet after stretching.

Hereinafter, the present invention will be described in detail. The polyolefin used in the present invention is not particularly limited. For example, homopolymers such as polyethylene, polypropylene, 1-butene and 1-pentene, and vinyl monomers such as vinyl acetate and vinyl alcohol , Vinyl chloride, acrylic acid, etc., preferably in a proportion of 10% by weight or less. Among them, high-density polyethylene is preferably used.

When high-density polyethylene is used, its density is preferably 0.94 g / cm ³ or more. If the density is too low, the mechanical strength and the elastic modulus may not be much improved even when the film is stretched.

When using high-density polyethylene,
Its melt index MI is 0.1 to 10 g / 10
Min, more preferably 1 to 7 g / 10 min. If the melt index is less than 0.1 g / 10 minutes, a load may be imposed on a molding machine such as an extruder.
If it exceeds 0 g / 10 minutes, molding may be difficult.

In the present invention, the above polyethylene may be used alone, and other polyolefin resins such as polypropylene, low-density polyethylene, ethylene-vinyl acetate copolymer, polyvinyl acetate, polyvinyl alcohol, etc. may be used in an amount of 10% by weight. You may use what was mixed with the polyolefin in the following ratios.

If necessary, a polyfunctional monomer such as triallyl isocyanurate, trimethylolpropane acrylate or diallyl phthalate may be added to the above polyethylene as a crosslinking aid, and benzophenone, thioxanthone, acetophenone, etc. May be added. Although the amount of these additives is not particularly limited, it is usually desirable that the amount be 1.0 to 2.0 parts by weight based on 100 parts by weight of polyethylene.

Hereinafter, a case where high-density polyethylene is used as the polyolefin will be specifically described. When high-density polyethylene is melt-molded with an extruder or the like, the melting temperature is 130 ° C. or higher, more preferably 140 ° C. or higher. When the melting temperature is lower than 130 ° C.,
Melting of the high-density polyethylene 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, causing discoloration or the like, or a decrease in mechanical strength accompanying a decrease in molecular weight may be caused. Therefore, the melting temperature is substantially 3
It is desirable that the temperature be not higher than 00 ° C.

The composition melted as described above is formed into a raw sheet, but the forming method is not particularly limited. That is, an appropriate molding method such as ordinary roll molding or calendar molding can be used.

The thickness of the raw sheet is not particularly limited, but is preferably 500 μm or less when rolling is not performed before the stretching step, and 4 mm or less when rolling is performed. desirable.

When the thickness of the raw sheet obtained as described above exceeds 500 μm, it is preferable to perform rolling before the stretching step. In this case, the rolling is performed in a usual manner, that is, the clearance between the 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. This is performed by reducing the thickness of the sheet and extending the sheet in the length direction.

If the temperature of the rolling roll at the time of rolling is too low, the rolling force becomes 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 the rolling cannot be expected, but also a burden is imposed on the subsequent stretching step. Conversely, if the rolling ratio is too large, the rolling force becomes large, 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 during the subsequent stretching step. is there. Therefore, the rolling ratio is preferably in the range of 2 to 10 times.

The rolling ratio in the present specification is defined by the following equation. Rolling ratio = thickness of raw sheet / thickness of raw sheet after rolling In the case of transferring a pattern to a polyethylene sheet before stretching, an uneven pattern may be transferred before the above-mentioned rolling. Since the uneven pattern may be slightly flattened, it is desirable to transfer the pattern preferably simultaneously with or after the rolling.

With respect to the method of transferring the uneven pattern onto the sheet, the unevenness of the heated metal roll is pressed against the sheet surface.
A method of transferring, a method of imparting unevenness by sand blasting or shot peening, a method of imparting unevenness by a roll press, and the like can be given.In particular, since a uniform uneven pattern is formed at a high transfer rate, it is heated. A method of transferring irregularities on the surface of a metal roll is preferably used. It is desirable that the concavo-convex pattern is formed uniformly on the sheet surface or is regularly dispersed.

When transferring a concavo-convex pattern to a sheet using a heated roll, the heating temperature of the roll is preferably in the range of 30 ° C. to the melting point of high-density polyethylene −5 ° C. When transferred at a temperature higher than the melting point of high-density polyethylene, the sheet may be melted and cut. Also, 3
When transferred at a temperature lower than 0 ° C., the rolling force increases,
In some cases, a burden is imposed on the molding machine and the pattern cannot be transferred uniformly.

Although the pattern can be transferred to one or both sides of the high-density polyethylene sheet, it is preferable to transfer the pattern to both sides, since stress concentration during stretching can be further reduced. Here, the pattern to be applied to the sheet is not particularly limited, and examples thereof include a twill pattern, a flat pattern, and a satin pattern. In particular, a satin pattern is suitably used.

Next, the raw sheet or the sheet rolled as described above is stretched. The stretching method is not particularly limited, and a usual roll stretching method, zone stretching method, or the like can be used.

In the present invention, a roll stretching method is preferably used because no special equipment is required, and since the stretching ratio can be easily controlled and the productivity is excellent.

The method of heating the sheet at the time of stretching is also not particularly limited, and hot air heating, hot water heating, infrared heating,
Microwave heating and the like can be used.
Since the apparatus is simple and temperature control is easy, hot air heating is preferably used.

Although the number of stretching is not particularly limited,
A multi-stage stretching method in which stretching at a low stretching ratio is performed a plurality of times is preferably used because stretching breakage does not occur. However, if the number of times of stretching is too large, the stability of stretching is increased and the stretching ratio is increased, but the size of the apparatus is increased.
Therefore, the number of stretching times is preferably 5 or less.

The stretching temperature is in the range of 50 ° C. or more and up to the melting point of the high-density polyethylene used, more preferably 6 ° C.
A temperature range of 0 ° C. or higher and the melting point of high-density polyethylene −10 ° C. is desirable.

In this specification, the melting point 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).

At a temperature higher than the melting point, the effect of improving the strength by stretching is not so much obtained, and the sheet may be stretch-cut. Further, the stretching ratio is desirably 5 times or more, more preferably 7 times or more. If the stretching ratio is less than 5 times, the strength and elastic modulus of the sheet may not be sufficiently increased.

[0032] The stretching ratio in the present specification is a value defined by the following equation. Stretching ratio = cross-sectional area of sheet before stretching / cross-sectional area of sheet after stretching Further, the sheet stretched by the above method may be compressed while heating. As a method of heat compression, a stretched sheet is inserted between heating rolls, a roll clearance is made smaller than the thickness of the sheet, and then the rolls are rotated in opposite directions, a stretched sheet is inserted between a pair of heated plates. Then, after making the interval between the pair of plates narrower than the thickness of the sheet, a method of pulling out the stretched sheet may be used. However, a method using a pair of heating rolls can be preferably used because the productivity is excellent and the sheet surface has less scratches.

The heating temperature at the time of heat compression is preferably at least 70 ° C. lower than the melting point of the polyolefin used and at most 5 ° C. higher than the melting point. When heated and compressed at a temperature lower than 70 ° C lower than the melting point,
The mechanical properties and transparency of the stretched sheet are not much improved,
Conversely, when heated and compressed at a temperature higher than the temperature of 5 ° C. higher than the melting point, the stretched sheet may be melted, and in the worst case, the stretched sheet is cut.

When high-density polyethylene is used, the heating and compression temperature is 60 to 1 depending on the resin grade.
It is desirable that the temperature be 40 ° C.

(Function) When a sheet containing polyolefin as a main component is stretched, partial stress concentration occurs due to unevenness in thickness of the sheet or adhesion of foreign matter, and necking occurs when the rolling ratio is increased. Breaks. On the other hand, in the invention according to the first aspect, since the stretching is performed after the surface of the sheet containing polyolefin as a main component is provided with a concavo-convex pattern in advance, it is possible to disperse the stress concentration points during the stretching by the concavities and convexities. Therefore, the draw ratio can be increased as compared with the conventional method, whereby the mechanical strength and the elastic modulus can be increased.

According to the second aspect of the present invention, since the above-mentioned uneven pattern is applied using a metal roll, it is difficult for scratches or the like to be generated on the sheet surface, and the uneven pattern can be easily applied uniformly to the sheet surface. it can.

According to the third aspect of the present invention, a rolling step is performed prior to the stretching, and a concavo-convex pattern is imparted simultaneously with or after the rolling step, so that a sheet stretched at a higher magnification can be obtained. In addition, the stress concentration points in the subsequent stretching can be more effectively dispersed, and the stretching ratio can be further increased.

According to the fourth aspect of the present invention, since the stretched sheet is heated and compressed, a sheet having a high density can be obtained while maintaining the weather resistance of the stretched sheet, and the mechanical strength is further improved. A polyolefin sheet can be obtained.

[0039]

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

Example 1 Weight average molecular weight 3.3 × 10
⁵ , a high-density polyethylene having a melt index (MI) of 1.0 g / 10 minutes and a melting point of 135 ° C. (manufactured by Nippon Polychem Co., Ltd.
Grade: HY540) was melt-kneaded at a resin temperature of about 200 ° C using a biaxial kneading extruder (product number: PCM30, manufactured by Ikegai Iron & Steel Co., Ltd.) and a calender molding machine controlling the roll temperature at 90 ° C. , Width 70mm x thickness 2.5m
m and wound up.

Thereafter, a hot roll heated to 120 ° C. (manufactured by Kodaira Seisakusho Co., Ltd., roll diameter: 65.12 cm) was rolled 9 times to obtain a rolled sheet having a thickness of about 300 μm and a width of 70 mm.

Thereafter, using a metal roll having a matte pattern formed on the surface and heated to 100 ° C., the metal roll is pressed against the front and back surfaces of the rolled sheet,
The satin pattern was transferred to the front and back surfaces of the rolled sheet. The metal roll has a surface roughness of R _max = 40.
μm was used.

Next, using a hot-air heating type two-stage stretching machine, the first stage stretching ratio was set to 1.8 times and the second stage stretching ratio was set to 2.0 times. The sheet was stretched to obtain the polyethylene sheet of Example 1.

Example 2 The polyethylene sheet obtained in Example 1 was further heated and compressed by a hot roll heated to 125 ° C. to obtain a polyethylene sheet of Example 2.

(Comparative Example 1) Using the rolled sheet of Example 1, without applying a satin pattern to the surface, using a hot-air heating type two-stage stretching machine, increasing the stretching ratio until just before the sheet breaks, and stretching. Thus, a high-density polyethylene sheet of Comparative Example 1 was obtained.

(Evaluation) For each of the polyethylene sheets obtained in Examples 1 and 2 and Comparative Example 1, the tensile strength, tensile modulus and surface properties were evaluated in the following manner.

Tensile strength and tensile modulus: Using a tensile tester (manufactured by Orientec, model name: Tensilon)
A tensile test was performed according to JIS K7113. In addition, the test piece was produced using the No. 2 dumbbell.

Surface properties: The surface of each of the obtained polyethylene sheets was visually observed, and a mark "場合" was given when the sheet was transparent, and a mark "△" was given when it was translucent. The results are shown in Table 1 below. The maximum stretching ratio in Table 1 is the product of the rolling ratio in the rolling step and the stretching ratio in the two-stage stretching.

[0049]

[Table 1]

As apparent from Table 1, the maximum stretch ratio of the polyethylene sheet obtained in Comparative Example 1 was 29.0 times, probably because the satin pattern was not applied. 37.6 GPa and 730M
Pa was low. On the other hand, in Examples 1 and 2, the maximum draw ratio could be increased to 35.4 times and 36.5 times, probably because of the addition of the satin pattern, so that a polyethylene sheet having a high tensile modulus and high tensile strength was obtained. It was possible.

[0051]

In the method for producing a polyolefin sheet according to the present invention, since the sheet is stretched after a concavo-convex pattern is formed on the sheet surface in advance, stress concentration points at the time of stretching are dispersed.
It is possible to stretch at a higher magnification than in the conventional method. Therefore, it is possible to provide a polyolefin sheet having higher mechanical strength and elastic modulus than the conventional method.

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Claims (4)

[Claims] 1. A method for producing a polyolefin sheet, comprising: imparting a concavo-convex pattern to the surface of a sheet containing polyolefin as a main component, and thereafter stretching the polyolefin sheet. 2. The method for producing a polyolefin sheet according to claim 1, wherein the step of providing the concavo-convex pattern is performed by pressing a metal roll against a surface of a sheet containing polyolefin as a main component. 3. The method according to claim 1, wherein the step of providing the concavo-convex pattern is performed simultaneously with or after rolling a sheet mainly composed of polyolefin.
3. The method for producing a polyolefin sheet according to item 1. 4. The method according to claim 1, further comprising a step of heating and compressing the obtained stretched sheet after stretching.
3. The method for producing a polyolefin sheet according to any one of 3.