JP2000117828A - Manufacture of stretched polyethylene sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the easy manufacturing method of a stretched polyethylene sheet by a method wherein a so-called general purpose polyethylene having a weight average molecular weight of 500,000 or less is super-stretch-formed at least 30 times. SOLUTION: A polyethylene sheet, which is produced by melting, kneading and forming a composition containing a high density polyethylene having its weight average molecular weight of 500,000 or less, a hydrogen withdrawal type photopolymerization initiator, a self-cleavage type photopolymerization initiator and a polymerizable monomer, is primarily stretched 10 times or more. After that, the polymerizable monomer in the polyethylene molded body is polymerized by being irradiated with ultraviolet rays. Further, the resultant polyethylene sheet is secondarily stretched 30 times or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a compound having a weight average molecular weight of 5
The present invention relates to a method for producing a stretched polyethylene sheet using a high-density polyethylene having a molecular weight of not more than 10,000.

[0002]

2. Description of the Related Art Generally, stretching a polyethylene molded article at a high magnification of 10 times or more is called super-stretch molding. Conventionally, as described in, for example, Japanese Patent Publication No. Hei 7-53423, there is known a method for producing a stretched polyethylene sheet by super-stretch-molding an ultra-high-molecular-weight polyethylene molded article having a large molecular weight.

[0003]

However, so-called general-purpose polyethylene molded articles having a weight-average molecular weight of 500,000 or less are:
Because of its low molecular weight, it was difficult to perform high-magnification stretch-molding, especially stretch-molding with a stretch ratio of 30 or more.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to solve these problems and provide a so-called general-purpose polyethylene having a weight average molecular weight of 500,000 or less. It is an object of the present invention to provide a method that can easily produce a stretched polyethylene sheet by performing super-stretch molding to 30 times or more.

[0005]

According to the first aspect of the present invention, there is provided a method for producing a stretched polyethylene sheet, comprising: a high-density polyethylene having a weight-average molecular weight of 500,000 or less; a hydrogen abstraction type photopolymerization initiator; Sheet obtained by melt-kneading and molding a composition containing an agent and a polymerizable monomer.
Primary uniaxial stretching to 0 times or more, then polymerize the polymerizable monomer in the polyethylene molded article by ultraviolet irradiation,
Further, the film is characterized in that the film is stretched to a total stretching ratio of 30 times or more by secondary uniaxial stretching.

According to a second aspect of the present invention, there is provided a method for producing a stretched polyethylene sheet according to the first aspect, wherein the glass transition temperature of the polymerizable monomer after polymerization is 100 ° C. or higher. It is characterized by the following.

In the present invention, a high-density polyethylene having a weight average molecular weight of 500,000 or less is used. Since high-density polyethylene has high crystallinity and exhibits high rigidity after stretching, it can be used in the present invention. It is difficult for polypropylene to exhibit high rigidity after stretching. Further, low-density polyethylene cannot be used because of insufficient rigidity.

[0008] As high-density polyethylene, the density is 0.
It is preferably 94 g / cm ³ or more. 0.94 density
If the thickness is less than g / cm ³ , it is difficult to expect an increase in strength and elastic modulus even after stretching, and the mechanical properties after stretching are inferior.

In the present invention, polyethylene having a weight average molecular weight of 500,000 or less is used. Those having a weight average molecular weight of 500,000 or more, and polyethylene having a weight average molecular weight of 1,000,000 or more can be stretched at a high magnification and exhibit high rigidity,
These ultrahigh molecular weight polyethylenes are not preferable because extrusion molding is not easy and a plasticizer such as a solvent may be required for stretching, which complicates the process.

In the present invention, the melt index (MI) is from 0.1 to 20, more preferably from 1 to 20.
Preferably, ten are used. When the melt index is less than 0.1, a burden is imposed on a molding device such as an extruder, and when the melt index exceeds 20, stretching molding may be difficult.

In the present invention, high-density polyethylene may be used alone, or a mixture of another polyolefin resin or a resin such as polystyrene which is easily compatible with polyethylene may be used.

In the present invention, a hydrogen abstraction type photopolymerization initiator and a self-cleaving type photopolymerization initiator are used in combination.

In the present invention, the hydrogen abstraction type photopolymerization initiator is in an excited state when exposed to light, for example, forms an excited transition state with a compound having hydrogen, such as polyethylene, and further extracts and extracts hydrogen. It is a photopolymerization initiator capable of creating a radical polymerization initiation point in polyethylene.

In the present invention, the self-cleavable photopolymerization initiator is in an excited state when exposed to light,
It is a photopolymerization initiator that generates a radical polymerization initiation point by causing cleavage, and is considered to be difficult to react with polyethylene.

The former, that is, the role of the hydrogen abstraction type photopolymerization initiator, is to abstract the hydrogen of the main chain of the polyethylene and create a reaction point in the polyethylene. That is, it enables the graft reaction. As the addition amount of the hydrogen abstraction type photopolymerization initiator, which will be described later, if the addition amount is excessive, in addition to the graft reaction, there is a possibility that the crosslinking reaction of polyethylene may be accelerated, and it is necessary to pay attention to the addition amount .

The latter, ie, the role of the self-cleaving photopolymerization initiator, is to polymerize the added polymerizable monomer. As described above, the hydrogen abstraction type photopolymerization initiator cannot be used in a large amount. Therefore, in order to completely polymerize the added polymerizable monomer, it is necessary to add the self-cleavable photopolymerization initiator. Incidentally, this self-cleavable photopolymerization initiator is difficult to react with polyethylene, and even when added in large amounts,
There is no risk of cross-linking the polyethylene.

In the present invention, it is possible to efficiently graft polymerize a polymerizable monomer to polyethylene by using these two photopolymerization initiators in combination.

As the polymerizable monomer used in the present invention, any monomer which can be polymerized and polymerized by a radical generated by a photopolymerization initiator as described above can be used, but the glass transition temperature after polymerization is 0. C. or higher, more preferably 100.degree. C. or higher can be suitably used. This is because these monomers have an effect of increasing the cohesive strength of polyethylene at the stretching temperature of polyethylene when polymerized into polyethylene. That is, the effect of artificially increasing the molecular weight of polyethylene is recognized.

In the present invention, the photopolymerization initiator includes:
Diethoxyacetophenone, benzoisobutyl ether, benzyldimethyl ketal, and the like can be used. As the self-cleavable photopolymerization initiator, benzophenone, Michler's ketone, isobutylthioxanthone, 2-ethylanthraquinone, and the like can be used.

In the present invention, the polymerizable monomers include triallyl isocyanurate, triallyl cyanurate, diallyl phthalate, and the like in consideration of the glass transition temperature after the above polymerization and the compatibility with polyethylene. Isobornyl methacrylate and the like can be used.

The mixing ratio of the self-cleaving photopolymerization initiator to polyethylene is preferably about 0.1 to 2 parts by weight based on 100 parts by weight of polyethylene. If the self-cleaving type photopolymerization initiator is less than 0.1, it may be difficult to polymerize the polymerizable monomer, and if it exceeds 2 parts by weight, no further effect can be obtained.

The proportion of the hydrogen-pulling photopolymerization initiator to polyethylene is preferably about 0.01 to 0.5 part by weight based on 100 parts by weight of polyethylene. Hydrogen abstraction type photopolymerization initiator is 0.0
If the amount is less than 1 part by weight, it may be difficult to cause a graft polymerization reaction between the polymerizable monomer and the polyethylene. Conversely, if the amount exceeds 0.5 part by weight, the crosslinking reaction of the polyethylene is likely to occur, and the subsequent stretch molding. May be difficult.

The amount of the polymerizable monomer is preferably about 1 to 5 parts by weight. If the amount of the polymerizable monomer is less than 1 part by weight, the modifying effect may not be sufficiently obtained.
There is a possibility that the effect cannot be expected any more.

When a composition containing high-density polyethylene, a hydrogen-pulling photopolymerization initiator, a self-cleaving photopolymerization initiator, and a polymerizable monomer is melt-kneaded and molded, the melting temperature is 130 ° C.
The above is more preferable, and the temperature is 150 ° C or more and 250 ° C or less. When the melting temperature is lower than 130 ° C., the melting of the high-density polyethylene may be incomplete, and a load is imposed on a molding machine such as an extruder. On the other hand, when the temperature exceeds 250 ° C., the polyethylene may be decomposed, causing discoloration or the like, or a decrease in strength due to a decrease in molecular weight may be caused.

The means for forming the polyethylene sheet is not particularly limited, and for example, a usual roll forming method, a calender forming method and the like can be adopted. The thickness of the polyethylene sheet is 2 to 5 mm
Is preferably within the range. If it is less than 2 mm, the thickness of the sheet after stretching becomes too small, and if it exceeds 5 mm,
Subsequent molding may be difficult.

In some cases, it is preferable to reduce the thickness of the polyethylene sheet by performing a rolling treatment prior to the first stretching. Rolling process, the gap between the pair of rolling rollers rotating in opposite directions is smaller than the thickness of the polyethylene sheet, inserting the polyethylene sheet between the rolling rolls,
This is to reduce the thickness of the polyethylene sheet and extend it in the length direction.

The temperature of the polyethylene sheet in this rolling step is about 70 to 125 ° C., preferably 90 to 120 ° C.
If the temperature is lower than 70 ° C., uniform rolling becomes difficult. If the temperature exceeds 125 ° C., the polyethylene sheet may be melted and cut during rolling.

If the rolling ratio in this rolling step is too small, not only the effect of rolling cannot be expected, but also a burden is imposed on the subsequent stretching step. On the other hand, if the rolling ratio is too large, not only uniform rolling becomes difficult, but also the thickness of the rolled polyethylene sheet becomes too small, and the polyethylene sheet may be cut during the subsequent primary stretching step. Therefore,
The rolling ratio is preferably about 2 to 10 times. The rolling ratio is represented by the following equation. Rolling ratio = thickness of sheet before rolling / thickness of sheet after rolling

The primary uniaxial stretching of the polyethylene sheet may be performed by a method in which the polyethylene sheet is sandwiched between two pairs of pinch rolls having different rotation speeds and is stretched in a uniaxial direction by stretching the polyethylene sheet in a heated state. .

In the case where the polyethylene sheet is rolled before the first stretching, the product of the rolling ratio and the stretching ratio of the first stretching is the first total uniaxial stretching ratio, and the first uniaxial stretching ratio is 10 times or more, preferably 15 times or more and 20 to 30 times or less. When the primary uniaxial stretching ratio is less than 10 times, it is difficult to finally perform the secondary stretching at a high magnification of 30 times or more. Conversely, if it exceeds 30 times, cracks are likely to occur and the whole is whitened, and stable stretching becomes difficult.

The temperature of the polyethylene sheet during stretching is 70
~ 120 ° C, preferably less than 70 ° C or 120 ° C
When it exceeds, stretching breakage is likely to occur.

In order to polymerize the polymerizable monomer with ultraviolet rays, it is desirable to use a high-pressure mercury lamp that can perform polymerization in a short time. The irradiation amount of the ultraviolet light is a peak illuminance of 30 m.
It is preferable to polymerize in a short time at an intensity of w / cm ² or more and a light amount of 50 mj / cm ² or more. If the polymerization takes a long time, there is a possibility that a phenomenon of separation from polyethylene may occur due to polymerization of the polymerizable monomer.

In order to further stretch the polyethylene sheet obtained by polymerizing the polymerizable monomer in the second stretching to a total stretching ratio of 30 times or more, similarly to the above-described first uniaxial stretching, the rotation speed is different. A method in which the polyethylene sheet is stretched in only one axial direction by being pulled between two pairs of pinch rolls while the polyethylene sheet is heated is sufficient.

The total stretching ratio of the first stretching and the second stretching is 30 times or more, preferably 40 times or more. The temperature of the polyethylene sheet for the second stretching is 70 to
The temperature is preferably set to 120 ° C. If the temperature is out of the range, stretching may be broken.

In the method for producing a stretched polyethylene sheet according to the first aspect of the present invention, a high-density polyethylene having a weight-average molecular weight of 500,000 or less, a hydrogen-pulling photopolymerization initiator, a self-cleaving photopolymerization initiator, A polyethylene sheet formed by melt-kneading a composition containing a polymerizable monomer
Since the primary uniaxial stretching is performed 0 times or more, and then the polymerizable monomer in the polyethylene molded body is polymerized by irradiating ultraviolet rays, the polyethylene is graft-modified and the cohesive force of the molecules is increased. Therefore, the film can be further stretched to a total stretch ratio of 30 times or more by the second uniaxial stretching.

In the method for producing a stretched polyethylene sheet according to the present invention, since the glass transition temperature of the polymerizable monomer after polymerization is 100 ° C. or higher, the glass transition temperature of ordinary polyethylene (about −100) is obtained. C), the cohesive force of the molecules is increased, and the second uniaxial stretching enables stretching to a total stretching ratio of 30 times or more.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Example 1 Weight average molecular weight
3 × 10 ^5, a melt index (MI) 1.0, high density polyethylene having a melting point of 135 ° C. (manufactured by Japan Polychem Corporation, grade: HY540) relative to 100 parts by weight of benzophenone as a hydrogen abstraction-type photopolymerization initiator (Nippon of 0.1 part by weight of a pharmaceutical company), 1 part by weight of benzyl dimethyl ketal (Irgacure 651 manufactured by Ciba Geigy) as a self-cleavable photopolymerization initiator, and triallyl isocyanurate (a product of Wako Pure Chemical Industries) 2 as a polymerizable monomer Parts by weight, and the same direction twin screw kneading extruder (trade name “P
CM30 "), melt-kneaded at a temperature of 200 ° C, formed into a 70 mm wide and 2.5 mm thick sheet by a calendering machine controlled at a roll temperature of 90 ° C, wound, and then heated to 120 ° C. Using a hot roll (made by Komatsu Ltd., roll diameter 6 inches), it was rolled 10 times.

Next, using a hot air heating type two-stage stretching machine,
The first stage stretching ratio is 1.0 times, and the second stage stretching ratio is 1.
The primary stretching operation was performed three times, and the total stretching ratio was 2.3 times. The stretching temperature was 100 ° C.

The stretching ratio of the rolling and the primary stretching was about 25 times, and the dimensions of the polyethylene sheet after the primary stretching were 35 mm in width and 200 μm in thickness and had a smooth surface. Furthermore, this polyethylene sheet is output at 120 W /
The polymerizable monomer contained therein was polymerized by passing under a 6 cm ² high pressure mercury lamp at a speed of 10 m / min. Then
Using a hot air heating type single-stage stretching machine, the polyethylene sheet was stretched to a stretching ratio of 1.4 times, and the secondary stretching operation at a total stretching ratio of 35 times was completed. The secondary stretching temperature is 110
° C. The dimensions of the polyethylene sheet after the second stretching were 30 mm in width and 150 μm in thickness.

The final stretching ratio was the highest ratio at which the secondary stretching ratio operation could be performed stably. Here, "stable" was determined to be stable when a stretching operation could be performed without causing stretching breakage for one hour.

Example 2 A sample was prepared in the same manner as in Example 1 except that the polymerizable monomer to be added was diallyl phthalate (a product of Wako Pure Chemical Industries, Ltd.).

Example 3 A sample was prepared in the same manner as in Example 1 except that the polymerizable monomer to be added was isobonyl phthalate (a product of Wako Pure Chemical Industries, Ltd.).

Comparative Example 1 A sample was prepared in the same manner as in Example 1 except that only polyethylene was used.

Comparative Example 2 A sample was prepared in the same manner as in Example 1 except that benzophenone as a hydrogen abstraction polymerization initiator was not added.

Comparative Example 3 The amount of benzophenone was 1 without adding Irgacure, a self-cleaving polymerization initiator.
A sample was prepared in the same manner as in Example 1 except that the amount was changed to parts by weight. A pull was prepared.

[Evaluation] With respect to the samples obtained in Examples 1 to 3 and Comparative Examples 1 to 3, the draw ratio and the tensile modulus (GP
Table 1 shows the results of measurement of a) and tensile strength (MPa). The stretching ratio is determined by measuring the width and thickness of the polyethylene sheet before the first stretching, calculating the cross-sectional area,
The width and thickness of the polyethylene sheet after the next stretching were measured, the sectional area was calculated, and the value obtained by dividing the initial sectional area by the subsequent sectional area was defined as the stretching ratio. The width and thickness of the polyethylene sheet were measured 10 times continuously at intervals of 20 cm from the sample.
The average value was used as the draw ratio of the sample.

The tensile strength and the tensile modulus are measured according to JIS K71.
The tensile properties of the samples were evaluated according to the tensile test method No. 13.

[0048]

[Table 1]

As shown in Table 1, the draw ratios of the samples of Examples 1 to 3 were 32 times or more, and the tensile elastic modulus was 4 times.
2 GPa or more, while the tensile strength is 810 MPa or more, the stretching ratio of the sample according to Comparative Examples 1 to 3 is 29 or less, the tensile modulus is 35 GPa or less,
The tensile strength was 810 MPa or less, and the samples according to Examples 1 to 3 were superior to the samples according to Comparative Examples 1 to 3 in all of the draw ratio, the tensile modulus, and the tensile strength.

The embodiment of the present invention has been described with reference to the drawings. However, the specific embodiment of the present invention is not limited to the illustrated embodiment, and is not limited to the scope of the present invention. Design changes are included in the present invention.

[0051]

According to the method for producing a stretched polyethylene sheet of the present invention as described in claim 1, since polyethylene is graft-modified and the cohesive force of the molecules is increased, the total stretching ratio can be increased by secondary uniaxial stretching. It is possible to stretch easily twice or more.

In the method for producing a stretched polyethylene sheet according to the present invention, the glass transition temperature (about -100 ° C.) of ordinary polyethylene is greatly increased, and the cohesive force of molecules is increased. Uniaxial stretching enables stretching to a total stretching ratio of 30 times or more.

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Claims (2)

[Claims] 1. A polyethylene sheet obtained by melt-kneading and molding a composition containing a high-density polyethylene having a weight-average molecular weight of 500,000 or less, a hydrogen-drawing photopolymerization initiator, a self-cleaving photopolymerization initiator, and a polymerizable monomer. Primary uniaxial stretching at least twice, then polymerizing the polymerizable monomer in the polyethylene molded article by irradiating ultraviolet rays, and further stretching at a total stretching ratio of 30 times or more by secondary uniaxial stretching. Method for producing a stretched polyethylene sheet. 2. The method according to claim 1, wherein the glass transition temperature of the polymerizable monomer after polymerization is 100 ° C. or higher.