JP2001293778A - Polyolefin sheet for draw molding and its production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyolefin sheet for draw molding which can be stretched in a high draw ratio to have high strength and a high modulus of elasticity and a method for producing the sheet. SOLUTION: The polyolefin sheet is made of a resin composition which contains a high density polyolefin as a main component and an α-olefin (co)polymer below 100,000 in weight average molecular weight and 40% or below in crystallinity as a subordinate component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a raw polyolefin sheet for stretch molding and a method for producing the same.

[0002]

2. Description of the Related Art As a method for imparting high strength and a high elastic modulus to a polyolefin molded article, a method of stretching orientation is known. Japanese Patent Publication No. 60-39542 discloses that after rolling a high-density polyolefin 1 to 7 times, it is stretched in the same direction as the rolling direction to 8 to 16 times the length of the raw material before rolling. Discloses a method for obtaining a sheet or tape having high strength and high elastic modulus. However, in the method disclosed in the above publication, for example, 2
When stretching at a high magnification of 0 times or more is performed, the sheet or tape is cut in the tensile stretching step, and there is a problem that high-magnification stretching cannot be performed.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polyolefin raw sheet for stretch molding which can be stretched at a high magnification, and has a high strength and a high elastic modulus, and a method for producing the same.

[0004]

According to the first aspect of the present invention,
High-density polyolefin as main component, weight average molecular weight 1
A polyolefin raw sheet for stretch molding, comprising a resin composition having an α-olefin (co) polymer having a crystallinity of 40% or less and having a crystallinity of 40% or less.

According to a second aspect of the present invention, there is provided the stretch-formed polyolefin raw sheet according to the first aspect, wherein the polyolefin is polyethylene.

According to a third aspect of the present invention, the α-olefin (co) polymer is an ethylene-propylene copolymer or an ethylene-1-butene copolymer. It is an anti-sheet.

<High-density polyolefin> The high-density polyolefin used in the present invention refers to a high-density polyolefin having a weight average molecular weight of 100,000 or more and a high density.
Polyethylene, polypropylene, poly-1-butene, poly-1-pentene, and the like can be mentioned, and in consideration of the elastic modulus after stretching, it is preferable to use polyethylene having a high theoretical elastic modulus. As such polyethylene, it is preferable to use a high-density polyethylene having a density of 0.94 g / cm ³ or more. When polyethylene having a density of less than 0.94 g / cm ³ is used, it is difficult to perform high-magnification stretch molding.

It is preferable to use polyethylene having a weight average molecular weight of 100,000 to 500,000.
If the weight average molecular weight is less than 100,000, the resin itself becomes brittle and the stretchability is impaired. If the weight-average molecular weight exceeds 500,000, not only is extrusion molding difficult, etc., but also the stretching molding step becomes a complicated step using a large amount of a plasticizer such as a solvent, which is not preferable.

When the above polyethylene is considered from the viewpoint of melt flow rate (hereinafter, MI), the range of 0.1 to 20 is preferable. In addition, the said MI is JIS K676.
It is an index indicating the melt viscosity of the thermoplastic resin defined as 0.

<Α-Olefin (co) polymer> The α-olefin (co) polymer used in the present invention includes ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene and 1-octene. Α-olefins such as -decene and 4-methyl-1-pentene alone or in combination of two or more
It is a (co) polymer obtained by polymerization. As a result, it may have the same chemical structure as described above. Examples of such a polymer include a polymer obtained by hydrogenating a part or all of the double bonds of a non-conjugated diene-based compound such as polybutadiene and polyisoprene.

The α-olefin (co) polymer has a weight average molecular weight of less than 100,000. When the weight average molecular weight is 100,000 or more, dispersibility in polyolefin becomes poor, and stretch moldability also becomes difficult.

The degree of crystallinity of the α-olefin (co) polymer is 40% or less. If the crystallinity exceeds 40%, the dispersibility in polyolefin becomes poor, and the stretch formability becomes difficult. By using such an α-olefin (co) polymer, stretch formability is improved, and a stretched sheet with a high draw ratio can be formed. The α-olefin (co) polymer may be used alone or in combination of two or more.

The stretch-formed polyolefin raw sheet of the present invention comprises a resin composition containing the high-density polyolefin as a main component and the α-olefin (co) polymer as an auxiliary component. The amount of the α-olefin (co) polymer is preferably 0.1 to 50 parts by weight, more preferably 0.5 to 20 parts by weight, based on 100 parts by weight of the high-density polyolefin. If the amount of the α-olefin (co) polymer is less than 0.1 part by weight, it is difficult to obtain a stretching effect, and if it exceeds 50 parts by weight, it becomes difficult to obtain a high-strength sheet even after stretching.

The polyolefin raw sheet for stretch molding of the present invention may contain, if necessary, other crystal nucleating agents, crosslinking agents, crosslinking aids, lubricants, fillers, pigments, low molecular weight polyolefin waxes and the like. good.

The above-mentioned nucleating agent is added for the purpose of improving the crystallinity, and examples thereof include calcium carbonate and titanium oxide.

The cross-linking agent and the cross-linking auxiliary are added for the purpose of partially cross-linking the molecular chains of the polyolefin resin and improving the heat resistance, creep performance and the like of the stretched polyolefin resin sheet obtained from the raw sheet. The crosslinking agent includes, for example, photopolymerization initiators such as benzophenone, thioxanthone and acetophenone. Examples of the crosslinking assistant include polyfunctional monomers such as triallyl cyanurate, triallyl isocyanurate, trimethylolpropane triacrylate, and diallyl phthalate.

<Production Method of Raw Sheet> The invention according to claim 4 is an α-olefin (co) polymer having a high-density polyolefin as a main component, a weight average molecular weight of less than 100,000 and a crystallinity of 40% or less. A method for producing a stretch-formed raw polyolefin sheet, comprising extruding a resin composition containing a coalesced component as a subcomponent in a molten state into a sheet. In the invention according to claim 5, the raw sheet obtained by the above method is further subjected to Tm and a temperature (Tm) 20 ° C. lower than Tm.
The method for producing a stretch-formed polyolefin raw sheet according to claim 4, further comprising a step of holding the sheet for a predetermined time in a temperature range between -20 ° C).

When the resin composition comprising the polyethylene and the α-olefin (co) polymer is extruded into a sheet in a molten state, the molding temperature is 130 ° C. or higher, more preferably 150 ° C. or higher. . When the extrusion molding temperature is lower than 130 ° C., the melting of the resin composition becomes incomplete, and a load is imposed on a molding machine such as an extruder. The high temperature side is not particularly limited, but if the molding temperature is too high, the polyolefin may be decomposed, causing discoloration or the like, or a decrease in strength due to a decrease in molecular weight. Therefore, it is preferable that the melting temperature is substantially 250 ° C. or less.

The composition melted by the above-mentioned method is formed into a raw sheet by extrusion. The extruded sheet is subjected to a melting point (Tm) of the high-density polyolefin and a temperature 20 ° C. lower than the Tm. It is preferable to add a step of holding the sheet for a certain period of time in the above temperature range, since the effect of the subsequent stretch formability is further improved. At a temperature higher than Tm, the molded state cannot be maintained, and
If the temperature is lower than 0 ° C. lower than the temperature (Tm−20 ° C.), the effect of the stretch formability of the present invention is hardly exhibited.

After extrusion of the sheet,
The thickness can be adjusted to a desired value by using a usual roll forming method, calendar forming method, or the like. The thickness of the raw sheet is preferably in the range of 2 to 15 mm. 2mm
If it is less than 15 mm, the thickness of the stretch-formed sheet obtained by the subsequent stretching treatment may be too small,
If the ratio exceeds the above, the stretch molding itself may become difficult.

Further, the raw polyethylene sheet subjected to the heat treatment may be stored and stored before moving to the stretching step. For example, after the heat treatment, the raw polyethylene sheet may be moved to the stretching step. Alternatively, the film may be stored at room temperature and then moved to a stretching step.

<Method of Stretching Raw Sheet> Since the above-mentioned raw sheet is relatively thick, it is preferable to perform a rolling treatment before stretching. The rolling process, for example, a clearance narrower than the thickness of the raw sheet, between a pair of rolling rolls rotated in opposite directions, insert the raw sheet, reducing the thickness of the sheet, This can be done by stretching in the length direction.

The raw sheet temperature in the rolling step is 70
To 120 ° C., more preferably 90 to 120 ° C.
° C. When the sheet temperature is lower than 70 ° C., a large rolling force is required between the rolling rolls, and uniform rolling may be difficult due to distortion of the rolling rolls. 120 ° C
Is exceeded, the sheet may be cut during rolling.

The roll ratio of the raw sheet obtained in the present invention is preferably 2 to 20 times. When the rolling ratio is less than 2 times, not only the rolling effect cannot be obtained, but also a burden is imposed on the subsequent stretching step. On the other hand, when the rolling ratio exceeds 20 times, the rolling force between the rolling rolls increases, and uniform rolling becomes difficult.
The rolling ratio is defined by the following equation. (Rolling ratio) = (Cross-sectional area of raw sheet) / (Cross-sectional area after rolling of raw sheet) The method of stretching the rolled sheet is not particularly limited, and a normal roll stretching method, zone stretching method, or the like. Can be used.

As a stretching method, for example, a uniaxial stretching method in which an original sheet is sandwiched between two pairs of pinch rolls having different speeds and pulled is preferable. When stretching is performed at a high stretching ratio, a multi-stage stretching method in which the above operation is repeated a plurality of times is preferable.

Various methods such as hot air heating, hot water heating, infrared heating, and microwave heating can be used for heating the sheet during stretching. In particular, the apparatus is simple and the temperature control is easy. Hot air heating is preferred in that respect.

The sheet temperature during the above stretching is 70
~ 130 ° C is preferred. If the temperature is out of the above temperature range of 70 ° C., the stretch tends to break.

[0028]

(Example 1) Weight average molecular weight 33
Ethylene-propylene copolymer having a weight average molecular weight of 50,000 and a crystallinity of 5% with respect to 100 parts by weight of high density polyethylene (trade name "HY540", manufactured by Nippon Polychem Co., Ltd.) having a melting point of MI = 1.0 and a melting point of 135 ° C. A resin composition obtained by mixing 1.0 part by weight of the coalesced mixture is coaxially twin-screw kneading extruder (Ikegai Iron & Steel Co., Ltd.)
And PCM30), melt-knead at a resin temperature of about 200 ° C., form a sheet having a width of 70 mm and a thickness of 2.5 mm using a calendering machine controlled at a roll temperature of 90 ° C., and wind the sheet. It rolled 10 times using a hot roll (made by Kodaira Seisakusho Co., Ltd., roll diameter 6 inches) heated to ° C.

Next, at a stretching temperature of 100 ° C., the stretching ratio of the first stage is increased by 2.0 times using a hot air heating type two-stage stretching machine.
The second stage stretching ratio was 1.7 times, and a stretched polyethylene sheet having a total stretching ratio of 32 times was obtained. Here, the total stretching ratio means the maximum stretching ratio that enables stable molding.

Example 2 In Example 1, a weight average molecular weight of 50,000 was used instead of the ethylene-propylene copolymer.
Molding was performed in the same manner as in Example 1 except that an ethylene-1-butene copolymer having a crystallinity of 15% was used, to obtain a stretched polyethylene sheet having a total stretch ratio of 32.

Example 3 In Example 1, the resin composition in the molten state was formed into a sheet by a calendering machine, and then the sheet was heated in a hot-air heating type thermostat controlled at 125 ° C. Molding was performed in the same manner except that the heat treatment was performed for 10 minutes to obtain a stretched polyethylene sheet having a total stretch ratio of 34 times. The heat treatment temperature is a temperature lower by 10 ° C. than the melting point of the high-density polyethylene used in Example 1.

(Comparative Example) A molded article was produced in the same manner as in Example 1 except that only high-density polyethylene was used, to obtain a stretched polyethylene sheet having a total stretch ratio of 26 times.

(Tensile strength test) The sheets obtained in the above Examples and Comparative Examples were subjected to JIS K711 using a tensile tester (trade name “Tensilon” manufactured by Orientec).
According to No. 3, a tensile test was performed. The results are shown in Table 1.

[0034]

[Table 1]

[0035]

As described above, a resin composition containing a high-density polyolefin as a main component, an α-olefin (co) polymer having a weight average molecular weight of less than 100,000 and a crystallinity of 40% or less as an auxiliary component. By using a stretch-formed polyolefin raw sheet made of a product, a polyolefin sheet drawn at a high magnification can be easily formed while exhibiting physical strength such as high strength and high elastic modulus.

Claims (5)

[Claims] 1. A stretch molding comprising a resin composition containing a high-density polyolefin as a main component and an α-olefin (co) polymer having a weight average molecular weight of less than 100,000 and a crystallinity of 40% or less as an auxiliary component. Polyolefin fabric sheet. 2. The stretch-formed polyolefin raw sheet according to claim 1, wherein the polyolefin is polyethylene. 3. The stretch-formed polyolefin raw sheet according to claim 2, wherein the α-olefin (co) polymer is an ethylene-propylene copolymer or an ethylene-1-butene copolymer. 4. A resin composition containing a high-density polyolefin as a main component, an α-olefin (co) polymer having a weight average molecular weight of less than 100,000 and a crystallinity of 40% or less as an auxiliary component, in a molten state. A method for producing a stretch-formed polyolefin raw sheet, which is extruded into a sheet. 5. The sheet-like material extruded into the above-mentioned sheet-like material is subjected to a melting point (T
m) and a step of holding the sheet for a certain time in a temperature range of 20 ° C. lower than Tm (Tm−20 ° C.).
A method for producing a stretch-formed polyolefin raw sheet according to claim 4.