JPH07149972A - Crosslinked polyolefin resin and film made thereof - Google Patents

Abstract

PURPOSE:To provide the resin excellent in all of elongation, strengths, deformation recovery, flexibility, spreadability and heat resistance and to provide the film. CONSTITUTION:The resin is prepared by giving a crosslinkage structure to a polyolefin resin comprising a polypropylene resin formed in the first stage polymerization in a multi-stage polymerization and at least one member selected from the group consisting of combinations of a copolymer of propylene with ethylene and/or at least one alpha-olefin with an ethylene homopolymer or a copolymer of ethylene with an alpha-olefin both of which are formed in the second or latter stage of polymerization.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crosslinked polyolefin resin obtained by imparting a crosslinked structure to a specific polyolefin resin and a film produced using the same, and more specifically to strength, elongation and deformation recovery. Excellent and
It has flexibility, extensibility and heat resistance, and is suitable for stretch packaging film, surface protection film, grass stretch film, agricultural stretch film, heat shrink film, adhesive plaster film, shrink film, and plasticized PVC substitute film. Also relates to cross-linked polyolefin resin and film that can be widely used.

[0002]

2. Description of the Related Art In order to modify the properties of a polyolefin resin represented by polypropylene, a method of incorporating an elastomer has been adopted. In particular, in order to improve the flexibility of the polyolefin resin, a method of increasing the proportion of the elastomer component, a method of increasing the molecular weight of the elastomer component, and the like have been tried. However, in these methods, the cost is high in the case of a mechanical mixing method using an extruder or the like, and dispersion failure occurs due to aggregation of the elastomer component. Therefore, in the method of adding the elastomer component to the polyolefin-based resin as described above, since the ratio and the molecular weight of the elastomer component are limited, one of the physical properties such as flexibility or deformation recovery required for the film application is generated. The current situation is that the results are insufficient and no satisfactory results have been obtained.

On the other hand, plasticized vinyl chloride (hereinafter referred to as plasticized PVC) is widely used for the above film applications. However, since plasticized PVC contains a large amount of plasticizer, the plasticizer migrates to the surface of the film and has a drawback that it adversely affects the physical properties. Also, from the viewpoint of environmental problems, the pros and cons of using plasticized PVC containing chlorine have been discussed in various fields in recent years.

For this reason, recently, a flexible and stretchable polyolefin resin has been actively developed as a material to replace plasticized PVC. Such polyolefin resins include polyethylene and ethylene-
Examples of the film include vinyl acetate copolymer and polybutadiene. However, in a film using such a polyolefin-based resin, the physical properties such as flexibility and deformation recovery are not sufficient, and the packaged film is easily peeled off or wrinkles occur in the film,
Often not suitable for actual use.

Further, Japanese Patent Application Laid-Open No. 61-44635 discloses a linear polyethylene copolymerized with various α-olefins, and Japanese Patent Application Laid-Open No. 62-51440 discloses a styrene-containing conjugate. Elastomers composed of dienes are disclosed. However, since the copolymer and elastomer have insufficient heat resistance and stretchability,
It was necessary to stack other resins for use.

Further, in JP-A-1-247441, in order to satisfy heat resistance, stretchability and strength,
Disclosed is a method for obtaining a thermoplastic elastomer composition by crosslinking polypropylene and an ethylene-α-olefin-based copolymer rubber in the presence of a crosslinking aid. The thermoplastic elastomer composition obtained by this method has improved strength and elasticity, and is said to be usable for automobile parts such as bumpers. However, in this method, when polypropylene and an ethylene-α-olefin copolymer rubber are mixed, poor dispersion of the copolymer rubber component is likely to occur. In order to maintain good dispersibility, when polypropylene and copolymer rubber having a low molecular weight are used,
The flexibility and the elongation of the resulting thermoplastic elastomer composition were insufficient, and this thermoplastic elastomer composition could not be molded by any method other than injection molding.

Further, Japanese Patent Publication No. 59-172172 discloses a film made of a composition obtained by mixing an ethylene copolymer, crystalline polypropylene and the like with a specific ethylene-α-olefin and subjecting the mixture to a crosslinking treatment. Has been done. However, even in this method, the above-mentioned problem of poor dispersion of the elastomer component is likely to occur, and the heat resistance and flexibility of the obtained film are insufficient.

[0008]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and its object is excellent in elongation, strength and deformation recovery, and flexibility and extensibility. Another object is to provide a crosslinked polyolefin resin having heat resistance and a film using the crosslinked polyolefin resin.

[0009]

The cross-linked polyolefin resin of the present invention is obtained by polymerization in two or more steps.
Polypropylene resin produced in the step polymerization,
At least one selected from the group consisting of a combination of polymer moieties of the following (b-1) and (b-2) produced in the polymerization of two or more steps, and a polyolefin resin composed of a cross-linked structure Is given, and thereby the above object is achieved.

(B-1) Copolymer of propylene and ethylene and / or at least one α-olefin; (b-2) ethylene homopolymer, or ethylene and α
-Copolymers with olefins.

The film of the present invention comprises the above polyolefin resin cross-linked product, and thereby achieves the above object.

(Polyolefin Resin) The polyolefin resin used in the present invention includes a polypropylene resin as the component (A), (b-1) propylene as the component (B), ethylene and / or at least one kind of resin. α
-A copolymer with an olefin; and (b-2) at least one member selected from the group consisting of a combination of polymer moieties of an ethylene homopolymer or a copolymer of ethylene and an α-olefin. To be done.

The component (A) may be either homopolypropylene or random polypropylene,
Further, it may be a copolymer of propylene and an α-olefin other than the propylene. Here, as the α-olefin, ethylene, 1-butene, 1-hexene, 4
-Methyl-1-pentene and the like can be mentioned.

Examples of the above-mentioned (b-1) include binary copolymers such as propylene / ethylene, propylene / 1-butene, propylene / 4-methyl-1-pentene, or propylene / ethylene / 1-butene, propylene / Examples thereof include terpolymers such as 1-butene / 4-methyl-1-pentene.

Examples of the above-mentioned (b-2) include ethylene homopolymers, copolymers of ethylene with α-olefins other than ethylene and propylene, and specifically ethylene / 1-butene, ethylene / 1-hexene, ethylene / 4-methyl-1-pentene and the like can be mentioned.

The above polyolefin resin has a ratio of the eluted components at 90 ° C. or higher of 5 measured by the cross fractionation method.
It is preferably in the range of ˜50% by weight. Elution component is 5
If it is less than 50% by weight, sufficient strength may not be obtained even if a cross-linking structure to be described later is added to the polyolefin resin, and if it exceeds 50% by weight, sufficient flexibility may not be obtained. Particularly, the proportion of the eluted components at 90 ° C. or higher measured by the preferred cross fractionation method is 5 to 40% by weight.

The cross fractionation method here means to measure the composition distribution (crystallinity distribution) of the resin according to the following method (temperature rising elution fractionation), and to determine the molecular weight and molecular weight distribution of the components by high temperature GPC (gel permeation). chromatogra
ph).

The polyolefin resin is first dissolved in o-dichlorobenzene at 140 ° C. or a temperature at which the resin is completely dissolved. Next, this solution is cooled at a constant temperature to form a thin polymer layer on the surface of an inert carrier prepared in advance. At this time, the resin components are generated in the order of high crystallinity and high molecular weight. Next, the temperature is raised continuously or stepwise, the concentration of the eluted components is detected in each predetermined temperature range, the composition distribution (crystallinity distribution) is measured (temperature rising elution fractionation), and the high temperature type GPC is used. (Gel permeation
Chromatograph) measures the molecular weight and molecular weight distribution of the eluted components.

The above polyolefin resin can be produced by the following multistage polymerization.

First, as the first-stage polymerization, propylene is first polymerized in the presence of a titanium compound and an aluminum compound to form a titanium-containing polypropylene resin. Next, in the polymerization after the second stage,
In the presence of the titanium compound and the aluminum compound, the titanium-containing polypropylene resin, propylene, and ethylene or α-olefin are copolymerized.

The titanium-containing polypropylene resin obtained by the first-stage polymerization is a propylene homopolymer, propylene-ethylene copolymer, or propylene-α-.
Olefin (1-butene, 1-hexene, 4-methyl-
1-pentene etc.) copolymer.

In the polymerization in the second and subsequent steps, propylene-ethylene copolymer, propylene-α-olefin copolymer, propylene-ethylene-α-olefin copolymer, ethylene homopolymer, ethylene-α-olefin copolymer. Can be coalesced.

As a method for producing such polypropylene resin, several methods have been proposed in the past. For example, in JP-A-4-224809, as titanium compounds, for example, titanium trichloride and magnesium chloride are co-ground, and n-butyl orthotitanate, 2-ethyl-
Using a solid Ti catalyst having a spherical shape and an average particle size of 15 μm, which is obtained by treating with 1-hexanol, ethyl p-toluate, silicon tetrachloride, diisobutyl phthalate, etc., an alkylaluminum such as triethylaluminum is used as an aluminum compound. A method for propylene polymerization using it has been proposed. Furthermore, during the polymerization, a silicon compound such as diphenyldimethoxysilane is added as an electron donor, or an iodine compound such as ethyl iodide is added. The most important feature of this production method is that the polymerization does not end in one step but is composed of two or more steps. By making the polymerization multi-stage, it becomes possible to successively make up plural kinds of polymers during the polymerization, and a blend type copolymer at a molecular level which is completely different from a usual polymer blend is produced.

Such a manufacturing method is disclosed in, for example, Japanese Patent Laid-Open No.
-96912, JP 4-96907 A, JP 3-174410 A, JP 2-170803 A.
JP-A No. 2-170802, JP-A No. 61-
The same is also disclosed in Japanese Patent Laid-Open No. 42553, Japanese Patent Laid-Open No. 3-205439, and Japanese Patent Laid-Open No. 3-97747. As the polyolefin resin used in the crosslinked polyolefin resin of the present invention, any resin obtained by any of these methods can be used without any trouble.

Examples of commercially available products of the polyolefin resin obtained by the above production method include "PER" manufactured by Tokuyama Soda Co., Ltd. and "Cataloy" marketed by Highmont Co., Ltd.

(Additive) In the present invention, a crosslinking aid is usually required to impart a crosslinked structure to the polyolefin resin. As the cross-linking aid, any of the commonly used polyfunctional monomers and monofunctional monomers may be used. For example, divinylbenzene (D
VB), trimethylolpropane trimethacrylate (TMPT), 1,9-nonanediol dimethacrylate, 1,10-decanediol dimethacrylate, trimellitic acid triallyl ester (TRIAM), triallyl isocyanurate and ethyl vinylbenzene. To be You may use these crosslinking aids in mixture of 2 or more types.

These crosslinking aids are preferably added in the range of 0.1 to 20 parts by weight, more preferably 0.8, based on 100 parts by weight of the polyolefin resin.
It is 10 to 10 parts by weight. If the amount of the crosslinking aid added is less than 0.1 parts by weight, the cross-linking of the polyolefin resin cross-linked product will be insufficient and sufficient strength cannot be obtained, and if it exceeds 20 parts by weight, the polyolefin resin cross-linked product will be cross-linked. There may be a problem with the moldability of the body.

Depending on the purpose, the above polyolefin resin may further include an antioxidant, a stabilizer, a pigment, an antifogging agent,
You may mix | blend additives, such as an antistatic agent and a flame retardant.

Any of the above-mentioned antioxidants and stabilizers may be used as long as they can prevent oxidative deterioration of the polymer. Examples thereof include commercially available phenolic antioxidants, phosphorus antioxidants, amine antioxidants, sulfur antioxidants and the like. These may be used alone or in combination of two or more.

Further, if necessary, carbon black, clay, talc, calcium carbonate, alumina, silica, kaolin, graphite, and the like may be added to the polyolefin resin.
A filler such as glass fiber may be added.

The crosslinking aid and other additives may be added to the polyolefin resin by mechanical melt mixing with an extruder or the like, or impregnation into the resin. When the above-mentioned crosslinking aid and additives are compounded by mechanical melt mixing, they can be carried out by a conventionally known method using an extruder, a Banbury mixer, a roll, a Brabender plastograph, a kneader and the like.

(Crosslinking) The crosslinked polyolefin resin of the present invention is obtained by adding a crosslinked structure to the above polyolefin resin.

The degree of crosslinking of the polyolefin resin can be expressed by the gel fraction, and the range of 10 to 70% is preferable in the measurement of the gel fraction of the crosslinked product using a xylene solvent described later. More preferable gel fraction is 10-6.
It is 0%, and particularly preferably 25 to 55%.

If the gel fraction is less than 10%, the strength may be insufficient, and if it exceeds 70%, the elongation may be poor.

To impart a crosslinked structure to the polyolefin resin, there are typically a method using an organic peroxide and a method using ionizing radiation.

The method for imparting a crosslinked structure with an organic peroxide is a method in which the above-mentioned polyolefin resin is blended with the above-mentioned crosslinking aid and an organic peroxide, and the resulting composition is subjected to heat treatment for crosslinking. is there. The heat treatment here means kneading the composition in a molten state. The kneading can be performed by a conventionally known technique using the above-mentioned extruder or the like. Preferably, the heat treatment is performed in an atmosphere of an inert gas such as nitrogen or carbon dioxide.

As the organic peroxide, dicumyl peroxide, di-tert-butyl peroxide, 2,5
-Dimethyl-2,5-bis (tert-butylperoxy) hexane, 2,5-dimethyl-2,5-bis (te
rt-Butylperoxy) hexyne-3,1,3-bis (tert-butylperoxyisopropyl) benzene, 1,1-bis (tert-butylperoxy) 3,3
3,5-trimethylcyclohexane, n-butyl-4,
4-bis (tert-butylperoxy) valerate,
Dibenzoyl peroxide, tert-butyl peroxybenzoate, etc. can be used.

Crosslinking can also be carried out by the so-called silane crosslinking method, which uses a silane compound instead of the above-mentioned crosslinking aid. In this method, a silane-grafted polyolefin-based resin obtained by graft-reacting a silane compound with a polyolefin-based resin by the above organic peroxide is cross-linked in the presence of water with a silanolization catalyst.
Examples of the silane compound include vinylethoxysilane, vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyl (β-methoxyethoxy) silane, and the like. Examples of the silanolation catalyst include dibutyltin diacetate, dibutyltin dilaurate, dibutyltin dioctoate and the like.

The amount of the organic peroxide added is preferably 0.01 to 2 parts by weight with respect to 100 parts by weight of the polyolefin resin. If the addition amount of the organic peroxide is less than 0.01 part by weight, the crosslinking of the crosslinked polyolefin resin is insufficient, and if it exceeds 2 parts by weight, there is a problem in the moldability of the crosslinked polyolefin resin. There is a risk.

In the method of crosslinking a polyolefin resin with ionizing radiation, a polyolefin resin containing a crosslinking aid is molded into a film or the like and then irradiated with ionizing radiation for crosslinking. Examples of the ionizing radiation include α rays, β rays, γ rays, and electron beams,
These irradiation doses are usually 1 to 50 Mrad. When the irradiation amount is less than 1 Mrad, the cross-linking of the polyolefin resin cross-linked product is insufficient, and improvement in strength and deformation recovery cannot be seen.
On the other hand, when the irradiation dose exceeds 50 Mrad, the effect of molecular chain scission becomes large, and the elongation of the obtained polyolefin resin cross-linked product may decrease.

The film of the present invention can be produced by a conventionally known method from the crosslinked polyolefin resin obtained as described above. For example, it can be produced by a conventionally known technique such as single extrusion or coextrusion by inflation molding or T die molding using a single or plural extruders. The thus-obtained film of the present invention has improved strength and elongation and is particularly excellent in deformation recovery, and also has flexibility, extensibility and heat resistance. This film may be used alone or may be laminated with another resin as long as it does not impair the effects of the present invention.

[0042]

The cross-linked polyolefin resin and film according to the present invention are excellent in strength and elongation, especially in deformation recovery by cross-linking a specific polyolefin resin, and have flexibility, extensibility and heat resistance. It also has.

The reason why the crosslinked polyolefin resin and film of the present invention have the above-mentioned excellent properties is as follows.
It is estimated as follows.

The polyolefin resin used in the present invention is obtained by polymerizing polypropylene resin in the first stage of polymerization.
The obtained polypropylene-based resin was further polymerized with propylene and ethylene or α-
Obtained by reacting an olefin, or ethylene, or ethylene and an α-olefin.

Therefore, in the polymerization after the second stage,
A flexible copolymer can be made compatible with a polypropylene resin at the molecular level, and the copolymer can be made into a uniform and very fine dispersion state as compared with the case of mixing a conventional polypropylene and an elastomer. be able to. Therefore, when imparting a crosslinked structure to the polyolefin-based resin, it is possible to perform the crosslinking very finely and uniformly,
It is presumed that the elongation, strength and deformation recovery of the obtained crosslinked polyolefin resin and film can be significantly improved.

In the conventional elastomer composition, it has been attempted to increase the proportion of the elastomer component or increase the molecular weight of the elastomer component in order to improve the flexibility. When the mixing of these components is carried out by mechanical mixing such as an extruder, the cost becomes high, and dispersion defects and molding defects due to aggregation of the elastomer components occur, and accordingly, there is a problem that the molecular weight of the elastomer components cannot be increased too much. It was happening.

On the other hand, in the polyolefin resin used in the present invention, since the copolymer having flexibility and the polypropylene resin are mixed by polymerization,
A large amount of the copolymer can be introduced in the polymerization after the second step, and the molecular weight of the copolymer can be freely controlled. As a result, there is no problem as in the above-mentioned conventional elastomer composition. By applying a cross-linking structure, it is possible to obtain a cross-linked polyolefin resin and a film which are excellent in strength, elongation and deformation recovery and have flexibility, extensibility and heat resistance.

[0048]

EXAMPLES The present invention will be specifically described below based on examples, but the present invention is not limited thereto.
In this example, the evaluation methods of the resin and the film are as follows.

CFC measurement Temperature rising elution fractionation (TREF = Temperature Rising Elu
section and high temperature GPC (SEC = Si)
ze Exclusion Chromatograph (CFC-1)
50A type: manufactured by Mitsubishi Petrochemical Co., Ltd.) was used to measure the components eluted from the polyolefin resin at 90 ° C. or higher.

Structure of polypropylene Using the above cross fractionation chromatograph, the components eluted at 90 ° C or higher were fractionated. About the obtained preparative sample, an infrared absorption spectrophotometer (SYSTEM200FT
-IR: Infrared absorption spectrum was measured using Perkin Elmer Japan Co., Ltd., and the peak from around 720 cm ^{-1 to} around 730 cm ^-1 was examined. Measurement of Tensile Properties Using a tensile tester (Tensilon UCT-500: manufactured by Orientec), a test piece having a width of 3 mm, a thickness of 0.4 mm and an initial length (grabbing interval) of 10 mm was pulled at a tensile speed of 200 m.
Tensile at m / min, elongation at break and stress at break were measured.

Measurement of stress relaxation Using a tensile tester (Autograph AG-500B: manufactured by Shimadzu Corporation), a test piece having a width of 3 mm, a thickness of 0.4 mm and an initial length (grabbing interval) of 10 mm was pulled at a tensile speed of 500 m.
The elongation was pulled up to 100% at m / min and held for 5 minutes. The tensile strength at that time was measured, and the rate of stress reduction (stress residual rate A) was calculated by the following formula: Stress residual rate A = (tensile strength after 5 minutes / initial tensile strength) × 100
(%) Measurement of gel fraction A predetermined amount (a gram) of a sheet is immersed in about 50 ml of xylene and dissolved at 120 ° C. for 24 hours. The insoluble matter remaining at this time was filtered through a 200-mesh wire net, the dry weight (b gram) of the obtained residue was measured, and the gel fraction was determined by the following formula.

Gel fraction B = (insoluble matter weight b / initial sheet weight a) × 100 (%) (Examples 1 to 6) The polyolefin resin shown in Table 1 was used in the number of parts shown in Table 2, and The crosslinking aid shown in 2 was mixed in the number of parts shown in Table 2 and melt-kneaded at 170 ° C. using a Brabender Plastograph. The resulting mixture is
It was press molded into a sheet having a thickness of 0.4 mm at 0 ° C. Then, the obtained sheet was irradiated with an electron beam having a predetermined irradiation amount shown in Table 2 at an accelerating voltage of 200 kV from both sides of the sheet to obtain a sheet-like crosslinked body.

Comparative Examples 1 and 2 Using only the polyolefin resins shown in Table 2, press molding was carried out in the same manner as in Example 1 to obtain sheets.

(Comparative Example 3) A mixture of ethylene-propylene-diene copolymer (EPDM) and polypropylene (pp) (content of pp: 30% by weight) was added with the peroxide aid shown in Table 2. And the organic peroxide (t-
Butyl peroxyisopropylbenzene) 0.2 (ph
r) Compounded and melt-kneaded at 170 ° C. using a Brabender Plastograph as in Example 1. The obtained mixture was press molded into a 0.4 mm sheet at 170 ° C. to obtain a crosslinked sheet.

Comparative Example 4 A sheet was obtained by pressing in the same manner as in Example 1 using plasticized PVC (polymerization degree: 1600) containing 30% by weight of a plasticizer.

The physical properties of the crosslinked materials and sheets obtained in Examples 1 to 6 and Comparative Examples 1 to 4 were evaluated. The results are also shown in Table 2.

[0057]

[Table 1]

[0058]

[Table 2]

It can be seen from Table 2 that the sheets of Examples 1 to 6 are improved in elongation at break, fracture stress and residual stress relaxation rate and are excellent in mechanical properties as compared with the sheets of Comparative Examples 1 to 4. Recognize.

[0060]

EFFECTS OF THE INVENTION According to the present invention, by cross-linking a specific polyolefin resin, the elongation, strength and deformation recovery are improved, and the polyolefin resin cross-link also has flexibility, extensibility and heat resistance. The body and film are obtained. Therefore, a film for stretch packaging, a surface protection film, a stretch film for grass, a stretch film for agriculture, a film for heat shrinkage, a film for plasters,
It can be widely used for shrink films, plasticized PVC substitute films and the like. Since this film does not use a plasticized PVC material, it does not adversely affect the physical properties and the like and does not cause environmental problems.

Claims (2)

[Claims] 1. A (A) polypropylene-based resin obtained by two or more stages of polymerization and produced in the first stage of polymerization, and the following (b-
Polyolefin resin cross-linked product in which a cross-linking structure is imparted to a polyolefin resin composed of at least one selected from the group consisting of the combination of the polymer moieties of 1) and (b-2): (b- 1) a copolymer of propylene and ethylene and / or at least one α-olefin; (b-2) an ethylene homopolymer, or ethylene and α
-Copolymers with olefins. 2. A film comprising the crosslinked polyolefin resin according to claim 1.