JPH05170938A - Cross-linked polyethylene resin film - Google Patents

Abstract

PURPOSE:To provide the subject film composed of a water-crosslinked ethylene- unsaturated silane compound copolymer, having a heat-sealing strength higher than a prescribed level, exhibiting sufficiently high crosslinking rate, having excellent film-processing stability and heat-resistance and useful for food packaging, etc. CONSTITUTION:The objective film to give a heat-sealed product having a heat- sealing strength of >=1kg/20mm contains a water-crosslinked ethylene copolymer composed essentially of (A) ethylene and (B) at least one kind of unsaturated silane compound of formula ((n) is 4-10) [e.g. 10-(triethoxysilyl)decene], containing 0.2-5wt.% of the unsaturated silane compound and having a molecular weight distribution (MW/MN) of <=20, a melt-flow rate of 0.1-20-g/min and a chlorine content of <=0.5wt.ppm.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a polyethylene resin film having a high heat-sealing strength when heat-sealed. More specifically, the present invention relates to a food packaging film comprising a water-crosslinked product of an ethylene-ethylenically unsaturated silane compound copolymer having a hydrolyzable silane group as a crosslinkable group.

[0002]

2. Description of the Related Art It is well known that low density polyethylene and other polyethylene resins are crosslinked to improve their mechanical strength and heat resistance, and various crosslinking means are known. One of such crosslinking means is irradiation with radiation, which is well known as a crosslinking means for polyethylene films. This method has an advantage that a general-purpose polyethylene film can be used, but requires special and expensive crosslinking equipment. Moreover, such a radiation-crosslinked polyethylene film is not satisfactory in terms of heat sealing performance.

Recently, as an alternative to conventional crosslinking methods,
A silicone graft polyethylene was developed by condensation of silane groups (see JP-B-48-1711, JP-A-47-8389 and JP-A-52-9073). Silicone-grafted polyethylene is one in which the silicone part is hydrolyzed and the cross-linking reaction proceeds by exposure to water, but since this hydrolysis occurs at a relatively low temperature, the enormous cross-linking required for chemical cross-linking occurs. Since it does not require equipment, application to cross-linked molded products is being considered. However, in this case, the production of the base polyethylene and the multiple steps of silicone grafting are required, and the polyethylene film produced and crosslinked in this way is satisfactory in terms of mechanical strength and heat sealing performance. is not.

On the other hand, there is known a method of crosslinking a copolymer of ethylene and vinylalkoxysilane by heating or mechanical processing (US Pat. Nos. 3,225,018 and 3,39).
(See No. 2,156). According to this method, the crosslinkable polyethylene is advantageous over the above-mentioned grafting method in that it can be obtained in a single step of only an ethylene polymerization step, but in this case, since crosslinking must be performed before molding, It is very difficult to form a polyethylene film after crosslinking. Further, a method for obtaining a crosslinked film by a copolymer of ethylene and vinyltrimethoxysilane by a high pressure radical method is shown. (JP-A-55-9612). However, the copolymer shown here is harmful to the human body because methanol is produced in the crosslinking treatment step, and is limited when used in the food packaging field.

[0005]

DISCLOSURE OF THE INVENTION The present invention is intended to solve the above problems and is intended to solve these problems by using a specific unsaturated silane compound as the unsaturated silane compound. is there. The crosslinked polyethylene resin film according to the present invention contains a water-crosslinked product of the following ethylene copolymer, and when heat-sealed: 1 kg /
A crosslinked polyethylene resin film for food packaging, which has a heat seal strength of 20 mm or more. Ethylene copolymer : ethylene and the following general formula: (C ₂ H ₅ O) ₃ Si (CH ₂ ) nCH = CH ₂ (where n is 4
It is -10. ) And at least one unsaturated silane compound, the unsaturated silane compound content is from 0.2 to 5% by weight, the molecular weight distribution (M _W / M _N ) is 20 or less, and the melt flow rate is 0.1 to 20 g / min,
An ethylene copolymer having a chlorine content of 0.5 ppm by weight or less.

[Detailed Description of the Invention] 1. Ethylene-unsaturated silane compound copolymer 1) Type of copolymer One group of this copolymer is a simple copolymer with an ethylene-unsaturated silane compound, and the other group is a polyethylene resin and It is a copolymer with a saturated silane compound, that is, a graft copolymer. The former is preferable from the viewpoints of processing stability of the copolymer, storage stability, and performance of the crosslinked product, for example, heat fusion property. 2) Unsaturated silane compound The unsaturated silane compound used in the present invention is represented by the following general formula. _{(CH 3 O) 3 Si (} CH 2) nCH = CH 2 where n = 2 to 10, preferably, an n = 4 to 10, specifically a 6- (triethoxysilyl) hexene. Most preferably n = 8, i.e. 10- (triethoxysilyl) decene.

3) Manufacture of Copolymer (1) Simple Copolymerization The ethylene-unsaturated silane compound copolymer may be prepared by using these unsaturated silane compounds such as those described in JP-A-55-9611. Thus, it is obtained by copolymerizing with ethylene. The copolymerization of ethylene and the unsaturated silane compound may be carried out under any conditions in which a copolymer of both is produced. Specifically, for example, the pressure is 500 to 4000 kg /
cm ² , preferably 1000 to 4000 kg / cm ² , temperature 10
0 to 400 ° C., preferably 150 to 350 ° C.,
In the presence of a radical polymerization initiator, and a comonomer capable of copolymerizing with ethylene if necessary, and a chain transfer agent, each monomer was added in a tank or tube reactor, preferably a tank reactor. Contact at the same time or in stages.

In the present invention, any radical polymerization initiator, comonomer and chain transfer agent known to be used for homopolymerization or copolymerization of ethylene can be used. As the polymerization initiator, an organic peroxide such as lauroyl peroxide, dipropionyl peroxide, benzoyl peroxide, di-t-butyl peroxide, t-butyl hydroperoxide, t-butyl peroxyisobutyrate, There are azo compounds such as molecular oxygen, azobisisobutyronitrile, azoisobutylpareronitrile.

The comonomers include (a) vinyl acetate, carboxylic acid vinyl esters such as vinyl pivalate, and (b)
(Meth) acrylic acid esters such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, (c) (meth) acrylic acid, maleic acid,
Olefinically unsaturated carboxylic acids such as fumaric acid,
(D) (meth) acrylonitrile, (meth) acrylic acid derivatives such as (meth) acrylamide, (v) vinyl methyl ether, vinyl ethers such as vinyl phenyl ether, and the like. Of these, preferred are vinyl esters of monocarboxylic acids having about 1 to 4 carbon atoms, such as vinyl acetate, and (meth) acrylic acid esters of alcohols having about 1 to 4 carbon atoms, such as methyl (meth) acrylate. Is. A plurality of such olefinically unsaturated compounds can be used in combination. In addition, "(meta)
“Acrylic acid” shall mean both acrylic acid and methacrylic acid.

As the continuous transfer agent, paraffin hydrocarbons such as methane, ethane, propane, butane, pentane, hexane and heptane, propylene, butene-1,
Examples thereof include α-olefins such as hexene-1, formaldehyde, acetaldehyde, aldehydes such as n-butyraldehyde, acetone, methyl ethyl ketone, ketones such as cyclohexanone, aromatic hydrocarbons and chlorinated hydrocarbons.

(2) Graft Copolymerization Another method for obtaining an ethylene-unsaturated silane compound copolymer is the above-mentioned unsaturated silane compound, for example, Japanese Patent Publication No.
As described in JP-A-1711, it comprises graft copolymerization with a polyethylene resin. That is,
The unsaturated silane compound-grafted polyethylene resin is an ethylene homopolymer, a copolymer of ethylene and α-olefin, a copolymer of ethylene and vinyl ester, a copolymer of (meth) acrylic acid or these esters, or a halogenated compound. It can be produced by heating a polyethylene resin such as polyethylene and an unsaturated silane compound in the presence of a free radical generator at a temperature equal to or higher than the decomposition temperature of the free radical generator (note that the generation of free radicals relative to the polyethylene resin is In addition to the method of decomposing the free radical generator, irradiation by high-energy radiation, or the like can also be used).

The free radical generator referred to here is
Any compound capable of generating a free radical site in the polyethylene resin under the reaction conditions can be used. Representative examples include organic peroxides such as dicumyl peroxide, benzoyl peroxide, t-butyl peroxide, and azo compounds such as azoisobutyronitrile and methylazoisobutyrate. The amounts of the unsaturated silane compound and the free radical generator used may be arbitrarily determined by the practitioner according to the desired quality and reaction conditions, and can be within a wide range, but generally polyethylene is used. The former is 0.5 to 15% by weight, and the latter is 0.01, based on the weight of the resin.
A range of 2 wt% is preferred. In the graft copolymerization step, a polyethylene resin, an unsaturated silane compound, and a compound of a free radical generator are mixed with a kneading device such as an extruder or a Banbury mixer at a temperature not lower than the melting point of the polyethylene resin and lower than the decomposition temperature, usually 150. It usually consists of heating at a temperature in the range of ~ 300 ° C.

In view of the stability and processability of the graft copolymer, the unsaturated silane compound used contains impurities such as an inorganic acid, an organic acid or a substance which may produce such a substance. Those that do not contain are preferable (the same applies to the above-mentioned simple copolymerization, that the unsaturated silane compound does not contain such impurities).

(3) Physical Properties of Copolymer The copolymer of the present invention is 0.2 to 5% by weight, preferably 0.2 to 2% by weight of an unsaturated silane compound in both the simple copolymer and the graft copolymer. It contains 0.5% by weight. Generally, a water-crosslinked product of a copolymer having a high unsaturated silane compound content has better mechanical strength and heat resistance, but if the content is too high, tensile elongation and heat seal strength decrease. The content range of 0.2 to 5% by weight is determined from this point. Further, the copolymer of the present invention is a system in which the unsaturated silane compound represented by the general formula is a homosystem or a composite system, and contains the predetermined amount shown above, more preferably its molecular weight distribution (weight average). The ratio of the molecular weight to the number average molecular weight) is 20 or less, preferably 4 to 15, the melt flow rate (MFR) is 0.1 to 20 g / 10 minutes, preferably 0.5 to 10 g / 10 minutes, and the density is 0.934 g. / Cm ²
An ethylene copolymer consisting essentially of ethylene having a chlorine content of 0.532 ppm or less and preferably 0.932 g / cm ² or less and a chlorine content of 0.5 ppm by weight or less, and preferably 0.2 ppm by weight or less. Is.

Here, if the unsaturated silane compound is less than 0.2% by weight, a sufficient degree of crosslinking cannot be obtained.
If it exceeds the above range, the storage stability, the moldability and the tensile properties of the crosslinked molded product deteriorate. When the molecular weight distribution exceeds 20, storage stability and molding processability deteriorate, and the crosslinked molded article also has insufficient tensile properties. If the MFR is less than 0.1 g / 10 minutes, the moldability and the tensile properties of the crosslinked molded article will be insufficient, whereas if it exceeds 20 g / 10 minutes, the tensile properties of the crosslinked molded article will be unsatisfactory. The density of this copolymer is 0.93.
4 g / cm ² or less, preferably 0.920 to 0.932
It is g / cm ² . If it exceeds 0.934 g / cm ² , the crosslinking property generally becomes poor. Further, if the chlorine content in this copolymer exceeds 0.5 ppm by weight, the storage stability, the moldability and the tensile properties of the crosslinked molded product deteriorate. This impurity is mixed by the unsaturated silane compound as the raw material.

In addition, a silane compound having a hydrolyzable organic group (specifically, vinyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, etc.) is added to the copolymer in an amount of 0.01% by weight to 5%. % By weight, preferably 0.05% to 3% by weight, more preferably 0.1%.
By adding 2% by weight to 2% by weight, the storage stability of the copolymer and the extruded appearance of the molded product can be further improved without lowering the crosslinking rate.

2. Water-crosslinked product of copolymer The water-crosslinked product of the copolymer according to the present invention is produced by water-crosslinking the silane groups introduced into the above copolymer. Since water crosslinking is promoted by a silanol condensation catalyst, it is preferable in the present invention that the copolymer film is exposed to water in the presence of this catalyst. In that case, one of the "in the presence of a catalyst" aspect of exposing the copolymer film to water is to mix the catalyst with the copolymer to form a film of this composition and bring it into contact with water. The other is to form a catalyst-free copolymer into a film and to contact the film with water in the presence of a catalyst (for example, by coating the film with a water-insoluble catalyst).

3. Silanol Condensation Catalyst As mentioned above, in the preferred embodiment of the present invention, a catalyst is used to accelerate the crosslinking reaction. Those which can be used as a catalyst for promoting dehydration condensation between silicone silanols are generally of interest in the present invention. Such silanol condensation catalysts are generally carboxylates of metals such as tin, zinc, iron, lead, cobalt, organic bases, inorganic acids, and organic acids. Specific examples of the silanol condensation catalyst include diptyl tin dilaurate, diptyl tin diacetate, diptyl tin dioctoate, stannous acetate, stannous caprylate, lead naphthenate, zinc caprylate, cobalt naphthenate, ethylamine, diptylamine, hexyl. Examples thereof include inorganic acids such as amine, pyridine, sulfuric acid and hydrochloric acid, organic acids such as toluenesulfonic acid, acetic acid, stearic acid and maleic acid. The amount of the silanol condensation catalyst to be used may be appropriately determined by the practitioner with reference to the examples given below for a given catalyst for a given copolymer. Generally speaking, the amount to be compounded in the composition is about 0.0001 to 5% by weight, preferably 0.1% to the amount of the copolymer in the mixed composition.
001 to 3% by weight, particularly preferably 0.01 to 1% by weight
Within the range of.

4. Composition Preparation As mentioned above, one embodiment of the production of the film of the present invention is
The polyethylene resin composition containing the silanol condensation catalyst is formed into a film and exposed to water. The compositions used to make the resin films of the present invention can be made by any means that can be used to incorporate various additives into the thermoplastic resin. Various methods can be applied as a method for preparing the composition used for producing the resin film of the present invention. The composition is usually prepared by melting or dissolving an ethylene-unsaturated silane compound copolymer or a silanol catalyst (particularly the former). For example, the copolymer is mixed with the copolymer in an extruder. Silanol condensation catalyst (as it is or solution or dispersion, or
(As a masterbatch) and auxiliary materials to be blended if necessary, and kneaded and extruded into desired molded product pellets).

As in the former case, the amount of silanol condensation catalyst is smaller than that of the copolymer. Therefore, as is often done to mix small amounts of components, it is possible to prepare a masterbatch in which a silanol condensation catalyst is mixed in a dispersion medium such as polyethylene in a high concentration, and to mix this into a copolymer so as to have a predetermined catalyst concentration. It is convenient. The composition used in the production of the resin film of the present invention may contain various auxiliary materials, as often found in known resin compositions. Such auxiliary materials include miscible thermoplastics, stabilizers,
Lubricants, antistatic agents, fillers, colorants, foaming agents, etc.

5. Film formation The method for producing a film from the above-mentioned polyethylene resin composition or a normal polyethylene resin containing no silanol condensation catalyst is any method applicable to thermoplastic resins in general, and polyethylene in particular. It is possible. Specifically, for example, an inflation method, a T-die method,
There are others. There is no limit to the thickness of the film produced. Generally, about 0.01 to 0.5 mm will be normal. In the present invention, such a film may be uniaxially or biaxially stretched, and may be a laminate with a film-like material of the same or different material (in the case of a laminate, contact of silane group-containing layer with water). Should be considered so as not to be unfairly harmed). Further, the film forming step may be carried out simultaneously with the preparation of the composition.

6. Coating with Silanol Condensation Catalyst If the silanol condensation catalyst is not incorporated into the polyethylene resin, the film is coated with the catalyst prior to exposing the film to water. Since the amount of catalyst present on the surface of the film may be small, it is usual to coat the catalyst with its solution or dispersion. Any suitable method can be used for coating the film surface with the catalyst solution or dispersion. Specifically, for example, there are a spraying method, a roll coater method, a method of passing a film through a catalyst bath, a method of contacting with a porous material (for example, a sponge) impregnated with a catalyst solution, and the like. The catalyst coating method is preferably selected in relation to the subsequent step of exposure to water (details described later). The solvent or dispersion medium for forming the catalyst liquid may be selected appropriately for a given catalyst. Those capable of dissolving or swelling in the target polyethylene resin can also be used under the condition that the film to be treated is not cut or deformed, and the solvent or dispersion medium may be water. ..

7. Crosslinking When the film containing or coated with the silanol catalyst is exposed to water, a crosslinking reaction occurs. The film is exposed to water at room temperature to about 200 ° C., usually at room temperature to about 200 ° C.
It may be contacted with water (liquid or vapor or water in air) at about 100 ° C. for about 0.1 second to 1 week, usually about 1 second to 1 hour. It can also be brought into contact with water under pressure. To improve the leakage of the film,
The water may contain a wetting agent or a surfactant, a water-soluble organic solvent and the like. The cross-linking step can be carried out in any manner that allows sufficient contact between the film and water, one specific example of which is to pass the film continuously through a water bath.

One of the embodiments in which a catalyst coating step should be provided separately from the crosslinking step consists of sequentially passing through a film catalyst bath and a water bath. In this case, the catalyst bath is the same as that used in the case where the catalyst solution has a specific gravity smaller than that of water and is immiscible with water, in addition to the case of being stored in a tank different from the water bath. It may be housed in a tank. Furthermore, if desired, a single bath of aqueous catalyst solution can be used for catalyst coating and water crosslinking if the catalyst is water soluble. Also,
The water to be crosslinked can be crosslinked not only by ordinary water but also by heated steam or moisture in the air. Further, by exposing the composition to water during the preparation and film formation, the crosslinking reaction can be carried out simultaneously with the film formation.

8. Heat-sealing The water-crosslinked film thus obtained may be used as it is, but it is often heat-sealed and formed into a bag or the like. Usually heat seal is 140-2
It is carried out under the conditions of a temperature of 00 ° C., a pressing force of 1 to 3 kg / cm ² for 0.5 to 3 seconds, and the cross-linked film of the present invention is a cross-linked film. Thus, a film having a heat seal strength of 1000 g / 20 mm or more, preferably 1300 g / 20 mm or more can be obtained even under relatively mild conditions.

The heat seal strength of the crosslinked film of the present invention is measured by the following method. Create a test piece with a width of 20 mm and a length of 100 mm from a film with a thickness of 60 μ, stack two test pieces along the edge, and in the width direction with a heat bar type seal tester, heat bar temperature 180 ° C., pressing force 1 kg. / cm ² in heat-sealed under the conditions of 1 second pressing, the 90 ° peel strength of the seal portion by using an autograph to measure at 500 mm / min tensile rate.

[0027]

EXAMPLES The ethylene copolymers produced in the following examples were evaluated for their physical properties and qualities by the following methods. (Evaluation of physical properties) (1) Content of unsaturated silane compound: measured by an infrared spectrophotometer. (2) Molecular weight distribution: weight average molecular weight (M _W ) and number average molecular weight (M _N ) are determined by gel diffusion chromatography (GPC).
The fractionated product was measured by a method of quantifying with a low-angle laser light scattering device, and determined by the following formula and method. The calibration curve is standard high density polyethylene NBS-SRM-147.
Made using 5. (Weight average molecular weight) ΔV · Σ (K / R) ⁻¹ / m where ΔV is the sampling volume K = 2π ² n ² / (λ ⁴ N) (dn / dc) ² (Hcos ² θ) n : Refractive index λ: Wavelength N: Avogadro's number dn / dc: Concentration increment of refractive index θ: Scattering angle R is the Rayleigh ratio difference between solution and solvent m is the injected polymer weight (number average molecular weight) is EE Droh And RA Mendel
Calculated based on Son's method.

(3) According to MFR JIS-K6760. (4) Density According to JIS-K6760. (5) Chlorine content (a) The copolymer is immersed in a methanol / acetone mixed solvent and heated at 50 ° C. for 24 hours, and then the solvent is separated from the copolymer. (B) To this solvent, add a methanol solution of sodium methylate, mix well, and stir. (C) To this solution, add promphenol blue indicator, and add nitric acid dropwise until the indicator turns yellow. (D) Next, the electrode of the automatic potentiometric titrator is put in and titrated with a silver nitrate solution while stirring.

Examples 1 and 2 Ethylene was added to a stirring autoclave having an internal volume of 1.5 l.
10- (triethoxysilyl) decene (chlorine content 20pp
m or less), and a mixture of propylene as a chain transfer agent, t-butylperoxyisobutyrate is added as a polymerization initiator, and the pressure is 2400 kg / cm ² and the temperature is 220 ° C. Ethylene-10- (triethoxysilyl) decene copolymer was continuously synthesized. Table 1 shows the polymerization conditions and the physical properties of the produced copolymer. Further, 5% by weight of a master batch containing 1% by weight of dibutyltin dilaurate was added to the obtained copolymer, and L / D = 24.
With a 40 mmφ full-flight Slew extruder, a blown film having a blow ratio of 1.5 and a thickness of 60 μm is formed into an inflation film at a temperature of 40 ° C. and a relative humidity of 80% for 1 week. It was left to crosslink. The characteristics of the obtained film are shown in Tables 2 and 3, and the film processing characteristics at an extrusion temperature of 210 ° C. are shown in Table 4.

Example 3 Ethylene was added to a stirring autoclave having an internal volume of 1.5 l.
6- (triethoxysilyl) hexene (chlorine content 20 pp
m or less) and propylene as a chain transfer agent are fed, t-butylperoxyisobutyrate is added as a polymerization initiator, and the pressure is 2000 kg / cm ² and the temperature is 220 ° C. Ethylene-6- (triethoxysilyl) hexene copolymer was continuously synthesized. Table 1 shows the polymerization conditions and the physical properties of the produced copolymer. Further, 5% by weight of a master batch containing 1% by weight of dibutyltin dilaurate was added to the obtained copolymer, and L / D = 24.
With a 40 mmφ full-flight Slew extruder, a blown film having a blow ratio of 1.5 and a thickness of 60 μm is formed into an inflation film at a temperature of 40 ° C. and a relative humidity of 80% for 1 week. It was left to crosslink. The characteristics of the obtained film are shown in Tables 2 and 3, and the film processing characteristics at an extrusion temperature of 210 ° C. are shown in Table 4.

Example 4 The copolymer alone obtained by the method shown in Example 1 was
L / D = 24, 40 mmφ full flight Slewie extruder, extrusion temperature 170 ° C., blow ratio 1.5, thickness 6
After being formed into a 0 μ blown film, it was dipped in a 10 wt% xylene solution of dibutyltin dilaurate for 1 second, and then left in a constant temperature and humidity chamber at a temperature of 40 ° C. and a relative humidity of 80% for 1 week for crosslinking. The characteristics of the obtained film are shown in Tables 2 and 3, and the film processing characteristics at an extrusion temperature of 210 ° C. are shown in Table 4.

Comparative Example 1 Melt index 2 g / 10 minutes and density 0.919 g
2 wt% of vinyltrimethoxysilane and 0.1 wt% of dicumyl peroxide were dispersed in low density polyethylene (Yukaron EH-30 manufactured by Mitsubishi Petrochemical Co., Ltd.) having / cc,
This was subjected to graft polymerization at an extrusion temperature of 200 ° C. by using a 50 mmφ Dalmagee screw extruder with L / D = 24. The resulting silicone-grafted polyethylene was molded into an inflation film and crosslinked by the method described in Examples 1 to 3. The characteristics of the obtained film are shown in Tables 2 and 3, and the film processing characteristics at an extrusion temperature of 210 ° C. are shown in Table 4.

Comparative Example 2 A stirring autoclave having an internal volume of 1.5 l was charged with ethylene,
A mixture of vinyltrimethoxysilane and propylene as a chain transfer agent was fed in, t-butylperoxyisobutyrate was added as a polymerization initiator, and the pressure was 2400.
Under the conditions of kg / cm ² and temperature of 220 ° C., ethylene-
Vinyltrimethoxysilane copolymer was continuously synthesized. Table 1 shows the polymerization conditions and the physical properties of the produced copolymer. Further, 5% by weight of a master batch containing 1% by weight of dibutyltin dilaurate was added to the obtained copolymer, and L /
D = 24, 40mmφ full flight Slew extruder, extrusion temperature 170 ° C, blow ratio 1.5, thickness 60μ
After forming into blown film of
It was left in a thermo-hygrostat at a temperature of 80 ° C. and a relative humidity of 80% for 1 week to crosslink. The characteristics of the obtained film are shown in Table-2 and Table-3.
And the film processing characteristics at an extrusion temperature of 210 ° C.
4 shows.

Comparative Example 3 Ethylene was added to a stirring autoclave having an internal volume of 1.5 l.
A mixture of vinyltriethoxysilane and propylene as a chain transfer agent was fed in, t-butylperoxyisobutyrate was added as a polymerization initiator, and a pressure of 2400 was added.
Under the conditions of kg / cm ² and temperature of 220 ° C., ethylene-
Vinyltrimethoxysilane copolymer was continuously synthesized. Table 1 shows the polymerization conditions and the physical properties of the produced copolymer. Further, 5% by weight of a master batch containing 1% by weight of dibutyltin dilaurate was added to the obtained copolymer, and L /
D = 24, 40mmφ full flight Slew extruder, extrusion temperature 170 ° C, blow ratio 1.5, thickness 60μ
After forming into blown film of
It was left in a thermo-hygrostat at a temperature of 80 ° C. and a relative humidity of 80% for 1 week to crosslink. The characteristics of the obtained film are shown in Table-2 and Table-3.
And the film processing characteristics at an extrusion temperature of 210 ° C.
4 shows.

Comparative Example 4 Ethylene was added to a stirring autoclave having an internal volume of 1.5 l.
Injecting a mixture of γ-methacryloyloxypropyltriethoxysilane and propylene as a chain transfer agent,
T-Butylperoxyisobutyrate was added as a polymerization initiator, and the pressure was 2400 kg / cm ² and the temperature was 220 ° C.
An ethylene-vinyltrimethoxysilane copolymer was continuously synthesized under the conditions of. Table 1 shows the polymerization conditions and the physical properties of the produced copolymer. Further, 5% by weight of a master batch containing 1% by weight of dibutyltin dilaurate was added to the obtained copolymer, and the mixture was blown with a 40 mmφ full flight Slewie extruder with L / D = 24 at an extrusion temperature of 170 ° C. After being molded into an inflation film having a thickness of 60 μ and a ratio of 1.5, it was left in a constant temperature and humidity chamber at a temperature of 40 ° C. and a relative humidity of 80% for 1 week to be crosslinked. The characteristics of the obtained film are shown in Tables 2 and 3, and the film processing characteristics at an extrusion temperature of 210 ° C. are shown in Table 4.

Comparative Example 5 Melt index 1 g / 10 min and density 0.920 g
An inflation film was molded by the method shown in Example 4 using low density polyethylene (Yukaron ZF-30 manufactured by Mitsubishi Petrochemical Co., Ltd.) having / cc. The characteristics of the obtained film are shown in Tables 2 and 3, and the extrusion temperature 210
The film processing characteristics at ° C are shown in Table-4.

Comparative Example 6 Ethylene was added to a stirring autoclave having an internal volume of 1.5 l.
10- (triethoxysilyl) decene (chlorine content 20pp
m or less), and a mixture of propylene as a chain transfer agent, t-butylperoxyisobutyrate is added as a polymerization initiator, and the pressure is 1600 kg / cm ^{2 at} a temperature of 260 ° C. Ethylene-10- (triethoxysilyl) decene copolymer was continuously synthesized. Table 1 shows the polymerization conditions and the physical properties of the produced copolymer.

Comparative Example 7 A stirring autoclave having an internal volume of 1.5 l was charged with ethylene,
10- (triethoxysilyl) decene (chlorine content 600
ppm), and a mixture of propylene as a chain transfer agent, t-butylperoxyisobutyrate as a polymerization initiator, and ethylene under the conditions of a pressure of 2400 kg / cm ² and a temperature of 220 ° C. A -10- (triethoxysilyl) decene copolymer was continuously synthesized. Table 1 shows the polymerization conditions and the physical properties of the produced copolymer.

[0039]

[Table 1]

[0040]

[Table 2]

[0041]

[Table 3]

[0042]

[Table 4]

[0043]

As described above, the present invention does not use vinyltrimethoxysilane as an unsaturated silane compound, but uses an ethylene copolymer introduced with a specific unsaturated silane compound represented by the above general formula. As a result, it was found in the case of using a polyethylene resin using vinyltrimethoxysilane, methanol is not generated during the crosslinking step, the film processing stability is excellent, and the crosslinking rate is practically sufficient, The obtained film has heat resistance and also has heat sealability which is practically equivalent to that of an ordinary low density polyethylene film.

Claims (1)

[Claims] 1. A crosslinked polyethylene resin film for food packaging, comprising a water-crosslinked product of the following ethylene copolymer and having a heat-sealing strength of 1 kg / 20 mm or more when heat-sealed. Ethylene copolymer : ethylene and the following general formula: (C ₂ H ₅ O) ₃ Si (CH ₂ ) nCH = CH ₂ (where n is 4
It is -10. ) And at least one unsaturated silane compound, the unsaturated silane compound content is from 0.2 to 5% by weight, the molecular weight distribution (M _W / M _N ) is 20 or less, and the melt flow rate is 0.1 to 20 g / min,
An ethylene copolymer having a chlorine content of 0.5 ppm by weight or less.