JP2734084B2 - Method for producing stretchable film or sheet - Google Patents

Description

The present invention relates to a method for producing an extensible film or sheet. More specifically, the present invention relates to a method for producing a film or sheet having high extensibility and flexibility suitable for use in a leak-proof gather portion of a used diaper, a backsheet of the used diaper, a film for V-process casting, and the like. .

[Conventional technology and its problems]

Conventional flexible films are manufactured using an ethylene resin having a very low density. However, this resin has a problem that blocking occurs when the resin is formed into a film due to a small number of crystal parts and a large amount of low molecular weight components.

As a countermeasure, a molding method in which a large amount of an anti-blocking agent such as synthetic silica, a lubricant such as metal soap or a plasticizer, etc. was added to the raw material resin in a large amount was devised, but the effect was insufficient in all cases. Often, problems occurred in texture, texture and hygiene.

It was also considered to blend another resin with the ultra-low-density polyethylene.However, if the amount is such that the above-mentioned drawbacks are eliminated, the original flexibility and elongation characteristics of the ultra-low-density polyethylene cannot be utilized. .

Furthermore, a method of modifying ultra-low-density polyethylene with a radical generator has been proposed, but according to this method, although the surface state and physical properties are good, in order to mold with the addition of the radical generator, There is a drawback that thermal stability becomes poor and gels and burns are easily generated.

For this reason, when a thin film is formed, there is a problem that the film is easily broken from the portion where the gel or the burn is generated, and the film is easily broken from the gel or the burn even in the formed film.

Ultra-low-density polyethylene has excellent extensibility and flexibility compared to ordinary polyethylene, but it has been difficult to produce a film suitable for practical use due to the above-mentioned problems.

[Means for solving the problem]

The present inventors have come into contact with the problems of the conventional technology as described above, solved the problems, and have conducted intensive studies to provide a method for obtaining a film having excellent flexibility and extensibility. It has been found that the problem can be solved by forming a specific multilayer structure using a copolymer, and the present invention has been completed.

That is, the gist of the present invention is that, when producing an extensible film or sheet having a multilayer structure, the density of the intermediate layer is 0.91 g /
and ethylene copolymer is less than cm ^3, the outer layers density 0.91g
ethylene copolymer 100 parts by weight of less than / cm ³ a radical generating agent as obtained by 0.001 parts by weight added or react,
A method for producing an extensible film or sheet, comprising a multilayer coextruded film or sheet, wherein the thickness of the intermediate layer is not less than the total thickness of both outer layers.

The density used for the inner and outer layers (both outer layers) of the present invention is 0.91
As an ethylene copolymer of less than g / cm ^3, a copolymer of ethylene and an α-olefin having 3 or more carbon atoms is preferable,
The ethylene copolymer has a melt index of 10 g /
It is good to be 10 minutes or less, preferably in the range of 0.1 to 2 g / 10 minutes, and more preferably in the range of 0.2 to 1 g / 10 minutes. Density is preferably 0.85~0.90g / cm ^3, more preferably 0.85~0.89g
/ cm ³ range. Further, the flow ratio is 30 or less, preferably 5 to 25, and more preferably 10 to 25.

When the above melt index is higher than the upper limit, the film becomes too brittle, and when the density is higher than the upper limit, the film lacks softness, the stretchability of the film becomes insufficient, and when the flow ratio is higher than 30, the film properties deteriorate. It is not preferable. The ethylene copolymer having an elongation of 600% or more, preferably 1000% or more is suitably used.

In the method of the present invention, the melt index is JIS K6
It is a value measured at 190 ° C according to 760, and elongation is JIS K6
It is a value measured according to the measurement method of elongation at break in the section of tensile test of 301, the density is a value measured according to JIS K6760, and the flow ratio is the above melt index measuring device Used, shearing force 10 ⁶ dynes / cm ³ (load 11131 g)
When the ratio of 10 ⁵ dynes / cm ² extrusion rate of (load 1113 g) (g / 10 min).

As the α-olefin to be copolymerized with ethylene, propylene, butene-1, pentene-1, hexene-1,
4-methylpentene-1 and the like. Among them, propylene and butene-1 are preferred.

The ethylene copolymer in the present invention also includes a terpolymer obtained by copolymerizing ethylene, an α-olefin having 3 or more carbon atoms and a non-conjugated diene. Examples of such non-conjugated dienes include 1,4-hexadiene, dicyclopentadiene, and ethylidene norbornene.

The ethylene copolymer is obtained by converting ethylene and an α-olefin using a Ziegler-Natta catalyst, in particular, a catalyst comprising a vanadium compound such as vanadium oxytrichloride or vanadium tetrachloride and an organoaluminum compound. Can be produced by copolymerizing

Incidentally, the ethylene content of the ethylene copolymer used in the present invention is preferably in the range of 40 to 90 mol%, and the α-olefin content is preferably in the range of 10 to 60 mol%.

As those commercially available as the ethylene copolymer, NORSOFLEX marketed by CdF Chimie EP
(FW1600, FW1900, MW1920, SMW2440, LW2220, LW250
0, LW2550), Flex resin marketed by Nippon Unicar (DFDA1137, DEDA1138, DEFD1210, DEFD90)
42), Tahma marketed by Mitsui Petrochemical Company (A408
5, A4090, P0180, P0480) JSR-EP (EP02P, EP07P, EP57P) marketed by Nippon Synthetic Rubber Co., Ltd. and the like.

The ethylene copolymer may contain an antiblocking agent, a heat stabilizer, an antioxidant, an ultraviolet absorber, an antistatic agent, a content, a stabilizer, and the like, if necessary.

In the present invention, the radical generator to be added to the ethylene copolymer used as the intermediate layer has a half-life of 1
Those having a decomposition temperature of 130 to 300 ° C. are preferable, for example, dicumyl peroxide, 2,5-dimethyl-
2,5 di (t-butylperoxy) hexane, 2,5-dimethyl-2,5 di (t-butylperoxy) hexyne-3,
α, α'-bis (t-butylperoxyisopropyl)
Benzene, dibenzoyl peroxide, di-t-butyl peroxide and the like can be mentioned.

The compounding amount of the radical generator is 0.0 with respect to the total amount of the ethylene-α-olefin copolymer and the linear polyethylene.
1 part by weight or less, preferably 0.001 to 0.1 part by weight, more preferably selected from the range of 0.01 to 0.1 part by weight, when the compounding amount is more than 0.1 part by weight, the melt index is too low film. It is not desirable because the film tends to be cut during molding and the surface of the film is rough.

In the present invention, the method of blending a radical generator with the above ethylene copolymer to decompose the radical generator and react with the polyethylene is not particularly limited, and can be carried out, for example, by the following method.

1) At the time of inflation molding, the ethylene copolymer and the radical generator are fed simultaneously or sequentially and melt-extruded.

2) The above ethylene copolymer and the radical generator are kneaded and reacted using a kneader such as an extruder or a Banbury mixer, and then pelletized, followed by inflation molding using the pellets.

3) A master batch containing a large amount of a radical generator, that is, a linear low-density polyethylene, a branched low-density polyethylene, a polyethylene such as a high-density polyethylene, and a large amount of a radical generator (typically about 5000 to 10000 ppm) are blended.
A masterbatch in the form of pellets is prepared in advance by melt-kneading at a temperature above the melting point of polyethylene and at which the radical generator hardly reacts with the polyethylene, and the masterbatch and the ethylene copolymer are blended and blown.

The radical generator itself is used as it is or dissolved in a solvent.

By reacting the above ethylene copolymer with a radical generator, the above polyethylene causes molecular coupling to increase the high molecular weight component and obtain a modified polyethylene having a reduced melt index.

Here, the peroxide mainly crosslinks the low molecular weight component, so that the texture of the film surface is improved and the blocking is not easily caused.

As a film forming method, a common three-layer or more co-extrusion film forming method can be applied.In particular, in an inflation film forming method, an extrusion temperature of 150 to 250 ° C. and a lip gap of 0.
When molding from a 7 to 4.0 mm annular die under the conditions of a blow-up ratio of 2 to 6, a frost line height of 10 to 100 cm, and a draft rate of 3 to 70, a particularly preferred film can be obtained. The draft rate is a value calculated by the following equation.

In the T-die film forming method, the film is formed from a die having an extrusion temperature of 150 to 250 ° C. and a lip gap of 0.5 to 4.0 mm using a three-layer or more co-pressing T-die forming machine at a draft rate of 10 to 40. Note that the draft rate of the T-die was calculated with BUR = 1.

Regarding the layer ratio, the thickness of the intermediate layer is set to be equal to or greater than the total thickness of both outer layers, more preferably, the thickness of the intermediate layer is set to be equal to or greater than twice the total thickness of both outer layers, and still more preferably 3 It is preferably at least twice.

3 (x + z) ≦ y When the intermediate layer is thinner than the total thickness of both outer layers, the thermal stability at the time of molding tends to be inferior, so that the moldability and the physical properties of the film are affected.

As the layer constitution of the film or sheet of the present invention, various resin constitutions are possible as long as the inner layer (x), the outer layer (z) and the intermediate layer (y) have the above-mentioned resin constitutions.
x / y / z, x / A / y / A / z, x / y / A / z, x / A / y / z, and other layer configurations (A represents another resin). The thickness of the whole film or sheet can be arbitrarily changed depending on the purpose of use, but is usually used in the range of 10 to 300 µ.

[Examples] Hereinafter, Examples will be shown to explain the present invention in more detail.
The present invention is not limited to the following examples unless it exceeds the gist.

Example 1 As a resin for the intermediate layer, an ethylene-propylene copolymer (melt index (MI): 0.4 g / 10 min, density: 0.86 g)
/ cm ³ , elongation: 1300%, flow ratio: 17, propylene copolymerization amount: 2
2% by weight).

As the resin for the inner and outer layers, a resin obtained by adding 0.01% by weight of 2,5-dimethyl-2,5-di (t-butylperoxy) hexyl-3 as a radical generator to the above ethylene-propylene copolymer was used.

This is a DELSA 40mmφ extruder 3 made by Modern Machinery
Based on an annular slit diameter 250mmφ, lip clearance 1.2mm
Using a three-layer inflation molding machine equipped with an inflation die and a cooling air ring, with an extrusion temperature of 150
℃, inner and outer layer extrusion rate 4kg / hr, middle layer extrusion rate 20kg / hr, blow-up ratio (BUR) 3.0, frost line height 70cm, take-off speed 6.8m / min.
A 0μ blown film was obtained.

Table 1 shows the results of measuring various physical properties of the obtained film. The physical properties in Table 1 were measured by the following measurement methods.

a) Blocking property of film A defective film in which two superimposed films in an inflation molded film were completely fused and could not be peeled off at all.

A commercially available cellophane tape is stuck on both sides of the edge of the blocked film. The cellophane tape does not come off when pulled, but it comes off when using a gum tape.

In the same manner, those which could be easily peeled off with cellophane tape were regarded as good.

b) Coefficient of friction (COF) of the film 160 × 80 and 160 with the extrusion direction of the film as the longitudinal direction
Cut out two test pieces of × 63.5 mm.

A 160 × 80 mm film is fixed to a plate with felt attached to the tiltable surface. (The tilt direction is the longitudinal direction.) A 160 × 63.5 mm film is fixed so as to cover the lower surface of a 1 kg weight having a lower surface of a 100 × 60 mm rectangle (with a sponge attached).

The weight is placed on the film attached to the inclined plate, the inclined plate is gradually inclined, and the angle at which the weight starts to slide (tanθ)
Measure

 The same operation is repeated three times and the average value is used.

c) Tensile elongation The tensile elongation was measured in accordance with the measuring method of elongation at break in the section of tensile test of JIS K6301. 900% or more was regarded as good.

d) Thermal stability Under the conditions of Example 1, evaluation was made by the number of burnt gels discolored from brown to black one hour after the start of inflation film formation. 1 in 30 minutes
If it was less than or equal to ケ, it was considered a problem pear.

Examples 2-3 Mixing conditions The layer ratio was changed as shown in Table 1. The resin and the organic peroxide were blended by a Henschel mixer, and then kneaded into pellets at 190 ° C. using a Derser 50 mmφ extruder. The layer ratio was changed by keeping the entire extrusion rate constant and changing the extrusion rate ratio of each layer. Otherwise, the same method as in Example 1 was used.

Example 4 Using the resin shown in Table 1, a film was formed by the following T-die forming method.

Extrusion using a T-die molding machine equipped with three 40mmφ extruders manufactured by Sumitomo Heavy Industries, Ltd. equipped with a T-die with a lip clearance of 0.7mm, a total length of 480mm and a cooling air knife (110mm from the die lip, at room temperature) Temperature 180 ° C, middle layer extrusion rate 3.4kg / hr, inner and outer layer extrusion rate 1.7kg / hr each, winding speed 8m /
The film was extruded into a film under the conditions of a draft rate of 17.5 and cooled at a cooling roll temperature of 20 ° C. to form a film having a thickness of 40 μm. Layer ratio 1/2/1.

Comparative Examples 1 to 4 Films were formed in the same manner as in Example 1 or Example 4, except that the layer ratio, the resin used, and the like were changed to those shown in Table 2.

The physical properties of the obtained film were measured and are shown in Table 2.

[Effects of the Invention] According to the production method of the present invention, a film having high extensibility can be stably obtained with high efficiency, and it can be used as a leak-proof gather portion of a diaper, a back sheet V process type casting film, and the like. Can be used to provide a suitable film.

Claims (1)

(57) [Claims] Upon 1. A producing stretch film or sheet of the multilayer structure, the middle layer density is ethylene copolymer is less than 0.91 g / cm ^3, the outer layers density 0.91 g / cm ³ less than the ethylene copolymer 0.001 to 0.1 part of a radical generator per 100 parts by weight of the polymer
A process for producing an extensible film or sheet, comprising a multilayer coextruded film or sheet obtained by adding or reacting parts by weight, wherein the thickness of the intermediate layer is not less than the total thickness of both outer layers.