JPH0764942B2 - Method for producing porous sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a porous sheet.

Specifically, by molding a composition comprising a polyolefin resin, a filler and a plasticizer into a sheet and stretching the sheet, the sheet has a good appearance and texture, is excellent in strength, and has a suitable moisture permeability. The present invention provides a method for producing a porous sheet having:
It can be applied to various uses such as packaging materials, battery separators, excess materials, and sanitary / medical materials.

[Conventional technology and its problems]

Heretofore, many attempts have been made as a means for producing a porous sheet by blending a filler with a polyolefin resin and uniaxially or biaxially stretching a sheet obtained by melt molding. However, in these sheets, problems remain in the anisotropy of the physical properties of the uniaxially stretched product, especially the tear strength in the longitudinal direction (stretching direction), and further the surface strength, and in the biaxially stretched product, the physical properties of the sheet remain. Although there is no problem in anisotropy, there is a problem in stretchable elongation surface strength, and both tend to have high rigidity in general, which is a defect depending on the application.

One of the methods for improving the anisotropy of sheet physical properties and surface strength is to carry out stretching at the lowest possible ratio to realize porosity, and as a method for imparting flexibility to the sheet, a low melting point is used. A method of adding a polymer, a rubber-like substance, a plasticizer or a surfactant can be considered, but molding stability and porosity, stretchability, mechanical properties such as tear strength and tensile strength, and further a balance of physical properties such as surface strength. Those who have satisfied the above have not yet been found.

As a method for improving the drawbacks of such a conventional porous sheet, the present applicant has disclosed in JP-A-57-47334 a composition comprising a polyolefin resin mixed with a filler and liquid polybutadiene or liquid polybutene. It was proposed in 58-15538 to use a composition comprising a linear low density polyethylene resin, a filler and a polyhydroxy saturated hydrocarbon.

Further, JP-A-61-144331 proposes a method of using polyester plasticizer such as adipic acid ester or epoxy-based plasticizer such as epoxidized soybean oil, and JP-A-62-10141 proposes a method of using triglyceride.

However, even in these methods, the film strength,
It has not been possible to obtain a porous sheet that satisfies all the properties such as moisture permeability, appearance and feel.

[Object of the Invention]

INDUSTRIAL APPLICABILITY The present invention has excellent extrudability in melt molding and also exhibits particularly excellent molding stability, and a uniaxially stretched sheet obtained by melt molding has mechanical properties such as tear strength and tensile strength and moisture permeability. Balance is good, both uniaxially stretched products and biaxially stretched products have strong surface strength and excellent stretchability, and particularly in low-magnification stretching, there are very few stretching spots caused by uneven stretching,
It is also an object of the present invention to provide a highly flexible porous sheet.

[Structure of Invention]

The gist of the present invention is to produce a porous sheet by stretching a sheet obtained by melt-molding a composition containing a polyolefin resin, a filler and a plasticizer, as a plasticizer, α-olefin and α, A method for producing a porous sheet is characterized by using a copolymer with a β-unsaturated dicarboxylic acid dialkyl ester.

Hereinafter, the present invention will be described in more detail.

As the polyolefin resin used in the present invention, high density polyethylene, medium density polyethylene and linear low density polyethylene are used alone or as a mixture of two or more kinds, and the melt index of the polyethylene is 0.
A range of 01 to 10 g / 10 min (measured by ASTM D-1238-70 at 190 ° C. and 2.16 kg) is preferable. Further, a branched low density polyethylene obtained by a high pressure method may be partially mixed with the polyethylene.

Crystalline polypropylene is also used. As the crystalline polypropylene, a homopolymer of propylene or a copolymer of propylene and other α-olefin is used alone or as a mixture of two or more kinds. Additives such as a heat stabilizer, an ultraviolet absorber, an antistatic agent, a pigment and a fluorescent agent can be added to these polyolefin resins according to a conventional method.

As the filler, an inorganic filler and an organic filler are used, and as the inorganic filler, calcium carbonate, talc, clay, kaolin, silica, diatomaceous earth, magnesium carbonate, calcium sulfate, aluminum hydroxide, zinc oxide, magnesium hydroxide. , Calcium oxide, magnesium oxide, titanium oxide, alumina, mica, asbestos powder, glass powder, shirasu balloon, zeolite, silicate clay, etc. are used, and particularly calcium carbonate, talc, clay, silica, diatomaceous earth, barium sulfate, etc. are suitable. is there.

As the organic filler, wood powder, cellulosic powder such as pulp, or the like is used. These may be used alone or as a mixture.

The average particle size of the filler is preferably 30 μm or less, more preferably 10 μm or less, most preferably 5 μm or less. If the particle size is too large, the denseness of the pores of the stretched product deteriorates. The surface treatment of the filler is dispersibility in resin,
Furthermore, in terms of stretchability, it is preferably carried out,
Treatment with fatty acids or their metal salts gives favorable results. The amount of surface treatment with fatty acid or its metal salt is
It is preferably 10 parts by weight or less with respect to 100 parts by weight. If the amount of surface treatment is large, white smoke may be generated or foaming may occur during kneading, granulation and molding, which is not preferable.

Α-olefin used as a plasticizer in the present invention
The α, β-unsaturated dicarboxylic acid dialkyl ester copolymer is obtained by solution polymerization or solvent-free polymerization of α-olefin and α, β-unsaturated dicarboxylic acid dialkyl ester in the presence of a radical polymerization initiator according to a conventional method. It is legally obtained by copolymerization and has a weight average molecular weight of 1,00.
The range of 0 to 20,000 is preferable.

The carbon number of the α-olefin is preferably in the range of 2 to 40, and particularly in the range of 2 to 20, it is easy to give a liquid copolymer, and the effect as a plasticizer in the present invention is particularly large.

On the other hand, as the alcohol used as the raw material for the α, β-unsaturated dicarboxylic acid dialkyl ester, an alcohol having 1 to 40 carbon atoms can be used, but an alcohol having 1 to 30 carbon atoms such as methanol, ethanol, butanol is practical. Yes preferred.

Preferred examples of the α, β-unsaturated dicarboxylic acid include maleic acid or fumaric acid and itaconic acid.

The molar ratio of the α, β-unsaturated dicarboxylic acid dialkyl ester and the α-olefin in the copolymer can be appropriately changed by changing the concentration ratio of both during the copolymerization reaction, but usually the dialkyl ester is used. The molar ratio of / α-olefin is in the range of 0.5 to 2, preferably 1.0 to 1.5.

Specific examples of the copolymer of α-olefin and α, β-unsaturated dicarboxylic acid dialkyl ester include the following.

α-olefin / maleic acid dimethyl ester copolymer (the following structural formula I), α-olefin / maleic acid diethyl ester copolymer (the following structural formula II) Structural formula I R: C ₁₀ -C ₁₂ α-olefin structural formula II R: C _{14 to} C ₁₆ α-olefin Polyolefin resin, filler and α-olefin-
The blending ratio of the α, β-unsaturated dicarboxylic acid dialkyl ester copolymer is preferably 25 to 400 parts by weight of the filler, and more preferably 60 to 300 parts by weight, with respect to 100 parts by weight of the polyolefin resin. The copolymer is also 1 to 10
0 parts by weight is preferable, and 1 to 50 parts by weight is more preferable.

If the blending amount of the filler is too small, the pores of the stretched sheet are not sufficiently formed and the degree of porosity is reduced, while if the blending amount is too large, the kneadability and dispersibility deteriorate, and And the surface strength is reduced. On the other hand, if the amount of the plasticizer copolymer blended is too large, satisfactory kneadability cannot be obtained, and the sheet formability and stretchability cannot be secured.

An ordinary blender or mixer is used for mixing the polyolefin resin, the filler and the copolymer.

As the mixer, a drum, a tumbler type mixer, a ribbon blender, a Henschel mixer, a super mixer or the like is used, and a high speed stirring type mixer such as a Henschel mixer is preferable.

Next, the kneading of the mixture is appropriately carried out by a conventionally known device such as an ordinary screw extruder, a twin screw extruder, a mixing roll, a Banbury mixer, a twin screw type kneader.

Molding of the sheet may be performed according to a normal sheet molding apparatus and molding method, and inflation molding with a circular die, T die extrusion molding with a T die, and the like may be appropriately adopted.

When the formed sheet is stretched, roll stretching is usually used in the case of uniaxial stretching, but tubular stretching may be used in which the uniaxial direction (take-up direction) is relatively emphasized. The stretching may be performed in one stage or in multiple stages of two or more stages.

In biaxial stretching, it is possible to perform low-magnification stretching in the same way as uniaxial stretching, even in simultaneous and sequential stretching, and at least in one direction 1.1
Double stretching allows uniform stretching and porosity. The stretching ratio at which porosity is achieved and which enables uniform stretching is 1.
1 to 3.0 times.

Furthermore, the dimensional accuracy of the film can be stabilized by performing heat treatment after stretching in both uniaxial stretching and biaxial stretching.
Further, surface treatment such as known corona treatment and frame treatment can be performed.

In the present invention, the porous sheet is formed to have a thickness of 0.01 to 0.5 mm, preferably 0.02 to 0.3 mm, and what is generally called a film is also included in the sheet of the present invention.

〔Example〕

Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist.

The raw materials used in the following Examples and Comparative Examples are listed in Tables 1 to 3.

Examples 1 to 16 and Comparative Examples 1 to 15 The polyolefin resins shown in Table 1 below and the fillers shown in Table 2 below were stirred and mixed in a Henschel mixer, and the plasticizer shown in Table 3 below was added to the mixture. Stir-mixed to obtain 10 kg of mixture. The types and compositions of the raw material components used are shown in Tables 4 and 5.

40 kg of the mixture obtained by repeating the above operation 4 times was kneaded and granulated by a twin-screw kneader (DSM-65, manufactured by Japan Steel Works, Ltd.), and then inflation-molded by a 50 mmφ extruder under the following conditions to obtain a thick film. A raw film having a size of 65 μm was obtained.

Cylinder temperature: 170-190-210 ℃ Head and die temperature: 210-210 ℃ Collection speed: 10m / powder Blow ratio: 2.5 Fold diameter: 550mm The obtained film was uniaxially stretched by a roll stretching machine under the following conditions.

Stretching temperature: 70 ° C. However, 60 ° C. in Examples 11 and 14 and 80 in Examples 12 and 16.
Performed at ° C.

Stretching ratio: 1.5 to 2.5 Stretching density: 20 m / min Table 5-5 to 7 shows uniform fluidity and bubble stability at the time of forming the raw film, the stretching conditions and the physical properties of the obtained stretched film.
Shown in.

The methods for measuring the moldability and physical property evaluation items are as follows.

1) Biaxial kneading When granulating raw material pellets by DSM, ○: Stable granulation with little vent up (from vent hole) and surging is possible ×: Stable granulation with vent up or surging, 2) Uniform flow In the inflation molding, ◯: The molten resin can be blown out uniformly from the entire circumference of the die. ×: The molten resin cannot be blown out uniformly from the entire circumference of the die. 3) Bubble stability Inflation molding ◎: No bubble fluctuation ○: Little bubble fluctuation Δ: Bubble fluctuation ×: Molding difficulty 4) Stretchability ◎: No cutting, uniform stretching, no stretching unevenness observed ○: No cutting, stretching unevenness Not observed Δ: No cutting, stretch unevenness is observed X: Cutting or stretch unevenness is noticeable 5) Porosity Calculated from the density of the film by the following formula D ₀ : Density of original film (g / cm ³ ) D: Density of stretched film (g / cm ³ ) 6) Tensile strength According to ASTM D 882-64T.

10mm width x 50mm length, tensile speed 500mm / min 7) Tear strength According to JIS P-8116.

There is a notch. 14mm width x 110mm length.

8) Water vapor permeability According to ASTM E96-80 (C).

9) Flexibility Feeling by hand, it was judged according to the following criteria.

◎: Extremely soft ○: Soft △: Slightly hard ×: Hard 10) Surface strength A cellophane tape was attached to the film surface, and the peeling state of the surface when quickly peeled off was observed and judged according to the following criteria.

◎: No surface peeling ○: Almost no surface peeling △: Some surface peeling ×: Large surface peeling Examples 17 to 32, Comparative Examples 18 to 22 Pellets composed of the composition containing the polyolefin resin, the filler and the plasticizer shown in Tables 8 and 9 were prepared in the same manner as in Examples 1 to 16, and the pellets were prepared. A 65 mmφ extruder was used to perform T-die molding under the following conditions to obtain a 90 μm-thick original film.

Cylinder temperature: 170-200-230 ° C Head, die temperature: 230-230 ° C Die width: 450mm Trading speed: 10m / min Original width: 330mm The obtained film was uniaxially stretched by a roll stretching machine under the following conditions.

Stretching temperature: 60 to 80 ° C. Stretching ratio: 1.2 to 2.5 Stretching speed: 20 m / min The obtained longitudinally stretched film was transversely stretched by a tenter under the following conditions.

Stretching temperature: 80 to 110 ° C. Stretching ratio: 2.0 to 3.0 Stretching speed: 20 m / min Raw material composition is shown in Tables 8 and 9, and stretch stability during transverse stretching and stretchability and physical properties of the obtained film are shown in Table- Shown in 10,11.

Here, the stretching stability in tenter transverse stretching was evaluated as follows.

◯: Stable stretching is possible without stretching breaks Δ: Stretching breakage occasionally occurs ×: Stretching breakage is large and the film does not connect [Advantages of the Invention] In the method of the present invention, (1) porosity is achieved at a low draw ratio.

(2) Stretching stress is low and low temperature stretching is possible.

(3) Uniform stretching is possible at a low stretching ratio.

The porous sheet obtained has the following characteristics: (1) Almost no stretching unevenness is observed.

(2) Excellent moisture permeability and gas permeability, and high water pressure resistance.

(3) It has excellent flexibility.

(4) There is little anisotropy in physical properties.

(5) Tear strength and tensile strength are high.

(6) The heat sealability is good and shrink wrapping is possible.

(7) Easy incineration and does not generate harmful gas.

It can be applied to various uses such as clothing, packaging, battery separator, excess material, and medical use.

Claims (1)

[Claims] 1. When a sheet obtained by melt-molding a composition containing a polyolefin resin, a filler and a plasticizer is stretched to produce a porous sheet, α-olefin and α, β are used as a plasticizer. -A method for producing a porous sheet, which comprises using a copolymer with an unsaturated dicarboxylic acid dialkyl ester.