JP3499652B2 - Moisture permeable film - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moisture-permeable film which has excellent moisture permeability and air permeability and also has flexibility.

[0002]

2. Description of the Related Art A porous film obtained by molding and stretching a resin such as polyethylene into a film or a sheet has excellent breathability, moisture permeability and waterproofness, and therefore, as a moisture permeable film, it can be used as a clothing or medical material. It is used in a wide range of applications such as filter materials.

A moisture permeable film is formed by a method in which a non-porous film is subjected to electric discharge machining and squeezing, or calcium carbonate particles are added to a resin such as polyethylene, and the resulting film is shaped into an acid to treat calcium carbonate. It is produced by a method such as elution, but in general, a resin composition containing a filler such as calcium carbonate is formed into a film and stretched uniaxially or biaxially to form microvoids (micropores).
Is manufactured by forming.

[0004]

However, in the case of a composition containing polyethylene resin as a main component, when a film-like molded product is generally stretched to produce a moisture-permeable film,
There is a problem that the moisture-permeable film has high rigidity and lacks flexibility, and when it is uniaxially stretched, tear strength and tensile breaking elongation in the stretching direction are lowered. Further, as a means for solving such inconvenience, there is a method of reducing the draw ratio, but in this case, there is a problem that the formation of microvoids is insufficient and the film does not have sufficient air permeability and moisture permeability. .

Further, when the composition is formed into a film, there is a problem that the melt extruded from the die causes necking or draw resonance, resulting in an uneven thickness of the moisture permeable film. The draw resonance refers to a phenomenon in which the width and thickness of the melt periodically pulsate when the melt extruded from the die is drawn.

[0006]

Means for Solving the Problems The inventors of the present invention have diligently studied to solve the above-mentioned inconvenience, and as a result, use a composition containing calcium carbonate and a resin having predetermined physical properties in a predetermined ratio, Further, by setting the melt tension of the composition within a predetermined range, it was found that the porous film can be provided with excellent moisture permeability, air permeability, flexibility, various strengths, and moldability, and the present invention was completed. .

That is, according to the present invention, 55 to 80 parts by weight of linear low density polyethylene (hereinafter referred to as LLDPE), 5 to 30 parts by weight of ethylene-α-olefin copolymer, and branched low density polyethylene. A moisture permeable film formed by molding a composition containing 80 to 200 parts by weight of calcium carbonate based on 100 parts by weight of a resin component composed of 5 to 20 parts by weight (hereinafter, referred to as LDPE).
The LLDPE is obtained by copolymerizing ethylene with an α-olefin having 4 to 12 carbon atoms and has a density of 0.905.
~ 0.940 g / cm ³ , melt flow rate 0.5
-10 g / 10 min. The ethylene-α-olefin copolymer is obtained by copolymerizing ethylene with an α-olefin having 3 to 10 carbon atoms and has a density of 0.85.
0 to 0.900 g / cm ³ , melt flow rate of 0.
5-15 g / 10 min. , DSC peak temperature is 10
Stress at 0 ° C or less and 200% elongation is 10 to 80 kg / c
m ^2, and the LDPE is obtained by polymerizing a high pressure process ethylene, its melt flow rate is 0.
5-10 g / 10 min. And a moisture permeable film having a melt tension of the composition of 1.5 to 4.0 g.

Further, according to the present invention, there is provided a moisture-permeable film obtained by molding the above composition by a T-die method or the like and further stretching it. The above moisture-permeable film has a thickness of 80 μm or less and a moisture permeability of 1000 g / m ² · 24 h.
rs. As described above, the tear strength is preferably 10 g or more.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The moisture-permeable film of the present invention is LL
DPE, ethylene-α-olefin copolymer, LDP
It is formed by molding a composition containing E and calcium carbonate.

LLDPE contains ethylene and α-olefin in the presence of a Ziegler type catalyst, a metallocene type catalyst, etc.
Although it is obtained by copolymerization at low pressure, it has many short chain branches originating from the comonomer α-olefin and exhibits low density. In addition, compared to conventional branched polyethylene, tensile strength,
It is characterized by excellent impact strength, ESCR (environmental stress fracture resistance) and heat sealability. LLDPE imparts particularly strength and durability to the moisture-permeable film.

In the moisture-permeable film of the present invention, LLD
The PE content is 55 in 100 parts by weight of LLDPE, ethylene-α-olefin copolymer, and LDPE.
It is preferably -80 parts by weight, more preferably 60-75 parts by weight.

In the LLDPE used in the present invention, it is preferable to use an α-olefin having 4 to 12 carbon atoms, more preferably 6 to 8 carbon atoms. Specific examples of the α-olefin include butene-1, hexene-1, 4-methylpentene-1, octene and the like.

The density of LLDPE (JIS K 67
It measured according to the method of 60. The same applies hereinafter. ) Is preferably 0.905 to 0.940 g / cm ³ .

Melt flow rate (JIS K 676
It measured according to the method of 0. The same applies hereinafter. ) Is 0.
5-10 g / 10 min. Is preferred. Melt flow rate is 0.5 g / 10 min. If less than, stretching unevenness occurs and moldability becomes unstable,
Also, 10 g / 10 min. This is because the strength is adversely affected if it exceeds.

The ethylene-α-olefin copolymer is obtained by copolymerizing ethylene and α-olefin, and imparts flexibility to the moisture-permeable film and improves tear strength and tensile breaking elongation. Further, by facilitating the openness at the time of stretching, good moisture permeability is imparted to the moisture permeable film.

In the moisture-permeable film of the present invention, the content of the ethylene-α-olefin copolymer is 5 to 30 parts by weight based on 100 parts by weight of LLDPE, ethylene-α-olefin copolymer and LDPE. It is preferably 10 to 25 parts by weight, and more preferably 10 to 25 parts by weight. When it is less than 5 parts by weight, flexibility and tear strength and tensile elongation at break are insufficient, and when it exceeds 30 parts by weight, rigidity is insufficient.

In the ethylene-α-olefin copolymer used in the present invention, the α-olefin has 3 to 10 carbon atoms.
It is preferable to use one having 10 carbon atoms, and more preferably one having 3 to 8 carbon atoms. Specific examples of the α-olefin include propylene, butene-1, hexene-1,
Octene-1 etc. are mentioned.

[0018] Also, the density of the ethylene -α- olefin copolymer is preferably from 0.850~0.900g / cm ^3, more preferably 0.860~0.880g / cm ^3.

The melt flow rate is 0.5 to 15 g / 1
0 min. Is preferably 0.8 to 8 g / 10
min. Is more preferable.

The peak temperature of DSC is preferably 100 ° C. or lower, more preferably 20 to 60 ° C. When it exceeds 100 ° C, the flexibility is ethylene-α-
This is because the tear strength, the tensile elongation at break, and the moisture permeability are insufficient, though they are improved as compared with the case where the olefin copolymer is not added. The DSC peak temperature is the main melting peak temperature observed in differential scanning calorimetry, and is defined by JIS
It was measured according to the method of K 7121.

Further, the stress at 200% elongation is JIS
10 to 80 kg / c as measured by K6301
It is preferably m ² and more preferably 15 to 70 kg / cm ² . The ethylene-α-olefin copolymer is an elastomer component, and its tensile stress has a close relationship with the stress state around the calcium carbonate particles.
It has a great influence on the peeling of the matrix on the surface of the calcium carbonate particles and the film opening process. That is, 20
When the stress at 0% elongation is less than 10 kg / cm ² , the open state becomes irregular and coarse pores are formed, resulting in insufficient strength of the film and reduced water resistance.
On the other hand, when it exceeds 80 kg / cm ² , the pores are insufficient, the air permeability and the moisture permeability are lowered, the orientation effect is increased, and the tear strength and the tensile breaking elongation are lowered.

LDPE is a branched low density polyethylene obtained by polymerizing ethylene by a high pressure method,
It functions to improve melt moldability by increasing the melt tension of the composition. In the moisture-permeable film of the present invention, L
The content of DPE is 5 to 100 parts by weight consisting of LLDPE, ethylene-α-olefin copolymer, and LDPE.
It is preferably 20 parts by weight, more preferably 8 to 17 parts by weight. If it is less than 5 parts by weight, the formability is adversely affected, and if it exceeds 20 parts by weight, the tear strength is insufficient.

The LDPE used in the present invention has a melt flow rate of 0.5 to 10 g / 10 min. Is preferred. Melt flow rate is 0.5 g / 10 min.
If it is less than 10 g / 10 min., Uneven stretching may occur and the strength balance of the film may be adversely affected. If it exceeds, the strength is insufficient. The strength balance is the strength ratio between the stretching direction of the film (hereinafter abbreviated as MD) and the direction perpendicular to the film (hereinafter abbreviated as TD), that is, MD.
Strength / TD strength. It is usually expressed using tensile strength, and the larger the value, the worse the strength balance.

In the present invention, calcium carbonate may be a heavy one or a light one, but 0.8 to 4.
It is preferable to use one having an average particle size of 0 μm and having its surface treated with a fatty acid in order to improve dispersibility in the resin. When the average particle size is less than 0.8 μm, it becomes difficult to uniformly disperse the particles during kneading, and calcium carbonate agglomerates are likely to occur in the film, and uniform stretching becomes difficult. This is because breakage is likely to occur. Further, when the average particle size exceeds 4.0 μm, the pores become large, so that the water resistance of the film is
Strength and the like decrease.

Calcium carbonate is preferably added in an amount of 80 to 200 parts by weight with respect to 100 parts by weight of the resin component consisting of LLDPE, ethylene-α-olefin copolymer and LDPE. If it is less than 80 parts by weight, the air permeability and moisture permeability will be insufficient, and if it exceeds 200 parts by weight, the water resistance, strength and moldability of the film will be reduced.

In the present invention, LLDPE, ethylene-
The composition composed of the α-olefin copolymer, LDPE, and calcium carbonate needs to have a melt tension of 1.5 to 4.0 g, and more preferably 1.7 to 3.5 g. More preferably, it is 1.8 to 3.2 g. The melt tension means a tension in a stretching direction when a strand formed by extruding a composition melted at 190 ° C. from a capillary viscometer (orifice diameter 1 mm) is continuously stretched. If the melt tension is less than 1.5 g, necking or draw resonance occurs when the composition is molded into a film, and the thickness and width of the film-shaped molded product become uneven. Therefore, the thickness and width of the product after stretching become non-uniform and the product value is impaired. When the melt tension exceeds 4.0 g, the melt moldability is good, but uneven drawing occurs during drawing, and mottled patterns are formed on the product, which impairs product value.

The melt tension generally shows a larger value as the proportion of the high molecular weight component in the composition increases, that is, as the melt flow rate decreases. Further, the larger the number of long chain branches of the polymer in the composition, the larger the value. Usually, the melt tension of the composition is a value obtained by averaging the melt tension of each component. Therefore, in the present invention, the LDPE having a long chain branch plays an important role in controlling the melt tension of the composition.

The moisture permeable film of the present invention has a thickness of 80 μm.
Hereafter, the water vapor transmission rate is 1000 g / m ² · 24 hrs. that's all,
When the tear strength is 10 g or more, there is no fear of stuffiness, the skin feels good, and the strength balance in the vertical and horizontal directions is good, for clothing,
A breathable film suitable for medical purposes.

Needless to say, the moisture-permeable film of the present invention may contain general additives such as antioxidants, flame retardants, antistatic agents, lubricants and dispersants, if necessary. .

Next, the method for producing the moisture-permeable film of the present invention will be described. As a method of manufacturing a moisture permeable film,
A method of electric discharge machining into a non-porous film for squeezing, a method of forming a composition into a film shape and then subjecting the composition to acid treatment to elute calcium carbonate, or a composition formed into a film shape uniaxially or biaxially And the like. The moisture-permeable film of the present invention may be produced using any of these methods, but is generally used is
This is a method in which the composition is formed into a film and then uniaxially stretched. Therefore, this method will be described in detail. First, each component and other blended composition are uniformly melted and kneaded by an extruder to produce pellets. Next, the pellets are formed into a film and then stretched in one direction to obtain a moisture permeable film.

In the step of producing pellets, the resin, calcium carbonate and other compounding compositions are mixed using an ordinary blender such as a corn blender or a ribbon blender, or a mixer such as a Henschel mixer, and then single screw extrusion. Kneading and pelletizing using a kneader such as a machine, a twin-screw extruder, a Banbury mixer, a mixing roll.

Next, the pellets are used to form a film. Specifically, both the inflation method and the T-die method are possible, but the T-die method has better thickness accuracy of the film-shaped molded article. That is, by stretching a film-shaped molded product having a uniform thickness, a good moisture-permeable film with less variation in various physical properties can be obtained.

For stretching the film-shaped molded product, a normal roll stretching machine is used, and after stretching in the longitudinal uniaxial direction, it is relaxed and heat-set. By stretching the film-shaped molded product, microvoids are physically generated between the calcium carbonate and the resin, so that the film is provided with air permeability and moisture permeability. In order to generate such microvoids on the film, it is about 120 to 50 depending on the use application.
It is suitable to perform 0% stretching, and the size of the fine pores is preferably 0.1 to 100 μm. This is because if the size of the fine pores is 0.1 μm or less, the air permeability and moisture permeability are poor, and if it is 100 μm or more, the waterproofness is adversely affected.

[0034]

EXAMPLES The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the following examples.

(Example 1) The melt flow rate was 2.5.
g / 10 min. , 65 parts by weight of LLDPE having a density of 0.915 g / cm ³ , and a melt flow rate of 3.5 g
/ 10 min. , Density 0.87 g / cm ³ , DSC peak temperature 38 ° C, stress at 200% elongation 60 kg
/ Cm ² ethylene-α-olefin copolymer 20
Weight part, and melt flow rate are 2.0 g / 10 mi
n. 1 part of calcium carbonate having an average particle size of 2.0 μm per 100 parts by weight of 15 parts by weight of LDPE.
20 parts by weight were added to prepare a composition having a melt tension of 2.5 g. Apply this composition to the tip with a T-die (die width, 7
00 mm, die lip, 1.0 mm) was used to mold at a molding temperature of 220 ° C. and a take-up speed of 25 m / min. Was formed into a film. This molded product was stretched 2.0 times in the flow direction at 40 ° C. using a roll stretching machine, then relaxed by 10% at 95 ° C. and heat-set, to give a moisture-permeable film having a thickness of 38 μm. Was manufactured.

The air permeability, moisture permeability, water resistance, tear strength, tensile elongation at break, and load at 3% elongation of the obtained moisture permeable film were evaluated by the following methods, and the melt molding stability and The occurrence of stretching unevenness was observed. The results are shown in Table 1. Air permeability Measurement was performed by the Gurley method. Moisture vapor transmission rate according to JIS Z 0208, 40 ° C, 90% R.V. H. Was measured at. Water resistance The measurement was performed according to JIS L 1092. Tear strength Measurement was performed in the longitudinal direction according to JIS L 8116. Tensile Fracture Elongation Measured in the longitudinal and transverse directions according to JIS K 7127. Load at 3% elongation Measurement was performed in the longitudinal direction according to JIS K 7127.

(Examples 2 to 4) A moisture permeable film was prepared in the same manner as in Example 1. LLD used in Table 1
PE, ethylene-α-olefin copolymer, LDPE,
And the physical properties of calcium carbonate, the thickness of the produced moisture-permeable film, and the draw ratio. Various evaluations were performed on the manufactured moisture-permeable film in the same manner as in Example 1. The results are shown in Table 1.

(Comparative Examples 1 to 5) A moisture permeable film was prepared in the same manner as in Example 1. LLD used in Table 1
PE, ethylene-α-olefin copolymer, LDPE,
And the physical properties of calcium carbonate, the thickness of the produced moisture-permeable film, and the draw ratio. Various evaluations were performed on the manufactured moisture-permeable film in the same manner as in Example 1. The results are shown in Table 1.

[0039]

[Table 1] The amounts of LLDPE, ethylene-α-olefin copolymer, and LDPE added are values in 100 parts by weight of these three components. The amount of calcium carbonate added is L
LDPE, ethylene-α-olefin copolymer, and L
The value is based on 100 parts by weight of DPE.

The moisture permeable films of the examples have good results in terms of air permeability, moisture permeability, water resistance, tear strength, tensile breaking elongation, load at 3% elongation, melt molding stability, and stretching unevenness. showed that. On the other hand, in the moisture-permeable film of Comparative Example 1, an ethylene-α-olefin copolymer having a stress at 200% elongation of more than 80 kg / cm ² is used, but the tear strength and the tensile elongation at break are low. Indicated.
Further, the moisture-permeable film of Comparative Example 2 uses an ethylene-α-olefin copolymer having a stress at 200% elongation of less than 10 kg / cm ² , but has a low water resistance. The moisture-permeable film of Comparative Example 3 is LDPE.
Therefore, the melt tension was less than 1.5 g, but the melt molding stability was low. The moisture permeable film of Comparative Example 4 had a melt flow rate of 0.5 g / 10 mi.
n. Since the LDPE of less than the above was used, the melt tension exceeded 4.0 g, and uneven stretching was observed. The moisture-permeable film of Comparative Example 5 contained no ethylene-α-olefin copolymer, had a large load at 3% elongation, and exhibited low values in tear strength and tensile elongation at break.

[0041]

The moisture-permeable film of the present invention comprises a composition containing calcium carbonate and a resin having predetermined physical properties in a predetermined ratio, and the melt tension of the composition is within a predetermined range. Therefore, breathability, breathability, flexibility,
Excellent in tensile strength, tensile elongation, tear strength, water resistance, and moldability.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiaki Takahashi 314-2 Nishihiro, Ichihara City, Chiba Prefecture (72) Inventor Ryoji Nishijima 2-15-6 Harujiro, Sakura City, Chiba Prefecture (56) Reference JP-A-7- 265358 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08L 23/00-23/36 C08K 3/00-13/08 C08J 5/18

Claims (3)

(57) [Claims] 1. 100 parts by weight of a resin component consisting of 55 to 80 parts by weight of linear low-density polyethylene, 5 to 30 parts by weight of ethylene-α-olefin copolymer, and 5 to 20 parts by weight of branched low-density polyethylene. A linear, low-density polyethylene is a moisture-permeable film formed by molding a composition containing 80 to 200 parts by weight of calcium carbonate, wherein the linear low-density polyethylene has 4 to 12 carbon atoms.
Bruno α- olefin of obtained by copolymerization, the density of 0.905~0.940g / cm ^3, melt flow rate is 0.5 to 10 g / 10min. And the ethylene-α-olefin copolymer is obtained by copolymerizing ethylene with an α-olefin having 3 to 10 carbon atoms,
The density is 0.850 to 0.900 g / cm ³ , and the melt flow rate is 0.5 to 15 g / 10 min. , DSC
Has a peak temperature of 100 ° C. or less and a stress at 200% elongation of 10 to 80 kg / cm ² , and the branched low-density polyethylene is obtained by polymerizing ethylene by a high-pressure method, and its melt flow rate is 0. 5-10 g / 10 min. And a melt tension of the composition is 1.5 to 4.0 g. 2. The moisture-permeable film according to claim 1, which is obtained by molding the composition by a T-die method. 3. The thickness is 80 μm or less, and the water vapor permeability is 1000.
g / m ² · 24 hrs. As described above, the tear strength is 10 g or more, and the moisture-permeable film according to claim 1 or 2.