JPS62201941A - Production of gas-permeable film or sheet - Google Patents

Abstract

PURPOSE:To obtain the titled film or sheet having excellent stretchability, gas permeability and moisture permeability, by extruding a powder compsn. obtd. by blending a liner low-density PE with specified calcium carbonate, elevating the temp. of the mixture with stirring and cooling it. CONSTITUTION:100pts.wt. linear low-density PE (A) cong. optionally an ethylene/ propylene copolymer, PP, etc. added thereto is mixed with 80-200pts.wt. calcium carbonate (B) composed of fine particles and coarse particles in a weight ratio of 0.1 to 10, wherein the particles have a particle size of 1-6mu and the ratio of the average particle size of the fine particle component to that of the coarse particle component is not lower than 1.5, thus obtaining a powder mixture. The mixture is heated to a temp. of not lower than the m.p. of the component A, but not higher than the decomposition temp. of the component A with stirring to form a coherent power. The powder is then cooled to a temp. of not higher than the m.p. of the component A to form a powder copsn. The compsn, is extruded into a film or sheet, which is then oriented to obtain the titled film or sheet.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a manufacturing method. Specifically, the present invention relates to a method for producing an air permeable film or sheet having improved air permeability and moisture permeability from a composition obtained by blending calcium carbonate particles as a filler into a resin.

Conventional technology Conventionally, raw films obtained by blending polyolefin resin with calcium carbonate as a filler and melt-molding,
Alternatively, a method of producing a film or sheet with good air permeability by stretching a sheet is widely practiced.

However, the quality of the molded product obtained after stretching is
C has not been obtained that satisfies all the required conditions regarding air permeability, moisture permeability, mechanical strength, flexibility, texture, etc. Rather than satisfying all conditions, the general idea is that characteristics should be emphasized in accordance with the final demand objective. For example, when used in disposable diapers, it is required to have characteristics in air permeability, moisture permeability, and texture. Linear low-density polyethylene is preferable as a polyolefin resin that satisfies these requirements (Japanese Patent Laid-open No. 58-149925, Japanese Patent Laid-open No. 149925, No. 60)
-185803).

If we try to improve the air permeability and moisture permeability (C),
During the manufacturing process, the process of uniformly blending the filler and the particle size of the filler are considered to be the most important factors in the stretching process.

In this application, the film obtained by the inflation method or the T-die method is referred to as a raw film or sheet, and the film obtained by stretching this is referred to as a stretched (or air permeable) film or sheet. Let us first distinguish between the two.

Problems 2 and 5 solved by the invention When calcium carbonate is selected as a filler, it is necessary to prevent particles from agglomerating and to achieve uniform dispersibility with the polyethylene. This is because the agglomeration of particles causes concentration of stress, which becomes a fracture nucleus and causes the growth of cracks.

Although several compounding methods have already been proposed, the inventor of the present application believes that the method of Japanese Patent Publication No. 57-32941 is the most excellent for producing raw films and sheets, and adopted that method. did. Although the resin used in this prior application is high-density polyethylene, it can also be used for homogeneous mixing of linear low-density polyethylene and calcium carbonate, which are treated in the present application.

That is, a powder mixture consisting of a predetermined amount of calcium carbonate particles having a constant particle size is heated under stirring to a temperature above the melting point of linear low-density polyethylene and below the decomposition point, thereby producing cohesive granules. After that, the particle composition is cooled under stirring to a temperature lower than the melting point of the polyolefin, and a raw film or sheet is produced by a conventional method called an inflation method or a T-die method.

In this process, the calcium carbonate particles gradually adhere to the surface of the polyethylene particles melted by VC, wrap them, and then repeat the phenomenon of replenishing the resin by melting and flowing from inside the resin particles and adhering the calcium carbonate to the surface, so that both particles become uniform. It is thought that mixing will proceed.

Furthermore, the raw film obtained here, sheet material is used to make air-permeable film, and the sheet is made by stretching methods. Stretching may be performed uniaxially or biaxially in a heating medium.

This resulted in a permeable film or sheet, but
It has become clear that K, which roughly improves air permeability and moisture permeability, requires investigation of the complex relationship between the particle size, particle size distribution, and formulation of the calcium carbonate to be used.

Means to solve problems The present invention focuses on the physical properties and air permeability of calcium carbonate.

This was discovered in the process of investigating the relationship between moisture permeability.

Usually, commercially available calcium carbonate particles are 1
~6 μm is the most common. If there are many particles of 0.1 μm or less, uniform dispersion becomes poor due to mutual agglomeration of particles, and
If it exceeds μm, the crazes generated due to exfoliation of the filler-matrix interface due to external stress will become too large and the matrix will be easily destroyed.

However, when considering air permeability and water vapor permeability, the particle size conditions for calcium carbonate have to become even more stringent. For example, during stretching, if there are too many particles below 1 μm9, the air permeability and water vapor permeability will be insufficient, and if there are too many particles above 6 μm, the film or sheet will break in the stretch or the texture will be significantly impaired. It cannot be used as supplies. Based on this background, it was concluded that the particle size to be selected should be limited to a range of 1 to 6 μm.

The amount to be blended must be considered from this point of view when the purpose is stretching. If the amount of calcium carbonate is less than 80 parts per 100 parts of the linear low-density polyethylene, porosity is insufficiently formed during stretching, and desired air permeability and moisture permeability cannot be obtained. On the other hand, if the amount exceeds 200 parts, the dispersibility of the particles and the processability of the film are poor, and not only the stretchability but also the mechanical strength and texture are insufficient, resulting in poor practicality.

Through the process described above, the inventor of the present application searched for the particle size and addition of calcium carbonate in accordance with the purpose of stretching. Next, we compared and examined the superiority and inferiority of air permeability and moisture permeability within this range.
We have found that particle size distribution has a significant effect on these performances.

Calcium carbonate particles with various particle sizes are commercially available, and by mixing these particles, a filler having an arbitrary distribution can be prepared. Note that the typical "average particle size" referred to herein refers to the specific surface area diameter measured by an air permeation method.

In this application, performance was investigated by blending calcium carbonate with two different particle sizes. As a result, a composition with a particle size distribution that clearly has two maximums is preferable for air permeability and moisture permeability.
- It was found that it gave good results.

That is, it is defined here as follows.

(Parts by weight relative to 100 parts by weight of the polyethylene) At this time, a blend of R/r = 1.5 and M/m = 0, 1 to 10 showed preferable results in terms of air permeability and permeability. Note that M+m-==80 to 200 parts.

That is, when the particle size ratio R·/r<1.5, the air permeability and moisture permeability were insufficient. Also, when the blending ratio M/m < 0.1 or M/m > 10, good air permeability and moisture permeability are achieved.
, not done.

The reason why R/r%M 7m has a significant effect on air permeability and moisture permeability within a certain range is that the stretching process is most effective when coarse particles and fine particles exist appropriately. This is thought to be due to the fact that Moreover, this effect is thought to be possible not only because the calcium carbonate particles are uniformly dispersed in the polyethylene, but also because the mutual dispersion of coarse particles and fine particles is also uniform.

Note that linear low-density polyethylene includes thermoplastic elastomers such as ethylene-propylene copolymer, ethylene-vinyl acetate copolymer, and ethylene-butene copolymer, high-density polyethylene, and low-density polyethylene (LDPE).
, polypropylene may be added. These are useful in giving the molded product sufficient flexibility, increasing its mechanical strength, and improving its feel, depending on the purpose of use.

EXAMPLES Hereinafter, the gist of the present application will be explained in more detail by writing together examples and comparative examples. The experiments shown here followed the following conditions up to experiment numbers 1 and 7. However, experiment number 8
According to the notes.

The blending amount is as follows: Calcium stearate 0.8 weight i 1 part These were mixed in a Henschel mixer for 30 minutes to form a cohesive granular composition at 150°C, and then cooled to 70°C with stirring to form a predetermined granular composition. Get it. Thereafter, after obtaining a film/l/mu with a 50 m/m 96 inflation extruder, it was stretched at a predetermined stretching ratio (displayed).Note: In experiment number 8, all operations of the above Henschel mixer were performed at room temperature. This is the case. Other conditions as stated).

Inflation extrusion conditions temperature Cylinder die 160-190℃ Take-up speed
Hm10, folding diameter 350 m/m Stretching conditions temperature 70°C 9 magnification 4.5 times and 3 times speed 1st to 3rd roll speed 3.4 to 31.60 10
M layer 45 summer n15+ and 30m/min Final film thickness 20μm Film evaluation method Air permeability The unit according to JIS P8117 method is expressed in seconds/100m1, and the smaller the number, the better, and the larger the worse. do.

The unit according to the moisture permeability JIS Z0208 method is expressed as 9/rri' 24 Hour, and the larger the value, the better, and the smaller the value, the worse.

Effects of the Invention The effects of the present application are clear from a comparison between Examples and Comparative Examples. When the conditions of the present application are followed, the stretching is good in all cases.
Both have excellent air permeability and moisture permeability, and can be used to produce the desired air permeable film or sheet. However, if the conditions of the present application are not met, the stretching is poor or the texture is poor in most cases, making it impossible to put it to practical use. The air-permeable film or sheet of the present invention can be widely applied to fields such as waterproof clothing, filtration materials, medical supplies, sanitary products, and disposable diapers.

Claims (1)

[Claims] A cohesive powder is produced by heating a powder mixture prepared by blending calcium carbonate with a linear low-density polyethylene resin to a temperature above the melting point and below the decomposition point of the polyethylene while stirring. is then cooled under stirring to a temperature lower than the melting point of the polyethylene to form a powder composition, and this composition is extruded into a raw film or sheet,
In the method of producing an air-permeable film or sheet by further stretching the calcium carbonate, the calcium carbonate consists of two particle parts, a fine particle part and a coarse particle part, and in this case, the particle size range for both is 1 to 6 μm.
Within the range, the ratio of the average particle diameter of the fine particle part and the coarse particle part is 1
．． 5 or more, and the weight ratio of the fine particle part to the coarse particle part is 0.1 to 10 with respect to 100 parts by weight of the polyethylene resin, and the total weight ratio is 80 to 200.