JPH05310980A - Production of stretchable porous film or sheet - Google Patents

Abstract

PURPOSE:To obtain the subject product, having excellent air and moisture permeability and excellent in stretchability without permeating liquids by forming a composition of a polymeric substance capable of exhibiting the rubber-like elasticity at ordinary temperature and a thermoplastic resin into a film and stretching the formed film. CONSTITUTION:A resin composition consisting essentially of (A) 100 pts.wt. polymeric substance capable of exhibiting the rubber-like elasticity at ordinary temperature (preferably a urethane rubber, etc., having 100-250 deg.C melting point) and (B) 10-100 pts.wt. thermoplastic resin poor in compatibility with the component (A) (preferably linear low-density polyethylene) is initially melt kneaded. The resultant kneaded composition is then formed into a film or a sheet, which is subsequently stretched at a lower temperature than the melting point of the components (A) and (B), preferably 60-110 deg.C in at least one direction, preferably in the two directions to afford the objective product. Furthermore, the formation of the film is preferably carried out at a lower temperature than the melting point of the components (A) and (B).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a stretchable porous film or sheet which is impermeable to liquids such as water, has breathability and moisture permeability, and has extremely excellent stretchability. It is a thing.

[0002]

2. Description of the Related Art Conventionally, a porous film is formed by, for example, forming a film from a resin composition obtained by adding an inorganic filler to a polyolefin resin, and stretching the film, or a porous film obtained by stretching the film. It is obtained by extracting the soluble filler from the film with water, acid or alkali.

However, in these methods, the presence of the inorganic filler in the porous film may not provide the required properties such as chemical resistance and electrical properties, which limits the use. There was a drawback.

Therefore, recently, there has been proposed a method of stretching a film formed by melt-kneading two or more kinds of thermoplastic resins having poor compatibility as described below.

That is, first, in the first method for producing a porous film, a mixture of a thermoplastic resin A and a thermoplastic resin B having a poor compatibility with the resin A and having a melting point higher by at least 20 ° C. is used. Melt and knead at a temperature higher than the melting point of resin B, form a sheet at a temperature higher than the melting point of resin A and lower than the melting point of resin A, and then stretch in at least one direction at a temperature lower than the melting point of resin A. (JP-A-58-198536).

As a second method for producing a porous film, 100 parts by weight of a polyolefin resin (A) and a thermoplastic resin (B) 10 to 1 having a low compatibility with (A) are used.
Melt and knead a resin mixture containing 100 parts by weight as an essential component,
The extruded film or sheet is (A) and (B) in a temperature range of not less than 10 ⁶ poises and not more than 300 ° C. and a melt viscosity of 10 ⁶ poises or less respectively. A film or sheet obtained by heat-treating for 60 seconds and then rapidly cooling is stretched in at least uniaxial direction (JP-A-63-63).
-270748).

[0007]

In the above method, the melting point is different, and the interface between the main component resin A and the high melting point thermoplastic resin B dispersed in a so-called island shape is stretched. Although it is made to be porous, in a film obtained by an ordinary extrusion machine, the thermoplastic resin B having a high melting point is formed into a film by the deformation due to the shearing force inside the extruder or the drawdown due to the take-out at the die outlet. Since the film is stretched in the flow direction and deformed into a linear or layered form, when this film is stretched, the uniaxial stretching in the flow direction of the film shows that the effective interfacial area for generating pores is very small. Therefore, voids are unlikely to occur, and the resulting film has a very small tear strength in the flow direction.

Moreover, when the film is uniaxially stretched in the axial direction, only pores having a small porosity can be obtained and the required air permeability may not be obtained.

Further, even when the biaxial stretching is carried out, it is more advantageous than when the uniaxial stretching in the flow direction or the axial direction is made to generate the voids. Therefore, a stretched film having a large porosity cannot be obtained in either uniaxial stretching or biaxial stretching.

Further, in the unstretched film and the stretched film in which the high melting point thermoplastic resin B is dispersed in a layer form, a phenomenon of peeling parallel to the film surface is also observed, and the delamination strength of the film becomes extremely weak. There are challenges.

On the other hand, in the above-mentioned method, although the above-mentioned problems are somewhat improved, since the thermoplastic resin is used, the same problem occurs.

In fact, although the porous film obtained by the above method has some improvement in moisture permeability, it cannot be said that the tensile strength is sufficient.

In particular, the films obtained by the above-mentioned methods (1) and (2) both have poor elasticity and stretchability of several percent in the longitudinal direction and several percent to several tens of percent in the transverse direction.
Therefore, this kind of, porous film is particularly required in the field of elasticity, for example, medical materials such as gloves and cut vans,
Further, when it is used for household products, pressure control valves, food packaging materials, etc., it is not always satisfactory.

The present invention has been completed in view of the above technical problems, and by using a polymer substance (A) showing rubber-like elasticity at room temperature as a main component of a film or sheet, a liquid such as water can be obtained. It is an object of the present invention to provide a method for producing a stretchable porous film or sheet that does not permeate, has excellent breathability and moisture permeability, and has particularly excellent stretchability.

[0015]

In order to achieve the above object, the present invention provides 100 parts by weight of a polymer substance (A) which exhibits rubber-like elasticity at room temperature and a phase relative to the polymer substance (A). A film or sheet obtained by melt-kneading a resin mixture containing 10 to 100 parts by weight of a poorly soluble thermoplastic resin (B) as an essential component and then forming the film into a polymer substance (A) and a thermoplastic resin ( It is characterized in that it is stretched in at least one direction at a temperature lower than the melting point of B).

The present invention will be described in detail below. The polymer substance (A) used in the present invention is not particularly limited as long as it exhibits rubber-like elasticity at room temperature, and specific examples thereof include natural rubber and synthetic rubber.

The natural rubber is not particularly limited as long as it is a rubber obtained from a growing plant.

The synthetic rubber is not particularly limited as long as it is a rubber other than the above-mentioned natural rubber, and specifically, for example, thermoplastic elastomer, styrene butadiene rubber, acrylonitrile butadiene rubber, butadiene rubber, isoprene rubber. , Chloroprene rubber, chlorosulfonated polyethylene, ethylene propylene rubber, butyl rubber, silicone rubber, polysulfide rubber, fluororubber, urethane rubber, acrylic rubber, polyisobutylene, isoprene, adduct rubber or chlorinated rubber, and hydrochloric acid rubber.

Of the polymer substance (A) which exhibits rubber-like elasticity at room temperature, the melting point is 50 to 50 in order to improve the moldability of the film or sheet in relation to the thermoplastic resin (B).
300 ° C., especially 100 to 250 ° C. is desirable,
Specific examples include urethane rubber and thermoplastic elastomers.

Specific examples of the thermoplastic elastomer include styrene-butadiene-styrene (SBS) and styrene-isoprene-styrene (SI).
-S) Further, styrene block polymers such as styrene-ethylene / butylene-styrene (S-EB-S) may be mentioned.

The thermoplastic resin (B) used in the present invention is a thermoplastic resin and is the above-mentioned polymer substance (A).
Is not particularly limited as long as it has poor compatibility with.

In this case, a thermoplastic resin (B) having a poor compatibility with the polymer substance (A) may be selected and used depending on the combination of the polymer substance (A) and the thermoplastic resin (B). Of.

As the thermoplastic resin (B), for example, polyolefin resin, polystyrene resin, polyvinyl chloride resin, polyamide resin, polyacrylate resin, polyester resin, polycarbonate resin or thermoplastic polyurethane resin, etc. Can be mentioned,
Of these, a polyolefin resin is particularly desirable from the viewpoints of various properties and productivity of the film / sheet, and manufacturing cost.

Examples of the polyolefin resin include linear low-density polyethylene, high-pressure polyethylene, low-pressure polyethylene, polypropylene, ethylene-propylene copolymers, polybutadiene, ionomer resin, ethylene-vinyl acetate copolymer resin and the like. Examples of the polyolefin-based resin, among these, those using linear low-density polyethylene, the production or processability of the film or sheet is more excellent, and the production cost is significantly low,
Moreover, the stretchable porous film / sheet obtained is most preferable because it has high mechanical strength.

The blending ratio of the polymer substance (A) and the thermoplastic resin (B) is 10 parts by weight of (B) to 100 parts by weight of (A).
When the compounding ratio of (B) is less than 10 parts by weight, it is difficult to obtain a stretchable porous film having desired air permeability and moisture permeability, while when it exceeds 100 parts by weight, the film or sheet layer ( Since A) and the dispersed phase (B) are reversed, the stretchability is significantly reduced, and a stretchable porous film having good air permeability cannot be obtained.

The stretchable porous film of the present invention can be manufactured by the method described below. First, a polymer material (A) that is a base resin and a resin composition that contains a thermoplastic resin (B) that is a dispersed phase as essential components are melted at a temperature equal to or higher than the melting point of these (A) and (B). Kneading is carried out, and thereby a resin composition in a uniformly mixed state as a whole is obtained. On this occasion,
Although (A) and (B) can be uniformly mixed by dry blending, it is particularly preferable to knead in advance using a biaxial kneader or the like because (B) can be dispersed more finely and uniformly.

In this case, examples of the kneader used include known kneaders such as a mixing roll, a Banbury mixer, a twin-screw kneader, a Henschel mixer, and an extrusion kneader. The resin composition in this mixed state is used. The product is formed into a film or a sheet by molding, and the molding temperature at this time is lower than the melting points of the polymer substance (A) and the thermoplastic resin (B). By doing so, the fine particles of the thermoplastic resin (B) are uniformly dispersed in the form of islands throughout the film or sheet containing the polymer substance (A) as the base resin.

To mold the resin composition into a film or a sheet, known molding equipment and molding methods may be used. For example, an inflation molding machine, a T-die molding machine, a calender roll, various extruders, etc. may be used. It can be adopted, then, the obtained film or sheet, for example, a roll stretching machine, simultaneous biaxial stretching machine, sequential biaxial stretching, longitudinal direction using a known stretching machine such as tenter stretching machine, i.e., one direction, or It suffices to stretch in the lengthwise and crosswise directions, that is, in two directions. By stretching in this way, it is possible to obtain a stretchable porous film in which fine communication holes are formed and which has excellent stretchability and air permeability.

In this case, the stretching direction may be one direction,
In order to obtain a stretchable porous film that is uniform and has excellent stretchability and air permeability at a relatively low stretch ratio, it is desirable to stretch in two directions.

In the present invention, the stretchable porous film
When forming the sheet, the stretching ratio of the unstretched film / sheet is 2 to 7 times in one direction, and if it is less than 2 times, the unstretched portion remains and uneven stretching occurs, so that a uniform film / sheet is obtained. In some cases, it may not be obtained, while if it exceeds 7 times, it may break, which is not desirable.

When the unstretched film / sheet is stretched, the stretching ratio is (length × width) 2 in the case of bidirectional stretching.
It is 10 to 10 times, and if it is less than 2 times, unstretched parts remain and uneven stretching occurs, so that it may not be possible to obtain a uniform film or sheet, or it may be difficult to obtain the required breathability and moisture permeability. If it exceeds, it may break, which is not desirable.

In the present invention, the stretching ratio means a value obtained by dividing the dimension after the stretching treatment by the dimension before the stretching treatment.

The temperature during this stretching is 20 to 1
It is desirable to set the temperature to 30 ° C., particularly 60 to 110 ° C., and if the above conditions are not satisfied, it will break or become porous, but it will be difficult to obtain communicating pores with independent bubbles, and breathability and moisture permeability will be obtained. May be damaged, which is not desirable.

In this way, the stretchable porous film
Although a sheet can be obtained, this stretchable porous film / sheet does not allow liquids such as water to pass therethrough, and has breathability and moisture permeability, and in particular, the stretchability is 1.5 to 3 times in the longitudinal direction, It is extremely superior, being 3 to 6 times in the lateral direction.

In the present invention, the degree of expansion and contraction means that the porous film or sheet is deformed by an external force for elongation,
Next, when this external force is removed, it means the limit to return to the original shape and size, and it is the value obtained by dividing the size of the porous film or sheet after expansion by the external force by the size before expansion.

By the way, in the present invention, the stretchable porous film / sheet obtained as described above is subjected to an annealing treatment, if desired, thereby reducing the final magnification from, for example, 4 times to 2 times. The stretchability, air permeability and moisture permeability of the stretchable porous film / sheet may be further improved by subjecting the stretchable porous film / sheet to a post-treatment. In this case, the annealing temperature is 50 to 200 ° C.
If the temperature is less than 50 ° C., the temperature will be too low and the fluidity of the polymer will be poor, so that there is a possibility that the stretching ratio cannot be uniformly set.
On the other hand, if the temperature exceeds 200 ° C., the polymer may be melted and the porosity may be lost.
℃ is desirable.

In the method for producing a stretchable porous film / sheet of the present invention, a film is formed after melt-kneading the above-mentioned polymer substance (A) and the resin composition containing the thermoplastic resin (B) as essential components. When forming a film or sheet by applying the thermoplastic resin (B)
It is most desirable to form a film in a temperature range where it is lower than the melt viscosity of the above for the reasons described below.

That is, when the melting point of the polymer substance (A) is higher than that of the thermoplastic resin (B), the melt viscosity of (A) becomes lower than that of (B) when the temperature is raised. Occurs. When the film is formed and stretched in this temperature range,
It becomes easier to disperse the fine particles of (B) in (A) more uniformly, and as a result, a stretchable porous film / sheet that is homogeneous and has further excellent breathability and moisture permeability and good stretchability is obtained. Be done.

Also in this case, as in the case described above, the temperature during this stretching is 20 to 130 ° C., especially 60.
It is desirable to set the temperature to ˜110 ° C., and if the above conditions are not satisfied, it may break or become porous, but it may be difficult to obtain communication holes due to independent bubbles, and air permeability and moisture permeability may be impaired. It is not desirable because it exists.

In this way, a stretchable porous film / sheet having further excellent properties can be obtained from the stretchable porous film / sheet described above.

In the present invention, an antioxidant, an ultraviolet stabilizer, an antistatic agent, a lubricant, which is usually used, is used as long as it does not deteriorate the physical properties of the stretchable porous film / sheet.
It may be one obtained by adding an appropriate amount of an additive such as a fluorescent agent.

[0042]

The present invention, which has the above-mentioned constitution and uses the polymer substance (A) showing rubber-like elasticity at room temperature as the matrix of the film or sheet, has the action of exerting remarkable stretchability by itself.

By using the polymer substance (A) which exhibits rubber-like elasticity at room temperature as the matrix of the film or sheet, the air permeability and moisture permeability and the strength are remarkably improved by stretching.

Although the reason for this is not clear, the thermoplastic resin (B) is easily dispersed in the polymer substance (A) exhibiting rubber-like elasticity at room temperature, and the compatibility between (A) and (B) is poor. Above, it is understood that the stretching causes (B) to become island-shaped in (A) instead of being layered, and (A) is used as a matrix, in which (B) is uniformly dispersed.

[0045]

EXAMPLES The present invention will now be described in detail based on examples, but the present invention is not limited thereto. Examples 1 to 7 and Reference Example At a ratio shown in Table 1, urethane rubber (hardness 90) and high-density polyethylene (HDPE MI 1.1 g / 10 min) or polypropylene (MI 8 g / 10 min) were sufficiently mixed in a biaxial kneader. After kneading, the film was extruded by a single-screw extruder under the conditions shown in Table 1.

Next, this film was stretched in one direction or two directions under the conditions shown in Table 1 and Table 2 to obtain a stretchable porous film.

Comparative Example 1 100 parts by weight of high-density polyethylene (HDPE) and 25 parts by weight of polycarbonate (PC) were sufficiently kneaded by a twin-screw extruder and extruded by a single-screw extruder under the conditions shown in Table 1. The film was formed.

Next, this film was stretched in one direction under the conditions shown in Tables 1 and 2 to obtain a porous film.

Comparative Example 2 100 parts by weight of high-density polyethylene (HDPE) and 45 parts by weight of polystyrene (PS) were sufficiently kneaded by a twin-screw kneader and then extruded by a single-screw extruder under the conditions shown in Table 1. Filmed

The obtained film was heat-treated at 210 ° C. for 10 seconds, and then stretched in one direction under the conditions shown in Tables 1 and 2 to obtain a porous film.

[0051]

[Table 1]

Tables 2 and 3 show the results obtained by measuring various characteristics of the above-mentioned Examples and Reference Examples and Comparative Examples.

[0053]

[Table 2]

[0054]

[Table 3]

Note 1) The tensile strength shown in Table 2 means the strength at break when a sample is sandwiched at a chuck interval of 40 mm using a universal tension testing machine and pulled at a pulling speed of 300 mm / min. Note 2) As shown in Table 2, the elasticity is the tensile strength, the tensile strength is a universal tension tester, the sample is sandwiched at a chuck interval of 40 mm, and the sample is pulled and deformed at a pulling speed of 300 mm / min, and then this external force is removed. Original shape
It is the limit of returning to the dimension, and it is the value obtained by dividing the dimension of the porous film or sheet after stretching by applying an external force by the dimension before stretching. Note 3) The moisture permeability shown in Table 3 was measured by the moisture permeable cup method according to JIS L-1099.

The results shown in Tables 2 and 3 show that each of the examples exhibits superior moisture permeability, has higher tensile strength, and is significantly more stretchable than those of the comparative examples. Is recognized.

Further, from the reference example, it is recognized that when the amount of the thermoplastic resin is too much, the tensile strength and the stretchability are lowered.

[0058]

INDUSTRIAL APPLICABILITY The present invention provides a stretchable porous film having the above-mentioned constitution, which has the maximum stretchability without the use of a special technique or apparatus and which is excellent in breathability and moisture permeability. It has an effect that it can be manufactured at low cost.

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Claims (4)

[Claims] 1. Essentially 100 parts by weight of a polymer substance (A) exhibiting rubber-like elasticity at room temperature and 10 to 100 parts by weight of a thermoplastic resin (B) having poor compatibility with the polymer substance (A). A film or sheet obtained by melt-kneading a resin composition as a component and then forming a film is stretched in at least one direction at a temperature lower than the melting points of the polymer substance (A) and the thermoplastic resin (B). A method for producing a stretchable porous film or sheet, which comprises: 2. The method for producing a stretchable porous film / sheet according to claim 1, wherein the polymer substance (A) is natural rubber or synthetic rubber. 3. The method for producing a stretchable porous film or sheet according to claim 1, wherein the thermoplastic resin (B) is a polyolefin resin. 4. Essentially 100 parts by weight of a polymeric substance (A) exhibiting rubber-like elasticity at room temperature and 10 to 100 parts by weight of a thermoplastic resin (B) having a poor compatibility with the polymeric substance (A). In the temperature range in which the melt viscosity of the polymer substance (A) is lower than the melt viscosity of the thermoplastic resin (B) when forming a film or sheet by melt-kneading the resin composition as a component and forming a film. A method for producing a stretchable porous film or sheet, which comprises forming a film.