JP2780041B2 - Method for forming T-die film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a T-die film forming method for forming a film (sheet) by melt-extruding a thermoplastic resin from a T-die.

[Conventional technology]

Conventionally, a thermoplastic resin is formed into a film using a T-die film forming apparatus, and the thermoplastic resin film is subjected to a stretching treatment or the like to cause the molecular orientation of the thermoplastic resin. The strength in the orientation direction is significantly increased, and by performing this stretching treatment at the same stretching ratio in the longitudinal and transverse directions of the thermoplastic resin film, the thermoplastic resin film has a high strength without directivity in strength. It is also known to be.

There has been proposed a method for producing a thermoplastic resin film having a large strength by utilizing this. For example, there is a method in which films having molecular orientation in a uniaxial direction are bonded to each other so that the orientation directions cross each other to obtain a high-strength film having no direction in terms of strength.

[Problems to be solved by the invention]

However, in this method, since the film is bonded,
Not only does the thickness of the film increase, but it also has disadvantages such as the necessity of a film forming step and a bonding step, and the complicated operation.

[Means for solving the problem]

The present inventors have solved the technical problem of obtaining a high-strength film using such a conventional T-die forming apparatus, and have been able to efficiently use a thermoplastic resin, particularly a polyolefin resin film, having improved impact strength and tensile strength. As a result of intensive studies on a method that can be manufactured well and stably, the lip of the T-die is moved at a specific speed by using a T-die capable of moving along the width direction of the extruded film. It was found that by performing the T-die molding, a film having excellent tensile strength and having substantially equal orientation in the vertical and horizontal directions was obtained, and the present invention was completed.

That is, the gist of the present invention is that a thermoplastic resin having a melt flow index at a molding temperature of 30 g / 10 minutes or less is T
In forming the die, one or both of the lips of the T-die is a movable lip which can move in the width direction of the film.
Using a die, molding while moving both or one of the movable lips at a relative speed not less than the value of the speed index (S) represented by the following equation (1) and not more than 10 times the speed index (S). And a method of forming a T-die film.

Here, G: width of linear slit (mm) MFI: melt flow index at molding temperature (g / 10 min) t: film thickness (mm) S: speed index (mm / min) Hereinafter, the present invention will be described in detail. .

The thermoplastic resin used in the present invention may be anything that is usually used for T-die film molding,
For example, polyolefin resins such as polyethylene, polypropylene, ethylene-propylene copolymer, polybutene-1, ethylene-vinyl acetate copolymer, polyamide resins such as nylon, styrene resins such as polystyrene, and vinyl chloride such as polyvinyl chloride And the like.

As the thermoplastic resin, the melt flow index at the molding temperature is usually 30 g / 10 minutes or less, preferably
Those having a range of 0.02 to 10 g / 10 minutes, more preferably 0.03 to 4 g / 10 minutes, are used. If the melt flow index is larger than the upper limit, the melt tension is essentially insufficient, resulting in poor film formation stability and reduced physical properties of the film.

In the present invention, the melt flow index (MFI) is a value measured at a molding temperature in accordance with JIS K6760.

Further, as the T-die film forming apparatus used in the present invention, any one of a commonly used type can be used, but the forming die is different from a normal T-die, and a die lip provided in a die slit is used. A T-die provided with a movable lip that can move along a direction (width direction of the film) crossing the extrusion direction is used. The die lip is preferably movable on both sides of the die slit, but may be movable only on one side.

An example of a die used in the present invention is shown in FIGS.

In FIG. 1, a die 1 has a structure in which each lip can slide in the width direction of the film across an extrusion slit.

In the present invention, the thermoplastic resin is molded under specific molding conditions using a T-die film molding apparatus equipped with the above-described T-die.

First, at least one of the movable lips 2 and 3 of the T-die film forming apparatus is reciprocated in the width direction of the film (the direction intersecting the extrusion direction). Since the film is oriented in a composite direction of the moving direction, a film in which the film is obliquely oriented is obtained as a whole film. The degree of molecular orientation of the film is appropriately selected and determined by adjusting the moving speed of the movable die lip, the resin extrusion speed, the take-up speed, and the like. In the case where both the movable lips are reciprocated, it is preferable to move the movable lips in directions opposite to each other in order to provide a uniform molecular orientation.

Further, the device shown in FIG. 2 is a movable die lip 2 (3).
Is an endless belt. In this case, the die lip can be continuously driven without reciprocating the die lip as shown in FIG.

In the present invention, in order to produce a film having excellent tensile strength, the relative speed of the movement of the movable die lips 2 and 3 (when moving the movable die lips 2 and 3 simultaneously in the opposite direction, the sum of the movement speeds of the two). , Or when only one of them is moved, the moving speed is not less than the value of the speed index (S) represented by the following equation (1), and
The S value is adjusted to 10 times or less, preferably 1.2 times to 10 times the S value, and more preferably 3 times to 10 times the S value.

Here, S: speed index (mm / min) G: width of linear slit (mm) MFI: melt flow index at molding temperature (g / 10 min) t: film thickness (mm)

The speed index (S) is an important index of the molding operation conditions of the present invention, and is determined by the fluidity (MFI) of the resin used, the film thickness (t), and the slit width (G) of the die used.
This defines the required relative movement speed (mm / min) of the lips on both sides.

When the moving speed specified above is lower than the speed index (S), the strength of the obtained film is not much different from that of the conventional T-die molded product, and the effect of the present invention cannot be sufficiently exhibited. When the moving speed is more than 10 times the speed index (S), there is no demerit in the physical properties of the obtained film, but there is a possibility that it may cause a slight problem from the viewpoint of the durability of the molding apparatus, which is not preferable. .

In addition, the extrusion speed and the take-off speed of the resin are generally set to such a speed as to be performed by T-die molding. As the molding conditions for molding a T-die using a polyolefin resin, the molding temperature is the melting point of the resin + 10 ° C. to 300 ° C., preferably 170 to 270 ° C.
At a draft rate of 1 to 100, preferably 1 to 50.

Example 1 High-pressure low-density polyethylene ｛density: 0.924 g / cm ³ , melt index (= melt flow index): 2.0 g /
10 min. To a 40φ extruder manufactured by Osaka Seiki Co., Ltd. with a linear slit width (gap of die lip) of 0.7 mm and a direction (width direction) crossing each lip on both sides of the linear slit in the extrusion direction. Using a T-die molding machine equipped with a T-die (T-die having the shape shown in FIG. 1) that can move in the opposite direction,
Molding temperature 190 ° C, molding temperature MFI 2.0g / 10min, draft rate:
Under the conditions of the moving speeds shown in Table 14 and Table 1, 50 μm T-die molded films were produced.

The obtained film was evaluated by the following measurement method. Table 1 shows the results.

Tensile strength Cut the film into strips and use a tensile tester for 500m
Pull at m / min and read the strength when the film cuts.

JIS Z1702 Draft rate (DR) ρm: Specific volume at the time of melting ρf: Specific volume of the film G: Die gap t: Film thickness Impact strength Dart drop impact method ASTM D1709 Shown by the average load (g) when breaking.

The falling distance was 26 inches. Examples 2 to 3 The same procedure was performed as in Example 1 except that the moving speed was changed to the conditions shown in Table 1. Table 1 shows the results.

Comparative Examples 1 and 2 The same operation as in Example 1 was performed except that the moving speed was changed to the conditions shown in Table 1. Table 1 shows the results.

As is clear from the results in Table 1, when the moving speed of the movable die lip is equal to or higher than the speed index S, the tensile strength of the film is improved in the balance between the MD direction and the TD direction, and the impact strength is also improved.

In addition, it was found that there was almost no difference in the contribution to the physical properties even when the movable die lip was moved only one of them or simultaneously.

〔The invention's effect〕

According to the method of the present invention, a film having an improved tensile strength balance and impact strength can be produced.

[Brief description of the drawings]

FIG. 1 and FIG. 2 are schematic explanatory views, partially broken, of a die used in the method of the present invention. In the figure, 1 indicates a die, and 2 and 3 indicate die lips, respectively.

Claims (1)

(57) [Claims] When a thermoplastic resin having a melt flow index at a molding temperature of 30 g / 10 minutes or less is molded by a T-die, one or both of the lips of the T-die is a movable lip capable of moving in the width direction of the film. Using a T-die, while moving both or one of the movable lips at a relative speed not less than the value of the speed index (S) represented by the following formula (1) and not more than 10 times the speed index (S): A method for forming a T-die film, which is formed. Where G: width of linear slit MFI: melt flow index at molding temperature (g / 10
Min) t: film thickness S: speed index (mm / min)