JP4651228B2 - Method for producing simultaneous biaxially stretched film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a high-quality simultaneous biaxially stretched film. More specifically, a simultaneous biaxially stretched film that suppresses unevenness in physical properties due to stretching stress and stress relaxation strain, and has uniform physical properties in the width direction, in particular, excellent mechanical properties, thermal dimensional stability, and optical properties. It is related with the manufacturing method.
[0002]
[Prior art]
Biaxially stretched films are mainly used for packaging and industrial applications. In these applications, however, uniformity of physical properties in the film width direction has been particularly demanded in recent years.
[0003]
In general, a biaxially stretched film is produced by extruding a molten resin film with an extruder, cooling and forming into a sheet on a cooling roll, and stretching the substantially unoriented unstretched film in the longitudinal and transverse biaxial directions, Thereby, a high-strength biaxially stretched film with sufficient molecular orientation can be obtained. The biaxial stretching method includes a sequential biaxial stretching method in which transverse stretching is performed subsequent to longitudinal stretching, and a simultaneous biaxial stretching method in which stretching is performed simultaneously in the longitudinal and transverse directions. In the simultaneous biaxial stretching method, the end of the unstretched film is gripped with a clip and mechanically stretched in the biaxial direction at the same time, that is, the clip interval is widened in the vertical direction and the width of the clip running rail is widened in the horizontal direction. The stretching is performed by
[0004]
In this simultaneous biaxial stretching method, there is a problem that the change in the surface magnification of the longitudinal stretching magnification locus x lateral stretching magnification locus that is gradually widened mechanically does not synchronize with the actual film stretching deformation. That is, a phenomenon occurs in which the film in the preheating zone is curved and deformed toward the stretching zone, and the central portion undergoes preceding deformation (referred to as reverse bowing phenomenon). There has been a case where a phenomenon (called a bowing phenomenon) occurs in which the central portion is deformed in a delayed manner due to bending deformation.
[0005]
These phenomena are caused by the contraction force acting on the transverse (or longitudinal), which is the perpendicular direction, when the film is deformed in the longitudinal (or transverse) uniaxial direction in simultaneous biaxial stretching of the film, that is, in the uniaxial direction. In addition to the stretching stress, the contraction force in the perpendicular direction acts on each other and simultaneously, so it is considered that these weighted forces act on the film surface.
[0006]
When the distortion of the film deformation caused by reverse bowing and the bowing phenomenon occurs in the width direction, the molecular orientation distribution in the width direction becomes non-uniform, resulting in uneven physical properties of the film in the width direction. Even if the film physical properties do not have a direct adverse effect on the film production process, when the film is used for packaging applications, the printing pitch shift, meandering, Troubles such as poor sealing and quality deterioration of film processed products such as bag-making curls may be caused. Therefore, the product cannot be handled as having the same physical properties over the entire width of the film, and only the central portion in the width direction is shipped as a product, and the end portion of the film remains in stock for applications that require a strict balance of physical properties. I had a production problem.
[0007]
[Problems to be solved by the invention]
The present invention solves the above problems, and provides a method for producing a simultaneous biaxially stretched film having uniform and excellent quality stability by minimizing distortion in the width direction of the surface magnification locus caused by the simultaneous biaxial stretching method. With the goal.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have analyzed the mechanical surface magnification locus and the actual film stretching deformation, and have reached the present invention.
That is, the present invention, the unstretched film edge is gripped by clips Oite the tenter simultaneous biaxial stretching method of aspect simultaneously biaxial stretching, the origin and end point of the longitudinal stretching ratio trajectory of the lateral draw ratio trace origin and It is a manufacturing method of the simultaneous biaxially stretched film characterized by making the advance rate which makes it precede from an end point, and makes a longitudinal draw ratio locus | trajectory precede a transverse draw ratio locus | trajectory 5 to 20% .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
The conceptual diagram showing the relationship between the longitudinal draw ratio locus and the transverse draw ratio locus in the present invention is shown in FIG. In the present invention, it is necessary that the start point and end point of the longitudinal draw ratio locus precede the start point and end point of the transverse draw ratio locus. The stretch ratio locus in the present invention refers to a change in stretch ratio from the stretch start point (start point) to the maximum stretch ratio reach point (end point).
[0010]
Near the entrance of the stretching zone, the film in the preheating zone is pulled toward the stretching zone, and a reverse bowing phenomenon occurs in which the film is curved and deformed. This reverse bowing phenomenon is a distortion that significantly deforms the center part in the vertical direction, but approximates the change in the surface magnification between the center part and the end part by making the origin of the longitudinal draw ratio locus precede the origin of the transverse draw ratio locus. This reverse bowing phenomenon can be suppressed to a small level.
[0011]
On the other hand, in the vicinity of the exit of the stretching zone, a bowing phenomenon occurs in which the stretched film is curved and deformed due to the stress relaxation in the heat treatment zone. This bowing phenomenon is a distortion caused by slowing down the vertical deformation at the center, but by making the end point of the longitudinal draw ratio locus reach before the end point of the transverse draw ratio locus, this bowing phenomenon can be kept small. it can.
[0012]
The leading rate that causes the longitudinal draw ratio locus to precede the transverse draw ratio locus varies depending on the stretching temperature condition and the shape of the stretching locus, but is preferably 5 to 20%. The preceding rate in the present invention refers to the rate of progress of the draw ratio, where the starting point of the longitudinal and transverse draw ratio locus is 0 and the end point is 1. When the leading ratio is 5% or less, the effect of the present invention is small, and when it is 20% or more, there is a risk that a neck is generated in the vicinity of the biaxially stretched stress yield point. Even if a neck occurs during stretching, a simultaneous biaxially stretched film can be obtained, but this is not preferable because thickness unevenness deteriorates and physical properties are significantly disturbed.
[0013]
The reverse bowing and bow ink phenomenon can be observed with an expansion change of the meshes in the biaxial stretching process by temporarily printing the meshes on the entire width of the unstretched film that travels. The measurement of reverse bowing and deformation is preliminarily arranged at a predetermined position with a laser transmission type optical sensor at the center and left and right ends on the straight line in the film width direction, and the time difference between the timing when the squares block the sensor light and pass The amount of bending deformation can be obtained from the clip speed at the sensor arrangement position. The ratio of the amount of bending deformation to the distance between the left and right sensors can be evaluated as reverse bowing deformation and bowing deformation.
[0014]
Further, the analysis of whether or not the film is uniformly stretched even during continuous production can be realized by measuring the film stretching stress applied to the clip. FIG. 2 shows the relationship between the stretching stress component and vector combined stress in the present invention and the inclination thereof. The stress component F _RD applied in the tangential direction of the clip traveling movement and the stress component F _VD applied in the normal direction can be actually measured, and the vector composite stress F _CP is obtained. Further from the clip traveling movement angle alpha, the longitudinal traveling direction of the stress component F _MD and horizontal stress component F _TD is obtained, the slope of the F _CP for F _TD phi is determined by ± angle. Stretching stress components F _RD and F _VD attach a sensor such as a strain gauge or a piezoelectric element to the base of the fixed clip that holds the film end or the arm that connects the rail running bearing device and the clip unit. Thus, it can be measured as a bending load and a tensile load. The sensor signal is transmitted / remotely received by the FM telemeter device and input to the computer as a stress signal. The change in mechanical angle α of the clip traveling movement can be input in advance, and can be obtained by calculating F _MD , F _TD, vector composite stress F _CP and its inclination φ.
[0015]
In the present invention, within the gradient φ is ± 45 ° of the F _CP for F _TD, it is preferable that further preferably selected the longitudinal stretching ratio trace to be within ± 35 °. The inclination φ of the F _CP outside this range increases, an increase in reverse bowing phenomenon and bowing phenomenon, i.e. significantly different area magnification trajectory of the film center and the ends are caused anisotropy in the molecular orientation balance, width Undesirable physical properties in the direction are not preferable. The longitudinal stretch ratio locus curve selected in the present invention is not particularly limited, but can be set by a combination of a quadratic or cubic function, a trigonometric function, an arc and a straight line, a curve, and the like.
[0016]
In the present invention, it is preferable that the longitudinal stretching ratio of simultaneous biaxial stretching is 2.5 to 4.5 times, and the ratio of the transverse stretching ratio to the longitudinal stretching ratio is 0.5 to 1.5. . The above range is a biaxial stretching ratio range of a simultaneous biaxially stretched film that has been put into practical use in order to give sufficient orientation. In this range, the longitudinal stretching ratio locus that is the focus of the present invention is compared with the transverse stretching magnification locus. The effect of leading, in particular, the effect of suppressing reverse bowing and the bowing phenomenon and uniform stretching can be remarkably exhibited, and the present invention is useful.
[0017]
Simultaneous biaxial stretching in the present invention can be performed using a pantograph type tenter, a screw type tenter, a linear motor type tenter, or the like. A linear motor type tenter in which each clip is driven independently by a linear motor type is most preferable because it has flexibility in that the change in the draw ratio can be arbitrarily controlled by controlling the variable frequency driver. That is, this method has advantages that it is easy to adjust the starting point and end point of the longitudinal draw ratio locus, and that the curve of the longitudinal and transverse draw ratio and locus can be selected delicately and freely.
[0018]
Examples of the film used in the present invention include polyamides, polyesters, polyolefin films and the like, but particularly effective for polyamide films. Examples of the polyamide film include nylon 6, nylon 66, homopolymers such as nylon 11 and nylon 12, mixtures thereof, and copolymers. The film may contain known additives such as stabilizers, antioxidants, fillers, lubricants, antistatic agents, antiblocking agents, colorants and the like.
[0019]
【Example】
The characteristic value expressing the anisotropy of the film physical properties used in the present invention was measured by the following method.
(1) Hot water shrinkage rate The hot water shrinkage rate is obtained by drawing parallel lines at intervals of a measurement length of 110 mm with an oil-based magic and slitting it into a sample piece having a width of 10 mm. The sample piece is conditioned under an atmosphere of 20 ° C. and a relative humidity of 65%, and the dimension between the parallel lines is accurately measured to obtain _LBA . Next, this sample piece was boiled for 5 minutes in hot water at 100 ° C., conditioned again in the above atmosphere, and then the dimension between parallel lines was measured to be _LTR. calculate.
Hot water shrinkage S _HW (%) = {(L _BA −L _TR ) / L _BA } × 100
(2) Hot water shrinkage rate Hot water shrinkage rate at an angle of 45 ° with the width direction as the starting line for the central position in the width direction of the obliquely biaxially stretched film and 35% of the total width from the center to the left and right. Then, the hot water shrinkage rate in the 135 ° direction is obtained, and the absolute value of the difference between the shrinkage rate S (∠45 °) at an angle of 45 ° and the shrinkage rate S (∠135 °) at an angle of 135 ° is calculated as an oblique difference in hot water shrinkage rate. It was.
Hydrothermal shrinkage oblique difference ΔS = | S (∠45 °) −S (∠135 °) |
Next, the present invention will be specifically described with reference to examples.
[0020]
Example 1
Nylon 6 resin is melt-extruded from a 600 mm wide T-type die, cooled and solidified into a sheet on a cooling roll, an unstretched polyamide film with a thickness of 150 μm is formed, and then water-absorbed in a hot water tank adjusted to 50 ° C. It was. Next, this film was supplied to a simultaneous biaxial stretching tenter driven by a linear motor , both ends were gripped by clips, and simultaneous biaxial stretching was performed at a longitudinal stretching ratio of 3.0 times and a transverse stretching ratio of 3.3 times. . Note this time, 10% longitudinal stretching ratio trace than the transverse stretching magnification trace the origin of the transverse stretching ratio trajectory at the end of the longitudinal draw ratio trace was preceded 20%, longitudinal stretching ratio trajectory inclination of F _CP phi is ± 20 ° Selected to be within. Further, the film was heat treated at 215 ° C. in a tenter oven, relaxed by 2% in length and width, cooled, trimmed at both ends of the film, and wound up with a winder. A simultaneously biaxially stretched polyamide film product roll having a thickness of 15 μm was obtained. The speed was 120 m / min.
[0021]
The maximum reverse bowing deformation of the obtained film is 5%, the maximum bowing deformation is 0%, and the diagonal difference in hot water shrinkage is 0.8% or less in both the central position and the 35% position, and is uniform in the width direction. It was balanced and almost the entire film width was practical as a product.
[0022]
Comparative Example 1
Although manufactured under the same conditions as in Example 1, the longitudinal draw ratio locus was not preceded by the transverse draw ratio locus, and the longitudinal draw ratio locus was approximately approximated to the transverse draw ratio locus. The inclination φ of the longitudinal draw ratio trajectory F _CP, which is outside the scope of ± 45 °, the maximum reverse bowing deformation 30% of the resulting film, the maximum bowing deformation was 10%. In addition, the diagonal difference in hot water shrinkage was 0.8% or less at the center position, but 1.8% at the 35% position, showing a remarkable anisotropy, and the practical film product width was narrow. The product yield greatly deteriorated.
[0023]
【The invention's effect】
According to the present invention, by suppressing as much as possible the distortion in the width direction of the surface magnification locus caused by the simultaneous biaxial stretching method, the physical properties are made uniform in the width direction, and particularly excellent in mechanical characteristics, thermal dimensional stability, and optical characteristics. Simultaneously biaxially stretched film with high quality and performance can be produced in high yield.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram illustrating the relationship between a longitudinal draw ratio locus and a transverse draw ratio locus in the present invention.
FIG. 2 is a diagram showing the relationship between the stretching stress component and vector composite stress and the inclination in the present invention.

Claims (5)

Oite the tenter simultaneous biaxial stretching method by grasping the unstretched film edges by clips to the aspect simultaneously biaxial stretching, the origin and end point of the longitudinal draw ratio trace is preceded origin and end point of the transverse stretching ratio trajectory vertical A method for producing a simultaneous biaxially stretched film, characterized in that a leading ratio for causing the draw ratio locus to precede the transverse draw ratio locus is 5 to 20% . The simultaneous biaxial according to claim 1, wherein the longitudinal draw ratio is 2.5 to 4.5 times, and the ratio of the transverse draw ratio to the longitudinal draw ratio is 0.5 to 1.5. A method for producing a stretched film. In the film stretching stress exerted on the clip, the stress component acting vertically (lengthwise) direction _{F MD,} a lateral (width) across the direction stress component and _{F TD,} the vector synthesis stress resulting from _{F MD} and _{F TD} and _{F CP} 3. The simultaneous biaxially stretched film according to claim 1 , wherein the slope φ of F _CP with respect to F _TD is within ± 45 ° in a range from the start point to the end point of the transverse stretch magnification locus. Manufacturing method. The method for producing a simultaneous biaxially stretched film according to any one of claims 1 to 3 , wherein the tenter is driven by a linear motor system. The method for producing a simultaneous biaxially stretched film according to claim 1 , wherein the film is a polyamide film.

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