JP2008015780A - Prediction method for stress, distortion and anisotropy of film in tenter heating process by use of finite element method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a finite element analysis method for predicting a stress state, distortion or orientation state during the course of a film forming process which needs baking at high temperature with volatilization of a solvent. <P>SOLUTION: For predicting the stress state, distortion or orientation state, a disappearance phenomenon of a material is substituted by contraction, and elastic analysis and viscoelastic analysis are continuously performed, whereby accurate finite element analysis is performed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an analysis method for efficiently predicting stress and strain generated by deformation by a load such as heat in a process of manufacturing a film by heating and baking in a tenter heating step by a finite element method.

  In general, a method for producing a plastic film is obtained by continuously fixing both ends in the width direction with a gripping means such as a pin or a clip, passing through a heating furnace set at a plurality of temperatures, and performing stretching and heat setting. . This so-called tenter method is widely used industrially as an apparatus capable of performing heating, stretching, heat setting and cooling in order to develop desired physical properties while resisting film shrinkage during the heating process.

  In particular, a thermoplastic film represented by a PET (polyethylene terephthalate) film is one of the methods capable of mass-producing a product having a high biaxial orientation.

  However, it has been extremely difficult to make the physical properties of the product film uniform in the horizontal direction by the conventional method. The cause is due to a so-called bowing phenomenon, that is, a phenomenon in which the central portion where the binding force is weak is delayed or preceded by both ends in the width direction held by the tenter. This bowing phenomenon is closely related to the strong anisotropy due to molecular orientation, and causes various problems such as optical axis misalignment, poor flatness, mechanical property anisotropy, curl and wrinkles, and is not suitable for its use. .

  For example, Patent Document 1, Patent Document 2, Non-Patent Document 1, and Non-Patent Document 2 represent the finite element method against the physical property unevenness in the width direction and physical property anisotropy represented by the Boeing phenomenon. There has been proposed a method for producing a film with less bowing phenomenon by estimating the propagation of stretching stress in the tenter process based on the theoretical analysis using the.

  On the other hand, a polyimide film having excellent heat resistance, cold resistance, electrical insulation, chemical stability, etc. and having flexibility is also produced using the one tenter method. Polyimide film is generally insoluble and infusible, so it is casted with an organic solvent solution of polyamic acid, which is a precursor, and is partially dried and / or cured in the subsequent drying process. It is heated and baked by a tenter heating method through a so-called gel film having, and converted into a polyimide film.

  Similarly, in this method for producing a polyimide film, there is a problem that molecules are strongly oriented in an oblique direction particularly at the end in the width direction, causing anisotropy in physical properties (Non-patent Document 3).

  In the case of a polyimide film, since it is insoluble and infusible as described above, the method described in (Patent Document 1) and (Patent Document 2) using the glass transition temperature cannot be applied.

  In addition, (Patent Document 3) describes a method for producing a polyimide film having a small birefringence by controlling the ratio of biaxial stretching, but this method is limited to a film forming machine equipped with a stretching machine. Troubles such as the film breaking during stretching may occur, and the polyimide species is limited.

  On the other hand, in a polyimide film manufacturing method characterized by strong contraction force despite no aggressive stretching operation, stress state and strain are predicted based on theoretical analysis using the finite element method It has been difficult to do so far. This is because the shrinkage force described above is due to volatilization of the solvent remaining in the film and chemical reaction (imidization reaction), and it is difficult to express the disappearance of the substance by finite element analysis. .

Therefore, the problem of anisotropy due to the orientation described above must be relied on by trial and error using a pilot scale or an actual production machine, which requires cost and labor.
Japanese Patent Laid-Open No. 4-59332 (Japanese Patent No. 2841755) Japanese Patent Laid-Open No. 3-193328 (Japanese Patent No. 2600406) Japanese Patent Laid-Open No. 3-193329 (Patent No. 2920973) Journal of Polymer Science 52 (10),. 1393 (1994) Journal of Applied Polymer Science 48 (8),. 1399 (1993) Polymer Engineering Science, 18 (16), 1216 (1978)

  The present invention has been made in view of the above problems, and its purpose is to provide a means for analyzing stress states and strains in the polyimide film manufacturing process by a finite element method, in order to approach the orientation mechanism. It is to provide.

  The present inventors have investigated in advance the amount of the film to be shrunk by solvent volatilization and chemical reaction and the film stiffness that changes every moment in the tenter process at the laboratory level scale using the target polyimide film resin. Then, finite element analysis was performed based on these numerical data, and the state of stress in the tenter heating furnace, the distortion of the film, etc., which cannot be usually known, have been evaluated.

The gist of the invention is summarized in the following 1) to 5).
1) Create a model in which the film in the tenter heating process in the process of manufacturing a polyimide film is divided into a plurality of elements, and the stress and strain generated by heating the film using the finite element method for the model In a finite element analysis method for predicting molecular orientation,
(1) A step of obtaining an elastic modulus of a film to be analyzed that changes every moment in a plurality of tenter heating furnaces under an actual heating temperature condition;
(2) determining the amount to be contracted;
(3) A finite element analysis method comprising a step of performing an elastic analysis by calculating an elastic modulus and a shrinkage amount for the model divided into the plurality of elements.
2) Create a model by dividing the film in the tenter heating process in the process of manufacturing the polyimide film into a plurality of elements, and generate stress and strain by heating the film using the finite element method for the model In a finite element analysis method for predicting molecular orientation,
(1) A step of obtaining an elastic modulus of a film to be analyzed that changes every moment in a plurality of tenter heating furnaces under a heating temperature in an actual tenter furnace;
(2) determining the amount to be contracted;
(3) performing a linear elastic analysis on the model divided into the plurality of elements by performing an integral calculation of an elastic modulus and a contraction amount;
(4) In a temperature region equal to or higher than the inflection temperature of the storage elastic modulus recognized by the dynamic viscoelasticity measurement of the film, calculating viscoelasticity model constants from dynamic viscoelasticity data and performing viscoelasticity analysis;
(5) The finite element analysis method characterized by adding the elastic analysis result and the viscoelastic analysis result for all elements of the model.
3) The finite element analysis method according to 1) or 2), wherein the analysis target is a polyimide film forming step.
4) In the above 1) or 2), the film before being carried into the tenter heating step contains a residual solvent of at least 20% by weight with respect to the solid content, and volatilizes in a tenter heating furnace. Finite element analysis method.
5) The finite element analysis method according to 1) or 2) above, wherein a chemical reaction occurs in the film in a region at least a half of a residence time in the tenter heating step.

  According to the present invention, a plastic film formed by a tenter heating method, particularly a polyimide film characterized by volatilization and chemical reaction of residual solvent in an actual process, stress state in a tenter heating furnace, The strain can be evaluated, and the molecular orientation anisotropy of the original film after film formation can be evaluated.

  An embodiment for evaluating the stress state and distortion of the film in the tenter heating furnace of the film and the raw material of the film by the finite element analysis method of the present invention will be described below, and will be specifically described with reference to the drawings.

  FIG. 1 is a flowchart according to the present invention for analyzing and predicting stress and strain generated in a film forming process.

  According to the analysis method by the finite element method, as a first step, first, a range to be modeled is set from the film forming line to be analyzed and the film size. Subsequently, the dimension of the model is determined, and the coordinate axes in the analysis are associated with MD (Machine Direction) and TD (Transverse Direction) of the film forming line.

  Here, since the film thickness is overwhelmingly small and negligible compared to the film production line, it is preferable to adopt a two-dimensional model unless the thickness unevenness problem is targeted.

  Although the range set in the above step is divided into elements (triangle or quadrilateral), it is preferable to apply the quadrilateral model unless dealing with large deformation problems such as biaxial stretching.

  Next, the time per increment of analysis is determined. This can be appropriately determined according to the actual line length of the modeled range, the line speed, and the desired analysis accuracy.

  In the film forming process by the tenter method, the nodes at both ends of the width are restrained by the tenter gripping means. In particular, when the film is formed while keeping the tenter width constant, both the MD direction and the TD direction are constrained in all increments. However, before the gripping by the tenter and after releasing the gripping, the constraint condition must be released.

  At the beginning of the analysis, the elements are carried into the first zone of the tenter furnace. Here, in a process involving solvent volatilization during the film formation process, such as a polyimide film, a large shrinkage stress acts in the first zone. Therefore, the disappearance phenomenon of the substance called solvent volatilization is replaced with an amount that the film tends to shrink. Since it is actually gripped by the tenter, it does not shrink in the TD direction, and the stress is expected to propagate in the MD direction.

  In order to reproduce these behaviors, it is preferable to obtain in advance the film elastic modulus that changes every moment in the first zone and the amount to shrink. Although the transition of these physical property values is extremely lacking in linearity, it is preferable to approximate, for example, two straight lines in order to simplify and converge the analysis. At each increment during the first zone dwell, the stress state and film distortion can be calculated and predicted by using the elastic analysis given the modulus and the amount to shrink.

  In general, a plastic film is suddenly lowered in rigidity at a high temperature region, and stress relaxation is observed. In particular, the polyimide film needs to be treated at a high temperature (about 500 ° C.) during the film forming process. In the present invention, an approximate solution of the Maxwell model generalized to the WLF parameter of the target film is obtained in advance.

  The analysis of stress and strain in a series of film forming processes is completed by coupling elastic analysis and viscoelastic analysis.

Finally, the analysis result is output. It is preferable to output not only the direct stresses σx and σy and the shear stress τxy but also the maximum and minimum principal stresses σ _I and σ _II and their directions θ _I and θ _II .

  If the film to be analyzed is rigid and easily oriented in the direction of stress, the molecular orientation angle of the actual film can be predicted from the direction of the maximum principal stress obtained by the analysis.

Further, the anisotropy A of stress can be calculated by the following equation (1) from the maximum principal stress σ _I and the minimum principal stress σ _II , and the actual molecular orientation of the film can be predicted.
Stress anisotropy A = | σ _I −σ _II | / | σ _I + σ _II | Formula (1)
Also, the displacement dx of each node is output, and the bow difference state of the film, that is, the bowing state, can be evaluated by calculating the displacement difference between the central portion and the end portion of the width.
As described above, even in the film process that requires the disappearance phenomenon of the solvent volatilization and the baking at a high temperature, the finite element analysis can be performed by the above-described steps.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  The contents of the present invention will be described below based on examples by taking a polyimide film forming process as an example. The present invention is not limited thereby.

  FIG. 2 is a diagram showing division of analysis elements. A quadrilateral plane stress element is divided into 10 parts in the TD direction and 511 parts in the MD direction (5110 elements 5632 nodes). The restraint by the tenter gripping means is applied to the end node of the element in the tenter furnace.

  FIG. 3 shows the elastic modulus transition of the first half of the heating furnace according to the elastic constitutive law. It shows that after the elastic modulus once suddenly decreases due to heating, it gradually increases.

  FIG. 4 shows the contraction amount transition in the first zone according to the elastic constitutive law. It shows that the shrinkage is completed in the range of about 1/5 of the residence time of the first zone.

FIG. 5 considers the elastic modulus transition and shrinkage transition for each increment obtained by bilinear approximation in FIG. 3 and FIG. 4, and further considers the elastic modulus in consideration of the film elastic modulus in the front and rear zones. It is the result of having performed. The arrow in the figure indicates the direction Θ _I of the maximum principal stress σ _I. The mesh curve connects the nodes and is a Boeing curve. In the first zone, an inversion of the bowing curve is observed along the way. This indicates that a so-called gel film in front of the zone is drawn and a softer film is drawn in the second zone.

  FIG. 6 is a plot showing the direction of stress after completion of heating based on the analysis of the entire tenter heating furnace, taking viscoelastic constitutive law into consideration. The orientation angle of the actual film is also plotted.

  Further, FIG. 7 is a plot showing the stress anisotropy A derived from the equation (1) using the maximum principal stress and the minimum principal stress obtained by the analysis. FIG. 8 shows the molecular orientation MOR-c of an actual film measured with a microwave molecular orientation meter MOA-6015A (Oji Scientific Co., Ltd.).

  From the result shown in FIG. 6 and the comparison between FIG. 7 and FIG. 8, it can be said that the analysis result well reproduces the actual orientation state.

  As described above, with the finite element analysis means according to the present invention, it is possible to predict the stress, strain (Boeing strain), and orientation state of the film obtained by the tenter heating process, particularly the polyimide film.

It is a figure which shows the analysis step of the finite element analysis method concerning this invention. It is a figure which shows the element division concerning this invention, and a constraint condition. It is a figure which shows transition of the elasticity modulus in a 1st zone. It is a figure which shows the quantity which a film tends to shrink within a 1st zone. It is a figure which estimates the direction of the distortion of the film in the 1st zone, and principal stress by the finite element analysis of this invention. It is a figure which compares the direction of the stress obtained by the finite element analysis method of this invention, and the orientation angle of an actual film. It is a figure which shows the stress anisotropy A estimated by the finite element analysis method. It is a figure which shows the molecular orientation MOR-c of the polyimide film of analysis object.

Claims (5)

Create a model in which the film in the tenter heating process in the process of manufacturing a polyimide film is divided into a plurality of elements, and stress, strain, molecules generated by heating the film using the finite element method for the model In a finite element analysis method for predicting orientation,
(1) A step of obtaining an elastic modulus of a film to be analyzed that changes every moment in a plurality of tenter heating furnaces under an actual heating temperature condition;
(2) determining the amount to be contracted;
(3) performing an elastic analysis on the model divided into the plurality of elements by calculating an elastic modulus and a contraction amount;
A finite element analysis method characterized by comprising: Create a model in which the film in the tenter heating process in the process of manufacturing a polyimide film is divided into a plurality of elements, and stress, strain, molecules generated by heating the film using the finite element method for the model In a finite element analysis method for predicting orientation,
(1) A step of obtaining an elastic modulus of a film to be analyzed that changes every moment in a plurality of tenter heating furnaces under a heating temperature in an actual tenter furnace;
(2) determining the amount to be contracted;
(3) performing a linear elastic analysis on the model divided into the plurality of elements by performing an integral calculation of an elastic modulus and a contraction amount;
(4) In a temperature region equal to or higher than the inflection temperature of the storage elastic modulus recognized by the dynamic viscoelasticity measurement of the film, calculating viscoelasticity model constants from dynamic viscoelasticity data and performing viscoelasticity analysis;
(5) The finite element analysis method characterized by adding the elastic analysis result and the viscoelastic analysis result for all elements of the model.   3. The finite element analysis method according to claim 1, wherein the object of analysis is a process for forming an aromatic polyimide film.   The finite film according to claim 1 or 2, wherein the film before being carried into the tenter heating step contains a residual solvent of at least 20% by weight with respect to the solid content and volatilizes in a tenter heating furnace. Element analysis method.   3. The finite element analysis method according to claim 1, wherein a chemical reaction occurs in the film in a region of at least a half of a residence time in the tenter heating step.

Images