JP7572144B2 - Manufacturing method of resin film - Google Patents

Description

The present invention relates to a method for producing a resin film and a resin film.

Regarding a film of a resin containing a polymer having an alicyclic structure and crystallinity, a technique is known in which the film is heated to promote crystallization of the polymer. For example, Patent Documents 1 to 3 propose a technique for producing a film by stretching a film of a resin containing a polymer having an alicyclic structure and crystallinity, and then heating the film to promote crystallization (see Patent Documents 1 to 3).

International Publication No. 2016/052303 International Publication No. 2018/061841 International Publication No. 2018/062067

However, with conventional manufacturing methods that produce films using resins that contain alicyclic structures and crystalline polymers, it has been difficult to produce resin films with excellent slip properties.

The present invention was devised in view of the above problems, and aims to provide a manufacturing method for producing a resin film with excellent slip properties using a resin that contains a polymer that has an alicyclic structure and is crystalline, and a resin film produced by the manufacturing method.

The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by a production method including a step 1 of preparing a pre-stretched film having a crystalline resin layer made of a crystalline resin containing a polymer having an alicyclic structure and crystallinity, a step 2 of heating the pre-stretched film at a specific temperature for a specific time, a step 3 of stretching the pre-stretched film at a specific stretching temperature and a specific areal ratio to obtain a stretched film, and a step 4 of lowering the temperature of the stretched film to room temperature, thereby completing the present invention.
That is, the present invention includes the following.

[1] A step 1 of preparing a pre-stretched film having a resin layer made of a crystalline resin containing a polymer having an alicyclic structure and crystallinity;
A step 2 of heating the pre-stretched film at a temperature Tp of not less than "Tc-10°C" and not more than "Tc+35°C" for a time tp (where Tc represents the crystallization peak temperature [°C] of the crystalline resin);
A step 3 of stretching the pre-stretched film subjected to the step 2 at a stretching temperature Ts equal to or lower than the temperature Tp at an areal magnification of 1.6 times or more and 6.3 times or less to obtain a stretched film;
A step 4 of lowering the temperature of the stretched film to room temperature;
The temperature Tp [° C.] and the time tp [seconds] satisfy the following formula (i),
10000≦{Tp-(Tc-15)} ² ×tp≦30000 (i)
A method for producing a resin film, wherein after the stretched film is obtained in step 3, the temperature of the stretched film is maintained at or below Ts until the temperature of the stretched film reaches room temperature in step 4.
[2] The method for producing a resin film according to [1], wherein the polymer containing an alicyclic structure and having crystallinity is a hydrogenated product of a ring-opening polymer of dicyclopentadiene.
[3] The pre-stretched film has two or more of the resin layers,
The method for producing a resin film according to [1] or [2], further comprising providing one or more intermediate layers made of a thermoplastic resin other than the crystalline resin between the resin layers.
[4] The method for producing a resin film according to [3], wherein the glass transition temperature of the thermoplastic resin is equal to or higher than the glass transition temperature of the crystalline resin and equal to or lower than "Ts+20°C".
[5] A resin film produced by the production method according to any one of [1] to [4],
The resin film has a surface having a static friction coefficient of 0.7 or less.
[6] The resin film according to [5], wherein the internal haze of the resin film is 1.0% or less.
[7] The resin film according to [5] or [6], wherein the b ^* of the resin film in the CIE-Lab color system is 1.0 or less.

The present invention provides a manufacturing method that can easily produce a resin film with excellent slipperiness using a resin that contains a polymer that has an alicyclic structure and is crystalline, and a resin film manufactured by the manufacturing method.

The present invention will be described in detail below with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples shown below, and may be modified and implemented as desired without departing from the scope of the claims of the present invention and their equivalents.

In the following description, a "long" film refers to a film that is 5 times or more longer than its width, preferably 10 times or more longer, specifically a film that is long enough to be wound into a roll for storage or transportation. There is no particular upper limit on the length, but it is usually 100,000 times or less longer than the width.

In the following description, the longitudinal direction of a long film is usually parallel to the film transport direction in the production line. The MD direction (machine direction) is the film transport direction in the production line, and is usually parallel to the longitudinal direction of a long film. The TD direction (transverse direction) is a direction parallel to the film surface, perpendicular to the MD direction, and usually parallel to the width direction of a long film.

In the following description, the in-plane retardation Re of a film is a value expressed as Re = (nx - ny) x d, unless otherwise specified. Here, nx represents the refractive index in the direction perpendicular to the thickness direction of the film (in-plane direction) that gives the maximum refractive index. ny represents the refractive index in the in-plane direction perpendicular to the direction of nx. d represents the thickness of the film. The measurement wavelength is 590 nm, unless otherwise specified.

[1. Overview of resin film manufacturing method]
The method for producing a resin film according to one embodiment of the present invention is a method for producing a resin film having a resin layer made of a crystalline resin by using a crystalline resin as a resin containing a polymer having a crystalline structure and an alicyclic structure. In the following description, a polymer having a crystalline structure and an alicyclic structure may be referred to as an "alicyclic crystalline polymer". Also, a resin layer made of a crystalline resin may be referred to as a "crystalline resin layer". The crystalline resin layer is a layer formed by a crystalline resin, and therefore may usually be a layer containing only a crystalline resin.

A method for producing a resin film according to one embodiment of the present invention includes the steps of:
A step 1 of preparing a pre-stretched film having a crystalline resin layer made of a crystalline resin containing an alicyclic crystalline polymer;
Step 2 of heating the pre-stretched film at a specific temperature Tp for a specific time tp;
A step 3 of stretching the pre-stretched film subjected to the step 2 at a specific stretching temperature Ts and a specific areal ratio to obtain a stretched film;
and step 4 of lowering the temperature of the stretched film to room temperature.

This manufacturing method produces a resin film having a crystalline resin layer made of a crystalline resin containing an alicyclic crystalline polymer. The resin film thus obtained has excellent slip properties.

In the following description, the temperature Tp to which the pre-stretched film is heated in step 2 may be referred to as the "preheating temperature." Also, the time tp during which the pre-stretched film is heated to the preheating temperature Tp in step 2 may be referred to as the "preheating time."

[2. Step 1 (Preparation of pre-stretched film)]
In step 1, a pre-stretched film having a crystalline resin layer made of a crystalline resin is prepared. The crystalline resin is a resin containing an alicyclic crystalline polymer as a polymer containing an alicyclic structure and having crystallinity, and may contain any component other than the alicyclic crystalline polymer as necessary. This crystalline resin is preferably a thermoplastic resin.

A polymer containing an alicyclic structure refers to a polymer that contains an alicyclic structure in the molecule. Such a polymer containing an alicyclic structure may be, for example, a polymer that can be obtained by a polymerization reaction using a cyclic olefin as a monomer, or a hydrogenated product thereof. By using an alicyclic crystalline polymer as a polymer containing an alicyclic structure, the mechanical properties, heat resistance, transparency, low moisture absorption, dimensional stability, and light weight of the resin film can be improved.

Examples of alicyclic structures include cycloalkane structures and cycloalkene structures. Among these, cycloalkane structures are preferred because they are more likely to produce resin films with excellent properties such as thermal stability. The number of carbon atoms contained in one alicyclic structure is preferably 4 or more, more preferably 5 or more, and preferably 30 or less, more preferably 20 or less, and particularly preferably 15 or less. When the number of carbon atoms contained in one alicyclic structure is within the above range, mechanical strength, heat resistance, and moldability are highly balanced.

In the alicyclic crystalline polymer, the ratio of the structural units containing an alicyclic structure to all structural units is preferably 30% by weight or more, more preferably 50% by weight or more, and particularly preferably 70% by weight or more. When the ratio of the structural units containing an alicyclic structure is high as described above, the heat resistance can be improved. The ratio of the structural units containing an alicyclic structure to all structural units can be 100% by weight or less. In the alicyclic crystalline polymer, the remainder other than the structural units containing an alicyclic structure is not particularly limited and can be appropriately selected depending on the purpose of use.

Alicyclic crystalline polymers have crystallinity. A "polymer having crystallinity" refers to a polymer that has a melting point Tm (i.e., the melting point can be observed by differential scanning calorimetry (DSC)).

The melting point Tm of the alicyclic crystalline polymer is preferably 200°C or higher, more preferably 230°C or higher, and preferably 290°C or lower. By using an alicyclic crystalline polymer having such a melting point Tm, a resin film with an even better balance between moldability and heat resistance can be obtained.

The melting point Tm of a polymer can be measured by the following method. First, the polymer is melted by heating, and the molten polymer is rapidly cooled with dry ice. Next, this polymer is used as a test specimen and the melting point Tm of the polymer can be measured at a heating rate of 10°C/min (heating mode) using a differential scanning calorimeter (DSC).

Examples of the alicyclic crystalline polymer include the following polymer (α) to polymer (δ). Among these, polymer (β) is preferred because it is easy to obtain a resin film having excellent heat resistance.
Polymer (α): A ring-opening polymer of a cyclic olefin monomer, which has crystallinity.
Polymer (β): A hydrogenated product of polymer (α) and has crystallinity.
Polymer (γ): An addition polymer of a cyclic olefin monomer, which has crystallinity.
Polymer (δ): A hydrogenated polymer (γ) having crystallinity.

Specifically, the alicyclic crystalline polymer is preferably a ring-opening polymer of dicyclopentadiene that has crystallinity, or a hydrogenated ring-opening polymer of dicyclopentadiene that has crystallinity. Among these, a hydrogenated ring-opening polymer of dicyclopentadiene that has crystallinity is particularly preferred. Here, a ring-opening polymer of dicyclopentadiene refers to a polymer in which the ratio of structural units derived from dicyclopentadiene to all structural units is usually 50% by weight or more, preferably 70% by weight or more, more preferably 90% by weight or more, and even more preferably 100% by weight.

The hydrogenated ring-opening polymer of dicyclopentadiene preferably has a high ratio of racemo dyads. Specifically, the ratio of racemo dyads in the repeating units of the hydrogenated ring-opening polymer of dicyclopentadiene is preferably 51% or more, more preferably 70% or more, and particularly preferably 85% or more. A high ratio of racemo dyads indicates high syndiotactic stereoregularity. Therefore, the higher the ratio of racemo dyads, the higher the melting point of the hydrogenated ring-opening polymer of dicyclopentadiene tends to be.
The ratio of the racemo dyads can be determined based on the ¹³ C-NMR spectrum analysis described in the Examples below.

The above polymers (α) to (δ) can be produced, for example, by the production method disclosed in WO 2018/062067.

The weight average molecular weight (Mw) of the alicyclic crystalline polymer is preferably 1,000 or more, more preferably 2,000 or more, and preferably 1,000,000 or less, more preferably 500,000 or less. An alicyclic crystalline polymer having such a weight average molecular weight has an excellent balance between moldability and heat resistance.

The molecular weight distribution (Mw/Mn) of the alicyclic crystalline polymer is preferably 1.0 or more, more preferably 1.5 or more, and preferably 4.0 or less, more preferably 3.5 or less. Here, Mn represents the number average molecular weight. An alicyclic crystalline polymer having such a molecular weight distribution has excellent moldability.

The weight average molecular weight (Mw) and molecular weight distribution (Mw/Mn) of the polymer can be measured in polystyrene equivalent values by gel permeation chromatography (GPC) using tetrahydrofuran as the developing solvent.

The crystallinity of the alicyclic crystalline polymer contained in the crystalline resin layer of the pre-stretched film before step 2 is preferably small, from the viewpoint of particularly easily producing a resin film with excellent slip properties. The specific crystallinity is preferably less than 10%, more preferably less than 5%, and particularly preferably less than 3%. In addition, the alicyclic crystalline polymer contained in the crystalline resin layer of the pre-stretched film does not have to be crystallized. The crystallinity of the polymer can be measured by X-ray diffraction.

The alicyclic crystalline polymer may be used alone or in any combination of two or more kinds in any ratio.

The proportion of the alicyclic crystalline polymer in the crystalline resin is preferably 50% by weight or more, more preferably 70% by weight or more, and particularly preferably 90% by weight or more. When the proportion of the alicyclic crystalline polymer is equal to or greater than the lower limit of the above range, the birefringence expression and heat resistance of the resin film can be improved. The upper limit of the proportion of the alicyclic crystalline polymer can be 100% by weight or less.

The crystalline resin may further contain optional components in combination with the alicyclic crystalline polymer. Optional components include, for example, antioxidants such as phenol-based antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants; light stabilizers such as hindered amine-based light stabilizers; waxes such as petroleum wax, Fischer-Tropsch wax, and polyalkylene wax; nucleating agents such as sorbitol-based compounds, metal salts of organic phosphoric acids, metal salts of organic carboxylic acids, kaolin, and talc; diaminostilbene derivatives, coumarin derivatives, and azole derivatives (e.g., benzoxazole derivatives, benzotriazole derivatives, benzimidazolate derivatives, and benzotriazole derivatives). Examples of the optional components include fluorescent brighteners such as benzothiazole derivatives, carbazole derivatives, pyridine derivatives, naphthalic acid derivatives, and imidazolone derivatives; ultraviolet absorbers such as benzophenone-based ultraviolet absorbers, salicylic acid-based ultraviolet absorbers, and benzotriazole-based ultraviolet absorbers; inorganic fillers such as talc, silica, calcium carbonate, and glass fiber; colorants; flame retardants; flame retardant assistants; antistatic agents; plasticizers; near-infrared absorbers; lubricants; fillers; and any polymer other than alicyclic crystalline polymers, such as soft polymers. One type of optional component may be used alone, or two or more types may be used in any ratio.

A crystalline resin containing an alicyclic crystalline polymer usually has a crystallization peak temperature Tc. The crystallization peak temperature Tc is not particularly limited, but is preferably 120°C or higher and preferably 220°C or lower.

Crystalline resins containing alicyclic crystalline polymers usually have a glass transition temperature Tg. Hereinafter, the glass transition temperature of the crystalline resin may be abbreviated as "Tg(1)" to distinguish it from the glass transition temperatures of other components. The glass transition temperature Tg(1) of the crystalline resin is not particularly limited, but is usually 85°C or higher and usually 170°C or lower.

The glass transition temperature Tg and crystallization peak temperature Tc of a resin can be measured by the following method. The resin is heated to 300°C in a nitrogen atmosphere to melt it, and the molten resin is quenched with liquid nitrogen. Using this resin as a sample, a differential scanning calorimeter (DSC) is used to increase the temperature at 10°C/min to determine the glass transition temperature Tg and crystallization peak temperature Tc of the resin.

The number of crystalline resin layers in the pre-stretched film may be one or two or more. When the pre-stretched film has two or more crystalline resin layers, the composition and thickness of the crystalline resin layers may be the same or different.

The thickness of each crystalline resin layer contained in the pre-stretched film is preferably 5 μm or more, more preferably 10 μm or more, and particularly preferably 15 μm or more, and is preferably 300 μm or less, more preferably 200 μm or less, even more preferably 100 μm or less, and particularly preferably 80 μm or less.

The pre-stretching film may be a film having only a crystalline resin layer. In this case, a resin film having only a crystalline resin layer can usually be produced. The pre-stretching film may also have an optional layer made of a resin other than a crystalline resin in combination with the crystalline resin layer. In this case, a resin film having a crystalline resin layer in combination with an optional layer can usually be produced.

The number and position of the optional layers may be any as long as they do not significantly impair the effects of the present invention. For example, the optional layer may be provided on one side of the crystalline resin layer, or on both sides of the crystalline resin layer. When the optional layers are provided on both sides of the crystalline resin layer, for example, the optional layer may be peeled off after the fourth step to expose the crystalline resin layer, thereby making it possible to utilize the excellent slipperiness of the exposed surface of the crystalline resin layer.

In particular, in a pre-stretched film having two or more crystalline resin layers, the optional layer is preferably provided between the crystalline resin layers. The optional layer provided between the crystalline resin layers in this way is sometimes called an "intermediate layer." The number of intermediate layers may be one or two or more. By providing an intermediate layer between the crystalline resin layers, it is possible to make the intermediate layer exhibit mechanical or optical properties while utilizing the excellent slip properties exhibited by the crystalline resin layer. Thus, depending on the composition of the intermediate layer, a resin film having various properties and excellent slip properties can be obtained.

Any layer such as the intermediate layer may be formed of a thermoplastic resin other than the above-mentioned crystalline resin. Such a thermoplastic resin may usually contain a polymer other than an alicyclic crystalline polymer and, if necessary, any component. Examples of the polymer include a polymer containing an alicyclic structure and not having crystallinity, polyethylene terephthalate, polyethylene naphthalate, an acrylic polymer, a methacrylic polymer, polyethylene, polypropylene, polycarbonate, polystyrene, triacetyl cellulose, polyvinyl chloride, polyimide, polyphenylene sulfide, polytetrafluoroethylene, polyether ether ketone, polyether sulfone, aramid, and combinations thereof. Among these, a polymer containing an alicyclic structure and not having crystallinity is preferred from the viewpoints of excellent adhesion to the crystalline resin layer, high orientation control, transparency, low moisture absorption, dimensional stability, and light weight. As a polymer containing an alicyclic structure and not having crystallinity, a norbornene-based polymer is more preferred. These polymers may be used alone or in combination of two or more types in any ratio.

Optional components that may be contained in the thermoplastic resin contained in any layer include, for example, the same examples as the optional components that may be contained in the crystalline resin. In addition, the optional components may be used alone or in combination of two or more types in any ratio.

The thermoplastic resin contained in any layer such as the intermediate layer usually has a glass transition temperature Tg. Hereinafter, the glass transition temperature of this thermoplastic resin may be abbreviated as "Tg(2)" to distinguish it from the glass transition temperature Tg(1) of the crystalline resin. The glass transition temperature Tg(2) of the thermoplastic resin is preferably Tg(1) or higher, more preferably "Tg(1)+10°C" or higher, particularly preferably "Tg(1)+20°C" or higher, and is preferably "Ts+20°C" or lower, more preferably "Ts+15°C" or lower, particularly preferably "Ts+10°C" or lower. The "Ts" represents the stretching temperature of the film before stretching in step 3. When the glass transition temperature Tg(2) of the thermoplastic resin is equal to or higher than the lower limit of the range, breakage during the stretching process can be suppressed. When the glass transition temperature Tg(2) of the thermoplastic resin is equal to or lower than the upper limit of the range, the film thickness controllability after stretching can be sufficiently ensured.

The thickness of the pre-stretched film can be appropriately set depending on the thickness of the resin film. The specific thickness of the pre-stretched film is preferably 1 μm or more, more preferably 5 μm or more, and preferably 1 mm or less, more preferably 200 μm or less.

The pre-stretch film may be a sheet of film, but is preferably a long film. By using a long pre-stretch film, it is possible to continuously manufacture the resin film by the roll-to-roll method, so that the productivity of the resin film can be effectively increased.

There are no limitations on the method for producing the pre-stretched film. Since the pre-stretched film does not contain organic solvents, resin molding methods such as injection molding, extrusion molding, press molding, inflation molding, blow molding, calendar molding, cast molding, and compression molding are preferred as methods for producing the pre-stretched film. Among these, extrusion molding is preferred because it is easy to control the thickness.

A pre-stretched film having a multilayer structure with two or more layers can be produced, for example, by molding the resins corresponding to each layer by a co-extrusion molding method. Examples of co-extrusion molding methods include the co-extrusion T-die method, the co-extrusion inflation method, and the co-extrusion lamination method. Among these, the co-extrusion T-die method is preferred. The co-extrusion T-die method includes the feed block method and the multi-manifold method, and the multi-manifold method is particularly preferred in that it can reduce thickness variation.

The manufacturing conditions in the extrusion molding method are preferably as follows. The cylinder temperature (molten resin temperature) is preferably Tm or higher, more preferably "Tm + 20 ° C" or higher, and preferably "Tm + 100 ° C" or lower, more preferably "Tm + 50 ° C" or lower. In addition, the cooling body that the molten resin extruded into a film first comes into contact with is not particularly limited, but a cast roll is usually used. The cast roll temperature is preferably "Tg (1) - 50 ° C" or higher, preferably "Tg (1) + 70 ° C" or lower, more preferably "Tg (1) + 40 ° C" or lower. Furthermore, the cooling roll temperature is preferably "Tg (1) - 70 ° C" or higher, more preferably "Tg (1) - 50 ° C" or higher, and preferably "Tg (1) + 60 ° C" or lower, more preferably "Tg (1) + 30 ° C" or lower. When a pre-stretched film is manufactured under such conditions, a pre-stretched film having a thickness of 1 μm to 1 mm can be easily manufactured. Here, "Tm" represents the melting point of the alicyclic crystalline polymer, and "Tg(1)" represents the glass transition temperature of the crystalline resin.

[3. Step 2 (preheating step)]
After obtaining the pre-stretched film in step 1, step 2 is performed in which the pre-stretched film is heated at a specific pre-heating temperature Tp for a pre-heating time tp. According to step 2, the temperature of the pre-stretched film can be adjusted to about the stretching temperature Ts before performing step 3 described below, so that stretching in step 3 can be performed smoothly. Furthermore, in such step 2, crystallization of the alicyclic crystalline polymer contained in the crystalline resin can partially proceed.

The preheating temperature Tp is usually at least "Tc - 10°C", preferably at least "Tc - 5°C", and usually at most "Tc + 35°C", preferably at most "Tc + 30°C", and particularly preferably at most "Tc + 25°C". "Tc" represents the crystallization peak temperature of the crystalline resin. When the preheating temperature Tp is within the above range, the slipperiness of the resin film obtained by the manufacturing method according to this embodiment can be improved, and furthermore, internal haze and coloration can usually be reduced.

The preheating time tp is usually set so that the preheating temperature Tp [°C] and the preheating time tp [seconds] satisfy the following formula (i): In formula (i), the units of the preheating temperature Tp and the crystallization peak temperature Tc of the crystalline resin are "°C", and the unit of the preheating time tp is "seconds".
10000≦{Tp-(Tc-15)} ² ×tp≦30000 (i)

More specifically, the parameter represented by {Tp-(Tc-15)} ² ×tp is usually 10,000 or more, preferably 12,000 or more, particularly preferably 14,000 or more, and usually 30,000 or less, preferably 28,000 or less, more preferably 26,000 or less, particularly preferably 24,000 or less. In the following description, the parameter represented by "{Tp-(Tc-15)} ² ×tp" may be referred to as the "preheating parameter". When the preheating parameter is within the above range, the slipperiness of the resin film obtained by the production method according to this embodiment can be increased, and furthermore, internal haze and coloration can usually be reduced. In addition, when the preheating parameter is equal to or greater than the lower limit of the above range, the crystallization of the alicyclic crystalline polymer can be advanced in step 2. Furthermore, when the preheating parameter is equal to or less than the upper limit of the above range, excessive progress of crystallization of the alicyclic crystalline polymer can be suppressed.

Step 2 can be carried out, for example, by exposing the pre-stretched film to an atmosphere adjusted to a pre-heating temperature Tp for a pre-heating time tp. In this case, step 2 can be carried out by a temperature control device capable of adjusting the temperature of the atmosphere of the pre-stretched film, such as an oven. Since the pre-stretched film is generally thin, when the above-mentioned temperature control device is used, the temperature of the pre-stretched film can usually be the same as the temperature of the atmosphere adjusted by the temperature control device. Therefore, the pre-heating temperature Tp can be the same as the set temperature of the temperature control device.

Alternatively, step 2 can be performed, for example, by contacting the pre-stretched film with a heating section whose temperature is adjusted to the pre-heating temperature Tp for a pre-heating time tp. In this case, step 2 can be performed by a heating device having the above-mentioned heating section, such as a hot plate. When the above-mentioned heating device is used, the temperature of the pre-stretched film can usually be the same as the temperature of the heating section. Therefore, the pre-heating temperature Tp can be the same as the set temperature of the heating device.

In particular, it is preferable to carry out step 2 using a device capable of heating the pre-stretched film without contact. Specific examples of such devices include ovens and heating furnaces.

As a preferred specific example, step 2 can be performed using a temperature-adjustable oven. For example, step 2 can be performed by storing the unstretched film in an oven and adjusting the temperature of the oven so as to satisfy the above-mentioned conditions.
As another preferred specific example, step 2 can be performed using an oven having a film transport path therein. For example, step 2 can be performed by transporting the pre-stretched film through the film transport path of an oven whose temperature is adjusted to satisfy the above-mentioned conditions for a time period that satisfies the above-mentioned conditions.

Step 2 is usually carried out so that the pre-stretched film is not substantially stretched. The pre-stretched film is "substantially stretched" when the pre-stretched film is stretched to a stretch ratio of 1.1 times or more in any direction.

Furthermore, in step 2, it is preferable that the pre-stretch film is in a taut state. The "taut state" of the pre-stretch film refers to a state in which tension is applied to the pre-stretch film. However, this taut state does not include a state in which the pre-stretch film is substantially stretched.

For example, the pre-stretch film can be placed in a tensile state by holding a part or the entirety of the pre-stretch film with an appropriate holding device. Typically, the edge of the pre-stretch film is held with the holding device. The holding device may be capable of continuously holding the entire length of the edge of the pre-stretch film, or may be capable of holding it intermittently at intervals. For example, the edge of the pre-stretch film may be held intermittently by holding devices arranged at a predetermined interval.

It is preferable that at least two sides of the pre-stretch film are held and kept in a tensed state. In this case, deformation of the pre-stretch film due to thermal shrinkage is prevented in the area between the held sides. In order to prevent deformation over a wide area of the pre-stretch film, it is preferable to hold the sides including the two opposing sides and keep the area between the held sides in a tensed state. For example, in a rectangular sheet of pre-stretch film, deformation can be prevented over the entire surface of the sheet of pre-stretch film by holding two opposing sides (e.g., the long sides or the short sides) and keeping the area between the two sides in a tensed state. In addition, in a long pre-stretch film, deformation can be prevented over the entire surface of the long pre-stretch film by holding two sides (i.e., the long sides) at the ends in the width direction and keeping the area between the two sides in a tensed state. In the pre-stretch film prevented from deformation in this way, even if stress occurs in the film due to thermal shrinkage, the occurrence of deformation such as wrinkles is suppressed.

To more reliably suppress deformation due to heating, it is preferable to hold more sides. Thus, for example, in the case of a sheet of pre-stretched film, it is preferable to hold all of its sides. As a specific example, in the case of a rectangular sheet of pre-stretched film, it is preferable to hold all four sides.

A holder capable of holding the edges of the pre-stretched film is preferably one that does not come into contact with the pre-stretched film in any area other than the edges of the pre-stretched film. By using such a holder, a resin film with superior smoothness can be obtained.

In addition, it is preferable that the holders be capable of fixing the relative positions of the holders while they are holding the pre-stretched film. Such holders do not move relative to each other, making it easier to suppress substantial stretching of the pre-stretched film.

Suitable holding devices include, for example, holders for rectangular pre-stretched films, such as clips that are provided at a predetermined interval on a frame material and can grip the sides of the pre-stretched film. Also, for example, a holding device for holding two sides at the ends in the width direction of a long pre-stretched film includes grippers that are provided on a tenter stretching machine and can grip the sides of the pre-stretched film.

When a long pre-stretched film is used, the edge at the end in the longitudinal direction of the pre-stretched film (i.e., the short edge) may be held, but instead of holding the edge, both longitudinal sides of the region of the pre-stretched film to be subjected to process 2 may be held. For example, a holding device that can hold the pre-stretched film in a taut state so as not to cause thermal shrinkage may be provided on both longitudinal sides of the region of the pre-stretched film to be subjected to process 2. Examples of such a holding device include a combination of two rolls, a combination of an extruder and a take-up roll, etc. By applying tension such as conveying tension to the pre-stretched film using these combinations, it is possible to suppress thermal shrinkage of the pre-stretched film in the region to be subjected to process 2. Therefore, if the above combination is used as a holding device, the pre-stretched film can be held while being conveyed in the longitudinal direction, allowing efficient production of resin films.

[4. Process 3 (stretching process)]
After the step 2, the unstretched film is stretched at a specific stretching temperature Ts and a specific areal ratio in the step 3. The stretching in the step 3 forms a crystalline resin layer and an optional layer, if necessary. A stretched film having the above-mentioned layers is obtained as a stretched film. Usually, steps 2 and 3 are performed consecutively, so that no other steps are performed between steps 2 and 3.

The stretching temperature Ts of the pre-stretched film in step 3 is usually equal to or lower than the preheating temperature Tp. The stretching temperature Ts may be lower than the preheating temperature Tp, for example, equal to or lower than Tp-5°C, equal to or lower than Tp-10°C, etc. The lower limit of the stretching temperature Ts is preferably equal to or higher than "Tg+5°C", more preferably equal to or higher than "Tg+10°C", from the viewpoint of obtaining a resin film with excellent uniformity by sufficiently softening the crystalline resin and performing uniform stretching.

The areal stretching ratio of the pre-stretched film in step 3 is usually 1.6 times or more, preferably 1.8 times or more, particularly preferably 2.0 times or more, and usually 6.3 times or less, preferably 5.0 times or less, particularly preferably 4.0 times or less. The areal stretching ratio is a stretching ratio expressed as the ratio of the "area of the stretched film" to the "area of the film before stretching", and is therefore expressed by the following formula (ii).
Area ratio = {(area of stretched film) / (area of film before stretching)} (ii)

When the areal stretching ratio in step 3 is within the above range, the slipperiness of the resin film obtained by the manufacturing method according to this embodiment can be improved, and furthermore, internal haze and coloration can usually be reduced. Furthermore, when the areal stretching ratio is equal to or greater than the lower limit of the above range, a sufficiently high unevenness can be formed on the surface of the crystalline resin layer by stretching. Furthermore, when the areal stretching ratio is equal to or less than the upper limit of the above range, excessive progression of oriented crystallization can be suppressed.

There are no particular limitations on the stretching method, and any stretching method can be used. Examples include uniaxial stretching methods, such as a method in which a pre-stretched film is uniaxially stretched in the longitudinal direction (longitudinal uniaxial stretching method) or a method in which a pre-stretched film is uniaxially stretched in the width direction (transverse uniaxial stretching method); biaxial stretching methods, such as a simultaneous biaxial stretching method in which a pre-stretched film is stretched in the longitudinal direction and at the same time in the width direction, and a sequential biaxial stretching method in which a pre-stretched film is stretched in one of the longitudinal and width directions and then stretched in the other direction; and a method in which a pre-stretched film is stretched in an oblique direction that is neither parallel nor perpendicular to the width direction (oblique stretching method).

The longitudinal uniaxial stretching method may be, for example, a stretching method that utilizes the difference in peripheral speed between rolls.
The transverse uniaxial stretching method may be, for example, a stretching method using a tenter stretching machine.
Furthermore, examples of the simultaneous biaxial stretching method include a stretching method in which a tenter stretching machine having a plurality of clips that are movably arranged along guide rails and can fix the pre-stretched film is used to stretch the pre-stretched film in the longitudinal direction by opening the clips, and at the same time, the pre-stretched film is stretched in the width direction by the spread angle of the guide rails.
In addition, examples of the sequential biaxial stretching method include a stretching method in which a pre-stretched film is stretched in the longitudinal direction by utilizing the difference in peripheral speed between rolls, and then both ends of the pre-stretched film are held with clips and stretched in the width direction by a tenter stretching machine.
Further, examples of the oblique stretching method include a stretching method in which a pre-stretched film is continuously stretched in an oblique direction using a tenter stretching machine that can apply a feeding force, a tensile force or a take-up force at different speeds to the left and right in the longitudinal or width direction of the pre-stretched film.

[5. Process 4 (cooling process)]
After step 3, step 4 is performed to lower the temperature of the stretched film to room temperature. The room temperature refers to an environmental temperature where no particular temperature control is performed, and can be, for example, a temperature of 10° C. or higher and 40° C. or lower. By lowering the temperature of the stretched film to room temperature in this manner, the stretched film can be obtained as a resin film. No other steps are carried out in between.

The above-mentioned step 4 is usually carried out so that the temperature of the stretched film is maintained at or below the stretching temperature Ts during the period from when the stretched film is obtained in step 3 until the temperature of the stretched film reaches room temperature in step 4. Therefore, step 4 usually does not include a case in which the temperature of the stretched film temporarily becomes higher than the stretching temperature Ts.

During the period in which the temperature of the stretched film is reduced in step 4, it is preferable that the stretched film is kept in a tensed state. This makes it possible to suppress the occurrence of deformations such as wrinkles due to shrinkage. When tension is applied to the stretched film, for example, the stretched film may be kept in a tensed state by holding the stretched film with an appropriate holder. For example, the same holder as that described as the holder that can be used to apply tension to the unstretched film in step 2 can be used as this holder.

Usually, by removing the stretched film from the stretching machine used in step 3, the stretched film begins to cool rapidly, and the temperature of the stretched film falls to room temperature in a short time. In detail, the stretching in step 3 is usually performed in a stretching machine equipped with an oven, so the stretched film begins to cool by being removed from the oven of the stretching machine. Since the stretched film is generally thin, the cooling proceeds quickly, and the temperature of the stretched film can reach room temperature in a short time. Therefore, step 4 can be performed, for example, by removing the stretched film from the stretching machine.

6. Optional steps
The method for producing a resin film according to the embodiment described above may further include any optional step in combination with the steps described above.

According to the above-described manufacturing method, a long resin film can be manufactured using a long pre-stretched film. Therefore, the manufacturing method of the resin film may include, for example, a step of winding up the long resin film manufactured in this manner into a roll. Furthermore, the manufacturing method of the resin film may include a step of cutting the long resin film into a desired shape.

[7. Produced resin film]
According to the above-mentioned manufacturing method, a resin film having a crystalline resin layer and further having any layer as necessary can be manufactured. In this resin film, the surface of the crystalline resin layer has excellent slip properties. Therefore, according to the above-mentioned manufacturing method, it is not necessary to apply a slip treatment to the surface or to attach a masking film, and a resin film having excellent slip properties can be easily manufactured.

The slipperiness can be expressed by the static friction coefficient. The resin film produced by the above-mentioned production method can have a surface with a small static friction coefficient. The specific static friction coefficient is preferably 0.70 or less, more preferably 0.60 or less, and particularly preferably 0.50 or less. Usually, the surface of the crystalline resin layer of the resin film can have a small static friction coefficient as described above.
The static friction coefficient can be measured in accordance with JIS K 7125. Specifically, the static friction coefficient between the surfaces of resin films can be measured by the method described in the Examples below.

The resin film produced by the above-mentioned production method can usually have a small internal haze. Specifically, the internal haze is preferably 1.0% or less, more preferably 0.8% or less, and particularly preferably 0.5% or less. A resin film having such a small internal haze has excellent transparency, and can improve the image clarity of an image display device including the resin film. The lower limit of the internal haze of the resin film is ideally 0.0%, but may be more than 0.0%.

Generally, haze includes light scattering caused by minute irregularities on the surface of the film and refractive index distribution inside the film. Internal haze refers to the total haze of the film minus the haze caused by light scattering caused by minute irregularities on the surface of the film. The internal haze of such a film can be measured by the following method.
A laminate is formed having a cycloolefin film, a transparent optical adhesive film, a transparent optical adhesive film, and a cycloolefin film in this order. The haze value of this laminate is measured using a haze meter. The measured haze value of the laminate corresponds to the sum of the haze value of two cycloolefin films and the haze value of two transparent optical adhesive films.
On the other hand, the cycloolefin film is laminated on both sides of the resin film through the transparent optical adhesive film to obtain a laminated test piece.Then, the haze of this laminated test piece is measured using a haze meter.The haze value of the laminated test piece obtained as a result of measurement is subtracted from the sum of the haze value of the two cycloolefin films and the haze value of the two transparent optical adhesive films to obtain the internal haze of the resin film.

The resin film produced by the above-mentioned production method can usually reduce coloration. The degree of coloration of the resin film can be expressed by the b ^* value of the CIE-Lab color system. The specific b ^* value of the resin film is preferably 1.0 or less, more preferably 0.8 or less, and particularly preferably 0.5 or less. Since a resin film with a small b ^* has little coloration, coloration on the screen of an image display device can be suppressed.

The b ^* value of the resin film can be measured by the following method: The transmittance of the resin film from 380 nm to 780 nm is measured at 1 nm intervals using a "V-7200" manufactured by JASCO Corporation. From the measurement results, the b ^* value in the CIE-Lab color system can be calculated.

The inventors speculate that the mechanism by which the above-mentioned manufacturing method can produce a resin film having the above-mentioned properties is as follows. However, the present invention is not limited to the mechanism described below, and can be modified as desired within the scope of the effects of the present invention.

When heat is applied to the pre-stretch film containing the crystalline resin layer in step 2, the heat can cause the crystallization of the alicyclic crystalline polymer contained in the crystalline resin layer to proceed. This crystallization usually proceeds partially in the alicyclic crystalline polymer. As a result, the crystalline resin layer has domains in which the alicyclic crystalline polymer has crystallized (hereinafter sometimes referred to as "crystallized domains") and domains in which the alicyclic crystalline polymer has not crystallized (hereinafter sometimes referred to as "non-crystalline domains"). Usually, it is considered that minute crystallized domains are uniformly dispersed in the crystalline resin layer, and the spaces between the crystallized domains are filled with non-crystalline domains. Then, when the pre-stretch film is stretched in step 3, the orientation of the molecules of the alicyclic crystalline polymer proceeds. At this time, the molecules of the alicyclic crystalline polymer in the non-crystalline domains are relatively largely oriented because the molecules are easy to move. On the other hand, the molecules of the alicyclic crystalline polymer in the crystallized domains are difficult to move, so they are oriented relatively little or not oriented at all. Therefore, the crystalline resin layer of the stretched film obtained by stretching contains non-crystalline domains containing relatively highly oriented molecules and crystallized domains containing relatively small oriented molecules. The surface of the crystalline resin layer may have a difference in surface shape depending on the difference in the degree of orientation between the domains. Such a difference in surface shape may appear as minute irregularities corresponding to the size of the crystallized domains.

In step 2, the preheating temperature Tp and preheating time tp are set to satisfy specific preheating parameters, thereby adjusting the degree of progress of crystallization of the alicyclic crystalline polymer. Therefore, in step 2, not all of the alicyclic crystalline polymer in the film is crystallized, but a specific amount of incomplete crystallization progresses, so the size and degree of dispersion of the crystallized domains described above are adjusted to an appropriate range. Furthermore, in step 3, the stretching temperature Ts and the areal stretching ratio are set to satisfy specific conditions, thereby adjusting the degree of molecular orientation of the alicyclic crystalline polymer, and the size of the unevenness on the film surface is adjusted to an appropriate range. And, this unevenness on the film surface provides excellent slipperiness.

If the crystallization of the alicyclic crystalline polymer further progresses after the stretching in step 3, it is considered that the degree of molecular orientation of the alicyclic crystalline polymer will improve throughout the film as a whole due to the progression of crystallization, and the surface irregularities will become smaller, resulting in a decrease in slipperiness. In contrast, in the manufacturing method according to the embodiment described above, in step 4, the stretched film is cooled to room temperature while controlling the temperature of the stretched film so that it does not become higher than the stretching temperature Ts, to obtain a resin film. Therefore, in step 4, crystallization does not progress to such an extent that slipperiness is impaired. Therefore, cooling is performed in step 4 without impairing the excellent slipperiness of the stretched film obtained in step 3, and a resin film with excellent slipperiness is obtained.

In addition, in the manufacturing method according to the embodiment described above, the size of the crystallization domains generated in step 2 is small. Furthermore, since the areal ratio of the stretching in step 3 is not excessively large, the progress of strong oriented crystallization is suppressed, and the expansion of the crystallization domains can be suppressed. Therefore, since the crystallization domains contained in the resin film are small, not only can the size of the unevenness on the film surface be adjusted to an appropriate range as described above, but also light scattering due to the crystallization domains can be suppressed. Therefore, whitening of the resin due to crystallization is suppressed, and the internal haze of the resin film can be reduced.

Furthermore, in the manufacturing method according to the embodiment described above, excessive heat is not applied to the crystalline resin in steps 2 to 4. This suppresses deterioration of the crystalline resin due to heat, and thus suppresses coloration of the resin. Generally, coloration of a resin due to deterioration appears yellow. Thus, by suppressing the above-mentioned deterioration, it is possible to suppress the film from turning yellow, and therefore the b ^* of the resin film can be reduced.

Conventionally, manufacturing methods using alicyclic crystalline polymers generally include a step of actively promoting the crystallization of the alicyclic crystalline polymer in order to utilize the excellent properties of the crystallized alicyclic crystalline polymer. However, because such crystallization is promoted by heat treatment, there is a tendency for the polymer to deteriorate and the associated discoloration to occur. In view of these conventional circumstances, the above-mentioned manufacturing method, which can suppress discoloration, is excellent as a manufacturing method for a film containing an alicyclic crystalline polymer, and in particular, it can be said that the above-mentioned manufacturing method was the first to realize a resin film that can simultaneously improve slipperiness and suppress discoloration.

In addition, when the resin film has an intermediate layer provided between multiple crystalline resin layers, the intermediate layer can be protected by the crystalline resin layer. Since the crystalline resin layer usually has excellent properties such as mechanical strength, chemical resistance, and heat resistance, the resin film having the intermediate layer can also have the above-mentioned properties as a whole. Therefore, it is possible to obtain a resin film that has excellent slip properties due to the action of the crystalline resin layer and excellent durability.

The in-plane retardation Re of the resin film can be any value depending on the application of the resin film. According to the manufacturing method of this embodiment, the birefringence of the resin film in the in-plane direction can be adjusted over a wide range, so that the resin film can have an in-plane retardation Re appropriate for the application.

For example, the in-plane retardation Re of the resin film may be preferably 10 nm or less, more preferably 5 nm or less, and particularly preferably 3 nm or less. In this case, the resin film can function as an optically isotropic film with respect to light passing through the resin film in the thickness direction.

For example, the in-plane retardation Re of the resin film is preferably 100 nm or more, more preferably 110 nm or more, and particularly preferably 120 nm or more, and is preferably 180 nm or less, more preferably 170 nm or less, and particularly preferably 160 nm or less. In this case, the resin film can function as a quarter-wave plate.

Furthermore, for example, the in-plane retardation Re of the resin film can be preferably 245 nm or more, more preferably 265 nm or more, particularly preferably 270 nm or more, and can be preferably 320 nm or less, more preferably 300 nm or less, particularly preferably 295 nm or less. In this case, the resin film can function as a 1/2 wavelength plate.

Since the crystallization of the alicyclic crystalline polymer progresses in step 2, the alicyclic crystalline polymer contained in the resulting resin film can have a certain degree of crystallinity or higher. The specific range of crystallinity can be selected appropriately depending on the desired performance, but is preferably 5% or higher, more preferably 10% or higher, even more preferably 20% or higher, and particularly preferably 30% or higher. By having an alicyclic crystalline polymer in which crystallization has progressed in this way, the resin film can have even higher bending resistance and chemical resistance in addition to the excellent effects described above. The crystallinity can be measured by X-ray diffraction.

The total light transmittance of the resin film is preferably 80% or more, more preferably 85% or more, and particularly preferably 88% or more. The total light transmittance of the resin film can be measured using an ultraviolet-visible spectrometer in the wavelength range of 400 nm to 700 nm.

The thickness of the resin film can be appropriately set according to the desired application, and is preferably 5 μm or more, more preferably 10 μm or more, particularly preferably 20 μm or more, and is preferably 200 μm or less, more preferably 100 μm or less, even more preferably 50 μm or less, particularly preferably 30 μm or less. When the thickness of the resin film is equal to or greater than the lower limit of the above range, the handling properties can be improved and the strength can be increased. When the thickness of the resin film is equal to or less than the upper limit, it is easy to wind up a long resin film.

The resin film may be a sheet of film or a long film.

The resin film can be used for any purpose. In particular, the resin film is suitable as, for example, an optical film such as an optically isotropic film and a retardation film, an electric/electronic film, a substrate film for a barrier film, and a substrate film for a conductive film. Examples of the optical film include a retardation film for a liquid crystal display device, a polarizing plate protective film, and a retardation film for a circular polarizing plate of an organic EL display device. Examples of the electric/electronic film include a flexible wiring board and an insulating material for a film capacitor. Examples of the barrier film include a substrate for an organic EL element, a sealing film, and a sealing film for a solar cell. Examples of the conductive film include a flexible electrode for an organic EL element or a solar cell, a touch panel member, and the like.

The present invention will be specifically described below with reference to examples. However, the present invention is not limited to the examples shown below, and may be modified as desired without departing from the scope of the claims of the present invention and the scope of equivalents thereto.

In the following explanation, the percentages and parts are by weight unless otherwise specified. Furthermore, the operations described below were carried out at room temperature and pressure unless otherwise specified.

[Evaluation method]
[Method of measuring weight average molecular weight Mw and number average molecular weight Mn]
The weight average molecular weight Mw and number average molecular weight Mn of the polymer were measured as polystyrene equivalent values using a gel permeation chromatography (GPC) system ("HLC-8320" manufactured by Tosoh Corporation). In the measurement, an H-type column (manufactured by Tosoh Corporation) was used as the column, and tetrahydrofuran was used as the solvent. The temperature during the measurement was 40°C.

[Method of measuring glass transition temperature Tg and crystallization peak temperature Tc]
The resin was heated to 300° C. in a nitrogen atmosphere to melt it, and the molten resin was quenched with liquid nitrogen. Using this resin as a sample, the glass transition temperature Tg and the crystallization peak temperature Tc of the resin were determined by heating at a rate of 10° C./min using a differential scanning calorimeter (DSC).

[Method for measuring hydrogenation rate of polymer]
The hydrogenation rate of the polymer was measured by ¹ H-NMR measurement at 145° C. using orthodichlorobenzene- ^d4 as a solvent.

[Method for measuring the ratio of racemo-dyads in a polymer]
The polymer was subjected to ^13C -NMR measurement by applying the inverse-gated decoupling method at 200°C using orthodichlorobenzene- ^d4 as a solvent. From the results of this ^13C -NMR measurement, a signal at 43.35 ppm derived from a meso dyad and a signal at 43.43 ppm derived from a racemo dyad were identified, with the peak at 127.5 ppm of orthodichlorobenzene- ^d4 being the reference shift. The proportion of the racemo dyad in the polymer was calculated based on the intensity ratio of these signals.

[Method of measuring thickness of film before stretching and thickness of resin film]
The thickness of the film was measured using a snap gauge ID-C112BS (manufactured by Mitutoyo Corporation).

[Method for measuring the static friction coefficient between resin films]
The resin film was cut into a size of 50 mm x 50 mm to obtain a test piece. The static friction coefficient of the surface of the resin film was measured using a surface property measuring instrument "Type 32" manufactured by Shinto Scientific Co., Ltd. in accordance with JIS K7125. The same resin film as that from which the test piece was cut was used as the counter member for this measurement (the member that comes into contact with the surface of the test piece during measurement).

[Method for measuring internal haze of resin film]
The resin film was cut into a size of 50 mm x 50 mm to obtain a test piece. Next, a cycloolefin film (Zeon Corporation's "ZEONOR FILM ZF14-040", thickness 40 μm) was attached to both sides of the test piece via a 50 μm thick transparent optical adhesive film (3M Corporation's "8146-2") to obtain a laminated test piece. The haze of this laminated test piece was measured using a haze meter (Nippon Denshoku Industries Co., Ltd.'s "NDH5000").

Separately, the sum of the haze value of two sheets of cycloolefin film and the haze value of two layers of transparent optical adhesive film was determined by the following method. A laminate was formed having a cycloolefin film, a transparent optical adhesive film, a transparent optical adhesive film, and a cycloolefin film in this order. The haze value of the laminate was measured using the haze meter as the sum of the haze value of two sheets of cycloolefin film and the haze value of two layers of transparent optical adhesive film.

The internal haze of the test piece as a resin film was calculated by subtracting the sum (0.04) of the haze value of two sheets of cycloolefin film and the haze value of two layers of transparent optical adhesive film from the haze value of the laminated test piece.

[Method of measuring chromaticity (b ^* ) of resin film]
The resin film was cut into a size of 50 mm x 50 mm to obtain a test piece. The transmittance of this test piece from 380 nm to 780 nm was measured at 1 nm intervals using a JASCO V-7200, and the b ^* of the CIE-Lab color system was calculated from the measurement results.

[Production Example 1. Production of hydrogenated product of ring-opened polymer of dicyclopentadiene]
A metallic pressure-resistant reactor was thoroughly dried and then purged with nitrogen. 154.5 parts of cyclohexane, 42.8 parts of a 70% cyclohexane solution of dicyclopentadiene (endo isomer content of 99% or more) (30 parts as the amount of dicyclopentadiene), and 1.9 parts of 1-hexene were added to the metallic pressure-resistant reactor, and the reactor was heated to 53°C.

A catalyst solution was prepared by adding 0.061 parts of a 19% diethylaluminum ethoxide/n-hexane solution to a solution prepared by dissolving 0.014 parts of tetrachlorotungsten phenylimide (tetrahydrofuran) complex in 0.70 parts of toluene and stirring for 10 minutes.
The catalyst solution was added to the pressure-resistant reactor to initiate the ring-opening polymerization reaction. The reaction was then continued for 4 hours while maintaining the temperature at 53° C., to obtain a solution of a ring-opening polymer of dicyclopentadiene.
The number average molecular weight (Mn) and weight average molecular weight (Mw) of the resulting ring-opened polymer of dicyclopentadiene were 8,750 and 28,100, respectively, and the molecular weight distribution (Mw/Mn) calculated from these was 3.21.

0.037 parts of 1,2-ethanediol was added as a terminator to 200 parts of the resulting solution of ring-opened dicyclopentadiene polymer, and the mixture was heated to 60°C and stirred for 1 hour to terminate the polymerization reaction. 1 part of a hydrotalcite-like compound (Kyowa Chemical Industry Co., Ltd.'s "Kyoward (registered trademark) 2000") was added to the mixture, which was heated to 60°C and stirred for 1 hour. 0.4 parts of a filter aid (Showa Chemical Industry Co., Ltd.'s "Radiolite (registered trademark) #1500") was then added, and the adsorbent and solution were filtered using a PP pleated cartridge filter (Advantec Toyo Co., Ltd.'s "TCP-HX").

100 parts of cyclohexane were added to 200 parts of the filtered ring-opened polymer solution (polymer amount 30 parts), and 0.0043 parts of chlorohydridocarbonyltris(triphenylphosphine)ruthenium was added, and a hydrogenation reaction was carried out at 6 MPa hydrogen pressure and 180°C for 4 hours. This produced a reaction liquid containing a hydride of the ring-opened polymer of dicyclopentadiene. The hydride precipitated from this reaction liquid, forming a slurry solution.

The hydride and the solution contained in the reaction liquid were separated using a centrifuge and dried under reduced pressure at 60°C for 24 hours to obtain 28.5 parts of a crystalline ring-opening polymer of dicyclopentadiene. The hydride rate of this hydride was 99% or more, and the racemo-dyad ratio was 89%.

[Production Example 2: Production of resin pellets]
A crystalline resin to be used as a material for a film was obtained by mixing 1.1 parts of an antioxidant (tetrakis[methylene-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate]methane;"Irganox (registered trademark) 1010" manufactured by BASF Japan Ltd.) with 100 parts of the hydrogenated product of the ring-opened polymer of dicyclopentadiene obtained in Production Example 1. The glass transition temperature Tg(1) of the crystalline resin was 93°C, and the crystallization peak temperature Tc was 135°C.

The crystalline resin was fed into a twin-screw extruder ("TEM-37B" manufactured by Toshiba Machine Co., Ltd.) equipped with four die holes with an inner diameter of 3 mm. The crystalline resin was molded into a strand-shaped molded body by hot melt extrusion molding using the twin-screw extruder. This molded body was chopped with a strand cutter to obtain pellets of the crystalline resin. The operating conditions of the twin-screw extruder are shown below.
・Barrel temperature setting: 270℃～280℃
Die setting temperature: 250°C
Screw rotation speed: 145 rpm
Feeder rotation speed: 50 rpm

[Example 1]
The pellets of the crystalline resin obtained in Production Example 2 were supplied to a hot melt extrusion film molding machine equipped with a T-die. The supplied crystalline resin was melted in the film molding machine, extruded through the T-die, and wound on a roll at a winding speed of 15 m/min to produce a long pre-stretched film (thickness 50 μm, width 1350 mm) made of the crystalline resin (Step 1). The operating conditions of the film molding machine are shown below.
・Barrel temperature setting: 280℃～290℃
Die temperature: 270°C
Screw rotation speed: 30 rpm

The pre-stretched film thus obtained was cut into a size of 200 mm in the MD direction and 200 mm in the TD direction to obtain a rectangular pre-stretched film. The cut pre-stretched film was attached to a batch-type biaxial stretching device (manufactured by Toyo Seiki Seisakusho). This attachment was performed by fixing the four sides of the pre-stretched film with clips from the biaxial stretching device so that the pre-stretched film was in a tensed state. With the four sides of the pre-stretched film thus fixed with clips, the pre-stretched film was held at a constant pre-heating temperature Tp = 130°C for a pre-heating time tp = 180 seconds (step 2).

Immediately afterwards, the unstretched film was stretched simultaneously in the MD and TD directions using the biaxial stretching machine at a constant stretching temperature Ts = 130°C for 20 seconds (step 3). The stretching ratio in the MD direction was 1.6 times, and the stretching ratio in the TD direction was 1.6 times, so the areal stretching ratio was 2.6 times. This stretching resulted in a stretched film as the stretched film.

Immediately afterwards, the obtained stretched film was removed from the biaxial stretching machine and allowed to cool naturally. By allowing it to cool, the temperature of the stretched film immediately dropped to room temperature without becoming higher than the stretching temperature Ts (step 4). This resulted in a resin film with a single-layer structure including a layer made of a crystalline resin. The obtained resin film was evaluated by the method described above.

[Example 2]
In step 2, the preheating time tp was changed to 290 seconds. Except for the above, the same operations as in Example 1 were carried out to produce and evaluate a resin film.

[Example 3]
In step 2, the preheating temperature Tp was changed to 145° C., and the preheating time tp was changed to 40 seconds. Except for the above, the same operations as in Example 1 were used to produce and evaluate a resin film.

[Example 4]
In step 2, the preheating temperature Tp was changed to 127° C., and the preheating time tp was changed to 250 seconds. Furthermore, in step 3, the stretching temperature Ts was changed to 127° C. Except for the above, a resin film was produced and evaluated by the same operations as in Example 1.

[Example 5]
In step 1, the film winding speed was changed to 7.5 m/min, so that the dimensions of the long unstretched film were changed to a thickness of 100 μm and a width of 1350 mm. In step 3, the stretch ratio in the MD direction was changed to 2.45 times, and the stretch ratio in the TD direction was changed to 2.45 times, so that the areal stretch ratio was changed to 6.0 times. Except for the above, the resin film was produced and evaluated by the same operations as in Example 1.

[Example 6]
In step 1, the film winding speed was changed to 25 m/min, so that the dimensions of the long unstretched film were changed to a thickness of 30 μm and a width of 1350 mm. In step 3, the stretching ratio in the MD direction was changed to 1.3 times, and the stretching ratio in the TD direction was changed to 1.3 times, so that the areal stretching ratio was changed to 1.7 times. Except for the above, the resin film was produced and evaluated by the same operations as in Example 1.

[Example 7]
In step 1, the film winding speed was changed to 25 m/min, so that the dimensions of the long pre-stretched film were changed to a thickness of 30 μm and a width of 1350 mm. In step 3, the stretching temperature Ts was changed to 110° C., and the stretching ratio in the MD direction was changed to 1.3 times, and the stretching ratio in the TD direction was changed to 1.3 times, so that the areal stretching ratio was changed to 1.7 times. Except for the above, the resin film was produced and evaluated by the same operations as in Example 1.

[Example 8]
In step 2, the preheating temperature Tp was changed to 160° C., and the preheating time tp was changed to 10 seconds. Furthermore, in step 3, the stretching temperature Ts was changed to 160° C. Except for the above, a resin film was produced and evaluated by the same operations as in Example 1.

[Example 9]
The pellets of the crystalline resin obtained in Production Example 2 and the pellets of the norbornene-based resin as a thermoplastic resin (ZEONOR 1430 manufactured by Nippon Zeon Co., Ltd.; glass transition temperature Tg(2)=143° C.) were supplied to a hot melt extrusion film molding machine equipped with a T-die. The supplied resin was melted in the film molding machine, co-extruded through the T-die, and wound up on a roll at a winding speed of 15 m/min to produce a long co-extruded film (thickness 50 μm, width 1350 mm) (step 1). The obtained co-extruded film had a layer structure of two types and three layers, namely "crystalline resin layer (thickness 10 μm)/norbornene-based resin layer (thickness 30 μm)/crystalline resin layer (thickness 10 μm)". The operating conditions of the film molding machine are shown below.
・Temperature setting for each barrel: 280℃～290℃
Die temperature: 270°C
Each screw rotation speed: 10 rpm

The co-extruded film described above was used as the pre-stretched film. Other than the above, the resin film was produced and evaluated using the same procedures as in Example 1.

[Example 10]
In step 2, the co-extruded film produced in Example 9 was used as the pre-stretched film, and the preheating temperature Tp was changed to 145° C. and the preheating time tp was changed to 40 seconds. Except for the above, a resin film was produced and evaluated by the same operations as in Example 1.

[Comparative Example 1]
In step 2, the preheating time tp was changed to 90 seconds. Except for the above, the same operations as in Example 1 were carried out to produce and evaluate a resin film.

[Comparative Example 2]
In step 2, the preheating time tp was changed to 360 seconds. Except for the above, the same operations as in Example 1 were carried out to produce and evaluate a resin film.

[Comparative Example 3]
In step 1, the film winding speed was changed to 25 m/min, so that the dimensions of the long pre-stretched film were changed to a thickness of 30 μm and a width of 1350 mm. In step 2, the preheating temperature Tp was changed to 115° C. In step 3, the stretching temperature Ts was changed to 115° C., and the stretching ratio in the MD direction was changed to 1.3 times, and the stretching ratio in the TD direction was changed to 1.3 times, so that the areal stretching ratio was changed to 1.7 times. Except for the above, the resin film was produced and evaluated by the same operations as in Example 1.

[Comparative Example 4]
In step 1, the film winding speed was changed to 25 m/min, so that the dimensions of the long unstretched film were changed to a thickness of 30 μm and a width of 1350 mm. In step 3, the stretching ratio in the MD direction was changed to 1.1 times, and the stretching ratio in the TD direction was changed to 1.1 times, so that the areal stretching ratio was changed to 1.2 times. Except for the above, the resin film was produced and evaluated by the same operations as in Example 1.

[result]
The results of the above-mentioned Examples and Comparative Examples are shown in Tables 1 and 2, respectively.

Claims (7)

A step 1 of preparing a pre-stretched film having a resin layer made of a crystalline resin containing a polymer having an alicyclic structure and crystallinity;
A step 2 of heating the pre-stretched film at a temperature Tp of not less than "Tc-10°C" and not more than "Tc+35°C" for a time tp (where Tc represents the crystallization peak temperature [°C] of the crystalline resin);
A step 3 of stretching the pre-stretched film subjected to the step 2 at a stretching temperature Ts equal to or lower than the temperature Tp at an areal magnification of 1.6 times or more and 6.3 times or less to obtain a stretched film;
A step 4 of lowering the temperature of the stretched film to room temperature;
The steps 3 and 4 are carried out consecutively,
The temperature Tp [° C.] and the time tp [seconds] satisfy the following formula (i),
10000≦{Tp-(Tc-15)} ² ×tp≦30000 (i)
A method for producing a resin film, wherein after the stretched film is obtained in step 3, the temperature of the stretched film is maintained at or below Ts until the temperature of the stretched film reaches room temperature in step 4. The method for producing a resin film according to claim 1, wherein the polymer containing an alicyclic structure and having crystallinity is a hydrogenated product of a ring-opening polymer of dicyclopentadiene. The pre-stretched film has two or more of the resin layers,
The method for producing a resin film according to claim 1 or 2, further comprising providing one or more intermediate layers between the resin layers, the intermediate layers being made of a thermoplastic resin other than the crystalline resin. The method for producing a resin film according to claim 3, wherein the glass transition temperature of the thermoplastic resin is equal to or higher than the glass transition temperature of the crystalline resin and equal to or lower than "Ts + 20°C". The method for producing a resin film according to any one of claims 1 to 4 , wherein the resin film has a surface having a static friction coefficient of 0.7 or less. The method for producing a resin film according to any one of claims 1 to 5 , wherein the resin film has an internal haze of 1.0% or less. The method for producing a resin film according to any one of claims 1 to 6 , wherein the resin film has a b ^* of 1.0 or less in the CIE-Lab color system.