JP7727892B2 - Film containing 4-methyl-1-pentene (co)polymer, and its manufacturing method and use - Google Patents

Description

The present invention relates to a film containing a 4-methyl-1-pentene (co)polymer. More specifically, the present invention relates to a film containing a 4-methyl-1-pentene (co)polymer that has excellent recyclability and releasability, effectively suppresses the occurrence of wrinkles, and is particularly suitable for use as a release film.

In recent years, there has been a demand for recycling, preferably material recycling, of plastic materials such as 4-methyl-1-pentene (co)polymers from the viewpoints of environmental protection, resource conservation, etc. Release films, which are the main use of 4-methyl-1-pentene (co)polymer films, are used in limited locations such as factories, and therefore are easy to collect after use, making material recycling feasible.
Incidentally, it is important to suppress thermal expansion of release films used in semiconductor encapsulation processes, etc., because large thermal expansion can cause wrinkles. To suppress thermal expansion, a three-layer structure of a 4-methyl-1-pentene (co)polymer layer, a heat-resistant resin layer, and a 4-methyl-1-pentene (co)polymer layer, with a stretched polyester film or the like used for the heat-resistant resin layer, has been proposed (see, for example, Patent Document 1). However, because a film with this structure is not a monomaterial, material recycling is difficult.

In the above-mentioned configuration, if only the 4-methyl-1-pentene (co)polymer layer is used as a single layer film, it is suitable for material recycling because it is a monomaterial, and it is possible to achieve excellent releasability derived from the 4-methyl-1-pentene (co)polymer. However, because the 4-methyl-1-pentene (co)polymer layer is unstretched, it is prone to wrinkles when used as a single layer film, and when it is used as a release film, particularly a release film in a molding process that involves heating, the wrinkles may adversely affect the appearance of the molded product.
Appropriate stretching of a polymer film is generally considered to be an effective means of suppressing wrinkles in the polymer film. However, 4-methyl-1-pentene (co)polymer films have poor stretching processability, such as being prone to uneven stretching, breakage, and cracking. To solve this problem, various stretching methods and raw sheets for stretching have been proposed (see, for example, Patent Documents 2 and 3). However, even with these methods, it is not necessarily easy to achieve uniform stretching without breakage or cracking, and it has not been possible to suppress wrinkles to a level sufficient for use as a release film.

JP 2017-100397 A Japanese Patent Application Publication No. 61-228931 JP 2011-088339 A

The present invention was made in consideration of the limitations of the prior art described above, and aims to provide a film containing 4-methyl-1-pentene (co)polymer that achieves excellent release properties derived from 4-methyl-1-pentene (co)polymer, is a monomaterial suitable for material recycling, and suppresses wrinkles to a level sufficient for use as a release film.

As a result of extensive research into solving the above-mentioned problems, the present inventors have found that a film containing a predetermined amount of 4-methyl-1-pentene (co)polymer, in which the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C and the sum of the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C and the thermal dimensional change rate in the longitudinal (MD) direction from 23°C to 150°C are each not more than predetermined values, can achieve high levels of releasability, mono-material properties, and wrinkle suppression that exceed those of conventional technology, and can solve the aforementioned problems, thereby completing the present invention.
That is, the present invention and each aspect thereof are as described in [1] to [8] below.

[1]
A film containing 90% by mass or more of a 4-methyl-1-pentene (co)polymer, in which the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C is 3% or less, and the sum of the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C and the thermal dimensional change rate in the longitudinal (MD) direction from 23°C to 150°C is 6% or less.
[2]
The film according to [1], wherein the film is a single-layer film.
[3]
The film according to [1] or [2], which is a biaxially stretched film in which the stretching ratios in both the machine direction (MD) and the transverse direction (TD) are 1.01 or more, and the area ratio expressed as the machine direction stretching ratio (MD direction stretching ratio) x the transverse direction stretching ratio (TD direction stretching ratio) is 1.02 to 2.00.
[4]
The film according to any one of [1] to [3], wherein the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C is 0% or more.
[5]
The method for producing a film according to any one of [1] to [4], comprising a step of biaxially stretching a raw film containing 90% by mass or more of a 4-methyl-1-pentene (co)polymer, wherein the biaxial stretching is carried out at a temperature of 50°C or higher and lower than the melting point of the 4-methyl-1-pentene (co)polymer.
[6]
[6] The manufacturing method according to [5], further comprising a step of performing a heat setting treatment at a temperature equal to or higher than the biaxial stretching temperature and lower than the melting point of the 4-methyl-1-pentene (co)polymer after the biaxial stretching step.
[7]
The film according to any one of [1] to [4], which is a release film.
[8]
The film according to any one of [1] to [4], which is a release film for a semiconductor encapsulation process.

The film of the present invention achieves technical effects that surpass the limitations of conventional technology, such as combining high levels of releasability, recyclability, and wrinkle-preventing performance. When the film of the present invention is used, for example, as a release film for semiconductor encapsulation, molded articles obtained by resin-encapsulating semiconductor chips, etc., can be easily released from the mold, and molded articles free of appearance defects due to wrinkles, etc. can be produced with high productivity. Furthermore, the release film can be recycled, achieving technical effects of great practical value.

FIG. 1 is a schematic diagram illustrating a method for evaluating wrinkles in an embodiment of the present invention. 1A to 1C are schematic diagrams showing an example of a method for producing a resin-encapsulated semiconductor using the film of the present invention.

The present invention relates to a film containing 90% by mass or more of a 4-methyl-1-pentene (co)polymer, in which the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C is 3% or less, and the sum of the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C and the thermal dimensional change rate in the longitudinal (MD) direction from 23°C to 150°C is 6% or less.
Here, the transverse (TD) direction refers to the direction within the plane of the film that is perpendicular to the longitudinal direction of the film during production, and hereinafter referred to simply as the "transverse direction" or "TD direction." The longitudinal (MD) direction refers to the longitudinal direction of the film during production, and hereinafter referred to simply as the "longitudinal direction" or "MD direction."
Since the film of the present invention contains 90% by mass or more of a 4-methyl-1-pentene (co)polymer, it is essentially a monomaterial, has excellent recyclability, and allows for material recycling. The film of the present invention can be preferably used as a release film used in a manufacturing process, and such a release film is used in a factory or the like where the manufacturing process is carried out, so it is relatively easy to recover after use. Therefore, excellent recyclability is particularly significant from the economic and environmental perspectives.
From the viewpoint of recyclability, the film of the present invention preferably contains 95% by mass or more, particularly preferably 98% by mass or more, of 4-methyl-1-pentene (co)polymer.
The film of the present invention may be composed solely of a 4-methyl-1-pentene (co)polymer, but may contain other components as long as the object of the present invention, particularly recyclability, is not impaired and the film does not contradict the requirement that the film contain 90 mass % or more of a 4-methyl-1-pentene (co)polymer.

4-methyl-1-pentene (co)polymer

The 4-methyl-1-pentene (co)polymer used in the film of the present invention may be a homopolymer of 4-methyl-1-pentene, or it may be a copolymer of 4-methyl-1-pentene with another olefin, preferably an α-olefin having 2 to 20 carbon atoms (excluding 4-methyl-1-pentene; the same applies below).

In the case of a copolymer of 4-methyl-1-pentene and an α-olefin having 2 to 20 carbon atoms, the olefin having 2 to 20 carbon atoms copolymerized with the 4-methyl-1-pentene can impart flexibility to the 4-methyl-1-pentene. Examples of α-olefins having 2 to 20 carbon atoms include ethylene, propylene, 1-butene, 1-hexene, 1-heptene, 1-octene, 1-decene, 1-tetradecene, 1-hexadecene, 1-heptadecene, 1-octadecene, and 1-eicosene. These olefins may be used alone or in combination of two or more.

In the case of a copolymer of 4-methyl-1-pentene and an α-olefin having 2 to 20 carbon atoms, it is preferable that the proportion of structural units derived from 4-methyl-1-pentene is 96% by mass or more, and the proportion of other structural units derived from olefins having 2 to 20 carbon atoms is 4% by mass or less. By reducing the content of structural units derived from α-olefins having 2 to 20 carbon atoms, the copolymer can be made harder, i.e., the storage modulus E' can be increased, which is advantageous for suppressing the occurrence of wrinkles during a sealing process, etc. On the other hand, by increasing the content of structural units derived from α-olefins having 2 to 20 carbon atoms, the copolymer can be made softer, i.e., the storage modulus E' can be decreased, which is advantageous for improving mold followability, etc.
The proportion of structural units derived from 4-methyl-1-pentene is more preferably 96 to 99% by mass, and the proportion of structural units derived from other olefins having 2 to 20 carbon atoms is particularly preferably 4 to 1% by mass.

The 4-methyl-1-pentene (co)polymer may have structural units derived from a copolymerization component other than an α-olefin having 2 to 20 carbon atoms. Examples of copolymerization components other than an α-olefin having 2 to 20 carbon atoms include α-olefins having more than 20 carbon atoms, cyclic olefins, aromatic vinyl compounds, conjugated dienes, non-conjugated polyenes, functional vinyl compounds, hydroxyl-containing olefins, and halogenated olefins. Examples of cyclic olefins, aromatic vinyl compounds, conjugated dienes, non-conjugated polyenes, functional vinyl compounds, hydroxyl-containing olefins, and halogenated olefins include the compounds described in paragraphs [0035] to [0041] of JP 2013-169685 A. These copolymerization components other than an α-olefin having 2 to 20 carbon atoms may be used alone or in combination of two or more.

4-methyl-1-pentene (co)polymers can be produced by methods known to those skilled in the art. For example, they can be produced by methods using known catalysts such as Ziegler-Natta catalysts and metallocene catalysts. The 4-methyl-1-pentene (co)polymer is preferably a highly crystalline (co)polymer. Crystalline copolymers may be copolymers having either an isotactic structure or a syndiotactic structure, but copolymers having an isotactic structure are particularly preferred in terms of physical properties and are also easily available. Furthermore, the stereoregularity and molecular weight of the 4-methyl-1-pentene (co)polymer are not particularly limited as long as it can be molded into a film and has the strength to withstand the temperatures and pressures encountered during molding. The 4-methyl-1-pentene copolymer may be a commercially available copolymer, such as TPX (registered trademark) manufactured by Mitsui Chemicals, Inc.

As described above, the film of the present invention may be composed solely of a 4-methyl-1-pentene (co)polymer, or may contain other components as long as the object of the present invention, particularly recyclability, is not impaired and the film does not contradict the requirement that the film contain 90 mass % or more of a 4-methyl-1-pentene (co)polymer.
The other components are not particularly limited, and may contain additives such as a stretching aid that have been conventionally used in films of 4-methyl-1-pentene (co)polymers or materials similar thereto, and various resins other than 4-methyl-1-pentene (co)polymers.
Preferred examples of the stretching aid include petroleum resins and terpene resins.
Other additives include weather stabilizers, heat stabilizers, antioxidants, ultraviolet absorbers, antistatic agents, antislip agents, antiblocking agents, antifogging agents, nucleating agents, lubricants, pigments, dyes, antioxidants, hydrochloric acid absorbers, inorganic or organic fillers, organic or inorganic foaming agents, crosslinking agents, crosslinking aids, adhesives, softeners, and flame retardants.
Examples of resins other than 4-methyl-1-pentene (co)polymers include thermoplastic resins such as thermoplastic polyolefin resins other than 4-methyl-1-pentene (co)polymers, thermoplastic polyamide resins, thermoplastic polyester resins, and thermoplastic vinyl aromatic resins, as well as thermosetting resins such as unsaturated polyester resins, epoxy resins, phenol resins, urea resins, melamine resins, diallyl phthalate resins, and silicone resins.
These other components may be used alone or in combination of two or more.

From the viewpoints of recyclability, production costs, etc., the film of the present invention is preferably a single-layer film, but this does not exclude the film being a multilayer film (laminate) as long as it satisfies the requirements of the present invention, particularly the content of 90% by mass or more of a 4-methyl-1-pentene (co)polymer. In the case of a multilayer film, the content of the 4-methyl-1-pentene (co)polymer is 90% by mass or more based on the mass of the entire multilayer film.
In the case of a multilayer film, all of the layers may contain a 4-methyl-1-pentene (co)polymer, or only some of the layers may contain a 4-methyl-1-pentene (co)polymer. However, since the 4-methyl-1-pentene (co)polymer accounts for 90 mass % or more based on the mass of the entire multilayer film, at least one layer containing the 4-methyl-1-pentene (co)polymer accounts for the majority of the multilayer film.

When the multilayer film has layers other than the layer containing 4-methyl-1-pentene (co)polymer (hereinafter also referred to as "other layers"), examples of such other layers include, but are not limited to, a matte layer (a layer with an uneven surface), a release layer, a conductive layer, an antistatic layer, an optical coating layer, an adhesive layer, an adhesive layer, and a gas barrier layer.

The thickness of the film of the present invention is not particularly limited, but is preferably 10 to 300 μm, and more preferably 30 to 150 μm, for example. When the thickness of the film of the present invention is within the above range, the film has good handleability when used as a roll and the amount of film to be discarded is small, which is preferable.
When the film of the present invention is a multilayer film, the thickness of the layer containing the 4-methyl-1-pentene (co)polymer is also preferably from 10 to 300 μm, more preferably from 30 to 150 μm.

Thermal Dimensional Change Rate of Film In order to solve the above-mentioned problems of the invention, the present invention provides a film containing a predetermined amount or more of a 4-methyl-1-pentene (co)polymer, the thermal dimensional change rate of which in the transverse (TD) direction is a predetermined value or less, and the sum of the thermal dimensional change rates in the transverse (TD) direction and the longitudinal (MD) direction is a predetermined value or less.
That is, in the film of the present invention, the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C is 3% or less, and the sum of the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C and the thermal dimensional change rate in the longitudinal (MD) direction from 23°C to 150°C is 6% or less.
In the film of the present invention, the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C is 3% or less, and the sum of the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C and the thermal dimensional change rate in the longitudinal (MD) direction from 23°C to 150°C is 6% or less. This effectively prevents wrinkles from occurring during heating, and when the film is used as a release film for sealing semiconductor chips, etc., molded products obtained by resin sealing semiconductor chips, etc. can be produced with a good appearance.

The thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C and the thermal dimensional change rate in the longitudinal (MD) direction from 23°C to 150°C of the film of the present invention are measured by holding the sample at 23°C for 5 minutes with a load of 0.005 N applied in the transverse (TD) direction and the longitudinal (MD) direction, and then raising the temperature from 23°C to 150°C at a heating rate of 10°C/min. These are thermal dimensional change rates calculated from the sample length at 23°C and the sample length at 150°C.
More specifically, a film sample cut to an appropriate size is subjected to a thermomechanical analysis using a thermomechanical analyzer, with a load of 0.005 N applied in the measurement direction (transverse (TD) direction or longitudinal (MD) direction), held at 23°C for 5 minutes, and then heated from 23°C to 150°C at a heating rate of 10°C/min. The sample lengths (distance between load points) in the measurement direction at 23°C and 150°C are measured, and the thermal dimensional change rate is calculated using the following formula (1):
Thermal dimensional change rate (%) (23 → 150°C) = {[(L ₂ - L ₁ )/L ₁ ] × 100}
...(1)
L ₁ : Sample length at 23°C (mm)
_L2 : Sample length at 150°C (mm)
As long as the above conditions are met, there are no particular limitations on the details of the measurement method, such as the equipment used for the measurement or the operation, and the measurement can be carried out appropriately using a method commonly used in the technical field. However, it is preferable to carry out the measurement using, for example, the method described in the Examples of the present specification.

The mechanism by which the occurrence of wrinkles is suppressed by keeping the thermal dimensional change rate in the transverse (TD) direction and the sum of the thermal dimensional change rates in the transverse (TD) direction and the machine direction (MD) directions below a specified value is not entirely clear, but it is presumed to be somehow related to the fact that using a film with relatively small thermal expansion/contraction suppresses uneven thermal expansion/contraction on the film surface due to heating/cooling during processing.

From the viewpoint of more effectively suppressing the occurrence of wrinkles, the film of the present invention preferably has a thermal dimensional change rate in the TD (transverse) direction from 23°C to 150°C of 2.5% or less, more preferably 2.0% or less, and even more preferably 1.5% or less. On the other hand, from the viewpoint of preventing adsorption errors, the film of the present invention preferably has a thermal dimensional change rate in the TD (transverse) direction from 23°C to 150°C of 0% or more, preferably greater than 0%.

From the viewpoint of more effectively suppressing the occurrence of wrinkles, the film of the present invention preferably has a sum of the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C and the thermal dimensional change rate in the longitudinal (MD) direction from 23°C to 150°C of 5.0% or less, and particularly preferably 4.5% or less.
Furthermore, the sum of the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C and the thermal dimensional change rate in the longitudinal (MD) direction from 23°C to 150°C is preferably -2% or more, more preferably -1% or more, and particularly preferably 0% or more.

As long as the film of the present invention satisfies the above conditions that the thermal dimensional change in the transverse (TD) direction from 23°C to 150°C is 3% or less, and the sum of the thermal dimensional change in the transverse (TD) direction from 23°C to 150°C and the thermal dimensional change in the longitudinal (MD) direction from 23°C to 150°C is 6% or less, there are no particular restrictions on the thermal dimensional change in the longitudinal (MD) direction from 23°C to 150°C. However, from the standpoint of making it easier to achieve the above conditions and more effectively suppressing the occurrence of wrinkles, etc., it is preferably 5% or less, and more preferably 4% or less. Furthermore, the thermal dimensional change in the longitudinal (MD) direction of the film of the present invention from 23°C to 150°C is preferably -2% or more, more preferably -1% or more, and particularly preferably 0% or more.

As described above, the film of the present invention may be a single-layer film or a multilayer film (laminate). In the case of a multilayer film, the above-mentioned thermal dimensional change rate is defined and measured for the entire multilayer film.
However, from the viewpoint of realizing the above-mentioned thermal dimensional change rate for the entire multilayer film, it is preferable that at least a part of each layer constituting the multilayer film satisfies the above-mentioned thermal dimensional change rate conditions, and in particular, in the case of a multilayer film, it is preferable that the layer containing 4-methyl-1-pentene (co)polymer, which occupies the majority of the film, satisfies the above-mentioned thermal dimensional change rate conditions.
It is particularly preferable that all of the layers constituting the multilayer film satisfy the above-mentioned conditions for the rate of thermal dimensional change.

The thermal dimensional change rate of the film in the transverse (TD) direction from 23°C to 150°C, and the sum of the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C and the thermal dimensional change rate in the longitudinal (MD) direction from 23°C to 150°C, can be adjusted by appropriately changing and setting the film material and manufacturing conditions.
In particular, in the production of a film, the thermal dimensional change rate of the film can be appropriately adjusted by performing stretching, preferably biaxial stretching, and appropriately setting the stretching conditions such as the stretching ratio and stretching temperature. Also, the thermal dimensional change rate of the film can be appropriately adjusted by appropriately employing a so-called heat setting treatment in which the stretched film is held at a predetermined temperature for a certain period of time.

Preferred physical properties of the film The film of the present invention can achieve excellent releasability by containing 90% by mass or more of 4-methyl-1-pentene (co)polymer.
The degree of releasability may be appropriately set depending on the purpose and form of use, and is not particularly limited. However, when expressed in terms of the contact angle with water, which is often used as an index of releasability, it is usually 90° to 130°, preferably 95° to 120°, more preferably 98° to 115°, and even more preferably 100° to 110°.

In many cases, the above-mentioned water contact angle can be achieved by including 90% by mass or more of 4-methyl-1-pentene (co)polymer, or by setting the content ratio of the 4-methyl-1-pentene (co)polymer to be 90% by mass or more. However, an additive (release agent) that can further improve the release property may be used, or a surface treatment may be performed.
There are no particular limitations on the type of release agent that can be used, and at least one selected from the group consisting of silicone-based release agents, melamine-based release agents, polyolefin-based release agents, epoxy-based release agents, acrylic-based release agents, fluorine-based release agents, cellulose-based release agents, paraffin-based release agents, epoxy-melamine-based release agents, and combinations thereof can be used as appropriate.
These release agents may be added to the resin constituting the film of the present invention, including the 4-methyl-1-pentene (co)polymer, or may be applied to the film of the present invention.
The surface of the film of the present invention may have an uneven shape if necessary, thereby further improving the mold releasability. The method for imparting unevenness to the surface of the film is not particularly limited, but a general method such as embossing can be used.

The film of the present invention can be suitably used as a process release film, and in this case, it preferably has heat resistance sufficient to withstand the temperature of the mold used during molding (typically 120 to 180°C). From this viewpoint, the 4-methyl-1-pentene (co)polymer constituting the film of the present invention is preferably crystalline, and the melting point of the 4-methyl-1-pentene (co)polymer is preferably 190°C or higher, and more preferably 200°C or higher and 240°C or lower.
By using a 4-methyl-1-pentene (co)polymer that is crystalline and/or has a melting point within the above range, it is possible to more effectively suppress the occurrence of wrinkles in a resin sealing process or the like, and to more effectively suppress the phenomenon of wrinkles being transferred to a molded product, resulting in poor appearance.

The resin containing 4-methyl-1-pentene (co)polymer constituting the film of the present invention preferably has a crystalline heat of fusion in the first heating step, as measured by differential scanning calorimetry (DSC) in accordance with JIS K7221, of 15 J/g or more and 60 J/g or less, and more preferably 20 J/g or more and 50 J/g or less. A heat of fusion of 15 J/g or more can more effectively exhibit heat resistance and mold releasability sufficient to withstand hot press molding in processes such as resin encapsulation. Furthermore, the dimensional change rate can be suppressed, thereby more effectively preventing the occurrence of wrinkles. On the other hand, a heat of fusion of 60 J/g or less provides the film with appropriate hardness, allowing the film to conform sufficiently to the mold during processes such as resin encapsulation, thereby more effectively preventing film breakage.

Stretched Film The film of the present invention may be an unstretched film. However, since unstretched 4-methyl-1-pentene (co)polymer films often have a large thermal dimensional change rate due to thermal expansion, it is preferable to use an oriented film from the viewpoints of appropriately controlling the thermal dimensional change rate and controlling the hardness to an appropriate value.
The stretched film in this embodiment may be a uniaxially stretched film or a biaxially stretched film. In the case of a uniaxially stretched film, it may be stretched either longitudinally or transversely, but it is preferable that the film is stretched at least in the transverse (TD) direction, since it is relatively easy to reduce or make negative the thermal expansion coefficient in the transverse (TD) direction by transverse stretching.

The method and apparatus for obtaining the stretched film of the above embodiment are not particularly limited, and the stretching may be performed by a method known in the art. For example, an unstretched raw film may be stretched using a heated roll or a tenter-type stretching machine.
The method for producing the raw film is not particularly limited, and for example, a raw film can be produced by forming a film from a raw material resin containing 90% by mass of 4-methyl-1-pentene (co)polymer by a method such as extrusion molding or press molding.
There is no particular limitation on the thickness of the raw film, which may be appropriately set taking into consideration the intended use, the draw ratio, etc., but it is usually 10 to 360 μm, preferably 30 to 180 μm.

There is no particular limitation on the stretching ratio, and it is sufficient to appropriately control the thermal dimensional change rate and set an appropriate value as needed to achieve favorable mechanical properties, but it is preferable that the stretching ratio be 1.01 times or more in both the machine direction (MD) and the transverse direction (TD).
The stretching ratio in either the machine direction (MD) or the transverse direction (TD) is more preferably 1.01 to 1.50 times, and particularly preferably 1.01 to 1.35 times.
It is more preferable that both the stretching ratios in the machine direction (MD) and the transverse direction (TD) are within the above-mentioned more preferable ranges, and it is even more preferable that they are within the above-mentioned particularly preferable ranges.
When the stretching ratio in either the machine direction (MD) or the transverse direction (TD) is 1.01 or more, thermal dimensional changes of the film, particularly thermal expansion, can be more effectively suppressed.
On the other hand, when the stretching ratio in either the machine direction (MD) or the transverse direction (TD) is 1.50 or less, the thermal shrinkage of the film can be more effectively suppressed, and uniform stretching without breakage or cracking can be easily performed.

In the above embodiment, the area ratio, which is expressed as the stretch ratio in the machine direction (MD)×the stretch ratio in the transverse direction (TD), is preferably 1.02 to 2.00 times.
When the ratio of the stretch ratio in the machine direction (MD) to the stretch ratio in the transverse direction (TD) is 1.02 or more, thermal dimensional changes of the film, particularly thermal expansion, can be more effectively suppressed.
On the other hand, when the ratio of the stretch ratio in the machine direction (MD) to the stretch ratio in the transverse direction (TD) is 2.00 or less, thermal expansion can be suppressed to a degree that the film does not thermally shrink, and uniform stretching can be easily performed without breakage or cracking.
The area ratio, which is expressed as the stretch ratio in the machine direction (MD) × the stretch ratio in the transverse direction (TD), is particularly preferably 1.03 times or more and less than 1.60 times.

When biaxial stretching is performed, the order of stretching is not particularly limited, and either simultaneous biaxial stretching or sequential biaxial stretching may be employed.
When sequential biaxial stretching is performed, stretching in the machine direction (MD) may be performed first, or stretching in the transverse direction (TD) may be performed first.
There are no particular limitations on the specific method, apparatus, etc. for stretching, and any method commonly used in the technical field can be appropriately adopted. For example, stretching in the machine direction (MD) can be performed by utilizing the difference in peripheral speed of rolls, and stretching in the transverse direction (TD) is generally performed using a tenter, but can also be performed using an expander roll or a cross guider.
From the viewpoint of productivity, it is preferable to employ the various stretching methods described above, but when the production volume is small or when a wide variety of products are produced in small quantities, it is also preferable to perform stretching in a batch system.

The temperature at which the stretching is carried out is not particularly limited and may be appropriately set taking into consideration the physical properties of the raw material resin containing 90% by mass of 4-methyl-1-pentene (co)polymer, etc., but stretching is preferably carried out at 50° C. or higher, and particularly preferably at 80° C. or higher. By stretching at a temperature above this range, a stretched film with little distortion after stretching and little thermal dimensional change can be efficiently produced.
Furthermore, stretching is preferably carried out at a temperature below the melting point of the 4-methyl-1-pentene (co)polymer used as the raw resin, and particularly preferably at a temperature at least 20°C lower than the melting point. As described above, it is difficult to specify a preferred stretching temperature because it varies depending on the melting point of the 4-methyl-1-pentene (co)polymer, but for example, when a typical 4-methyl-1-pentene (co)polymer is used, stretching is preferably carried out at less than about 230°C, and particularly preferably at less than about 210°C. By stretching at a temperature below the above-mentioned temperature, a stretched film can be produced efficiently while sufficiently suppressing breakage and the like.

After the above-mentioned stretching step, preferably after the biaxial stretching step, the stretched film is subjected to a heat setting treatment (heat setting treatment) in which the stretched film is held at a predetermined temperature for a certain period of time, thereby making it possible to appropriately adjust the thermal dimensional change rate of the film.
The heat setting temperature is not particularly limited, but from the viewpoint of effectively removing distortion, it is preferably equal to or higher than the temperature in the biaxial stretching step and is preferably lower than the melting point of the 4-methyl-1-pentene (co)polymer used as the raw material resin. For example, heat setting is preferably performed at a temperature of 50°C or higher and 230°C or lower, and more preferably at a temperature of 80°C or higher and 210°C or lower.
The time for the heat setting treatment is not particularly limited, but is usually 5 to 300 seconds, and particularly preferably 10 to 120 seconds.
The raw film before stretching may or may not have a tensile yield point, but within the range of the stretching ratio described above in this embodiment, even a film having a yield point can be preferably used.
In addition, when the film before stretching has a yield point, it is preferable to set the stretching ratio so that the yield point is not reached in order to prevent cracking. The presence or absence of a yield point can be confirmed by measuring the tensile stress/strain characteristics of the raw film. More specifically, the presence or absence of a tensile yield point of the raw film can be confirmed by measuring the tensile stress/strain characteristics according to JIS K7161, and determining the point at which the strain increases without increasing the stress as the yield point.
The presence or absence of a tensile yield point in the original film can also be estimated by performing the same measurement on the stretched film. In this case, if the presence of a yield point is observed in the stretched film, it is assumed that the original film also had a yield point.

The film of the present invention can be preferably used as a release film for manufacturing processes , and particularly preferably, can be placed between a semiconductor chip or the like and the inner surface of a mold when a resin is injected into the mold after the semiconductor chip or the like is placed therein. By using the film of the present invention as a release film for manufacturing processes, problems such as poor release from the mold and the generation of burrs can be effectively prevented.
The resin used in the above manufacturing process may be either a thermoplastic resin or a thermosetting resin, but thermosetting resins are widely used in the technical field, and it is particularly preferable to use epoxy-based thermosetting resins.
The most typical example of the above manufacturing process is the encapsulation of semiconductor chips, but the invention is not limited to this, and the film of the present invention can also be applied to fiber-reinforced plastic molding processes, plastic lens molding processes, and the like.

FIG. 2 is a schematic diagram showing an example of a method for producing a resin-encapsulated semiconductor using the film of the present invention.
As shown in FIG. 2( a), the film 15 of the present invention is supplied from a rolled wound material into the upper mold 13 by rolls 16-1 and 16-2. The film 15 is then placed on the inner surface of the upper mold 13. If necessary, the inner surface of the upper mold 13 may be vacuumed through suction port 12a to adhere the film 15 to the inner surface of the upper mold 13. A semiconductor chip 17, which is mounted on a substrate, is placed in the lower mold 14 of the molding device. An encapsulating resin is placed on the semiconductor chip 17, or a liquid encapsulating resin is injected to cover the semiconductor chip 17. The encapsulating resin 18 is then accommodated between the upper mold 13 and the lower mold 14, on which the film 15 is placed and adhered by evacuation and suction. Next, as shown in FIG. 2( b), the upper mold 13 and the lower mold 14 are closed with the film 15 of the present invention interposed therebetween, and the encapsulating resin 18 is cured.

As the mold is closed and hardened, the sealing resin 18 flows into the mold as shown in Figure 2(c), flows into the cavity, and fills in, surrounding the sides of the semiconductor chip 17. The encapsulated semiconductor chip 17 (semiconductor package 17-2) is then removed by opening the upper mold 13 and lower mold 14. After the mold is opened and the molded product is removed, the film 15 can be reused multiple times, or a new film can be supplied and the product can be subjected to the next resin molding process.

By adhering the film of the present invention to the upper mold, interposing it between the mold and the sealing resin, and then resin molding, adhesion of the resin to the mold is prevented, the resin molding surface of the mold is not soiled, and the molded product can be easily released from the mold.
The (release) film can be newly supplied for each resin molding operation, or can be newly supplied for each of several resin molding operations.

The encapsulating resin may be a liquid resin or a resin that is solid at room temperature, but any encapsulating material that becomes liquid during resin encapsulation can be appropriately used. Specifically, epoxy resins (such as biphenyl-type epoxy resins, bisphenol epoxy resins, and o-cresol novolac-type epoxy resins) are primarily used as encapsulating resin materials. Other encapsulating resins that can be used include polyimide-based resins (bismaleimide-based resins) and silicone-based resins (thermosetting addition type). Resin encapsulation conditions vary depending on the encapsulating resin used, but can be appropriately set within the ranges of, for example, a curing temperature of 120°C to 180°C, a molding pressure of 10 to 50 kg/cm ² , and a curing time of 1 to 60 minutes.

The order of the process of placing the film 15 on the inner surface of the upper mold 13 and the process of placing the semiconductor chip 17 is not particularly limited; they may be performed simultaneously, or the film 15 may be placed after the semiconductor chip 17 has been placed, or the semiconductor chip 17 may be placed after the film 15 has been placed.

As such, film 15 uses 4-methyl-1-pentene (co)polymer, which has high mold releasability, allowing semiconductor package 17-2 to be easily demolded. Furthermore, film 15 has moderate flexibility, allowing it to conform well to the mold shape while also being resistant to wrinkling due to the heat of molding dies 13 and 14. This prevents wrinkles from being transferred to the resin sealing surface of sealed semiconductor package 17-2, and prevents areas where resin is not filled (resin chipping), allowing for a sealed semiconductor package 17-2 with a good appearance.

Furthermore, instead of the compression molding method shown in Figure 2, in which a solid sealing resin material 18 is pressurized and heated, a transfer molding method in which a fluid sealing resin material is injected may also be used.

The film of the present invention can be used not only in processes for resin-encapsulating semiconductor elements, but also as a release film in processes for molding and releasing various molded products using molding dies, presses, etc., such as processes for resin-encapsulating LED elements, pressing processes for FPCs (flexible printed circuit boards), manufacturing processes for coated substrates, molding and releasing fiber-reinforced plastics such as CFRP, and molding and releasing plastic lenses.

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

In the following Examples and Comparative Examples, the physical properties and characteristics were evaluated by the following methods.
(thermal dimensional change rate)
The film sample was cut into a length of 20 mm and a width of 4 mm in the longitudinal and transverse directions of the film, and measured using a TA Instruments TMA (thermomechanical analyzer, product name: Q400) with a chuck distance of 8 mm and a load of 0.005 N applied, held at 23°C for 5 minutes, and then heated from 23°C to 150°C at a heating rate of 10°C/min. The dimensional changes in each direction were measured, and the dimensional change rate was calculated using the following formula (1):

Thermal dimensional change rate (%) (23 → 150°C) = {[(L ₂ - L ₁ )/L ₁ ] × 100}
...(1)
L ₁ : Sample length at 23°C (mm)
_L2 : Sample length at 150°C (mm)

(Wrinkle evaluation)
As shown in Figure 1, a film 5 was sandwiched between a film holding frame 1 and a mold 4 including a vacuum suction area 2, and the entire structure was heated with a planar heater (not shown). The surface temperature of the film 5 was measured, and when it reached 150°C, vacuum suction was performed. Thereafter, the film 5 on the vacuum suction area 2 was evaluated for the presence or absence of wrinkles according to the following criteria.
◯: The film has no wrinkles.
×: The film is wrinkled.

(Presence or absence of yield point (tensile yield point))
A tensile test was carried out using a thermostatic oven equipped tensile tester "RTC-1225" manufactured by A&D Co., Ltd. under the conditions of a sample width of 15 mm, a chuck distance of 50 mm, and a speed of 300 mm/min.
The measurement temperatures were 160°C and 200°C.
Following JIS K7161, the point at which strain increases without an increase in stress was defined as the yield point, and the presence or absence of this point was confirmed.

[Example 1]
Opulent (registered trademark) X44B (thickness 50 μm, manufactured by Mitsui Chemicals Tohcello Inc.: 4-methyl-1-pentene (co)polymer: 99% by mass or more) was used as a raw film (unstretched film) of 4-methyl-1-pentene (co)polymer, and sequential biaxial stretching was performed using a batch biaxial stretching machine (KARO IV manufactured by Bruckner). More specifically, the raw film was first stretched in the MD direction during film formation, and then stretched in the TD direction.
The detailed stretching conditions are as follows.
Distance between chucks: 180 mm in both MD and TD directions
Preheating temperature: 160°C
Preheating time: 60 seconds Stretching temperature: 160°C
The biaxially stretched films were subjected to measurement of thermal dimensional change and evaluation of wrinkles by the methods described above. The results are shown in Table 1.
Similarly, the presence or absence of a tensile yield point was confirmed using the biaxially stretched film by the above method. Tensile yield points were observed at 160°C and 200°C, confirming that the raw film had a tensile yield point.

(Examples 2, and 4 to 6)
Using the raw 4-methyl-1-pentene (co)polymer film having the same tensile yield point as in Example 1, biaxially stretched films were produced and evaluated in the same manner as in Example 1, except that the stretching temperature and/or stretch ratio was changed as shown in Table 1. The results are shown in Table 1.

Example 3
A biaxially stretched film was produced and evaluated in the same manner as in Example 2 (without changing the apparatus, chuck distance, preheating temperature, preheating time, or stretching speed), except that simultaneous biaxial stretching was performed instead of sequential biaxial stretching (stretching was performed simultaneously in the MD and TD directions during film formation of the raw film) using the 4-methyl-1-pentene (co)polymer film raw sheet having the tensile yield point used in Example 1. The results are shown in Table 1.

Example 7
The 4-methyl-1-pentene (co)polymer film raw sheet having the same tensile yield point as in Example 1 was stretched in the same manner as in Example 6, and then heat-set by holding the stretched film at 200°C for 60 seconds while chucked.
The biaxially stretched film after heat setting was subjected to measurement of thermal dimensional change rate and evaluation of wrinkles by the above-mentioned methods. The results are shown in Table 1.

(Comparative Example 1)
The raw 4-methyl-1-pentene (co)polymer film (unstretched film) having a tensile yield point used in Example 1 was directly subjected to measurement of thermal dimensional change rate and evaluation of wrinkles without being subjected to biaxial stretching, etc. The results are shown in Table 1.

(Comparative Example 2)
The raw 4-methyl-1-pentene (co)polymer film (unstretched film) having the tensile yield point used in Example 1 was uniaxially stretched in the MD direction at 160° C. and a stretch ratio of 1.10.
The uniaxially stretched film was subjected to measurement of thermal dimensional change and evaluation of wrinkles by the methods described above. The results are shown in Table 1.

(Comparative Example 3)
Using the raw 4-methyl-1-pentene (co)polymer film having the tensile yield point used in Example 1, a biaxially stretched film was produced in the same manner as in Example 3, except that the stretching temperature and stretch ratio were changed as shown in Table 1. The results are shown in Table 1.
Cracking occurred during stretching, and no stretched film was obtained that could be used to evaluate wrinkles or thermal dimensional change.

The film of the present invention combines high levels of releasability, recyclability, and wrinkle-preventing performance that could not be achieved with conventional technology. When this film is used, for example, as a release film for semiconductor encapsulation, molded articles obtained by resin-encapsulating semiconductor chips or the like can be easily released from the mold, and molded articles free from appearance defects due to wrinkles or the like can be produced with high productivity. In addition, the release film can be recycled, thereby achieving technical effects with great practical value, and therefore the film has high applicability in various fields of industry, including the semiconductor process industry.
Furthermore, the film of the present invention can be used not only for semiconductor encapsulation but also for LED resin encapsulation, FPC presses, coating substrates, fiber-reinforced plastic molding processes, etc., and is therefore highly applicable in various fields of industries other than the semiconductor industry that involve these processes.

1: Film holding frame 2: Vacuum suction area 4: Mold
5: Film 12a: Suction port 13: Upper mold 14: Lower mold 15: Films 16-1, 16-2: Roll 17: Semiconductor chip 17-2: Semiconductor package 18: Sealing resin

Claims (7)

The film contains 90% by mass or more of a 4-methyl-1-pentene (co)polymer, and has a thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C of 3% or less, and the sum of the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C and the thermal dimensional change rate in the longitudinal (MD) direction from 23°C to 150°C of 6% or less, and is a biaxially stretched film in which the stretch ratios in both the longitudinal (MD) direction and the transverse (TD) direction are from 1.01 to 1.50, and the area ratio expressed as the stretch ratio in the longitudinal (MD) direction x the stretch ratio in the transverse (TD) direction is 1.02 to 2.00 . The film of claim 1, wherein the film is a single-layer film. The film according to claim 1 or 2 , wherein the thermal dimensional change rate in the transverse (TD) direction from 23°C to 150°C is 0% or more. 4. The method for producing a film according to claim 1 , comprising a step of biaxially stretching a raw film containing 90% by mass or more of a 4-methyl-1-pentene (co)polymer, wherein the biaxial stretching is carried out at a temperature of 50° C. or higher and lower than the melting point of the 4-methyl-1-pentene (co)polymer. The method according to claim 4 , further comprising a step of performing a heat setting treatment at a temperature equal to or higher than the biaxial stretching temperature and lower than the melting point of the 4-methyl-1-pentene (co)polymer after the biaxial stretching step. The film of claim 1 which is a release film. The film according to claim 1 , which is a release film for use in a semiconductor encapsulation process.