JP4997030B2 - Multilayer film - Google Patents

Description

  The present invention relates to a multilayer film useful for housing food, daily necessities, secondary batteries and the like.

As a packaging material to contain retort foods such as curry, refills such as shampoo and liquid detergent, and secondary batteries, polyolefin film on one side of the aluminum foil layer and polyamide on the other side Composite multilayer films having layers have been widely used (for example, Patent Document 1). Since polyolefin has thermal adhesiveness, it is possible to seal the packaging material by heat sealing by setting the polyolefin film to the inside of the packaging material. Moreover, polyamide is excellent in mechanical strength and can improve the durability of the packaging material.

However, the polyolefin film and the aluminum foil are conventionally bonded via an anchor coating agent or an adhesive. For this reason, it has not been possible to use a liquid having a strong permeability or a strong dissolving power that attacks the anchor coating agent or the adhesive.

In addition, in the conventional technology, an aluminum foil that has not been surface-treated is used, and a liquid that erodes aluminum can be used as a content even if it does not affect the adhesive layer. There wasn't.

As a technique for solving these problems, a method of treating the surface of an aluminum foil with a chromic acid chemical (chromate treatment) is widely known (for example, Patent Document 2). By the film formed by this treatment, the corrosion resistance of the aluminum foil is remarkably improved, and the film can be bonded to the polyolefin film by heat lamination without using any anchor coat agent or adhesive. However, this technique involves a serious problem of using chromium, which is an environmentally hazardous substance.

Non-chromium chemical conversion coating treatments such as boehmite treatment (hydrothermal treatment) and phosphate treatment are known as aluminum surface treatments that do not use chromium, and these surface treatments can provide the same corrosion resistance as chromate treatment. However, if an attempt is made to bond a polyolefin film and an aluminum foil treated with a non-chromium chemical conversion coating by thermal lamination without using an anchor coating agent or an adhesive, the temperature range in which the film can be manufactured, that is, the polyolefin film is processed by a processing machine. Sufficient adhesive strength cannot be obtained in the temperature range where lamination can be performed without fusing.
WO99 / 40634 pamphlet JP 2003-288865 A

The present invention relates to a multilayer film having a polyolefin film layer on one side and a polyamide layer on the other side of an aluminum foil layer that has been treated with a non-chromium conversion coating, and the aluminum foil and the polyolefin film are directly, that is, an anchor coating agent. Another object of the present invention is to provide a multilayer film that is bonded without applying any adhesive or the like and has sufficient adhesive strength.

The inventor of the present invention maintains that the polyolefin film is not melted even in the thermal laminate layer made of the acid-modified polyolefin (α) and the peak top melting point on the highest temperature side in the DSC melting curve of α. A multilayer film in which an aluminum foil is treated with a non-chromium chemical conversion coating, and the aluminum foil is laminated on the thermal laminate layer is a polyolefin film and an aluminum foil. Can be bonded without causing any trouble that the polyolefin film is fused to the processing machine even at a high temperature at which the above heat laminating layer is almost completely melted. I found out that I can do it.

That is, the present invention is a multilayer film having a polyolefin resin film (A) on one surface of an aluminum layer (B) treated with a non-chromium chemical conversion film and a polyamide layer (C) on the other surface. The film (A) includes an acid-modified polyolefin resin (α) layer (A-1) and a crystalline propylene polymer (β) layer (A-2), and the acid-modified polyolefin resin (α when the peak top melting point of the highest temperature side in the DSC melting curve of) was Tm _alpha, (crystallinity of _β) (Xc (Tm α) the crystalline propylene polymer at a temperature Tm _alpha) is more than 60% It is a multilayer film in which the layer (B) is directly laminated on the layer (A-1).

The present invention also provides:
1) A step of laminating an aluminum layer (B) treated with a non-chromium chemical conversion film on one side of a polyolefin resin film (A), and 2) a polyamide layer (C) on the layer (B). Wherein the film (A) includes a layer (A-1) of the acid-modified polyolefin resin (α) and a layer (A-2) of the crystalline propylene polymer (β), and the acid When the peak top melting point on the highest temperature side in the DSC melting curve of the modified polyolefin resin (α) is Tm _α , the crystallinity of the crystalline propylene polymer (β) at the temperature Tm _α (Xc (Tm _α )) ) Is 60% or more, and in step 1), the layer (B) is laminated on the layer (A-1) by thermal lamination at a temperature (T _R ) that satisfies the following (1). Production of the multilayer film It is also provided.
Xc (T _R ) <60% of α and Xc (T _R ) ≧ 60% of β (1)
Here, Xc _{(T R)} is crystallinity at a temperature _{T R.}

In the multilayer film of the present invention, the polyolefin resin layer and the non-chromium conversion coating-treated aluminum layer are bonded together with sufficient adhesive strength without applying an anchor coating agent or an adhesive. It is useful as a packaging material for contents such as liquids that are highly permeable and soluble, and liquids that attack untreated aluminum.

An example of the multilayer film of the present invention is shown in FIG. As shown in FIG. 1, the multilayer film of the present invention has a polyolefin resin film (A) on one surface of an aluminum layer (B) treated with a non-chromium chemical conversion film, and a polyamide on the other surface. Layer (C). You may further have a layer (D) of a polyester-type resin on a layer (C). The film (A) includes at least two layers, that is, a layer (A-1) of the acid-modified polyolefin resin (α) and a layer (A-2) of the crystalline propylene-based polymer (β). 1) is in a position in contact with the layer (B). The layer (A-2) is the side having the layer (A-1) of the film (A) so that it becomes the innermost surface when the multilayer film is formed into a bag shape so that the film (A) is inside. Located on the opposite innermost side.

(A) Polyolefin resin film The polyolefin resin film (A) comprises an acid-modified polyolefin resin (α) layer (A-1) and a crystalline propylene polymer (β) layer (A-2). )including.

The acid-modified polyolefin resin (α) constituting the layer (A-1) may be any polyolefin resin modified with an unsaturated carboxylic acid or a derivative thereof. Examples of unsaturated carboxylic acids include, for example, maleic acid, itaconic acid, fumaric acid, and examples of derivatives thereof include, for example, maleic acid monoester, maleic acid diester, maleic anhydride, itaconic acid monoester, Examples include itaconic acid diester, itaconic anhydride, fumaric acid monoester, fumaric acid diester, fumaric anhydride and the like. Examples of the polyolefin resin include linear polyethylene, ultra-low density polyethylene, high density polyethylene, ethylene-vinyl acetate (VA) copolymer, ethylene-ethyl acrylate (EA) copolymer, and ethylene-methacrylate copolymer. Examples include ethylene polymers, propylene polymers, and styrene elastomers. When the film (A) is composed of only the layer (A-1) and the layer (A-2), the layer (A) is formed by coextrusion with the crystalline propylene polymer (β) constituting the layer (A-2). The polyolefin resin is most preferably a propylene-based polymer so that sufficient interlayer strength can be obtained between A-1) and the layer (A-2). In addition, acid-modified polyolefin resin ((alpha)) can be used individually or in combination of 2 or more. In addition, a polyolefin resin that is not acid-modified may be blended within a range that does not contradict the object of the present invention.

The layer (A-1) is a layer that is directly bonded to the layer (B) in the thermal lamination of the film (A) and the layer (B) described later. When the highest temperature side peak top melting point in the DSC melting curve of the layer (A-1) an acid-modified polyolefin resin constituting the (alpha) was Tm _alpha, Tm _alpha is lower the temperature lower that the hot lamination However, it can be appropriately selected depending on the purpose of use of the multilayer film. When using a multilayer film as a packaging material for contents, such as strong permeating or solubilizing power liquid is preferably Tm _alpha is 100 ° C. or higher, more preferably 120 ° C. or higher. Moreover, when performing heat processing, such as a retort process, Tm _alpha should be high, but when the upper limit of the heat resistance of the crystalline propylene polymer (β) constituting the layer (A-2) described later is considered. the upper limit of Tm _alpha is preferably 155 ° C., more preferably from 0.99 ° C.. Note that the Tm _alpha when a mixture of resin (alpha) consists of two or more thereof, is a value determined from the DSC melting curve of the mixture.

In this specification, unless otherwise specified, DSC melting curves are obtained by using DSC Q1000 model of TA Instruments (TA Instruments Japan Co., Ltd.) and holding the sample at 230 ° C. for 5 minutes. Obtained by performing DSC measurement with a temperature program of cooling to −10 ° C. at a temperature decrease rate of 10 ° C./min, holding at −10 ° C. for 5 minutes, and then heating to 230 ° C. at a temperature increase rate of 10 ° C./min. It is a curved line.

Specific examples of the acid-modified polyolefin resin (α) include Admer (trade name) manufactured by Mitsui Chemicals, Adtex (trade name) manufactured by Nippon Polyolefin Co., Ltd., and Polybond (trade name) manufactured by Crompton Co., Ltd. Examples include Bond First (trade name) manufactured by Sumitomo Chemical Co., Ltd.

A layer (A-2) is a layer located in the innermost side opposite to the side with the layer (A-1) of a film (A) as above mentioned. The crystalline propylene polymer (β) constituting the layer (A-2) is not melted at the laminating temperature and adhered to the processing machine when the film (A) is thermally laminated with the layer (B). The acid-modified polyolefin resin (α) constituting the layer (A-1) has a crystallinity (Xc (Tm _α )) at a peak top melting point Tm _α of 60% or more. Preferably, the crystallinity is 70% or more, more preferably 80% or more. When the crystallinity is less than 60%, troubles such as the film (A) being fused to the processing machine at the time of thermal lamination are very likely to occur.

In the present specification, the degree of crystallinity (Xc (T)) at temperature T means the ratio of maintaining the crystalline state without melting at temperature T. For example, the crystallization of polymer (β) The degree (Xc (Tm _α )) is calculated as the ratio of the melting enthalpy at the temperature Tm _α or higher to the total melting enthalpy in the DSC melting curve of β. In addition, the said crystallinity in case a polymer ((beta)) is a mixture which consists of a 2 or more combination is a value determined from the DSC melting curve of the said mixture.

The crystalline propylene polymer (β) may be anything as long as it satisfies the above crystallinity. For example, a propylene homopolymer, a random copolymer of propylene and a small amount of a comonomer (eg, ethylene, 1-butene, etc.). Polymers and propylene-based block polymers (for example, propylene-ethylene block copolymers, propylene-ethylene-1-butene block copolymers, propylene-1-butene block copolymers, etc.) are included. The crystalline propylene polymer can be used alone or in combination of two or more.

Commercial examples of the crystalline propylene polymer (β) include F-704NP, F-300SP, F-724NP, E-185G and E-150GK manufactured by Prime Polymer Co., Ltd., FB3HAT manufactured by Nippon Polypro Co., Ltd. , FY6, FY4, EC7 and EC9, and PC600S and PC412A manufactured by Sun Allomer Co., Ltd.

Since the crystalline propylene polymer (β) has thermal adhesiveness, when the resulting multilayer film is processed into a bag shape with the layer (A-2) inside, and the opening of the bag is heat sealed. Can be processed well when sealed.

The polyolefin resin film (A) may contain another polyolefin resin layer between the layer (A-1) and the layer (A-2). Examples of the other layers include layers having functions such as water absorption and oxygen absorption.

The polyolefin-based resin film (A) has an acid-modified polyolefin resin (α), a crystalline propylene-based polymer (β) and other resins as desired, and has a desired thickness by co-extrusion by a T-die method or an inflation method. It can be obtained by forming a film.

(B) Non-chromium conversion coating treated aluminum layer The non-chromium conversion coating treatment is a coating treatment performed without using chromium, and includes hot water treatment (boehmite treatment) and chromium. Coating treatment with no chemicals, for example, phosphates such as zinc phosphate and manganese phosphate and metal salts of organic acids. The layer (B) in the present invention can be obtained by subjecting an untreated aluminum foil to the above treatment.

(C) Polyamide layer Polyamide is excellent in mechanical strength, and by having this layer, durability of the resulting multilayer film can be enhanced. The polyamide used is not particularly limited. For example, nylon 6, nylon 11, nylon 12, nylon 66, nylon 610, nylon 6T, nylon 6I, nylon 9T, nylon M5T, nylon nylon 612, Kevlar (trademark of Kevlar, DuPont) ), Nomex (trademark of DuPont).

Examples of commercially available polyamides include UBE nylon (nylon 6), UBE nylon 66 (nylon 66), UBESTA (nylon 12) manufactured by Ube Industries, Ltd., and alamin (nylon 6, 66, 610, etc.) manufactured by Toray Industries, Inc. ), Toyobo nylon manufactured by Toyobo Co., Ltd. (nylon 6, 66, 6T, etc.), Novamid manufactured by Mitsubishi Engineering Plastics Co., Ltd. (nylon 6, 66, 12), Unitika nylon 6, manufactured by Unitika Ltd., Unitika nylon 66 and Leona (nylon 66) manufactured by Asahi Kasei Chemicals Corporation are listed.

(D) Polyester resin layer This layer is a protective layer optionally laminated on the layer (C). Layer (C) has excellent mechanical strength, but is very fragile to highly permeable and soluble liquids. A multilayer bag composed of the above (A) to (C) is made so that the layer (C) is the outermost layer, and the contents such as liquid having high permeability and solubility are put therein. When the bag mouth is heat-sealed, the contents may spill. Therefore, it is advantageous to have a further layer (D) on top of the layer (C).

The polyester resin constituting the layer (D) is not particularly limited, and examples thereof include polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN), polytrimethylene terephthalate (PTT), and polybutylene naphthalate. Includes phthalate (PBN).

Examples of commercially available polyester resins include Viropet (PET and PBT) manufactured by Toyobo Co., Ltd., Toraycon (PBT) manufactured by Toray Industries, Inc., Novaduran (PBT) manufactured by Mitsubishi Engineering Plastics Co., Ltd., and Unitika Co., Ltd. ), And Teijin Chemicals' PET resin, Teonex (PEN) and PBN resin.

The production of the multilayer film of the present invention
1) A step of laminating an aluminum layer (B) treated with a non-chromium chemical conversion coating on one surface of a polyolefin resin film (A), and 2) a polyamide layer (C) on the layer (B). Including a step of laminating. Here, the film (A) includes a layer (A-1) of the acid-modified polyolefin resin (α) and a layer (A-2) of the crystalline propylene polymer (β). The layer (B) is laminated on the layer (A-1) by thermal lamination at a temperature (T _R ) that satisfies (1).
Xc (T _R ) <60% of α and Xc (T _R ) ≧ 60% of β (1)
Here, Xc _{(T R)} is crystallinity at a temperature _{T R.}

The heat lamination, the above range of temperatures to satisfy (1) (heat roll temperature T _R), can be carried out by conventional methods. Preferably, it is performed at a temperature such that Xc (T _R ) of α <50%, more preferably <40%, and Xc (T _R ) of β ≧ 70%, more preferably ≧ 80%. If the temperature is higher than the above range, the polyolefin film (A) may be fused to the heat roll and cannot be laminated. If the temperature is lower than the above range, the adhesive strength between the film (A) and the layer (B) is insufficient. There is a case.

Step 2) can be performed by adhering the layer (B) side of the film obtained in step 1) and the polyamide layer (C) by a dry laminating method. As the adhesive, an ordinary two-pack type of a polyol main agent and an isocyanate curing agent can be used. Specifically, Takelac (polyol-based main agent) / Takenate (isocyanate-based curing agent) two-component type manufactured by Mitsui Chemicals Polyurethane Co., Ltd. can be mentioned.

The multilayer film further having the layer (D) on the layer (C) is obtained by dry laminating the layer (D) on the layer (C) of the film obtained in the above step 2) in the same manner as in the above step 2). It can be obtained by bonding by the method. The same adhesive can be used as in step 2) above.

In the multilayer film of the present invention thus obtained, the polyolefin resin film and the non-chromium chemical conversion coated aluminum layer are bonded together with sufficient adhesive strength without applying an anchor coating agent or an adhesive. Therefore, it is useful as a packaging material, particularly a packaging material for contents such as a liquid having a high permeability and solubility or a liquid that attacks untreated aluminum. The contents include, for example, retort foods such as curry, refill items such as shampoos and liquid detergents, disposable packs such as industrial chemicals, solutions and solvents, secondary batteries, and the like.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to a following example.

Examples 1-2 and Comparative Examples 1-2
(1) Production of polyolefin film (A) Acid-modified polyolefin resin (α) for layer (A-1) and crystalline propylene-based weight for layer (A-2) shown in Table 1 A film (A) having a layer (A-1) / layer (A-2) thickness ratio of 1/3 and a total thickness of 60 μm was produced using the union (β) and a feed block type multilayer coextrusion T die. . The T-die outlet resin temperature was 240 ° C. and the take-up speed was 10 m / min. Further, the (A-1) layer was subjected to corona treatment so that the wetting index was 55 mN / m or more.

(2) Boehmite treatment of aluminum foil An untreated aluminum foil (super foil, thickness 40μm) manufactured by Toyo Aluminum Co., Ltd. is fed into a water bath and immersed in boiling water for 30 minutes, and then the immersed portion is wound up. Was repeated to obtain a boehmite-treated aluminum foil (B).

(3) Thermal lamination of polyolefin film (A) and aluminum foil (B) The polyolefin film (A) obtained above and the aluminum foil (B) treated with boehmite are mixed with dielectric heat generated by Tokuden Corporation. Using a formula laminator JD-DW, thermal lamination was performed so that the polyolefin film layer (A-1) was in contact with the aluminum foil. The temperature of the hot roll was the peak top melting point (141 ° C.) in the DSC melting curve of the acid-modified polyolefin resin (α) used, the pressure was 0.3 MPa, and the take-up speed was 2 m / min. Further, thermal lamination was similarly performed at a heat roll temperature of 135 ° C.

(4) Dry lamination of polyamide film (C) On the aluminum foil of the film obtained by the above thermal lamination, a nylon film (emblem ONUM, thickness 15 μm) of Unitika Co., Ltd. was used as an adhesive. Using a two-pack type of Takelac A-310 / Takenate A-3 (12/1 mass ratio) manufactured by Chemical Polyurethane Co., Ltd., dry lamination was performed using a plain metal test laminator MODEL200. After lamination, curing was performed at 40 ° C. for 90 hours.

The following test was done about the film obtained by said (1), (3) and (4).

Heat seal strength of polyolefin film The layers (A-2) of the polyolefin film (A) obtained in the above (1) are set so that the machine direction of the film becomes the tensile direction of the T-peel test. Using a HG-100 heat seal tester manufactured by Toyo Seiki Seisakusho Co., Ltd., fusion was performed under conditions of a temperature of 175 ° C., a time of 2 seconds, and a pressure of 0.2 MPa. Next, an AE-CT type tensile tester manufactured by Toyo Seiki Seisakusho Co., Ltd. was used as a T-peeling test. The heat seal strength between each other was measured.

Thermal laminating property-1
On the polyolefin film (A) of the film obtained in the above (3), 10 rows × 10 rows are cut in a grid pattern at intervals of 3 mm both vertically and horizontally, and an adhesive tape is applied thereon, and the adhesive tape is immediately peeled off. . A case where the film was peeled off without adhering to the adhesive tape was marked with ◯, and the other case was marked with x.

Thermal laminating property-2
The polyolefin film (A) and the boehmite-treated aluminum foil (B) are arranged so that the layer (A-1) and the layer (B) are in contact with each other and the machine direction of the film is the tensile direction of the T-peel test. Using an HG-100 heat seal tester manufactured by Toyo Seiki Seisakusho Co., Ltd., fusion was performed under the conditions of a temperature of 141 ° C., a time of 2 seconds, and a pressure of 0.3 MPa. Next, as a T-shaped peel test, an AE-CT type tensile tester manufactured by Toyo Seiki Seisakusho Co., Ltd. was used. The peel width was 25 mm, the peel speed was 100 mm / min, and the peel angle was 180 °. The laminate strength between the aluminum foils was measured. The same measurement was performed when the fusing temperature was changed to 135 ° C.

Solvent resistance Two 20cm x 15cm film pieces were cut out from the film obtained in (4) above, and the polyolefin film (A) was stacked on the inside, and the three sides were fused by heat sealing. And made a bag. After adding 100 mL of an organic solvent of dimethyl carbonate (DMC) / diethyl carbonate (DEC) / ethylene carbonate (EC) = 1/1/1 (volume ratio), the bag mouth was closed by heat sealing. The bag filled with the organic solvent was subjected to an accelerated deterioration test for 100 days using an environmental tester set to a temperature of 60 ° C. and a humidity of 90%. The case where there was no abnormality such as liquid leakage was marked with ○, and the case where some abnormality was found was marked with ×.

The materials used are as follows.
Admer QE060: manufactured by Mitsui Chemicals, maleic anhydride modified polypropylene, Tm _α = 141 ° C., temperature at which Xc = 60%: 126 ° C.
F-704NP: manufactured by Prime Polymer Co., Ltd., homopolypropylene, temperature at which Xc (141) = 86%, Xc = 60%: 156 ° C.
F-300SP: Prime Polymer Co., Ltd., homopolypropylene, Xc (141) = 82%, temperature at which Xc = 60%: 155 ° C.
F-730NV: manufactured by Prime Polymer Co., Ltd., propylene random copolymer, Xc (141) = 23%, temperature at which Xc = 60%: 126 ° C.

As is apparent from Table 1, the propylene polymer (β) constituting the layer (A-2) is one having a crystallinity Xc (Tm _α ) of 60% or more and the layer (B) is treated with boehmite. The multilayer films of Examples 1 and 2 that have been described have sufficient heat seal strength and are excellent in heat laminating properties and solvent resistance.

On the other hand, Comparative Example 1 using F-730NV having a crystallinity of 23% as the crystalline propylene polymer (β) was heat laminated at 141 ° C. in the same manner as in Example 1. The film could not be peeled off due to adhesion to the hot roll, and could not be laminated. Therefore, when the heat roll was performed by lowering the temperature of the heat roll to 125 ° C. so that the crystallinity of F-730NV became 60% or more, the lamination was possible, but the adhesive strength was not sufficient, and Solvent property was not sufficient. The temperature at which the crystallinity of F-730NV becomes 60% is 126 ° C.

In Comparative Example 2, an untreated aluminum foil was used as the layer (B). When heat laminating was performed in the same manner as in Example 1, sufficient adhesive strength could not be obtained, and the solvent resistance was insufficient. Therefore, the temperature of the hot roll was increased to 150 ° C. and 156 ° C., and thermal lamination was performed. However, the adhesive strength and solvent resistance were still insufficient, and when the temperature was further increased to 160 ° C., the polyolefin film adhered to the hot roll. It could not be peeled off and could not be laminated. Note that the degree of crystallinity of β (F-704NP) at 160 ° C. is 50%.

FIG. 1 is an example of the multilayer film of the present invention.

Explanation of symbols

A Polyolefin resin film B Aluminum layer treated with non-chromium chemical conversion film C Polyamide layer D Polyester resin layer A-1 Acid-modified polyolefin resin layer A-2 Crystalline propylene polymer layer

Claims (6)

A multilayer film having a polyolefin resin film (A) on one surface of an aluminum layer (B) treated with a non-chromium chemical conversion film and a polyamide layer (C) on the other surface, A) includes a layer (A-1) of the acid-modified polyolefin resin (α) and a layer (A-2) of the crystalline propylene polymer (β), in the DSC melting curve of the acid-modified polyolefin resin (α). highest when the temperature-side peak top melting point was Tm _alpha, the crystalline propylene polymer at a temperature Tm _alpha (beta) of crystallinity _(Xc (Tm α)) is not less than 60%, the layer (B ) Is laminated directly on the layer (A-1). The multilayer film according to claim 1, further comprising a polyester resin layer (D) on the layer (C). The multilayer film of Claim 1 or 2 whose Tm ( _alpha) is 100-155 degreeC. The molded object which consists of a film of any one of Claims 1-3. The molded object of Claim 4 which is an exterior material of a secondary battery. 1) A step of laminating an aluminum layer (B) treated with a non-chromium chemical conversion film on one side of a polyolefin resin film (A), and 2) a polyamide layer (C) on the layer (B). Wherein the film (A) includes a layer (A-1) of the acid-modified polyolefin resin (α) and a layer (A-2) of the crystalline propylene polymer (β), and the acid When the peak top melting point on the highest temperature side in the DSC melting curve of the modified polyolefin resin (α) is Tm _α , the crystallinity of the crystalline propylene polymer (β) at the temperature Tm _α (Xc (Tm _α )) ) Is 60% or more, and in step 1), the layer (B) is laminated on the layer (A-1) by thermal lamination at a temperature (T _R ) that satisfies the following (1). The multilayer film of claim 1, wherein Absence of production method,
Xc (T _R ) <60% of α and Xc (T _R ) ≧ 60% of β (1)
Here, Xc _{(T R)} is crystallinity at a temperature _{T R.}

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