JP6058949B2 - Biaxially stretched polyester film for in-mold molding - Google Patents

Description

  The present invention relates to a polyester film for in-mold molding, and more particularly to a polyester film for in-mold molding that is useful when a printed film remains integrally with a molded product.

  In-mold molding, in which a printed film is inserted into a mold and decorated at the same time as injection molding, allows for beautiful decoration at low cost, so it can be used in automobile interior parts, electronic equipment casings, etc. Widely used. There are two types of in-mold molding, one is a method of peeling the film after injection molding, and the other is a method in which the film remains integrally with the molded product after injection molding. . In the former method, a stretched polyester film is widely used because of its high heat resistance, dimensional stability, printability, thickness accuracy, and low cost. However, in the latter method, it follows a complicated three-dimensional shape. It is necessary to use an acrylic film having a very high moldability. On the other hand, the acrylic film has a problem that the thickness accuracy is inferior and unnecessary portions become burrs after molding, and the development of a film that replaces this is desired.

  For example, Patent Document 1 discloses an in-mold molding polyester film having a breaking elongation at 100 ° C. of 200 to 600% and a breaking stress of 3 to 30 MPa. There was no example in which the degree was 350% or more and the breaking stress was 30 MPa or less, and the moldability was insufficient as an alternative to the acrylic film.

  Patent Document 2 discloses a polyester film containing an extender and having a stress at 400% elongation in the range of 2 to 20 MPa in an atmosphere of 120 ° C., but is an unstretched film. Thickness accuracy could not be obtained.

JP 2006-281732 A JP 2010-70581 A

  The present invention intends to provide a polyester film that can be molded in-mold with large deformation even if it is stretched to obtain sufficient thickness accuracy.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above-mentioned problems can be solved by using a polyester film having a breaking elongation at 120 ° C. and a breaking stress in a specific range, and have reached the present invention. .

That is, the gist of the present invention is as follows.
(1) Polyethylene terephthalate (A) containing 4 to 15 mol% of a diethylene glycol residue with respect to all glycol components, and an amorphous copolymer polyester obtained by modifying a polyethylene terephthalate resin with diol, and 1,4-cyclohexane as the diol component a polyester film having a thickness of 30~200μm consisting dimethanol from 10 to 70 mol% including non-crystalline polyester (B), polyethylene terephthalate (a) / amorphous polyester (B) / polyethylene terephthalate (a) The amorphous polyester (B) layer has a certain layer constitution, and the thickness constitution ratio is 50 to 95% of the total thickness, the breaking elongation at 120 ° C. is 350% to 500%, and the breaking stress is 10 MPa to 30 MPa. And the thickness unevenness is 5% or less. Biaxially oriented polyester film for Rudo molding.
(2) The biaxially stretched polyester film for in-mold molding according to (1), wherein (A) contains 0.1 to 1% by mass of an antioxidant.
(3) A method for producing a biaxially stretched polyester film for in-mold molding according to any one of ( 1) to (2) , wherein an unstretched laminated film is stretched in the longitudinal direction and the transverse direction by a sequential biaxial stretching method. At this time, the in-mold molding is characterized in that the surface magnification of biaxial stretching is 9.0 to 12.3, and the ratio of the stretching ratio in the longitudinal direction and the transverse direction is 0.8 to 1.2. For producing biaxially stretched polyester film.

  According to the present invention, it is possible to perform in-mold molding with a beautiful decoration because it is less expensive than an acrylic film, has a good thickness accuracy, and generates less burrs.

  The polyester film of the present invention needs to have a breaking elongation at 120 ° C. of 350% to 500% and a breaking stress of 10 MPa to 30 MPa. It is preferable that the breaking elongation at 120 ° C. is 370% to 500% and the breaking stress is 10 MPa to 25 MPa. More preferably, the breaking elongation at 120 ° C. is 400% to 500%, and the breaking stress is 10 MPa to 20 MPa.

  When the elongation at break at 120 ° C. is less than 350%, the film does not follow and breaks when the in-mold molding is performed, and the appearance of the molded product is impaired.

  In a stretched film obtained by stretching polyester to a surface magnification of 9.0 times or more in order to obtain thickness accuracy, it is difficult to obtain a film having a breaking elongation exceeding 120% at 120 ° C., so the upper limit is 500%.

  When the breaking stress at 120 ° C. is less than 10 MPa, the film may break when in-mold molding is performed, and the appearance of the molded product may be impaired.

  When the breaking stress at 120 ° C. exceeds 30 MPa, the resin injected to every corner of the mold does not spread when in-mold molding is performed, and the shape of the obtained molded product tends to be defective.

  The thickness unevenness of the polyester film of the present invention needs to be 5% or less. Preferably it is 4% or less. A method for measuring thickness spots will be described later.

  When the thickness unevenness exceeds 5%, when in-mold molding is performed, deformation appears on the printed design and the printed design is distorted.

  In order to make the thickness unevenness 5% or less, the polyester film needs to be biaxially stretched. The method of biaxially stretching the polyester film can be selected within the scope of known techniques, such as sequential biaxial stretching, tenter simultaneous biaxial stretching, and inflation simultaneous biaxial stretching. The range of the surface magnification of the biaxial stretching is preferably 9.0 times to 12.3 times, and preferably 9.7 times to 10.0 times in order to achieve thickness spots and breaking elongation at 120 ° C. More preferably. When the surface magnification of biaxial stretching is 12.3 times or more, it is difficult to make the breaking elongation at 120 ° C. 350% or more, and when it is less than 9.0 times, the thickness unevenness is 5% or less. Is difficult.

  Moreover, it is preferable that ratio of the draw ratio of a vertical direction and a horizontal direction shall be 0.8-1.2. Outside this range, the breaking elongation at 120 ° C and the anisotropy of the breaking stress become large, and when in-mold molding is performed, the printed design is distorted and the printed design is distorted and the appearance is impaired. Become.

  Biaxial stretching is performed at a temperature higher than the glass transition temperature (Tg) of the polyester, but as long as the thickness variation is 5% or less, it is preferable that the elongation at 120 ° C. can be increased. When the stretching temperature exceeds Tg + 30 ° C., it becomes difficult to make the thickness unevenness 5% or less.

  The dry heat shrinkage of the polyester film of the present invention is preferably -0.5 to 1.0%, more preferably -0.3 to 0.5%. It is a value when treated at 160 ° C. for 15 minutes. Both the MD direction and the TD direction are preferably in the above range. If it is out of the above range, when in-mold molding is performed, deformation spots are generated, and the printed design is distorted and the aesthetic appearance is impaired.

  In the polyester film of the present invention, it is preferable to laminate at least one layer of polyethylene terephthalate (A) containing 4 to 15 mol% of diethylene glycol residue and the amorphous polyester resin layer (B) with respect to all glycol components. More preferably, the diethylene glycol residue is contained in an amount of 6 to 12 mol%.

  When the diethylene glycol residue is less than 4 mol% with respect to all glycol components, it becomes difficult for the elongation at break at 120 ° C to exceed 350%. When diethylene glycol residue exceeds 15 mol%, thermal stability is low and foaming may be caused by pyrolysis gas during film formation.

  The polyester film of the present invention preferably contains an antioxidant for improving thermal stability. Among them, polyethylene terephthalate (A) preferably contains 0.1 to 1% by mass of an antioxidant. Since the generation of bubbles is suppressed by the antioxidant, as a result, the elongation at break of the film is increased, and the upper limit of the diethylene glycol residue can be increased.

  As the antioxidant, a hindered phenol-based antioxidant can be suitably used. For example, N, N′-hexamethylenebis (3,5-di-tert-butyl-4-hydroxy-hydrocinnamamide), 3,5-di-tert-butyl-4-hydroxy-benzylphosphonate— Diethyl ester, 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxy-benzyl) benzene, pentaerythrityl-tetrakis [3- (3,5- Di-t-butyl-4-hydroxyphenyl) propionate], tetrakis (2,4-di-t-butylphenyl) -4,4′-biphenylylene-di-phosphonite, triethylene glycol-bis-3- ( 3-t-butyl-4-hydroxy-5-methyl-phenyl) propionate and the like.

  Among these hindered phenolic antioxidants, particularly when used for polyethylene terephthalate (A), N, N′-hexamethylenebis (3,5-di-t-butyl-4-hydroxy- Hydrocinnamamide), 3,5-di-t-tyl-4-hydroxy-benzylphosphonate-diethyl ester, 1,3,5-trimethyl-2,4,6-tris (3,5-di-) at least one compound selected from the group consisting of t-butyl-4-hydroxy-benzyl) benzene and pentaerythrityl-tetrakis [3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] Is preferred.

  Moreover, although the polyethylene terephthalate (A) of this invention can be polymerized using a well-known polymerization catalyst, it is preferable to use a germanium catalyst. When a germanium catalyst is used, the polymerized polyester has low crystallinity, and therefore, the elongation at break at 120 ° C. tends to increase.

  Furthermore, the polyethylene terephthalate (A) of the present invention may be copolymerized with other monomers as long as the effects of the present invention are not hindered. For example, isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, dodecanedioic acid, dimer acid, maleic anhydride Examples thereof include dicarboxylic acids such as acid, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid and cyclohexanedicarboxylic acid, 4-hydroxybenzoic acid, ε-caprolactone and lactic acid.

  Examples of alcohol components include 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol, cyclohexanedimethanol, triethylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol. And ethylene oxide adducts of bisphenol A and bisphenol S.

  Further, a small amount of trifunctional compounds such as trimellitic acid, trimesic acid, pyromellitic acid, trimethylolpropane, glycerin, pentaerythritol, and the like may be used. Two or more of these copolymer components may be used in combination.

  The amorphous polyester (B) of the present invention refers to a polyester resin that exhibits substantially no crystallinity. That is, it means a resin having a crystallinity of 5% or less when the resin is allowed to stand for 20 hours or more in an arbitrary temperature range from the glass transition temperature to the melting point. As such an amorphous polyester resin, for example, a polyalkylene terephthalate resin such as polyethylene terephthalate or a polyalkylene-2,6-naphthalate resin such as poly-ethylene-2,6-naphthalate is acid-modified and / or diol-modified. A crystalline copolyester is preferred. The degree of crystallinity is obtained from the X-ray diffraction intensity of the crystal part and the X-ray diffraction intensity of the amorphous part.

  Examples of acid-modifying components used for copolymerization include isophthalic acid, phthalic acid, 2,6-naphthalenedicarboxylic acid, 5-sodium sulfoisophthalic acid, oxalic acid, succinic acid, adipic acid, sebacic acid, dodecanedioic acid, dimer acid , Maleic anhydride, maleic acid, fumaric acid, itaconic acid, citraconic acid, mesaconic acid, cyclohexanedicarboxylic acid and other dicarboxylic acids, 4-hydroxybenzoic acid, ε-caprolactone, lactic acid and other oxycarboxylic acids, and trimellitic acid And polyfunctional compounds such as trimesic acid and pyromellitic acid. These acid-modifying components may be used alone or in combination of two or more.

  Further, as diol-modifying components used for copolymerization, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,2- Cyclohexanedimethanol, 1,6-hexanediol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, glycols such as ethylene oxide adducts of bisphenol A and bisphenol S, and polyfunctional compounds such as trimethylolpropane, glycerin, pentaerythritol Etc. These diol-modified components may be used alone or in combination of two or more.

  Among such amorphous polyesters (B), from the viewpoints of heat resistance, mechanical properties, transparency and the like, a dibasic acid component mainly containing terephthalic acid and 1,4-cyclohexanedimethanol are used in an amount of 10 to 70. A polyester resin composed of a diol component containing mol% is preferred.

  The glass transition temperature of the amorphous polyester (B) is preferably lower than the glass transition temperature of the polyester (A) + 10 ° C. If the temperature is higher than this, biaxial stretching of the laminated film becomes difficult. The glass transition temperature is adjusted by adjusting the components used for the copolymerization. Sebacic acid is preferably used as the copolymer component.

  The amorphous polyester (B) used in the multilayer polyester film may contain other polymer components as long as the required properties are not impaired. These polymer components may be molecularly compatible or incompatible.

  30-200 micrometers is preferable and, as for the thickness of the polyester film of this invention, 40-150 micrometers is more preferable.

  Specific layer configurations of the polyester film include A / B, A / B / A, B / A / B, A / B / A / B / A, and the like. A preferred configuration includes A / B / A. In addition to the amorphous polyester (B) layer and the polyethylene terephthalate (A) layer, an adhesive layer or the like may be laminated on the laminated polyester film of the present invention in order to impart interlayer adhesion.

  In the polyester film of the present invention, the thickness constitution ratio of the amorphous polyester (B) layer is preferably 50 to 95%, more preferably 65 to 85% of the total thickness. The thickness constitution ratio here is a percentage of the thickness of the amorphous polyester (B) layer with respect to the total thickness of the film. When the thickness of the amorphous polyester resin layer exceeds 95% of the total thickness, the heat resistance, mechanical properties, good stretchability, and thickness accuracy obtained by the contribution of the polyethylene terephthalate (A) layer are impaired. Further, when the thickness of the amorphous polyester (B) layer is less than 50% of the total thickness, it is difficult to obtain the intended breaking stress at 120 ° C., which is not preferable.

Next, the present invention will be specifically described by way of examples.
The raw materials of the film and the method for measuring the characteristic values in the examples and comparative examples are as follows.

1. Example of polyester production

(1) DEG10
A slurry having a molar ratio of terephthalic acid and ethylene glycol of 1 / 1.6 is continuously fed to an esterification reaction vessel in which bis (β-hydroxyethyl) terephthalate and its low polymer are present, at a temperature of 250 ° C. and a pressure of The reaction was carried out under the condition of 0.2 MPa, and a PET oligomer having an esterification reaction rate of 95% was continuously obtained with a residence time of 8 hours.
This PET oligomer was transferred to a polymerization reactor, and 9.5 mol% of diethylene glycol with respect to the total glycol, germanium dioxide as a polycondensation catalyst, and Irganox 1010 (manufactured by BASF) as an antioxidant were added to the polyester after polymerization. 2% by mass, reduced pressure in the polycondensation reactor and finally polycondensation reaction at 0.9 hPa, 280 ° C. for 3 hours, relative viscosity 1.38, melting point 238 ° C., glass A polyester resin DEG10 having a transition temperature of 70 ° C. was obtained. The diethylene glycol residue relative to the total glycol component was 9.5 mol%.

(2) DEG16, DEG12, DEG8, DEG4, DEG2
(1) Same as (1) except that the charging ratio of diethylene glycol to all glycol components was changed to 15.5 mol%, 11.5 mol%, 7.5 mol%, 3.5 mol%, and 1.5 mol%, respectively. Was performed.
The diethylene glycol residues were 15.2 mol%, 12.1 mol%, 8.1 mol%, 3.7 mol%, and 2.2 mol%, respectively, and the melting points were 231 ° C, 236 ° C, and 241 ° C, respectively. The glass transition temperatures were 248 ° C., 252 ° C., and 66 ° C., 68 ° C., 70 ° C., 74 ° C., and 76 ° C., respectively.

(3) DEG8-2
A polyester resin DEG8-2 having a relative viscosity of 1.38, a melting point of 240 ° C., and a glass transition temperature of 70 ° C. was obtained except that Irganox 1010 was not added. The diethylene glycol residue with respect to all glycol components was 8.1 mol%.

(4) CHDM30
Ethylene glycol as a glycol component and 34.5 mol% of cyclohexanedimethanol with respect to all glycol components and terephthalic acid as an acid component were charged into an esterification tank and reacted at 250 ° C. for 3 hours to obtain an esterified product. Next, Irganox 1010 (manufactured by BASF) was added to 0.6% by mass with respect to the polyester after polymerization, and melt polymerization was performed at 280 ° C. under a reduced pressure of 1.3 hPa under a germanium catalyst. 38, a polyester resin CHDM30 having a glass transition temperature of 75 ° C. was obtained. The cyclohexanedimethanol residue with respect to all the glycol components was 30 mol%.

2. Measuring method

(1) Thickness unevenness The average value when thickness was measured at intervals of 5 mm in the width direction of the polyester film was calculated using the following formula, where Tave was the average value, Tmax was the maximum value, and Tmin was the minimum value.
Thickness unevenness (%) = (Tmax−Tmin) / Tave × 100

(2) Tensile evaluation The breaking stress and breaking elongation were measured using a tensile tester (manufactured by Shimadzu Corporation) with the chuck portion covered with a heating chamber as a measuring device. From the obtained polyester film, samples of 100 mm in the longitudinal direction and 10 mm in the width direction were taken in the longitudinal direction (MD) and the transverse direction (TD), respectively, and fixed by being sandwiched between chucks set at an interval of 50 mm. At that time, the atmosphere in which the sample exists was maintained at 120 ° C. by a heating chamber installed in the chuck portion of the tensile tester. Pulling was performed at a speed of 200 mm / min, and the load was measured with a load cell attached to the testing machine. The load at the time of breaking of the unloading curve was read, and the breaking stress (MPa) was calculated by dividing by the sample cross-sectional area before tension. The breaking elongation was calculated from the initial chuck interval (L0) and the chuck interval (L1) at the time of breaking using the following formula, and was defined as the breaking elongation (%).
Elongation at break (%) = (L1-L0) / L0 × 100
Each of MD and TD was measured with the number of tests n = 5, and an average value of all measurement results of stress and elongation at break was obtained.

(3) Evaluation of in-mold moldability A label is created by printing on the film, and this label is placed in the cavity of the female mold under the differential pressure mold so that the printed side of the label is in contact with the cavity surface of the mold. After that, it was fixed to the inner wall of the mold by sucking the mold, and then a polypropylene resin was injected over the lower female mold to form a label bonding member in which the label was integrally fused to the outer wall. The shape of the member was a cup shape having a bottom surface diameter of 50 mm, an opening surface diameter of 60 mm, and a depth of 30 mm.
The moldability was evaluated based on the presence or absence of label breakage and the presence or absence of printing distortion.

Example 1
Using DEG10 as the polyethylene terephthalate (A) and CHDM30 as the amorphous polyester (B), each was melted by a separate extruder at a temperature of 270 ° C, and the melt was merged with a composite adapter, then extruded from a T-die and cooled. The film was rapidly cooled with a drum to obtain a three-layer unstretched laminated film having an A / B / A configuration. At this time, the discharge amount of each extruder was adjusted so that the thickness composition ratio would be 1/4/1.
An unstretched laminated film is first stretched 3.0 times in the longitudinal direction at 80 ° C by the roll stretching method, then 3.3 times in the transverse direction at 100 ° C by the tenter stretching method, and then relaxed by 3% in the lateral direction. Then, heat treatment was performed at a temperature of 225 ° C. Further, after cooling the film, the film was wound into a roll by a winder to obtain a laminated biaxially stretched polyester film having a thickness of 50 μm. Table 1 shows the thickness spots and tensile evaluation results of this film.

Examples 2-6, Comparative Examples 1-2
The procedure was the same as in Example 1 except for the changes shown in Table 1. Table 1 shows the thickness spots and the tensile evaluation results.

Comparative Example 3
The same operation as in Example 2 was conducted except that a single-layer unstretched film of DEG8 was used. Table 1 shows the thickness spots and the tensile evaluation results.

Since Examples 1 to 6 had a low breaking stress and a high elongation at break, even when in-mold molding was performed, there was no label breakage or printing distortion, and the films were suitable for in-mold molding.
In Example 2, it can be seen from the comparison with Example 4 that does not contain an antioxidant that the breaking stress and the breaking elongation are improved by the addition of the antioxidant.

  In Comparative Example 1, the breaking elongation was low, and in Comparative Example 2, since the film was bubbled by thermal decomposition, the breaking elongation was low.

Since the comparative example 3 had high breaking stress, in-mold molding had printing distortion and there was a molding defect.

Claims (3)

Polyethylene terephthalate (A) containing 4 to 15 mol% of diethylene glycol residue with respect to the total glycol component, and an amorphous copolymer polyester obtained by modifying a polyethylene terephthalate resin with a diol, and 1,4-cyclohexanedimethanol as a diol component a polyester film having a thickness of 30~200μm consisting 10-70 mol% including non-crystalline polyester (B), the layer configuration is a polyethylene terephthalate (a) / amorphous polyester (B) / polyethylene terephthalate (a) The amorphous polyester (B) layer has a thickness constitution ratio of 50 to 95% of the total thickness, a breaking elongation at 120 ° C. of 350% to 500%, and a breaking stress of 10 MPa to 30 MPa, In-mall characterized by having a thickness spot of 5% or less Biaxially oriented polyester film for molding. (A) is according to claim 1 Symbol placement in-mold molding biaxially oriented polyester film which characterized in that it contains an antioxidant 0.1-1% by weight. The method for producing a biaxially stretched polyester film for in-mold molding according to any one of claims 1 to 2 , wherein the unstretched laminated film is stretched in the longitudinal direction and the transverse direction by a sequential biaxial stretching method, Biaxially stretched polyester for in-mold molding, characterized in that the biaxially stretched surface magnification is 9.0 to 12.3 times, and the ratio of the longitudinal and lateral stretch ratios is 0.8 to 1.2. A method for producing a film.