JPH0592468A - Transparent polyester film and sheet, and manufacture thereof - Google Patents

Abstract

PURPOSE:To provide the polyester film and sheet which are high crystalline and excellently transparent and its manufacture. CONSTITUTION:Polyester resin whose at least 80mol% of repeated unit is composed of 1,3-propyleneterephthalate, is melted and formed, and then the film or sheet obtained by said method is quickly cooled, and is once prepared into the film or sheet of low crystallinity. After its curing, the film or the sheet is heat treated.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a transparent polyester film and sheet having high crystallinity and excellent transparency, and a method for producing the same.

[0002]

BACKGROUND OF THE INVENTION Aromatic polyesters represented by polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) have excellent heat resistance and balance of mechanical strength and gas permeation resistance. Due to its excellent physical properties, it is widely used in a wide range of engineering plastics. Of these polyesters, PBT exhibits high crystallinity and can be said to exhibit the above-mentioned excellent properties, but on the other hand, it cannot be used in applications where transparency is required due to its high crystallinity. It was Also, since PET has a low crystallization rate, it is relatively easy to obtain a transparent film of low crystallinity by rapidly cooling the molten polymer,
As it is, the mechanical strength, gas permeation resistance, etc. are insufficient, so it is necessary to promote crystallization by annealing.
However, if the annealing temperature is raised to increase the crystallization efficiency, the solution becomes cloudy, and if the crystallization efficiency is increased by an additive such as a nucleating agent, the additive itself loses transparency. Further, while gradually cooling from the molten state, a highly crystalline polymer can be obtained, but a product with high transparency cannot be obtained due to scattering of visible light due to spherulites. It is an object of the present invention to provide a polyester film, a sheet and a method for producing the same, which have excellent performance.

[0003]

Means for Solving the Problems As a result of intensive investigations by the present inventors to solve the above problems, as a raw material polyester, an aromatic polyester having a specific repeating unit introduced in a specific amount was used, and By processing the obtained film, sheet under specific conditions, it has high crystallinity,
The present inventors have completed the present invention by finding that a film or sheet that does not whiten and loses transparency even under a heating atmosphere can be provided. That is, the present invention is
A film or sheet obtained by melt-molding a polyester resin having 80 mol% or more of 1,3-propylene terephthalate is rapidly cooled to prepare a film or sheet having a low crystallinity, and after aging, heat-treating the film or sheet. A transparent polyester film characterized by a method for producing a sheet, and a relative crystallinity of 50% or more obtained by the method, and having heat shrinkage resistance under a heating atmosphere of 150 ° C.,
Further, the present invention relates to a transparent polyester film or sheet having a light transmittance of 80% or more.

Raw material compounds necessary for forming the polyester resin used in the present invention will be described below. First, the raw material compound necessary for forming a terephthaloyl group is terephthalic acid or its ester-forming derivative, and examples of the derivative include those selected from dialkyl esters or diacyl compounds. Of these, preferred is terephthalic acid or its dialkyl ester, and particularly preferred is dimethyl terephthalate.
In addition, the diol residue forming the main constituent unit is 1,3-
It is introduced by using propanediol as a monomer raw material. The polyester resin used in the present invention comprises 80% by mole or more of repeating units of ester units of 1,3-propanediol and terephthalic acid or its ester-forming derivative, and is produced by using the above-mentioned essential raw material compounds. It includes both polypropylene terephthalate (PPT) homopolyester and multicomponent copolyesters. As a comonomer raw material for constituting such a copolyester, conventionally known carboxylic acids and derivatives thereof, hydroxycarboxylic acids and derivatives thereof, phenols and derivatives thereof, aliphatic alcohols and derivatives thereof, alicyclic alcohols and derivatives thereof , Amines and derivatives thereof, hydroxyamines and derivatives thereof, amides and derivatives thereof, isocyanates and derivatives thereof, isocyanurates and derivatives thereof, and the like, or two or more thereof. Specific raw material compounds include dimethyl 2,6-naphthalenedicarboxylate, dimethyl 2,7-naphthalenedicarboxylate, dimethyl diphenate, dimethyl 4,4′-diphenyldicarboxylate, dimethyl adipate, dimethyl sebacate, 1,4 -Dimethyl cyclohexylene dicarboxylate, ethylene glycol, diethylene glycol,
Triethylene glycol, 1,4-butanediol, 1,5
-Pentanediol, 1,6-hexanediol, neopentyl glycol, 1,10-decanediol, 1,4-cyclohexanedimethanol, 1,4-cyclohexanediol, p-xylidene glycol, dimer diol, ethylene oxide addition of hydroquinone Body, ethylene oxide adduct of 2,2-bis (4-hydroxyphenyl) propane, ethylene oxide adduct of bis (4-hydroxyphenyl) sulfone, 2,2-bis (3,5-dibromo-4-hydroxyphenyl) propane Ethyleneoxy adduct of 2,6-dihydroxynaphthalene, ethylene oxide adduct, trimethyl trimesic acid, trimethyl trimellitate, trimethylolpropane, pentaerythritol, stearyl alcohol, methyl o-benzoylbenzoate, p-hydroxyethoxide Examples include methyl diphenylcarboxylate, polytetrahydrofuran, polyethylene glycol and the like. The copolyester of the present invention can contain the above comonomer in an amount of 20 mol% or less, preferably 10 mol% or less, based on all constituent units. If the mole fraction is more than 20 mol%, the crystallinity of the film or sheet is lowered, not only heat shrinkage and mechanical strength are impaired, but also the whitening phenomenon of the film or sheet appears, which is not preferable because the transparency is lowered. ..

These polyester resins can be produced by interfacial polycondensation, melt polymerization, solution polymerization or the like utilizing conventionally known condensation reaction or transesterification reaction. Further, it is possible to further increase the degree of polymerization by using a solid-phase polymerization method in which the obtained resin is heat-treated under reduced pressure or in the presence of an inert gas. The intrinsic viscosity of the polyester resin of the present invention obtained by such a production method is preferably 0.7 or more. Here, the intrinsic viscosity is a value measured in orthochlorophenol at 25 ° C. When the intrinsic viscosity is lower than 0.7, the molding processability is impaired and the mechanical strength of the film or sheet is deteriorated, which is not preferable. Incidentally, the polyester resin of the present invention, depending on the purpose within the range that does not impair the effects of the present invention, other thermoplastic resins may be used in a supplementary small amount, or a known substance generally added to the thermoplastic resin, for example, ultraviolet rays. It is also possible to add stabilizers such as absorbents, antistatic agents, flame retardants, flame retardant aids, colorants, lubricants, plasticizers, crystallization accelerators, crystal nucleating agents, fillers and the like.

The polyester resin obtained by such a manufacturing method is dried and then extruded into a sheet by an extruder equipped with, for example, a T-die, and the extruded sheet is contacted with a casting drum (chill roll) set at a low temperature. Then, by rapidly cooling, a film or sheet having low crystallinity, transparency and non-orientation can be obtained. In addition to the above, the polyester resin can be formed into a film or a sheet by an inflation method, a pressing method, or the like, but the extrusion method using a T-die as described above is particularly preferable.

With respect to the preferable thickness of the film or sheet, when the thickness of the film or sheet is large, only the surface portion of the film or sheet tends to be transparent by rapid cooling, and the inside tends to be gradually cooled and whitening tends to occur. If the thickness of the film or sheet is too thin, the mechanical strength of the film or sheet itself is not exerted, and the excellent practical effect is diminished. Therefore, when the preferable range of the thickness of the film or sheet is specified numerically, it is 0.01 to 2.5 mm, more preferably 0.02 to 1 mm. Also, by quenching the film,
After the sheet is manufactured, it may be uniaxially or biaxially stretched so as to have a predetermined thickness.

In the present invention, the film and sheet are extruded and then aged. This is performed by a method of immersing the film or sheet in a heating medium of a predetermined temperature such as warm water, a method of putting it in a dryer of a predetermined temperature, a method of blowing warm air, a method of radiant heat such as infrared rays, etc. . the film,
The aging temperature of the sheet is preferably in the range that satisfies the following formula (1). Formula (1) T _a ≤T _cc (° C) (where T _a : aging temperature T _cc : heating rate by differential thermal analysis based on JIS K7121)
Cold crystallization temperature (° C) of resin measured at 10 ° C / min) When the aging temperature is higher than _Tcc (° C), the film or sheet becomes cloudy due to rapid crystallization, which is not preferable. or,
When the aging temperature is low, aging is required for an extremely long time, which is not preferable in terms of productivity and the like, and the aging temperature is preferably 30 ° C or higher. The time required for aging depends on the glass transition temperature of the polyester resin, the cold crystallization temperature, the temperature range between the glass transition temperature and the cold crystallization temperature, and the aging temperature and the thickness of the film or sheet. The larger the temperature range, the lower the aging temperature, and the thicker the film or sheet, the longer the aging time. The aging may be carried out at a constant temperature, at two or more stages, or continuously changing the temperature, as long as the above conditions are satisfied. Further, in the process of performing the aging treatment, the film or sheet can be heat-fixed to the heat medium by a jig, a pressurized fluid, a depressurized fluid, or the like.

The film or sheet is aged and then further heat-treated to be sufficiently cold-crystallized, and thereafter, the transparency and high crystallinity are stably maintained. Incidentally, the heat treatment, similar to the aging treatment, a method of immersing the film or sheet in a heating medium of a predetermined temperature, such as hot water, a method of putting it in a dryer of a predetermined temperature, a method of blowing hot air or , A method using radiant heat such as infrared rays, etc., and the treatment temperature and treatment time are appropriately selected within a range that sufficiently achieves cold crystallization, and the conditions can be set in one step, multiple steps, or continuously. It is possible.

If the preferable relative crystallinity (CR) of the transparent highly crystalline film or sheet after heat treatment is specified, CR is 50%.
That is all. That is, the relative crystallinity of the film or sheet is
When it is less than 50%, the advantages based on crystallinity such as gas permeability resistance, heat resistance, and surface hardness cannot be exhibited, so that a crystallinity of the final product of 50% or more is practically desirable, and according to the present invention, It has become possible to provide such films and sheets.
The relative crystallinity is a value obtained by the DSC measurement method described later.

Further, since the transparency of the film or sheet largely depends on the smoothness of the surface thereof, it is desirable that the press plate or the cooling roller is as smooth as possible when high transparency is required. However, the film,
When the sheet is required to have a solid feeling, it is possible to make the surface of the film and the sheet uneven so as to reduce the transparency. If the light transmittance of the film or sheet subjected to these treatments is lower than 80%, the advantages based on transparency will be lost. Those having a light transmittance of 80% or more and having a light transmittance of 80% or more even after heat treatment at 150 ° C. are practically desirable. According to the present invention, it is possible to provide such a film or sheet.

[0012]

As described above, the highly crystalline transparent film or sheet made of the specific resin obtained by the present invention is
A film or sheet having a low crystallinity is prepared by rapidly cooling the melt-formed film or sheet, and after aging, heat treatment is performed to increase the crystallinity without impairing the transparency. Has excellent effect. 1) The heat resistance of the resin is high, the transparency does not decrease even under high temperature conditions of about 150 ° C, the light transmittance is 80% or more, and the high crystallinity makes it excellent in heat shrinkage resistance and gas barrier property.
Suitable for foods for microwave cooking and packaging. 2) Since it imparts transparency without impairing mechanical properties, it can be used as a window glass protective film and the like.

[0013]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
The measurement conditions of the main characteristic values are as follows. (1) Melting point, cold crystallization temperature, glass transition temperature Measured at a temperature rise temperature of 10 ° C./min by differential thermal analysis (DSC) based on JIS K7121. (2) Relative Crystallinity The film or sheet was cut into a sample for DSC measurement, and the film was subjected to differential thermal analysis. The relative crystallinity is calculated by the following formula. CR = [(ΔHm− | ΔHcc |) / | (ΔHc) _HOMO |] × 100 (%) (however, ΔHm; heat of crystal fusion by temperature rise measurement at 10 ° C / min ΔHcc; temperature rise measurement at 10 ° C / min Transition heat of cold crystallization peak due to (ΔHc) _HOMO ; heat of crystallization by measurement of temperature decrease at 10 ° C / min from molten state of unmodified homopolyester) Crystal melts after progress of cold crystallization during temperature increase measurement Therefore, in order to obtain the relative crystallinity inherent to the sample, the absolute value of the transition heat (ΔHcc) of the cold crystallization peak is subtracted from the heat of crystal fusion (ΔHm). (3) Light transmittance The film or sheet was cut out and measured according to JIS K7105. (4) Heat shrinkage Cut out a film or sheet, fill in a 10 cm square mark, and put it in a blast dryer set at a temperature of 150 ° C.
After charging for a minute, the change in the area of the mark was calculated, and the heat shrinkage rate (X) was calculated by the following formula. X = (A ₁ −A ₂ ) / A ₁ × 100 (%) (however, A ₁ ; mark area before heating (cm ² ) A ₂ ; mark area after heating (cm ² )) (5) Light transmittance and relative crystallinity after heating Cut out a film or sheet and put it in a blast dryer at a temperature of 150 ° C for 10 minutes, then determine the light transmittance based on JIS K7105 and the relative value from the above condition (2). The crystallinity was determined.

Production Example 1 (Synthesis of Polyester A) 330 parts by weight of dimethyl terephthalate, 258 parts by weight of 1,3-propanediol, and 0.2 parts by weight of titanium tetrabutoxide as a catalyst were reacted with a double helical stirrer and a distillation tube. After being charged in a machine and sufficiently replaced with nitrogen, the temperature was raised to 160 ° C. under normal pressure and stirring was started. Further, the temperature was gradually raised and the by-product methanol was distilled off. When the temperature reached 250 ° C, gradually depressurize the reactor,
Stirring was continued for 3.0 hours at a pressure of 0.1 torr to obtain a polypropylene terephthalate resin (PPT) having an intrinsic viscosity of 0.78 in orthochlorophenol at 25 ° C. The obtained resin was pelletized, and solid-phase polymerization was performed at 195 ° C. under a nitrogen stream to obtain a high polymerization degree polyester having an intrinsic viscosity of 1.35. The above-mentioned characteristic evaluation was performed on the obtained polyester. The results are shown in Table 1.

Production Examples 2 to 6 (Synthesis of Polyesters B to F) 2,2-bis (4-hydroxyphenyl) propane ethylene oxide 2 mol adduct (polyesters B and C) and bis (4-hydroxyphenyl) as comonomers The same production apparatus as in Production Example 1 was prepared by using a predetermined amount of a sulfone-ethylene oxide 2 mol adduct (polyester D), dimethyl 2,6-naphthalenedicarboxylate (polyester E), and 1,4-cyclohexanedimethanol (polyester F). To obtain copolyester. Each of the obtained copolyesters was solid-phase polymerized to obtain a high polymerization degree polyester. The ratio of 1,3-propylene terephthalate units introduced into polyester was determined by ¹ H-NMR using trifluoroacetic acid-d as a solvent.
It was analyzed by the method. The results are shown in Table 1. The characteristic values of polyester G (polyethylene terephthalate) and polyester H (polybutylene terephthalate) used in the following comparative examples are also shown.

Examples 1 to 5 and Comparative Examples 1 to 3 In order to clarify the difference in the characteristics of the film and sheet due to the difference in the raw material polyester, the quenching condition from the molten state,
The polyesters A to H were evaluated with the thickness of the film and the sheet, the aging conditions, and the heat treatment conditions kept constant. That is, 24
Films and sheets prepared by extruding a molten polymer at 0 ° C (270 ° C for polyester G) from a T-die onto a cooling roll at 25 ° C and adjusting the extrusion speed so that the thickness of the film or sheet is 0.15mm. The conditions for rapid cooling, film and sheet thickness were adjusted. These films and sheets were aged in a constant temperature bath at various temperatures and times shown in Table 2, and then
A heat treatment was carried out by placing in a dryer at 120 ° C. (140 ° C. in Comparative Example 2) for 10 minutes. Table 2 shows the evaluation results of the transparency, crystallinity, and heat shrinkage resistance of these films and sheets.
Shown in.

Comparative Examples 4 to 6 Polyesters A, B and F were melt-formed into films and sheets in the same manner as in Example 1 and then immediately put into a dryer at 120 ° C. for 10 minutes without aging. Heat treatment was performed. The evaluation results are shown in Table 2.

[0018]

[Table 1]

[0019]

[Table 2]

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Claims (4)

[Claims] 1. A film or sheet obtained by melt-molding a polyester resin in which 80 mol% or more of repeating units is 1,3-propylene terephthalate is rapidly cooled to prepare a film or sheet having a low crystallinity, and after aging, A method for producing a transparent polyester film or sheet, which comprises heat-treating the film or sheet. 2. The method for producing a transparent polyester film or sheet according to claim 1, wherein the film or sheet is formed by a T-die method. 3. The method according to claim 1 or 2, which has a relative crystallinity of 50% or more, has heat shrinkage resistance in a heating atmosphere of 150 ° C., and retains a light transmittance of 80% or more. A transparent polyester film or sheet. 4. The thickness of the film or sheet is 0.01 to 2.5 m
The transparent polyester film or sheet according to claim 3, which is m 2.