JP2009214489A - Method of manufacturing laminated biaxially stretched polyester film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated biaxially stretched polyester film excellent in an optical diffuseness having a low degree of brilliance by a comparatively small particle additive amount. <P>SOLUTION: The laminated biaxially stretched polyester film is characterized in that the polyester film is composed of at least two layers of coextrusion layer, where on side surface layer is made of copolymerized polyester or the mixture of the copolymerized polymer and polyethylene telephthalate, which contains 0.3-20 wt.% of particle having an average particle diameter of 1.0-20 μm and has the melting point of the surface layer lower than the melting point of the other layers by 5°C or more. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention is for packaging applications that require a matte appearance, glass and molded object bonding applications that require matting, label applications, antireflection applications, and backlight unit diffusers and projectors. The present invention relates to a biaxially stretched polyester film that is used as a substrate for a screen and has excellent matting properties and light diffusibility.

  As for a method for producing a laminated biaxially stretched film having a matte property and a light diffusibility, according to, for example, Patent Document 1, a gloss (gloss value) is low and a haze value is low. A method for producing a film with high transmittance is described. Patent Document 2 describes a method for producing a film having excellent light diffusibility by controlling the stretching speed.

  The film produced by the production method of Patent Document 1 has a low haze value and inferior light diffusibility. Further, the film produced by the production method of Patent Document 2 has a concern that the amount of particles added to the film becomes relatively large, and the life of the filter provided in the flow path of the aggregated particles or the molten polyester resin is shortened.

JP 2004-230893 A JP 2007-178788 A

  The present invention has been made in view of the above circumstances, and a solution to the problem is to provide a laminated biaxially stretched polyether film having a relatively low glossiness, a low glossiness, and a matte property. There is to do.

  As a result of intensive studies in view of the above problems, the present inventor has found that the above problems can be easily solved by adopting a specific configuration, and the present invention has been completed.

  That is, the gist of the present invention is a polyester film composed of at least two coextruded layers, and one surface layer is composed of a copolyester or a mixture of copolyester and polyethylene terephthalate, and the average particle size is 1.0 to The laminated biaxially stretched polyether film is characterized in that it contains 0.3 to 20% by weight of 20 μm particles, and the melting point of the surface layer is lower by 5 ° C. or more than the melting point of other layers.

Hereinafter, the present invention will be described in detail.
The film of the present invention is a film having at least two coextruded layers, that is, a layer A (sublayer) containing particles and another layer B. A single layer is not preferred because the amount of particles added becomes large in order to achieve the desired matting and light diffusing properties. Further, the melting point of the polyester of the A layer containing particles needs to be lower by 5 ° C. or more than the polyester constituting the other layers. If the difference between the melting points is less than 5 ° C., the heat setting temperature in the film forming process approaches the melting point of the film, so that the film tends to break in the transverse stretching process. Moreover, the structure of a layer can take the structure of A / B layer, A / B / A layer, and A / B / C layer, and A layer comprises the surface layer of the at least single side | surface of a film.

  Polyesters used for the B layer are polyethylene terephthalate (PET) produced from ethylene glycol and terephthalic acid, polyethylene-2,6-naphthalate (PEN) produced from ethylene glycol and naphthalene-2,6-dicarboxylic acid, 1, Poly (1,4-cyclohexanedimethylene terephthalate) (PCDT) produced from 4-bishydroxymethylcyclohexane and terephthalic acid, from ethylene glycol, naphthalene-2,6-dicarboxylic acid and biphenyl-4,4′-dicarboxylic acid The poly (ethylene 2,6-naphthalate bibenzoate) (PENBB) produced is exemplified. Among them, it is preferable to contain an ethylene terephthalate unit composed of ethylene glycol and terephthalic acid and / or an ethylene-2,6-naphthalate unit composed of ethylene glycol and naphthalene-2,6-dicarboxylic acid, and these units are 90% or more. A polyester containing 95% or more is preferable.

  The polyester used in the A layer is a copolyester or a mixture of copolyester and polyethylene terephthalate. Copolyester is an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, ethylene glycol, diethylene glycol, tetramethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol The main component is an ester with a glycol such as the above, 30 mol% or less of the dicarboxylic acid component is a dicarboxylic acid component other than the main component, and / or 30 mol% or less of the diol component is a diol component other than the main component. Some polyester.

  The polyester is obtained by directly polymerizing an aromatic dicarboxylic acid and a glycol, or by a transesterification reaction between an aromatic dicarboxylic acid dialkyl ester and a glycol, followed by polycondensation, or an aromatic dicarboxylic acid diglycol. It can also be obtained by a method such as polycondensation of an ester. Typical examples of the polyester include a copolymer of terephthalic acid (main component) isophthalic acid (subcomponent) and ethylene glycol, and a copolymer of terephthalic acid, ethylene glycol (main component) propylene glycol (subcomponent). There is.

  Further, the melting point of the polyester of the A layer is preferably 5 ° C. or more lower than the melting point of the polyester of the other layers, 190 ° C. or more, and more preferably 200 ° C. or more as described above. If the difference from the melting point of the polyester of the B layer is less than 5 ° C, a film excellent in light diffusibility cannot be produced. On the other hand, if the melting point of the polyester of the A layer is less than 190 ° C, the heat setting temperature of the film is maximum. However, it becomes 184 ° C., and the thermal shrinkage rate of the film tends to increase.

  The particles contained in the A layer are inorganic or organic particles, and the average particle size thereof is 1.0 to 20 μm, preferably 2.0 to 15 μm, more preferably 2.5 to 10 μm. If the average particle size is less than 1.0 μm, the light diffusibility is inferior. On the other hand, if the average particle size is more than 20 μm, the increase in the pressure of the filter in the polyester extrusion process at the time of film production increases and the productivity is reduced. To do.

  The content of such particles is 0.3 to 20% by weight or less, preferably 0.5 to 15% by weight with respect to the A layer. If it is less than 0.3% by weight, the matte property and the light diffusibility are inferior. On the other hand, addition exceeding 20% by weight makes it difficult to produce a high concentration particle masterbatch and cannot be substantially added.

  The inorganic or organic particles used in the present invention may be a single component, or two or more components may be used simultaneously. Specific examples of the particles include inorganic fine particles such as calcium carbonate, silica, aluminum oxide, barium carbonate, barium sulfate, and glass, and organic particles such as melamine resin, polystyrene, organic silicone resin, and acrylic-styrene copolymer. It is done.

  The ratio that the thickness of the A layer of the film of the present invention occupies the thickness of the entire film is usually 1 to 20%. If the ratio is less than 1%, the matte property tends to be inferior, and if it exceeds 20%, the film strength may be lowered.

  In this invention, it is preferable that the heat setting temperature of a film manufacturing process shall be melting | fusing point (Tm) -6-Tm-18 degreeC of A layer, More preferably, it is the range of Tm-7-Tm-15 degreeC. When the heat setting temperature exceeds Tm-6, the haze is lowered and the light diffusibility tends to be lowered. On the other hand, when the heat setting temperature is lower than Tm-18, the haze and the total light transmittance tend to decrease. After biaxial stretching, heat treatment in the temperature range of Tm-6 to Tm-18 ° C maximizes the film surface roughness and further reduces the total light transmittance, so that it has good matting and light diffusibility. Can be obtained.

  The reason why the film surface roughness is maximized is not clear, but the polyester constituting the A layer has a component having a melting point lower than Tm and a component having a higher melting point, and the stretch orientation of a part of the component having a melting point lower than Tm is canceled. It is thought that this phenomenon was manifested.

  The reason why the total light transmittance can also be maintained high is considered to be that the stretch orientation of a part of the component having a melting point lower than Tm was canceled and the void formed around the particles was reduced.

  The heat setting time is preferably 1.5 to 10 seconds. If the heat setting time is less than 1.5 seconds, the film may not be heated sufficiently, and if it exceeds 10 seconds, the productivity may decrease.

  Next, although the manufacturing method of the film of this invention is demonstrated concretely, as long as the structural requirements of this invention are satisfied, it is not specifically limited to the following illustrations.

  When the film of the present invention is produced, the polyester is supplied to at least two extruders, heated to a temperature equal to or higher than the melting point of each polyester, and melted. Next, the molten polymer from each extruder is merged with a feed block through a gear pump and a filter and extruded from a die as a molten sheet. Subsequently, the molten sheet is rapidly cooled to below the glass transition temperature on a rotary cooling drum to obtain an amorphous unstretched film. At this time, in order to improve the flatness of the unstretched film, the adhesion between the unstretched film and the rotating cooling drum may be improved by an electrostatic application adhesion method, a liquid application adhesion method, or the like.

  And a uniaxially stretched film is obtained by extending | stretching an unstretched film in the longitudinal direction (longitudinal stretching) using a roll stretching machine. The stretching temperature at this time is stretched in a temperature range of minus 10 ° C. to plus 40 ° C. of the glass transition temperature (Tg) of the raw material resin. The draw ratio is preferably 1.5 to 6.0 times, more preferably 2.0 to 5.0 times. Furthermore, longitudinal stretching may be performed in only one stage, or may be performed in two or more stages. Next, the biaxially stretched film is obtained by stretching the uniaxially stretched film in the width direction (lateral stretching) using a tenter stretching machine. The stretching temperature at this time is stretched in a temperature range of + 50 ° C. from the glass transition temperature (Tg) of the raw material resin. The draw ratio is preferably 2.5 to 6.0 times, more preferably 3.0 to 5.0 times. Further, the transverse stretching may be performed only in one stage, or may be performed in two or more stages. Moreover, you may perform simultaneous biaxial stretching which performs vertical and horizontal simultaneously.

  And a laminated film is manufactured by heat-processing a biaxially stretched film. The heat treatment temperature at this time is usually Tm-6 to Tm-18 ° C, and the heat setting time is usually 1.5 to 10 seconds. Moreover, when heat-treating a biaxially stretched film, the biaxially stretched film may be relaxed within 20%.

  The present invention can provide a method for producing a matte laminated biaxially stretched polyester film having excellent matte properties and light diffusibility even if the amount of added particles is suppressed by keeping the heat treatment temperature of the film production conditions in a certain range. The industrial value of the invention is high.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to a following example, unless the summary is exceeded. The measurement methods and terms used in the examples and the present invention are defined as follows.

(1) Average particle diameter of layer A After ashing the surface in the film stretching direction to 1 μm with a low-temperature ashing plasma apparatus, at least the major axis and minor axis of particles having a particle diameter of 1 μm or more are measured with a scanning electron microscope. It calculates | requires about 100 pieces and makes an arithmetic mean the average particle diameter.

(2) Haze, total light transmittance The value is measured using a bulb type turbidimeter NDH-300A (manufactured by Nippon Denshoku Industries Co., Ltd.).

(3) Surface roughness Ra of surface roughness
Measurement is performed using a three-dimensional non-contact surface shape measurement system MN537N-M100 (Ryoka System Co., Ltd.).

(4) Melting point of polyester Using a MD instrument 2910 manufactured by TA Instruments Inc., a polyester raw material or a film sample sample is heated and melted at 300 ° C. and then rapidly cooled, and measured from 0 ° C. to 300 ° C. at a temperature rising rate of 20 ° C./min. The endothermic peak temperature in crystal melting is taken as the melting point.

(5) Glossiness Measured by incident light on the film on the surface of the single-layer film or the surface of the A-layer according to method 3 (60 ° glossiness) of JIS Z-8741-1983.

(Raw material adjustment)
・ Polyester a
Using 100 parts by weight of dimethyl terephthalate and 60 parts by weight of ethylene glycol as starting materials, 0.09 parts by weight of magnesium acetate tetrahydrate as a catalyst is placed in the reactor, the reaction start temperature is set to 150 ° C., and the methanol is distilled off gradually. The reaction temperature was raised to 230 ° C. after 3 hours. After 4 hours, the transesterification reaction was substantially terminated. After adding 0.04 part of ethyl acid phosphate to this reaction mixture, 0.04 part of antimony trioxide was added, and a polycondensation reaction was carried out for 4 hours. That is, the temperature was gradually raised from 230 ° C. to 280 ° C. On the other hand, the pressure was gradually reduced from normal pressure, and finally 0.3 mmHg. After the start of the reaction, the reaction was stopped at a time corresponding to an intrinsic viscosity of 0.63 due to a change in stirring power of the reaction tank, and the polymer was discharged under nitrogen pressure. The obtained polyester a has an intrinsic viscosity of 0.63 and a melting point of 253 ° C.

・ Polyester b
This is a copolyester resin having an intrinsic viscosity of 0.70 and a melting point of 198 ° C., which is obtained by synthesizing a copolyester containing 22 mol% of isophthalic acid using dimethyl terephthalate, dimethyl isophthalate and ethylene glycol.

・ Polyester c
Polyester a is kneaded with 10% by weight of crosslinked styrene-acrylic organic particles having an average particle diameter of 4 μm.

・ Polyester d
A synthetic calcium carbonate particle having an average particle diameter of 0.7 μm was added during polycondensation of polyethylene terephthalate, and was synthesized by a polyethylene terephthalate resin having an intrinsic viscosity of 0.68 with a content of 1.0% by weight and a melting point of 253 ° C. is there.

・ Polyester e
Polyester a is kneaded with silica particles having an average particle size of 80 μm and contains 10% by weight.

Example 1:
Polyester comprising polyester / polyester b / polyester c ratio of 12/55/33 (weight ratio) forming the surface layer (A layer) is supplied to a vented twin-screw extruder (sub) to form an intermediate layer a is supplied to another twin-screw extruder with a vent (main) and melted at a melting temperature of 280 ° C., and then the molten polymer from each extruder is merged with a feed block through a gear pump and a filter, and a casting drum is passed through a die. 2 types and 3 layers of unstretched films were obtained. The unstretched film thus obtained was fed into a longitudinal stretching roll, first stretched 3.0 times at a film temperature of 83 ° C., then led to a tenter and stretched 3.6 times in the transverse direction at 95 ° C. to obtain a biaxially oriented film. It was. Next, the obtained biaxially oriented film was introduced into a heat setting zone and heat-treated at 210 ° C. to obtain a polyester film having a thickness described in Table 1 below.

Example 2:
The ratio of polyester a / polyester b / polyester c forming the surface layer (A layer) was the same as in Example 1 except that the mixture was heat treated at 220 ° C. using a mixture of 32/35/33 (weight ratio).

Comparative Example 1:
A film was obtained under the same conditions as in Example 1 except for heat treatment at 225 ° C.

Comparative Example 2:
A film was obtained under the same conditions as in Example 1 except for heat treatment at 180 ° C.

Comparative Example 3:
A film having a ratio of polyester a / polyester c of 81/19 (weight ratio) was used for the surface layer (A layer) to obtain a film described in Table 1.

Comparative Example 4:
A film having a ratio of polyester a / polyester d of 30/70 (weight ratio) was used for the surface layer (A layer) to obtain the film described in Table 1.

Comparative Example 5:
A film having a ratio of polyester a / polyester c of 98.3 / 1.7 (weight ratio) was used for the surface layer (A layer) to obtain the film described in Table 1.

Comparative Example 6:
Film formation was attempted in the same manner as in Example 1 using polyester e instead of polyester c, but the production of the film was abandoned due to an increase in the pressure of the filter in the polyester extrusion process during film production.

Comparative Example 7:
A polyester master a was kneaded with crosslinked styrene-acrylic organic particles having an average particle size of 4 μm to make a particle masterbatch containing 30% by weight. However, a film in which 20% by weight of particles were added to the surface layer without forming a resin chip was obtained. could not.

  The evaluation results of the collected films are summarized in Table 1 below.

  The films of Examples 1 and 2 are films having excellent matting properties and light diffusibility. On the other hand, Comparative Example 1 is a film having low haze and low light diffusibility. In Comparative Example 2, haze and total light transmittance were reduced. Since Comparative Example 3 did not contain a low melting point polyester component in the surface layer, the total light transmittance was lowered. In Comparative Example 4, the particle diameter of the surface layer was small, and in Comparative Example 5, the haze was low and the light diffusibility was inferior because the particle addition concentration of the surface layer was small.

  The film of the present invention can be used, for example, in packaging applications that are required to have a matte appearance, glass and molded product bonding applications that require matting, label applications, antireflection applications, and diffusion of backlight units. It can be suitably used as a base material for plates and projector screens.

Claims (1)

It is a polyester film composed of at least two coextruded layers, and one surface layer is composed of copolymer polyester or a mixture of copolymer polyester and polyethylene terephthalate, and particles having an average particle diameter of 1.0 to 20 μm are 0.3 to A laminated biaxially stretched polyether film containing 20% by weight and having a melting point of the surface layer of 5 ° C. or more lower than the melting point of other layers.