KR101762318B1 - Polyester multi layer foam sheet and method for preparation thereof - Google Patents

Abstract

The present invention relates to a polyester-based multilayer foamed sheet and a method for producing the same, and the multilayer foamed sheet of the present invention can be produced by simply foaming a polyester sheet laminated by three or more layers by coextrusion, And it is possible to prevent the delamination between layers to increase the life of the sheet. By containing the ultraviolet absorber, the stability against ultraviolet rays can be increased, thereby preventing deterioration of the film.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a polyester-based multilayer foamed sheet,

The present invention relates to a polyester-based multilayer foamed sheet excellent in UV resistance and heat resistance and a method for producing the same.

The conventional multilayer foamed sheet has been produced by forming a single-layered foam and then laminating it through a separate bonding process, or by extruding two or more kinds of resins upon extrusion.

As a lamination method using the bonding process, a thermal lamination method using heat and a method using an adhesive are known. However, when the thermal bonding method is used, there may arise a problem that the foamed sheet has curl due to heat or the foamed sheet has a reduced size, The adhesive may penetrate into the pores in the foam sheet and cause a problem of lowering optical properties such as reflectance. When the multilayer foamed sheet according to the above-described methods is applied to a backlight device of a display device, different types of sheets having different thermal expansion coefficients for a long period of time exposed to high-temperature heat generated by the lamp repeatedly expand and contract, Thereby causing the phenomenon of peeling. This leads to a decrease in display performance. Further, an additional process is required for the adhesion process for sheet stacking, which is costly.

On the other hand, as a lamination method using extrusion foaming, there is a chemical foaming method in which a foaming agent is added to a polymer resin to form a foam by forming pores simultaneously with extrusion. However, it is difficult to control the size and uniformity of foaming, It is not applicable to the micro-foaming which requires the bubble size of the foam.

The foam sheet exhibits excellent reflective performance and is used for a reflective plate of a backlight unit for display. However, the conventional foam sheet is curled when exposed to heat generated in a lamp for a long time, , A fine oligomer is precipitated on the surface, which deteriorates the luminance uniformity and deteriorates the optical performance. In addition, when exposed to ultraviolet rays generated from the lamp for a long time, the foam sheet deteriorates and color discoloration such as yellowing may occur, thereby shortening the life of the display device.

Accordingly, an object of the present invention is to provide a polyester-based multilayer foamed sheet which can be produced by a simple process and is improved in deterioration due to delamination or ultraviolet rays.

Another object of the present invention is to provide a process for producing the above polyester-based multilayer foamed sheet.

It is still another object of the present invention to provide a light reflector using the polyester-based multilayer foamed sheet.

It is still another object of the present invention to provide a display device using the light reflector.

In order to achieve the above object, the present invention provides a polyester resin composition comprising a first layer comprising a first polyester resin, and a second polyester resin which is the same as the first polyester resin but has an intense viscosity, Wherein the second layer is laminated on both sides of the first layer, wherein the second layer is laminated on both sides of the first layer.

To achieve these and other objects,

1. A method for producing a polyester resin, comprising the steps of: 1) polymerizing an acid component containing an aromatic dicarboxylic acid as a main component and an alkylene glycol to produce a first polyester resin;

2) solid-phase-polymerizing the first polyester resin to prepare a second polyester resin having an intense viscosity higher than that of the first polyester;

3) co-extruding a second sheet comprising the second polyester resin and an ultraviolet absorber on both sides of a first sheet made of the first polyester resin to produce a multilayer sheet; And

4) A method for producing a polyester-based multilayer foamed sheet, comprising the step of gas-bubbling the multilayer sheet produced above.

In order to accomplish the above-mentioned further object, the present invention provides a light reflector using the polyester-based multilayer foamed sheet.

According to another aspect of the present invention, there is provided a display device using the light reflector.

The multilayer foamed sheet of the present invention can be produced by simply foaming a polyester sheet laminated in three or more layers by coextrusion, thereby reducing the processing cost, preventing delamination between layers, and enhancing the life of the sheet. It is possible to increase the stability against ultraviolet rays and to prevent deterioration of the film.

(Foam layer) comprising a first polyester resin and a second layer comprising a polyester resin and a second polyester resin, the components of which are the same as those of the first polyester resin but have an intense viscosity, and an ultraviolet absorber Skin layer), and the second layer is laminated on both sides of the first layer, respectively.

The polyester-based multilayer foamed sheet according to the present invention comprises a second sheet (skin sheet) having excellent heat resistance and UV resistance, and a first sheet (foam sheet) having high-density fine pores therein and exhibiting excellent reflection characteristics, Or more alternately stacked.

The second layer of the polyester-based multilayer foamed sheet can be laminated on both sides of the first layer, and at least one side of the second layer is melt-kneaded and co-extruded.

The intrinsic viscosity of the first polyester resin is 0.58 to 0.65 dl / g, preferably 0.60 to 0.65 dl / g, and the intrinsic viscosity of the second polyester resin is 0.75 to 0.85 dl / g, preferably 0.79 to 0.82 Dl / g.

In the polyester-based multilayer foamed sheet of the present invention, the first layer includes a first polyester resin, wherein the first polyester-based resin is a conventional polyethylene terephthalate (PET) -based resin, an aromatic dicarboxylic Can be produced by esterification and condensation polymerization of an acid component mainly composed of an acid and an alkylene glycol in a conventional manner. The polymerization catalyst may further include additives such as antimony trioxide (Sb ₂ O ₃ ), germanium oxide (GeO ₂ , and the like) as the polymerization catalyst, ), And the like can be used. As the slip agent, silica, calcium carbonate, titanium oxide, alumina, barium sulfate and the like can be used.

The polymerization temperature of the condensation polymerization step may be 240 to 280 캜, preferably 260 to 280 캜.

The aromatic dicarboxylic acid may be at least one selected from the group consisting of dimethyl terephthalic acid, terephthalic acid, isophthalic acid, dimethyl-2,5-naphthalene dicarboxylic acid, naphthalene dicarboxylic acid, cyclohexanedicarboxylic acid, diphenoxyethanedicarboxylic acid, Dicarboxylic acid, diphenyl ether dicarboxylic acid, anthracene dicarboxylic acid,?,? - bis (2-chlorophenoxy) ethane-4,4-dicarboxylic acid, and mixtures thereof .

The alkylene glycol may be selected from the group consisting of ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, hexylene glycol, and mixtures thereof.

In the polyester-based multilayer foamed sheet of the present invention, the second layer is composed of a second polyester resin and a second sheet containing an ultraviolet absorber for the purpose of enhancing the UV resistance and lifetime of the display device, Can be produced by adding an ultraviolet absorber to a second polyester resin which is the same as the first polyester resin but has a larger intrinsic viscosity by compounding.

The ultraviolet absorber usable in the present invention is preferably a 1,3,5-triazine compound, more preferably 2- (4,6-diphenyl-1,3,5-triazin-2-yl) -5 -Hexyloxy phenol. According to U.S. Patent No. 5288778A, the above-mentioned di-lylene-based compound increases the stability against ultraviolet rays in the polymer and does not decompose within the melting temperature of the polyester.

The ultraviolet absorber May be added in an amount of 0.01 to 3% by weight, preferably 0.1 to 1% by weight based on the total weight. If the content of the ultraviolet absorber is more than 3% by weight, the ultraviolet absorptive effect becomes saturated, meaning that the amount of the ultraviolet absorber is not increased. On the contrary, the ultraviolet absorber is bleed out and the surface properties and workability of the sheet are deteriorated. If the content of the ultraviolet absorber is less than 0.01% by weight, the ultraviolet absorption effect is insufficient and the stability against ultraviolet rays can not be sufficiently satisfied.

In the polyester-based multilayer foamed sheet of the present invention, it is preferable that the first layer has a thickness of 700 to 1000 탆 and the second layer has a thickness of 5 to 20 탆.

The present invention also provides a method for producing a polyester resin, comprising the steps of: 1) preparing a first polyester resin by cumulatively adding an acid component containing an aromatic dicarboxylic acid as a main component and an alkylene glycol; 2) solid-phase-polymerizing the first polyester resin to produce a second polyester resin having an intense viscosity higher than that of the first polyester resin; 3) co-extruding a second sheet (skin sheet) comprising the second polyester resin and an ultraviolet absorber on both sides of a first sheet (foam sheet) made of the first polyester resin to prepare a multilayer sheet ; And 4) foaming the produced multilayer sheet by gas blowing. The present invention also provides a method for producing a polyester-based multilayer foamed sheet.

In the step 2), the second polyester resin can be produced by solid phase polymerization of the first polyester resin for 20 to 24 hours at a temperature of 200 to 240 DEG C and under vacuum.

The second layer preferably contains the second polyester resin in an amount of 60 to 90 wt%, and the first polyester resin containing the ultraviolet absorber is preferably added within the range that the ultraviolet absorber does not bleed out, By weight.

Step 4) can be produced by precipitating a multilayer sheet produced by co-extrusion so that the second sheet is alternately laminated on both sides of the first sheet in three or more layers, and then heating it after precipitating in a gas at high pressure.

Specifically, in the present invention, the multi-layer sheet is precipitated using a gas such as carbon dioxide, nitrogen or air, preferably carbon dioxide or nitrogen under a high pressure of 30 to 70 bar, preferably 50 to 60 bar, Followed by hot foaming. Through such a process, the gas is filled in the inside of the sheet at a high density, so that a finer foam sheet can be produced. In this case, the gas filling time may be 10 to 200 hours, but it is preferably 24 to 72 hours in consideration of the processability and the process cost.

The multilayer polyester foam sheet according to the present invention has an excellent reflectance at a wavelength of 400 to 700 nm and a reflectance of 97 to 98% as compared with a standard sample BASO _4, and has excellent heat resistance and UV resistance.

The multilayer polyester foam sheet of the present invention can be produced by foaming a polyester sheet laminated in three or more layers by coextrusion using coextrusion, thereby reducing the process cost, preventing delamination between layers to increase the life of the sheet, By containing an absorbent, the stability against ultraviolet rays can be increased and deterioration of the film can be prevented. Further, by constituting the skin layer of the solid-phase-polymerized polyester resin, the heat resistance of the foam sheet is increased and the generation of the surface oligomer is minimized, so that the performance of the display device can be maintained and the service life can be extended.

Therefore, the multilayer foamed sheet of the present invention can be usefully used as a light reflector such as a back light unit or a lighting apparatus of a display device.

Accordingly, the present invention provides a light reflector using the polyester-based multilayer foamed sheet, and a display device using the light reflector.

[Example]

Hereinafter, the present invention will be described in more detail with reference to the following examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Production Example 1: Production of first polyester resin (A)

An esterification reactor (primary reactor) equipped with a packing separation tower capable of stirring at about 200 rpm and separating 1,3-propanediol from water in a reaction effluent, A reactor having an inverter type stirrer capable of stirring at 10 rpm, a condenser for condensing the effluent, and a condensation polymerization reactor (secondary reactor) equipped with a vacuum pump were used.

After 100 moles of terephthalic acid and 120 moles of ethylene glycol were added to the first reactor, the reaction mixture was pressurized to about 1.2 kg / cm < 2 >, heated to 260 DEG C, reacted for about 4 hours, The reaction was complete. After completion of the esterification reaction, 0.035% by weight of antimony trioxide (Sb ₂ O ₃ ) was added as a condensation polymerization catalyst relative to terephthalic acid, and 0.07% by weight of silica particles having an average particle diameter of 2.5 μm as a slip agent was added to the terephthalic acid And then stirred for about 5 minutes. The esterification reaction was then transferred to a condensation polymerization reactor (secondary reactor). In the condensation polymerization reactor, the polymerization reaction was stopped when a constant electric power value reached to the stirrer motor while heating to 280 ° C while slowly applying a vacuum, and the polyester resin was obtained as pellets. The intrinsic viscosity (IV) of the polyester resin thus obtained was 0.61 dl / g.

Production Example 2: Preparation of Second Polyester Resin (B)

The polyester resin (A) obtained in Preparation Example 1 was subjected to solid phase polymerization at a temperature of 220 캜 under vacuum for about 20 hours to obtain a solid-state polymerized polyester resin (B) having an intrinsic viscosity of 0.802 dl / g.

Production Example 3: Production of polyester resin (C) containing ultraviolet absorber

1 part by weight of 2- (4,6-diphenyl-1,3,5-triazine-2-yl) -5-hexyloxyphenol as an ultraviolet absorber was added to the first polyester resin (A) And 10 wt% of a brightener were added and mixed to obtain a polyester resin (C) containing an ultraviolet absorber.

Example 1

The first polyester (A) obtained in Production Example 1 was used as a raw material for the first layer, and the polyester (B) and the polyester (C) obtained in Production Examples 2 and 3 were added in amounts of 90% by weight and 10% Were used as raw materials for the second layer, and these were fed to two extruders, respectively. Layered structure of a second layer / a first layer / a second layer using a co-extrusion die, and then a multilayer polyester sheet was produced by a usual method for producing a polyester sheet. The thickness of the resin layer before foaming was 15/300/15 (mu m) as the second layer / first layer / second layer.

Next, the multilayer polyester sheet prepared above was placed in a high-pressure vessel, filled with carbon dioxide, and then precipitated at a high pressure of 50 bar for 30 hours. The carbon dioxide-filled sheet was taken out and allowed to stand at room temperature and atmospheric pressure for 1 hour or more, and then heated and bubbled in a hot air oven at 240 캜 for 10 seconds to obtain a multilayer foamed sheet.

Example 2 and Comparative Examples 1 to 7

A multilayer foamed sheet was obtained in the same manner as in Example 1, except that each component was mixed with the composition shown in Table 1 below.

Composition ratio (% by weight) Thickness before foaming (탆) Second layer The first layer Second layer The first layer Example 1 (B) / (C) = 90/10 (A) = 100 15 300 Example 2 (B) / (C) = 60/40 (A) = 100 15 300 Comparative Example 1 (B) / (C) = 90/10 (A) = 100 100 130 Comparative Example 2 (B) / (C) = 50/50 (A) = 100 15 300 Comparative Example 3 (B) / (C) = 10/90 (A) = 100 15 300 Comparative Example 4 - (A) = 100 - 330 Comparative Example 5 - (A) = 100 - 200 Comparative Example 6 (B) = 100 (A) = 100 15 300 Comparative Example 7 (C) = 100 (A) = 100 15 300

Test Example

The properties of the foamed sheets prepared in Examples 1 and 2 and Comparative Examples 1 to 7 were evaluated in the following manner, and the results are shown in Table 2 below.

1) Rate of foaming

Foaming ratio = (density of sheet before foaming) / (density of sheet after foaming)

2) Reflectance

The sample was measured using Hunterlab spectrometer, and BaSO ₄ was used as a standard sample.

3) UV resistance

The foamed sheets prepared in the above Examples and Comparative Examples were left under hot air at 180 캜 for 10 minutes, and then the rate of change of the amount of the surface oligomer was compared with that before heating. The amount of the surface oligomer was cut at a constant surface area of 100 cm < ² > before and after standing at 180 DEG C for 10 minutes under hot air, and then the oligomers of the sheet surface were extracted for 1 minute using DMF. Then, the amount of oligomers precipitated was determined by liquid chromatography.

Surface Oligomer Change Rate = (amount of oligomer after exposure (% by mass)) / (amount of oligomer before exposure (% by mass))

The yellowing of the sheet was confirmed by measuring the Yellowness Index (YI) using a spectrometer of Hunter Lab, USA.

4) Heat resistance

The foamed sheets prepared in Examples and Comparative Examples were exposed for 500 hours at a constant temperature and humidity of 60 ° C and a relative humidity of 90%, and the occurrence of turbidity due to oligomers was visually observed and classified as good / bad according to the following criteria .

Good: No cloudiness

Bad: Cloudiness occurs

Further, the bleed-out of the UV stabilizer under the same conditions as above was visually observed and classified as good / bad according to the following criteria.

Good: No exoskeleton absorber bleed out

Bad: Absorbent bleed-out occurs

　
　 Foaming rate
(%) reflectivity
(%) UV resistance Heat resistance Surface Oligomer Change Rate △ YI Bleed
out Cloudiness Example 1 3.3 97 1.2 2.4 Good Good Example 2 3.3 97 1.2 2.2 Good Good Comparative Example 1 2.5 92 1.1 2.2 Good Good Comparative Example 2 3.3 97 1.7 2.2 Good Bad Comparative Example 3 3.4 97 1.9 2.1 Bad Bad Comparative Example 4 3.7 98 2.3 7.1 Bad Bad Comparative Example 5 1.6 85 2.2 7.3 Bad Bad Comparative Example 6 2.7 90 1.1 7.0 Good Good Comparative Example 7 3.2 97 2.2 2.0 Bad Bad

As shown in Table 2, the foam sheet of the present invention exhibited an excellent reflectance of 97% or more, excellent in UV resistance due to low rate of surface oligomer change and sheet yellowing, excellent in heat resistance due to no whitening phenomenon and no bleeding out .

Claims (14)

A first layer comprising a first polyester resin, and a second layer comprising a second polyester resin, the components of which are the same as the first polyester resin, but which have a higher intrinsic viscosity, and an ultraviolet absorber, Wherein the second layer is laminated on both surfaces of the polyester-based multilayer foamed sheet. The method according to claim 1,
Wherein the first polyester resin has an intrinsic viscosity of 0.58 to 0.65 dl / g. The method according to claim 1,
Wherein the second polyester resin has an intrinsic viscosity of 0.79 to 0.82 dl / g. The method according to claim 1,
Wherein the first polyester resin is produced by polycondensation of an acid component containing an aromatic dicarboxylic acid and an alkylene glycol. 5. The method of claim 4,
Wherein the aromatic dicarboxylic acid is at least one selected from the group consisting of dimethylterephthalic acid, terephthalic acid, isophthalic acid, dimethyl-2,5-naphthalenedicarboxylic acid, naphthalenedicarboxylic acid, cyclohexanedicarboxylic acid, diphenoxyethanedicarboxylic acid, di Dicarboxylic acid, anthracene dicarboxylic acid,?,? - bis (2-chlorophenoxy) ethane-4,4-dicarboxylic acid, and mixtures thereof, from the group consisting of phenyl dicarboxylic acid, diphenyl ether dicarboxylic acid, Wherein the polyester-based multilayer foamed sheet is a polyester-based multilayer foamed sheet. 5. The method of claim 4,
Wherein the alkylene glycol is selected from the group consisting of ethylene glycol, trimethylene glycol, tetramethylene glycol, pentamethylene glycol, hexamethylene glycol, hexylene glycol, and mixtures thereof. The method according to claim 1,
Wherein the ultraviolet absorber is a 1,3,5-triazine compound. The method according to claim 1,
Wherein the ultraviolet absorber is contained in an amount of 0.01 to 3% by weight based on the total weight of the second layer. The method according to claim 1,
Wherein the first layer has a thickness of 700 to 1000 占 퐉 and the second layer has a thickness of 5 to 20 占 퐉. 1) a step of polymerizing an acid component containing an aromatic dicarboxylic acid and an alkylene glycol to produce a first polyester resin;
2) solid-phase-polymerizing the first polyester resin to prepare a second polyester resin having an intense viscosity higher than that of the first polyester;
3) co-extruding a second sheet comprising the second polyester resin and an ultraviolet absorber on both sides of a first sheet made of the first polyester resin to produce a multilayer sheet; And
4) A method for producing a polyester-based multilayer foamed sheet, comprising the step of foaming the multilayer sheet produced above 11. The method of claim 10,
Wherein the second sheet comprises 60 to 90% by weight of the second polyester resin and 10 to 40% by weight of the first polyester resin containing the ultraviolet absorber. 11. The method of claim 10,
Wherein the gas foaming is carried out by depositing the multilayer sheet in a gas selected from carbon dioxide, nitrogen or air under a high pressure of 30 to 70 bar and then heating the gas in step 4). A light reflector using the polyester-based multilayer foamed sheet of any one of claims 1 to 9. A display device using the light reflector of claim 13.