KR101589397B1 - Foamed sheet - Google Patents

Abstract

A resin sheet having at least a three-layer structure composed of a thermoplastic resin layer for forming the foam layer 11 and a thermoplastic resin layer for forming the non-foam layer 12 is integrally formed, At least one foam layer of the foam sheet has a non-foam layer on both sides thereof, and the foam layer is made of a thermoplastic resin having a different composition from the non-foam layer, The average diameter of the bubbles 13 having a diameter of 10 mu m or less and the density of the foam layer of the foam layer is 1.0 x 10 ⁶ pores per square or more and the thickness of the non- / ≪ / RTI > and the ratio of the entire non-foam layer in the entire foam sheet is 10% by mass or more.

Description

Foam sheet {FOAMED SHEET}

The present invention relates to a foam sheet formed of a thermoplastic resin.

BACKGROUND ART In a liquid crystal display device or the like, a backlight panel that emits light from the rear side of a liquid crystal layer is used. Such a backlight panel is capable of reducing the number of light sources, and thus the adoption of an edge light method which is advantageous for energy saving is increasing. In the edge light type backlight panel, a light reflecting plate is provided adjacent to the light guide plate (light guide plate). The light emitted from the light source into the light guide plate and leaked to the light reflection plate side is sent back to the liquid crystal layer side by the light reflection plate, so that the outgoing light from the light source can be efficiently emitted to the liquid crystal layer side, The brightness of the apparatus can be further increased.

Patent Documents 1 and 2 disclose the use of a resinous sheet (foam sheet) having bubbles as a light reflecting plate.

Japanese Laid-Open Patent Publication No. 2009-209171 Japanese Laid-Open Patent Publication No. 2010-152035

BACKGROUND ART In recent years, a foaming sheet used for a light reflector has been made thinner due to its weight reduction and cost reduction. The inventors of the present invention found that when a foamed sheet having a highly reduced thickness as a light reflecting plate is used, the light reflecting plate tends to be warped at the time of installing the backlight, and such warping causes a change in the contact state between the light conducting plate and the reflecting plate, Respectively.

To attain both reduction of the thickness of the light reflection plate and suppression of the warp, it is effective to make the reflection plate highly rigid. Japanese Laid-Open Patent Publication No. 2011-230431 discloses that the rigidity of a light reflecting plate is increased by providing a non-foam layer in addition to the surface layer of the foam sheet. However, in the technique described in Patent Document 3, since the stiffness is increased by further laminating the resin film to the surface layer of the foam sheet, cost and labor are required.

Further, Japanese Unexamined Patent Publication (Kokai) No. 2001-88235 and Japanese Unexamined Patent Publication (Kokai) No. 2000-218646 disclose a resin porous body having a surface layer portion and an inner layer portion formed integrally with each other so that the density of the surface layer portion is higher than the density of the inner layer portion ) To foam plates are described. However, in these methods, it is difficult to maintain the foaming property and thickness of the surface layer at a constant level, and there is a significant restriction in quality.

It is an object of the present invention to provide a foam sheet which is made of a thermoplastic resin and which is superior in rigidity while being in a thin film state and which can nevertheless be manufactured with a smaller number of processings and is also superior in quality uniformity .

The above object is achieved by the following means.

<1> A method for producing a foamed molded article, which comprises a step of integrally molding a resin sheet having at least three layers of a thermoplastic resin layer for forming a foamed layer and a thermoplastic resin layer for forming a non-foamed layer, As a sheet,

Wherein at least one foam layer of the foam sheet has a non-foam layer on both sides thereof,

Wherein the foam layer and the non-foam layer are made of a thermoplastic resin having a different composition,

The average diameter of the foamed layer having air bubbles and 10㎛ or less, and a bubble can (氣泡數) density of the foam layer is at least 1.0 × 10 ⁶ gae / ㎣,

Wherein the non-foam layer has a thickness of 15 μm or more per layer and / or a ratio of the entire non-foam layer in the entire foam sheet is 10 mass% or more.

(2) The thermoplastic resin constituting the non-foamed layer has crystallinity and the thermoplastic resin is in a state of 168 hours under atmospheric pressure (0.1 MPa) under conditions of 23 1 C and 50 5% RH (relative humidity) The foam sheet according to &lt; 1 &gt;, wherein the crystallization behavior is not observed by the heat measurement after the adjustment.

<3> A polyester resin composition comprising an aromatic polyester resin having one or more non-foam layers, wherein the ratio of the 1,4-butane diol component in the total diol component constituting the aromatic polyester resin is 10 The foam sheet according to <1> or <2>, wherein the foam sheet has a mass% or more.

<4> The foam sheet according to <3>, wherein the non-foam layer comprises polybutylene terephthalate or a blend resin of polybutylene terephthalate and polyethylene terephthalate.

<5> The foam sheet according to any one of <1> to <4>, wherein the foam layer comprises polyethylene terephthalate.

<6> A method for producing a foamed sheet according to any one of <1> to <5>, which comprises the following steps (a) to (c)

(a) A resin sheet having at least a three-layer structure composed of a thermoplastic resin layer for forming a foamed layer and a thermoplastic resin layer for forming a non-foamed layer is produced by integral molding by coextrusion fair,

(b) impregnating (impregnating) the resin sheet with an inert high-pressure gas, and

(c) heating the resin sheet to foam the thermoplastic resin layer for forming the foam layer.

<7> The production method according to <6>, wherein the thermoplastic resin layer for forming the non-foamed layer does not foam in the step (c).

As used herein, the term &quot; thermoplastic resin &quot; is used to mean a blend resin composed of two or more thermoplastic resins in addition to a resin made of one kind of thermoplastic resin. Therefore, the term &quot; composition of thermoplastic resin &quot; means the type of the thermoplastic resin when the thermoplastic resin is composed of one kind of thermoplastic resin, and if the thermoplastic resin is a blend resin composed of two or more kinds of thermoplastic resins, .

In the present specification, any raw material, member or constitution of "made of thermoplastic resin" or "formed of thermoplastic resin" is not limited to the form in which the raw material, member or constitution is composed only of thermoplastic resin, It is also meant to include the form in which the additive of the branch is constituted by the compounded composition.

Specifically, a form in which 80 to 100 mass% is composed of a thermoplastic resin is a "thermoplastic resin" or a "thermoplastic resin". The content of "thermoplastic resin" or "thermoplastic resin" is preferably 90 to 100% by mass. And more preferably 95 to 100 mass% is composed of a thermoplastic resin. This is also the case when the thermoplastic resin is specified by a more specific resin name.

The foam sheet of the present invention is excellent in rigidity while being in a thin film state. In addition, the foam sheet of the present invention can be manufactured with less process water while precisely controlling the distinction between the foam layer and the non-foam layer. Further, the foam sheet of the present invention is excellent in quality uniformity.

These and other features and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings, as appropriate.

1 is a schematic view showing a longitudinal section of one embodiment of a foam sheet of the present invention.

Hereinafter, embodiments of the foam sheet according to the present invention will be described in detail with reference to the drawings, but the present invention is not limited to these embodiments.

One embodiment of the foam sheet of the present invention is shown in Fig. The foam sheet 10 has a structure including a foam layer 11 and a non-foam layer 12 on both sides of the foam layer. The foam sheet of the present invention may further include a foam layer on the outside of the non-foam layer 12 in the structure shown in Fig. Further, a non-foam layer may be provided on the outer side of the foam layer provided outside the non-foam layer 12.

In the foam sheet of the present invention, both the foam layer and the non-foam layer are formed of a thermoplastic resin. The composition of the thermoplastic resin forming the foam layer and the composition of the thermoplastic resin forming the non-foam layer are different from each other.

[Foam layer]

The foam layer of the foam sheet of the present invention is made of a thermoplastic resin. The thermoplastic resin is not particularly limited, but is preferably a thermoplastic polyester resin from the viewpoints of cost and foamability. Examples of the thermoplastic polyester resin include polyethylene terephthalate, polytrimethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, and blend resins thereof. Among them, polyethylene terephthalate can be suitably used. When the foam sheet of the present invention has a plurality of foam layers, it is preferable that all the foam layers have the same composition.

Further, the foam layer is preferably made of a thermoplastic resin to which a bubble nucleating agent is added as an additive. By adding a perfluorinated nucleus agent, it is possible to generate more bubble nuclei in the thermoplastic resin. This makes it possible to form a foam layer having finer bubbles because the generated bubbles inhibit mutual growth of bubbles in the foaming step to be described later. There is no particular limitation on the above-mentioned nucleating agent, but a polyester-based elastomer can be suitably used.

The perfluorinated nucleating agent is preferably blended in an amount of 0.1 to 10 parts by mass based on 100 parts by mass of the thermoplastic resin.

The foamed layer may contain at least one selected from the group consisting of a crystallization nucleating agent, a crystallization accelerator, an antioxidant, an antistatic agent, an ultraviolet ray inhibitor, a light stabilizer, a fluorescent brightener, a pigment, a dye, a compatibilizer, A filler, a filler), a reinforcing agent, a flame retardant, a cross-linking agent, a crosslinking assistant, a plasticizer, a thickener, and a viscosity reducing agent.

The foam layer of the foam sheet of the present invention has bubbles. The bubbles are preferably independent bubbles. More specifically, it is preferable that 70% or more of the total number of guns of the foam sheet is closed cell, more preferably 80 to 100%, still more preferably 90 to 100%, still more preferably 95 to 100% Are independent bubbles.

The average diameter of the bubbles is 10 mu m or less, but is preferably 7.0 mu m or less, more preferably 5.0 mu m or less, further preferably 3.0 mu m or less, from the viewpoint of achieving both thinning and high reflectance (high reflectance) More preferably 2.0 m or less.

The average bubble diameter is usually not less than 0.5 mu m, and may be not less than 1.0 mu m. The average diameter of the bubbles is measured by the method described below.

The foam layer density of the foamed layer is 1.0 x 10 ⁶ / ㎣ or more, preferably 1.0 × 10 ⁷ / ㎣ to 1.0 × 10 ¹¹ / 관점 from the viewpoint of achieving both thinning and high reflectance, More preferably from 1.0 × 10 ⁸ particles / cm 2 to 1.0 × 10 ¹¹ particles / cm 3. The density of the foamed water in the foamed layer may be less than or equal to 1.0 × 10 ¹⁰ / 되고 or less than or equal to 1.0 × 10 ⁹ /.. The density of bubble water in the foam layer was measured by the method described below.

In the foamed sheet of the present invention, since at least one foamed layer is provided with a non-foamed layer on both sides thereof, the rigidity of the foamed sheet can be maintained in a desired range by the presence of the non-foamed layer even if the thickness is considerably reduced .

In the foamed sheet of the present invention, the thickness of the foamed layer is preferably 0.1 mm or more, more preferably 0.2 mm or more, 0.3 mm or more, and 0.4 mm or more from the viewpoints of optical properties and flexural rigidity .

On the other hand, from the viewpoint of cost and suitability for a backlight device for a liquid crystal TV, thinning is required. Therefore, from this viewpoint, the thickness of the foam layer is preferably 0.8 mm or less, more preferably 0.6 mm or less, still more preferably 0.5 mm or less, and 0.3 mm or less.

[Non-foaming layer]

The non-foam layer of the foam sheet of the present invention is made of a thermoplastic resin having a composition different from that of the thermoplastic resin constituting the foam layer. That is, in the same foam sheet, the foam layer and the non-foam layer are made of thermoplastic resins having different compositions. The resin constituting the non-foamed layer is not particularly limited, but it has crystallinity, and is subjected to temperature rise measurement after 168 hours of state adjustment under the conditions of 23 ± 1 ° C. and 50 ± 5% RH under atmospheric pressure (0.1 MPa) It is preferable that the crystallization behavior can not be observed.

Concretely, even when heat measurement is carried out at a temperature elevation profile at 40 to 300 ° C under a pressure of 0.1 MPa (760 mmHg) using a differential scanning calorimeter, the crystallization of the resin matrix It is preferable that no exothermic peak is observed. For example, the sample is held at 300 DEG C under a pressure of 760 mmHg in a nitrogen atmosphere with a differential thermal analyzer (differential thermal analyzer, model: DSC7, for example) / Min to 40 占 폚 and a resin which does not show an exothermic peak when the temperature is raised from 300 占 폚 to a temperature raising rate of 10 占 폚 / minute after holding at 40 占 폚, It can be employed as a resin.

As a suitable example of the resin constituting the non-foam layer, there may be mentioned one or more aromatic polyester resins. The aromatic polyester resin is preferably obtained by dehydration condensation of an aromatic dicarboxylic acid and a diol. In this case, the total diol component constituting the aromatic polyester resin (in the case of a blend resin composed of an aromatic polyester resin having two or more kinds of resins constituting the non-foamed layer, the total diol Is preferably at least 10% by mass, more preferably at least 15% by mass, even more preferably at least 20% by mass, still more preferably at least 25% by mass , Still more preferably not less than 30 mass%, still more preferably not less than 35 mass%, still more preferably not less than 40 mass%. Further, the ratio may be 50 mass% or more, further 60 mass% or more, further 70 mass% or more, further 80 mass% or more, and further 90 mass% or more. The non-foam layer is preferably made of polybutylene terephthalate or a blend resin of polybutylene terephthalate and polyethylene terephthalate.

More specifically, the non-foam layer is preferably made of a resin containing polybutylene terephthalate and polyethylene terephthalate in a mass ratio of (I) below, more preferably made of a resin containing a mass ratio of (II) , And more preferably in a mass ratio of (III).

(I) polybutylene terephthalate: polyethylene terephthalate = 100: 0 to 10: 90

(II) polybutylene terephthalate: polyethylene terephthalate = 100: 0 to 20: 80

(III) polybutylene terephthalate: polyethylene terephthalate = 100: 0 to 30:70

In the foam sheet of the present invention, it is preferable that all the non-foam layers have the same composition.

In addition, the ratio of the 1,4-butane diol component in the total diol component is a value calculated by converting each component into the diol structure.

The non-foam layer of the present invention plays the role of reinforcing the thinned foam layer to enhance the rigidity of the entire foam sheet. In order to sufficiently exhibit the above function, it is preferable that the thickness of the non-foam layer is 15 탆 or more. On the other hand, the unnecessary thickness of the non-foamed layer is unnecessary and is usually 40 탆 or less, and more preferably 20 탆 or less.

From the same viewpoint, the proportion of the entire non-foamed layer occupying the entire foam sheet of the present invention is preferably 10 mass% or more, more preferably 10 to 30 mass%, further preferably 14 to 25 mass% Do.

In the present invention, when the thickness of the non-foam layer of the foam sheet is less than 15 m, the ratio of the entire non-foam layer in the entire foam sheet is set to 10 mass% or more. If the ratio of the total non-foam layer occupied in the entire foam sheet is less than 10 mass%, the thickness of the foam layer is set to 15 탆 or more.

The non-foamed layer may contain, in addition to the above-mentioned thermoplastic resin, a coloring agent, a crystallization accelerator, an antioxidant, an antistatic agent, an ultraviolet ray inhibitor, a light stabilizer, a fluorescent whitening agent, a pigment, a dye, a compatibilizing agent, Various additives such as a thickening agent and a reducing agent may be contained.

[Production of foam sheet]

The method for producing the foam sheet of the present invention will be described below.

The foam sheet of the present invention is prepared by integrally molding a resin sheet of at least a three-layer structure comprising a thermoplastic resin layer for forming a foamed layer and a thermoplastic resin layer for forming a non-foamed layer, . More specifically, it is preferable to be produced through the following steps (a) to (c).

(a) a step of producing a resin sheet of at least a three-layer structure comprising a thermoplastic resin layer for forming a foamed layer and a thermoplastic resin layer for forming a non-foamed layer by integral molding by co-extrusion,

(b) impregnating the resin sheet with an inert high-pressure gas, and

(c) heating the resin sheet to foam the thermoplastic resin layer for forming the foam layer.

The resin sheet of at least three-layer structure manufactured in the step (a) is a three-layer structure composed of a thermoplastic resin layer for forming a foam layer and a thermoplastic resin layer for forming a non-foam layer provided on both surfaces thereof However, it is also possible to have a configuration of four or more layers suitably in accordance with the shape of the foam sheet to be targeted. The thermoplastic resin layer for forming the foamed layer is made of the thermoplastic resin constituting the above-mentioned foamed layer, and the thermoplastic resin layer for forming the non-foamed layer is made of the thermoplastic resin constituting the aforementioned non-foamed layer.

In the step (b), the resin sheet obtained from the step (a) is impregnated with an inert gas. It is preferable that a resin sheet obtained by the above step (a) and a separator are rolled up to form a roll, the roll is kept in a pressurized inert gas atmosphere, and the resin sheet is impregnated with an inert gas. The separator may be any as long as it has voids in which an inert gas and an organic solvent to be used as needed freely go in and out, and can neglect penetration of an inert gas into itself. A suitable example of the separator is a resinous nonwoven fabric or a metal net.

It is preferable that the resin sheet obtained from the step (a) is impregnated with an inert gas in a non-stretched (non-stretched) state. If stretched, the gas may not sufficiently penetrate into the sheet.

An organic solvent may be contained in the resin sheet before impregnating the roll-formed resin sheet with an inert gas. When the organic resin is contained in the resin sheet, the degree of crystallization (degree of crystallization) of the thermoplastic resin sheet can be improved, and the rigidity of the sheet is improved, so that traces of the separator on the sheet surface are less likely to remain. Further, the effect of shortening the penetration time of the inert gas can also be expected.

Examples of the organic solvent include organic solvents such as benzene, toluene, methyl ethyl ketone, ethyl formate, acetone, acetic acid, dioxane, m-cresol, aniline, acrylonitrile, dimethyl phthalate, nitroethane, . Among them, acetone is suitably used.

Examples of the inert gas include helium, nitrogen, carbon dioxide, and argon. Among them, carbon dioxide is preferable because it can be contained in a large amount in the thermoplastic resin. The penetration pressure of the inert gas is preferably 30 to 70 kg / cm ² , more preferably 50 to 70 kg / cm ² . The penetration time of the inert gas is usually one hour or more, and it is preferable to infiltrate the inert gas until it becomes saturated.

In the step (c), the resin sheet impregnated with the inert gas obtained from the step (b) is foamed. In the foaming step, the thermoplastic resin layer for forming the foamed layer is foamed, and the thermoplastic resin layer for forming the non-foamed layer is formed under the condition that foam is not performed. Specifically, the foam layer can be formed by removing the separator from the roll and heating the resin sheet to a temperature equal to or higher than the softening point of the thermoplastic resin for forming the foam layer. This heating is preferably carried out at a temperature lower than the melting point of the foam layer. If the foamed layer is polyethylene terephthalate, the heating temperature for foaming is 150 to 240 캜, preferably 180 to 230 캜.

Various methods can be conceived to foam the thermoplastic resin layer for forming the foam layer and prevent the thermoplastic resin layer for forming the non-foam layer from being foamed. For example, adding a nucleating agent to a thermoplastic resin layer for forming a foaming layer, or adding a crystallization nucleating agent and a crystallization accelerator to a thermoplastic resin layer for forming a non-foaming layer may improve the foamability of each resin layer to some extent Can be controlled. Further, by employing a specific resin as the thermoplastic resin used for forming each layer, it becomes possible to more strictly control the foamability. Suitable examples of such a thermoplastic resin are as described above.

The thickness of the foam sheet of the present invention is preferably 0.2 to 1.0 mm, more preferably 0.2 to 0.8 mm, even more preferably 0.2 to 0.6 mm, still more preferably 0.3 to 0.6 mm, still more preferably Is 0.4 to 0.6 mm. The specific gravity of the foam sheet of the present invention is preferably 0.2 to 0.7, more preferably 0.3 to 0.7, still more preferably 0.4 to 0.65. The specific gravity may be 0.5 or less.

The application of the foam sheet of the present invention is not particularly limited and can be used, for example, as a diaphragm for a light reflector or a loudspeaker. In particular, it can be suitably used as a light reflector. More specifically, it is suitable as a light reflector used for a backlight panel such as a liquid crystal display device.

The foam sheet obtained by the above production method preferably has a light reflectance of 98% or more. The light reflectance can be measured by measuring spectral transmittance at a wavelength of 550 nm at a wavelength of 4 nm using a spectrophotometer (spectrophotometer, U-4100 manufactured by Hitachi High-Tech Co., Ltd.). At that time, an aluminum oxide white plate (210-0740, manufactured by Hitachi High-Tech Fielding Co., Ltd.) is used as a reference, and the measured value is taken as a relative value with respect to the reference.

The foam sheet of the present invention may be coated with a paint containing the various additives described above, and such foam sheet is also included in the foam sheet of the present invention.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited thereto.

Example

(Measurement / evaluation method)

Hereinafter, the present invention will be described in detail by way of examples. Measurement and evaluation were carried out in the following manner.

(1) sheet thickness

The thicknesses at the center of the four corners and the four sides of the foam sheet were measured by a micrometer, and the average value of eight points in total was taken as the sheet thickness.

(2) Non-foaming layer thickness

SEM photographs were taken of the longitudinal cross-section of the foam sheet, and the line along the surface of the foam sheet and the line along the interface between the foam layer and the non-foam layer on the SEM photograph were taken so that both lines were parallel to each other , And the distance between the parallel lines was defined as the thickness of the non-foamed layer.

(3) Average bubble diameter

ASTM D3576-77. A SEM photograph was taken of the longitudinal section of the foam sheet, and a straight line was drawn in the horizontal direction and the vertical direction with respect to the stacking direction of each layer of the foam sheet on the SEM photograph, and the average t. The magnification of the photograph was taken as M, and substituted into the following equation to obtain an average cell diameter d. (d = t / (0.616 x M))

(4) Bubble number density

SEM photographs were taken of the longitudinal cross-section of the foam sheet, randomly selected areas of 100 x 100 mu m in the foam layer on the SEM photograph, counting the number of bubbles n present therein, The number of bubbles present per mm 2 was calculated. The obtained numerical value was multiplied by 3/2 to obtain the bubble number density in terms of the number of bubbles per bubble.

(5) Storage modulus

A sample width of 10 mm was measured with a viscoelasticity measuring device manufactured by Anton Paerl under the conditions of a twist mode, a measurement frequency of 1 Hz, an oscillation angle of gamma = 0.1% and a measurement temperature of 25 占 폚, And the storage elastic modulus was measured under the condition of an interval of 20 mm.

(Example 1)

The foam sheet 10 shown in Fig. 1 was prepared as follows.

2 parts by mass of a polyester elastomer (grade: PrimaLoi 1942N, manufactured by Mitsubishi Chemical Corporation) was added to 100 parts by mass of polyethylene terephthalate (grade: RT-553C, manufactured by Japan Unipet, IV value = 0.84) and kneaded Layered resin sheet having a surface layer composed of polybutylene terephthalate (grade: Nova Duerang 5026, manufactured by Mitsubishi Engineering-Plastics, Inc., IV value = 1.2) was provided on both sides thereof as an intermediate layer for forming a foamed layer, And was formed by integral molding by co-extrusion. The mass ratio of each layer of the resin sheet was: surface layer: intermediate layer: surface layer = 7: 86: 7, and the thickness of the resin sheet was 0.36 mm.

A separator, which is an olefin-based nonwoven fabric, was wound on the sheet, and the roll was put in a roll state. Thereafter, the roll was put in a pressure vessel and pressurized with carbon dioxide gas at 6 MPa to permeate carbon dioxide gas into the resin sheet. The penetration time was 72 hours. After completion of the infiltration, the roll was taken out from the pressure vessel, and the resin sheet was supplied to a hot air furnace which was set at a temperature equal to or higher than the softening point of the resin constituting the intermediate layer of the resin sheet. The obtained foam sheet had a thickness of 0.53 mm, a specific gravity of 0.585, an average cell diameter of the foam layer of 1.5 mu m, and a cell density of 3.94 x 10 ⁸ cells / cm. The thickness of the non-foam layer of the surface layer was all 16.8 占 퐉. The obtained foamed sheet had a storage elastic modulus of 745 MPa and a light reflectance of 98% or more.

Further, even if the obtained foam sheet was provided on a light guide panel type 45-inch backlight panel, no warpage was caused and no luminance unevenness occurred.

(Example 2)

A resin sheet was molded and foamed in the same manner as in Example 1, except that the mass ratio of each layer of the resin sheet was changed from surface layer: intermediate layer: surface layer = 8: 84: 8.

The obtained foam sheet had a thickness of 0.53 mm, a specific gravity of 0.643, an average cell diameter of the foam layer of 1.5 m, and a cell density of 3.77 x 10 ⁸ cells / cm. The thickness of the non-foam layer of the surface layer was all 19.6 占 퐉. The obtained foam sheet had a storage elastic modulus of 1862 MPa and a light reflectance of 98% or more.

Further, even if the obtained foam sheet was provided on a light guide panel type 45-inch backlight panel, no warpage was caused and no luminance unevenness occurred.

(Example 3)

A resin sheet was molded and foamed in the same manner as in Example 1, except that the mass ratio of each layer of the resin sheet was changed from surface layer: intermediate layer: surface layer = 10: 80: 10.

The obtained foam sheet had a thickness of 0.55 mm, a specific gravity of 0.476, an average cell diameter of the foam layer of 1.5 占 퐉, and a cell density of 4.23 占⁰⁸ / cell. The thickness of the non-foam layer of the surface layer was all 19 and 2 占 퐉. The obtained foam sheet had a storage elastic modulus of 640 MPa and a light reflectance of 98% or more.

Further, even if the obtained foam sheet was provided on a light guide panel type 45-inch backlight panel, no warpage was caused and no luminance unevenness occurred.

(Example 4)

The resin constituting the surface layer of the resin sheet was obtained in the same manner as in Example 1 except that 30 parts by mass of polybutylene terephthalate (grade: NOVA DURANG 5026, manufactured by Mitsubishi Engineering KK, IV value = 1.2) and polyethylene terephthalate (grade: RT- Except that the mass ratio of each layer of the resin sheet was changed from the surface layer: the intermediate layer: the surface layer = 10: 80: 10 to the blend resin consisting of 70 parts by mass of the polypropylene resin To form a resin sheet, followed by foaming.

The obtained foam sheet had a thickness of 0.53 mm, a specific gravity of 0.585, an average cell diameter of the foam layer of 1.5 mu m, and a cell density of 3.94 x 10 ⁸ cells / cm. The thickness of the non-foam layer of the surface layer was all 24.0 占 퐉. The obtained foamed sheet had a storage elastic modulus of 745 MPa and a light reflectance of 98% or more.

Further, even if the obtained foam sheet was provided on a light guide panel type 45-inch backlight panel, no warpage was caused and no luminance unevenness occurred.

The resins constituting the non-foamed layer of the foam sheet obtained from Examples 1 to 4 were all crystalline, and under the conditions of 23 ± 1 ° C. and 50 ± 5% RH under atmospheric pressure (0.1 MPa) No crystallization behavior was observed in the heat measurements after 168 hours of conditioning.

(Comparative Example 1)

2 parts by mass of a polyester elastomer (grade: PrimaLoi 1942N, manufactured by Mitsubishi Chemical Corporation) was added to 100 parts by mass of a polyethylene terephthalate (grade: RT-553C, manufactured by Japan Unipet, IV value = 0.84) .

This sheet was foamed in the same manner as in the method described in Example 1. The obtained foam sheet had a thickness of 0.53 mm, a specific gravity of 0.510, an average cell diameter of the foam layer of 1.5 占 퐉, and a cell density of 3.75 占⁰⁸ cells / cm. Further, the thickness of the non-foam zone existing near the surface was 6.8 mu m. The obtained foam sheet had a storage elastic modulus of 379 MPa and a light reflectance of 98% or more.

Further, when the obtained foam sheet was provided on a light guide plate type 45-inch backlight panel, luminance unevenness due to warping of the sheet occurred.

The above results are summarized in Table 1 below.

[Table 1]

From the above results, it was found that the foam sheet of the present invention has excellent storage elastic modulus. That is, if a resin sheet having a specific layer structure obtained by integral molding is used, a foam sheet in which the separation between the foam layer and the non-foam layer is more precisely controlled can be obtained simply by foaming the foam sheet. As a result, It is possible to provide a foam sheet excellent in uniformity in terms of quality and performance.

While the invention has been described in conjunction with the embodiments thereof, it is to be understood that the invention is not to be limited to any details of the description except as otherwise indicated, and that the invention is broadly construed as broadly as spirit and scope of the invention as set forth in the appended claims. I think it should be interpreted.

This application claims priority based on Japanese Patent Application No. 2012-137365 filed on June 18, 2012 in Japan, which is hereby incorporated by reference as its description.

10 foam sheet
11 foam layer
12 Non-foaming layer
13 air bubbles

Claims (7)

A foamed sheet manufactured by integrally molding a resin sheet of at least a three-layer structure comprising a thermoplastic resin layer for forming a foamed layer and a thermoplastic resin layer for forming a non-foamed layer,
Wherein at least one foam layer of the foam sheet has a non-foam layer on both sides thereof,
Wherein the foam layer and the non-foam layer are made of a thermoplastic resin having a different composition,
The average diameter of the foamed layer having air bubbles and 10㎛ or less, and a bubble can (氣泡數) density of the foam layer is at least 1.0 × 10 ⁶ gae / ㎣,
Wherein the non-foam layer has a thickness of 15 μm or more per one layer, or the ratio of the entire non-foam layer in the entire foam sheet is 10% by mass or more, or the thickness of the non-foam layer is 15 μm or more The ratio of the entire non-foam layer occupying the entire foam sheet is 10% by mass or more,
The thermoplastic resin constituting the non-foamed layer has a crystallinity but is observed under the atmospheric pressure (0.1 MPa) by heat measurement after being conditioned for 168 hours under conditions of 23 1 C and 50 5% RH (relative humidity) The crystallization behavior is not observed. A foamed sheet manufactured by integrally molding a resin sheet of at least a three-layer structure comprising a thermoplastic resin layer for forming a foamed layer and a thermoplastic resin layer for forming a non-foamed layer,
Wherein at least one foam layer of the foam sheet has a non-foam layer on both sides thereof,
Wherein the foam layer and the non-foam layer are made of a thermoplastic resin having a different composition,
The average diameter of the foamed layer having air bubbles and 10㎛ or less, and a bubble can (氣泡數) density of the foam layer is at least 1.0 × 10 ⁶ gae / ㎣,
Wherein the non-foam layer has a thickness of 15 μm or more per one layer, or the ratio of the entire non-foam layer in the entire foam sheet is 10% by mass or more, or the thickness of the non-foam layer is 15 μm or more The ratio of the entire non-foam layer occupying the entire foam sheet is 10% by mass or more,
Wherein the ratio of the 1,4-butane diol component in the total diol component constituting the aromatic polyester resin is 10% by mass or more, the aromatic polyester resin being composed of one or more kinds of the non-foamed layers. 3. The method of claim 2,
Wherein the non-foam layer comprises polybutylene terephthalate or a blend resin of polybutylene terephthalate and polyethylene terephthalate. 4. The method according to any one of claims 1 to 3,
Wherein the foamed layer is made of polyethylene terephthalate. A process for producing a foamed sheet according to any one of claims 1 to 3, comprising the following steps (a) to (c):
(a) a step of producing a resin sheet having at least a three-layer structure composed of a thermoplastic resin layer for forming a foamed layer and a thermoplastic resin layer for forming a non-foamed layer by integral molding by co-
(b) impregnating the resin sheet with an inert high-pressure gas, and
(c) heating the resin sheet to foam the thermoplastic resin layer for forming the foam layer. 6. The method of claim 5,
Wherein the thermoplastic resin layer for forming the non-foamed layer does not foam in the step (c). delete

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