JP6782585B2 - Resin sheet - Google Patents

Description

The present invention relates to a resin sheet having a foam layer made of a thermoplastic resin and a transparent resin layer made of a thermoplastic resin.

Foamed resin sheets are lighter and cheaper than materials such as glass, metal materials, and wood, and are expected to be used in various fields. For example, it is expected that foamed resin sheets will be used for partitions, storage shelf doors, and the like. In this case, it is desirable that not only the lightness but also the appearance is taken into consideration, and it is preferable that good smoothness is shown on the surface of the foamed resin sheet.

The following Patent Documents 1 and 2 are known as techniques for imparting smoothness to the surface of a foamed resin sheet.
Patent Document 1 discloses a laminated sheet in which a non-foamed resin film is laminated on the surface of a polystyrene-based resin foamed sheet (hereinafter, also simply referred to as a foamed sheet). Patent Document 1 discloses that the surface of a foamed sheet is cooled to a high density during extrusion molding, and a non-foamed resin film is laminated to form a surface having a beautiful appearance.
Patent Document 2 discloses an invention of a plate which is a resin single plate having non-foaming layers on both sides of the foaming layer. In Patent Document 2, both surfaces of the molten resin containing a foaming agent extruded from a mold die into the atmosphere are cooled, and then cooling plate sizing is performed to form a non-foamed layer on the surface of the foamed layer. It is disclosed that a plastic plate is manufactured.

Japanese Unexamined Patent Publication No. 2000-143863 Japanese Unexamined Patent Publication No. 2014-172381

However, the above-mentioned prior art has the following problems. That is, the laminated sheet described in Patent Document 1 has insufficient smoothness and glossiness on the surface of the laminated sheet in order to be used for the above partition or the door of the storage shelf. Further, the laminated sheet of Patent Document 1 is manufactured through a plurality of steps such as a cooling step, a curing step, and a laminating step in addition to the extrusion step of the foamed sheet, and has a manufacturing disadvantage that the manufacturing steps are numerous and complicated. It had a problem of adverse effects on practical use due to this.
Further, in the plate described in Patent Document 2, although the non-foamed layer is formed on the surface of the foamed layer, the surface roughness (10-point average roughness) is about 8 to 15 in view of the numerical values of Examples. However, it is not a sufficient level from the viewpoint of surface smoothness.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a resin sheet having a foam layer made of a thermoplastic resin and a transparent resin layer, which has sufficient surface smoothness and glossiness.

The resin sheet of the present invention is a resin sheet having a total thickness of 1000 μm or more and 10000 μm or less, which is formed by laminating a foam layer made of a thermoplastic resin and a transparent resin layer made of a thermoplastic resin by coextrusion . The expansion ratio is 1.1 times or more, the transparent resin layer is located on at least one surface side of the resin sheet, the thickness of the transparent resin layer is 50 μm or more, and the thickness is orthogonal to the extrusion direction of the resin sheet. The average bubble diameter of the bubbles in the foam layer in the vertical cross section is 120 μm or more and 500 μm or less, and the number of bubbles with a bubble diameter of 500 μm or less in the unit area of the foam layer in the vertical cross section orthogonal to the extrusion direction of the resin sheet is 27.0 cells / The mm is ² or more, the haze of the resin sheet is 95% or more, and the arithmetic average roughness (Ra) of the surface of the resin sheet on the transparent resin layer side measured in accordance with JIS B0601: 2001 is 0. It is characterized in that it is 7 μm or less, and the 20-degree mirror surface gloss of the surface of the resin sheet on the transparent resin layer side measured in accordance with JIS Z8741: 1997 is 50% or more.

In the resin sheet of the present invention, there are no bubbles or excessive large bubbles in the foam layer, and fine bubbles are formed. Therefore, the resin sheet has a high mirror glossiness in the transparent resin layer on the surface, can reduce the arithmetic mean roughness, and has various aesthetic advantages due to the excellent surface smoothness. It can be used for various purposes.

(A) is a cross-sectional view showing a cross section of a resin sheet according to the first embodiment of the present invention, and (b) shows a cross section of a resin sheet which is a first modification of the first embodiment of the present invention. It is a cross-sectional view, and (c) is a cross-sectional view showing a cross section of a resin sheet which is a second modification of the first embodiment of the present invention. It is explanatory drawing explaining the manufacturing method of the resin sheet of this invention.

Hereinafter, the resin sheet of the present invention will be described in order.
In the following description, with respect to the direction of the resin sheet of the present invention, the extrusion direction without particular notice means the flow direction of the sheet during coextrusion molding of the resin sheet, and the width direction means the extrusion direction. It means a direction orthogonal to the direction. Further, regarding the bubbles contained in the foam layer in the present invention, the term “bubble diameter” means the longest diameter of the bubbles in the observed state. The average bubble diameter of the bubbles in the foam layer on the cut surface was obtained by measuring the longest diameter of the bubbles whose entire shape was confirmed in the foam layer on the cut surface and performing an arithmetic mean based on the number of measurements. Means a value.

[1] Resin Sheet First, an outline of the resin sheet 100 according to the present embodiment will be described. As shown in FIG. 1A, the resin sheet 100 includes a foam layer 10 made of a thermoplastic resin and containing air bubbles, and a transparent resin layer 20 made of a thermoplastic resin. The resin sheet 100 is formed by co-extruding and laminating the foam layer 10 and the transparent resin layer 20. The transparent resin layer 20 is located on one surface side of the resin sheet 100.
The overall thickness of the resin sheet 100 is adjusted to be 500 μm or more and 10000 μm or less, which is an appropriate thickness range for coextrusion. The thickness of the transparent resin layer 20 is 50 μm or more, so that the influence of air bubbles contained in the foamed layer 10 does not hinder the surface smoothness of the transparent resin layer 20. The thickness of the transparent resin layer 20 referred to here means the thickness of one transparent resin layer 20 arranged as the outermost layer of the resin sheet 100. For example, when the transparent resin layers 20 are arranged on both sides of the resin sheet 100 as shown in FIG. 1A, the total thickness of the transparent resin layers 20 is 100 μm or more. On the other hand, the thickness of the foam layer 10 can be appropriately determined in consideration of the total thickness and the thickness of the transparent resin layer 20.
As a method for measuring the total thickness of the resin sheet 100, the thickness of the foamed layer 10, and the thickness of the transparent resin layer, the methods described in Examples described later are referred to.

In the present invention, the average bubble diameter of the bubbles contained in the foamed layer 10 in the vertical cross section orthogonal to the extrusion direction of the resin sheet is 500 μm or less, whereby the surface of the transparent resin layer 20 laminated on the foamed layer 10 is smoothed. Sex is guaranteed. Further, the resin sheet 100 has an arithmetic average roughness (Ra) of 0.7 μm or less on the surface 22 on the transparent resin layer 20 side measured in accordance with JIS B0601: 2001, and conforms to JIS Z8741: 1997. The 20-degree mirror surface gloss of the surface 22 on the transparent resin layer 20 side measured in the above is 50% or more. As described above, the surface of the resin sheet 100 has an appropriately small arithmetic mean roughness (Ra), an appropriate gloss, and an excellent appearance.
As the method for measuring the average cell diameter, the method described in Examples described later is referred to.

In the resin sheet 100, the foamed layer 10 is a layer formed by foaming a thermoplastic resin with a foaming agent, and contains a plurality of bubbles inside. On the other hand, the transparent resin layer 20 is a non-foamed resin layer having substantially no bubbles inside. Here, substantially no bubbles means that there are no bubbles intentionally generated by using a foaming agent or the like.

The conventional partition board is provided with a resin layer such as non-expanded polystyrene as the outermost layer and a resin layer such as non-expanded polystyrene containing a silicone diffusing agent as a core layer in order to obtain light diffusivity as well as surface smoothness. Aspects are known. On the other hand, the resin sheet 100 of the present invention having the above structure is excellent in practicality because it has a structure that is easy to manufacture while maintaining the same surface smoothness as a conventional partition board, and can be used for various purposes. is there. Further, the resin sheet 100 is reduced in weight by providing the foamed resin layer 10 as the core layer, and the light incident on the sheet by the bubbles contained in the foamed resin layer 10 can be emitted without using a silicone diffuser. Since it can be diffused well and the resin can be used as a recycled raw material, the manufacturing cost can be reduced and reused as compared with the conventional partition board. Further, the resin sheet 100 is also excellent in designability because fine bubbles of the foamed resin layer 10 can be visually recognized through the transparent resin layer 20 which is the outermost layer.

In the resin sheet 100 shown in FIG. 1A, a transparent resin layer 20 having a thickness of 50 μm or more is located on both surface sides (outermost surface side) of the resin sheet 100 via the foam layer 10. According to this aspect, the resin sheet 100 is excellent in smoothness and appearance on both sides, and can be appropriately applied to a usage mode such as a partition that can be visually recognized from both sides. Specifically, the resin sheet 100 shown in FIG. 1A is arranged on both sides, and one foamed resin layer 10 is arranged between the transparent resin layers 20, and the resin sheet 100 has a three-layer structure as a whole. Eggplant.

The present invention is not limited to the aspect of the resin sheet 100 shown in FIG. 1 (a). As a modification of the resin sheet 100, an intermediate transparent resin having a plurality of foam layers 10 and between one foam layer 10 (first foam layer 131) and another foam layer 10 (second foam layer 132). Includes aspects with layer 30. More specifically, for example, as shown in FIG. 1 (b), the present invention is provided with a transparent resin layer 20 on both side surfaces (outermost surface side) and an intermediate transparent resin layer 30 in the middle in the thickness direction, and is transparent. The resin sheet 200 having a five-layer structure including a foam layer 10 between the resin layer 20 and the intermediate transparent resin layer 30 is included. As the number of foam layers 10 increases, it is possible to increase the diffusivity of the incident light of the sheet. Therefore, an embodiment having a plurality of foam layers 10 such as the resin sheet 200 is preferable when high diffusibility is required.

Further, as a different modification of the present invention, the transparent resin layer 20 may be provided only on one surface of the sheet, as in the resin sheet 220 shown in FIG. 1 (c). The resin sheet 220 is a two-layered sheet having a transparent resin layer 20 laminated on one surface of the foam layer 10. Since the transparent resin layer 20 is excellent in smoothness and appearance as described above, for example, the resin sheet 220 can be used as a printing substrate having the transparent resin layer 20 as a printing surface.

Next, the details of the resin sheet 100 will be described.
As described above, the thickness of the resin sheet 100 is 500 μm or more and 10000 μm or less, and can be appropriately adjusted within such a range. Compared with a resin sheet having the same thickness and made of a non-foaming resin layer, the resin sheet 100 is provided with a foaming layer, so that the weight is reduced. From the viewpoint of the rigidity of the resin sheet, the thickness of the resin sheet 100 is preferably 1000 μm or more, more preferably 2000 μm or more, still more preferably 3000 μm or more. On the other hand, from the viewpoint of the light weight of the resin sheet, 8000 μm or less is preferable, 6000 μm or less is more preferable, and 4000 μm or less is further preferable.

The foam layer 10 and the transparent resin layer 20 provided on the resin sheet 100 are both made of a thermoplastic resin. Further, as shown in FIG. 1 (b), the optionally provided intermediate transparent resin layer 30 can also be made of a thermoplastic resin in the same manner. The foam layer 10, the transparent resin layer 20, and the intermediate transparent resin layer 30 provided optionally may be made of the same thermoplastic resin, or may be made of different thermoplastic resins for each layer. When two or more foam layers 10 or transparent resin layers 20 are provided in the resin sheet 100, one foam layer 10 and another foam layer 10 or one transparent resin layer 20 and another foam resin layer 20 , It may be composed of the same thermoplastic resin, or it may be composed of different thermoplastic resins for each layer.

As the thermoplastic resin, a resin corresponding to the "transparent plastic" known in JIS K7361 (1997) is preferably used. Specific examples of the thermoplastic resin include polystyrene resin, polypropylene resin, acrylic resin, polycarbonate resin, thermoplastic polyester resin, and cyclic olefin resin.

Examples of the polystyrene resin include polystyrene, styrene-α-methylstyrene copolymer, styrene-p-methylstyrene copolymer, polystyrene, a styrene-acrylic acid ester copolymer containing styrene as a main component, and a styrene-methacrylic acid ester copolymer weight. Combined, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-maleic anhydride copolymer, styrene-polyphenylene ether copolymer, styrene-butadiene copolymer, styrene-acrylonitrile copolymer, acrylonitrile -Butadiene-styrene copolymer, acrylonitrile-styrene acrylate copolymer, styrene-methylstyrene copolymer, styrene-dimethylstyrene copolymer, styrene-ethylstyrene copolymer, styrene-diethylstyrene copolymer, high impact Examples thereof include polystyrene (impact resistant polystyrene resin), which are used alone or in combination of two or more. The polystyrene resin has a styrene-based unit or styrene component content of more than 50 mol%, preferably 70 mol% or more, and particularly preferably 80 mol% or more.

Examples of the polypropylene resin include polypropylene, a copolymer of a propylene component and another polymerizable monomer component, a mixture of the propylene (co) polymer and another polymer, and the like. Specifically, propylene homopolymer (h-PP), propylene-ethylene random copolymer, propylene-ethylene-butene random copolymer (r-PP), propylene-ethylene block copolymer (b-PP). Etc. are exemplified. The polypropylene resin has a propylene-based unit or propylene component content of more than 50 mol%, preferably 70 mol% or more, and particularly preferably 80 mol% or more.

The acrylic resin is a homopolymer of an acrylic acid alkyl ester and / or a methacrylic acid alkyl ester (collectively referred to as (meth) acrylic acid ester below) or a combination of (meth) acrylic acid esters. A (meth) acrylic acid ester-based copolymer having a unit based on a polymer or (meth) acrylic acid ester of 50 mol% or more and a unit based on another comonomer of 50 mol% or less, and two or more of these. It is a mixture or the like. In addition, (meth) acrylic acid is a concept including acrylic acid and methacrylic acid, and means one or both of them.
Examples of the homopolymer or copolymer of the above (meth) acrylic acid ester include polymethylmethacrylate, ethylpolymethacrylate, propylpolymethacrylate, butylpolymethacrylate, methylpolyacrylate, ethyl polyacrylate, and the like. Examples thereof include a methyl methacrylate-ethyl methacrylate copolymer, a methyl methacrylate-butyl methacrylate copolymer, and a methyl methacrylate-ethyl acrylate copolymer. Of these, polymethyl methacrylate, methyl polyacrylate, methyl methacrylate-ethyl methacrylate copolymer, or methyl methacrylate-ethyl acrylate copolymer is preferable, and polymethyl methacrylate is more preferable.

Examples of the (meth) acrylic acid ester-based copolymer include a methyl methacrylate-styrene-butylene copolymer, a methyl (meth) methyl acrylate-styrene copolymer, and an ethyl (meth) acrylic acid-styrene copolymer. , Or methyl methacrylate-acrylonitrile-butadiene-styrene copolymer and the like. Of these, a methyl methacrylate-styrene-butylene copolymer or a methyl methacrylate-styrene copolymer is preferable.

Examples of the polycarbonate resin include bisphenol A (4,4'-dihydroxydiphenyl-2,2-propane) polycarbonate, bisphenol F (4,4'-dihydroxydiphenyl-2,2-methane) polycarbonate, and bisphenol S (4). , 4'-Dihydroxydiphenylsulfone) polycarbonate, 2,2-bis (4-dihydroxyhexyl) propane) polycarbonate and the like. Of these, an optical grade polycarbonate resin is particularly preferable.

Examples of the thermoplastic polyester resin include aromatic ring-containing polyesters (for example, polyethylene terephthalate, polybutylene terephthalate, polycyclohexanedimethylene terephthalate and polyethylene naphthalate) and aliphatic polyesters (for example, polybutylene adipate, polyethylene adipate and poly-ε-caprolactone). Can be mentioned. As the polyethylene terephthalate, amorphous polyethylene terephthalate (A-PET) having excellent transparency is preferably used.

Examples of the cyclic olefin resin include homopolymers of cyclic olefins, copolymers of cyclic olefins, copolymers of cyclic olefins with ethylene and α-olefins, and mixtures of two or more of these. Examples of the cyclic olefin polymer include the trade name "Apel" or "Topus" of Mitsui Chemicals, Inc., or the trade name "Zeonex" or "Zeonoa" of Nippon Zeon Corporation.

The thermoplastic resin used for each layer constituting the resin sheet of the present invention may be used alone or in admixture of two or more. When one type of thermoplastic resin is used, the resin used for each layer may be the same or different. When two or more kinds of thermoplastic resins are mixed and used, or when other resins and the like are mixed and used within the range which does not impair the object of the present invention, each thermoplastic resin to be used. The refractive indexes of are similar or equal. If the difference in the refractive index of each thermoplastic resin or the difference in the refractive index between the thermoplastic resin and other resins is large, the mixed resin becomes cloudy and the transparency and image sharpness deteriorate, depending on the mixing ratio. It is desirable that the difference in refractive index is small. Specifically, the difference in refractive index is preferably 0.05 or less, more preferably 0.04 or less, further preferably 0.03 or less, and the difference in refractive index is optimally 0 (zero).

The thermoplastic resin used for each layer constituting the resin sheet of the present invention can be appropriately selected from the above. As the resin used for the foamed layer 10, polystyrene resin is preferable, and branched polystyrene resin is particularly preferable, from the viewpoint of excellent low water absorption, rigidity, and foamability among the above thermoplastic resins. Since the foamed layer 10 made of the branched polystyrene resin is good at suppressing the occurrence of foam breakage, the appearance of the resin sheet 100 can be made particularly good. As the resin used for the intermediate transparent resin layer 30, polystyrene resin is preferable, and branched polystyrene resin is particularly preferable, from the viewpoint of low water absorption and excellent rigidity among the above thermoplastic resins.
Further, as the resin used for the transparent resin layer 20 located on the surface side of the resin sheet, the above-mentioned thermoplastic resin can be appropriately selected and used, but polystyrene resin is preferable from the viewpoint of recycling, and linear polystyrene resin is particularly preferable. preferable.

To the extent that the object and effect of the present invention are not impaired, the foam layer 10, the transparent resin layer 20, or the intermediate transparent resin layer 30 is a resin other than the above-mentioned thermoplastic resin, an elastomer, a bubble modifier, an antioxidant, a heat stabilizer. , A weather resistant agent, an ultraviolet absorber, a flame retardant, an antibacterial agent, a functional additive such as a shrinkage inhibitor, or an additive such as an inorganic filler can be contained in an amount of one or more. The total amount of the additives is preferably 10 parts by mass or less with respect to 100 parts by mass of the thermoplastic resin in each layer.

The haze (Hz) of the resin sheet of the present invention is preferably 80% or more, more preferably 90% or more, and further preferably 95% or more. A high haze means that the resin sheet has a high degree of fogging. The haze can be measured using a turbidity meter (for example, Haze Meter NDH7000SP manufactured by Nippon Denshoku Industries Co., Ltd.) according to JIS K7136 (2000).
Further, the total light transmittance (TT) of the resin sheet of the present invention is preferably 50% or less, and more preferably 40% or less. On the other hand, the lower limit is preferably 10% or more, more preferably 20% or more, and further preferably 30% or more. The total light transmittance can be measured using a turbidity meter (for example, Haze Meter NDH7000SP manufactured by Nippon Denshoku Industries Co., Ltd.) according to JIS K7361-1: 1997. The resin sheet satisfying the haze and the total light transmittance can be suitably used for partitioning and the like because it has a certain amount of light transmittance and is difficult to transmit through the back surface side.

The foamed layer 10 is a thermoplastic resin layer containing a large number of bubbles in the layer, and is involved in the light diffusivity, weight reduction, or appearance of the resin sheet 100. For example, the foamed layer 10 is formed by foaming the above-mentioned thermoplastic resin when a foaming agent is added and coextruded with the transparent resin layer 20. The thickness of the foamed layer 10 is determined in consideration of the total thickness of the resin sheet 100 and the thickness of the transparent resin layer 20. Specifically, the lower limit of the thickness (α) of the foamed layer 10 with respect to the total thickness of the resin sheet 100 is preferably 20%, more preferably 25%, and even more preferably 30%. On the other hand, the upper limit is preferably 85%, more preferably 75%, even more preferably 65%, and particularly preferably 50%. Within the above range, the resin sheet 100 can be obtained with a smooth surface and excellent design while ensuring the lightness of the resin sheet 100.

The bubbles contained in the foam layer 10 in the vertical cross section orthogonal to the extrusion direction of the resin sheet preferably have an average cell diameter ([D]) of 500 μm or less. As a result, the weight of the resin sheet 100 can be reduced, and the loss of smoothness of the transparent resin layer 20 due to the unevenness of the bubbles can be prevented. That is, according to the study by the present inventors, even if the thickness of the transparent resin layer 20 is 50 μm or more, when the bubbles contained in the foam layer 10 co-extruded and laminated exceed the average cell diameter of 500 μm, it is relative. It was found that bubbles having a large diameter affect the surface of the transparent resin layer 20 and it tends to be difficult to obtain good smoothness.
Further, since the foamed layer 10 having an average cell diameter of 500 μm or less contains a large number of relatively fine bubbles, it can impart good designability to the resin sheet 100 by being visually recognized through the transparent resin layer 20. When the resin sheet 100 has a plurality of foamed layers, it is preferable that the average cell diameter ([D]) of each foamed layer is 500 μm or less.

Since the foam layer 10 contains a large number of fine bubbles, good surface smoothness can be obtained and the design is also excellent. From the viewpoint, foaming observed from substantially perpendicular to the in-plane direction of the resin sheet 100. The number of bubbles having a bubble diameter of 500 μm or less in the unit area of the layer 10 is preferably 10 cells / mm ² or more. The above-mentioned bubble diameter means the longest diameter of the bubble observed from above.
When the number of bubbles having a bubble diameter of 500 μm or less is 10 cells / mm ² or more, it is preferable because a resin sheet 100 having sufficient fine bubbles and excellent design can be obtained. From the above viewpoint, the number of bubbles having a bubble diameter of 500 μm or less in the unit area of the foam layer 10 is more preferably 20 cells / mm ² or more, and further preferably 30 cells / mm ² or more.
The details of the method of observing air bubbles on the flat surface of the sheet are as follows. First, the resin sheet 100 to be observed is magnified 100 times from the upper surface to the in-plane direction so that the extrusion direction and the width direction are vertical and horizontal. .. Based on the obtained photograph, the number of clear bubbles in the outer shell existing in the range of 2 mm in the extrusion direction and 2 mm in the width direction of the foam layer 10 is measured, and the measurement result is converted into a unit of the number per 1 mm ² . The number of bubbles in the foam layer 10 is determined. In measuring the number of bubbles, bubbles having only a part within the range of 2 mm in the extrusion direction and 2 mm in the width direction, that is, bubbles on the boundary line within the range are excluded.

Further, from the viewpoint of obtaining good surface smoothness and excellent designability as described above, the resin sheet 100 is a foam layer having a vertical cross section (cross section in the width direction of the resin sheet 100) orthogonal to the extrusion direction of the resin sheet 100. The ratio of the number of bubbles having a diameter of more than 500 μm (the number of large cells Y) to the total number of cells is preferably 1% or less per predetermined area of the foam layer 10. The total number of cells means the number of cells having a bubble diameter of 500 μm or less [the number of fine cells X] + the number of cells having a diameter of more than 500 μm [the number of large cells Y].
When the ratio of the number of bubbles having a bubble diameter exceeding 500 μm is in the above range, it is preferable because a resin sheet having excellent surface smoothness and excellent design can be obtained. When the resin sheet 100 has a plurality of foamed layers, it is preferable that the ratio of the number of bubbles having a bubble diameter of more than 500 μm in each foamed layer satisfies the above range.
In the method for measuring the number X of fine bubbles and the number Y of large bubbles described above, the cross section is exposed by cutting with a microtome in the width direction of the resin sheet 100 to be observed, and the cross section is exposed to a microscope (emergence mode). Take a magnified shot at 50x. Based on the obtained photograph, the number of bubbles existing in the thickness direction (thickness region) and the width direction (6 mm) of one foam layer 10 is counted. At this time, the number of bubbles having a bubble diameter of 500 μm or less is measured as the number X of fine cells, and the number of bubbles having a bubble diameter of more than 500 μm is measured as the number Y of large bubbles. The measurement result is converted into a unit of the number per 1 mm ^2, and the number X of fine cells and the number Y of large cells in the foam layer 10 are obtained. In measuring the number of bubbles, bubbles having only a part in the thickness direction (thickness region) and width direction (6 mm) of the foam layer 10, that is, bubbles on the boundary line within the range are excluded. To do.

As described above, the foam layer 10 in the resin sheet 100 preferably contains a large number of bubbles having a relatively small bubble diameter, and in order to realize such a configuration, for example, the foaming ratio of the foam layer 10 is 1 times. It is preferable that the amount is more than twice and not more than twice. When the foaming ratio of the foamed layer 10 is in the above range, a sheet having excellent designability can be obtained, which is preferable. From the viewpoint of the design of the resin sheet, it is more preferably 1.05 times or more and 1.8 times or less, and further preferably 1.1 times or more and 1.6 times or less. When the resin sheet 100 has a plurality of foamed layers, it is preferable that each foamed layer satisfies the foaming ratio.
As a method for measuring the foaming ratio of the foamed layer 10, a sheet containing only the transparent resin layer 20 containing no foaming agent is prepared in advance, the mass per unit volume of the non-foamed transparent resin sheet is confirmed, and the standard mass is used. Next, the total basis weight is measured using a resin sheet 100 (or a comparative example corresponding thereto) having a predetermined shape to be measured, and the thickness of the transparent resin sheet and the standard mass in the measurement result of the layer thickness are used. The weighing of the transparent resin layer 20 is calculated. The basis weight of the foam layer 10 is calculated from the basis weight of the entire resin sheet 100 having a predetermined shape, the basis weight of the transparent resin layer 20, and the standard mass, and the magnification of the foam layer 10 is calculated.

The foaming agent used together with the thermoplastic resin to form the foam layer 10 is not particularly limited, and is appropriately selected from known physical foaming agents or chemical foaming agents. The mode of use of the foaming agent is not particularly limited, but for example, the foaming agent can be used by dry blending with the thermoplastic resin constituting the foam layer 10.
Examples of the physical foaming agent include aliphatic hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, normal hexane and isohexane, alicyclic hydrocarbons such as cyclopentane and cyclohexane, methyl chloride and ethyl chloride. Organic physical foaming agents such as fluorinated hydrocarbons such as hydrocarbons chloride, 1,1,1,2-tetrafluoroethane, and 1,1-difluoroethane, and inorganic physical foaming agents such as nitrogen, carbon dioxide, air, and water. Agents can be mentioned.
Examples of the chemical foaming agent include dinitrosopentamethylenetetramine, azodicarboxylicamide, P, P'-oxybisbenzenesulfonyl hydrazide, 4,4'-oxybisbenzenesulfonyl hydrazide, P-toluenesulfonylhydrazide, and P-toluenesulfonylacetone. Hydrazide, hydrazodicarboxylic amide, sodium carbonate, sodium hydrogen carbonate and the like can be mentioned.
It is preferable to select sodium hydrogen carbonate or azodicarbonamide as the foaming agent because the expansion ratio of the foam layer 10 is suppressed to an appropriate range and the diameter of the formed bubbles can be easily adjusted to a small diameter.
The amount of the foaming agent is appropriately adjusted according to the target foaming ratio, but is approximately 0.5 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the thermoplastic resin constituting the foamed layer. ..

Next, the transparent resin layer 20 will be described.
As described above, the transparent resin layer 20 in the present invention has a thickness ([T]) of 50 μm or more, an arithmetic mean roughness (Ra) of 0.7 μm or less, and a 20-degree mirror glossiness of 50% or more. And has excellent smoothness.
In the resin sheet 100, the transparent resin layer 20 is located on at least one surface side. As shown in FIGS. 1A and 1B, the transparent resin layer 20 is located on the surface side of both the resin sheet 100 and the resin sheet 200, so that the resin sheet 100 has good smoothness and appearance on both surfaces. Therefore, it is preferable that the transparent resin layers 20 are formed on both surfaces of the resin sheet 100, and in that case, the thickness of the transparent resin layers 20 on both surfaces is preferably 50 μm or more. The transparency of the transparent resin layer 20 is not as strict as the light transmittance is quantified and shown, but means the degree to which the light transmission is significantly felt when the light is passed through, and is relatively relative. It suffices if the light transmittance is larger than that of the foam layer 10. The transparency in the transparent resin layer 20 may be either colorless and transparent or colored transparent, and the transparent resin layer 20 may be colored with a colorant such as a pigment or a dye in order to enhance the design.

Although the thickness of the transparent resin layer 20 is 50 μm or more, at least one layer arranged on the surface side of the resin sheet 100 is less susceptible to the influence of air bubbles contained in the foam layer 10 laminated by coextrusion. The thickness of the transparent resin layer 20 is preferably 70 μm or more, more preferably 100 μm or more, further preferably 200 μm or more, particularly preferably 300 μm or more, and preferably 600 μm or more. Most preferred.

Further, the thickness of the transparent resin layer 20 is preferably in the relationship of the following formula (1) with respect to the average cell diameter ([D]).
[Number 1]
Average bubble diameter of bubbles contained in the foam layer ([D]) (μm) / Thickness of transparent resin layer ([T]) (μm) ≤ 2 (1)
By ensuring that the thickness of the transparent resin layer 20 is appropriately large with respect to the average cell diameter of the foam layer 10, the bubbles contained in the foam layer 10 significantly affect the surface smoothness of the transparent resin layer 20. It is possible to avoid it. From the above viewpoint, the D / T value is more preferably 1.6 or less, further preferably 1 or less, and particularly preferably 0.5 or less.

Since the arithmetic average roughness (Ra) of the transparent resin layer 20 is 0.7 μm or less, the surface smoothness of the resin sheet is excellent. From the above viewpoint, the arithmetic mean roughness (Ra) is more preferably 0.5 μm or less, further preferably 0.2 μm or less, and particularly preferably 0.05 μm or less. The arithmetic average roughness (Ra) of the transparent resin layer 20 can be measured in accordance with JIS B0601: 2001.

Since the 20-degree mirror surface gloss of the transparent resin layer 20 is 50% or more, the surface gloss of the resin sheet is excellent. From the above viewpoint, the 20-degree mirror glossiness of the transparent resin layer 20 is more preferably 70% or more, and further preferably 100% or more. Further, the mirror glossiness of the transparent resin layer 20 at 60 degrees and 85 degrees is preferably 50% or more, and more preferably 100% or more. The 20-degree, 60-degree, and 85-degree mirror glossiness of the transparent resin layer 20 can be measured in accordance with JIS Z8741: 1997.

The surface 22 of the resin sheet 100 on the transparent resin layer 20 side is preferably a mirror roll transfer surface 122 because the above-mentioned arithmetic mean roughness and 20-degree mirror glossiness can be easily realized. The mirror surface roll transfer surface 122 means a surface on which the state of the surface of the roll whose surface has been mirror-finished is transferred. The mirror roll transfer surface 122 is formed by passing a laminate having at least one co-extruded foam layer 10 and a transparent resin layer 20 arranged on the surface side between two opposing rolls and rotating the rolls in a predetermined direction. It is formed by transferring the mirror surface state of the roll surface to the transparent resin layer 20 by taking it over.

Details of a desirable manufacturing method of the resin sheet 100 including the formation of the mirror surface roll transfer surface 122 described above will be described later.

Next, the intermediate transparent resin layer 30 will be described. As shown in FIG. 1B, the intermediate transparent resin layer 30 includes a foam layer 10 (first foam layer 131) and a foam layer 10 (second foam layer 132) in the resin sheet 100 having a plurality of foam layers 10. ) Is placed between. The intermediate transparent resin layer 30 is an arbitrary layer in the present invention. The rigidity of the resin sheet 100 can be increased by providing the intermediate transparent resin layer 30. Further, the multilayer resin sheet 100 provided with the intermediate transparent resin layer 30 and having a plurality of foam layers 10 diffuses light more effectively than the resin sheet 100 composed of one foam layer 10 at the same foaming magnification. The resin sheet 100 can be made to be excellent in designability, or can exhibit the same diffusivity even if the thickness is thin, and is excellent in light weight. From the above viewpoint, when the resin sheet 100 is more excellent in design and lightness, it is preferable to use the resin sheet 100 having a plurality of foam layers 10, and among them, the resin sheet 100 is easy to manufacture, so it has a five-layer structure (transparent). It is particularly preferable to use the resin layer 20 / foamed 131 / intermediate transparent resin layer 30 / foamed layer 132 / transparent resin layer 20).

The intermediate transparent resin layer 30 can be formed by coextruding together with the foam layer 10 and the transparent resin layer 20 using a resin having the same composition as the thermoplastic resin that can be used for the foam layer 10 and / or the transparent resin layer 20. it can. The thickness of the intermediate transparent resin layer 30 is not particularly limited, and can be determined in consideration of the thicknesses of the resin sheet 100, the foam layer 10, and the transparent resin layer 20. From the viewpoint of achieving both sufficient rigidity and light weight of the resin sheet 100, the thickness of the intermediate transparent resin layer 30 with respect to the total thickness of the resin sheet 100 is preferably 20% or more and 70% or less, and 25% or more and 65% or more. % Or less, more preferably 30% or more and 60% or less. When the resin sheet 100 has a plurality of intermediate transparent resin layers, it is preferable that each of the intermediate transparent resin layers satisfies the above ratio.

[2] Method for Manufacturing Resin Sheet Next, a method for manufacturing the resin sheet 100 (hereinafter, also referred to as the present manufacturing method) will be described with reference to FIG. FIG. 2 is an explanatory diagram illustrating a method for manufacturing the resin sheet 100 of the present invention, and is a coextruding device 300 connecting at least two extruders, a T-die 310, and a plurality of take-up rolls (in the present embodiment, the first). A laminated body 150 (hereinafter, also referred to as a molten laminated body 150) in a molten state formed by co-extruding a plurality of resin materials using one roll 320, a second roll 330, and a third roll 340) faces each other. It shows a state in which the resin sheet 100 is manufactured by taking it in a predetermined direction while narrowly pressing it with two rolls.
In this manufacturing method, a resin material containing a molten thermoplastic resin is introduced into each of the plurality of extruders, and the resin material is further introduced into the T die 310 and laminated and merged into the T die 310. The resin sheet 100 of the present invention is produced by discharging the resin sheet 100 from the provided lip 311 and then cooling the resin sheet 100. In this production method, a resin material containing a foaming agent is introduced into at least one of the plurality of extruders, and a resin material containing no foaming agent is introduced into at least one of the other extruders. A resin sheet 100 is manufactured by coextruding in a state where the transparent resin layer 20 which is a foamed layer is laminated. The stacking order of the resin materials extruded from each extruder and laminated and merged is the same as the stacking configuration of the resin sheet of the present invention described above.
The melting temperature (extrusion temperature) of the resin constituting each layer is not particularly limited and varies depending on the type of resin used, but from the viewpoint of obtaining a resin sheet 100 having an excellent balance of surface smoothness and mechanical properties. Therefore, the extrusion temperature is preferably in the range of 160 ° C. or higher and 260 ° C. or lower, more preferably in the range of 170 ° C. or higher and 250 ° C. or lower, and further preferably in the range of 180 ° C. or higher and 240 ° C. or lower. ..

In the present production method, it is preferable to further include the following steps in order to improve the smoothness and appearance of the transparent resin layer 20 in the resin sheet 100. That is, the cooling take-up section that takes over the resin sheet 100 by sandwiching the molten laminate 150 discharged from the lip 311 between the opposing rolls (first roll 320 and the second roll 330) and taking it in a predetermined direction and cooling it. 360 is provided. Here, by mirror-processing the surface of at least one of the opposing rolls, it is possible to transfer the mirror surface property of the surface to the surface of the resin sheet 100 (hereinafter, also simply referred to as mirror surface transfer). .. As a result, the resin sheet 100 having a smooth surface can be formed. According to such a manufacturing method, the non-foaming transparent resin layer 20 can be arranged on the surface of the manufactured resin sheet, and the foamed layer 10 laminated on the transparent resin layer 20 can be arranged, which is lightweight. A resin sheet 100 having good surface smoothness can be produced.

The present manufacturing method for manufacturing the resin sheet 100 will be specifically described below. In the following description, when it is referred to as upstream or downstream without particular notice, the side close to the coextruder 300 from an arbitrary point in the extrusion direction of the laminate 150 extruded from the coextruder 300 is referred to as the upstream side. The side far from the coextrusion device 300 from the relevant point is called the downstream side.

As the T-die 310 used when coextruding a plurality of resin layers, for example, a T-die called a multi-manifold die is used. The multi-manifold die is a T-die having a plurality of manifolds inside and capable of merging the molten resins extruded from each manifold in a laminated state and discharging them from the die. Further, instead of using the above-mentioned multi-manifold, the molten resin attached between each extruder and the T-die and extruded from each extruder as described in the direction of JP-A-55-117636 is laminated and merged. It is also possible to use a device called a feed block that is made to have a multi-layer structure.

The molten laminate 150 discharged from the lip 311 provided on the T-die 310 is sent to the cooling take-up unit 360. The cooling mechanism in the cooling trading unit 360 is not particularly limited, but in general, any or all of the rolls facing each other provided in the cooling trading unit 360 may be used as cooling rolls. Examples of the cooling roll include those in which the roll has a double structure of an inner cylinder and an outer cylinder, and the surface of the roll is cooled by flowing a cooling solvent between them. The resin sheet 100 is manufactured by passing the molten laminate 150 between two opposing rolls (for example, the first roll 320 and the second roll) and taking it in a predetermined direction while cooling it. In the resin sheet 100 produced in this way, a transparent resin layer 20 made of a non-foaming resin is arranged on the surface side, and the transparent resin layer 20 exhibits excellent surface smoothness.

In order to improve the surface smoothness of the resin sheet 100, it is preferable to arrange a mirror-finished roll on the cooling take-up portion 360 and transfer the surface of the roll to the transparent resin layer 20 of the resin sheet 100. As a result, the surface of the transparent resin layer 20 can be used as a mirror roll transfer surface.
A general method for transferring the surface of a mirrored roll to the surface of a resin sheet is as follows. Mirror-finished rolls, which are general metal rolls that do not substantially exhibit elasticity on the surface, are arranged facing each other at appropriate intervals. The resin material (molten laminate) is discharged from the extruder to the facing portion where the rolls arranged facing each other are closest to each other, and a liquid pool (so-called bank) of the resin material is formed on the upstream side of the facing portion. , Take up the molten laminate in the downstream direction. Thereby, the surface of the roll can be transferred to the surface of the molten laminate passing through the facing portion to form a mirror roll transfer surface. However, in the case of producing the resin sheet 100 including the foam layer 10, when the resin sheet 100 is passed between the first roll 320 and the second roll 330 which are arranged to face each other with the liquid pool formed, the bubbles contained in the foam layer 10 are broken. It is easy to foam, which may deteriorate the appearance of the resin sheet 100.

Therefore, as a more preferable embodiment, one roll (for example, the first roll 320) is a touch roll having elasticity on the roll surface, and the opposite roll (for example, the second roll 330) receives the molten laminate 150 and takes over. It is good to use a cast roll to be sent to. In such an embodiment, by feeding the molten laminate 150 while pressing it against the cast roll with the touch roll, it is possible to suppress the formation of the liquid pool (bank) and take it in a predetermined direction while performing cooling and mirror transfer. .. Here, it is preferable that the surface of the cast roll is mirror-finished. In such an embodiment, the elasticity of the touch roll facing the cast roll suppresses the formation of the bank, and the molten laminate 150 discharged from the lip 311 can be smoothly introduced between the facing rolls, and bubbles can be introduced. It is possible to manufacture a resin sheet 100 which is prevented from breaking bubbles and has an excellent appearance.

As the cast roll, a general metal roll that does not substantially exhibit elasticity on the surface and has a mirror-finished surface can be used. Preferably, the cast roll is a cooling roll. As a result, cooling can be performed at the same time while pressing the molten laminate 150.

On the other hand, the touch roll is a roll having elasticity on the surface, and a typical one is a soft touch roll whose roll surface is made of a rubber member such as silicone rubber, or a metal member whose roll surface is steel or the like. It is a constructed hard touch roll. The hard touch roll also includes a roll having a thin film metal layer on the surface of an elastic member such as a silicone rubber roll.
Due to the elastic deformation of the surface of the touch roll, the molten laminate 150 can be easily pressed uniformly against the opposite cast rolls, and the molten laminate 150 can be pressed evenly. As a result, the surface of one side of the molten laminate 150 and the mirror-finished surface of the cast roll can be sufficiently adhered, and the mirror-finished surface is evenly transferred to the surface of the molten laminate 150. can do. As a result, the resin sheet 100 having excellent surface smoothness and suppressed gloss unevenness can be manufactured.
A soft touch roll is more preferable from the viewpoint that the elastic deformation of the surface is larger and the molten laminate 150 is easily pressed against the opposite cast roll. In general, the soft touch roll has a lower cooling efficiency on the surface than the hard touch roll, but for example, as shown in FIG. 2, the cooling roll is located downstream of the first roll 320, which is the soft touch roll. By further providing the three rolls 340, the cooling efficiency of the cooling take-up unit 360 can be increased. As shown in FIG. 2, the third roll 340 is arranged to face the second roll 330 at a position where an appropriate gap is maintained, for example. In such an embodiment, the molten laminate 150 is sent out while being cooled while the molten laminate 150 is pressed against the second roll 330, which is a cooling roll, by the first roll 320, which is a touch roll, and then the second roll 330 and the second roll 330. The resin sheet 100 is manufactured by being sent out while being cooled while being narrowed between the three rolls 340 and the three rolls 340. By providing the third roll 340, which is a cooling roll, both sides of the molten laminate 150 (resin sheet 100) can be efficiently cooled. The auxiliary roll 350 in the drawing is an auxiliary member for adjusting the tension of the resin sheet 100 to be taken in a predetermined direction.
Further, as the third roll 340, a general metal roll that does not substantially exhibit elasticity on the surface and has a mirror-finished surface may be used. It is more preferable that the mirror-finished third roll 340 is a cooling roll. By arranging the mirror-processed third roll 340 facing the second roll 330, the surface facing the second roll 330 can be mirror-transferred, and both sides of the molten laminate 150 can be mirror-transferred. ..

In the above, the method of manufacturing the resin sheet 100 having a three-layer structure shown in FIG. 1A has been described as the present manufacturing method, but this is an example, and a resin sheet having a layer structure other than the three-layer structure is manufactured. In this case, using a distribution pin and a multi-manifold die corresponding to the number of target layers, or a distribution pin and a feed block, a thermoplastic resin constituting each layer is introduced into each extruder and laminated on the T die 310. It is preferable to form the molten laminate 150 by discharging with. The gap between the opposing rolls (for example, the first roll 320 and the second roll 330) can be appropriately adjusted in consideration of the thickness of the manufactured resin sheet.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to these examples. The evaluation method of each evaluation item used in Examples and Comparative Examples is as follows, and the results are shown in Table 1. The amount of the foaming agent used for the foam layer in each resin sheet (the amount of the foaming agent MB added in 100 parts by mass of the resin constituting the foam layer (parts by mass)) is shown in Table 1.
<Layer thickness measurement method>
The total thickness of the resin sheet, the thickness of the outermost transparent resin layer, the thickness of the intermediate transparent resin layer, and the thickness of the foamed layer were measured as follows. The resin sheet was cut in the thickness direction with a microtome to form a cross section. The cut surface was magnified and photographed with a microscope (Digital Microcorp VHX-900 manufactured by KEYENCE CORPORATION) at a magnification of 50 times. Based on the obtained photographs, the total thickness of the resin sheet in the thickness direction, the thickness of the outermost transparent resin layer, the thickness of the intermediate transparent resin layer, and the thickness of the foamed layer were randomly measured at 10 points, respectively. The arithmetic mean value was calculated and used as the total thickness, the thickness of the outermost transparent resin layer, the thickness of the intermediate transparent resin layer, and the thickness of the foamed layer. When a plurality of transparent resin layers and foamed layers on the outermost surface were present, they were divided into front and back surfaces, and arithmetic mean values measured at 10 points at random were adopted for each.
<Calculation method of total thickness ratio α of foam layer>
The ratio of the total thickness of the foamed layer to the total thickness of the resin sheet obtained by the above-mentioned measurement of the layer thickness was calculated, and the total thickness ratio α (%) of the foamed layer was calculated. The total thickness of the foamed layer means the thickness of the foamed layer when the foamed layer is one layer in the resin sheet, and the total thickness of each foamed layer when the foamed layer is a plurality of layers. To do.
<Measurement method of mirror gloss>
Using each of the resin sheets obtained in Examples and Comparative Examples, the mirror glossiness at incident angles of 20 degrees, 60 degrees, and 85 degrees was measured by a method according to JIS Z8741: 1997. PG-IIM manufactured by Nippon Denshoku Industries Co., Ltd. was used for the measurement of the mirror surface gloss.
<Evaluation method of surface smoothness>
Arithmetic mean roughness (Ra) and 10 points were used as evaluations of the surface smoothness of the transparent resin layer, which is the outermost layer, by a method in accordance with JIS B0601: 2001 using the resin sheets obtained in Examples and Comparative Examples. Average roughness Rzjis) was measured. For the above measurement, SE1700α manufactured by Kosaka Laboratory Co., Ltd. was used, and the measurement was performed under the condition of cutoff λc = 0.8 mm.
<Measuring method of foaming magnification of foamed layer>
Sheets containing only the transparent resin layer provided on the resin sheets in each Example and Comparative Example were prepared in advance, and the mass per unit volume was confirmed and used as the standard mass. The total basis weight was measured using the resin sheets having the predetermined shapes obtained in Examples and Comparative Examples, and the weighing of the transparent resin layer was calculated from the thickness of the transparent resin layer and the standard mass in the measurement result of the layer thickness. .. The basis weight of the foamed layer was calculated from the total basis weight, the basis weight of the transparent resin layer, and the standard mass, and the magnification of the foamed layer was calculated.
<Measuring method of average cell diameter D in foam layer>
Each resin sheet was cut in the width direction with a microtome to prepare a cut surface, and each cut surface was magnified and photographed at a magnification of 50 times with the above-mentioned microscope (epi-illumination mode). Based on the obtained photograph, the major axis of the bubble whose entire shape was confirmed on the cut surface was measured, and the average value was calculated to obtain the average cell diameter D. In addition, the bubbles whose entire shape has been confirmed are those in which a part of the shape is missing or cut, or the bubbles whose outer shape is unclear by being integrated with the adjacent bubbles, etc. It is a bubble.
<Method of measuring the number of fine bubbles in the foam layer (plane)>
A 100-fold magnified image was taken with a microscope from substantially perpendicular to the in-plane direction of the resin sheet so that the extrusion direction and the width direction of each resin sheet were vertical and horizontal. Based on the obtained photographs, the number of clear bubbles in the outer shell existing within the range of 2 mm in the extrusion direction and 2 mm in the width direction of the foam layer was measured. The measurement result was converted into a unit of the number per 1 mm ^{2, and} the number of bubbles in the foamed layer was determined. In measuring the number of bubbles, bubbles having only a part within the range of 2 mm in the extrusion direction and 2 mm in the width direction, that is, bubbles on the boundary line within the range were excluded.
<Method of measuring the number of bubbles in the foam layer (cross section)>
Each resin sheet was cut with a microtome in the width direction to form a cross section, and the cross section was magnified and photographed at 50 times with the above-mentioned microscope (emergence mode). Based on the obtained photographs, the number of bubbles existing in the width direction of 6 mm and in the thickness direction (thickness region) of one foam layer was counted. At this time, the number of bubbles having a major axis of 500 μm or less was measured as the number X of fine cells, and the number of bubbles having a major axis exceeding 500 μm was measured as the number Y of large bubbles. The measurement result was converted into a unit of the number per 1 mm ^2, and the number X of fine bubbles and the number Y of large bubbles in the foamed layer were obtained.
In addition, the ratio of the number Y of large bubbles to the total of the number X of fine cells and the number Y of large cells per unit area was calculated and is also shown in Table 1.
In measuring the number of bubbles, the bubbles having a width of 6 mm and only a part of the bubbles existing in the range of the thickness direction (thickness region) of one foam layer, that is, the bubbles on the boundary line within the range Excluded.
<Evaluation of optical properties>
Haze (Hz) randomly cuts three test pieces of 50 mm × 50 mm size (thickness is the thickness of the resin sheet) from the resin sheet, and according to JIS K7136 (2000), a turbidity meter (Nippon Denshoku Industries Co., Ltd.) The haze of the test piece was measured using a company-made Haze Meter NDH7000SP). The arithmetic mean values of the three test pieces obtained are shown in Table 1 as hertz (Hz).
The total light transmittance (TT) was measured by preparing a test piece in the same manner as above and using a turbidity meter (Haze Meter NDH7000SP manufactured by Nippon Denshoku Industries Co., Ltd.) in accordance with JIS K7361-1: 1997. .. The arithmetic mean values of the three test pieces obtained are shown in Table 1 as total light transmittance (TT).
<Appearance evaluation>
The surface of one side of the resin sheet was visually observed from a distance of 1 m under an indoor light and evaluated as follows.
It had smoothness and luster, and the appearance was very good.
It was smooth or glossy and had a good appearance ...
Roughness was seen and the appearance was poor.
<Bubbling evaluation>
During the production of the resin sheet, a visual evaluation was performed to see if a bubble rupture phenomenon occurred when passing between the first roll and the second roll and when passing between the second roll and the third roll. The above visual evaluation was performed by visually observing the appearance of the sheet passing between the rolls under an indoor light and evaluating the presence or absence of bubble rupture.

The resin sheets of the following Examples and Comparative Examples have a plurality of single-screw extruders and a multi-manifold type laminated T-die (lip width (w) 300 mm) connected to all of the plurality of single-screw extruders. An attached coextruder was used. The shaft diameter of each single-screw extruder and the resin introduced therein are shown in the following description of each Example and Comparative Example. The lip spacing of the T-die was 4.5 mm, and the parallel land length of the lip portion was 5.0 mm. The resin constituting each layer was introduced into each single-screw extruder, and co-extruded at an extrusion rate of 40 kg / hr. The discharge ratio of each extruder was adjusted so as to have the layer thickness shown in Table 1. Similar to the extruder shown in FIG. 2, the resin discharged from the T-die was sent out by a roll unit composed of a rubber touch roll and a cooling roll, and the roll mirror surface was transferred to prepare a resin sheet which is a thermoplastic resin laminated plate. .. The pick-up speed was adjusted according to the target product thickness. The temperature of each roll was adjusted separately using three oil temperature control pumps.

<Example 1>
Under the following conditions, a resin sheet of 3 types and 5 layers, which is composed of the outermost transparent resin layer, the foamed layer, the intermediate transparent resin layer, the foamed layer, and the outermost transparent resin layer in this order from one surface, is formed. It was prepared and used as Example 1.
A branched polystyrene resin (“HP-780” manufactured by DIC Corporation) for the intermediate transparent resin layer was introduced into a single-screw extruder having a shaft diameter of 65 mm. A single shaft with a shaft diameter of 40 mm, which is a dry blend of branched polystyrene resin for foam layer (“HP-780” manufactured by DIC Corporation) and baking soda-based chemical foaming agent MB (Polythrene ES275 manufactured by Eiwa Kasei Kogyo Co., Ltd.) as a foaming agent. Introduced into the extruder. General-purpose polystyrene (“679” manufactured by PS Japan Corporation) for the transparent resin layer, which is the outermost layer, was introduced into a single-screw extrusion having a shaft diameter of 30 mm.
As described above, the resin material introduced into each extruder was co-extruded from a multi-manifold die equipped with a distribution pin of 3 types and 5 layers in a state of being laminated in 3 types and 5 layers. The discharge ratio of each extruder was appropriately adjusted so that each layer of the manufactured resin sheet had the design thickness. The outermost transparent resin layer having two layers in the thickness direction in Example 1 had the same thickness by adjusting the distribution pin. As for the foamed layer, the two foamed layers had the same thickness. Then, the molten laminate of 3 types and 5 layers was cooled with a roll having the same configuration as that of the cooling take-up unit 360 shown in FIG. 2, and was taken up in a predetermined direction to obtain a resin sheet. As the roll corresponding to the first roll 320 in FIG. 2, a soft touch roll having a surface made of a silicone rubber roll was used, and the surface was mirror-finished as a roll corresponding to the second roll 330 and the third roll 340. A cooling roll which is a metal roll and has a cooling mechanism was used. The configuration of the cooling take-up unit is the same for the examples and comparative examples described later.
<Example 2>
The resin for the intermediate transparent resin layer was a general-purpose polystyrene resin (“680” manufactured by PS Japan Corporation), and the same resin sheet as in Example 1 was used except that the thickness of each layer was changed as shown in Table 1, and the transparent resin layer was used. Example 2 was obtained in which the foam layer, the intermediate transparent resin layer, the foam layer, and the transparent resin layer were formed in this order.
<Example 3>
The same resin sheet as in Example 1 was used except that the thickness of each layer was changed as shown in Table 1, and the layers were composed of a transparent resin layer, a foam layer, an intermediate transparent resin layer, a foam layer, and a transparent resin layer in this order. Example 3 was obtained.
<Example 4>
From one side, a transparent resin layer, a foamed layer, and a transparent resin layer are formed in this order to form a two-kind, three-layer resin sheet, and the thickness of each layer is changed as shown in Table 1, except that the resin sheet is the same as that of Example 1. A resin sheet was prepared in the same manner and used as Example 4.
<Example 5>
A resin sheet similar to that of Example 1 was used except that the thickness of each layer was changed as shown in Table 1, and the transparent resin layer, the foam layer, the intermediate transparent resin layer, the foam layer, and the transparent resin layer were formed in this order. Example 5 was obtained.
<Example 6>
Example 6 was obtained in which the same resin sheet as in Example 4 was used except that the thickness of each layer was changed as shown in Table 1, and the transparent resin layer, the foamed layer, and the transparent resin layer were formed in this order.
<Example 7>
Example 7 was obtained in which the same resin sheet as in Example 4 was used except that the thickness of each layer was changed as shown in Table 1, and the transparent resin layer, the foamed layer, and the transparent resin layer were formed in this order.
<Example 8>
Example 8 was obtained in which the same resin sheet as in Example 4 was used except that the thickness of each layer was changed as shown in Table 1, and the transparent resin layer, the foamed layer, and the transparent resin layer were formed in this order.
<Example 9>
Example 9 was obtained in which the same resin sheet as in Example 4 was used except that the thickness of each layer was changed as shown in Table 1, and the transparent resin layer, the foamed layer, and the transparent resin layer were formed in this order.
<Comparative example 1>
A resin sheet of two types and three layers, in which a foam layer, an intermediate transparent resin layer, and a foam layer are formed in this order from one side without providing the outermost transparent resin layer, was used as Comparative Example 1.
<Comparative example 2>
A resin sheet was prepared in the same manner as in Example 1 except that the thickness of the transparent resin layer on the outermost surface was changed as shown in Table 1, and used as Comparative Example 2.
<Comparative example 3>
A resin sheet was prepared in the same manner as in Example 1 except that the thickness of each layer was changed as shown in Table 1 and the amount of the foaming agent used was increased three times, which was used as Comparative Example 3.

As shown in Table 1, in all the examples, the thickness of the transparent resin layer which is the outermost layer is 50 μm or more, the average cell diameter D of the bubbles contained in the foam layer is 500 μm or less, and the transparent resin layer which is the outermost layer. The surface on the side had an arithmetic mean roughness Ra of 0.7 μm or less and a 20-degree mirror surface gloss of 50% or more. It was confirmed that each of the examples having such a configuration was a resin sheet having a very good or good appearance and satisfying the desired problems of the present invention.

The resin sheet of Example 1 in which the thickness of the transparent resin layer was adjusted to 75 μm and the surface of the roll was transferred to the surface of the transparent resin layer had an arithmetic mean roughness Ra = 0.61 μm and a 20-degree glossiness = 59. , The surface smoothness was good. The resin sheet of Example 5 produced in the same manner as in Example 1 except that the thickness of the transparent resin layer was changed to 245 μm had an arithmetic mean roughness Ra = 0.18 μm and a 20-degree glossiness = 106. The surface smoothness was very good. On the other hand, the resin sheet of Comparative Example 2 produced in the same manner as in Example 1 except that the thickness of the transparent resin layer was changed to 30 μm had an arithmetic mean roughness Ra = 0.72 μm and a 20-degree glossiness = 49. , The surface smoothness was poor. From this, it is understood that the thickness of the transparent resin layer of the resin sheet affects the surface smoothness. From the viewpoint of obtaining good surface smoothness, the above results show that the thickness of the transparent resin layer of the resin sheet of the present invention is 50 μm or more, preferably 200 μm or more.

In Comparative Example 1, the surfaces of the two mirror-finished rolls (second roll 330 and third roll 340) were transferred to the surface of the outermost layer as in the examples, but the surface smoothness was good. I couldn't get it. It is presumed that this is because the outermost layer is not a transparent resin layer but a foamed layer, so that the mirror roll transfer surface was not satisfactorily formed due to the influence of the bubbles formed near the surface of the foamed layer.

In Comparative Example 3, although the thickness of the transparent resin layer was designed to be 50 μm or more, good smoothness could not be obtained. In Comparative Example 3, some of the bubbles in the foamed layer were coalesced, and fine bubbles and large bubbles were mixed. In the foamed layer in Comparative Example 3, large bubbles were significantly measured, and the average cell diameter of the large cells exceeded twice the thickness of the transparent resin layer which is the outermost layer. From this, when the foam layer located under the transparent resin layer has significantly large bubbles that are more than twice the thickness of the transparent resin layer, the large bubbles have an undesired effect on the smoothness of the surface. It was inferred that it could be given.

The above embodiment includes the following technical ideas.
(1) A resin sheet having a total thickness of 500 μm or more and 10000 μm or less, which is made of a thermoplastic resin and in which a foam layer containing bubbles and a transparent resin layer made of a thermoplastic resin are laminated by coextrusion.
The transparent resin layer is located on at least one surface side of the resin sheet, and the thickness of the transparent resin layer is 50 μm or more.
The average bubble diameter of the bubbles in the foam layer in the vertical cross section orthogonal to the extrusion direction of the resin sheet is 500 μm or less.
The arithmetic mean roughness (Ra) of the surface of the resin sheet on the transparent resin layer side measured in accordance with JIS B0601: 2001 is 0.7 μm or less.
A resin sheet having a 20-degree mirror glossiness of a surface on the transparent resin layer side of the resin sheet measured in accordance with JIS Z8741: 1997 of 50% or more.
(2) The resin sheet according to 1 above, wherein the surface of the resin sheet on the transparent resin layer side is a mirror roll transfer surface.
(3) The above 1 or 2 in which the number of bubbles having a bubble diameter of 500 μm or less in a unit area of the foam layer observed from substantially perpendicular to the in-plane direction of the resin sheet is 10 cells / mm ² or more. Resin sheet.
(4) Any one of 1 to 3 above, wherein the ratio of the number of bubbles having a bubble diameter of more than 500 μm to the number of total cells in the foam layer in the vertical cross section orthogonal to the extrusion direction of the resin sheet is 1% or less. The resin sheet described in.
(5) The resin sheet according to any one of 1 to 4 above, wherein the transparent resin layers are located on both surfaces of the resin sheet and each has a thickness of 50 μm or more.
(6) The resin sheet according to any one of 1 to 5 above, which has a plurality of the foamed layers and has an intermediate transparent resin layer between one foamed layer and the other foamed layer.
(7) The resin sheet according to any one of 1 to 6 above, wherein the thickness of the transparent resin layer located on at least one surface of the resin sheet is 200 μm or more.
(8) The resin sheet according to any one of 1 to 7 above, wherein the foaming ratio of the foamed layer exceeds 1 times and is 2 times or less.
(9) The resin sheet according to any one of 1 to 8 above, wherein the ratio (α) of the total thickness of the foamed layer to the total thickness of the resin sheet is 25% or more and 60% or less.

10 ... Foam layer 20 ... Transparent resin layer 22 ... Surface 30 ... Intermediate transparent resin layers 100, 200, 220 ... Resin sheet 122 ... Mirror surface roll transfer surface 131 ... First Foam layer 132 ... Second foam layer 150 ... Laminated body 300 ... Single shaft extruder 310 ... T die 311 ... Lip 320 ... First roll 330 ... Second Roll 340 ... Third roll 350 ... Auxiliary roll 360 ... Cooling trading department

Claims (9)

A resin sheet having an overall thickness of 1000 μm or more and 10000 μm or less, which is made of a thermoplastic resin and is formed by laminating a foam layer containing bubbles and a transparent resin layer made of a thermoplastic resin by coextrusion.
The foaming ratio of the foamed layer is 1.1 times or more,
The transparent resin layer is located on at least one surface side of the resin sheet, and the thickness of the transparent resin layer is 50 μm or more.
The average bubble diameter of the bubbles in the foam layer in the vertical cross section orthogonal to the extrusion direction of the resin sheet is 120 μm or more and 500 μm or less.
The number of bubbles having a bubble diameter of 500 μm or less in the unit area of the foam layer in the vertical cross section orthogonal to the extrusion direction of the resin sheet is 27.0 cells / mm ² or more.
The haze of the resin sheet is 95% or more,
The arithmetic mean roughness (Ra) of the surface of the resin sheet on the transparent resin layer side measured in accordance with JIS B0601: 2001 is 0.7 μm or less.
A resin sheet having a 20-degree mirror glossiness of a surface on the transparent resin layer side of the resin sheet measured in accordance with JIS Z8741: 1997 of 50% or more. The resin sheet according to claim 1, wherein the surface of the resin sheet on the transparent resin layer side is a mirror roll transfer surface. The number of bubbles following cell diameter 500μm in a unit area of the foam layer, 10 / mm ² or more in the resin according to claim 1 or 2, which is observed from the pair Shi vertical upward in the in-plane direction of the resin sheet Sheet. The method according to any one of claims 1 to 3, wherein the ratio of the number of bubbles having a bubble diameter of more than 500 μm to the number of total cells in the foam layer in the vertical cross section orthogonal to the extrusion direction of the resin sheet is 1% or less. Resin sheet. The resin sheet according to any one of claims 1 to 4, wherein the transparent resin layer is located on both surface sides of the resin sheet. The resin sheet according to any one of claims 1 to 5, which has a plurality of the foamed layers and has an intermediate transparent resin layer between one foamed layer and the other foamed layer. The resin sheet according to any one of claims 1 to 6, wherein the thickness of the transparent resin layer located on at least one surface side of the resin sheet is 200 μm or more. The resin sheet according to any one of claims 1 to 7, wherein the foaming ratio of the foamed layer is 1.1 times or more and 2 times or less. The resin sheet according to any one of claims 1 to 8, wherein the ratio (α) of the total thickness of the foamed layer to the total thickness of the resin sheet is 25% or more and 60% or less.

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