Forming sheet

Abstract

To enhance significantly the rigidity and strength of the resin sheet without substantially increasing or decreasing the actual thickness of the resin sheet itself.SOLUTION: In a molded sheet formed by transferring a protruding and recessed shape onto the surface of a resin sheet, the protrusions are uniformly arranged within the plane as a single shape unit, such as a cylindrical or polygonal prism shape, as shown in the honeycomb shape of Figure 1, and the resin sheet is a biaxially oriented resin sheet, such as a biaxially oriented polypropylene sheet.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a shaped sheet. [Background technology]

[0002] Polypropylene sheets are widely used, primarily for food trays, due to their excellent moldability, heat resistance, and chemical resistance. However, because molded polypropylene sheets lack sufficient mechanical strength, injection molding has been the norm for large molded products such as building materials, vehicles, and automobile parts. On the other hand, molded polypropylene sheets have the advantage of being easily recyclable as a monomaterial, making them suitable for the recent need to reduce environmental impact, and their use in industrial products has been anticipated.

[0003] Therefore, as a method for increasing the rigidity of polypropylene sheet molded products, for example, Patent Document 1 discloses a technology in which multiple sheets of two-type, three-layer oriented polypropylene films, each with a high-melting-point polypropylene film and a low-melting-point polypropylene film on both surface layers, are laminated together and heat-laminated to form a moldable laminated sheet. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. 2020 / 75755 Summary of the Invention [Problem to be solved by the invention]

[0005] The laminated sheet described in Patent Document 1 has a problem in that, because the high rigidity and strength of the sheet itself correlate with its thickness, if a thicker film is made to obtain a stronger resin sheet, it becomes difficult to meet the social need for reducing the amount of plastic used. Furthermore, for example, in a method of increasing the stretch ratio to increase strength, there is a limit to the stretch ratio of the sheet itself, and increasing the stretch ratio results in a thinner thickness, making it difficult to increase the stretch ratio while maintaining a constant thickness. Therefore, the problem to be solved by the present invention is to dramatically improve the rigidity and strength of a resin sheet without significantly increasing or decreasing the substantial thickness of the raw resin sheet itself. [Means for solving the problem]

[0006] As a result of intensive research into solving the above-mentioned problems, the inventors have discovered that by imparting a textured shape by transfer to at least one surface of a resin sheet that has been given strength by biaxial stretching, and by making the convex portions into cylindrical or polygonal pillar shapes that are uniformly arranged within the surface as one shape unit, it is possible to dramatically improve the rigidity and strength of the resin sheet without significantly increasing or decreasing the actual thickness of the resin sheet raw material itself, and have completed the present invention.

[0007] That is, the present invention relates to a shaped sheet obtained by transferring a concave-convex shape onto the surface of a resin sheet, wherein the convex portions are configured so as to be uniformly arranged within the plane as cylindrical or polygonal prism-shaped units, and wherein the resin sheet is a biaxially oriented resin sheet. [Effects of the Invention]

[0008] According to the present invention, it is possible to dramatically improve the rigidity and strength of a resin sheet without significantly increasing or decreasing the substantial thickness of the raw resin sheet itself. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a plan view of a shaped sheet of the present invention. [Figure 2] FIG. 2(1) is an AA end view of the shaped sheet of FIG. 1, and FIG. 2(2) is a conceptual diagram of a cross section of the shaped sheet having an uneven back surface. [Figure 3] FIG. 3 is a photograph of the shaped sheet obtained in Example 1. [Figure 4] FIG. 4 is a partial cross-sectional view of the embossing roll used in Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] As described above, the shaped sheet of the present invention is a shaped sheet obtained by transferring a concave-convex shape to the surface of a resin sheet, and is characterized in that the convex portions are configured so that they are uniformly arranged within the plane as cylindrical or polygonal prism-shaped units, and the resin sheet is a biaxially oriented resin sheet.

[0011] Here, the uneven shape given to the shaped sheet is such that the convex portions are formed uniformly and continuously in the plane with a cylindrical shape or a polygonal prism shape as one shape unit. Here, the cylindrical shape is a circle or an ellipse in a plan view, and the polygonal prism shape is a trigonal to octagonal, rhombic, or parallelogram shape in a plan view. It is preferable that these shape units are formed continuously in a single shape in the plane, but multiple shapes may be mixed, for example, with rhombic shapes present in the gaps between the circular shapes.

[0012] In the present invention, it is particularly preferred that the convex portions have a polygonal columnar shape, and in particular, that they be formed in a so-called honeycomb shape, in which hexagonal columnar shapes, each of which is a hexagonal column as a shape unit, are regularly arranged within the plane, in order to achieve a significant strength improvement effect. An example of such a honeycomb-shaped convex portion is shown in FIG. 1, in which the concave portions of the concave-convex portions are configured to surround the hexagonal convex portions. FIG. 2(1) is an end view taken along the line AA in FIG. 1. Here, for example, it is preferred that the distance W1 between opposing sides of the hexagonal shape is 5 to 10 mm and the width W2 of the concave portions is 0.2 to 2 mm, in order to improve the strength and rigidity of the shaped sheet. Furthermore, the height of the convex portions, i.e., the height h from the bottom of the concave portion excluding the bulging portions to the top of the convex portions, is preferably 3 to 90%, particularly 5 to 60%, of the total sheet thickness H. Furthermore, it is preferred that the total sheet thickness H be 0.2 to 5 mm, particularly 0.3 to 3 mm, in order to achieve a good balance between thinness and strength.

[0013] Furthermore, in the present invention, as shown in Figure 2(1), it is preferable to have a bulge portion a1 on the outer edge of the top surface of the hexagonal prism, as this improves the rigidity and strength of the shaped sheet. Also, when a concave-convex shape is imparted by transfer, a convex portion c may be formed on the back side of the transfer surface so as to face the concave portion b, as shown in Figure 2(2).

[0014] Next, examples of resin materials constituting the resin sheet include crystalline resin sheets such as polyolefins such as polyethylene and polypropylene, polyamide, polyacetal, polyethylene terephthalate, polybutylene terephthalate, polyphenylene sulfide, polyether ether ketone, liquid crystal polymers, and polytetrafluoroethylene; and amorphous resins such as polyvinyl chloride, polystyrene, polymethyl methacrylate, acrylonitrile-butadiene-styrene, polycarbonate, modified polyphenylene ether, polyethersulfone-polyetherimide, and polyamideimide. Among these, polyolefins, polyethylene terephthalate, and polycarbonate are preferred because they are transparent and highly versatile resins, and polyolefins, especially polypropylene, are preferred because of their significant effect of improving strength and rigidity.

[0015] The resin sheet described above is biaxially stretched, and the stretching ratio is, for example, 2 to 10 times in the TD direction and 2 to 10 times in the MD direction, and particularly preferably 3 to 8 times in the TD direction and 3 to 8 times in the MD direction. Furthermore, it is preferable to stretch the sheet in the TD direction and the MD direction simultaneously, that is, by a so-called simultaneous biaxial stretching method. In this case, it is preferable to set the stretching ratio in the TD direction and the MD direction to a range of 3 to 7 times, which is essentially the same, from the viewpoint of achieving both physical strength, moldability, and shape stability.

[0016] Furthermore, when a polypropylene sheet is used as the resin sheet, it is preferable that the crystallinity by X-ray diffraction when the shaped sheet is cut and X-rays are irradiated from the cut surface be 70% or more, as this increases the strength of the resin sheet itself.

[0017] Here, the crystallinity measured by X-ray diffraction may be measured by a conventional method, and can be calculated from the ratio of the peak area of ​​the crystalline component to the total peak area in X-ray diffraction (the peak area of ​​the crystalline component plus the halo pattern area of ​​the amorphous component). For example, it can be measured according to the Hermans-Weiding method described in Weidinger A. Hermans P.H., Macromol Chem Phys [1961:50;98-115]. As mentioned above, the crystallinity must be 70% or more, but a crystallinity of 75% or more, or even 80% or more, is preferred in terms of improving the rigidity of the molded article.

[0018] In addition, the thickness of the resin sheet is preferably 60 μm or more, and particularly 80 μm or more, 90 μm or more, or 150 μm or more is preferred from the standpoint of sheet rigidity, while the upper limit is preferably 400 μm or less, particularly 350 μm or less, from the standpoint of achieving a good balance between the thickness and strength of the shaped sheet.

[0019] Here, when a polypropylene sheet is used as the resin sheet, it is preferable that the molecular weight distribution (Mw / Mn) of the polypropylene constituting the polypropylene sheet is in a relatively wide range of 6 to 20, since this not only results in good film thickness precision, but also allows for both high rigidity and high extensibility, and makes film production easier.

[0020] Furthermore, the polypropylene constituting the polypropylene sheet preferably has a xylene-insoluble content of more than 96.5% by mass and not more than 99.5% by mass. The xylene-insoluble content in polypropylene corresponds to a crystalline isotactic component. In contrast, the xylene-soluble component contained in small amounts in polypropylene corresponds to a non-crystalline atactic component and has a lower molecular weight than the xylene-insoluble component. Furthermore, when the xylene-insoluble content of the polypropylene polymer is more than 96.5% by mass and not more than 99.5% by mass, the rigidity and heat resistance, particularly the rigidity, of the in-mold molded product are improved.

[0021] Furthermore, it is preferable that the crystalline component of the polypropylene has a stereoregularity (mmmm) of 97.5 to 99.5% because this will result in good rigidity, heat resistance, and heat resistance of the molded product obtained by in-mold molding a sheet made of polypropylene.

[0022] The MFR of the polypropylene is 1 to 15 g / 10 min, preferably 2 to 6 g / 10 min. When the MFR is within the above range, the polypropylene has excellent formability when formed into a sheet.

[0023] It is preferable that the polypropylene constituting the resin sheet contains a nucleating agent from the viewpoint of transparency, but in the present invention, by using a smaller amount of this nucleating agent than usual, it is possible to reduce haze and further improve transparency.

[0024] Here, the content of the crystal nucleating agent relative to 100 parts by mass of polypropylene is preferably less than 0.18 parts by mass, and particularly preferably 0.15 parts by mass or less.

[0025] The polypropylene preferably has a crystallization rate parameter (t1 / 2) of more than 1 second, more preferably 2 seconds or more. Decreasing the amount of nucleating agent added tends to decrease the crystallization rate and increase (t1 / 2). When (t1 / 2) is greater than the lower limit, excellent thickness accuracy is likely to be achieved. While there are no particular limitations on the upper limit of (t1 / 2), it is preferably about 5 seconds or less.

[0026] [Other additives] The polypropylene used for the resin sheet may contain additives other than the crystal nucleating agent within a range that does not impair the effects of the present invention. Examples of other additives include conventional additives commonly used in polyolefins, such as antioxidants, neutralizing agents, chlorine absorbers, heat stabilizers, light stabilizers, ultraviolet absorbers, internal lubricants, external lubricants, antiblocking agents, antistatic agents, antifogging agents, flame retardants, dispersants, copper inhibitors, plasticizers, crosslinking agents, peroxides, oil extenders, and other organic and inorganic pigments. The amount of each additive added may be a known amount.

[0027] [Laminated sheet] The resin sheet of the present invention is preferably used as a laminated sheet laminated with a biaxially oriented propylene film, particularly when a thickness of 200 μm or more is required.

[0028] Examples of biaxially oriented films that serve as raw materials for such laminate sheets include AB type, in which a biaxially oriented olefin resin film (B) having a melting point of 110 to 160°C is laminated on one side of a biaxially oriented polypropylene film (A), AAB type, in which a film (A) is laminated on one side of a biaxially oriented polypropylene film (A) and a film (B) is laminated on that, and BAB type, in which a film (B) is laminated on both sides of a biaxially oriented polypropylene film (A), and these can be used in appropriate combinations. Among these, particularly preferred is a film in which multiple BAB type films are stacked and AB type or AAB type films are laminated on both surfaces so that layer A is on the surface.

[0029] The above-mentioned AB type, BAB type and AAB type biaxially stretched films can be produced by the so-called coextrusion method.

[0030] The laminate sheet can be produced by stacking a plurality of the biaxially stretched films described above to form a laminate sheet precursor (pMS), and then by a pressing step of hot-pressing the laminate sheet precursor (pMS) on its surface while heating it. Here, hot-pressing the laminate sheet precursor (pMS) on its surface is preferred because it improves uniformity and allows the production of a laminate sheet with minimal unevenness in physical properties.

[0031] As a method for producing the laminated sheet precursor (pMS) through a pressing step in which the laminated sheet precursor (pMS) is hot-pressed on a surface, for example, a method in which the laminated sheet precursor (pMS) is continuously hot-pressed with a planar mold using a continuous pressure device, and then cold-pressed, can be mentioned.

[0032] The continuous pressure device used here is, for example, a pressure device with a continuous compression molding mechanism (CCM), which has multiple heating zones and cooling zones, and has a mechanism in which the laminated sheet precursor (pMS) is hot-pressed using upper and lower planar dies in the heating zone, and a mechanism that can subsequently, continuously, cool-press the laminated sheet using upper and lower planar dies in the cooling zone to age it.

[0033] The use of such a continuous pressure device increases the degree of freedom in designing the size in the MD direction. In addition, because the sheet is continuously transferred from the heating zone to the cooling zone and pressed, it is possible to obtain a laminated sheet with excellent surface quality and transparency, in addition to excellent uniformity in stiffness and strength.

[0034] The laminated sheet obtained in this manner maintains a moderate degree of orientation of the polypropylene constituting each layer, while the layers are sufficiently fused together, resulting in a laminated sheet with high overall rigidity.As described above, this sheet exhibits unique properties, such as excellent in-plane strength uniformity, minimal physical property irregularities, and uniform strength in the TD direction, especially when made into a large area.

[0035] The biaxially oriented polypropylene sheet obtained in this manner is a multilayer sheet having a structure in which layers a made of biaxially oriented polypropylene film and layers b made of an olefin resin with a melting point of 110 to 160°C are alternately laminated.

[0036] As a method for shaping the resin sheet described above to impart a concave-convex shape, for example, an embossing roll as shown in the cross-sectional view of Figure 4 is used as a heated roll in combination with a rubber roll. Specifically, the resin sheet is heated to near its softening point in advance, introduced into the gap between the embossing roll and the rubber roll, and the resin sheet is pressed against the embossing roll to transfer the concave-convex shape. The shaped resin sheet is then cooled to obtain a shaped sheet.

[0037] [Molded Products] The shaped sheet of the present invention has high strength and rigidity relative to its thickness, and can be used as a structural material as is, or can be processed into various molded products according to the purpose by vacuum forming or vacuum-pressure forming. Furthermore, due to its excellent rigidity, it can be widely used industrially as an aluminum substitute, a CFRP substitute, or a steel plate substitute, and can be used for, for example, automotive exterior materials, automotive interior materials, automotive structural materials, flying car exterior materials, building exterior wall materials, building interior materials, solar cell substrates, perovskite solar cell substrate sheets, quantum stealth optical materials, logistics drone body materials, surfboards, wind power generation blades, ship exterior wall materials, lithium ion battery case materials, lithium ion battery electrode substrates, hydrogen tank structural materials, food trays, medical trays, etc. [Example]

[0038] The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto. (raw materials) BAB co-extruded film 1: manufactured by Santox, layer structure: B / A / B, thickness: 50 μm, thickness ratio of B / A / B: 5 / 90 / 5, stretch ratio: 5x9 A: Polypropylene (ethylene content 0.2% by mass, Mw / Mn = 9, xylene insoluble content 98.2% by mass, mmmm = 98.3, nucleating agent content 0.05% by mass, t1 / 2: 2.3 seconds) B: Ethylene-propylene random copolymer (melting point 151°C) BAA co-extruded film: Co-extruded film manufactured by Santox, Layer structure: B / A / A, Thickness: 50 μm, B / A / A thickness ratio: 5 / 90 / 5, Stretching ratio: 5x9 A: Polypropylene (ethylene content 0.2% by mass, Mw / Mn = 9, xylene insoluble content 98.2% by mass, mmmm = 98.3, nucleating agent content 0.05% by mass, t1 / 2: 2.3 seconds) B: Ethylene-propylene random copolymer (melting point 151°C)

[0039] Example 1 Eighteen sheets of the BAB coextruded film 1 were stacked, and BAA film 1 was layered on both surfaces of the stack with the A layer facing outwards to obtain a precursor (pMS1). The stack was then inserted into a pressure device with a continuous pressure molding mechanism, and a 1 mm thick transparent laminated sheet (MLS) was obtained by repeatedly pressing, releasing the pressure, and feeding out the laminated sheet. Next, the transparent laminated sheet (MLS) was shaped using an embossing device equipped with an embossing roll having honeycomb-shaped projections and recesses with the cross-sectional shape shown in Figure 4 and a rubber roll. The height h of the projections of the resulting shaped sheet was 250 μm. A photograph of the result is shown in Figure 3. The obtained shaped sheet had a higher rigidity than the transparent laminated sheet (MLS) before shaping.

[0040] Example 2 A transparent laminate sheet (MLS) with a thickness of 1 mm was obtained in the same manner as in Example 1, and a shaped sheet with a convex height h of 500 μm was obtained by setting the transfer pressure higher. The obtained shaped sheet had a higher sense of rigidity than the transparent laminate sheet (MLS) before shaping. [Explanation of symbols]

[0041] a Convex part a1 bulge b recess c Convex part on the back

Claims

1. A shaped sheet obtained by transferring a concave-convex shape to the surface of a resin sheet, characterized in that the convex portions are configured so as to be uniformly arranged within the plane as cylindrical or polygonal prism-shaped units, and the resin sheet is a biaxially oriented resin sheet.

2. 2. The shaped sheet according to claim 1, wherein the convex portions of the shaped sheet are each a hexagonal column as a shape unit, and the hexagonal columns are continuously arranged in a honeycomb pattern.

3. 3. The shaped sheet according to claim 2, wherein the convex portion has a hexagonal column shape and has a bulging portion whose outer edge bulges upward.

4. The shaped sheet according to claim 3, wherein the thickness of the shaped sheet excluding the bulging portions of the convex portions is 60 μm or more, and the shaped sheet is made of a polyolefin having a crystallinity of 70% or more by X-ray diffraction when the cut surface of the shaped sheet is irradiated with X-rays.

5. 5. The shaped sheet according to claim 4, wherein the resin sheet is a biaxially oriented polypropylene sheet.

6. The shaped sheet according to claim 5, wherein the biaxially oriented polypropylene sheet is a multilayer sheet having a structure in which layers A made of biaxially oriented polypropylene film and layers B made of an olefin-based resin having a melting point of 110 to 160°C are alternately laminated.

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