Composite materials

Abstract

[The technical problem to be solved] The objective of this invention is to provide a method for breaking a composite material without causing cracks on the end faces of the brittle material layers after the breakage, or severe thermal degradation on the end faces of the resin layers after the breakage, and to obtain sufficient flexural strength in the composite material after the breakage. Technical means to solve the problem The present invention provides a method for forming a composite material by separating a brittle material layer and a resin layer. The method includes the following steps: a resin removal step, in which the resin layer is irradiated with laser light oscillating and excited by a CO2 laser source along a predetermined separation line of the composite material to form a processing groove along the predetermined separation line; and a brittle material removal step, which, after the resin removal step, involves irradiating the brittle material layer with laser light oscillating and excited by an ultrashort pulse laser source along the predetermined separation line to form a processing mark along the predetermined separation line. The processing mark formed in the brittle material removal step opens on the resin layer side and does not penetrate the brittle material layer.

Description

Technical Field

[0001] The present invention relates to a method for breaking a composite material formed by laminating a brittle material layer and a resin layer, and a composite material (composite material sheet) obtainable thereby. In particular, the present invention relates to a method for breaking a composite material without causing cracks on the end surfaces of the broken brittle material layer or severe thermal degradation of the end surfaces of the broken resin layer, and while achieving sufficient bending strength in the broken composite material, and to a composite material obtainable thereby. Prior Art

[0002] The outermost surface of an image display device used in a television or personal computer is often provided with a protective material for protecting the image display device. Typically, a glass plate is used as the protective material. However, as image display devices such as smartphones, smart watches, and in-car displays become increasingly smaller, thinner, and lighter, the demand for thin protective materials that combine both protective and optical functions is increasing. Examples of such protective materials include composite materials composed of a layer of brittle material such as glass, which performs a protective function, and a layer of resin such as polarizing film, which performs an optical function. These composite materials must be cut into predetermined shapes and sizes depending on the intended use.

[0003] Conventionally, as a method for breaking a composite material formed by laminating a brittle material layer and a resin layer, a method described in Patent Document 1 has been proposed. The method described in Patent Document 1 includes the following steps: a resin removal step, in which the resin layer is irradiated with laser light oscillating from a laser light source such as a CO2 laser light source along the predetermined breaking line of the composite material to remove the resin forming the resin layer, thereby forming a processing groove along the predetermined breaking line; and a brittle material removal step, in which, after the resin removal step, the brittle material layer is irradiated with laser light oscillating from an ultrashort pulse laser light source along the predetermined breaking line to remove the brittle material forming the brittle material layer, thereby forming a processing mark along the predetermined breaking line; and the processing mark is a through hole penetrating the brittle material layer. According to the method described in Patent Document 1, a composite material can be separated without causing cracks to form on the end faces of the brittle material layer after separation or without causing serious thermal degradation on the end faces of the resin layer after separation.

[0004] The method described in Patent Document 1 can obtain a predetermined bending strength in the composite material after being cut, but it is still desired to obtain a more sufficient bending strength.

[0005] In addition, Non-Patent Document 1 describes the use of the filamentation phenomenon of ultrashort pulse laser light in processing technology using ultrashort pulse laser light, and the application of a multi-focus optical system or a Besso beam optical system to an ultrashort pulse laser light source. Furthermore, Non-Patent Document 2 describes the two-point bending stress of a thin glass substrate. Prior Art Literature Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-122966 Non-patent literature

[0007] Non-Patent Literature 1: John Lopez et al., “GLASS CUTTING USING ULTRASHORT PULSED BESSEL BEAMS,” [online], October 2015, International Congress on Applications of Lasers & Electro-Optics (ICALEO), [retrieved July 17, 2020], URL: https: / / www.researchgate.net / publication / 284617626_GLASS_CUTTING_USING_ULTRASHORT_PULSED_BESSEL_BEAMS Non-Patent Document 2: Suresh T. Gulati et al., “Two Point Bending of Thin Glass Substrate”, 2011, SID 11 DIGEST, p. 652-654 Summary of the Invention

[0008] Problems that the invention aims to solve The present invention is developed to solve the problems of the above-mentioned prior art. Its purpose is to provide a method for separating a composite material without causing cracks to form on the end faces of the brittle material layer after separation or causing serious thermal degradation of the end faces of the resin layer after separation, and to obtain sufficient bending strength in the composite material after separation, and a composite material that can be obtained thereby.

[0009] Means used to solve problems To solve the aforementioned problems, the present inventors conducted active research and found that by forming processing marks only on the resin layer side of the brittle material layer, sufficient bending strength can be obtained in the composite material after separation, thereby completing the present invention.

[0010] That is, in order to solve the aforementioned problems, the present invention provides a method for cutting a composite material, which is a method for cutting a composite material formed by stacking a brittle material layer and a resin layer, the method comprising the following steps: a resin removal step, which is to irradiate the resin layer along the predetermined cutting line of the aforementioned composite material with laser light oscillating and excited from a laser light source to remove the resin forming the aforementioned resin layer, thereby forming a processing groove along the aforementioned predetermined cutting line; and a brittle material removal step, which is to irradiate the brittle material layer along the aforementioned predetermined cutting line after the aforementioned resin removal step with laser light oscillating and excited from an ultrashort pulse laser light source to remove the brittle material forming the aforementioned brittle material layer, thereby forming a processing mark along the aforementioned predetermined cutting line; the aforementioned processing mark formed in the aforementioned brittle material removal step is open on the side of the aforementioned resin layer and does not penetrate the aforementioned brittle material layer.

[0011] According to the composite material cutting method of the present invention, in the brittle material removal step, the brittle material layer is irradiated with laser light oscillated from an ultrashort pulse laser light source to remove the brittle material forming the brittle material layer. Therefore, cracks are not generated on the end faces of the brittle material layer after the cutting (end faces perpendicular to the thickness direction of the composite material (the direction in which the brittle material layer and the resin layer are stacked)). Furthermore, in the composite material cutting method of the present invention, prior to the brittle material removal step, in the resin removal step, the resin layer is irradiated with laser light oscillated from a laser light source to remove the resin forming the resin layer. Therefore, severe thermal degradation is not generated on the end faces of the resin layer after the cutting (end faces perpendicular to the thickness direction of the composite material (the direction in which the brittle material layer and the resin layer are stacked)). In other words, according to the composite material cutting method of the present invention, a composite material can be cut without causing cracks on the end faces of the brittle material layer after the cutting, or without causing severe thermal degradation on the end faces of the resin layer after the cutting. Furthermore, according to the composite material breaking method of the present invention, the processing marks formed during the brittle material removal step open on the resin layer side and do not penetrate the brittle material layer. In other words, during the brittle material removal step, the processing marks are formed only on the resin layer side of the brittle material layer. Therefore, as recognized by the present inventors, sufficient bending strength can be achieved in the composite material after breaking.

[0012] Furthermore, in the composite material cutting method of the present invention, the phrase "irradiating the resin layer with laser light along the intended cutting line of the composite material" means irradiating the resin layer with laser light along the intended cutting line as viewed through the thickness of the composite material (the direction in which the brittle material layer and the resin layer are stacked). Furthermore, in the composite material cutting method of the present invention, the phrase "irradiating the brittle material layer with laser light along the intended cutting line" means irradiating the brittle material layer with laser light along the intended cutting line as viewed through the thickness of the composite material (the direction in which the brittle material layer and the resin layer are stacked). Furthermore, in the composite material cutting method of the present invention, the type of laser light source used in the resin removal step is not particularly limited, as long as it can remove the resin forming the resin layer by oscillating laser light. However, from the perspective of increasing the relative movement speed of the laser light relative to the composite material (processing speed), a CO2 laser light source or a CO2 laser light source that can oscillate laser light with a wavelength in the infrared region is preferably used. Furthermore, in the composite material breaking method of the present invention, the processing mark formed in the brittle material layer removal step can be a dotted line processing mark along the predetermined breaking line, or can be a processing mark connected along the predetermined breaking line by setting the relative movement speed of the laser light excited by the oscillation of the ultrashort pulse laser light source and the brittle material layer along the predetermined breaking line to be smaller, or by setting the repetition frequency of the pulse oscillation of the ultrashort pulse laser light source to be larger. Furthermore, in the composite material cutting method of the present invention, when the composite material has resin layers laminated on both sides of the brittle material layer, "opening on the resin layer side" means opening on the side of any one of the resin layers on both sides.

[0013] In the aforementioned brittle material removal step of the composite material separation method of the present invention, the depth of the aforementioned processing mark can be adjusted, for example, by adjusting the power of the laser light oscillated and excited by the aforementioned ultrashort pulse laser light source, and the positional relationship between the focus of the laser light oscillated and excited by the aforementioned ultrashort pulse laser light source and the aforementioned brittle material layer. In the preferred method described above, "the positional relationship between the focal point of the laser beam and the brittle material layer" refers to the positional relationship with respect to the thickness direction of the composite material. Furthermore, in the preferred method described above, "the depth of the processing mark" refers to the distance between one end of the processing mark on the resin layer side (the open end of the processing mark) and the bottom of the processing mark on the brittle material layer side (the end of the processing mark opposite the open end). In the preferred method described above, the intensity of the energy used to form the processing mark (removing the brittle material) can be adjusted by adjusting the power of the laser beam. Furthermore, by adjusting the positional relationship between the laser beam's focus and the brittle material layer, the energy used to form the processing mark can be distributed along the thickness direction of the composite material along the intended separation line. Therefore, according to the preferred method described above, the brittle material can be removed only on the resin layer side of the brittle material layer, resulting in a processing mark formed only on the resin layer side of the brittle material layer. Furthermore, the depth of the processing mark can be adjusted.

[0014] According to the present inventors, the smaller the depth of the processing mark, the more sufficient bending strength can be obtained in the composite material after separation. Therefore, in the composite material cutting method of the present invention, ideally, the depth of the processing mark is less than 90% of the thickness of the brittle material layer, and more preferably less than 65%. In addition, if the depth of the machining mark is too small, the composite material cannot be separated. Therefore, the depth of the machining mark should be at least 10% of the thickness of the brittle material layer. In the above preferred method, "the depth of the aforementioned processing marks is less than 90% of the thickness of the aforementioned brittle material layer, preferably less than 65%" means that the average depth of the processing marks along the predetermined breaking line is less than 90% of the thickness of the brittle material layer, preferably less than 65%.

[0015] The composite material cutting method of the present invention preferably further includes a composite material cutting step, wherein the composite material cutting step is performed after the aforementioned brittle material removal step, by applying an external force along the aforementioned predetermined cutting line to thereby cut the aforementioned composite material. According to the above preferred method, the composite material can be separated reliably.

[0016] In the composite material cutting method of the present invention, the thickness of the brittle material layer is, for example, greater than 5 μm and less than 200 μm.

[0017] In addition, in order to solve the aforementioned problems, the present invention also provides a composite material, which is formed by laminating a brittle material layer and a resin layer; wherein the surface roughness of a first portion on the resin layer side of at least one end face of the brittle material layer is greater than the surface roughness of a second portion on the side opposite to the resin layer of the one end face of the brittle material layer. The composite material of the present invention is a composite material (composite material sheet) obtained by the aforementioned composite material dividing method of the present invention. When the composite material of the present invention is obtained by the composite material dividing method of the present invention, a first portion of the end surface of the brittle material layer of the composite material of the present invention corresponds to a portion where a processing mark is formed, and a second portion of the end surface of the brittle material layer corresponds to a portion where no processing mark is formed. The composite material of the present invention does not have the entire end surface of the brittle material layer as the first part with a large surface roughness, but rather a part of the end surface close to the resin layer is the first part, and the remaining part is the second part with a small surface roughness, so it has sufficient bending strength.

[0018] Specifically, regarding the composite material of the present invention, the surface roughness of the first portion is less than 300 nm in terms of the calculated average height Sa, and the surface roughness of the second portion is less than 12 nm in terms of the calculated average height Sa. The surface roughness of the first portion, as measured by the arithmetic mean height Sa, is preferably less than 120 nm, more preferably less than 100 nm, even more preferably less than 80 nm, and most preferably 50 nm. Furthermore, the surface roughness of the first portion, as measured by the arithmetic mean height Sa, is preferably not less than 12 nm. The arithmetic mean height Sa is specified by ISO 25178 and is a parameter that expands the arithmetic mean roughness Ra into three dimensions.

[0019] According to the present inventors' understanding, the smaller the thickness of the first portion with large surface roughness (the dimension of the first portion along the thickness direction of the brittle material layer) is, the more sufficient bending strength can be obtained in the composite material. Therefore, in the composite material of the present invention, the thickness of the first portion is ideally less than 90% of the thickness of the brittle material layer, and more preferably less than 65%. In the above preferred configuration, "the thickness of the aforementioned first portion is less than 90% of the thickness of the aforementioned brittle material layer, preferably less than 65%" means that the average value of the thickness of the first portion in the end face of the brittle material layer is less than 90% of the thickness of the brittle material layer, preferably less than 65%.

[0020] In the composite material of the present invention, the thickness of the brittle material layer is, for example, not less than 5 μm and not more than 200 μm.

[0021] According to the composite material of the present invention, a flexural strength of 200 MPa or more can be obtained when the composite material is bent into a convex protrusion on the side of the brittle material layer. “The flexural strength of the composite material is 200 MPa or more” means that the average flexural strength of a plurality of composite materials having the same ratio of the thickness of the first portion to the thickness of the brittle material layer is 200 MPa or more. Effects of the Invention

[0022] According to the present invention, a composite material can be severed without causing cracks to form on the end faces of the brittle material layer after the separation, or causing serious thermal degradation on the end faces of the resin layer after the separation, and sufficient bending strength can be obtained in the composite material after the separation. Simple diagram description

[0023] FIG1 is an explanatory diagram schematically illustrating the procedure of a composite material cutting method according to a first embodiment of the present invention. FIG. 2 is an explanatory diagram schematically illustrating the procedure of the composite material cutting method according to the first embodiment of the present invention. FIG3 is a diagram schematically illustrating an example of a method for forming a processing mark in the brittle material removal step of the composite material dividing method according to the first embodiment of the present invention. FIG4 is a cross-sectional view schematically showing the structure of a composite material sheet after being cut in the composite material cutting step of the cutting method according to the first embodiment of the present invention. FIG5 is an explanatory diagram schematically illustrating the procedure of the composite material cutting method according to the third embodiment of the present invention. FIG6 is a diagram schematically illustrating the experimental outline of Example 1. FIG. 7 is a graph showing the evaluation results of the bending strength of the brittle material ply of the reference example. FIG. 8 is a graph showing evaluation results of the bending strength of the composite material sheets of Example 1 and Comparative Example. Implementation Method

[0024] <First embodiment> The following describes a method for cutting a composite material according to a first embodiment of the present invention with reference to the accompanying drawings. Figures 1 and 2 are schematic diagrams illustrating the process of the composite material cutting method according to the first embodiment of the present invention. Figure 1(a) is a cross-sectional view showing the resin removal step of the cutting method according to the first embodiment, Figure 1(b) is a cross-sectional view showing the brittle material removal step of the cutting method according to the first embodiment, and Figure 1(c) is a cross-sectional view showing the composite material cutting step of the cutting method according to the first embodiment. Figure 2(a) is a top view showing the brittle material removal step of the cutting method according to the first embodiment, and Figure 2(b) is a perspective view showing the brittle material removal step of the cutting method according to the first embodiment. Furthermore, the ultrashort pulse laser light source 30 is omitted from Figure 2. The breaking method of the first embodiment is a method of breaking the composite material 10 formed by laminating the brittle material layer 1 and the resin layer 2 along the thickness direction (the lamination direction of the brittle material layer 1 and the resin layer 2, the up-down direction in FIG. 1 , the Z direction).

[0025] The brittle material layer 1 and the resin layer 2 are laminated using any suitable method. For example, the brittle material layer 1 and the resin layer 2 can be laminated using a roll-to-roll method. Alternatively, the brittle material layer 1 and the resin layer 2 can be laminated by aligning their longitudinal sides while conveying the long strips of brittle material layer 1 and resin layer 2 along their longitudinal directions. Alternatively, the brittle material layer 1 and the resin layer 2 can be cut into predetermined shapes and then laminated. The brittle material layer 1 and the resin layer 2 are typically laminated using any suitable adhesive or bonding agent (not shown).

[0026] Examples of the brittle material forming the brittle material layer 1 include glass, and single crystal or polycrystalline silicon. Glass can be classified by composition, including soda-lime glass, borate glass, aluminosilicate glass, quartz glass, and sapphire glass. Furthermore, glass can be classified by alkaline content, including alkali-free glass and low-alkali glass. The content of alkali metal components (e.g., Na₂O, K₂O, Li₂O) in glass is preferably 15% by weight or less, more preferably 10% by weight or less.

[0027] The thickness of the brittle material layer 1 is preferably 200µm or less, more preferably 150µm or less, more preferably 120µm or less, and particularly preferably 100µm or less. On the other hand, the thickness of the brittle material layer 1 is preferably 5µm or greater, more preferably 20µm or greater, and even more preferably 30µm or greater. If the thickness of the brittle material layer 1 falls within this range, it can be laminated with the resin layer 2 via roll-to-roll lamination.

[0028] When the brittle material forming the brittle material layer 1 is glass, the light transmittance of the brittle material layer 1 at a wavelength of 550 nm is preferably 85% or greater. When the brittle material forming the brittle material layer 1 is glass, the refractive index of the brittle material layer 1 at a wavelength of 550 nm is preferably 1.4 to 1.65. When the brittle material forming the brittle material layer 1 is glass, the density of the brittle material layer 1 is preferably 2.3 g / cm3 to 3.0 g / cm3, more preferably 2.3 g / cm3 to 2.7 g / cm3.

[0029] When the brittle material forming the brittle material layer 1 is glass, a commercially available glass plate may be used as is, or a commercially available glass plate may be ground to the desired thickness before use. Examples of commercially available glass plates include Corning's "7059," "1737," or "EAGLE2000," AGC's "AN100," NH Techno Glass's "NA-35," Nippon Electric Glass's "OA-10," and SCHOTT's "D263" or "AF45."

[0030] The resin layer 2 may be exemplified by a single-layer film formed of the following substances, or a laminated film consisting of a plurality of layers: acrylic resins such as polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polymethyl methacrylate (PMMA), cyclic olefin polymers (COP), cyclic olefin copolymers (COC), polycarbonate (PC), urethane resins, polyvinyl alcohol (PVA), polyimide (PI), polytetrafluoroethylene (PTFE), polyvinyl chloride (PVC), polystyrene (PS), cellulose triacetate (TAC), polyethylene naphthalate (PEN), ethylene vinyl acetate (EVA), polyamide (PA), silicone resins, epoxy resins, liquid crystal polymers, various resin foams, and other plastic materials.

[0031] When the resin layer 2 is a laminated film composed of multiple layers, various adhesives or bonding agents such as acrylic adhesives, urethane adhesives, and silicone adhesives may be present between the layers. Furthermore, a conductive inorganic film such as indium tin oxide (ITO), Ag, Au, or Cu may be formed on the surface of the resin layer 2 . The dividing method of the first embodiment is particularly suitable for use when the resin layer 2 is a polarizing film or a retardation film, or other optical films that can be used in displays. The thickness of the resin layer 2 is preferably 20-500 μm.

[0032] 1 , the resin layer 2 is an example of a laminated film in which a polarizing film 21 and a release liner 23 are laminated via an adhesive 22 .

[0033] The first embodiment of the breaking method includes a resin removal step, a brittle material removal step, and a composite material breaking step. Each step will be described in order below.

[0034] [Resin removal step] As shown in FIG. 1( a ), in the resin removal step, the resin layer 2 is irradiated with laser light L1 oscillating from a laser light source 20 along the predetermined separation line of the composite material 10 to remove the resin forming the resin layer 2, thereby forming a processing groove 24 along the predetermined separation line. The examples shown in Figures 1 and 2 illustrate a situation where a straight line DL extending along the Y direction, one of two orthogonal directions (X and Y) within the plane of the composite material 10 (within the XY 2-dimensional plane), serves as the predetermined separation line. The predetermined separation line DL can be physically drawn on the composite material 10 using a visually recognizable marking, or its coordinates can be pre-entered into a control device (not shown) that controls the relative position of the laser light L1 and the composite material 10 in the XY 2-dimensional plane. The predetermined separation line DL shown in Figures 1 and 2 is an imaginary line whose coordinates have been pre-entered into the control device and is not actually drawn on the composite material 10. Furthermore, the predetermined separation line DL is not limited to a straight line; it can also be a curved line. The predetermined separation line DL is determined based on the intended use of the composite material 10, allowing the composite material 10 to be separated into any desired shape appropriate for the intended use.

[0035] In the first embodiment, the laser light source 20 is a CO2 laser light source that oscillates and excites the laser light L1 with a wavelength of 9 to 11 μm in the infrared region. However, the present invention is not limited thereto. The laser light source 20 may also be a CO laser light source whose oscillation-excited laser light L1 has a wavelength of 5 μm. Furthermore, visible light and ultraviolet (UV) pulse laser sources can also be used as the laser light source 20. Examples of visible light and UV pulse laser sources include those with oscillation-excited laser light L1 having a wavelength of 532 nm, 355 nm, 349 nm, or 266 nm (higher harmonics of solid-state laser sources using Nd:YAG, Nd:YLF, or YVO4 as the medium), excimer laser sources with oscillation-excited laser light L1 having a wavelength of 351 nm, 248 nm, 222 nm, 193 nm, or 157 nm, and F2 laser sources with oscillation-excited laser light L1 having a wavelength of 157 nm. Alternatively, the laser light source 20 may be a pulsed laser light source, wherein the wavelength of the laser light L1 oscillated and excited is outside the ultraviolet region and the pulse width is in the femtosecond or picosecond range. Using the laser light L1 oscillated and excited by this pulsed laser light source can induce ablation processing based on a multiphoton absorption process. Furthermore, the laser light source 20 may also be a semiconductor laser light source or a fiber laser light source whose oscillation-excited laser light L1 has a wavelength in the infrared region. As mentioned above, in the first embodiment, a CO 2 laser light source is used as the laser light source 20 , so the laser light source 20 will be referred to as “CO 2 laser light source 20 ” hereinafter.

[0036] For irradiating the composite material 10 along the intended separation line with laser light L1 (scanning the laser light L1), for example, a single composite material 10 may be placed on an XY2-axis stage (not shown) and fixed (e.g., by suction). The XY2-axis stage is then driven by a control signal from a control device to change the relative position of the composite material 10 with respect to the laser light L1 on the XY2-dimensional plane. Alternatively, the position of the composite material 10 may be fixed, and the laser light L1 oscillated and excited from the CO2 laser light source 20 may be deflected using a galvanometer mirror or polygon mirror driven by a control signal from the control device to change the position of the laser light L1 irradiating the composite material 10 on the XY2-dimensional plane. Furthermore, it is also possible to combine the aforementioned scanning of the composite material 10 using the XY2-axis stage with scanning of the laser light L1 using a galvanometer mirror or the like.

[0037] The oscillation mode of the CO2 laser light source 20 can be either pulsed or continuous. The spatial intensity distribution of the laser light L1 can be Gaussian, or, to suppress damage to the brittle material layer 1 not targeted for removal by the laser light L1, a diffractive optical element (not shown) can be used to shape the distribution into a flat top. The polarization state of the laser light L1 is unlimited and can be linear, circular, or random.

[0038] Laser light L1 is irradiated onto the resin layer 2 (a laminated film composed of a polarizing film 21, an adhesive 22, and a release liner 23) along the intended separation line DL of the composite material 10. This causes the resin forming the resin layer 2 to be irradiated by the laser light L1 (the portion of the polarizing film 21, the adhesive 22, and the release liner 23 illuminated by the laser light L1) to absorb infrared light and experience a localized temperature rise, causing the resin to scatter. This resin is then removed from the composite material 10, forming a processed groove 24 in the composite material 10. To prevent the scattered resin removed from the composite material 10 from reattaching to the composite material 10, a dust collection mechanism is preferably provided near the intended separation line DL. To prevent the width of the processed groove 24 from increasing, the laser light L1 is preferably focused so that the spot diameter at the irradiation location on the resin layer 2 is 300µm or less, and more preferably, the spot diameter is 200µm or less.

[0039] Furthermore, when using a resin removal method based on the principle that the resin irradiated by the laser light L1 will locally increase in temperature due to infrared absorption, the energy required to form the processing groove 24 can be roughly estimated based on the thickness of the resin layer 2, regardless of the type of resin or the layer structure of the resin layer 2. Specifically, the energy required to form the processing groove 24 can be estimated using the following equation (1) based on the thickness of the resin layer 2 using the following equation (2). Input energy [mJ / mm] = average power of laser beam L1 [mW] / processing speed [mm / s]···(1) Input energy [mJ / mm = 0.5 × thickness of resin layer 2 [µm]···(2) The actual input energy setting is preferably set to 20% to 180% of the input energy calculated by the above formula (2), and more preferably to 50% to 150%. The reason for setting a margin for the input energy calculated in the above manner is to consider that the input energy required to form the processing groove 24 will vary depending on the light absorption rate (light absorption rate at the wavelength of the laser light L1) of the resin forming the resin layer 2, the melting point of the resin, the decomposition point and other thermal properties. Specifically, for example, a sample of the composite material 10 to which the breaking method of the first embodiment is to be applied can be prepared for preliminary testing. That is, a plurality of input energies within the above-mentioned appropriate range are used to form the processing groove 24 in the resin layer 2 of the sample, thereby determining the appropriate input energy.

[0040] [Brittle material removal step] As shown in FIG1(b) and FIG2, in the brittle material removal step, after the resin removal step, the brittle material layer 1 is irradiated with laser light (ultrashort pulse laser light) L2 oscillatingly excited (pulsed oscillation) from an ultrashort pulse laser light source 30 along the predetermined breaking line DL to remove the brittle material forming the brittle material layer 1, thereby forming a processing mark 11 along the predetermined breaking line DL. The pattern of irradiating the laser light L2 along the predetermined separation line DL (the pattern of scanning the laser light L2) can be the same as the pattern of irradiating the laser light L1 along the predetermined separation line DL, so detailed description is omitted here.

[0041] The brittle material forming the brittle material layer 1 is removed by utilizing the filamentation phenomenon of the laser light L2 oscillated and excited from the ultrashort pulse laser light source 30 or by applying a multi-focus optical system (not shown) or a Besso beam optical system (not shown) to the ultrashort pulse laser light source 30 .

[0042] In the brittle material removal step of the first embodiment, the depth of the processing mark 11 is adjusted by adjusting the power of the laser light L2 oscillated by the ultrashort pulse laser light source 30 and the positional relationship between the focal point of the laser light L2 oscillated by the ultrashort pulse laser light source 30 and the brittle material layer 1. Consequently, the processing mark 11 formed in the brittle material removal step of the first embodiment opens on the resin layer 2 side (the processing groove 24 side) and does not penetrate the brittle material layer 1 (does not open on the side opposite to the resin layer 2 side). In other words, in the brittle material removal step, the processing mark 11 is formed only on the resin layer 2 side of the brittle material layer 1. This point will be explained in more detail below.

[0043] FIG3 is a diagram schematically illustrating an example of a method for forming the machining mark 11 in the brittle material removal step of the breaking method of the first embodiment. In addition, FIG3 omits the illustration of the machining groove 24 (see FIG1 and FIG2 ). In the example shown in Figure 3, a multi-focal optical system is employed for the ultrashort pulse laser light source 30. Specifically, the multi-focal optical system shown in Figure 3 is composed of three conical lenses 31a, 31b, and 31c. Assuming the spatial intensity distribution of the laser light L2 oscillated from the ultrashort pulse laser light source 30 is a Gaussian distribution, the laser light L2 oscillating from point A, where the intensity is higher, follows the optical path indicated by the solid line in Figure 3 and is focused at the focal point AF. Meanwhile, the laser light L2 oscillating from point B, where the intensity is lower, follows the optical path indicated by the dashed line in Figure 3 and is focused at a focal point BF different from the focal point AF. As described above, the laser light L2 oscillating from the ultrashort pulse laser light source 30 is focused at multiple focal points by the multi-focal optical system.

[0044] As shown in Figure 3, the positional relationship between the laser light L2's focal point and the brittle material layer 1 is adjusted so that the focal point BF of the laser light L2, oscillating from point B (where the intensity is relatively low), is located on the brittle material layer 1 side of the composite material 10, while the focal point AF of the laser light L2, oscillating from point A (where the intensity is relatively high), is located on the resin layer 2 side of the composite material 10. This allows the energy used to form the processing mark 11 to be distributed across the thickness of the composite material 10. Specifically, the energy on the resin layer 2 side is greater than the energy on the brittle material layer 1 side. This distribution in the brittle material layer 1 can be altered by adjusting the positional relationship between the laser light L2's focal point and the brittle material layer 1. Furthermore, by adjusting the power of the laser light L2 oscillating from the ultrashort pulse laser light source 30, the intensity of the energy used to form the processing mark 11 (removing the brittle material) (the intensity at points A and B) can be adjusted. Thus, only the brittle material on the resin layer 2 side of the brittle material layer 1 can be removed, and the processing mark 11 can be formed only on the resin layer 2 side of the brittle material layer 1, and the depth of the processing mark 11 can be adjusted.

[0045] Furthermore, the aforementioned Non-Patent Document 1 describes the use of the filamentation phenomenon of ultrashort pulse laser light and the application of multi-focus optical systems or Besso beam optical systems to ultrashort pulse laser light sources. Furthermore, Trumpf of Germany sells products related to glass processing that utilize multi-focus optical systems for ultrashort pulse laser light sources. As mentioned above, the use of the filamentation phenomenon of ultrashort pulse laser light and the application of multi-focus optical systems or Besso beam optical systems to ultrashort pulse laser light sources are well known, and therefore further detailed description is omitted here.

[0046] The processing marks 11 formed in the brittle material removal step of the first embodiment are dashed line-shaped processing marks that follow the planned separation line DL. The distance P between processing marks 11 (see Figure 2(a)) is determined by the repetition frequency of the pulse oscillation and the relative movement speed (processing speed) of the laser beam L2 with respect to the composite material 10. To facilitate and stabilize the composite material separation step described later, the distance P between processing marks 11 is preferably set to 10µm or less. The distance P between processing marks 11 is more preferably set to 5µm or less. The diameter of processing marks 11 is generally formed to be 5µm or less. Furthermore, the depth of the machining mark 11 is preferably set to be no more than 90% or no more than 80% of the thickness of the brittle material layer 1, more preferably no more than 70% or no more than 60% of the thickness of the brittle material layer 1, and even more preferably no more than 50% of the thickness of the brittle material layer 1. If the depth of the machining mark 11 is too small, the composite material 10 cannot be separated in the composite material separation step described later. Therefore, the depth of the machining mark 11 is preferably set to be no less than 10% of the thickness of the brittle material layer 1, and more preferably no less than 30% of the thickness of the brittle material layer 1.

[0047] The wavelength of the laser light L2 oscillated by the ultrashort pulse laser light source 30 is preferably between 500 nm and 2500 nm, which exhibits high light transmittance when the brittle material forming the brittle material layer 1 is glass. To effectively generate nonlinear optical phenomena (multiphoton absorption), the pulse width of the laser light L2 is preferably less than 100 picoseconds, more preferably less than 50 picoseconds. The oscillation mode of the laser light L2 can be a single pulse oscillation or a multi-pulse oscillation in a burst mode.

[0048] In the brittle material removal step of the first embodiment, the brittle material layer 1 is irradiated with laser light L2 oscillated from an ultrashort pulse laser light source 30 from the side opposite to the processed groove 24 formed in the resin removal step. In the example shown in Figures 1(a) and 1(b), the CO2 laser light source 20 is positioned below the composite material 10 in the Z direction, facing the resin layer 2, and the ultrashort pulse laser light source 30 is positioned above the composite material 10 in the Z direction, facing the brittle material layer 1. After the processed groove 24 is formed by laser light L1 oscillated from the CO2 laser light source 20 in the resin removal step, oscillation of the laser light L1 is stopped, and in the brittle material removal step, laser light L2 oscillated from the ultrashort pulse laser light source 30 is used to form the processed mark 11. However, the present invention is not limited to this, and the following method may also be used: the CO2 laser light source 20 and the ultrashort pulse laser light source 30 are both arranged on the same side relative to the composite material 10 (upper or lower side in the Z direction), and the composite material 10 is turned upside down in such a manner that the resin layer 2 and the CO2 laser light source 20 are opposite to each other during the resin removal step, and the brittle material layer 1 and the ultrashort pulse laser light source 30 are opposite to each other during the brittle material removal step. If the laser light L2 oscillated and excited by the ultrashort pulse laser light source 30 is irradiated from the side opposite to the processing groove 24, even if resin residue is generated at the bottom of the processing groove 24, an appropriate processing mark 11 can be formed on the brittle material layer 1 without being affected by the residue.

[0049] However, the present invention is not limited to this and may further include a cleaning step for cleaning the processed grooves 24 formed in the resin removal step before the brittle material removal step to remove any residual resin from the resin layer 2. Furthermore, during the brittle material removal step, the brittle material layer 1 may be irradiated with laser light L2 oscillated and excited by an ultrashort pulse laser light source 30 from the processed grooves 24 to form the processing marks 11. During the cleaning process, various wet and dry cleaning methods can be applied. Examples of wet cleaning methods include chemical immersion, ultrasonic cleaning, dry ice blasting, and micro- and nano-bubble cleaning. Dry cleaning methods can use lasers, plasma, ultraviolet light, ozone, and other methods. In order to remove the resin residue that forms the resin layer 2 in the cleaning step, even if the brittle material layer 1 is irradiated with laser light L2 oscillated and excited from the ultrashort pulse laser light source 30 from the processing groove 24 side in the brittle material removal step, the laser light L2 can still form an appropriate processing mark 11 on the brittle material layer 1 without being affected by the resin residue.

[0050] [Composite material cutting steps] As shown in FIG1(c), in the composite material breaking step, after the brittle material removal step, an external force is applied along the predetermined breaking line DL to break the composite material 10. In the example shown in FIG1(c), the composite material 10 is broken into composite material sheets 10a and 10b. Examples of methods for applying external force to the composite material 10 include mechanical destruction (convex folding), heating near the intended cutting line DL using infrared laser light, vibration using an ultrasonic roller, and suction and lifting using a suction cup. When using convex folding to cut the composite material 10, it is preferable to apply external force to cause the resin layer 2 side to convex (and the brittle material layer 1 side to concave), and to start cutting from the resin layer 2 side of the brittle material layer 1 where the processing mark 11 is formed.

[0051] FIG4 is a cross-sectional view schematically illustrating the structure of composite material sheets 10a and 10b after being cut in the composite material cutting step of the cutting method according to the first embodiment. FIG4(a) is a cross-sectional view showing the overall structure of composite material sheets 10a and 10b, and FIG4(b) is an enlarged view of the first portion 12 of the end surface of the brittle material layer 1, as viewed from the direction of arrow ZZ in FIG4(a). As shown in Figure 4, the surface roughness of a first portion 12 on the resin layer 2 side of one end surface (the end surface after being cut) of the composite material sheets 10a and 10b is greater than the surface roughness of a second portion 13 on the opposite side of the end surface from the resin layer 2. The first portion 12 corresponds to the portion where the processing mark 11 is formed, and the second portion 13 corresponds to the portion where the processing mark 11 is not formed. Therefore, the thickness of the first portion 12 (the dimension of the first portion 12 along the thickness direction (Z direction) of the brittle material layer 1) is preferably no more than 90% or no more than 80% of the thickness of the brittle material layer 1, more preferably no more than 70% or no more than 60% of the thickness of the brittle material layer 1, and even more preferably no more than 50% of the thickness of the brittle material layer 1. Furthermore, the thickness of the first portion 12 is preferably no less than 10% of the thickness of the brittle material layer 1, and more preferably no less than 30% of the thickness of the brittle material layer 1. One end surface (the end surface after being cut) of the brittle material layer 1 of the composite sheets 10a and 10b protrudes further toward the end surface (the left side of the drawing in FIG4(a) ) than the end surface (the end surface after being cut) on the same side of the resin layer 2. The amount of protrusion 14 varies depending on the spot diameter of the laser light L1 oscillated and excited by the CO2 laser light source 20 at the irradiation position of the resin layer 2, and can be, for example, less than 200µm, less than 100µm, or less than 50µm. The lower limit of the protrusion 14 is preferably as small as possible, for example, greater than 1µm or greater than 5µm.

[0052] According to the separating method of the first embodiment described above, after removing the resin forming the resin layer 2 in the resin removal step to form the processing grooves 24 along the intended separating line DL, the brittle material forming the brittle material layer 1 in the brittle material removal step is removed to form processing marks 11 along the same intended separating line DL. The processing marks 11 formed in the brittle material removal step are dashed line-shaped processing marks along the intended separating line DL, and the distance P between processing marks 11 is as small as 10 μm or less. Therefore, in the composite material separating step, applying an external force along the intended separating line DL facilitates separation of the composite material 10. Furthermore, according to the breaking method of the first embodiment, in the brittle material removal step, the brittle material layer 1 is irradiated with laser light L2 oscillated from the short-pulse laser light source 30 to remove the brittle material forming the brittle material layer 1. Therefore, cracks are not generated on the end surfaces of the brittle material layer 1 after breaking. Furthermore, according to the breaking method of the first embodiment, in the resin removal step prior to the brittle material removal step, the resin layer 2 is irradiated with laser light L1 oscillated from the CO2 laser light source 20 to remove the resin forming the resin layer 2. Therefore, severe thermal degradation of the end surfaces of the resin layer 2 after breaking is not generated. In other words, according to the breaking method of the first embodiment, the composite material 10 can be broken without causing cracks on the end surfaces of the brittle material layer 1 after breaking or without causing severe thermal degradation of the end surfaces of the resin layer 2 after breaking. Furthermore, according to the breaking method of the first embodiment, the processing mark 11 formed in the brittle material removal step opens on the resin layer 2 side and does not penetrate the brittle material layer 1. In other words, in the brittle material removal step, the processing mark 11 is formed only on the resin layer 2 side of the brittle material layer 1. Therefore, sufficient bending strength can be obtained in the composite material sheets 10a and 10b after breaking.

[0053] <Second embodiment> In the separating method of the first embodiment, the processing mark 11 formed in the brittle material removal step is a dotted line processing mark. In contrast, in the separating method of the second embodiment, during the brittle material removal step, the relative movement speed of the laser light L2 oscillated by the ultrashort pulse laser light source 30 and the brittle material layer 1 along the predetermined separation line DL is set to a lower speed, or the repetition frequency of the pulse oscillation of the ultrashort pulse laser light source 30 is set to a higher speed. This creates a continuous, integrated processing mark along the predetermined separation line DL. The separating method of the second embodiment, because it forms a continuous, integrated processing mark, offers the advantage of being able to more easily separate the composite material 10 than the separating method of the first embodiment. The breaking method of the second embodiment is the same as the breaking method of the first embodiment except that the processing marks are formed to form a connected whole, so detailed description is omitted. By using the cutting method of the second embodiment, the composite material 10 can be cut without causing cracks to form on the end face of the brittle material layer 1 after cutting, or causing serious thermal degradation on the end face of the resin layer 2 after cutting, and sufficient bending strength can be obtained in the composite material sheet after cutting.

[0054] <Third embodiment> In the first and second embodiments described above, a method for separating a composite material 10 formed by laminating a brittle material layer 1 and a resin layer 2 in the thickness direction is described. However, the present invention is not limited thereto and can also be applied to a situation where a composite material in which resin layers are laminated on both sides of a brittle material layer is separated in the thickness direction. FIG5 is a schematic diagram (cross-sectional view) illustrating the process of a composite material cutting method according to a third embodiment of the present invention. FIG5 omits the CO2 laser light source 20 and laser light L1, and the ultrashort pulse laser light source 30 and laser light L2. Furthermore, FIG5 omits the composite material cutting steps. As shown in FIG5(a), the third embodiment's breaking method involves breaking a composite material 10A along the thickness direction (Z direction) by laminating resin layers 2a and 2b on either side of a brittle material layer 1. The lamination method for the brittle material layer 1 and the resin layers 2a and 2b, as well as the materials used to form the brittle material layer 1 and the resin layers 2a and 2b, are the same as those of the first embodiment, and therefore detailed description will be omitted.

[0055] The breaking method of the third embodiment is similar to the breaking method of the first embodiment, including a resin removal step, a brittle material removal step, and a composite material breaking step. The following describes each step, focusing on the differences from the first embodiment.

[0056] [Resin removal step] As shown in Figures 5(b) and 5(c), in the resin removal step, similar to the first embodiment, laser light L1 oscillated and excited from a CO2 laser source 20 is irradiated onto the resin layer along the predetermined separation line DL of the composite material 10A to remove the resin forming the resin layer, thereby forming a processing groove along the predetermined separation line DL. However, in the third embodiment, resin layers 2a and 2b are laminated on either side of the brittle material layer 1. Therefore, as shown in Figure 5(b), processing grooves 24a are formed in one resin layer 2a, and as shown in Figure 5(c), processing grooves 24b are formed in the other resin layer 2b. In the examples shown in Figures 5(b) and 5(c), processing grooves 24a on the lower side in the Z direction are formed first, followed by processing grooves 24b on the upper side in the Z direction. However, the formation order can also be reversed. For example, a pair of CO2 laser light sources 20 can be positioned on the side facing the resin layer 2a and the side facing the resin layer 2b, respectively. The CO2 laser light source 20 positioned on the side facing the resin layer 2a can then be used to form the processing groove 24a in the resin layer 2a, while the CO2 laser light source 20 positioned on the side facing the resin layer 2b can be used to form the processing groove 24b in the resin layer 2b. In this case, the processing grooves 24a and 24b can be formed simultaneously, rather than sequentially. Alternatively, a single CO2 laser light source 20 may be arranged on the side opposite to either the resin layer 2a or the resin layer 2b, and after forming a processing groove 24a in one of the resin layers 2a (or forming a processing groove 24b in the resin layer 2b) using the CO2 laser light source 20, the composite material 10A is turned upside down, and the same CO2 laser light source 20 is used to form a processing groove 24b in the other resin layer 2b (or form a processing groove 24a in the resin layer 2a).

[0057] [Brittle material removal step] As shown in FIG5(d), in the brittle material removal step, similarly to the first embodiment, after the resin removal step, the brittle material layer 1 is irradiated with laser light L2 oscillated from an ultrashort pulse laser light source 30 along the predetermined separation line DL to remove the brittle material forming the brittle material layer 1, thereby forming a processing mark 11 along the predetermined separation line DL. Similar to the first embodiment, the processing mark 11 formed in the brittle material removal step is a dotted line along the predetermined separation line DL, and the distance between processing marks is preferably set to 10µm or less. However, similarly to the second embodiment, the brittle material removal step can also form processing marks that are connected and integrated along the predetermined separation line DL. In the third embodiment, processing grooves 24a and 24b are formed on both sides of the brittle material layer 1. Therefore, laser light L2 oscillated and excited from an ultrashort pulse laser light source 30 is irradiated onto the brittle material layer 1 from either of the processing grooves 24a and 24b, forming processing marks 11. Therefore, for example, when irradiating the processing groove 24a with laser light L2, a cleaning step is preferably included. This step cleans the processing groove 24a before the brittle material removal step to remove any residual resin from the resin layer 2a. Similarly, when irradiating the processing groove 24b with laser light L2, a cleaning step is preferably included. This step cleans the processing groove 24b before the brittle material removal step to remove any residual resin from the resin layer 2b.

[0058] 5( d ) shows a processing mark 11 that opens on the resin layer 2 a and does not penetrate the brittle material layer 1 . However, the present invention is not limited thereto, and a processing mark that opens on the resin layer 2 b and does not penetrate the brittle material layer 1 may also be formed.

[0059] [Composite material cutting steps] In the composite material cutting step, similar to the first embodiment, after the brittle material removal step, an external force is applied along the planned cutting line DL to cut the composite material 10A. When cutting the composite material 10A by convex folding, in the example shown in FIG5(d), it is preferable to apply the external force to cause the resin layer 2a side to convex (and the brittle material layer 1 side to concave), and to start cutting from the resin layer 2a side of the brittle material layer 1 where the processing mark 11 is formed.

[0060] By using the cutting method of the third embodiment, the composite material 10A can be cut without causing cracks to form on the end face of the brittle material layer 1 after cutting, or without causing serious thermal degradation on the end faces of the resin layers 2a and 2b after cutting, and sufficient bending strength can be obtained in the composite material sheet after cutting.

[0061] The following describes an example of the test results of separating a composite material 10 using the separating method of the first embodiment (Examples 1-3) and the separating method of the comparative example. Furthermore, as a reference example, the following describes an example of the test results of separating a brittle material layer 1 using only a brittle material layer 1 instead of a composite material 10, forming a processing mark 11 in the same brittle material removal step as in the separating method of the first embodiment, and then separating the brittle material layer 1.

[0062] <Example 1> FIG6 is a diagram schematically illustrating the experimental summary of Example 1. Hereinafter, the experimental summary and results of Example 1 will be described with reference to FIG1 and FIG6 as appropriate. In the composite material 10 used in Example 1, the brittle material layer 1 is formed of alkali-free glass and has a thickness of 100µm. Furthermore, the resin layer 2 is formed of a polarizing film (formed from polyvinyl alcohol) 21, an adhesive 22, and a release liner 23. The total thickness of the polarizing film 21 and adhesive 22 is 80µm, and the thickness of the release liner 23 is 40µm (the total thickness of the resin layer 2 is 120µm). As shown in Figure 6(a), the composite material 10 is a square with in-plane (XY2-dimensional) dimensions of 150mm x 150mm. The dashed line in Figure 6(a) represents the planned breaking line.

[0063] In Example 1, during the resin removal step, a Coherent "E-400i" (oscillation wavelength 9.4 µm, pulse repetition frequency 25 kHz, laser light L1 power 18 W, Gaussian beam) was used as the CO2 laser light source 20. Laser light L1 oscillated from the CO2 laser light source 20 was focused by a focusing lens to a spot diameter of 120 µm and then irradiated onto the resin layer 2 of the composite material 10. The relative movement speed (processing speed) of the laser light L1 relative to the composite material 10 was set at 400 mm / s. As shown in FIG6(a), the laser light L1 was scanned along the predetermined separation line to separate the composite material sheet 10c having an in-plane dimension of 110 mm × 60 mm. As a result, a processing groove 24 with a groove width of 150 µm was formed (see FIG1). In the resin removal step of Example 1, the input energy calculated using the aforementioned formula (2) was 60 mJ / mm. In contrast, the actual input energy obtained from the aforementioned formula (1) was 45 mJ / mm, which is 75% of the calculated input energy.

[0064] Next, in the brittle material removal step, a Coherent "Monaco 1035-80-60" laser (oscillation wavelength 1035 nm, laser light L2 pulse width 350 to 10,000 femtoseconds, maximum pulse oscillation repetition frequency 50 MHz, average power 60 W) was used as the ultrashort pulse laser light source 30. Laser light L2, oscillated at a predetermined output from the ultrashort pulse laser light source 30, was irradiated onto the brittle material layer 1 of the composite material 10 from the side opposite the processing groove 24 (the brittle material layer 1 side) through a multi-focus optical system. The relative movement speed (processing speed) of the laser light L2 relative to the composite material 10 was set at 1200 mm / s and the repetition frequency was set at 1 MHz. The laser light L2 was scanned along the predetermined separation line, forming a processing mark 11 with a dotted line pitch of 1.2 µm and a depth (average value) of 80 µm (approximately 1 µm in diameter).

[0065] Finally, in the composite material cutting step, the composite material 10 is manually folded along the predetermined cutting line to separate the composite material sheets 10c.

[0066] Optical microscopic observation and evaluation of the end surfaces of the composite sheet 10c obtained in Example 1 above revealed no cracks in the brittle material layer 1 on all four end surfaces. Furthermore, the discoloration region of the resin layer 2 associated with thermal degradation was less than 100 µm inward from the end surface, indicating no significant thermal degradation. The surface roughness of the composite sheet 10c was measured at two locations on one end surface (as shown in FIG6(a) : one location P1 on one end in the X direction, and the other location P2 on the other end in the X direction). The results showed that the arithmetic mean height Sa of the first location, corresponding to the location with the processing mark 11, was 31 nm at measurement location P1, and 34 nm at measurement location P2. Furthermore, the arithmetic mean height Sa of the second location, corresponding to the location without the processing mark 11, was 0 nm at both measurement locations P1 and P2. The arithmetic mean height Sa was measured using the "Non-Contact (Optical Probe)" evaluation method specified in ISO 25178. Specifically, using the Olympus 3D measurement laser microscope "LEXT OLS5000," the in-plane resolution of the end face was set to 100 nm, and the height resolution perpendicular to the end face was set to 12 nm. The arithmetic mean height Sa was measured for an in-plane area of ​​130 µm x 100 µm at each measurement point P1 or P2. The same applies to Examples 2 and 3 described below.

[0067] A two-point bending test was also conducted on the composite sheet 10c. In the two-point bending test, as shown in Figure 6(b), the composite sheet 10c was first placed on the fixed portion 40 of a uniaxial stage comprising a fixed portion 40 and movable portions 50a and 50b, with the composite sheet 10c sandwiched between the movable portions 50a and 50b. As described later, the composite sheet 10c was placed on the fixed portion 40 so that movement of the movable portion 50b would cause the brittle material layer side of the composite sheet 10c to convexly bend (i.e., with the brittle material layer 1 side facing upward). Next, as shown in Figure 6(c), the position of the movable portion 50a was fixed, while the movable portion 50b was moved toward the movable portion 50a at a speed of 20 mm / minute, applying bending stress to the composite sheet 10c. Then, the bending strength of the composite material sheet 10c is evaluated by the value of the distance D between the movable portion 50a and the movable portion 50b when the composite material sheet 10c is broken.

[0068] Specifically, the distance D is substituted into the equation (3) described in Non-Patent Document 2 (the same as the following equation (3)), and the maximum stress σmax is calculated and evaluated as the bending strength. [Mathematical formula 1] In the above formula (3), E refers to the Young's modulus of the composite sheet 10c, t refers to the thickness of the composite sheet 10c, and ψ refers to the angle formed by the tangent line at the end of the composite sheet 10c and the vertical direction (Z direction). The Young's modulus E of the composite sheet 10c is 70 GPa, which is the Young's modulus of the brittle material layer 1. The Young's modulus of the resin layer 2 is much smaller than that of the brittle material layer 1, so the Young's modulus E of the composite sheet 10c is mainly affected by the Young's modulus of the brittle material layer 1. Furthermore, the angle ψ is calculated by photographing the composite sheet 10c in the Y direction as shown in FIG. 6(c) with one end of the composite sheet 10c within the field of view during the two-point bending test, and then calculating the angle ψ based on the photographed image taken just before the composite sheet 10c is destroyed.

[0069] Here, as a reference example, only the brittle material layer 1 was used. Under the same conditions as in Example 1, a processing mark 11 was formed in the brittle material removal step, and a test was conducted on the brittle material layer 1. The brittle material layer 1 (brittle material layer fragment) after being separated was then subjected to a two-point bending test similar to that shown in FIG6 , and its bending strength (maximum stress σmax) was evaluated using the aforementioned equation (3). The Young's modulus E of the brittle material layer 1 was set to 70 GPa. In the reference example, the depth of the processing mark 11 was adjusted by adjusting the positional relationship between the focus of the laser light L2 oscillating from the ultrashort pulse laser light source 30 and the brittle material layer 1. After producing 10 pieces of four types of brittle material layers 1, each with a processing mark 11 depth (average value) of 40%, 60%, 70%, and 80% of the thickness of the brittle material layer 1, the bending strength of each type of brittle material layer after segmentation was evaluated.

[0070] Figure 7 shows the evaluation results of the bending strength of a brittle material layer according to a reference example. Figure 7(a) shows the relationship between the depth ratio of the machining mark 11 (ratio to the thickness of the brittle material layer 1) and the bending strength of the brittle material layer. In Figure 7(a), the data plotted with "○" represents the average value of 10 samples, and the vertical lines extending upward and downward from the "○" represent the variation in the measured values. Figure 7(b) shows an optical microscope image of the end surface of a brittle material layer with a machining mark 11 depth ratio (ratio to the thickness of the first portion 12) of 40%. Figure 7(c) shows an optical microscope image of the end surface of a brittle material layer with a machining mark 11 depth ratio (ratio to the thickness of the first portion 12) of 60%. Figure 7(d) shows an optical microscope image of the end surface of a brittle material layer with a machining mark 11 depth ratio (ratio to the thickness of the first portion 12) of 70%. FIG7(e) schematically shows an image obtained by observing the end surface of a brittle material layer with a depth ratio of the processing mark 11 (thickness ratio of the first portion 12) of 80% using an optical microscope. As shown in Figure 7, when the depth ratio of the machining mark 11 is 90% or less (in the example shown in Figure 7, the depth ratio of the machining mark 11 is 40-80%), the average flexural strength of the brittle material ply after separation is over 200 MPa, achieving high flexural strength. Furthermore, the smaller the depth ratio of the machining mark 11 (the smaller the depth of the machining mark 11), the greater the flexural strength of the brittle material ply after separation. In particular, when the depth ratio of the machining mark 11 is 65% or less (in the example shown in Figure 7, the depth ratio of the machining mark 11 is 60% or less), the average flexural strength of the brittle material ply after separation reaches over 300 MPa, and further, over 400 MPa, achieving sufficiently high flexural strength. The results shown in Figure 7 represent the flexural strength of the brittle material ply, and similar results can be expected for the composite material sheet 10c of Example 1.

[0071] <Comparative Example> The composite sheet was tested under the same conditions as in Example 1, except that a machining mark penetrating the brittle material layer 1 was formed during the brittle material removal step (i.e., the machining mark depth ratio was 100%). The composite sheet was separated. The end surfaces of the composite sheet were observed and evaluated using an optical microscope. As in Example 1, no cracks occurred in the brittle material layer 1 on all four end surfaces. Furthermore, the discoloration area of ​​the resin layer 2 associated with thermal degradation was less than 100 µm inward from the end surface, indicating no significant thermal degradation. However, after performing a two-point bending test on the composite sheet of the comparative example, it was found that the bending strength of the composite sheet was less than the bending strength of the composite sheet 10c of Example 1.

[0072] Figure 8 shows the results of evaluating the flexural strength of a composite sheet 10c according to Example 1 and a composite sheet according to a comparative example. Figure 8(a) shows the relationship between the depth ratio of the machining mark 11 (ratio to the thickness of the brittle material layer 1) and the flexural strength of the composite sheet. The data plotted with "○" in Figure 8(a) represents the average value of 8 sheets for Example 1 and the average value of 10 sheets for the comparative example. Vertical lines extending upward and downward from the "○" represent variations in the measured values. Figure 8(b) shows an optical microscope image of the end surface of a composite sheet 10c according to Example 1, where the depth ratio of the machining mark 11 (thickness ratio of the first portion 12) is 80%. Figure 8(c) shows an optical microscope image of the end surface of a composite sheet according to the comparative example, where the depth ratio of the machining mark 11 (thickness ratio of the first portion 12) is 100%. As shown in FIG8 , compared to the comparative example in which the processing mark 11 penetrates the brittle material layer 1 , the embodiment 1 in which the processing mark 11 does not penetrate the brittle material layer 1 can obtain a high bending strength of more than 200 MPa, and further more than 250 MPa, on average, in the composite material sheet after being cut.

[0073] <Example 2> As a condition for the brittle material removal step, the output of the laser light L2 oscillated and excited from the ultrashort pulse laser light source 30 is made higher than that in Example 1. Otherwise, the test is conducted under the same conditions as in Example 1 to separate the composite material sheets. The surface roughness of two locations (the same measurement locations P1 and P2 as in Example 1) on one end surface of the composite material sheet obtained by Example 2 was measured. The result showed that the arithmetic mean height Sa of the first location, which corresponds to the location where the processing mark 11 is formed, was 103 nm, whichever was smaller, and the arithmetic mean height Sa of the second location, which corresponds to the location where the processing mark 11 is not formed, was 0 nm at both locations.

[0074] <Example 3> As a condition for the brittle material removal step, the output of the laser light L2 oscillated and excited from the ultrashort pulse laser light source 30 is made higher than that of Example 2. Otherwise, the test is conducted under the same conditions as Example 1 to separate the composite material sheets. The surface roughness of two locations (the same measurement locations P1 and P2 as in Example 1) on one end surface of the composite material sheet obtained by Example 3 was measured. The result showed that the arithmetic mean height Sa of the first location, which corresponds to the location where the processing mark 11 was formed, was 222 nm, whichever was smaller, and the arithmetic mean height Sa of the second location, which corresponds to the location where the processing mark 11 was not formed, was 0 nm at both locations.

[0075] 1: Brittle material layer 2,2a,2b: Resin layer 10,10A: Composite material 10a, 10b, 10c: Composite sheet 11: Processing marks 12: Part 1 13: Part 2 14: Protrusion 20: Laser light source (CO2 laser light source) 21:Polarizing film 22: Adhesive 23: Peel backing 24,24a,24b: Processing groove 30: Ultrashort pulse laser light source 31a, 31b, 31c: Conical lenses 40:Fixed part 50a, 50b: movable part A: Points with higher intensity AF,BF: Focus B: Point with lower intensity D: The distance between movable parts DL: Disconnection Predetermined Line L1: Laser light L2: Laser light P: Distance between processing marks P1, P2: Measurement location ZZ: Arrow direction ψ: angle

Claims

1. A composite material formed by laminating a brittle material layer and a resin layer; wherein the surface roughness of a first portion on the resin layer side of at least one end face of the aforementioned brittle material layer is greater than the surface roughness of a second portion on the opposite side of the aforementioned end face of the aforementioned brittle material layer; however, the aforementioned end face is an end face in a direction orthogonal to the lamination direction of the aforementioned brittle material layer and the aforementioned resin layer.

2. The composite material of claim 1, wherein the surface roughness of the first part is less than 300 nm based on the calculated average height Sa, and the surface roughness of the second part is less than 12 nm based on the calculated average height Sa.

3. The composite material as claimed in claim 1 or 2, wherein the thickness of the aforementioned first part is less than 90% of the thickness of the aforementioned brittle material layer.

4. The composite material as claimed in claim 3, wherein the thickness of the aforementioned first part is less than 65% of the thickness of the aforementioned brittle material layer.

5. The composite material as claimed in claim 1 or 2, wherein the thickness of the aforementioned brittle material layer is 5µm or more and 200µm or less.

6. The composite material of claim 1 or 2, wherein the bending strength of the composite material when bent into the aforementioned brittle material layer side protrusion is 200 MPa or more.

Images