Cover tape and electronic component packaging

Abstract

To provide a cover tape capable of heat sealing with less thermal energy while suppressing occurrence of blocking, and to provide an electronic component package using the cover tape.SOLUTION: A cover tape according to the present invention has at least a base material layer and a heat seal layer, wherein the heat seal layer contains (A) a polystyrene-based resin and (B) an ethylene- (meth) acrylic acid-based copolymer, and the contents of the component (A) and component (B) are more than 80 parts by mass and 95 parts by mass or less and 5 parts by mass or more and less than 20 parts by mass, respectively, based on the total of 100 parts by mass of the component (A) and component (B).SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cover tape and an electronic component package. [Background technology]

[0002] As electronic devices become smaller, the electronic components used are also becoming smaller and more powerful. In the assembly process of electronic devices, components are automatically mounted on printed circuit boards. To transport such surface-mount electronic components, electronic component packages are used in which electronic components are housed in a carrier tape in which pockets are thermally formed in succession to match the shapes of the electronic components so that the electronic components can be continuously supplied.

[0003] Electronic component packages are produced by placing electronic components in pockets of a carrier tape, overlaying a cover tape having a heat seal layer as a lid material on the top surface of the carrier tape, and continuously heat sealing both ends of the cover tape in the longitudinal direction with a heated sealing bar (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-173673 A Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, various electronic components such as capacitors, resistors, ICs, LEDs, connectors, and switching elements have become significantly smaller, lighter, and thinner, and the number of components mounted on a substrate has also increased. Therefore, from the viewpoint of improving the productivity of electronic component packages, there is an increasing demand for high-speed sealing of cover tapes. In addition, from the viewpoint of energy saving, there is a demand for reducing the energy required for heat sealing.

[0006] One possible means of meeting these demands would be to lower the softening temperature of the heat seal layer of the cover tape; however, in that case, as the softening temperature of the heat seal layer decreases, the tapes tend to stick to each other more easily, making blocking more likely to occur.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a cover tape that can be heat sealed with less thermal energy while suppressing the occurrence of blocking, and an electronic component packaging body using the same. [Means for solving the problem]

[0008] In order to solve the above problems, one aspect of the present invention provides a cover tape having at least a base layer and a heat seal layer, the heat seal layer containing a polystyrene-based resin (A) and an ethylene-(meth)acrylic acid-based copolymer (B), and the contents of the (A) component and the (B) component are more than 80 parts by mass and not more than 95 parts by mass, and 5 parts by mass or more and less than 20 parts by mass, respectively, relative to 100 parts by mass of the total of the (A) component and the (B) component.

[0009] The cover tape described above is less susceptible to blocking and can be heat sealed with less thermal energy, which makes it possible to increase the speed and temperature of heat sealing while preventing production line stoppages due to blocking, thereby improving productivity and saving energy in the manufacture of electronic component packages.

[0010] The component (A) may contain a copolymer of a styrene-based hydrocarbon and a conjugated diene-based hydrocarbon, and high-impact polystyrene, which makes it easier to ensure a stable peel strength.

[0011] The component (B) may contain an ethylene-methyl methacrylate copolymer from the viewpoints of achieving sealing properties with less thermal energy and suppressing blocking.

[0012] Another aspect of the present invention provides an electronic component packaging body comprising a carrier tape having a storage section, an electronic component stored in the storage section of the carrier tape, and the above-mentioned cover tape heat-sealed to the carrier tape as a lid material. Effect of the Invention

[0013] According to the present invention, it is possible to provide a cover tape that can be heat-sealed with less thermal energy while suppressing the occurrence of blocking, and an electronic component package using the same. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic cross-sectional view showing an embodiment of a cover tape. [Diagram 2] 1 is a partially cutaway perspective view showing one embodiment of an electronic component package. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Preferred embodiments of the present invention will now be described in detail.

[0016] [Cover tape] The cover tape of this embodiment includes at least a base layer and a heat seal layer.

[0017] FIG. 1 is a schematic cross-sectional view showing an embodiment of a cover tape. The cover tape 50 shown in FIG. 1(a) includes a base layer 1, a heat seal layer 2 provided on one side of the base layer 1, and an intermediate layer 3 provided between the base layer 1 and the heat seal layer 2. The cover tape 52 shown in FIG. 1(b) includes two intermediate layers 3a and 3b provided between the base layer 1 and the heat seal layer 2. The cover tape of this embodiment may have a two-layer structure without an intermediate layer, or may have a structure further including a layer such as an antistatic layer on the opposite side of the base layer 1 from the heat seal layer 2. The cover tape of this embodiment may also have a structure further including a layer such as an antistatic layer on the opposite side of the base layer 1 from the heat seal layer 2, as long as the heat sealability of the heat seal layer is not impaired.

[0018] (base material layer) The substrate layer may be a film formed from a resin composition containing one or more thermoplastic resins selected from the group consisting of polyester resins such as polyethylene terephthalate and polyethylene naphthalate, polyolefin resins such as polypropylene, polyamide resins such as nylon, polystyrene resins, polyethylene resins, and polycarbonate resins. From the viewpoint of mechanical strength, these films are preferably biaxially oriented films, and from the viewpoints of transparency and toughness, more preferably biaxially oriented polyethylene terephthalate films.

[0019] Examples of polystyrene resins include polymers having a molar ratio of 1 / 2 or more of styrene units in the molecular chain, such as polystyrene, high impact polystyrene (HIPS: high impact polystyrene), styrene-butadiene copolymer or its hydrogenation product, styrene-isoprene copolymer or its hydrogenation product, graft copolymer of styrene and ethylene, styrene-butene-butadiene copolymer, copolymer of methacrylic acid and styrene, etc. These can be used alone or in combination of two or more (mixture).

[0020] Examples of polyethylene resins include those having ethylene units in a molecular chain at a molar ratio of 1 / 2 or more, such as low-density polyethylene, linear low-density polyethylene, very low-density polyethylene, ethylene-α-olefin, ethylene-vinyl acetate copolymer, ethylene-(meth)acrylic acid copolymer, ethylene-methyl (meth)acrylate copolymer, ethylene-ethyl (meth)acrylate copolymer, ethylene-propylene rubber, etc. These can be used alone or in combination (mixture) of two or more.

[0021] In order to obtain extrusion stability during film formation, the base layer may contain various additives such as commonly used antioxidants and lubricants.

[0022] The substrate layer may be a single layer or may have a multi-layer structure.

[0023] The thickness of the base layer may be 5 to 100 μm, 10 to 80 μm, or 12 to 30 μm, from the viewpoints of mechanical strength and heat conductivity during heat sealing.

[0024] (Middle class) The intermediate layer can be provided for the purpose of strengthening the adhesive strength between the base layer and the heat seal layer, and can contain a thermoplastic resin. Examples of the thermoplastic resin include: (i) Polyethylene resins such as low-density polyethylene, linear low-density polyethylene, and very low-density polyethylene (ii) Ethylene-1-butene, copolymers of ethylene and unsaturated carboxylic acids, ethylene-(meth)acrylic acid ester copolymers, ethylene-vinyl acetate copolymers, and further terpolymers with acid anhydrides, and mixtures thereof (iii) Styrene-ethylene graft copolymers, styrene-propylene graft copolymers, styrene-ethylene-butadiene block copolymers, and mixtures thereof. etc.

[0025] As the thermoplastic resin, from the viewpoints of the above-mentioned purpose and ease of layer formation, a polyethylene-based resin is preferred, and a low-density polyethylene resin or a linear low-density polyethylene resin is more preferred.

[0026] The intermediate layer may have a structure of two or more layers. In this case, the heat seal layer and the intermediate layer are co-extruded to improve the extrusion stability of the heat seal layer, while another intermediate layer can improve the adhesion between the co-extruded film and the base layer. The intermediate layer having a structure of two or more layers may be, for example, a first intermediate layer on the side in contact with the heat seal layer, which contains one or more of the resins shown in (i), (ii) and (iii) above, and a second intermediate layer on the side in contact with the base layer, which contains one or more of the resins shown in (i) and (ii) above.

[0027] In order to obtain extrusion stability during film formation, the intermediate layer may contain various additives such as commonly used antioxidants and lubricants.

[0028] The thickness of the intermediate layer may be 3 to 70 μm, 5 to 60 μm, or 10 to 50 μm from the viewpoint of ensuring the adhesive strength between the base layer and the heat seal layer and the peel strength of the cover tape.

[0029] The cover tape of the present embodiment may have two or more base layers and / or intermediate layers. For example, the base layer and intermediate layer of such a cover tape may have a three-layer structure of base layer / intermediate layer / base layer, or a four-layer structure of intermediate layer / base layer / intermediate layer / base layer.

[0030] When the cover tape of the present embodiment has two or more base layers and / or intermediate layers, a known adhesive can be used to strengthen the adhesive strength between the layers. Examples of the adhesive include isocyanate-based adhesives and ethyleneimine-based adhesives. The adhesive layer preferably has a thickness of 5 μm or less in order to prevent the cover tape from having a large variation in peel strength.

[0031] (Heat seal layer) The heat seal layer may contain a polystyrene resin (A) (hereinafter, sometimes referred to as component (A)) and an ethylene-(meth)acrylic acid copolymer (B) (hereinafter, sometimes referred to as component (B)). A cover tape having such a heat seal layer can easily ensure sealing properties for carrier tapes made of various materials, such as polystyrene carrier tapes and polycarbonate carrier tapes.

[0032] The heat seal layer can contain, as the component (A), a copolymer of a styrene-based hydrocarbon and a conjugated diene-based hydrocarbon, and high-impact polystyrene, or may contain a mixture of these.

[0033] Examples of styrene-based hydrocarbons include styrene, α-methylstyrene, various alkyl-substituted styrenes, etc. Examples of conjugated diene-based hydrocarbons include butadiene, isoprene, etc.

[0034] From the viewpoint of facilitating a stable peel strength of the cover tape, the heat seal layer can contain, as the component (A), a styrene-butadiene copolymer and high-impact polystyrene, or may contain a mixture of these.

[0035] From the viewpoint of adjusting the peel strength and film-forming properties, the (A) component may include a block copolymer (A-1) (hereinafter also referred to as the (A-1) component) of 50% by mass or more and 95% by mass or less of a styrene-based hydrocarbon and 5% by mass or more and 50% by mass or less of a conjugated diene-based hydrocarbon, a block copolymer (A-2) (hereinafter also referred to as the (A-2) component) of 10% by mass or more and less than 50% by mass of a styrene-based hydrocarbon and more than 50% by mass or less and 90% by mass or less of a conjugated diene-based hydrocarbon, and an impact-resistant polystyrene (A-3) (hereinafter also referred to as the (A-3) component). In this case, the content ratio of each may be 20 to 40 parts by mass of the (A-1) component, 35 to 60 parts by mass of the (A-2) component, and 5 to 15 parts by mass of the (A-3) component relative to 100 parts by mass of the total of the (A-1) component, the (A-2) component, and the (A-3) component.

[0036] Examples of the ethylene-(meth)acrylic acid copolymer (B) include ethylene-acrylic acid copolymer (EAA), ethylene-methacrylic acid copolymer (EMAA), ethylene-methyl methacrylate copolymer (EMMA), ethylene-ethyl acrylate copolymer (EEA), ethylene-methyl acrylate copolymer (EMA), and ethylene-glycidyl methacrylate-methyl acrylate copolymer (EGMA-MA). These can be used alone or in combination (mixture) of two or more.

[0037] From the viewpoints of achieving sealing ability with less thermal energy and suppressing blocking, the ethylene content of the component (B) may be 60 to 95 mass %, or 65 to 90 mass %.

[0038] In order to obtain extrusion stability during film formation, the heat seal layer may contain various additives such as commonly used antioxidants and lubricants.

[0039] From the viewpoint of suppressing the occurrence of blocking and enabling heat sealing with less thermal energy, the contents of the (A) component and the (B) component in the heat seal layer may be more than 80 parts by mass and not more than 95 parts by mass and 5 parts by mass and less than 20 parts by mass, or may be 82 parts by mass or more and not more than 95 parts by mass and 5 parts by mass or more and not more than 18 parts by mass, relative to 100 parts by mass of the total of the (A) component and the (B) component. Also, from the viewpoint of payout property, the contents of the (A) component and the (B) component in the heat seal layer may be 84 parts by mass or more and not more than 95 parts by mass and 5 parts by mass or more and not more than 16 parts by mass, or may be 85 parts by mass or more and not more than 95 parts by mass and 5 parts by mass or more and not more than 15 parts by mass, relative to 100 parts by mass of the total of the (A) component and the (B) component.

[0040] The total content of the (A) component and the (B) component in the heat seal layer may be 50 mass% or more, 70 mass% or more, 90 mass% or more, or may be 100 mass% based on the total amount of the heat seal layer.

[0041] Each of the above-mentioned layers can be made into a film by, for example, an inflation method, a T-die method, a casting method, a calendar method, etc. In this case, the components constituting each layer are blended using a mixer such as a Henschel mixer, a tumbler mixer, or a Meisel mixer, and the blend is directly made into a film using an extruder, or the blend is kneaded and extruded once using a single-screw or twin-screw extruder to obtain pellets, and the pellets are then further extruded using an extruder to make a film.

[0042] The heat seal layer may be formed by a method of forming a film by extrusion molding such as inflation molding or T-die extrusion, a method of dissolving the above-mentioned components (A) and (B) in a solvent and coating the film of the base layer, or a method of coating the components as an aqueous emulsion.

[0043] When forming a film for a heat seal layer by extrusion molding, it is preferable to co-extrude with an intermediate layer in order to improve extrusion stability. For example, the resin constituting the intermediate layer and the resin constituting the heat seal layer are melt-kneaded using separate single-screw or twin-screw extruders, and the two are laminated and integrated through a feed block or a multi-manifold die, and then extruded from a T-die to obtain a two-layer film in which the intermediate layer and the heat seal layer are laminated.

[0044] The film for the heat seal layer obtained by extrusion molding may be laminated with a base layer by a general method such as dry lamination or extrusion lamination to form a cover tape.

[0045] The total thickness of the cover tape can be 30 to 100 μm, or may be 35 to 80 μm, or may be 40 to 70 μm. If it is within such a range, it is easy to ensure the strength and sealing property of the tape.

[0046] The cover tape of this embodiment is suitable for packaging electronic components. Examples of electronic components include ICs, LEDs (light-emitting diodes), resistors, liquid crystals, capacitors, transistors, piezoelectric resistors, filters, quartz crystal oscillators, diodes, connectors, switches, volumes, relays, inductors, etc. The electronic components may be intermediate products using the above-mentioned components, or may be final products.

[0047] In the above-mentioned applications, it is preferable to impart antistatic properties to the base layer and the heat seal layer in order to prevent dust adhesion and dissipate the charge of the cover tape itself. To impart antistatic properties, surfactant-type antistatic agents, conductive metal oxide particles, and electronically conductive polymers can be used as commonly used antistatic agents. These antistatic agents can be kneaded into the resin depending on the performance to be expressed, but from the viewpoint of efficiently expressing the effect, they can be applied to both surface layers of the cover tape using a gravure coater or the like.

[0048] Cover tapes for packaging electronic components can, for example, be heat sealed to carrier tapes.

[0049] The carrier tape may be provided with pockets for storing electronic components by pressure forming, vacuum forming, or other methods. Materials that can be easily molded into sheets, such as polyvinyl chloride (PVC), polystyrene (PS), polyester (A-PET, PEN, PET-G, PCTA), polypropylene (PP), polycarbonate (PC), polyacrylonitrile (PAN), and acrylonitrile-butadiene-styrene copolymer (ABS), can be used as the material for the carrier tape. These resins can be used alone or in combination. The carrier tape may be a laminate consisting of multiple layers.

[0050] The cover tape of this embodiment can be used in combination with a carrier tape such as a polystyrene carrier tape or a polycarbonate carrier tape.

[0051] <Electronic component packaging> The electronic component packaging body of this embodiment comprises a carrier tape having a storage section capable of storing an electronic component, the electronic component stored in the storage section of the carrier tape, and a cover tape of this embodiment heat-sealed to the carrier tape as a lid material.

[0052] Fig. 2 is a partially cutaway perspective view showing one embodiment of an electronic component package. The electronic component package 200 shown in Fig. 2 includes an embossed carrier tape 16 provided with a storage section 20, an electronic component 40 stored in the storage section 20, and a cover film 50 heat-sealed to the embossed carrier tape 16. The embossed carrier tape 16 is provided with feed holes 30 that can be used for transporting various electronic components such as ICs in an encapsulation process or the like. In addition, a hole (not shown) for inspecting the electronic components is provided at the bottom of the storage section 20.

[0053] The electronic components and carrier tape may be those mentioned above.

[0054] The electronic device package of this embodiment can be used as a carrier tape body wound into a reel for storing and transporting electronic devices.

[0055] The electronic device package of this embodiment can be produced by a method including a step of heat-sealing the cover tape of this embodiment to a carrier tape having electronic devices housed in housing portions.

[0056] The heat sealing of the cover tape can be performed using a member called a sealing iron, which can apply a predetermined amount of heat and a predetermined pressure to the heat seal layer. The cover tape can be heat-sealed to the surface of the carrier tape by pressing such a sealing iron onto the carrier tape from above the cover tape. As a specific method, a repeated sealing method in which the sealing iron is pressed multiple times while the embossed carrier tape is being transported, or a continuous sealing method in which the sealing iron is continuously applied to the cover tape side to heat seal it can be applied.

[0057] The sealing temperature may be from 100 to 240°C, or from 120 to 220°C.

[0058] According to the above-described manufacturing method, by using the cover tape of this embodiment, it is possible to increase the speed and temperature of heat sealing, thereby improving productivity and saving energy in the manufacture of electronic component packages. EXAMPLES

[0059] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0060] Example 1 As a polystyrene-based resin, 35 parts by mass of a styrene-butadiene copolymer (manufactured by Denka Co., Ltd., product name "Clearlen 170ZR", styrene / butadiene mass ratio = 83 / 17), 55 parts by mass of a styrene-butadiene copolymer (manufactured by JSR Corporation, product name "TR2000", styrene / butadiene mass ratio = 40 / 60), 5 parts by mass of a high-impact polystyrene (manufactured by Toyo Styrene Co., Ltd., product name "HIPS H870"), and as an ethylene-(meth)acrylic acid-based copolymer, 5 parts by mass of an ethylene-methyl methacrylate copolymer (manufactured by Sumitomo Chemical Co., Ltd., product name "Acryft WH303-F", methyl methacrylate content: 18% by mass, ethylene content: 82% by mass) were kneaded in a twin-screw extruder to obtain a resin composition constituting a heat seal layer. This resin composition and a linear low-density polyethylene (manufactured by Ube Maruzen Polyethylene Co., Ltd., product name "Yumerit 2040F") as a first intermediate layer were co-extruded by a T-die method to obtain a two-layer film (total thickness 30 μm) of a first intermediate layer (thickness 20 μm) / heat seal layer (thickness 10 μm). This two-layer film was laminated by an extrusion lamination method with a biaxially oriented polyethylene terephthalate film (manufactured by Toyobo Co., Ltd., product name "Ester Film E5100", thickness 16 μm) via a second intermediate layer (thickness 13 μm) made of low-density polyethylene resin, to obtain a cover tape of Example 1.

[0061] (Examples 2 to 8, Comparative Examples 1 to 3) The cover tapes of Examples 2 to 8 and Comparative Examples 1 to 3 were obtained in the same manner as in Example 1, except that the polystyrene resin and the ethylene-(meth)acrylic acid copolymer were used in the compositions shown in Table 1.

[0062] Details of the raw materials shown in Table 1 are as follows: SBC: styrene-butadiene copolymer (manufactured by Denka Co., Ltd., product name "Clearlen 170ZR", styrene / butadiene mass ratio = 83 / 17) SBR: Styrene-butadiene copolymer (manufactured by JSR Corporation, product name "TR2000", styrene / butadiene mass ratio = 40 / 60) HIPS: High impact polystyrene (manufactured by Toyo Styrene Co., Ltd., product name "HIPS H870") EMMA: Ethylene-methyl methacrylate copolymer (manufactured by Sumitomo Chemical Co., Ltd., product name "Acryft WH303-F", methyl methacrylate content: 18% by mass, ethylene content: 82% by mass) EGMA-MA: Ethylene-glycidyl methacrylate-methyl acrylate copolymer (manufactured by Sumitomo Chemical Co., Ltd., product name "Bondfast BF-7M", glycidyl methacrylate content: 6% by mass, methyl acrylate content: 27% by mass, ethylene content: 67% by mass) EMA: Ethylene-methyl acrylate copolymer (manufactured by Japan Polyethylene Co., Ltd., product name "Rexpearl EB240H", methyl acrylate content: 20% by mass, ethylene content: 80% by mass) EEA: Ethylene-ethyl acrylate copolymer (manufactured by Ube Maruzen Polyethylene Co., Ltd., product name "UBE Polyethylene ZE735", ethyl acrylate content: 19% by mass, ethylene content: 81% by mass)

[0063] The cover tapes of each Example and Comparative Example were evaluated by the following methods. The results are shown in Table 1.

[0064] [Evaluation of low temperature sealing properties] Using a taping machine (manufactured by Nagata Seiki Co., Ltd., product name "NK-600"), a 21.5 mm wide cover tape was heat sealed to a 24 mm wide polystyrene carrier tape (manufactured by Denka Co., Ltd., product name "EC-R") under the conditions of a seal head width of 0.5 mm x 2, a seal head length of 24 mm, a seal pressure of 0.5 kgf, a feed length of 12 mm, a seal time of 0.3 seconds, and a seal iron temperature of 140 ° C. Thereafter, the peel strength was measured when the cover tape was peeled at a peel angle of 170 ° to 180 ° at a peel speed of 300 mm per minute in an atmosphere of 23 ° C. and 50% relative humidity, and the low-temperature sealability was evaluated according to the following criteria. <Judgment criteria> A: Peel strength is 0.2N or more C: Peel strength is less than 0.2N

[0065] [Evaluation of blocking resistance] A 21.5 mm wide record-wrapped cover tape was left to stand for one day in an atmosphere with a temperature of 23°C and a relative humidity of 50%, and then it was unwound at a speed of 2000 mm per minute and the load applied during unwrapping was measured with a digital force gauge.

[0066] The cover tape was also manually unwound, and the presence or absence of blocking was confirmed, and the blocking resistance was evaluated according to the following criteria. A: No blocking B: There is some blocking here and there. C: There is overall blocking.

[0067] [Table 1]

[0068] As shown in Table 1, it was confirmed that the cover tapes of Examples 1 to 8 were capable of heat sealing with less thermal energy while suppressing the occurrence of blocking.

[0069] On the other hand, the cover tape of Comparative Example 1, in which the heat seal layer did not contain an ethylene-(meth)acrylic acid-based copolymer, had a low peel strength when sealed at low temperatures, and the cover tapes of Comparative Examples 2 and 3, in which the content of the ethylene-(meth)acrylic acid-based copolymer in the heat seal layer exceeded the range according to the present invention, had a large load when unwound and also suffered from blocking. [Explanation of symbols]

[0070] 1...base material layer, 2...heat seal layer, 3, 3a, 3b...intermediate layer, 16...embossed carrier tape, 20...accommodation section, 30...feed hole, 40...electronic component, 50, 52...cover tape, 200...electronic component package.

Claims

1. The film has at least a base layer and a heat seal layer, the heat seal layer contains a polystyrene-based resin (A) and an ethylene-(meth)acrylic acid-based copolymer (B); The cover tape has a content of the (A) component and a content of the (B) component that are more than 80 parts by mass and not more than 95 parts by mass, and a content of the (A) component and the (B) component that are more than 5 parts by mass and not more than 20 parts by mass, respectively, relative to 100 parts by mass of the total of the (A) component and the (B) component.

2. 2. The cover tape of claim 1, wherein the component (A) comprises a copolymer of a styrene-based hydrocarbon and a conjugated diene-based hydrocarbon and a high-impact polystyrene.

3. 3. The cover tape according to claim 1, wherein the component (B) comprises an ethylene-methyl methacrylate copolymer.

4. An electronic component packaging body comprising: a carrier tape having a storage section; an electronic component stored in the storage section of the carrier tape; and the cover tape according to any one of claims 1 to 3 heat-sealed to the carrier tape as a lid material.

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