396 results about "Phenylene" patented technology

The invention provides a core material for a vacuum insulation panel, the vacuum insulation panel and a preparation method and application of the vacuum insulation panel. The core material for the vacuum insulation panel comprises aramid fibers and a binding material, and the aramid fibers comprise at least one of poly (m-phenylene isophthalamide) fibers, poly (p-phenylene terephthalamide) fibers and heterocyclic aramid fibers; the length of the aramid fiber ranges from 1 mm to 10 mm. The vacuum insulation panel comprises a core material for the vacuum insulation panel and a barrier film material, and the barrier film material wraps the core material for the vacuum insulation panel. In the process of preparing the vacuum insulated panel and the process of cutting and producing the core material for the vacuum insulated panel, dust and fine fibers are not generated, and environmental pollution and health risks are avoided.

The invention belongs to the technical field of preparation of single-walled carbon nanotube fibers, and particularly relates to a preparation method of high-conductivity single-walled carbon nanotube fibers, which comprises the following steps: preparing a single-walled carbon nanotube crude product by a chemical vapor deposition method, pickling and purifying, and oxidizing and purifying at high temperature to obtain a single-walled carbon nanotube; the preparation method comprises the following steps: adding a single-walled carbon nanotube into a poly [2, 5-dihydroxy-1, 4-phenylene pyridine diimidazole] aqueous solution, dispersing, and collecting supernatant liquid to obtain a single-walled carbon nanotube purified liquid; adding chlorosulfonic acid into the single-walled carbon nanotube purified solution in an argon atmosphere to obtain a single-walled carbon nanotube spinning solution; and injecting the single-walled carbon nanotube spinning solution into a coagulating bath in an argon atmosphere to prepare the single-walled carbon nanotube fiber. According to the invention, the poly [2, 5-dihydroxy-1, 4-phenylenediimidazole] is adopted to selectively disperse the metallic single-walled carbon nanotubes, and the gold single-walled carbon nanotubes in the single-walled carbon nanotube fibers are high in purity, so that the conductivity can be improved.

The invention relates to the technical field of nuclear waste treatment, in particular to a cucurbituril-based supramolecular organic framework material as well as a preparation method and application thereof. A construction unit of the supramolecular organic framework material is constructed by taking cucurbit [8] uril (CB8) as a subject and terephthalyl viologen ligand 1, 1 ''-(1, 4-phenylene) bis ([4, 4 '-bipyridyl]-1-onium) salt (PBV. 2X) as an object through the bonding effect of the subject and the object; in the molecular structure of the supramolecular organic framework material, the construction units are staggered and stacked in parallel in the space, and NO3 <-> is located at the gap of the adjacent CB8. The supramolecular organic framework material disclosed by the invention has high structural stability and cationic framework characteristics, and a rigid framework and a pyridine conjugated system of CB8 endow the material with excellent chemical / irradiation stability, so that the material shows ultrahigh removal rate on ReO4 <-> / TcO4 <-> in extreme environments (strong acid, strong alkali and high irradiation).

The invention discloses a fluorinated COF enhanced PVDF-HFP composite gel polymer electrolyte. The fluorinated COF enhanced PVDF-HFP composite gel polymer electrolyte is prepared from the following raw materials: polyvinylidene fluoride-co-hexafluoropropylene, a fluorinated covalent organic framework containing an ether oxygen bond and a carbon-carbon unsaturated double bond, bis (trifluoromethylsulfonyl) imide anion ionic liquid and fluorine-containing imide lithium salt, the fluorinated covalent organic framework containing the ether-oxygen bond and the carbon-carbon unsaturated double bond is prepared by carrying out condensation reaction on a perfluorophenylene-containing module and the ether-oxygen bond-containing aromatic module. According to the electrolyte, PVDF-HFP is used as a polymer matrix, bis (trifluoromethylsulfonyl) imidogen ionic liquid is used as a functional phase and a plasticizer, imide lithium salt is used as a lithium ion source, fluorinated COF containing ether oxygen bonds and olefinic bonds is introduced, and the electrolyte has high ionic conductivity, high lithium ion transference number, excellent mechanical property and interface stability; the method is especially suitable for a high-safety lithium metal battery system.

The invention discloses a sulfur-containing all-solid-state polymer electrolyte membrane, a preparation method and a lithium metal battery, and belongs to the technical field of polymer electrolytes.The method comprises the steps that 1, 4-phenylene-diacrylate and dimethyl tetrasulfide are evenly mixed and cooled to the room temperature after a reverse vulcanization reaction, and a polymer solid is obtained; the preparation method comprises the following steps: dissolving a polymer solid in dimethyl sulfoxide, adding bis (trifluoromethanesulfonyl) lithium imide, uniformly stirring and mixing, casting in a PTFE (Polytetrafluoroethylene) mold, uniformly spreading, and carrying out vacuum drying to obtain the sulfur-containing all-solid-state polymer electrolyte membrane. The ion transmission function of a liquid electrolyte is replaced by the solid ion conduction property, and the physical isolation function of a diaphragm is replaced by a compact and firm physical structure, so that the Li < + > diffusion energy barrier is reduced, the electrochemical window is widened, the interface impedance is reduced, and the interface compatibility between the positive and negative electrode materials and the solid electrolyte is improved; the lithium metal battery assembled by the electrolyte has excellent electrochemical performance and cycle performance.

The invention relates to an epoxy hardener and a preparation method thereof and a preparation method of a visbreaking uncovering protective film, and the preparation method of the epoxy hardener comprises the following steps: adding 2, 2 '-(1, 3-phenylene)-dioxazoline and a phenolic hydroxyl group or carboxyl group-containing bifunctional monomer into a first solvent, stirring at normal temperature to obtain a first solution, heating to a first temperature, and stirring at normal temperature to obtain a second solution; the first temperature is 155 DEG C to 165 DEG C, and refluxing for 3.5 hours to 4.5 hours; adding a terminated monomer containing carboxyl or phenolic hydroxyl into a reaction system of the first solution, and continuing to carry out reflux reaction for 2.5-3.5 hours at the first temperature; and after the reaction is finished, purifying and drying to obtain the epoxy curing agent. The epoxy curing agent disclosed by the invention has compatibility with low-polarity glue and has a relatively high curing degree in a high-temperature environment; the viscosity-reducing uncovering protective film has the advantages that the viscosity is reduced at high temperature, and the uncovering design efficiency of different types of PCBs is improved.

An extrusion product, such as a film, pipe, or cable / wire sheath, includes a first layer and a second layer. The first layer includes a polymeric material (A) having repeating units of the formula: -0-Ph-0-Ph-CO-Ph I and repeating units of the formula: -0-Ph-Ph-0-Ph-CO-Ph II, where Ph represents a phenylene moiety. The second layer may be a polyaryletherketone (PAEK), such as polyetheretherketone (PEEK). The first layer is intended to reduce the formation of deposits on the die of an extrusion device during extrusion of the product. A method for producing a product including the first layer and the second layer, as well as the use of the polymeric material (A) to reduce the formation of deposits on the die of an extrusion device during extrusion of a second polymeric material, are also described.

Disclosed is a resin composition, including 100 parts by weight of maleimide resin and 0.3 parts by weight to 10.0 parts by weight of organophosphine compound having a structure shown in Formula (1), wherein —R— includes a substituted or unsubstituted phenylene group, biphenylene group, or naphthylene group. Also disclosed are a use of the resin composition in preparing a product, and at least a portion of the product made from the resin composition. The product includes a prepreg, a resin film, a laminate, a printed circuit board, or a cured insulator.

The invention belongs to the technical field of biosensing of organic electrochemical transistors, and particularly relates to an organic electrochemical transistor based on a spirobifluorene polymer as well as a preparation method and application of the organic electrochemical transistor. An active layer of the organic electrochemical transistor is composed of poly [benzo [2, 1, 3] thiadiazole-4, 7-diyl-[5-[3, 6-bis (octyloxy)-9, 9 '-spirobis [9H-fluorene]-2-yl]-1, 3-phenylene]], an ionic gel layer is prepared by mixing PVDF-HFP, EMIM TFSI and Li TFSI, and a gate electrode is modified with MnO2 nanoparticles and poly [benzo [2, 1, 3] thiadiazole-4, 7-diyl-[5-[3, 6-bis (octyloxy)-9, 9'-spirobis [9H-fluorene]-2-yl]-1, 3-phenylene]-1, 3] thiadiazole-4, 7-diyl-[5 and 2, 3-phenylene]]. The organic electrochemical transistor can be used for detection of hydrogen peroxide, is high in detection sensitivity, good in selectivity and wide in application range, and provides a new solution for detection of hydrogen peroxide.

The invention discloses a two-dimensional copper nanosheet / graphene / aramid fiber composite film material and a preparation method and application thereof, and the method comprises the following steps: (1) adding copper nanosheets and graphene into a mixed solution of poly-p-phenylene terephthamide, potassium hydroxide and dimethyl sulfoxide, and uniformly dispersing to obtain a mixed solution; forming a copper nanosheet / graphene / aramid fiber composite solution; and (2) filtering and drying the copper nanosheet / graphene / aramid fiber composite solution to obtain the two-dimensional copper nanosheet / graphene / aramid fiber composite film material. The preparation method is simple and easy to implement, the cost can be effectively controlled, and the prepared two-dimensional copper nanosheet / graphene / aramid fiber composite film material has efficient electromagnetic shielding performance.

The invention relates to the technical field of solar cells, in particular to a perovskite solar cell and a preparation method thereof, and a photovoltaic module wherein the perovskite solar cell comprises a substrate structure, and a hole transport layer, a perovskite absorption layer and an electron transport layer which are sequentially stacked on one side of the substrate structure from near to far; the hole transport layer comprises a first material and a second material, and the first material is a phosphonic acid compound containing carbazolyl; and the second material comprises at least one of (4-(pyrene-1-yl) phenyl) phosphonic acid, (4-(6-fluoro-9H-thieno [2, 3,: 4, 5] thieno [3, 2-b] indole-9-yl) butyl) phosphonic acid, (4-(5H-benzo [4, 5] thieno [3, 2-c] indole-9-yl) butyl) phosphonic acid and ((9H-carbazole-3, 6-diyl) bis (4, 1-phenylene)) bisphosphonic acid. According to the technical scheme, the contact uniformity between the hole transport layer and the substrate structure and between the hole transport layer and the perovskite absorption layer in the perovskite solar cell is improved, and the overall electrochemical performance of the perovskite solar cell is effectively improved.

To provide a resist composition capable of producing a resist pattern having good line edge roughness.SOLUTION: The resist composition contains a compound represented by formula (I), a resin having an acid-labile group, and an acid generator. [In the formula, R2 represents * -X1-Ph - L1 - OH. Ph represents a substituted or unsubstituted phenylene; R3 represents a halogen atom, a hydroxy group, a haloalkyl group or an alkyl group, and - CH2 - included in the alkyl group may be replaced by - O - or - CO -. m2 is an integer of 1 to 4, m3 is an integer of 0 to 3, provided that 1 ≤ m2 + m3 ≤ 4, and one or more of L1, R1, R2, and R3 have a halogen atom. ] SELECTED DRAWING: None

A paving material composition containing: an epoxy resin; an epoxy resin curing agent containing a reaction composition (A) containing a reaction product of styrene and a polyamine compound represented by the following formula (1); and an aggregate.wherein X is a phenylene group.

The application relates to a nitrogen-containing organic compound, a perovskite solar cell and a preparation method thereof and an electric device. The structure of the nitrogen-containing organic compound is shown in the figure; the structure of Ar is shown in the figure; the structure of L1 is shown in the figure; the N atom in formula (III) is connected with L2; L2 is selected from one of C2-C8 alkylene, phenylene, naphthylene and biphenylene; L3-L4 are independently selected from one of a bond, a single bond, O, S and -C(R7)2-; R1 is selected from one of phosphonic acid, carboxylic acid and cyanophosphonic acid; R2 is selected from one of phenyl, substituted phenyl, pyridyl, anilino and benzoyl; R7 is selected from one of hydrogen and C1-C4 alkyl; m, n and p are independently selected from integers of 0-3, and q is selected from integers of 0-4. The anchoring ability, carrier transport ability and defect passivation ability of the nitrogen-containing organic compound are high, and the stability under the action of light and heat is high.

The invention relates to the technical field of rubber, in particular to an off-road tire base rubber composition. Based on 100 parts by weight of natural rubber components, the natural rubber composition further comprises the following components in parts by weight: 20-40 parts of carbon black, 5-15 parts of silicon dioxide hydrate, 5-20 parts of nano zinc oxide, 1-3 parts of stearic acid, 1-3 parts of p-phenylenediamine, 1-3 parts of a ketoamine anti-aging agent, 1-3 parts of bis (triethoxysilyl) propyl tetrasulfide, 1-5 parts of carbon nanotubes CNT, 1-4 parts of N, N '-m-phenylene bismaleimide, 0.5-2 parts of sulfur and 0.5-2 parts of a sulfenamide accelerant. The modulus of the rubber material is improved by adding the CNT, so that the consumption of carbon black is reduced, and heat generation is reduced; by adding nano zinc oxide and carbon nanotubes, the heat conductivity of the rubber material is improved; and by adding the N, N '-m-phenylene bismaleimide, the heat resistance of the rubber material is improved.

Provided is an adhesive composition for laminated optical films, which is used for bonding at least two optical films, and which contains a curable component, metal oxide particles, and a compound represented by general formula (1) (wherein X represents a reactive group; (In the formula, Y represents an alkylene group having 1-12 carbon atoms and optionally having a branched chain, or a phenylene group optionally having a substituent, and R1 and R2 each independently represent a hydrogen atom, an aliphatic hydrocarbon group optionally having a substituent, an aryl group, or a heterocyclic group).

Combination of the following formula (I) where - R 1 to R 2 independent C1- to C8-hydrocarbyl, which contains at least one sp 3 -hybridized carbon atom comprising the C1- to Cs-hydrocarbyl via a sp 3 -hybridized carbon atom of C1 to C8 -hydrocarbylsan the P atom of formula (I) is bonded; - L 1 , A and L 2 are independently selected from the group consisting of a direct bond, substituted or unsubstituted phenylene, substituted or unsubstituted naphthylene, wherein at least one of L 1 , A and L 2 substituted or unsubstituted phenylene is and / or at least one of L 1 , A and L 2 substituted or unsubstituted naphthylene is; - whereupon, if one or more of L 1 , A and L 2substituted is / are, the one or more substituent(s) is / are independently selected from the group consisting of D, C1- to C6-alkyl and substituted or unsubstituted C6- to C 12 -Aryl, where, if the respective C6 - to C 12 -Aryl is substituted, the one or more substituent(s) is / are independently selected from the group consisting of D and C1 to C6 alkyl; - R 3 to R 9 are independently selected from the group consisting of H, D, C1- to C6-alkyl and substituted or unsubstituted C6- to C 12 -Aryl, where, if the respective C6 - to C 12 -Aryl is substituted, the one or more substituent(s) is / are independently selected from the group consisting of D and C1 to C6 alkyl.

The application belongs to the technical field of lithium ion batteries, and discloses a poly-m-phenylene isophthalamide-based electrostatic spinning flame-retardant separator and application thereof. The m-phenylene isophthalamide-based electrostatic spinning separator, namely PMIA-based electrostatic spinning separator, is prepared by mixing modified PZS microspheres, PMIA and an organic solvent, and then adopting an electrostatic spinning method. The modified PZS microspheres are prepared by in-situ growth of an inorganic layer SiO2 on the surface of polyphosphazene PZS microspheres with flame-retardant properties. The polyphosphazene PZS microspheres are prepared by a polymerization reaction between tannic acid and hexachlorocyclotriphosphazene. The spinning separator prepared by the application has very excellent porosity, liquid absorption rate and ionic conductivity, and good thermal stability and flame retardancy.

Provided are a resin composition capable of producing a molded article having enhanced durability, and a molded article including the resin composition.SOLUTION: The resin composition contains a semi-aromatic polyamide having a structural unit represented by formula (1), carbon fibers, and a water-soluble carbodiimide. In Formula (1), Ar1 represents a phenylene or naphthylene group, and a plurality of Ar1 contained in the semi-aromatic polyamide may be the same as or different from each other. P is an integer of 4 to 12. [Chemical Formula 1] SELECTED DRAWING: None

The invention relates to a xylylene diisocyanate composition as well as a preparation method and application thereof. The xylylene diisocyanate composition comprises at least 98% of xylylene diisocyanate and has defoaming time less than or equal to 15 seconds. The resin lens prepared from the xylylene diisocyanate composition provided by the invention has a relatively low haze index.

The present invention relates to catalyst composition for cyclic carbonate production from CO2 and epoxides under mild conditions, which can effectively catalyze the cyclic carbonate synthesis and provides good selectivity to cyclic carbonate, wherein said catalyst composition comprising:a) the metal complex as shown in structure (I):wherein,M represents transition metal atom;R1, R2, and R3 represent independent group selected from hydrogen atom, halogen atom, alkyl group, alkenyl group, alkynyl group, alkoxy group, amine group, phenyl group, benzyl group, cyclic hydrocarbon group comprising hetero atom, perfluoroalkyl group, or nitro group;R4 represents group selected from alkylene group, cycloalkylene group, or phenylene group;X represents group selected from hydrogen atom, acetate group, or triflate group; andb) the organic compound as the co-catalyst selected from compound containing nitrogen, compound of quaternary ammonium salts, or compound of iminium salts.

An aromatic polysulfone having repeating units comprising the structure represented by the following general formula (S-1) and terminal structures represented by the following general formula (Se-1). -ph 1 -SO2-ph 2 -O- (S-1) [In formula (S-1), ph 1 and ph 2 Each can be independently a phenylene group that may have substituents. [(Ra)] x -Ar-O- (Se-1) [In formula (Se-1), Ar is an aromatic hydrocarbon group that may have substituents; Ra is a salt of sulfonic acid group or sulfonic acid group; x is an integer greater than 2, and multiple Ra can be the same or different.]

The invention relates to the technical field of organic synthesis, in particular to a preparation method of crude poly (p-phenylene terephthamide). According to the method, phase-to-phase switching between non-aqueous suspension and ionic liquid homogeneous phase is adopted, and AB type end group balance, alternating end sealing and interface confinement branching are combined to realize end group accurate control and molecular weight distribution convergence. The method comprises the following steps: emulsifying an N-methyl pyrrolidone / calcium chloride solution in paraffin oil; carrying out polycondensation with p-phenylenediamine and paraphthaloyl chloride at a low temperature, and adding p-aminobenzoyl chloride to carry out dynamic balance on an end group; after layering, transferring into 1-butyl-3-methylimidazole chloride / N, N-dimethylacetamide for continuous polycondensation; cooling and re-emulsifying, and alternately adding benzoyl chloride and p-toluyl chloride for end sealing; trimesoyl chloride is added to a phase interface to realize limited branching; and carrying out ionic liquid homogenization, amine termination and alcohol / water sedimentation washing to obtain the product. The method effectively relieves end group drift, inhibits high molecular weight tailing and improves the filtering performance, and is suitable for preparation of high-reliability aramid fibers.

The invention discloses wide-temperature-range silicone rubber-based rubber for aerospace thermal protection, a composite material and a preparation method of the wide-temperature-range silicone rubber-based rubber. According to the invention, three monomers, i.e., methylcyclosiloxane, hexaethylcyclotrisiloxane and phenylene silicon monomer, are subjected to ring opening and condensation copolymerization to obtain polysiloxane macromolecules containing three different chain link structures. A phenylene structure is introduced into a silicon rubber main chain, so that the silicon elastomer main chain is limited to form a volatile cyclic oligomer through a chain back-biting reaction and a chain segment rearrangement exchange reaction, the thermal stability is improved, and the initial decomposition temperature is up to 450.16 DEG C; the regularity of a molecular chain is broken by introducing ethyl, so that the glass-transition temperature is as low as 120.2 DEG C, and no crystallization phenomenon occurs. The base adhesive has excellent cold resistance, radiation resistance, ablation resistance, high temperature resistance and the like, and can be used as the base adhesive to be applied to the aspects of aerospace craft protective coatings, dynamic seal putty adhesives, sealants and the like.

The application discloses a preparation method of heat-conducting bamboo integrated material, and comprises the following steps: carrying out alkali treatment on bamboo chips to obtain alkali-treated bamboo chips; mixing boron nitride and polyvinyl alcohol to prepare a suspension; immersing the alkali-treated bamboo chips in the suspension and carrying out vacuum pressure impregnation to obtain modified bamboo chips; mixing boron nitride and poly-methylene polyphenylene isocyanate to obtain a composite adhesive; coating the composite adhesive on the upper and lower surfaces of the modified bamboo chips, assembling, hot-pressing, and curing to obtain the heat-conducting bamboo integrated material. According to the preparation method, the double-layer three-dimensional heat-conducting network of the 'boron nitride / polyvinyl alcohol impregnation layer' combined with the 'interlayer PMDI / boron nitride adhesive layer' is constructed, the boron nitride is distributed in the bamboo chips from the surface to the inside, and thus the heat-conducting bamboo integrated material with excellent heat-conducting performance and mechanical properties is prepared.

The present invention relates to a press jacket for a press roller, in particular for a press roller of a shoe press for dewatering a fibrous web, in particular a paper, cardboard, tissue or pulp web, or a conveyor belt, in particular for a machine for producing or treating a fibrous web, in particular a paper, cardboard or tissue machine, wherein the press jacket or the conveyor belt comprises at least one polyurethane-containing layer, wherein the polyurethane is formed by reacting a prepolymer and a crosslinking component, wherein the prepolymer is a reaction product of an isocyanate component and a polyol component, wherein the isocyanate component contains phenylene diisocyanate (PPDI), and wherein the crosslinking component contains bis(4-amino-2-chloro-3,5-diethylphenyl)methane (MCDEA) and 4,4'-methylenebis(2-ethylaniline) (MBOEA).

The invention relates to the technical field of biomedical materials, in particular to a COF heterojunction nanosphere with biomimetic mineralization and antibacterial functions and a preparation method and application thereof. The preparation method comprises the following steps: mixing a magnolol solution, a 1, 3, 5-tris (4-aminophenyl) benzene solution, a polyvinylpyrrolidone solution, a 2, 5-dimethoxybenzene-1, 4-dicarboxaldehyde solution and acetic acid, so as to obtain COFDMTP-coated Honokiol nanospheres; the preparation method comprises the following steps: mixing 4, 4 '-((2, 5-diformyl-1, 4-phenylene) bis (oxy)) dibutyric acid, COFDMTP (at) Honokiol nanospheres, acetonitrile and an acetic acid solution, and reacting to obtain the COFFPBA (at) Honokiol heterojunction nanospheres. The heterojunction nanosphere provided by the invention not only can promote the mineralization of acid-etched enamel, but also can effectively inhibit the growth of oral bacteria and reduce the occurrence of decayed teeth.

Provided is a speaker diaphragm that can uniformly increase rigidity throughout the entire area. A speaker diaphragm 1 of the present invention includes a base material having a resin matrix 2 with a thermoplastic resin as a main component and fibers 3 dispersed in the resin matrix 2, the fibers 3 being poly-p-phenylene benzobisoxazole fibers, the average length of the fibers 3 being 0.5 mm or more and 3.0 mm or less, and the content of the fibers in the base material being 3 mass% or more and 15 mass% or less.

A thermoplastic composition (C) comprising the following ingredients: a poly(biphenyl ether sulfone) (P1), a non-halogenated polyphosphonate (P2), and a white pigment (A1). The composition (C) may further comprise optional ingredients such as a melt stabilizer (A2), a poly(aryl ether ketone) (P3), a poly(para-phenylene sulfide) (P4), a non-halogenated flame retardant synergist (A3), and / or any additives (A4) different than ingredients (P1) to (P4) and (A1) to (A3). A method for improving fire resistance, melt viscosity, and ability to color-match, comprising compounding neat PPSU (P1) with the non-halogenated polyphosphonate (P2), the white pigment (A1), and any optional ingredients. A shaped article, especially an aircraft interior component, comprising or made from the composition (C).

Medical electrode comprising a base body (101) on which an electrically conductive first layer (102) and a cover layer (103) are arranged, the cover layer comprising an overhang (107) which partially covers the first layer (102), and an electrically conductive second layer (105) which is arranged on the first layer (102), the second layer (105) comprising an electrically conductive polymer selected from the group consisting of a polyacetylene, a polyvinyl alcohol, a polyfluorene, a polyphenylene, a polyphenylene vinylene, a polypyrene, a polyazulene, a polynaphthalene, a polypyrrole, a polycarbazole, a polyindole, a polyazepine, a polyaniline, a polyacene, a polythiophene, a polythiophene vinylene, a poly-p-phenylene sulfide, a polypyridine or functionalized derivatives, precursors or mixtures thereof;wherein the top layer (103) further comprises a recess (108), wherein the second layer (105) is arranged exclusively within the recess (108), and wherein the outwardly facing surface of the second layer (105) is spaced apart from the outwardly facing surface of the top layer (103), leaving a free area within the recess (108).