Superhydrophilic and oleophilic polymethacrylimide foams and methods of making the same

Abstract

The application belongs to the technical field of poly-methyl-acrylimide foam preparation, and particularly relates to super-hydrophilic and super-oleophilic poly-methyl-acrylimide foam and a preparation method thereof. The poly-methyl-acrylimide foam is prepared by using polyvinyl alcohol and metal oxide powder as raw materials, and the poly-methyl-acrylimide foam is soaked in a weak acid solution, so that the polyvinyl alcohol on the surface of the filler is dissolved, and a surface etching reaction between the weak acid solution and the metal oxide powder is utilized to construct a micro-nano rough structure on the surface of the poly-methyl-acrylimide foam, so that the poly-methyl-acrylimide foam has good affinity with polar and non-polar polymers, and the super-hydrophilic and super-oleophilic characteristics are realized. The problems of insufficient impregnation of the poly-methyl-acrylimide foam surface and resin, and insufficient bonding strength between the adhesive and the foam interface are overcome.

Description

Technical Field

[0001] This invention belongs to the field of polymethacrylimide foam preparation technology, specifically to superhydrophilic and oleophilic polymethacrylimide foam and its preparation method. Background Technology

[0002] Polymethacrylimide (PMI) foam is a closed-cell, uniformly distributed, isotropic, 100% rigid structural foam with excellent structural stability, high mechanical strength, and high-temperature resistance. It is currently the polymer rigid foam material with the highest specific strength and specific stiffness, commonly known as the "King of Foams," and is widely used in aerospace, weaponry, and other fields. As one of the main core materials in foam sandwich composite structures, like other closed-cell rigid foams, insufficient impregnation of the foam surface with the resin during the composite material preparation process leads to weak adhesion between the skin and the foam core layer of the foam sandwich composite material. In particular, insufficient adhesion between the adhesive and the foam interface has been one of the main causes of skin debonding and bulging in foam sandwich composite materials. Traditional solutions include adjusting the composition and viscosity of the adhesive or spending considerable effort cleaning the foam surface, but the adhesion effect is difficult to guarantee. Summary of the Invention

[0003] To address the shortcomings of the existing technologies, this invention provides a superhydrophilic and oleophilic polymethacrylamide (PMI) foam and its preparation method. First, using polyvinyl alcohol (PVA) and metal oxide powder as raw materials, a PMI-coated metal oxide powder, i.e., a filler, is prepared. Then, the filler is used as a raw material and applied to the preparation of PMI foam. Next, the PMI foam is immersed in a weak acid solution, and the PMI on the filler surface is dissolved using the weak acid aqueous solution. Then, an etching reaction is performed with the metal oxide powder to construct a micro / nano rough structure on the PMI foam surface. The PMI foam with this micro / nano rough structure exhibits excellent affinity for both polar and non-polar polymers, achieving superhydrophilic and oleophilic properties. This results in a superhydrophilic and oleophilic PMI foam, overcoming the problems of insufficient impregnation of the foam surface with the resin and insufficient bonding strength between the adhesive and the foam interface.

[0004] Based on the above technical objectives, the present invention adopts the following technical solution:

[0005] This invention protects a method for preparing a filler, comprising the following steps:

[0006] Polyvinyl alcohol (PVA) polymer particles are dissolved in hot water to prepare a PVA aqueous solution. Then, metal oxide powder is mixed with the PVA aqueous solution and ball-milled. The mixture is then filtered and dried to obtain a filler, which is a metal oxide powder coated with PVA. The metal oxide powder is capable of reacting with a weak acid, facilitating its reaction with the weak acid after PMI foam preparation to construct a micro / nano rough structure on the PMI foam surface. In this step, the purpose of PVA is to uniformly coat the metal oxide powder; therefore, a slightly higher amount of PVA is used compared to the metal oxide powder during preparation.

[0007] Preferably, the metal oxide is selected from MgO, ZnO, Al2O3, and CaO.

[0008] Preferably, the particle size of the metal oxide powder is less than 300 mesh; if it is larger than 300 mesh, it is impossible to form a micro-nano structure. Based on the micro-nano structure and the contact angle of less than 90°, the superhydrophilic and oleophilic properties of PMI foam are achieved.

[0009] Preferably, the molecular weight of the polyvinyl alcohol polymer particles is greater than 2000. A molecular weight greater than 2000 makes it easier to form a film and facilitates the coating of metal oxide powder.

[0010] Preferably, the metal oxide powder is a metal oxide that can react with a weak acid, which is selected from glacial acetic acid, formic acid or benzoic acid.

[0011] The present invention also protects a filler prepared by the above-described preparation method.

[0012] The present invention also protects a superhydrophilic and oleophilic polymethacrylimide foam, which is prepared using the above-mentioned filler.

[0013] Preferably, the superhydrophilic and oleophilic polymethacrylimide foam is made from the following raw materials in parts by weight: 100 parts of matrix resin monomer, 5-10 parts of thickener, 20-50 parts of filler, 0.01-0.05 parts of retarder, 0.1-0.5 parts of initiator, 0.7-5 parts of crosslinking agent, 3-12 parts of foaming agent, and 0.2-5 parts of nucleating agent. Too much filler will affect foaming and foam density, while too little filler is not conducive to the micro-nano rough structure of the superhydrophilic and oleophilic polymethacrylimide foam.

[0014] Preferably, the matrix resin monomer is composed of acrylonitrile monomers and acrylic monomers, with a mass ratio of acrylonitrile monomers to acrylic monomers of 1:0.95~1.05. The thickener is polyacrylonitrile with a molecular weight >80000, the retarder is an allyl monomer, the initiator is a perazo compound or a peroxide compound, the foaming agent is selected from at least one of isopropanol, formamide, and tert-butyl methacrylate, the crosslinking agent is selected from at least one of allyl methacrylate, allyl acrylate, and magnesium methacrylate, and the nucleating agent is selected from at least one of tert-butyl methacrylate, isobutyl methacrylate, and N-methylformamide.

[0015] This invention also protects a method for preparing superhydrophilic and oleophilic polymethacrylimide foam, comprising the following steps:

[0016] Weigh the raw materials according to the following weight proportions: 100 parts of matrix resin monomer, 5 to 10 parts of thickener, 20 to 50 parts of filler, 0.01 to 0.05 parts of retarder, 0.1 to 0.5 parts of initiator, 0.7 to 5 parts of crosslinking agent, 3 to 12 parts of foaming agent, and 0.2 to 5 parts of nucleating agent, and set aside.

[0017] After dissolving the matrix resin monomer, it is mixed with a retarder, initiator, crosslinking agent, foaming agent and nucleating agent to obtain a mixture.

[0018] The filler is mixed into the mixture to obtain a mixed reaction slurry.

[0019] The thickener is mixed into the mixed reaction slurry to obtain a viscous mixed reaction slurry.

[0020] The viscous mixed reaction slurry was polymerized at 30℃~60℃ for 24h~48h to obtain the PMI foaming precursor polymer.

[0021] PMI foam is obtained by heat treatment of the PMI foaming precursor polymer.

[0022] PMI foam was immersed in a weak acid solution, and the weak acid solution was used to etch the metal oxide powder on the surface of the PMI foam to construct a micro-nano rough structure on the surface of the PMI foam, thus obtaining superhydrophilic and oleophilic PMI foam.

[0023] Preferably, the heat treatment conditions are as follows: first, treat at 105℃ for 3-5 hours to remove moisture from the PMI foaming precursor polymer; then treat at 150℃ for 10-12 hours to ensure uniform heating inside and outside the PMI foaming precursor polymer; then foam at 180℃-240℃ for 0.5-3 hours; finally, treat at 160℃ for 4-5 hours and at 100℃ for 5-6 hours to gradually cool the inside and outside of the PMI foam, avoiding excessive temperature difference between the inside and outside of the PMI foam that could cause foam deformation or cracking; finally, allow it to cool naturally to room temperature.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. This invention, based on traditional PMI foam preparation, modifies the PMI foam matrix by adding filler, specifically polyvinyl alcohol-coated metal oxide powder. Secondly, it modifies the surface structure by constructing a micro-nano rough structure on the PMI foam surface through weak acid etching. This modification improves the impregnation and adhesion between the PMI foam and adhesives by altering the intrinsic properties of the PMI foam. Compared to traditional external modifications, this invention offers significant advantages such as strong foam adaptability and low processing cost.

[0026] 2. The technical challenges of this invention are twofold: first, the selection and pretreatment of the filler, which must prevent the filler from reacting with methacrylic acid in the PMI reaction components while facilitating subsequent etching reactions with weak acids; and second, the construction of a micro-nano rough structure on the foam surface. Regarding the first challenge, polyvinyl alcohol (PVA) is selected for this invention. PVA is soluble in water but insoluble in the PMI reaction monomers. During the polymerization of the viscous mixed reaction slurry, the PVA coating prevents the reaction between methacrylic acid in the matrix resin monomers and metal oxides. Regarding the second challenge, placing the PMI foam in a weak acid aqueous solution causes the PVA in the filler layer of the PMI foam to dissolve in the water, allowing the metal oxide particles on the PMI foam surface to react with the acid and be removed, thereby forming a micro-nano rough structure on the PMI foam surface.

[0027] 3. The superhydrophilic and oleophilic PMI foam prepared by the method of this invention possesses both superhydrophilic and oleophilic properties. Hydrophilicity and oleophilicity generally refer to two types of functional groups; oleophilic groups are generally nonpolar, while hydrophilic groups are generally polar. The superhydrophilic and superoleophilic properties indicate that this surface has excellent affinity with both polar and nonpolar polymers. The contact angle between the superhydrophilic and oleophilic PMI foam and water, commonly used epoxy resins, and unsaturated polyester resins is close to 0 degrees. When co-cured with commonly used prepregs, the adhesion strength between the skin and the foam is greater than 5 N / cm. In the process of preparing sandwich composite materials using superhydrophilic and oleophilic PMI foam, the selection space of matrix resin materials can be effectively expanded, and the surface treatment process of superhydrophilic and oleophilic PMI foam can be greatly simplified, thereby significantly reducing the process and material costs of sandwich composite material preparation, resulting in significant economic and social benefits. Attached Figure Description

[0028] Figure 1 The image shows a physical picture of the foam sandwich structure composite material prepared using the superhydrophilic and oleophilic PMI foam of Example 1. Detailed Implementation

[0029] The specific embodiments of the present invention are described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention. Unless otherwise specified, the experimental methods described in the embodiments of the present invention are conventional methods.

[0030] Considering the problems of insufficient impregnation of the foam surface with resin and insufficient bonding strength between the adhesive and the foam interface in the preparation of composite materials using existing PMI foams, this invention first provides a filler, which is a metal oxide powder coated with polyvinyl alcohol. The filler is then applied to conventional PMI foam, and after dissolving the polyvinyl alcohol in a weak acid solution, it reacts completely with the metal oxide powder to construct a micro-nano rough structure on the PMI foam surface. This surface exhibits excellent affinity for both polar and non-polar polymers, thereby achieving the superhydrophilic and oleophilic properties of the PMI foam. Compared with existing technologies, this invention starts from the structure of the PMI foam and overcomes the technical defects of traditional solutions by preparing a superhydrophilic and oleophilic PMI foam.

[0031] The technical solution of the present invention will be further studied using the following embodiments, as detailed below:

[0032] Example 1

[0033] A method for preparing superhydrophilic and oleophilic PMI foam includes the following steps:

[0034] S1. Polyvinyl alcohol polymer particles are dissolved in hot water to prepare a 5wt% polyvinyl alcohol aqueous solution. Then, MgO powder is mixed with the polyvinyl alcohol aqueous solution at a mass ratio of 20:100. The mixture is ball-milled for 30 minutes and then filtered, dried and dispersed to obtain polyvinyl alcohol-coated MgO powder, i.e., filler.

[0035] S2. Weigh the raw materials according to the following weight proportions: 100 parts of matrix resin monomer (methacrylonitrile and acrylic acid in a mass ratio of 1:1), 5 parts of thickener (polyacrylonitrile polymer), 20 parts of filler (MgO powder coated with polyvinyl alcohol), 0.01 parts of retarder (allyl alcohol), 0.1 parts of initiator (methyl ethyl ketone peroxide), 0.7 parts of crosslinking agent (allyl methacrylate), 5 parts of foaming agent (formamide), and 0.2 parts of nucleating agent (tert-butyl methacrylate).

[0036] S3. Take 100 parts of the matrix resin monomer, and then add the retarder, initiator, crosslinking agent, foaming agent and nucleating agent in sequence. Stir mechanically for 30 minutes to disperse and obtain a mixture.

[0037] S4. Add the filler to the mixture while stirring. After the addition is complete, stir for another 30 minutes to obtain the mixed reaction slurry.

[0038] S5. Add the thickener to the mixed reaction slurry in batches and stir to dissolve, so as to obtain a viscous mixed reaction slurry.

[0039] S6. Inject the viscous mixed reaction slurry into a sealed mold and polymerize it in a water bath at 50°C for 24 hours. After the mixed reaction slurry has completely solidified, the PMI foaming precursor polymer is obtained. Demold the PMI foaming precursor polymer.

[0040] S7. Place the PMI foaming precursor polymer in a hot air furnace, first treat it at 105℃ for 3 hours, then at 150℃ for 12 hours, then at 240℃ for 0.5 hours, finally at 160℃ for 4 hours, and finally at 100℃ for 6 hours, and then cool it naturally to room temperature to obtain PMI foam.

[0041] S8. Peel and cut the PMI foam to the required size, then soak it in 50% glacial acetic acid for 30 minutes to obtain superhydrophilic and oleophilic PMI foam.

[0042] Example 2

[0043] The preparation steps are the same as in Example 1, except that the mass of the filler is replaced from 20 parts to 30 parts and the mass of the foaming agent is replaced from 5 parts to 8 parts.

[0044] Example 3

[0045] A method for preparing superhydrophilic and oleophilic PMI foam includes the following steps:

[0046] S1. Polyvinyl alcohol polymer particles are dissolved in hot water to prepare a 5wt% polyvinyl alcohol aqueous solution. Then, ZnO powder is mixed with the polyvinyl alcohol aqueous solution at a mass ratio of 30:100. The mixture is ball-milled for 30 minutes and then filtered, dried and dispersed to obtain polyvinyl alcohol-coated ZnO powder, i.e., filler.

[0047] S2. Weigh the raw materials according to the following weight proportions: 100 parts of matrix resin monomer (methacrylonitrile and acrylic acid in a mass ratio of 1:0.95), 8 parts of thickener (polyacrylonitrile polymer), 40 parts of filler (ZnO powder coated with polyvinyl alcohol), 0.03 parts of retarder (allyl alcohol), 0.2 parts of initiator (methyl ethyl ketone peroxide), 3 parts of crosslinking agent (allyl methacrylate), 3 parts of foaming agent (formamide), and 3 parts of nucleating agent (tert-butyl methacrylate).

[0048] S3. Take 100 parts of the matrix resin monomer, and then add the retarder, initiator, crosslinking agent, foaming agent and nucleating agent in sequence. Stir mechanically for 30 minutes to disperse and obtain a mixture.

[0049] S4. Add the filler to the mixture while stirring. After the addition is complete, stir for another 30 minutes to obtain the mixed reaction slurry.

[0050] S5. Add the thickener to the mixed reaction slurry in batches and stir to dissolve, so as to obtain a viscous mixed reaction slurry.

[0051] S6. Inject the viscous mixed reaction slurry into a sealed mold and polymerize it in a water bath at 30°C for 48 hours. After the mixed reaction slurry has completely solidified, the PMI foaming precursor polymer is obtained. Demold the PMI foaming precursor polymer.

[0052] S7. Place the PMI foaming precursor polymer in a hot air furnace, first treat it at 105℃ for 4 hours, then at 150℃ for 11 hours, then at 200℃ for 1 hour, finally at 160℃ for 4.5 hours, and finally at 100℃ for 5 hours, and then cool it naturally to room temperature to obtain PMI foam.

[0053] S8. Peel and cut the PMI foam to the required size, then soak it in 50% formic acid for 10 minutes to obtain superhydrophilic and oleophilic PMI foam.

[0054] Example 4

[0055] A method for preparing superhydrophilic and oleophilic PMI foam includes the following steps:

[0056] S1. Polyvinyl alcohol polymer particles are dissolved in hot water to prepare a 5wt% polyvinyl alcohol aqueous solution. Then, CaO powder is mixed with the polyvinyl alcohol aqueous solution at a mass ratio of 10:100. The mixture is ball-milled for 30 minutes and then filtered, dried and dispersed to obtain polyvinyl alcohol-coated CaO powder, i.e., filler.

[0057] S2. Weigh the raw materials according to the following weight proportions: 100 parts of matrix resin monomer (methacrylonitrile and acrylic acid in a mass ratio of 1:1), 10 parts of thickener (polyacrylonitrile polymer), 50 parts of filler (CaO powder coated with polyvinyl alcohol), 0.05 parts of retarder (allyl alcohol), 0.5 parts of initiator (methyl ethyl ketone peroxide), 5 parts of crosslinking agent (allyl methacrylate), 12 parts of foaming agent (formamide), and 5 parts of nucleating agent (tert-butyl methacrylate).

[0058] S3. Take 100 parts of the matrix resin monomer, and then add the retarder, initiator, crosslinking agent, foaming agent and nucleating agent in sequence. Stir mechanically for 30 minutes to disperse and obtain a mixture.

[0059] S4. Add the filler to the mixture while stirring. After the addition is complete, stir for another 30 minutes to obtain the mixed reaction slurry.

[0060] S5. Add the thickener to the mixed reaction slurry in batches and stir to dissolve, so as to obtain a viscous mixed reaction slurry.

[0061] S6. Inject the viscous mixed reaction slurry into a sealed mold and polymerize it in a water bath at 60°C for 30 hours. After the mixed reaction slurry has completely solidified, the PMI foaming precursor polymer is obtained. Demold the PMI foaming precursor polymer.

[0062] S7. Place the PMI foaming precursor polymer in a hot air furnace, first treat it at 105℃ for 5 hours, then at 150℃ for 10 hours, then at 180℃ for 3 hours, then at 160℃ for 5 hours, and finally at 100℃ for 5.5 hours, and then cool it naturally to room temperature to obtain PMI foam.

[0063] S8. Peel and cut the PMI foam to the required size, then soak it in 50% benzoic acid for 5 minutes to obtain superhydrophilic and oleophilic PMI foam.

[0064] Comparative Example 1

[0065] A method for preparing PMI foam, which is the same as the preparation steps in Example 1, except that no filler is used to prepare PMI foam, includes the following steps:

[0066] S1. Weigh the raw materials according to the following weight proportions: 100 parts of matrix resin monomer (methacrylonitrile and acrylic acid in a mass ratio of 1:1), 5 parts of thickener (polyacrylonitrile polymer), 0.01 parts of retarder (allyl alcohol), 0.1 parts of initiator (methyl ethyl ketone peroxide), 0.7 parts of crosslinking agent (allyl methacrylate), 5 parts of foaming agent (formamide), and 0.2 parts of nucleating agent (tert-butyl methacrylate).

[0067] S2. Take 100 parts of the matrix resin monomer, and then add the retarder, initiator, crosslinking agent, foaming agent and nucleating agent in sequence. Stir mechanically for 30 minutes to obtain a mixture.

[0068] S3. Add the thickener to the mixture in batches and stir to dissolve, so as to obtain a viscous mixed reaction slurry.

[0069] S4. Inject the viscous mixed reaction slurry into a sealed mold and polymerize it in a water bath at 50°C for 24 hours. After the mixed reaction slurry has completely solidified, the PMI foaming precursor polymer is obtained. Demold the PMI foaming precursor polymer.

[0070] S5. Place the PMI foaming precursor polymer in a hot air furnace, first treat it at 105℃ for 3 hours, then at 150℃ for 12 hours, then at 240℃ for 0.5 hours, finally at 160℃ for 4 hours, and finally at 100℃ for 6 hours, and then cool it naturally to room temperature to obtain PMI foam.

[0071] Examples 1 to 4 of this invention all yielded high-performance superhydrophilic and oleophilic PMI foams. The superhydrophilic and oleophilic PMI foam obtained in Example 1 is used as an example for further research. Specific research methods and results are shown below:

[0072] Table 1. Summary of experimental data for the preparation method of superhydrophilic and oleophilic PMI foam

[0073]

[0074] Table 1 shows that the superhydrophilic and oleophilic PMI foam prepared by the method of the present invention has both superhydrophilic and hydrophilic properties, with contact angles with water, epoxy resin, and unsaturated polyester resin all less than 5 degrees. The addition of fillers has little effect on the mechanical properties of PMI foam. Compared with conventional PMI foam sandwich composite materials (i.e., sandwich composite materials prepared using PMI foam in Comparative Example 1), the skin glass strength of the sandwich composite material prepared using superhydrophilic and oleophilic PMI foam is increased by 52.6%.

[0075] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing superhydrophilic and oleophilic polymethacrylimide foam, characterized in that, Includes the following steps: Weigh the raw materials according to the following weight proportions: 100 parts of matrix resin monomer, 5-10 parts of thickener, 20-50 parts of filler, 0.01-0.05 parts of retarder, 0.1-0.5 parts of initiator, 0.7-5 parts of crosslinking agent, 3-12 parts of foaming agent, and 0.2-5 parts of nucleating agent, and set aside. The filler was prepared according to the following steps: polyvinyl alcohol polymer particles were dissolved in hot water to prepare a polyvinyl alcohol aqueous solution, then metal oxide powder was mixed with the polyvinyl alcohol aqueous solution and ball-milled, and then filtered and dried to obtain the filler. The particle size of the metal oxide powder is less than 300 mesh, and the metal oxide powder is a metal oxide that can react with weak acid. Polyvinyl alcohol has a molecular weight greater than 2000; After dissolving the matrix resin monomer, it is mixed evenly with retarder, initiator, crosslinking agent, foaming agent, nucleating agent, filler and thickener to obtain a viscous mixed reaction slurry; The viscous mixed reaction slurry was subjected to a polymerization reaction to obtain the PMI foaming precursor polymer; PMI foam precursor polymer is heat-treated to obtain PMI foam; PMI foam is immersed in a weak acid solution to dissolve the polyvinyl alcohol on the surface of the filler. Then, it is etched with metal oxide powder to construct a micro-nano rough structure on the surface of PMI foam, thus obtaining superhydrophilic and oleophilic polymethacrylimide foam.

2. The method for preparing superhydrophilic and oleophilic polymethacrylimide foam according to claim 1, characterized in that, The metal oxide is selected from MgO, ZnO, Al2O3 or CaO.

3. The method for preparing superhydrophilic and oleophilic polymethacrylimide foam according to claim 1, characterized in that, The weak acid is selected from glacial acetic acid, formic acid, or benzoic acid.

4. The method for preparing superhydrophilic and oleophilic polymethacrylimide foam according to claim 1, characterized in that, The matrix resin monomers are composed of acrylonitrile monomers and acrylic monomers in a mass ratio of 1:0.95~1.

05. The thickener is polyacrylonitrile with a molecular weight >80000, the retarder is an allyl monomer, the initiator is a perazo compound or a peroxide compound, the foaming agent is selected from at least one of isopropanol, formamide, and tert-butyl methacrylate, the crosslinking agent is selected from at least one of allyl methacrylate, allyl acrylate, and magnesium methacrylate, and the nucleating agent is selected from at least one of tert-butyl methacrylate, isobutyl methacrylate, and N-methylformamide.

5. The method for preparing superhydrophilic and oleophilic polymethacrylimide foam according to claim 1, characterized in that, The polymerization conditions are: polymerization at 30℃~60℃ for 24h~48h.

6. The method for preparing superhydrophilic and oleophilic polymethacrylimide foam according to claim 1, characterized in that, The heat treatment conditions are as follows: first, treat at 105℃ for 3 to 5 hours, then at 150℃ for 10 to 12 hours, followed by foaming at 180℃ to 240℃ for 0.5 to 3 hours, then at 160℃ for 4 to 5 hours, and finally at 100℃ for 5 to 6 hours, and finally naturally cooled to room temperature.

7. The method for preparing superhydrophilic and oleophilic polymethacrylimide foam according to claim 1, characterized in that, The etching reaction conditions are: immersion at room temperature for 5 to 30 minutes.

8. A superhydrophilic and oleophilic polymethacrylimide foam, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 7.

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