Preparation method of high-temperature-resistant parting strip for air filtration

Abstract

The embodiment of the invention provides a preparation method of a high-temperature-resistant parting strip for air filtration, which comprises the following steps of: 1, taking the following raw materials in percentage by weight: 60-70% of superfine fiber, 10-25% of (0.6-0.8) D * 12mm synthetic fiber and 5-30% of chopped fiber, adding acidic water into all the raw materials, and stirring and dispersing all the raw materials into acidic slurry, 2, preparing the acid slurry into a parting strip blank; 3, coating the acrylic resin liquid diluted in proportion on the surface of the parting strip blank; and fourthly, redundant acrylic resin on the surface of the parting strip blank is pumped out through a vacuum pump, the parting strip blank coated with the acrylic resin is dried, and the finished parting strip is obtained. The high-melting-point superfine fibers are resistant to high temperature and suitable for the high-temperature-resistant filter; the prepared partition plate strip product has good high-temperature resistance, and the application scene problem of a high-temperature filter is solved.

Description

Technical Field

[0001] The invention relates to the technical field of filtration, and in particular to a method for preparing a high temperature resistant spacer strip for air filtration. Background Art

[0002] The high temperature resistant high efficiency filter made of high temperature resistant spacers as the main raw material is an air purification device specially designed for high temperature environments. It can still maintain good filtering performance under high temperature conditions and provide a clean high temperature environment for industrial production. With the development of industrialization, more and more production needs to be carried out in a high temperature and clean environment, such as the biopharmaceutical industry, food and beverage industry, automotive coating industry, electronic components industry, aerospace industry, energy industry and laboratory research.

[0003] In the biopharmaceutical industry, many process operations need to be carried out in a high-temperature clean environment, such as a high-temperature sterilization tunnel or a high-temperature drying room. High-temperature resistant and high-efficiency filters can effectively filter tar, soot, dust and other particulate matter generated during the production process to ensure that the production environment of the drug meets GMP requirements. In addition, high-temperature resistant and high-efficiency filters can also be used in heating equipment during the preparation, extraction, and synthesis of pharmaceuticals to ensure air quality during the production process.

[0004] In the food production process, high temperature resistant and high efficiency filters can be used in tunnel furnaces, industrial ovens and other equipment to purify the air and prevent food from being contaminated during high temperature processing. At the same time, high temperature resistant and high efficiency filters can also be used in low temperature environments such as cold air storage and refrigerated trucks to ensure the hygiene and safety of food during storage and transportation.

[0005] The automobile painting production line needs to dry and cure the car body in a high-temperature drying room. At this time, the high-temperature resistant and high-efficiency filter can effectively filter out dust, oil mist and other particles in the air to ensure the quality of painting. In addition, the high-temperature resistant and high-efficiency filter can also be used in the processing and assembly of automobile parts to ensure the cleanliness of the parts.

[0006] In the production process of electronic products, high-temperature welding, drying, curing and other processes are required. High-temperature resistant and high-efficiency filters can effectively filter out harmful substances such as dust and solder smoke in the air to ensure product quality and safety. At the same time, high-temperature resistant and high-efficiency filters can also be used in the packaging, storage and transportation of electronic components to prevent components from being contaminated.

[0007] In the aerospace field, high temperature and high efficiency filters play a vital role. Aircraft and rocket engines generate extremely high temperatures and pressures during operation, accompanied by a large amount of exhaust gas emissions. These exhaust gases contain a large amount of harmful substances, posing a serious threat to the environment and personnel safety. High temperature and high efficiency filters can effectively remove these harmful substances, ensuring the normal operation of aircraft and rocket engines while reducing the impact on the environment and personnel.

[0008] In the energy field, such as coal-fired power plants and nuclear power plants, high-temperature and high-efficiency filters are needed to remove pollutants from the air. Coal-fired power plants produce a lot of smoke and harmful gases during operation, and these pollutants will have a serious impact on the environment and personnel health. High-temperature and high-efficiency filters can effectively remove these pollutants, ensure the normal operation of power plants, and reduce the impact on the environment. In nuclear power plants, high-temperature and high-efficiency filters are used to remove radioactive substances to ensure the safe operation of nuclear power plants.

[0009] In scientific laboratories, many experiments need to be carried out under high temperature conditions. Harmful gases, steam or dust may be generated during these experiments. High temperature resistant and high efficiency filters can effectively remove these pollutants, protect the health of experimenters, and ensure the accuracy of experimental results.

[0010] In summary, high temperature and high efficiency filters have been widely used in many fields such as industrial production, automobile manufacturing, aerospace, energy, medical and health care, and laboratory research. With the advancement of science and technology and the improvement of environmental awareness, the application of high temperature and high efficiency filters will be more extensive, playing a greater role in protecting the environment, improving production quality, and ensuring the health of personnel.

[0011] In the process of implementing the present invention, the applicant discovered that there are at least the following problems in the prior art:

[0012] As the core material of high temperature resistant and high efficiency filter, high temperature resistant and high efficiency filter paper, its high temperature resistance and stability of filtering efficiency are the key. Ordinary hot melt adhesive generally has a softening point of 100-120℃, while the use environment of high temperature resistant filter can be used for a long time in an environment of 350℃, and the maximum temperature of instant use can reach 400℃, so ordinary hot melt adhesive cannot meet the demand, which will cause the filter to collapse and the filter area to be insufficient. Therefore, it is necessary to solve the filter material problem in various application scenarios under high temperature environment, and it is necessary to have high temperature resistant filter partition strips to replace hot melt adhesive as filter partition strips to meet the demand of high temperature resistant filter. Summary of the invention

[0013] The embodiment of the present invention provides a method for preparing high temperature resistant spacers for air filtration, which can solve the technical problem that filter spacers prepared by common hot melt adhesive in the prior art are not resistant to high temperatures.

[0014] To achieve the above object, an embodiment of the present invention provides a method for preparing a high temperature resistant spacer for air filtration, comprising:

[0015] Step 1: Take various raw materials by weight, 60-70% of ultrafine fiber, 10-25% of (0.6-0.8)D×12mm synthetic fiber, 5-30% of short-cut fiber, and the sum of the weight ratios of various raw materials is 100%, add acidic water to all the raw materials, the weight of the acidic water is 20-30 times the sum of the weights of all the raw materials, stir and disperse all the raw materials into slurry, and the slurry is acidic slurry;

[0016] Step 2: preparing the acidic slurry into a spacer blank;

[0017] Step 3: applying the acrylic resin solution diluted in proportion to the surface of the spacer blank;

[0018] Step 4: Use a vacuum pump to extract excess acrylic resin on the surface of the spacer blank, and dry the spacer blank coated with acrylic resin to obtain a finished spacer, wherein the moisture content of the finished spacer is less than 5%.

[0019] The above technical solution has the following beneficial effects: ultrafine fibers with a high melting point are resistant to high temperatures and are suitable for high temperature resistant filters; the prepared partition strip products have good high temperature resistance, solving the application scenario problem of high temperature filters. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0021] Figure 1 It is a flowchart of the steps of a method for preparing a high temperature resistant spacer for air filtration according to an embodiment of the present invention;

[0022] Figure 2 The invention relates to a spacer strip prepared by a method for preparing a high temperature resistant spacer strip for air filtration according to an embodiment of the invention. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] like Figure 1 As shown, in combination with an embodiment of the present invention, a method for preparing a high temperature resistant spacer for air filtration is provided, comprising:

[0025] Step 1: Take various raw materials by weight, 60-70% of ultrafine fiber, 10-25% of (0.6-0.8)D×12mm synthetic fiber, 5-30% of short-cut fiber, and the sum of the weight ratios of various raw materials is 100%, add acidic water to all the raw materials, the weight of the acidic water is 20-30 times the sum of the weights of all the raw materials, stir and disperse all the raw materials into slurry, and the slurry is acidic slurry;

[0026] Step 2: preparing the acidic slurry into a spacer blank;

[0027] Step 3: applying the acrylic resin solution diluted in proportion to the surface of the spacer blank;

[0028] Step 4: Use a vacuum pump to extract excess acrylic resin on the surface of the spacer blank, and dry the spacer blank coated with acrylic resin to obtain a finished spacer, wherein the moisture content of the finished spacer is less than 5%.

[0029] Preferably, the ultrafine fibers in the first step are glass fibers.

[0030] Preferably, the first step specifically includes:

[0031] Acidic water is added to all raw materials, the pH value of the acidic water is 2.6-3.2, and the weight of the acidic water is 20-30 times the total weight of all raw materials. All raw materials are stirred and dispersed into slurry, which is acidic slurry. The pH value of the acidic slurry is 2.5-3.0, and the total concentration of all raw materials in the slurry is less than 0.05%.

[0032] Preferably, the second step specifically includes:

[0033] The acidic slurry is made into spacer blanks by a wet forming method.

[0034] Preferably, in the fourth step, the spacer blank coated with acrylic resin is dried to obtain a finished spacer, wherein the moisture content of the finished spacer is less than 5%, specifically comprising:

[0035] The spacer strips coated with acrylic resin are passed through three groups of drying cylinders at a paper feeding speed of 15-30m / min in sequence. The spacer strips are dried by burning natural gas in each group of drying cylinders. The surface temperatures of the three drying cylinders are 60℃-90℃, 110℃-150℃, and 120℃-90℃ respectively. The moisture content of the dried spacer strips is less than 5%, so as to obtain finished spacer strips.

[0036] Preferably, in the fourth step, the steam temperatures in the three groups of drying cylinders are 80° C., 140° C., and 100° C. respectively.

[0037] Preferably, in the third step, the acrylic resin liquid diluted in proportion refers to an acrylic resin liquid prepared by mixing and stirring 1 part of acrylic resin and 5 parts of water by weight.

[0038] Preferably, the first step specifically includes:

[0039] Take each raw material by weight ratio, ultrafine fiber is 60%, (0.6-0.8)D×6mm synthetic fiber is 10%, short-cut fiber is 30%, and the sum of the weight ratios of each raw material is 100%. Add acidic water to all the raw materials, the weight of the acidic water is 20 times the sum of the weights of all the raw materials, and the pH value of the acidic water is 2.8. Stir all the raw materials to disperse into a slurry, the slurry is an acidic slurry, and the pH value of the acidic slurry is 2.8.

[0040] Preferably, the first step specifically includes:

[0041] Take each raw material according to the weight ratio, ultrafine fiber is 70%, (0.6-0.8)D×6mm synthetic fiber is 15%, short-cut fiber is 15%, and the sum of the weight ratios of each raw material is 100%. Add acidic water to all the raw materials, the weight of the acidic water is 30 times the sum of the weights of all the raw materials, and the pH value of the acidic water is 3.2. Stir all the raw materials to disperse into a slurry, the slurry is an acidic slurry, and the pH value of the acidic slurry is 3.0.

[0042] Preferably, in the fourth step, the spacer blank coated with acrylic resin is dried to obtain a finished spacer, wherein the moisture content of the finished spacer is less than 5%, specifically comprising:

[0043] The spacer strips coated with acrylic resin are passed through three groups of drying cylinders at a paper feeding speed of 20m / min in sequence. The spacer strips are dried by burning natural gas in each group of drying cylinders. The surface temperatures of the three drying cylinders are 60℃-90℃, 110℃-150℃, and 120℃-90℃ respectively. The moisture content of the dried spacer strips is less than 5%, so as to obtain finished spacer strips.

[0044] The above technical solution of the embodiment of the present invention is described in detail below in conjunction with specific application examples. For technical details not introduced during the implementation process, please refer to the relevant description in the previous text.

[0045] A method for preparing a high temperature resistant spacer for air filtration according to an embodiment of the present invention uses glass fiber as a basic skeleton to prepare the high temperature resistant spacer for air filtration, and the steps are as follows:

[0046] Step 1: Take the raw materials by weight: 60-70% of ultrafine fiber (such as glass fiber), 10-25% of (0.6-0.8)D×12mm synthetic fiber and 5-30% of short-cut fiber, D represents the diameter, and the sum of the three components is 100%, add 20-30 times the weight of the raw material and water with a pH value of 2.6-3.2 to the raw material, mix, stir and disperse into an acidic slurry, and ensure that the pH value of the acidic slurry is 2.5-3.0; wherein the ultrafine fiber is the main substrate; preferably, the raw materials by weight are: 60% ultrafine fiber, 25% synthetic fiber, and 15% short-cut fiber; or, 65% ultrafine fiber, 15% synthetic fiber, and 25% short-cut fiber, or 70% ultrafine fiber, 10% synthetic fiber, and 20% short-cut fiber;

[0047] Step 2: The slurry is made into a spacer blank according to an existing wet forming method;

[0048] Step 3: After the slurry is dehydrated to obtain the spacer blank during the wet forming process, the acrylic resin liquid diluted in proportion is applied to the surface of the spacer blank to increase the strength of the spacer blank;

[0049] Step 4: For the spacer blanks coated with acrylic resin liquid, after the excess acrylic resin is extracted with a vacuum pump, the blanks are passed through three groups of drying cylinders at a paper feeding speed of 15-30m / min. The temperature is raised by burning natural gas in the drying cylinders. The surface temperature of the drying cylinders is 60℃-90℃, 110℃-150℃, and 120℃-90℃ respectively, so as to dry the spacer blanks and make the moisture content of the finished spacer bars after drying less than 5%. For each group of drying cylinders, when the surface temperature of the drying cylinders is lower than the lowest value of their respective temperature ranges, the drying effect of the spacer blanks coated with acrylic resin liquid is not good and cannot meet the requirements; when the surface temperature of the drying cylinders is higher than the highest value of their respective temperature ranges, the moisture content of the spacer blanks is too low, the spacer blanks are easy to break, and the service life is reduced.

[0050] In the third step, an acrylic resin liquid is prepared by mixing 1 part of acrylic resin and 5 parts of water by weight and stirring.

[0051] In the first step, the ultra-fine fibers are selected from glass fibers.

[0052] In the fourth step, the steam temperatures in the three groups of drying cylinders are 80°C, 140°C, and 100°C respectively. Because it is not convenient to detect the temperature inside the drying cylinder, the external temperature (i.e., the steam temperature) is detected to determine whether the surface temperature of the drying cylinder meets the requirements.

[0053] The spacer strips prepared by the method for preparing a high temperature resistant spacer strip for air filtration according to the embodiment of the present invention are as follows: Figure 2 shown.

[0054] The first embodiment is as follows:

[0055] The raw materials are taken by weight: 60% glass fiber, 10% (0.6-0.8)D×6mm synthetic fiber and 30% short-cut fiber, 20 times the weight of the raw materials are added with water with a pH value of 2.8, mixed and stirred into slurry, and the pH value of the slurry is ensured to be within 2.6-3.2, specifically 2.8, and the acidic environment softens the fibers; the slurry is made into a spacer blank according to the existing wet papermaking molding method; acrylic resin liquid (composed of 1 part of acrylic resin and 5 parts of water by weight) is applied to the surface of the spacer blank, and the spacer blank is passed through three groups of drying cylinders at a speed of 15m / min in sequence, and the surface temperatures of the three groups of drying cylinders are 60℃-90℃, 110℃-150℃, and 120℃-90℃ in sequence, so as to dry the spacer blank so that the moisture content of the dried spacer is less than 5%, thereby obtaining the high temperature resistant partition strip of the present invention.

[0056] The second embodiment is as follows:

[0057] Take the raw materials by weight: 70% glass fiber, 15% (0.6-0.8)D×6mm synthetic fiber and 15% short-cut fiber, add 30 times the weight of water with a pH value of 3.2 to the raw materials, mix and stir to form a slurry, and ensure that the pH value of the slurry is 3.0; make the slurry into a spacer blank according to the existing wet papermaking molding method; apply acrylic resin liquid (composed of 1 part of acrylic resin and 5 parts of water by weight) to the surface of the spacer blank, and pass the spacer blank through three groups of drying cylinders at a speed of 20m / min in sequence. The surface temperatures of the three groups of drying cylinders are 60℃-90℃, 110℃-150℃, and 120℃-90℃ in sequence to dry the spacer strips so that the moisture content of the dried spacer strips is less than 5%, thereby obtaining the high-temperature resistant partition strip material of the present invention.

[0058] The performance parameters of the high-temperature resistant spacers prepared by the preparation method of the high-temperature resistant spacers for air filtration according to the embodiment of the present invention are shown in Table 1. All performance indicators are within the qualified range. It also includes the performance parameters of the other two types of spacers: the first type of spacers and the second type of spacers (using a different material composition from that of the present method).

[0059] Table 1

[0060]

[0061] The beneficial technical effects achieved by the embodiments of the present invention are as follows:

[0062] 1. Ordinary hot melt adhesives have a low softening point, usually around 110°C, and are not suitable for high temperature resistant filters; ultrafine fibers with a high melting point are resistant to high temperatures and are suitable for high temperature resistant filters; the prepared partition strip products have good high temperature resistance, which solves the application scenario problems of high temperature filters, fills the gap in domestic high temperature resistant partition strip products, solves the difficulties of high temperature filters in my country's air purification industry, and promotes the further development of the air purification industry.

[0063] 2. The raw materials contain ultrafine fibers and small-sized synthetic fibers, which are prone to bubbles, difficulty in dispersion, and flocculation during the dispersion process. Before the wet papermaking forming method, highly acidic water is added to the raw materials for dispersion and pulping treatment, so that the total concentration of all raw materials in the wet forming process is ultra-low (less than 0.05%), so that the material will not flocculate during the strip separation process.

[0064] 3. Use acrylic resin liquid to coat the formed spacers, and add two-component synthetic fibers to the raw materials to enhance the strength of the filter paper.

[0065] It should be understood that the specific order or hierarchy of steps in the disclosed process is an example of an exemplary method. Based on design preferences, it should be understood that the specific order or hierarchy of steps in the process can be rearranged without departing from the scope of protection of the present disclosure. The attached method claims present the elements of the various steps in an exemplary order and are not intended to be limited to the specific order or hierarchy described.

[0066] In the above detailed description, various features are grouped together in a single embodiment to simplify the disclosure. This method of disclosure should not be interpreted as reflecting an intention that the embodiments of the claimed subject matter require more features than are clearly stated in each claim. On the contrary, as reflected in the appended claims, the invention is in a state of having less than all the features of the disclosed individual embodiments. Therefore, the appended claims are hereby expressly incorporated into the detailed description, with each claim standing on its own as a separate preferred embodiment of the invention.

[0067] The disclosed embodiments are described above to enable any person skilled in the art to implement or use the present invention. Various modifications of these embodiments are obvious to those skilled in the art, and the general principles defined herein may also be applied to other embodiments without departing from the spirit and scope of the present disclosure. Therefore, the present disclosure is not limited to the embodiments given herein, but is consistent with the broadest scope of the principles and novel features disclosed in this application.

[0068] The above description includes examples of one or more embodiments. Of course, it is impossible to describe all possible combinations of components or methods for the purpose of describing the above embodiments, but it should be recognized by those skilled in the art that the various embodiments may be further combined and arranged. Therefore, the embodiments described herein are intended to cover all such changes, modifications and variations that fall within the scope of protection of the appended claims. In addition, with respect to the term "comprising" used in the specification or claims, the word is covered in a manner similar to the term "including", just as "including," is explained as a transitional word in the claims. In addition, any term "or" used in the specification of the claims is intended to mean "non-exclusive or".

[0069] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a high temperature resistant spacer for air filtration, characterized in that: include: Step 1: Take various raw materials by weight, 60-70% of ultrafine fiber, 10-25% of (0.6-0.8)D×12mm synthetic fiber, D represents diameter, 5-30% of short chopped fiber, the sum of the weight ratios of various raw materials is 100%, add acidic water to all raw materials, the weight of the acidic water is 20-30 times the sum of the weights of all raw materials, stir and disperse all raw materials into slurry, the slurry is acidic slurry; Step 2: preparing the acidic slurry into a spacer blank; Step 3: applying the acrylic resin solution diluted in proportion to the surface of the spacer blank; Step 4: Use a vacuum pump to extract excess acrylic resin on the surface of the spacer blank, and dry the spacer blank coated with acrylic resin to obtain a finished spacer, wherein the moisture content of the finished spacer is less than 5%.

2. The method for preparing the high temperature resistant spacer strip for air filtration according to claim 1, characterized in that: The ultra-fine fibers in the first step are glass fibers.

3. The method for preparing the high temperature resistant spacer strip for air filtration according to claim 1, characterized in that: The first step specifically includes: Acidic water is added to all raw materials, the pH value of the acidic water is 2.6-3.2, and the weight of the acidic water is 20-30 times the total weight of all raw materials. All raw materials are stirred and dispersed into slurry, which is acidic slurry. The pH value of the acidic slurry is 2.5-3.0, and the total concentration of all raw materials in the slurry is less than 0.05%.

4. The method for preparing the high temperature resistant spacer strip for air filtration according to claim 1, characterized in that: The second step specifically includes: The acidic slurry is made into spacer blanks by a wet forming method.

5. The method for preparing the high temperature resistant spacer strip for air filtration according to claim 1, characterized in that: In the fourth step, the spacer blank coated with acrylic resin is dried to obtain a finished spacer, wherein the moisture content of the finished spacer is less than 5%, which specifically includes: The spacer strips coated with acrylic resin are passed through three groups of drying cylinders at a paper feeding speed of 15-30m / min in sequence. The spacer strips are dried by burning natural gas in each group of drying cylinders. The surface temperatures of the three drying cylinders are 60℃-90℃, 110℃-150℃, and 120℃-90℃ respectively. The moisture content of the dried spacer strips is less than 5%, so as to obtain finished spacer strips.

6. The method for preparing the high temperature resistant spacer strip for air filtration according to claim 5, characterized in that: In the fourth step, the steam temperatures in the three groups of drying cylinders are 80°C, 140°C, and 100°C respectively.

7. The method for preparing the high temperature resistant spacer strip for air filtration according to claim 1, characterized in that: In the third step, the acrylic resin liquid diluted in proportion refers to the acrylic resin liquid obtained by mixing and stirring 1 part of acrylic resin and 5 parts of water by weight.

8. The method for preparing the high temperature resistant spacer strip for air filtration according to claim 1, characterized in that: The first step includes: Take each raw material by weight ratio, 60% of ultrafine fiber, 10% of (0.6-0.8)D×6mm synthetic fiber, 30% of short-cut fiber, and the sum of the weight ratios of each raw material is 100%. Add acidic water to all the raw materials, the weight of the acidic water is 20 times the sum of the weights of all the raw materials, and the pH value of the acidic water is 2.

8. Stir all the raw materials to disperse into a slurry, the slurry is an acidic slurry, and the pH value of the acidic slurry is 2.

8.

9. The method for preparing the high temperature resistant spacer strip for air filtration according to claim 5, characterized in that: The first step includes: Take each raw material according to the weight ratio, ultrafine fiber is 70%, (0.6-0.8)D×6mm synthetic fiber is 15%, short-cut fiber is 15%, and the sum of the weight ratios of each raw material is 100%. Add acidic water to all the raw materials, the weight of the acidic water is 30 times the sum of the weights of all the raw materials, and the pH value of the acidic water is 3.

2. Stir all the raw materials to disperse into a slurry, the slurry is an acidic slurry, and the pH value of the acidic slurry is 3.

0.

10. The method for preparing the high temperature resistant spacer strip for air filtration according to claim 9, characterized in that: In the fourth step, the spacer blank coated with acrylic resin is dried to obtain a finished spacer, wherein the moisture content of the finished spacer is less than 5%, which specifically includes: The spacer strips coated with acrylic resin are passed through three groups of drying cylinders at a paper feeding speed of 20m / min in sequence. The spacer strips are dried by burning natural gas in each group of drying cylinders. The surface temperatures of the three drying cylinders are 60℃-90℃, 110℃-150℃, and 120℃-90℃ respectively. The moisture content of the dried spacer strips is less than 5%, so as to obtain finished spacer strips.

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