防伪纸中纤维素基质中铁磁微丝的保留研究

I. Zapodeanu, M. Codescu, M. Burlacu, V. Midoni, R. Erdei, D. Pătroi, E. Patroi, E. Manta, K. Kappel
{"title":"防伪纸中纤维素基质中铁磁微丝的保留研究","authors":"I. Zapodeanu, M. Codescu, M. Burlacu, V. Midoni, R. Erdei, D. Pătroi, E. Patroi, E. Manta, K. Kappel","doi":"10.21741/9781945291999-1","DOIUrl":null,"url":null,"abstract":"Prepared by the Taylor – Ulitovsky technique, the glass-coated microwires are formed from a metallic core, with the diameter 3 to 50 μm, surrounded by an insulating layer from glass, with the thickness of 1 to 20 μm. Embedded in the cellulose matrix, the ferromagnetic glasscoated microwires allow their use as security element for the authentication of valuable papers in the electronic validation process. The authentication of the security paper is realised with a special detector, by “YES” or “NO” answer. This paper can be used as anti-shoplifting or validating elements to identify the counterfeit products. The paper presents the experimental results related to the retention of ferromagnetic microwires in the cellulose matrix, a complex process characterised by specific features, primarily due to the shape and diameter/length ratio of the microwires. The ferromagnetic retention yield was η = 65 – 90%, for the prepared papers with basis weight more than 50 g/m. Introduction Faced with increasing of goods counterfeiting, a wide range of methods are currently used to protect consumer goods, bank, state and commercial documents. Thanks to impossibility to produce security elements without proper equipment and under special conditions imposed by the very high degree of accuracy, the advanced technologies offer the solution, ensuring a high degree of protection against falsification. Investment and research efforts are being made to diversify the field of high security elements. The moment of launching the technology for glass-coated microwires (GMW) fabrication [1,2] has become revolutionary on the high-tech technology market, opening up the gates of a large variety of technological benefits for the existing applications and also setting the foundation for new applications [3-9]. The advantages of ferromagnetic GMWs securing [10] were: possibility of identifying at distance; stable magnetic properties even at high temperatures and corrosive media; wide range of functional temperatures; stability at shielding – the codes shielded by metallic panels can be read; stability at the mechanical action; small sizes and low consumption and, for the microfibbers from the last generation, with special properties, allowing the possibility to the information magnetic encoding): very large amount of the generated codes; the information can be read both from a stationary source and from a source in motion; the encoding is impossible to destroy, both in the Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 1-10 doi: http://dx.doi.org/10.21741/9781945291999-1 2 continuously and in variable magnetic field, (reliable encoding); possibility to read the information from any code randomly oriented in space. The structure of the paper consists of vegetable fibers (wood or non-wood), in which auxiliary materials, such as fillers, gluing agents, pigments, additives etc. are incorporated. Depending on the application field of paper, some structural features are imposed to the network: number of fiber-fiber contacts and of sizes of interfibrillar spaces, density and roughness of the surfaces. These properties are depending on the fibbers nature, on their processing degree, on the amount and properties of the auxiliary, and also on the processing technique used for forming and finishing of network. The term of filler defines any non-fibrous material added to the paper pulp to improve the optical properties of the paper, but also other features such as porosity, smoothness, printing ability etc. By incorporating of pigments into the paper pulp, the papers optical inhomogeneity increases, the amount of reflected and refracted light in the paper sheet increases, and the whiteness and opacity is improved. At the same time, the pigment particles retained in the sheet structure increase the interfibrillar spaces and reduce the possibility to set-up interfibrillar bonds having negative effects on the paper resistance indices. The fillers retention into the paper sheet is realised mainly by filtration for the particles with large sizes and by colloidal phenomena for fine particles. The introduction of filling is primarily determined by technical considerations, since certain characteristics of the paper, particularly optical indices and printing ability, are limited if only fibrous materials are used. Currently fillers can also serve as partial substitutes for fibrous materials in some cases, thereby helping to reduce the production costs. Developed by the Taylor-Ulitovsky process, the GMWs consist of a cylindrical metal core that is covered with a glass-insulating layer, the diameter of the metal core is 3 50 μm, and the thickness of the glass insulation is 1 20 μm. The length of such microwires, under laboratory conditions, reaches approx. 1 km. The ferromagnetic glass-coated microwires, cut at ca. 7 mm lengths, is included in the paper composition also as filling material, but in the paper pulp and in the paper sheet structure, the microwire segments have a certain behaviour that differentiates them from the classical materials of filling. Unlike these materials, the ferromagnetic microwires introduced into the paper in very small amounts do not significantly influence the rheological characteristics of the paste and the paper resistance characteristics. The appearance of wires, the diameter, length and the microwires density are also specific characteristics that differentiate the materials currently used to fill the paper. The importance of retention efficiency in the case of ferromagnetic microwires is primarily due to the need to achieve a certain microwires density in the paper sheet, in order to ensure its security without affecting the paper quality and functionality. 2. Experimentals The Taylor-Ulitovsky technique for GMWs preparation consists in placing in a high-frequency inductor of a glass tube with a metallic rod inside (Fig. 1). Under the influence of the generated electromagnetic field, the metal melts, forming a drop. In contact with the molten metal, a part of the glass tube softens and a coating is formed from the glass covering the drop. For a particular working regime [11], this glass soaked by pulling also trains the metal, leading to microwires formation, which is collected on the spool. Different metal core structures can be obtained: polycrystalline crystals of different sizes (microcrystalline, nanocrystalline) or amorphous. For experimental research were used Fe77B13Si10 GMWs, which are structurally, by X-ray diffraction and magnetically, by vibrating sample magnetometry, characterized. Achieving certain density of GMW in the paper sheet structure, as in the fillers case, depends on the action of factors with a particular influence on intelligent material retention in the papermaking process. Knowing and controlling these influences will ultimately allow finally reaching the density that is sufficient for paper securing. In this respect, have been experimented Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 1-10 doi: http://dx.doi.org/10.21741/9781945291999-1 3 several programs in which the basic recipe for realisation of the GMWs secured paper has been supplemented with several variables specific to each influenced factor studied. Fig. 1. Aspect during the Fe77B13Si10 ferromagnetic glass-coated microwires drawing. Table 1. The studied parameters and the experimented recipes used to for paper preparation Parameter S/H ratio, [wt. %] S/H Schopper – Riegler degree, [SR] Microwires amount, [g] Retentor amount, [%] Paper weight, [g/m] Nature of the fibrous materials 100 S or 100 H 30 0.005; 0.007; 0.009 Schopper – Riegler degree SR of the cellulosic material 60/40 30/20; 40/30; 50/40; 60/50 0.009 GMWs amount 60/40 30/20; 40/30; 50/40; 60/50 0,005; 0,007; 0,009; 0,011 Softwood / hardwood cellulosic pulp ratio from the fibrous composition of paper 20/80; 30/70; 40/60; 50/50 45/30 0.007 Amount of retention emulsion, dosed in the paper manufacturing receipts 60/40 30/20 0; 0.2; 0.4; 0.6; 0.8 Paper weight 60/40 30/20 50; 70; 90; 110 The GMWs with 7 mm lengths are embedded as filler into the cellulose matrix (the pulp), the main receipt of the mixture, in wt.%, being: bleached cellulose sulphate from softwood (S) pulp (different amounts: 30 100%; Schopper – Riegler degree: 30 60 SR); bleached cellulose sulphate from hardwood (H) pulp (different amounts: 30 100%; Schopper – Riegler degree 20 50 SR); paper filling material: 15% calcium carbonate; gluing emulsion: 1,5% alkyl–dimercetene (AKD); retention additive: 0,5% polyamide–amine and different amounts of GMW (for 10 sheets with paper weight q = 75 g/m) – 0.005g; 0.007g; 0.009g and 0.011g. The particularities of the experimented recipes for paper sheets preparation are chosen to highlight the influence of different Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 1-10 doi: http://dx.doi.org/10.21741/9781945291999-1 4 process parameters (Table 1). The Schopper-Riegler test provides a measure of the rate at which a dilute suspension of pulp may be dewatered. It has been shown that the drainability is correlated to the surface conditions and swelling of the fibbers, and constitutes a useful index of the amount of mechanical treatment to which the pulp has been subjected. The retention efficiency (η) was expressed as the ratio of the amount of GMW initially used to prepare the cellulosic paste and the remaining GMW amount in the laboratory prepared sheet (in each experiment, the retention yield was determined for 10 sheets of paper). 3. Results and discussions 3.1 Structural characterization for Fe77B13Si10 ferromagnetic glass-coated microwires After preparation, the GMWs were structurally characterized by X-ray diffraction investigations. The glass-coating was","PeriodicalId":20390,"journal":{"name":"Powder Metallurgy and Advanced Materials","volume":null,"pages":null},"PeriodicalIF":0.0000,"publicationDate":"2018-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"A study of the ferromagnetic microwires retention in cellulose matrix in the security papers\",\"authors\":\"I. Zapodeanu, M. Codescu, M. Burlacu, V. Midoni, R. Erdei, D. Pătroi, E. Patroi, E. Manta, K. Kappel\",\"doi\":\"10.21741/9781945291999-1\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"Prepared by the Taylor – Ulitovsky technique, the glass-coated microwires are formed from a metallic core, with the diameter 3 to 50 μm, surrounded by an insulating layer from glass, with the thickness of 1 to 20 μm. Embedded in the cellulose matrix, the ferromagnetic glasscoated microwires allow their use as security element for the authentication of valuable papers in the electronic validation process. The authentication of the security paper is realised with a special detector, by “YES” or “NO” answer. This paper can be used as anti-shoplifting or validating elements to identify the counterfeit products. The paper presents the experimental results related to the retention of ferromagnetic microwires in the cellulose matrix, a complex process characterised by specific features, primarily due to the shape and diameter/length ratio of the microwires. The ferromagnetic retention yield was η = 65 – 90%, for the prepared papers with basis weight more than 50 g/m. Introduction Faced with increasing of goods counterfeiting, a wide range of methods are currently used to protect consumer goods, bank, state and commercial documents. Thanks to impossibility to produce security elements without proper equipment and under special conditions imposed by the very high degree of accuracy, the advanced technologies offer the solution, ensuring a high degree of protection against falsification. Investment and research efforts are being made to diversify the field of high security elements. The moment of launching the technology for glass-coated microwires (GMW) fabrication [1,2] has become revolutionary on the high-tech technology market, opening up the gates of a large variety of technological benefits for the existing applications and also setting the foundation for new applications [3-9]. The advantages of ferromagnetic GMWs securing [10] were: possibility of identifying at distance; stable magnetic properties even at high temperatures and corrosive media; wide range of functional temperatures; stability at shielding – the codes shielded by metallic panels can be read; stability at the mechanical action; small sizes and low consumption and, for the microfibbers from the last generation, with special properties, allowing the possibility to the information magnetic encoding): very large amount of the generated codes; the information can be read both from a stationary source and from a source in motion; the encoding is impossible to destroy, both in the Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 1-10 doi: http://dx.doi.org/10.21741/9781945291999-1 2 continuously and in variable magnetic field, (reliable encoding); possibility to read the information from any code randomly oriented in space. The structure of the paper consists of vegetable fibers (wood or non-wood), in which auxiliary materials, such as fillers, gluing agents, pigments, additives etc. are incorporated. Depending on the application field of paper, some structural features are imposed to the network: number of fiber-fiber contacts and of sizes of interfibrillar spaces, density and roughness of the surfaces. These properties are depending on the fibbers nature, on their processing degree, on the amount and properties of the auxiliary, and also on the processing technique used for forming and finishing of network. The term of filler defines any non-fibrous material added to the paper pulp to improve the optical properties of the paper, but also other features such as porosity, smoothness, printing ability etc. By incorporating of pigments into the paper pulp, the papers optical inhomogeneity increases, the amount of reflected and refracted light in the paper sheet increases, and the whiteness and opacity is improved. At the same time, the pigment particles retained in the sheet structure increase the interfibrillar spaces and reduce the possibility to set-up interfibrillar bonds having negative effects on the paper resistance indices. The fillers retention into the paper sheet is realised mainly by filtration for the particles with large sizes and by colloidal phenomena for fine particles. The introduction of filling is primarily determined by technical considerations, since certain characteristics of the paper, particularly optical indices and printing ability, are limited if only fibrous materials are used. Currently fillers can also serve as partial substitutes for fibrous materials in some cases, thereby helping to reduce the production costs. Developed by the Taylor-Ulitovsky process, the GMWs consist of a cylindrical metal core that is covered with a glass-insulating layer, the diameter of the metal core is 3 50 μm, and the thickness of the glass insulation is 1 20 μm. The length of such microwires, under laboratory conditions, reaches approx. 1 km. The ferromagnetic glass-coated microwires, cut at ca. 7 mm lengths, is included in the paper composition also as filling material, but in the paper pulp and in the paper sheet structure, the microwire segments have a certain behaviour that differentiates them from the classical materials of filling. Unlike these materials, the ferromagnetic microwires introduced into the paper in very small amounts do not significantly influence the rheological characteristics of the paste and the paper resistance characteristics. The appearance of wires, the diameter, length and the microwires density are also specific characteristics that differentiate the materials currently used to fill the paper. The importance of retention efficiency in the case of ferromagnetic microwires is primarily due to the need to achieve a certain microwires density in the paper sheet, in order to ensure its security without affecting the paper quality and functionality. 2. Experimentals The Taylor-Ulitovsky technique for GMWs preparation consists in placing in a high-frequency inductor of a glass tube with a metallic rod inside (Fig. 1). Under the influence of the generated electromagnetic field, the metal melts, forming a drop. In contact with the molten metal, a part of the glass tube softens and a coating is formed from the glass covering the drop. For a particular working regime [11], this glass soaked by pulling also trains the metal, leading to microwires formation, which is collected on the spool. Different metal core structures can be obtained: polycrystalline crystals of different sizes (microcrystalline, nanocrystalline) or amorphous. For experimental research were used Fe77B13Si10 GMWs, which are structurally, by X-ray diffraction and magnetically, by vibrating sample magnetometry, characterized. Achieving certain density of GMW in the paper sheet structure, as in the fillers case, depends on the action of factors with a particular influence on intelligent material retention in the papermaking process. Knowing and controlling these influences will ultimately allow finally reaching the density that is sufficient for paper securing. In this respect, have been experimented Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 1-10 doi: http://dx.doi.org/10.21741/9781945291999-1 3 several programs in which the basic recipe for realisation of the GMWs secured paper has been supplemented with several variables specific to each influenced factor studied. Fig. 1. Aspect during the Fe77B13Si10 ferromagnetic glass-coated microwires drawing. Table 1. The studied parameters and the experimented recipes used to for paper preparation Parameter S/H ratio, [wt. %] S/H Schopper – Riegler degree, [SR] Microwires amount, [g] Retentor amount, [%] Paper weight, [g/m] Nature of the fibrous materials 100 S or 100 H 30 0.005; 0.007; 0.009 Schopper – Riegler degree SR of the cellulosic material 60/40 30/20; 40/30; 50/40; 60/50 0.009 GMWs amount 60/40 30/20; 40/30; 50/40; 60/50 0,005; 0,007; 0,009; 0,011 Softwood / hardwood cellulosic pulp ratio from the fibrous composition of paper 20/80; 30/70; 40/60; 50/50 45/30 0.007 Amount of retention emulsion, dosed in the paper manufacturing receipts 60/40 30/20 0; 0.2; 0.4; 0.6; 0.8 Paper weight 60/40 30/20 50; 70; 90; 110 The GMWs with 7 mm lengths are embedded as filler into the cellulose matrix (the pulp), the main receipt of the mixture, in wt.%, being: bleached cellulose sulphate from softwood (S) pulp (different amounts: 30 100%; Schopper – Riegler degree: 30 60 SR); bleached cellulose sulphate from hardwood (H) pulp (different amounts: 30 100%; Schopper – Riegler degree 20 50 SR); paper filling material: 15% calcium carbonate; gluing emulsion: 1,5% alkyl–dimercetene (AKD); retention additive: 0,5% polyamide–amine and different amounts of GMW (for 10 sheets with paper weight q = 75 g/m) – 0.005g; 0.007g; 0.009g and 0.011g. The particularities of the experimented recipes for paper sheets preparation are chosen to highlight the influence of different Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 1-10 doi: http://dx.doi.org/10.21741/9781945291999-1 4 process parameters (Table 1). The Schopper-Riegler test provides a measure of the rate at which a dilute suspension of pulp may be dewatered. It has been shown that the drainability is correlated to the surface conditions and swelling of the fibbers, and constitutes a useful index of the amount of mechanical treatment to which the pulp has been subjected. The retention efficiency (η) was expressed as the ratio of the amount of GMW initially used to prepare the cellulosic paste and the remaining GMW amount in the laboratory prepared sheet (in each experiment, the retention yield was determined for 10 sheets of paper). 3. Results and discussions 3.1 Structural characterization for Fe77B13Si10 ferromagnetic glass-coated microwires After preparation, the GMWs were structurally characterized by X-ray diffraction investigations. 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摘要

由泰勒- Ulitovsky技术,金属的玻璃微丝形成核心,直径3 - 50μm,从玻璃绝缘层包围,1到20μm的厚度。嵌入在纤维素基质中,铁磁玻璃涂层微线允许它们作为电子验证过程中有价值文件认证的安全元素。通过“是”或“否”的回答,通过一个特殊的检测器来实现安全纸的认证。本文可以作为防入店行窃或识别假冒产品的验证元素。本文介绍了与铁磁微丝在纤维素基质中的保留有关的实验结果,这是一个具有特定特征的复杂过程,主要是由于微丝的形状和直径/长度比。铁磁潴留率η= 65 - 90%,准备论文的基础重量超过50 g / m。面对越来越多的商品假冒,目前使用了各种各样的方法来保护消费品,银行,国家和商业文件。由于不可能产生安全元素没有适当的设备和在特殊的条件下实施的精确度很高,先进技术提供解决方案,确保高度的防范伪造。投资和研究正在努力多样化高安全领域的元素。玻璃涂层微线(GMW)制造技术的推出[1,2]已经成为高科技技术市场上的革命性技术,为现有应用打开了各种技术效益的大门,也为新的应用奠定了基础[3-9]。铁磁gmw固定[10]的优点是:可以远距离识别;稳定的磁性甚至在高温和腐蚀性介质;功能温度范围广;屏蔽时的稳定性——金属板屏蔽的代码可以读取;稳定的机械作用;小尺寸和低消耗,对于上一代的微纤维来说,具有特殊的性能,允许对信息进行磁编码的可能性):生成的代码量非常大;所述信息既可以从静止源读取,也可以从运动源读取;编码是不可能破坏的,无论是在粉末冶金和先进材料- RoPM&AM 2017材料研究论坛LLC材料研究进展8 (2018)1-10 doi: http://dx.doi.org/10.21741/9781945291999-1 2连续和可变磁场,(可靠编码);从空间中任意方向的代码中读取信息的可能性。纸的结构由植物纤维(木材或非木材)组成,其中加入了辅助材料,如填料,胶粘剂,颜料,添加剂等。根据纸张的应用领域,某些结构特征被施加到网络上:纤维-纤维接触的数量和纤维间空间的大小,表面的密度和粗糙度。这些属性根据识别性质、加工程度,辅助的数量和属性,和处理技术用于网络的形成和完成。填充物是指添加到纸浆中的任何非纤维材料,以改善纸张的光学性能,以及其他特征,如孔隙度、平滑度、印刷能力等。通过在纸浆中掺入颜料,增加了纸张的光学不均匀性,增加了纸张上的反射光和折射光,提高了纸张的白度和不透明度。同时,保留在薄片结构中的色素颗粒增加了纤维间的空间,减少了纤维间键形成的可能性,对纸张阻力指标产生了负面影响。填料在纸张中的保留主要是通过大颗粒的过滤和细颗粒的胶体现象来实现的。填料的引入主要取决于技术方面的考虑,因为如果只使用纤维材料,纸张的某些特性,特别是光学指数和印刷能力是有限的。目前,填料在某些情况下也可以作为纤维材料的部分替代品,从而有助于降低生产成本。采用Taylor-Ulitovsky工艺研制的gmw由外包玻璃绝缘层的圆柱形金属芯组成,金属芯的直径为350 μm,玻璃绝缘层的厚度为120 μm。这种微导线的长度,在实验室条件下,达到大约。1公里。铁磁玻璃包覆微线,切割在大约。 长度为7mm的微丝段在纸的组成中也作为填充材料,但在纸浆和纸张结构中,微丝段具有与传统填充材料不同的特定行为。与这些材料不同的是,将极少量的铁磁微线引入纸中,对浆料的流变特性和纸的电阻特性没有显著的影响。电线的外观、直径、长度和微线密度也是区分目前用于填充纸张的材料的具体特征。在铁磁微丝的情况下,保留效率的重要性主要是由于需要在纸张中达到一定的微丝密度,以确保其安全性而不影响纸张质量和功能。2. 制备gmw的泰勒-乌里托夫斯基技术是在玻璃管的高频电感中放置金属棒(图1)。在产生的电磁场的影响下,金属熔化,形成液滴。在与熔融金属接触时,玻璃管的一部分变软,覆盖液滴的玻璃形成涂层。对于一个特定的工作状态[11],这种玻璃浸泡通过拉也训练金属,导致微线的形成,这是收集在阀芯。可以得到不同的金属芯结构:不同尺寸的多晶晶体(微晶、纳米晶)或非晶。实验研究采用Fe77B13Si10 gmw,通过x射线衍射和磁性,通过振动样品磁强计,对其进行了结构表征。在纸张结构中达到一定的GMW密度,如填料,取决于造纸过程中对智能材料保留有特殊影响的因素的作用。了解和控制这些影响将最终使纸张达到足够的密度。在这方面,已经试验了粉末冶金和先进材料- RoPM&AM 2017年材料研究论坛有限责任公司材料研究学报8 (2018)1-10 doi: http://dx.doi.org/10.21741/9781945291999-1 3几个项目,其中实现gmw担保论文的基本配方已经补充了针对所研究的每个影响因素的几个变量。图1所示。Fe77B13Si10铁磁玻璃包覆微丝拉丝过程中的一个方面。表1。参数S/H比,[wt. %] S/H Schopper - Riegler度,[SR]微丝量,[g] Retentor量,[%]纸重,[g/m]纤维材料性质100 S或100 H 30 0.005;0.007;0.009纤维素材料的Schopper - Riegler度SR 60/40 30/20;40/30;50/40;60/50 0.009 GMWs量60/40 30/20;40/30;50/40;60/50 0005;0007;0009;0.011纸张纤维成分中的软木/硬木纤维素纸浆比例为20/80;30/70;40/60;50/50 45/30 0.007保留乳液量,在纸质制造单据中添加60/40 30/ 200;0.2;0.4;0.6;0.8纸张重量60/40 30/20 50;70;90;长度为7mm的gmw作为填料嵌入纤维素基质(纸浆)中,混合物的主要接收物(wt.%)为:从软木(S)纸浆中漂白的硫酸盐纤维素(不同量:30 - 100%;Schopper - Riegler度:30 - 60 SR);硬木(H)纸浆漂白硫酸盐纤维素(不同量:30 - 100%;Schopper - Riegler度20 50 SR);纸张填充材料:15%碳酸钙;胶乳:1.5%烷基二美塞烯(AKD);保留添加剂:0.5%聚酰胺胺和不同量的GMW(10张纸,纸重q = 75 g/m) - 0.005g;0.007克;0.009g和0.011g。选择纸张制备实验配方的特殊性,以突出不同粉末冶金和先进材料的影响- RoPM&AM 2017材料研究论坛LLC材料研究进展8 (2018)1-10 doi: http://dx.doi.org/10.21741/9781945291999-1 4个工艺参数(表1)。Schopper-Riegler试验提供了稀浆悬浮液脱水速率的度量。研究表明,滤干性与纤维的表面条件和膨胀有关,是衡量纸浆受到的机械处理程度的有用指标。保留效率(η)表示为最初用于制备纤维素糊的GMW量与实验室制备的纸张中剩余GMW量的比值(每次实验中,确定10张纸的保留率)。3.结果与讨论 Fe77B13Si10铁磁玻璃包覆微丝制备完成后,通过x射线衍射对其进行了结构表征。玻璃涂层是
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A study of the ferromagnetic microwires retention in cellulose matrix in the security papers
Prepared by the Taylor – Ulitovsky technique, the glass-coated microwires are formed from a metallic core, with the diameter 3 to 50 μm, surrounded by an insulating layer from glass, with the thickness of 1 to 20 μm. Embedded in the cellulose matrix, the ferromagnetic glasscoated microwires allow their use as security element for the authentication of valuable papers in the electronic validation process. The authentication of the security paper is realised with a special detector, by “YES” or “NO” answer. This paper can be used as anti-shoplifting or validating elements to identify the counterfeit products. The paper presents the experimental results related to the retention of ferromagnetic microwires in the cellulose matrix, a complex process characterised by specific features, primarily due to the shape and diameter/length ratio of the microwires. The ferromagnetic retention yield was η = 65 – 90%, for the prepared papers with basis weight more than 50 g/m. Introduction Faced with increasing of goods counterfeiting, a wide range of methods are currently used to protect consumer goods, bank, state and commercial documents. Thanks to impossibility to produce security elements without proper equipment and under special conditions imposed by the very high degree of accuracy, the advanced technologies offer the solution, ensuring a high degree of protection against falsification. Investment and research efforts are being made to diversify the field of high security elements. The moment of launching the technology for glass-coated microwires (GMW) fabrication [1,2] has become revolutionary on the high-tech technology market, opening up the gates of a large variety of technological benefits for the existing applications and also setting the foundation for new applications [3-9]. The advantages of ferromagnetic GMWs securing [10] were: possibility of identifying at distance; stable magnetic properties even at high temperatures and corrosive media; wide range of functional temperatures; stability at shielding – the codes shielded by metallic panels can be read; stability at the mechanical action; small sizes and low consumption and, for the microfibbers from the last generation, with special properties, allowing the possibility to the information magnetic encoding): very large amount of the generated codes; the information can be read both from a stationary source and from a source in motion; the encoding is impossible to destroy, both in the Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 1-10 doi: http://dx.doi.org/10.21741/9781945291999-1 2 continuously and in variable magnetic field, (reliable encoding); possibility to read the information from any code randomly oriented in space. The structure of the paper consists of vegetable fibers (wood or non-wood), in which auxiliary materials, such as fillers, gluing agents, pigments, additives etc. are incorporated. Depending on the application field of paper, some structural features are imposed to the network: number of fiber-fiber contacts and of sizes of interfibrillar spaces, density and roughness of the surfaces. These properties are depending on the fibbers nature, on their processing degree, on the amount and properties of the auxiliary, and also on the processing technique used for forming and finishing of network. The term of filler defines any non-fibrous material added to the paper pulp to improve the optical properties of the paper, but also other features such as porosity, smoothness, printing ability etc. By incorporating of pigments into the paper pulp, the papers optical inhomogeneity increases, the amount of reflected and refracted light in the paper sheet increases, and the whiteness and opacity is improved. At the same time, the pigment particles retained in the sheet structure increase the interfibrillar spaces and reduce the possibility to set-up interfibrillar bonds having negative effects on the paper resistance indices. The fillers retention into the paper sheet is realised mainly by filtration for the particles with large sizes and by colloidal phenomena for fine particles. The introduction of filling is primarily determined by technical considerations, since certain characteristics of the paper, particularly optical indices and printing ability, are limited if only fibrous materials are used. Currently fillers can also serve as partial substitutes for fibrous materials in some cases, thereby helping to reduce the production costs. Developed by the Taylor-Ulitovsky process, the GMWs consist of a cylindrical metal core that is covered with a glass-insulating layer, the diameter of the metal core is 3 50 μm, and the thickness of the glass insulation is 1 20 μm. The length of such microwires, under laboratory conditions, reaches approx. 1 km. The ferromagnetic glass-coated microwires, cut at ca. 7 mm lengths, is included in the paper composition also as filling material, but in the paper pulp and in the paper sheet structure, the microwire segments have a certain behaviour that differentiates them from the classical materials of filling. Unlike these materials, the ferromagnetic microwires introduced into the paper in very small amounts do not significantly influence the rheological characteristics of the paste and the paper resistance characteristics. The appearance of wires, the diameter, length and the microwires density are also specific characteristics that differentiate the materials currently used to fill the paper. The importance of retention efficiency in the case of ferromagnetic microwires is primarily due to the need to achieve a certain microwires density in the paper sheet, in order to ensure its security without affecting the paper quality and functionality. 2. Experimentals The Taylor-Ulitovsky technique for GMWs preparation consists in placing in a high-frequency inductor of a glass tube with a metallic rod inside (Fig. 1). Under the influence of the generated electromagnetic field, the metal melts, forming a drop. In contact with the molten metal, a part of the glass tube softens and a coating is formed from the glass covering the drop. For a particular working regime [11], this glass soaked by pulling also trains the metal, leading to microwires formation, which is collected on the spool. Different metal core structures can be obtained: polycrystalline crystals of different sizes (microcrystalline, nanocrystalline) or amorphous. For experimental research were used Fe77B13Si10 GMWs, which are structurally, by X-ray diffraction and magnetically, by vibrating sample magnetometry, characterized. Achieving certain density of GMW in the paper sheet structure, as in the fillers case, depends on the action of factors with a particular influence on intelligent material retention in the papermaking process. Knowing and controlling these influences will ultimately allow finally reaching the density that is sufficient for paper securing. In this respect, have been experimented Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 1-10 doi: http://dx.doi.org/10.21741/9781945291999-1 3 several programs in which the basic recipe for realisation of the GMWs secured paper has been supplemented with several variables specific to each influenced factor studied. Fig. 1. Aspect during the Fe77B13Si10 ferromagnetic glass-coated microwires drawing. Table 1. The studied parameters and the experimented recipes used to for paper preparation Parameter S/H ratio, [wt. %] S/H Schopper – Riegler degree, [SR] Microwires amount, [g] Retentor amount, [%] Paper weight, [g/m] Nature of the fibrous materials 100 S or 100 H 30 0.005; 0.007; 0.009 Schopper – Riegler degree SR of the cellulosic material 60/40 30/20; 40/30; 50/40; 60/50 0.009 GMWs amount 60/40 30/20; 40/30; 50/40; 60/50 0,005; 0,007; 0,009; 0,011 Softwood / hardwood cellulosic pulp ratio from the fibrous composition of paper 20/80; 30/70; 40/60; 50/50 45/30 0.007 Amount of retention emulsion, dosed in the paper manufacturing receipts 60/40 30/20 0; 0.2; 0.4; 0.6; 0.8 Paper weight 60/40 30/20 50; 70; 90; 110 The GMWs with 7 mm lengths are embedded as filler into the cellulose matrix (the pulp), the main receipt of the mixture, in wt.%, being: bleached cellulose sulphate from softwood (S) pulp (different amounts: 30 100%; Schopper – Riegler degree: 30 60 SR); bleached cellulose sulphate from hardwood (H) pulp (different amounts: 30 100%; Schopper – Riegler degree 20 50 SR); paper filling material: 15% calcium carbonate; gluing emulsion: 1,5% alkyl–dimercetene (AKD); retention additive: 0,5% polyamide–amine and different amounts of GMW (for 10 sheets with paper weight q = 75 g/m) – 0.005g; 0.007g; 0.009g and 0.011g. The particularities of the experimented recipes for paper sheets preparation are chosen to highlight the influence of different Powder Metallurgy and Advanced Materials – RoPM&AM 2017 Materials Research Forum LLC Materials Research Proceedings 8 (2018) 1-10 doi: http://dx.doi.org/10.21741/9781945291999-1 4 process parameters (Table 1). The Schopper-Riegler test provides a measure of the rate at which a dilute suspension of pulp may be dewatered. It has been shown that the drainability is correlated to the surface conditions and swelling of the fibbers, and constitutes a useful index of the amount of mechanical treatment to which the pulp has been subjected. The retention efficiency (η) was expressed as the ratio of the amount of GMW initially used to prepare the cellulosic paste and the remaining GMW amount in the laboratory prepared sheet (in each experiment, the retention yield was determined for 10 sheets of paper). 3. Results and discussions 3.1 Structural characterization for Fe77B13Si10 ferromagnetic glass-coated microwires After preparation, the GMWs were structurally characterized by X-ray diffraction investigations. The glass-coating was
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