1 前言 日常生活中,商品的包装已经无处不在.作为包装业四大材料之一的塑料,其用量稳居第二位,紧随纸和纸板包装材料,占25％.根据全球综合数据资料库Statista统计,2019年,全球合成树脂总产量达到3.68亿t,消费量估计在2.55亿t左右.我国塑料消费量已经占全球比例的15％,仅塑料包装行业的产值就达到了4,297亿元,其用量已经达到千万吨水平.这其中,食品用塑料包装在我国塑料包装总量中占到了25％左右.

The microstructure of coating layers has important effects on final properties of paper. Eco-friendly bio-latex derived from sustainable starch has being increasingly used in paper coatings to substitute part of the petroleum-based synthetic latex as pigment binder. The influence of starch-based bio-latex on microstructure and surface properties of coatings such as surface composition, surface morphology, void fraction and water absorbency was studied in this paper. X-ray photoelectron spectroscopy (XPS) results showed that bio-latex addition led to a nearly linear decrease in surface carbon content for coatings dried at high temperature. Scanning electron microscope (SEM) images demonstrated that bio-latex addition may cause a lack of binder film at the coating surface that binds pigment particles, which was in agreement with the XPS results. The coatings demonstrated a marginal increase in surface roughness and some decrease in gloss with the addition of bio-latex, as was expected when starch-based binder was used. Unexpectedly, the void fraction of coatings increased slightly, which was contrary to the case in conventional cooked starch. The coatings had a significant decline in water contact angle after bio-latex addition, indicating a considerable increase in water absorbency. The changes in coating microstructure may be attributed to the unique core-shell structure and water-swollen nature of starch-based bio-latex particles.

Despite its biodegradability, adequate cohesive strength and comparatively low cost, the use of cooked starch as a paper coating binder is limited due to its high viscosity and serious negative impact on the gloss. Starch-based bio-latex with size in the nanometer or sub-micrometer range has been developed recently to overcome these shortcomings. In this study, ultrafine starch particle（UFSP） was prepared by mechanical milling using a DYNO mill in combination with light chemical pretreatment. Model coating colors containing different dosages of UFSP were applied to base paper and the properties of the coated papers were evaluated. The results showed that the UFSP was disc-shaped with a median particle diameter of 167 nm. Water retention capacity of the coating colors was improved considerably with the addition of UFSP, i.e., the water retention value decreased by nearly 40% when styrene-butadiene latex was replaced by UFSP at a dosage of 3 pph（per hundred parts of pigment）. The high shear rate viscosities of the coating colors containing no more than 2 pph of USFP were similar to that of the control coating color at shear strain rate higher than 2000 s -1 . The properties and performances of the coated papers were comparable to the control coated paper with single synthesized latex binder. The gloss and the print gloss of paper samples with or without USFP were 59.7% and 58.2%, 79.0% and 78.8%, respectively. Surface strength of paper samples with or without USFP were 0.96 and 0.90 m/s, respectively, while the ink absorptivity values were 34% and 33%. This study demonstrates a promising approach to obtain submicrometer sized starch for paper coating.

Starch-based bio-latex has been widely studied for the purpose of partially substituting petroleum-based latex as coating binder due to its environmental-friendly and sustainable natures. To engineer coating structure, it is essential to understand the bio-latex distribution during coating layer drying. In this work, bio-latex concentration at the surface and along the thickness direction of model coatings on a nonabsorbent film consolidated under various conditions was detected with ATR-IR, ESCA and Cryo-SEM. techniques in'order to understand whether bio-latex redistribute during coating drying and how the migration occurs. The results showed that bio-latex particles moved differentially with respect to kaolin clay pigment toward the coating surface and accumulated at surface during the initial liquid drying period, however, they deprived from coating surface in the end and aggregated at the top region of coating layer. A mechanism was proposed to explain this unexpected finding, which was attributed to the sphere-like morphology with nano or submicron size and highly hydrophilic, water-swollen natures of starch-based bio-latex binder. The small-sized bio-latex particles migrated to the surface due to their higher Brownian mobility relative to pigment initially, and in the later drying stage would move back into the coating pores with water because of its water affinity as the air-water interfaces receded from the surface into the capillaries. (C) 2017 Elsevier B.V. All rights reserved.

The resistance of wood-fiber paper to water, grease, and water vapor is usually attained by immersing the base paper in hydrophobic oil, laminating with a plastic or metal film, or the application of a barrier coating. Oil impregnation and the addition of films may make the paper difficult to recycle or persistent in the environment owing to their strong binding force and nondegradability. Environmental concerns have attracted worldwide attention to eco-friendly barrier coatings. In this study, degradable polyvinyl alcohol（PVA） and kaolin clay pigment were used to prepare coatings that were applied to a base paper. By measuring the barrier properties of the coated paper, including the water absorptiveness（Cobb60 value）, Hercules sizing degree, oil resistance（Kit rating）, and water vapor transmission rate（WVTR）, an optimal coating formulation and process were proposed. To examine the barrier mechanism of the PVA/kaolin clay coating, we characterized the coating microstructures using a scanning electron microscopy（SEM） and a mercury porosimeter. The results showed that the Cobb60 value and water vapor transmission rate of the coated paper decreased by 61.4% and 98.6%, respectively, compared with the base paper, for a pre-coating weight of 0.98 g/m~2 and a top-coating weight of about 3.23 g/m~2. Furthermore, the Hercules sizing degree rose by a factor of 337.2, while the oil resistance（Kit rating） increased from 0 to 12. The optimum drying temperature for a wet coating layer was found to be 170℃, and the optimum weight ratio of PVA to kaolin clay in the coating was determined to be 50∶50. It was assumed that the PVA/kaolin clay coating improved the smoothness of the paper considerably and decreased the pore size by filling the pores on the paper surface and forming an even film, thus enhancing the paper barrier performance. The coated paper also exhibited good repulpability.

分析了帘式涂布技术的发展及其所面临的挑战.帘式涂布不仅具有理想的仿形涂布效果,而且也拥有对原纸的作用力小、操作维护费用低等突出特点,应用前景广阔.近十年来发展迅速,尤其在特种涂布纸领域.帘式涂布的独特涂布原理引发了特殊的技术问题,如涂料的除气效果及其幕帘的稳定性和拉伸形变问题,只有完善地解决这些问题,才能满足帘式涂布运行性和涂布纸质量的要求.

应用实验室单张纸帘式涂布机,对分别以聚乙烯醇类增稠剂1788、丙烯酸乳液类增稠剂PR328、羧甲基纤维素(CMC)和碱润胀类增稠剂Top007为增稠剂的不同配方的涂料体系进行帘式涂布实验.结果表明,相同操作条件下,PR328体系涂层质量较好,CMC体系下涂层出现了大量“火山坑”现象;随着延展形变和延展速率的提高,涂层的破坏情况加剧;当延展形变相差不大时,高速度的涂布过程更容易出现表面缺陷;延展黏度大的涂料体系,涂层的表面覆盖率更高.

研究了重质碳酸钙(GCC)和高岭土体系下,组分间相互作用对涂料流变特性的影响.研究发现,涂料体系剪切流变性和延展流变性没有相关性;相同涂料体积分数下,高岭土体系的延展黏度和剪切黏度均高于GCC体系;与高岭土体系相比,增稠剂与GCC粒子作用效果更加明显;而随着胶乳的加入,模型涂料体系的延展黏度随之降低.

分析了除气前造纸涂料中气泡的分布特点,研究了不同目数筛网及不同筛网组合方式对振筛除气的影响,并进行了工厂中试试验.结果表明,在实验所选组合方式中,325-400-400目的组合方式最佳,且中试振动筛与实验室振动筛的除气效果相近,但中试振动筛的过筛速率更高.

The influences of guide rod,thickener,coatings solid content and pigments formulation of coatings on curtain stability in curtain coating were studied.The results showed that the stability of curtain could be improved by increasing the binding force between coatings and guide rod.For the coatings without surfactant,when PVA dosage was I.5 parts,the operational minimum flow increase from 1.64 cm2/s to 3.07 cm2/s;for coatings with surfactant,when PVA dosage increased from 0.5 part to 1.5 parts,the operational minimum flow decreased from 1.95 cm2/s to 1.55 cm2/s.Coatings solid content had a little effects on curtain stability.When clay content increased from 20 parts to 40 parts,the operational minimum flow increased from 1.92 cm2/s to 2.24 cm2/s.