A Practical Criterion for Rheological Modeling of the Peeling of Pressure Sensitive Adhesives

The transient extensional viscosity of non-crosslinked pressure sensitive adhesives (PSA's) and physically-crosslinked PSA's is measured and compared with theoretical predictions based on the linear viscoelastic (LVE) properties of the PSA's and the use of linear and quasi-linear constitutive equations. Based on a previously-derived expression for the relative contributions of individual relaxation modes of a polymeric material to its transient extensional viscosity, a criterion for whether large extensional deformations can be modeled on the basis of the LVE spectrum is proposed and evaluated for each PSA. The relevance to adhesion is demonstrated in peel tests, where the deformation of adhesive is quantified in images of the peel front under the assumption of uniaxial elongation and used to obtain theoretical peel forces in excellent agreement with measurements. This demonstrates the applicability of the criterion to the peeling process.     

A Practical Criterion for Rheological Modeling of the Peeling of Pressure Sensitive Adhesives

The transient extensional viscosity of non-crosslinked pressure sensitive adhesives (PSA's) and physically-crosslinked PSA's is measured and compared with theoretical predictions based on the linear viscoelastic (LVE) properties of the PSA's and the use of linear and quasi-linear constitutive equations. Based on a previously-derived expression for the relative contributions of individual relaxation modes of a polymeric material to its transient extensional viscosity, a criterion for whether large extensional deformations can be modeled on the basis of the LVE spectrum is proposed and evaluated for each PSA. The relevance to adhesion is demonstrated in peel tests, where the deformation of adhesive is quantified in images of the peel front under the assumption of uniaxial elongation and used to obtain theoretical peel forces in excellent agreement with measurements. This demonstrates the applicability of the criterion to the peeling process.     

Pressure Sensitive Adhesives Based on VectorR SIS Polymers I. Rheological Model and Adhesive Design Pathways

Dexco Polymers (a Dow/Exxon partnership) has been manufacturing Vector^R SIS polymers since 1990.¹ This paper describes experiments carried out to study Vector SIS polymers and model pressure sensitive adhesive (PSA) formulations based on Exxon Chemical's Escorez^R 1310LC tackifier. The adhesive behavior of tackified polymers was quantitatively analyzed by applying the rheological principle of time-temperature superposition² and the mapping approach,^3,4 and the pressure sensitive rheological model⁵ developed earlier. This model⁵ was developed by expanding and modifying an equation [adhesive fracture strength = (intrinsic adhesion) × (bulk energy dissipation)] proposed by Gent et al.^6,7 and Andrews et al.^8,9 This study delivers two key results. The first is that the fracture strength of the PSA/steel bond is the multiplication of three terms: the intrinsic (or interfacial) adhesion, the bonding and the debonding terms (Fig. 1). The debonding term is correlated with the logarithm of the loss modulus at the PSA debonding frequency or with the logarithm of the monomeric friction coefficient of the block copolymer/tackifier system. Both the loss modulus and the monomeric friction coefficient measure the energy dissipation in the bulk adhesive. The second is that PSA design pathways can be established by a mapping approach in the rheological space of the plateau modulus versus the loss modulus peak position in the frequency scale (Fig. 2). Plateau modulus is the bonding parameter because it measures the wetting capability of the adhesive with the substrate surface. The loss modulus peak position is the debonding parameter because it corresponds approximately to the time scale (or the frequency scale) in which one deforms the adhesive to maximize energy dissipation. Therefore, the tackifier and oil combination lowers the plateau modulus, but increases the T_g of the polyisoprene phase of the SIS polymer. This increase in T_g is equivalent to the lowering of the rate of local rearrangement (frequency of segment jumps) of the polyisoprene chains of the block copolymer. An optimal “tackification pathway” in this rheological space is achieved by tailoring the tackifier type and T_g, and the amount of oil used in the PSA.

In brief, the PSA rheological model and mapping approach described in this work for Vector SIS polymers give a comprehensive understanding and adhesive design pathways. This concept and approach not only allow raw material suppliers to improve and design better tackifier and polymer products, but also provide PSA formulators a quantitative tool to achieve PSA end property results.     

影响压敏胶粘带180°剥离强度因素的研究

本文探讨了试验板表面的粗糙度、温湿度、基材、试验板的放置时间及胶层厚度对压敏胶粘带 1 80°剥离强度的影响。实验结果表明 ,与溶剂型丙烯酸酯压敏胶相比 ,乳液型丙烯酸酯压敏胶对试验板的表面粗糙度更为敏感 ;试验板粘贴胶带后的放置时间对橡胶型胶带影响较大 ,而对丙烯酸酯型压敏胶的影响小 ;温湿度对 1 80°剥离强度也有很大影响 ;基材厚度相同时 ,胶在PET膜上的剥离强度比在OPP膜上的剥离强度大 ;随着PET厚度从 1 2 μm增大到 3 8μm ,剥离强度从 2 73N/cm上升至 4 2 9N/cm ;在OPP膜上 ,胶层从 1 0 μm增至 4 0 μm时 ,1 80°剥离强度从 2 2 3N/cm上升至 3 81N/cm     

天然橡胶乳液压敏胶粘剂

本文介绍了天然橡胶胶乳压敏胶的基本情况，内容包括基本组成、主要优缺点和改进方法。     

橡胶型压敏胶粘剂的研制

本文介绍了以天然橡胶、丁苯橡胶和α-萜烯树脂为主体材料制备压敏胶的工艺过程,及对影响性能的一些因素进行了分析讨论。     

The Mechanisms of Peeling of Uncross-Linked Pressure Sensitive Adhesives

We analyze the peeling properties of an uncross-linked pressure sensitive adhesive. 90° peeling master curves on Pyrex^TM and PMMA (polymethylmetacrylate) are constructed The shift coefficients a_T are compared with the ones obtained from rheometrical shear tests.

With our machine, the peeling front is kept fixed, enabling us to observe the mechanisms of deformation of the adhesive. We count four different mechanisms of peeling in cohesive failure, and three in interfacial peeling (the last being unstable); they correspond to various slopes that we identify. The flow patterns at slow reduced velocities are two-dimensional. Then they undergo transitions to three-dimensional periodic complex flows, due to instabilities in the flow of thin adhesives. Interpretation of these peeling master curves are discussed in terms of rheology and physico-chemistry. It appears necessary to take into account the elongational properties of the adhesive, as well as the surface energy properties, to predict adhesion.     

Pressure Sensitive Adhesives Based on Oleic Acid

Existing pressure sensitive adhesives (PSA) are mostly based on petrochemical‐based polymers. This study reveals a new class of bio‐based polymers that can be used as PSA. The polymers are hydroxyl‐containing polyesters from the step‐growth polymerization of epoxidized oleic acid (EOA), an AB‐type monomer containing both a carboxylic acid group (A) and an epoxy group (B). The monomer is derived from epoxidation of renewable methyl oleate followed by selective hydrolysis of the ester group. The polymers (PEOA) of EOA were characterized for their chemical structure and molecular weight. The PEOA after being cured with a very small amount of a crosslinking agent could serve as a PSA with high peel strength, high tack force, superior shear resistance, excellent aging resistance, and excellent thermal stability. The PSA contains 99 wt% of green renewable materials. The PSA were also characterized for their viscoelastic properties and thermal properties.     

Peeling of Acrylic Pressure Sensitive Adhesives: Cross-Linked versus Uncross-Linked Adhesives

In this paper we analyze the adhesive properties of two kinds of adhesives, determined by a 90[ddot] peeling test on a Pyrex^TM substrate. Simultaneously, we observe the mechanisms of flow at the peeling front. An uncross-linked acrylic pressure-sensitive adhesive is used, whereas the second one, of the same class, is slightly cross-linked. The mechanisms of peeling are compared with the ones of our previous study (Benyahia et al [8]) and are found to be identical in the case of uncross-linked adhesives. On the other hand, we find new regimes of flow when the adhesive is cross-linked.

To investigate these differences further, we determine the rheometrical properties of the adhesives in dynamic shear tests and in uniaxial elongational experiments. Furthermore, surfaces are characterized.

A discussion of the peeling curves is finally presented, showing the combined effects of the rheological properties and the surface ones. Conditions for predicting the type of regimes and transitions are also investigated.     

The Influence of Surfactants on the Peel Strength of Water-based Pressure Sensitive Adhesives

In order to study the effect of surfactants on the adhesive properties, peel measurements were performed with two series of model polymers of ethylhexylmethacrylate (PEHMA), the first prepared by emulsion polymerization with four anionic surfactants, and the second by post-adding the same surfactants to a surfactant-free latex. Cohesive fracture is observed at low peel rates; the peel strength depends on the bulk mechanical properties and is independent of the emulsifier. A transition to another type of separation occurs at higher peel rates, which seems to be an interfacial failure by visual inspection. Surface analytical studies, however, give evidence that this “interfacial” failure is, in fact, a mixed failure, leaving traces of the polymer on the substrate surface. The peel rate at this transition as well as the peel strength at mixed fracture are influenced by the surfactants. Large differences were observed between the four surfactants as well as between both series of polymers, leading to the conclusion that the surfactants have a different mobility within the film. This is also reflected by a different aging behaviour of the films.     

Elastic Analysis of the Loop Tack Test for Pressure Sensitive Adhesives

The behavior of pressure sensitive adhesive (PSA) tapes is sometimes examined via the loop tack test, in which a loop of the tape is brought into contact with a flat surface and then pulled away. A numerical analysis of the test is presented here. The loop is treated as an elastica, but with a nonlinear moment-curvature relation, so that the material is assumed to be elastic and inextensible. Debonding at the edge of the contact region is assumed to occur when the adhesive reaches a critical elongation. This elongation is assumed to depend on the maximum contact pressure and, in part of the results, on the length of time of contact. Shapes of the loop and values of the corresponding forces are obtained using a shooting method, and the effects of the stiffness and thickness of the adhesive and backing are examined.     

皮肤用亲水性聚氨酯压敏胶的制备及性能研究

针对目前我国透皮制剂所用橡胶类压敏胶的缺点,制备了一种亲水性聚氨酯压敏胶,并对其性能进行了研究。该压敏胶是由二异氰酸酯与多元醇的混合物进行反应生成预聚体,再经扩链制得的。通过在聚氨酯主链上引入亲水的聚乙二醇嵌段来赋予压敏胶亲水性。研究结果表明该聚氨酯压敏胶具有优良的粘结性能及反复揭帖性,具有良好的药物、皮肤相容性及良好的药物控释性能。     

Properties of Polyisoprene-Based Pressure Sensitive Adhesives Crosslinked by Electron Beam Irradiation

Many pressure sensitive adhesives are based on partially-crosslinked blends of an elastomer and a tackifying resin. In this work, a model pressure sensitive adhesive system was studied based on anionically-polymerized polyisoprenes. The effects of the initial molecular weight of the polyisoprene and the degree of crosslinking on the adhesive properties were investigated. The adhesives were crosslinked by electron beam irradiation to achieve particular levels of gel content. The dependence of gel content on dose and molecular weight is in good agreement with statistical crosslinking theory. The molecular weight of the soluble fraction was always dominated by that of the initial elastomer. With regard to creep resistance, it was observed that high gel content could compensate for low molecular weight. This was not true of the peel behavior.     

Mechanical Properties of Acrylic Pressure Sensitive Adhesives and Their Relationships to Industry Standard Testing

Dynamic mechanical and tensile stress-strain properties were measured for four sets of acrylic pressure sensitive adhesives, and were compared to industry standard “applications” peel and shear properties. Correlations were established showing that more than half of the range of performance shown by commercial PSA's is controlled by the bulk mechanical properties of the adhesive polymer. A few exceptions stand out clearly. Also, room temperature performance properties were found to correlate better with DMA at higher temperatures than with room temperature DMA. The contribution of tensile properties to peel strength and failure mode is discussed. The results can be used to relate PSA performance to well-known concepts in other areas of materials science, e.g. fracture toughness, rubber elasticity, and rheology, and to key variables in the adhesive formulation or selection process.     

Creep Resistance of Pressure Sensitive Mounting Tapes

The first part of the paper deals with an approach towards a systematic testing procedure to evaluate the creep behavior of single lap shear specimens bonded with PSA mounting tapes under the influence of temperature and humidity. The study includes commercial tapes as well as self-formulated pressure sensitive adhesives based on styrene block copolymers. The second part of the paper relates the obtained data, consisting of the time-dependent sample deformation and time-to-failure, to the observed failure modes. The results show that the creep behavior of a pressure sensitive adhesive is not only dependent on the environmental, conditions but also on the substrate material and its surface composition. The results for the self-formulated adhesives reveal the possibility of enhancing creep resistance of PSA's by adding fillers to the formulation. The paper closes with a modification of the Burgers model that is suitable for describing the creep/creep recovery behavior of tested lap shear specimens. The effect of nonlinear behavior in cyclic loading experiments is described and a thesis for the relation of nonlinear creep behavior to damaging processes in the adhesive bond is presented.     

丙烯酸酯类水基压敏胶研究进展

对近年来用接枝、核／壳、有机硅、交联、共混、反应性或高分子乳化剂改性丙烯酸酯类水基压敏胶的研究进展和发展趋势进行了综述。     

热熔压敏胶粘接性能的流变学研究

研究了苯乙烯嵌段共聚物系热熔压敏胶的动态流变学行为和持粘力之间的联系,主要研究了决定持粘力的流变学参数.研究证明,持粘力受到体系的蠕变过程的控制,可以通过较高温度下得到的持粘力数据来预测室温持粘力的大小.研究了液体树脂含量对持粘力的影响,提出损耗角正切(tan δ)最小值及其对应的温度是决定热熔压敏胶持粘力的关键流变学参数.     

SIS型热熔压敏胶影响因素分析

通过熔融混合制备SIS型热熔压敏胶,重点考察了增黏树脂、软化油、SIS结构参数等因素对热熔压敏胶黏度、初黏、剥离强度的影响。采用单因素实验法系统探讨软化油、增黏树脂、主体树脂等对热熔压敏胶黏度、初黏、剥离等性能的影响,并进一步探讨增黏树脂内在物理化学结构对热熔压敏胶的影响,结果表明:增黏树脂软化点高低对热熔压敏胶的黏度和剥离强度有重大影响。通过正交试验法得出:影响黏度的关键因素是油含量,影响剥离强度的关键因素是增黏树脂,影响初黏的关键因素是油含量和增黏树脂。     

溶剂型丙烯酸酯压敏胶的制备与性能研究

以丙烯酸丁酯(BA),丙烯酸异辛酯(2-EHA),丙烯酸羟丙酯(HPA)以及甲基丙烯酸甲酯(MMA)为聚合单体,采用普通自由基聚合合成了一系列溶剂型丙烯酸酯共聚物压敏胶.讨论了交联剂MDI用量不同对压敏胶热性能与使用性能的影响,并研究了加入氢化松香树脂对压敏胶性能的影响.用TGA以及DSC对其热性能进行了表征,并测试了...     

Epoxidation of Styrene-Isoprene-Styrene Block Copolymer and Its Use for Hot-Melt Pressure Sensitive Adhesives

The epoxidation of styrene-isoprene-styrene block copolymer (SIS) with performic acid generated in situ from hydrogen peroxide and formic acid was studied, and the hot-melt pressure sensitive adhesives (HMPSA) were prepared with epoxidized SIS (ESIS), SIS and the tackifier ESCOREZ-2203LC. The ¹H nucleal magnetic resonance and Fourier transform infrared spectra revealed that the epoxidation reaction mainly occurred in 1,4-isoprene units of SIS, and the reactivity of the cis-1,4-structure was higher than that of the trans-1,4-structure. Analysis by Gel Permeation Chromatography (GPC) showed that the molecular weight of SIS increased and the molecular weight distribution widened after epoxidation. Differential scanning calorimetry analysis showed that ESIS was compatible with SIS and ESCOREZ-2203LC. The addition of certain amount of polar ESIS in the HMPSA was beneficial to the improvement of 180° peel strength when the substrates were polar materials, such as PVC and steel. With the increase in peeling rate, the peel failure mode changed to adhesion failure from cohesion failure.