Hot Tack Research Articles

Hot-Melt Adhesives

AbstractHot-melt adhesives facilitate fast production processes because the adhesives set simply by cooling. Formulations contain polymers to provide strength and hot tack (resistance to separation while adhesive is hot), and tackifiers and/or oils to dilute the polymer entanglement network, adjust the glass-transition temperature, lower the viscosity, and improve wet-out (molecular contact of the adhesive with the substrate over the entire bonding area). Some adhesives also contain waxes to speed setting, lower viscosity, and improve heat resistance. Obtaining adequate strength and heat resistance from nonreactive hot melts requires that some component of the hot melt separate out into a dispersed but interconnected hard-phase network upon cooling. The hard phases are commonly either glassy styrene domains (for adhesives based on styrenic block copolymers) or organic crystallites (for adhesives based on waxes, olefinic copolymers, or ethylene copolymers). This article will describe first the material properties relevant to the processing and performance of hot-melt adhesives, then the chemistry and function of the specific raw materials used in hot melts, and will conclude with illustrative application examples and corresponding formulations.

Film Properties for Good Performance on Vertical Form-Fill-Seal Packaging Machines

Technological improvements of flexible form, fill and seal packaging machines are yielding exceptional line speeds, productivity rates and bag features. This paper discusses the evolution of vertical packaging machine development and how it has impacted plastic film properties (e.g. COF, sealing temperature range, hot tack) required for optimal performance.

Lactic acid based polymers as hot melt adhesives for packaging applications

The suitability of biodegradable copolymers based on poly( l-lactide) (PLLA) and poly( ε-caprolactone) (PCL) with molar ratio of 81:19 for a packaging hot melt adhesive was evaluated. Typical hot melt adhesive properties such as open time, setting time, hot tack development, viscosity and weight loss were measured for an unstabilized and for two chemically stabilized samples. Mechanical testing included tensile strength, lap shear strength and elongation measurements. The results show that PLLA/PCL copolymer is a potential candidate for a biodegradable hot melt adhesive for a packaging application. Most of the measured properties were comparable to a conventional, non-biodegradable poly(ethylenevinylacetate) (EVA) based hot melt adhesive, which was used as a typical commercial reference. The stability of the PLLA/PCL copolymer is, however, a limiting factor: mechanical properties change within few days depending on the geometry of the samples. Also the degradation during processing of the PLLA/PCL copolymers was severe. The drying of the samples before processing or the use of nitrogen as a protective gas during processing seemed to have no observable effect on the stability. However, chemically stabilized polymers performed better during processing and also retained their mechanical properties better than the unstabilized copolymer.

Properties of films made from ternary blends of metallocene and conventional polyolefins

AbstractThin films were blown from a composition of 75% linear low density polyethylene (LLDPE) and 25% LDPE. The LLDPE content was made up of different % of metallocene‐based and conventional octene‐based LLDPE. Tensile strength, dart impact strength, hot tack strength, heat seal strength, and the barrier properties of these films were measured. All the properties showed significant improvement when conventional LLDPE (cLLDPE) was replaced by metallocene‐based LLDPE (mLLDPE), even to the extent of only 25%. The blends of 50% mLLDPE and 50% LDPE showed attractive properties. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 53–57, 2001

The Influence of Polymer Processing Additives (PPAS) on the Surface and Optical Properties of Polyolefin Plastomer Blown Film

Polyolefin plastomer films formulated with slip and antiblock were blown on a wide die gap with and without two DynamarTM polymer processing additives (PPAs). A wide die gap was used so that melt fracture-free film could be obtained with no PPA present for comparison purposes. The films were analyzed for the following properties: surface tension (on treated films), gloss, haze, clarity, transmittance, hot tack, heat seal, COF and block. In addition, the surface of films was examined using ESCA (Electron Spectroscopy for Chemical Analysis) and SSIMS (Static Secondary Ion Mass Spectrometry) to determine the surface chemical composition. PPAs when used at typical dose levels were shown to have essentially no effect on the surface and optical properties of plastomer films.

EFFECT OF METALLOCENE POLYETHYLENE ON HEAT SEALING PROPERTIES OF LOW DENSITY POLYETHYLENE BLENDS

Laminations made with blends of metallocene polyethylene (m-PE) and high-pressure low density polyethylene (LDPE) were prepared to investigate the effect of the former resin on heat sealing performance. According to various experimental studies of seal strength, hot tack and differential scanning calorimeter (DSC), it could be concluded that percentages around 15% of m-PE allow the obtainment of the optimal balance for heat sealing properties and cost. Using the interdiffusion theory of heat sealing, a thorough discussion of the results was done.

HIGH CLARITY LINEAR LOW DENSITY POLYETHYLENES FOR FOOD PACKAGING APPLICATIONS

The food packaging market includes many rapidly developing, increasingly demanding film applications. Important characteristics for food packaging are heat seal and hot tack properties, puncture resistance, and low temperature properties. Each type of polyethylene has unique strengths and weaknesses that contribute to the overall property balance and define specific markets in which the polyethylene can effectively compete. In the past two decades, many new polyethylenes have been introduced into packaging markets. These new polyethylenes have provided increasing toughness, allowing film manufacturers to produce films at reduced gauges, while maintaining physical properties. High pressure low density polyethylene (LDPE) continues to be a key player in many food packaging markets, especially those in which high clarity is required. A major disadvantage of LDPE is poor impact and tear strength. For increased impact and tear strength, film extruders have traditionally turned to linear low density polyethylenes (LLDPE) and have been forced to sacrifice clarity. These new high clarity LLDPE's allow film extruders to economically produce products with both toughness and clarity using existing equipment.

Hot tack of metallocene catalyzed polyethylene and low-density polyethylene blend

Hot tack of metallocene catalyzed polyethylene and low-density polyethylene blend

Hot tack of metallocene catalyzed polyethylene and low-density polyethylene blend

Films made of metallocene catalyzed polyethylene (mPE), low-density polyethylene (LDPE), and their blend were prepared to investigate how LDPE influences the hot tack of film. Experimental results showed hot tack is independent of film thickness. The addition of 30 wt % of LDPE can increase the hot tack of mPE film. The thermograms of differential scanning calorimetry (DSC) suggest the respective partial melting and recrystallization of those smaller size crystals at the bond forming and joint fracture stages play very important roles. The large amount of partial melting and high flow may induce a higher degree of molecular diffusion. Higher residual crystallinity and recrystallization at the hot tack testing process may induce higher resistant to bond fracture. Those two positive influences show that the mPE/LDPE film has the higher hot tack. The evidence from optical (higher optical transmission and lower haze) as well as viscoelastic (higher storage modulus and lower melt viscosity) properties further support this hypothesis. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1769–1773, 1999

New Resins For Fresh-Cut Produce Packaging

Through the use of molecular design, a new AFFINITY* polyolefin plastomer (POP-1) has been designed for use in the packaging of fresh-cut produce items that have high respiration rates. These items cannot be successfully packaged in the same films used for fresh-cut produce items that have lower respiration rates, such as iceberg lettuce. Produce items having high respiration rates include most fruits and many dark green vegetables such as broccoli and spinach. Film made from the new resin combines a high oxygen transmission rate with other necessary performance properties that are normally sacrificed with increasing oxygen transmission rate. Other properties achieved include sufficient modulus for use on vertical form/fill/seal machinery, excellent optics for maximum consumer appeal, easy processing on both extrusion and packaging equipment, and excellent seal performance including low initiation temperatures for both heat seal and hot tack, high hot tack strength and a broad seal window.

HOT TACK TESTING: A REVIEW

Hot tack is a primary function of flexible packaging. It has taken on more emphasis with the development of sealant copolymers and ionomers as well as the development of coextrusion to meet the packaging industry’s need for heat seal reliability when running at high speeds with more demanding configurations. As with many new terms, “hot tack” has not been precisely defined as yet. This paper, however, will discuss two important aspects of hot tack testing: the multilayered structure with a “hot tack” sealant and methods for relating test results to actual packaging machine performance, with major emphasis on two popular test methods–the automatic test equipment and the spring test.

AUTOMATIC INSTRUMENT FOR HOT TACK TESTING

There have been some earlier efforts to develop a system for testing the hot tack strength of heat sealable materials. However, these test methods were laborious to use, were not fully quantitative, and the user-effect on the test results was high To overcome these problems, Topwave Instruments developed a completely new model of Hot Tack Tester. Special care focused on versatile and accurate simulation of process conditions, automatic handling of samples and user- friendly operation (software) features, the goal being total user-independence. The result is equipment which provides values of the following parameters which are user-selectable: sealing temperature, sealing time, sealing pressure, cooling (delay) time, and loading (peeling) speed.

New Grades of Adhesive Copolymers for Flexible Packaging

New grades of high performance ethylene acrylic acid (EAA) copolymers have been produced for use as an adhesive or heat seal layer in specialty film applications. Comparison is made of film produced with this new resin and film made from ionomer resin and from linear low density polyethylene (LLDPE) and ethylene/vinyl acetate (EVA) copolymer resins. Measurements included the properties required for a superior flexible packaging film: hot tack, heat seal optics and film strength (tear, im pact, and tensile).

Notes from the Packaging Laboratory: Hot Tack Measurements of Thin Sealant Films

Sample preparation can greatly influence the results of laboratory testing of packaging sealant strength. Factors such as test strip width, edge uniformity, sealing die temperature and die load are recognizable variables to control. A design of experiments approach was used to explore the rank importance of these factors and any interactive effects that may occur. A generally well-behaved ethylene vinyl acetate (EVA) sealant on a high density polyethylene (HDPE) film was used for these tests. Experimental results indicate that sample width, die temperature and die pressure are the most influential factors. Unexpectedly, edge effects, namely a regular sine wave pattern and a generally random irregular edge had little influence on hot tack results. This document is ABE340, one of a series of the Agricultural and Biological Engineering Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. First published December 2002. 
 https://edis.ifas.ufl.edu/ae211