Aqueous Cold Seal Adhesive Blocking Resistance
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Solution Overview
Problem
Current cold-seal adhesives face challenges with residual tackiness leading to blocking issues during film production and storage, which compromises seal strength, and they often contain allergenic natural rubber latex and organic solvents.
Innovation Solution
An aqueous cold-seal adhesive comprising a mixture of a first polymer with a low glass transition temperature and a second polymer with a high glass transition temperature, both prepared in the presence of protective colloids, forming a coating that is autoadhesive yet blocking-resistant, and free from organic solvents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If acrylic dispersions are used for cold seal applications, then they provide a synthetic alternative to natural rubber latex, but they cause blocking problems when coils of coated films are produced due to residual tackiness
Solution Approach 1:
The patent uses a composite adhesive system combining polyacrylonitrile (providing tackiness and adhesion) with polyvinyl alcohol (providing blocking resistance). This composite approach allows the adhesive to simultaneously achieve the desired tackiness for cold sealing while preventing blocking during film production and storage, resolving the contradiction between synthetic alternative requirements and blocking resistance.
2Object-generated harmful factors
If residual film tackiness is reduced to prevent blocking, then blocking resistance improves, but seal strength of the cold seal is impaired
Solution Approach 1:
The patent optimizes the compositional parameters of the adhesive by precisely controlling the ratio of polyacrylonitrile to polyvinyl alcohol, the molecular weight of the polymers, and the amount of protective colloid. These parameter changes enable the adhesive to maintain adequate tackiness for strong sealing while the polyvinyl alcohol component provides sufficient blocking resistance, thus resolving the contradiction between blocking resistance and seal strength.
3Ease of operation
If natural rubber latex is used for cold seal adhesives, then cold seal functionality is achieved, but allergenic potential and quality fluctuations occur
Solution Approach 1:
The patent replaces natural rubber latex with synthetic polymers (polyacrylonitrile and polyvinyl alcohol) that are free from allergenic properties. This substitution eliminates the harmful allergenic potential while maintaining the cold seal functionality, effectively resolving the contradiction between operational ease and harmful factors.
4Object-affected harmful factors
If aqueous polymer dispersions are used to eliminate organic solvents, then allergenic potential and solvent content are reduced, but application effectiveness with conventional technologies may be impaired
Solution Approach 1:
The patent optimizes parameters including solids content (30-70% by weight), pH (adjusted to 3-9 using buffers), and the inclusion of protective colloids during polymerization. These parameter adjustments ensure the aqueous dispersion has appropriate viscosity, flow characteristics, and adhesion properties for effective application using conventional technologies while maintaining the allergen-free and solvent-free benefits.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides improved blocking resistance without impairing seal strength, is allergenic and solvent-free, and can be applied using conventional technologies, ensuring effective cold-sealing at ambient temperatures with enhanced film handling and storage properties.
Implementation Method 1
Cold-seal adhesives are bonding compositions which, following application to and drying on a substrate, are not tacky to the touch, yet bond to one another when pressed against one another at room temperature with pressure
Implementation Method 2
the first polymer being preparable by emulsion polymerization of free-radically polymerizable monomers in the presence of at least one protective colloid
Implementation Method 3
both polymers prepared in the presence of protective colloids
Implementation Method 4
following application to and drying on a substrate
Data Source
AI summary
Described is an aqueous cold seal adhesive in the form of an aqueous polymer dispersion comprising a mixture of a first polymer and a second polymer, wherein the first polymer is an emulsion polymer prepared in the presence of a protective colloid and is composed to an extent of at least 60% by weight of principal monomers selected from the group consisting of C1 to C20 alkyl (meth)acrylates and has a glass transition temperature of less than 0°C; and wherein the second polymer is an emulsion polymer prepared in the presence of a protective colloid and is composed to an extent of at least 60% by weight of principal monomers selected from the group consisting of vinylaromatics having up to 20 C atom, and has a glass transition temperature of at least 50°C. Also described are cold sealable coated polymer films coated with the aqueous cold seal adhesive and a method for producing a cold-sealed pack by applying the aqueous cold seal adhesive to a packaging substrate.