Two-Stage Polymer Latex for Rotogravure Paper Coating
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Solution Overview
Problem
Existing polymer latexes for paper coating struggle to balance high binding strength with good printability, particularly in rotogravure printing, as increasing printability often reduces binding strength and vice versa.
Innovation Solution
A two-stage polymerization process is employed, where the first monomer mixture contains styrene, butadiene, and ethylenically unsaturated carboxylic acid, and the second mixture includes alkyl acrylate or methacrylate, with a focus on maintaining low Tg values for both phases to create a 'soft' polymer latex, reducing crosslinking and improving flexibility and printability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If acrylate is incorporated into the composition to improve printability, then printability is improved, but binding strength is reduced
Solution Approach 1:
The patent divides the polymer latex into two distinct phases: a soft phase (containing butadiene and styrene for printability) and a hard phase (containing itaconic acid and acrylic acid for binding strength). This segmentation allows each phase to independently contribute its specialized function without compromising the other, resolving the contradiction between printability and binding strength.
Solution Approach 2:
The patent creates a composite latex structure combining polymers with different Tg values and functional properties. The hard phase provides adhesion and binding strength while the soft phase provides flexibility and printability. This composite approach allows simultaneous achievement of both printability and binding strength that cannot be obtained with a single homogeneous polymer composition.
2Strength
If styrene/butadiene content is increased to improve binding strength, then binding strength is improved, but printability is reduced
Solution Approach 1:
The patent segments the latex composition into specialized phases: the hard phase (with high styrene/butadiene content) provides binding strength, while the soft phase (with low Tg acrylate components) provides printability. This segmentation allows high SB content to be present without sacrificing printability, as the soft phase compensates for the reduced flexibility.
Solution Approach 2:
Different regions of the latex particles have different compositions and properties. The hard phase regions provide local adhesion and binding, while the soft phase regions provide local flexibility and printability. This local differentiation allows each property to be optimized in its appropriate domain without compromising the other.
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 process results in polymer latexes that offer excellent printability and binding strength for rotogravure printing, with a significant improvement in suitability for the application by maintaining low Tg values and reducing crosslinking density, enhancing the latex's flexibility and odor profile.
Implementation Method 1
A two-stage polymerization process is employed, where the first monomer mixture contains styrene, butadiene, and ethylenically unsaturated carboxylic acid, and the second mixture includes alkyl acrylate or methacrylate
Data Source
AI summary
A polymer latex for paper coating, in particular, for coating surfaces to be printed by rotogravure printing processes is prepared by (a) polymerising a first monomer mixture in a first polymerisation step, to produce a first polymer latex, the first monomer mixture comprising, (i) from 23 to 65 wt % of an ethylenically unsaturated aromatic monomer, (ii) from 0.5 to 7 wt% of an ethylenically unsaturated carboxylic acid, and (iii) from 30 to 70 wt % of a conjugated diene, the said percentages being based on the total of components (i), (ii) and (iii), and (b) further polymerising a second monomer mixture in the presence of the first polymer latex in a second polymerisation step, the second monomer mixture comprising (based on the second monomer mixture), (i) from 0 to 35 wt % of an ethylenically unsaturated aromatic monomer, (ii) from 0.5 to 7 wt % of an ethylenically unsaturated carboxylic acid, and (iii) from 58 to 96.5% wt%, of an alkyl acrylate or alkyl methacrylate, (iv) from 0 to 7.5 wt % of an ethylenically unsaturated nitrile monomer; wherein, the weight of the monomers polymerized in the first step account for 25 to 95 % of the total monomer weight of the first and second monomer mixtures, the second monomer mixture contain no more than 5 wt % of conjugated diene; the total amount of ethylenically unsaturated aromatic monomer and ethylenically unsaturated nitrile monomer in the second monomer mixture is at least 3 wt % of the total second monomer mixture, the second monomer mixture has a Tg (as calculated using the Fox equation) of not more than 30 °C.