Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From reactant having at least one -n=c=x group as well as...
Patent
1996-07-19
1998-05-12
Cooney, Jr., John M.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From reactant having at least one -n=c=x group as well as...
524457, 528 52, 528 61, 528 75, 528 76, 528 80, 528 83, 528 85, C08G 1812, C08G 1861
Patent
active
057506302
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to novel water-soluble or water-dispersible polyurethane compounds and to compositions that contain the novel compounds and are useful, for instance, as low adhesion backsize for adhesive tapes. The invention also relates to processes for preparing the novel compounds, compositions and tapes.
BACKGROUND
A pressure-sensitive adhesive tape is essentially a pressure-sensitive adhesive coated on a flexible substrate backing. The tapes are usually stored in rolls in which each successive adhesive layer is in contact with the backing of the underlying layer. If the adhesive is a tackified block copolymer and there is too much adhesion between the adhesive layer and the backing, when the tape is unrolled for use the adhesive layer may stick to the backing and delaminate or separate from the adhesive side of the tape.
To prevent such delamination, and for ease of unwinding, the non-adhesive side of the tape i.e., the flexible substrate backing, is usually coated with a low adhesion backsize. A low adhesion backsize needs a balance of various properties to be effective. It should have flexibility and strength. The low adhesion backsize should adhere to, and form an even film on, the backing for even distribution of releasability. It should not contaminate the pressure-sensitive adhesive.
Polyurethanes that are known to be suitable for use as low adhesion backsize and inherently possess releasability have generally been soluble only in organic solvents. Since the low adhesion backsize is applied from solution, the use of organic solvent is necessitated, and after the low adhesion backsize has been applied to the tape backing the organic solvent must be removed and disposed of. Environmental considerations have led to a search for water-soluble, water-dispersible or water-borne compounds suitable for use as low adhesion backsize to eliminate or reduce the need for organic solvents.
DISCLOSURE OF THE INVENTION AND DETAILED DESCRIPTION
According to one aspect of the present invention there is provided a water-soluble or water-dispersible polyurethane polymer whose polymer chain includes segments derived from a silicone polycarbinol and whose polymer chain is end-capped with a silane.
To enhance the water-solubility or water-dispersibility of the polymer it is possible to include ethylene oxide moieties in the polymer chain. Although this enhances water-dispersibility, it renders the polymer moisture-sensitive, which is undesirable. It is therefore normally preferred to include few or no ethylene oxide units in those segments of the polymer chain that are not derived from the silicone polycarbinol. An alternative and preferred method of enhancing water-dispersibility is to include in the polymer chain a compound that bears a group that is water-soluble or can be rendered water-soluble. For example, if the compound 2,2-bis(hydroxymethyl)propionic acid is incorporated in the polymer chain carboxyl groups will be dependent from the polymer chain. If the polymer with the pendant carboxyl groups is reacted with a base, e.g., triethylamine, the carboxyl groups will be converted to carboxylate anions and will have a solubilizing effect. It will be appreciated that compounds bearing ionizable groups other than the carboxyl group can be used in a similar manner, with an appropriate acid or base to cause ionization to form a water-solubilizing anion or cation. Other compounds are discussed below.
According to another aspect of the present invention there is provided a water-soluble or water-dispersible polyurethane polymer which is the product of reaction between: urea linkages and is the product of reaction between:
It is noted that the higher the amount of silicone polycarbinol present, the better the release properties obtained. Similarly, the larger the quantity of silane chain terminating agent, in conjunction with the silicone polycarbinol the better the release properties. It is possible to tailor the release properties of the polymer by varying the amounts of silicone polycarbi
REFERENCES:
patent: 4287109 (1981-09-01), Schlak et al.
patent: 5356706 (1994-10-01), Shores
patent: 5543171 (1996-08-01), Shores
Cooney Jr. John M.
Minnesota Mining and Manufacturing Company
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