Soft, transparent and processable thermoplastic polyurethane

Details Soft, transparent and processable thermoplastic polyurethane Soft, transparent and processable thermoplastic polyurethane

1999-10-08

2001-09-25

Sergent, Rabon (Department: 1711)

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...

C528S061000, C528S064000, C528S065000

Reexamination Certificate

active

06294638

ABSTRACT:

The present invention is directed to a thermoplastic polyurethane resin and more particularly to a molding composition containing this resin, suitable in optical applications.
SUMMARY OF THE INVENTION
A soft, transparent and processable TPU prepared by reacting (i) a diisocyanate (ii) chain extender and (iii) a mixture of polyether polyols is disclosed. The mixture of polyetherpolyols includes (A) a C
4
polyether polyol and (B) a C
2
-C
3
polyether polyol where the weight ratio of A/B is about 85/15 to 15/85. The inventive thermoplastic polyurethane is characterized by its clarity, processability and softness and is especially suitable in optical application.
Transparent polyurethane elastomers and thermoplastics are known and their preparation and properties have been well documented, see for instance Oertel, G, 1994 Polyurethane Handbook, 2
nd
edition, New York, N.Y., Hanser Publishers. The dependence of material properties on the structure of relevant systems has been discussed in a paper entitled “Structure-Property Relationship of Transparent Polyurethane Elastomers from the Geometric Isomers of Methyelene Bis(4-cyclohexyl Isocyanate)” by Shio-Wen Wong et al. IRC '85 Kyoto; International Rubber Conference Proceedings, Editors: Japan Society of Rubber Industry, Kyoto, Japan, Oct. 15-18, 1985, Paper 16D07, p. 347-58.
The art-skilled have recognized that although transparent, the utility of the relevant resins is constrained by difficult processing and shortcomings in some important mechanical properties. A need has been established for a processable resin which would also meet the requirements for optical clarity and mechanical properties.
DETAILED DESCRIPTION OF THE INVENTION
The soft, transparent and processable thermoplastic polyurethane resin of the present invention is a product of a reaction of
(i) a diisocyanate
(ii) a chain extender, and
(iii) a mixture of polyether polyols.
The diisocyanate (i) is used in an amount of about 15 to 45%, preferably 25 to 35%, the chain extender (ii) is used in an amount of about 3 to 15%, preferably 5 to 12% and the mixture of polyether polyols, reactant (iii) is used in an amount of 40% to 80%, preferably 55% to 65%; all percents are relative to the total weight of reactants (i), (ii) and (iii). A key feature of the inventive resin is the compositional makeup of the mixture of polyether polyols, reactant (iii) above. Accordingly, the components of the mixture include as component (A) a C
4
polyether polyol having a number average molecular weight of about 500 to 2500, and as component (B) a C
2
-C
3
polyether polyol having a number average molecular weight of about 1800 g/mol to 6000. Critically, the weight ratio of A/B is in the range of about 85/15 to 15/85.
Organic diisocyanates suitable as reactant (i) in the present context are known in the art and are readily available in commerce. Diisocyanates suitable for use in the context of this invention include aliphatic, cycloaliphatic, aromatic and heterocyclic diisocyanates, all of which are known in the art, such as are disclosed in German Offenlegungsschriften 2,302,564; 2,423,764; 2,549,372; 2,402,840 and 2,457,387 incorporated by reference herein. Such diisocyanates include both substituted and unsubstituted hexamethylene diisocyanate, isophorone diisocyanate, the various tolylene, diphenyl methane and xylene diisocyanate and their hydrogenation products. Aliphatic diisocyanates are preferred. Among the aliphatic diisocyanates, mention may be made of 4,4′-diisocyanatodicyclohexyl methane, 1,6-hexamethylene diisocyanate (HDI), and hydrogenated 4,4′-biphenyl diisocyanate, isophorone diisocyanate, and cyclohexane diisocyanate. One or more aliphatic diisocyanates may be used in the practice of the invention. Most preferably, the diisocyanate reactant is 4,4′-diisocyanatodicyclohexyl methane.
The inclusion of small amounts of one or more isocyanates having more than two isocyanate groups in the molecule is permissible for as long as the resulting resin retains its thermoplasticity. Generally, the inclusion of such isocyanates should not exceed 10% relative to the weight of the diisocyanates. Examples of such isocyanates having a higher functionality include trimerized toluene diisocyanate (Desmodur IL), biuret of hexamethylene diisocyanate (Desmodur N100) and isocyanurate of hexamethylene diisocyanate (Desmodur N3300).
The chain extender suitable as reactant (ii) in the present invention is known in the art. Suitable extenders have been described in German Offenlegungsschriften 2,302,564; 2,423,764; 2,549,372; 2,402,840; 2,402,799 and 2,457,387 incorporated by reference herein. These include low molecular weight polyhydric alcohols, preferably glycols, polyamines, hydrazines and hydrazides. Aminoalcohols, such as ethanolamine, diethanol amine, N-methyldiethanolamine, triethanolamine and 3-amino-propanol may also be used. Preferred chain extenders include ethylene glycol, butylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, tripropylene glycol, neopentyl glycol, propylene glycol, 1,4-butanediol, dicyclohexylmethanediamine, ethylene diamine, propylene diamine, isophorone diamine as well as mixtures and derivatives thereof. The preferred chain extenders are ethylene glycol, diethylene glycol, 1,4-butanediol and 1,6-hexanediol. Chain extenders with functionalities greater than 2 may also be used as long as the resulting resin retains its thermoplasticity. Examples of such extenders having higher functionalities include trimethylolpropane, glycerin, and diethylenetriamine. Generally, the addition of such chain extenders which have higher functionalities should not exceed 10 percent relative to the weight of the difunctional chain extenders.
The mixture of polyether polyols (reactant (iii)) includes, as component (A), a C
4
polyether polyol having a number average molecular weight of about 500 to 2500, preferably 800 to 1200 g/mol conforming structurally to
HO—(CH
2
—CH
2
—CH
2
—CH
2
—O)
n
—H
and,
as component (B) a C
2
-C
3
polyether polyol having a number average molecular weight of about 1800 g/mol to 6000, preferably 3500 to 4500 g/mol, conforming structurally to
where x and z independently denote integers of 1 to 10, preferably 7 to 9, and where y denotes 35 to 80, preferably 50 to 60 and wherein the weight ratio of A/B is in the range of about 85/15 to 15/85, preferably 70/30 to 30/70.
The preparation of the inventive TPU is conventional. Procedures for making TPU have been reported in the literature (see, for instance, Saunders and Frisch, High Polymers Series, Vol 1 &2, 1964; Hsieh, K., Liao, D., Chern, Y; Thermoplastic Polyurethanes, 41, 381-395, 1997). The process for the preparation of the TPU of the invention is preferably catalyzed. Conventional catalysts for the preparation of TPU are known. Among the suitable catalysts, mention may be made of triethylamine, N,N′-dimethylpiperazine, N-methylmorpholine, titanic esters, tin diacetate, tin dioctoate, tin dilaurate, dibutyltin dilaurate, dibutyltin diacetate, tetrabutyl titanate and stannous octoate.
Conventional additives may be included in the inventive molding composition, these include lubricants (amid waxes, fatty acids, fatty acid esters, fatty alcohols, hydrocarbon waxes) UV stabilizers, hindered amine stabilizers and hydroxyphenyl benzotriazole heat stabilizers-antioxidant. In embodiments where release properties coupled with freedom from haze are desirable, the inclusion of amide wax was found to be particularly useful. The inclusion of such amide wax in amounts up to about 0.3%, preferably about 0.02 to 0.15% relative to the weight of the TPU, is particularly useful.
The characteristic term “soft”, used herein in reference to the inventive TPU, refers to a Shore A hardness value of about 60 to 80 preferably 70 to 78.
The term “transparent”, in context of this invention, means a property of light transmission, determined as Total Light transmission (TLT) of not less than 85%, preferably not less than 90% in accordance with ASTM 1003 measured using a Datacolor SF600

Affiliated with

Also associated with

Rating

Soft, transparent and processable thermoplastic polyurethane does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Soft, transparent and processable thermoplastic polyurethane, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Soft, transparent and processable thermoplastic polyurethane will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2488810