Patented Softtouch
SOFT TOUCH COATING COMPOSITION
DESCRIPTION
The present invention relates an improved soft touch coating composition, in particular to a soft touch coating composition having improved properties in terms of maintenance of their features over the time
As it is known, soft touch coating products are desired by the consumers because of their pleasant tactile feeling, non-slip grip and ergonomic comfort. In addition to its unique tactile touch property, the coating has to function constantly over the desired service time demanded in the market where daily interaction between the users and the coating surfaces occur, such as in the consumer electronic goods and automobile interior surfaces. Apart from robust adhesion to the coated surface, the coating itself has to perform well when exposed to common chemicals, such as human sweat, various cosmetics, including sun screens, food items, such as coffee and ketchups.
In case of Polyurethane-based soft touch coatings, a di-functional polyol binder is normally required in order to achieve the desired tactile feeling for the coating surface. In most cases, polyester-based diols or polyols are used as binders. These types of diols normally react relatively slow at the desired cure temperature. In order to process the coating composition effectively, it has to dry within an acceptable period of time. A suitable catalyst is added to promote the reaction between the polyol and the polyfunctional isocyanates. Such catalysts normally cause rapid reaction between the binder and the cross linker immediately after the two components are mixed.
Soft touch coatings known in the prior arts do normally provide most of the desired performance characteristics when the coating is freshly applied under a control application environment. However, when applied in a mass production environment, where process parameters are not precisely controlled, the resulting soft touch coating products often experience unexpected random failures in various physical property performances. Most commonly seen performance deteriorations are adhesion loss and stickiness already after six months of use. Chemical resistance properties are normally also reduced but are less apparent than adhesion loss or becoming sticky. In particular, a deterioration of the coating performances can be expected when the coating is exposed to harsh environments or demanding usage conditions.
The main aim of the present invention is to provide a soft touch coating composition, and in particular a polyurethane-based soft touch coating composition, which enables the above problems to be overcome. Within this aim, an object of the present invention is to provide a soft touch coating composition with improved resistance to common chemicals, such as human sweat, cosmetics, food items, beverages and similar.
Another object of the present invention is to provide a soft touch coating composition with improved resistance to harsh environments.
Yet another object of the present invention is to provide a soft touch coating composition that does not have performance deteriorations such as adhesion loss and stickiness after a relatively short period of use
Last but not least object of the present invention is to provide a soft touch coating composition which is highly reliable, relatively simple to produce and with competitive costs.
It has now been surprisingly found that by appropriately selecting the binder (i.e. the polyol) used in the preparation of soft touch coating compositions, it is possible to obtain a soft touch coating composition having robust long term physical performance under demanding usage conditions.
Thus, the present invention relates to a polyurethane soft touch coating composition characterized in that it comprises the reaction product of:
A) a non-hydrolysable polyol binder; and
B) an organic polyisocianate.
In fact, it has been found that the nature of the di-functional binders determines the performance of the soft touch coating when it is exposed to harsh environments under extended period of time.
The binders most commonly used are normal hydrolysable polyesters and they are extremely susceptible to poor performance. Non-hydrolysable binders such as polyether or polycarbonate diols have been found to provide stable performance. Polyesters where the ester linkage is protected from hydrolysis with structures to provide steric hindrance have been also found to be effective.
As better shown in the examples below, the polyurethane soft touch coating composition according to the invention is not able to scratch off after six weeks aging test with artificial sweat under standard conditions.
For the purposes of the present invention, the scratch test after six weeks aging with artificial sweat under standard conditions is the one reported below under the heading STAND ARS TEST CONDITIONS.
Preferably, compounds usable as binders A for the production of the soft touch coating composition of the invention are non-hydrolysable binders such as polyether, polycarbonate or polyester diols where the ester linkage is protected from hydrolysis with structures to provide steric hindrance. Such binders may in each case be used individually or in combination with one another.
Any desired organic polyisocyanates, preferably diisocyanates may be used, individually or in combination, as component B for the production of the soft touch coating composition of the invention.
The polyisocyanates may, for example, be of an aromatic, aliphatic and/or cycloaliphatic nature and have a molecular weight of preferably 126 - 500. These may also comprise diisocyanates containing ether or ester groups. Examples of suitable diisocyanates are trimethylene diisocyanate, tetramethylene diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate, propylene diisocyanate, ethylene diisocyanate, 2,3- dimethylethylene diisocyanate, 1-methyltrimethylene diisocyanate, 1,3-cyclopentylene diisocyanate, 1,4-cyclohexylene diisocyanate, 1,2-cyclohexylene diisocyanate, 1,3-phenylene diisocyanate, 1,4-phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4-diisocyanatodiphenylether, 1,5- dibutylpentamethylene diisocyanate, 2,3- bis(8-isocyanatooctyl)-4-octyl-5- hexylcyclohexane, 3-isocyanatomethyl-l-methylcyclohexyl isocyanate and/or 2,6- diisocyanatomethyl caproate.
In principle, the components A and B are reacted in the manner known to the person skilled in the art. Details on the condition used are given in the examples below.
In addition to the components A and B, the polyurethane soft touch coating composition of the present invention may contain conventional coating additives.
Examples of conventional coating additives are matting agents, levelling agents, rheological agents, such as highly disperse silica, polymeric urea compounds or layered silicates, thickeners, defoamers, wetting agents, anticratering agents, dispersants, UV stabilizers, light stabilizers and catalysts. The additives are used in conventional amounts known to the person skilled in the art, for example, of 0.1 to 5 wt.%, relative to the solids content of the coating composition.
Conventional coating solvents may also be present in the preparation of the soft-touch coating compositions of the invention.
EXAMPLES
The following compounds were used in the preparation of comparison and inventive polyurethane soft touch coating compositions.
Polyols
Polyol A: Desmophen 1652 polyol, Bayer Science Material; Polyol B: T5652 polyol, Asahi Kasei;
Polyol C: Desmophen 670BA polyol, Bayer Science Material;
Polyol D: SY-951 polyol, DSM;
Polyol E: PolyTHF650 polyol, BASF;
Polyol F: PE6003 polyol, Human Chemicals co.
Polyisocyanates
Desmodur N-75, Bayer Science Material.
Matting Agents
TS100 matting agent, Evonik Deggusa;
OK520 matting agent, Evonik Deggusa.
Flow Control Agents
Aerosil R974.
Wax
ZA-07 wax, Gifu-Shellac.
Levelling Agents
BYK370 levelling agent, BYK Chemie;
BYK103 levelling agent, BYK Chemie
UV Adsorber
Tinuvin 1130, CIBA.
Light Stabilizer
Tinuvin 292, CIBA.
COMPARATIVE EXAMPLES I-III AND EXAMPLE IV- V.
In the following Table 1 the weight ratios of the compounds used for the preparation of formulation A are reported.
Table 1 - Formulation A {continued)
I II III IV V
(comp.) (comp.) (comp.) (invention) (invention)
Flow Control Agent 1.54
Wax 6.00 6.01 5.95
Drier/Catalyst
1.00
10% Zinc Octoate
Drier/Catalyst
10% DBTL in 1.68 2.49 2.49 2.61 2.49 Butyl Acetate
Levelling Agent BYK 370 0.98 0.98 1.05 0.98
Levelling Agent BYK 103 3.99
UV Adsorber 1.00
Light Stabilizer 0.80
Vehicle Solvent:
Butyl Acetate 14.82 19.54 19.56 28.59 22.57
Methoxy Propyl Acetate 5.99 9.97 9.98 10.46 9.98
Texanol 10.28
Xylene 3.79 7.96 7.97 8.37 7.97
Total 100.00 100.00 100.00 100.00 100.00
For all examples, formulation B was prepared by mixing 25.82 parts b.w. Desmodur N-75 with 37.09 parts b.w. of Butyl Acetate and 37.09 parts b.w. of Xylene Vehicle Solvents.
Then, 50 parts b.w. of each of Formulations A-I to A-V were mixed with formulation B according to the amounts given in Table 2 to prepare a polyurethane coating composition.
In the examples, after thoroughly mixing formulation A and formulation B together, the mixture composition was immediately sprayed and subsequently cured at temperature of 80 °C for 40 min. The cured coating was then covered with artificial sweat solution at pH 2.60 and tested with damp heat cycles for hydrolysis property. The test conditions and test results are as shown below.
STAND ARS TEST CONDITIONS.
Preparation of artificial sweat:
Material used: 1.00 ± 0.01 g of urea (Pro Analysis quality), 5.00 ± 0.01 g of sodium Chloride (Analytical quality) and 1.14 ± 0.02 g DL-lactic acid (>88 %, Analytical quality).
Preparation procedure:
1) The materials mentioned above were added to 900 ml DI water. The solution was stirred until all the added reagents completely dissolved;
2) After calibration, a pH-meter was attached to the solvent and the pH value was adjusted to 2.60 ± O. lOusing dilute ammonia solution (1 %);
3) A further amount of DI water was added to adjust the volume of solution to 1000 ml.
Damp heat cycle:
The damp heat cycle was the following:
25 °C with 95% relative humidity (9 hours);
Temperature increase from 25 °C to 55 °C (3 hours);
55 °C with 95% relative humidity (9 hours).
Scratch resistance test
A Scratch Resistant test was carried out on the above-prepared coating compositions after a continued period in a humidity chamber and covered with artificial sweat. The results are reported in Table 3.
The above results shows the surprising effects of the polyurethane soft touch coating composition according to the invention.
Formulation A-I to A-III, which do not pass the test, are based on conventional normal hydrolysable polyesters since Desmophen 1652 (Formulation A-I) is a linear polyester and Desmophen 670BA is a slightly branched polyester. By using this latter in combination with a polycarbonate polyol (T5652 polyol - see formulation A-II) the situation is slightly improved, but since the hydrolysable polyesters is the predominant binder the test was not passed.
Conversely, when using a polyether polyol (PolyTHF650 - formulation A-IV) or when using a highly modified, sterically hindered polyester (PE6003 - formulation A-V) the test was successfully passed.
It has been seen how the polyurethane soft touch coating composition according to the invention makes it possible to fully achieve the set aim and objects.
As shown by the resistance test carried out on both inventive and comparative composition, the polyurethane soft touch coating composition of the invention can withstand exposure to relatively harsh environment maintaining robust long term physical performance.
The polyurethane soft touch coating composition according to the present invention may advantageously be used for coating manufatured articles.
Manufactured article, such as consumer electronic articles or an automobile interior surfaces, in which at least a portion of their surface is coated with a polyurethane soft touch coating composition as described herein are also part of the present invention.
On the basis of the foregoing description, other characteristics, modifications or improvements are possible and evident to the average person skilled in the art. These characteristics, modifications and improvements must therefore be considered part of the present invention.
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Source: https://patents.google.com/patent/WO2012089827A1/en
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