TW201629153A - Transparent flexible thermoset polyurethane films with good dimensional stability and method for manufacturing the same - Google Patents

Abstract

The present invention provides a polyurethane resin composition and a method for transforming said composition into thermoset polyurethane films. These films are particularly useful for applications in electronic devices, such as displays.

Description

Transparent flexible thermosetting polyurethane film with good dimensional stability and manufacturing method thereof

The present invention relates to a polyurethane resin composition and a film thereof having high refractive index, good optical and mechanical properties, good high temperature dimensional stability and good chemical resistance, and a method for producing the same. The polyurethane film is suitable for use in the electronics industry, such as flat panel displays and touch panels.

Transparent plastic film is widely used in liquid crystal displays (LCDs), flexible electronic devices and touches due to its high transparency, light weight, ease of design, impact resistance and economic advantages such as continuous manufacturing of refraction (R2R) processes. Screen panel. Conventional plastic films such as polyesters, polycarbonates, and cellulose derivatives have low heat resistance and generally require a coating to improve their chemical resistance. On the other hand, the polyurethane film exhibits good mechanical properties, abrasion resistance and chemical resistance.

WO2010/148424, EP2801586 A1 and EP2246378 disclose polyurethane resin compositions comprising mercaptans for optical lenses in the thickness range of millimeters A molded optical device of a component or similar size. WO 2008/061839 discloses coating formulations based on a similar composition. None of these documents discloses a method for producing a polyurethane film from selected isocyanates and polyols.

Therefore, those skilled in the art would like to design liquid crystal displays, flexible electronic devices and touch screen panels to have flexible transparent polymer films, which further exhibit good chemical resistance, good optical and mechanical properties, and good high temperature dimensional stability. Sex.

Accordingly, the present invention provides a polyurethane resin composition comprising at least one isocyanate and at least one thiol selected from the group consisting of tetrathiol and/or polythiol.

The polyurethane resin composition can be converted into a thermosetting polyurethane film to obtain characteristics such as flexibility, transparency, good chemical resistance, good optical and mechanical properties, and good high temperature dimensional stability. The film is very suitable for use in electronic device applications, especially display devices.

The at least one thiol is preferably an ester of a polyhydric alcohol, more preferably an ester of a tetraol, pentaol or hexaol. The thiol compound is particularly advantageous for obtaining a thermosetting polyurethane film, and a thiol of an ester composition of neopentyl alcohol or butyltetraol is mentioned herein. Thus, in a preferred embodiment of the invention, at least one ester of thiol pentaerythritol or butanol is used.

In general, it is to be understood that all the features and specific examples of the invention may be combined.

It has been observed that pentaerythritol tetrakis-mercaptopropionate (PETMP) will give particularly good results when forming a flexible thermosetting polyurethane film having the above-mentioned predetermined bonding properties. Therefore, according to the present invention, at least one thiol in the polyurethane resin composition Preferred is pentaerythritol tetrakis-mercaptopropionate.

As the isocyanate used in the polyurethane resin composition of the present invention, there are tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2-methylpentamethylene diisocyanate, 2, 2,4-trimethylhexamethylene diisocyanate, dodecamethylene diisocyanate, 1,4-diisocyanate cyclohexane, 3-isocyanatomethyl-3,3,5-trimethyl Cyclohexyl isocyanate, 4,4'-diisocyanatodicyclohexylmethane, 4,4'-diisocyanate-3,3'-dimethyldicyclohexylmethane, 4,4,-diisocyanide Acid-2,2-dicyclohexylpropane and mixtures thereof. Therefore, the isocyanate is preferably selected from the group consisting of tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2-methylpentamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate. , dodecyl diisocyanate, 1,4-diisocyanate cyclohexane, 3-isocyanatomethyl-3,3,5-trimethylcyclohexyl isocyanate, 4,4'-diisocyanate Acid dicyclohexylmethane, 4,4'-diisocyanate-3,3'-dimethyldicyclohexylmethane, 4,4'-diisocyanate-2,2-dicyclohexylpropane and mixtures thereof The group formed. In particular, good results can be obtained using a mixture of 1,6-hexamethylene diisocyanate and 3-isocyanatomethyl-3,3,5-trimethylcyclohexyl isocyanate. Therefore, in the present invention, the isocyanate is preferably a mixture of 1,6-hexamethylene diisocyanate and 3-isocyanatomethyl-3,3,5-trimethylcyclohexyl isocyanate, especially Combine PETMP or TMPMP. Further, in the present invention, at least one isocyanate can exist in the form of a trimer, a urethane, a biuret, a ureaform or a uretdione.

It has also been found that when the NCO-SH is maintained within a certain range, the polyurethane resin composition can be made into a film-forming property. The NCO:SH ratio is preferably from 10:1 to 1:10, preferably from 5:1 to 1:5, more preferably from 2:1 to 1:2. When the NCO-SH ratio is from 1.01:1 to 1.2:1, excellent results can be achieved. Therefore, in the present invention, the NCO:SH ratio is particularly preferable in this range.

According to the invention, the composition may further comprise a solvent and a selective antifoaming agent, a heat stabilizer and/or a wetting agent.

The solvent may be selected from aromatic hydrocarbons (such as xylene or toluene), ketones (such as acetone, 2-butanone, methyl isobutyl ketone, diacetone alcohol), alcohols (such as methanol, ethanol, isopropanol, butanol, 1- Methoxy-2-propanol), ether (such as 1,4-dioxane, ethylene glycol n-propyl ether) or ester (such as ethyl acetate, butyl acetate, 1-methoxy-2-acetic acid propyl ester) Or include a mixture of these solvents. The solvent is preferably ethanol, isopropanol, butanol, ethyl acetate, butyl acetate, 2-methoxypropyl alcohol, diacetone alcohol, xylene or toluene.

As described above, according to the present invention, the polyurethane resin composition can be easily converted into a flexible transparent film having a predetermined bonding property, which is advantageous for display applications of electronic devices. Accordingly, another object of the invention is a method of making a polyurethane film comprising casting a polyurethane composition according to the present invention. The meaning of the term "casting" as used in the present invention is as used in the art of film forming. Typically, the application of the film is applied to a substrate using the polyurethane resin composition of the present invention. Based on economic considerations, a large number of substrates or large-area substrates are coated as quickly as possible in the polar phase, so the first coating step is preferably carried out in a continuous process. For example, the coating can be carried out by wet coating, preferably by continuous wet coating. Using a wet coating process, it is easier and easier to anticipate The coated film of the present invention is produced at a reduced cost and has a uniform and consistent surface quality. Preferably, the wet coating process is selected from the group consisting of roll coating, roll coating, gravure coating, extrusion, spray coating, air knife and dipping/dip coating. The solvent casting process is particularly advantageous for casting a film according to the present invention when it is a flexible transparent polyurethane film, which is preferred for display applications. Therefore, the casting step in the method according to the invention is preferably a solvent casting step. Solvent casting is common in the art, for example, using a bar coater, a doctor die, a slot die, and the like. In general, solvent casting of the polyurethane resin composition of the present invention involves casting the composition onto a substrate. The substrate can be part of a belt or drum casting machine and comprises a metal and/or polymeric material. Preferably, the substrate comprises a polymeric substrate, such as a polyimide substrate, since the polyurethane film is readily separable from such substrates. The method according to the invention more preferably involves a drying step, preferably immediately after application of the composition of the invention onto the substrate. Drying methods can include indirect heating, irradiation heating, and air stream drying. It can be separated or combined in different regions to improve the accuracy of controlling the surface of the substrate into a film and drying the film. Additionally, one or more curing steps can be performed after the film is cast onto the substrate and dried. Curing can be carried out by thermal curing at 50 ° C to 100 ° C in the first curing step and 130 ° C to 200 ° C in the second curing step. The thermal curing step can be carried out for 15 to 100 minutes, and the first and second curing steps are included, or a curing step is performed using only the conditions described in the second curing step. Finally, the cooling step can involve a chill roll or cold air or both. Depending on the situation, additional coatings and/or protective layers may be added after the selective cooling step, for example for transport protection.

A further object of the invention is a thermosetting polyurethane film obtained by the process of the invention. In terms of its application, such as display devices, the maximum processing temperature is preferably at least 140 ° C, and the glass transition temperature Tg is at least 80 ° C according to ASTM D3418. The maximum processing temperature is defined as some film after contact for a period of time above this temperature. The nature will no longer meet specific requirements. The properties include film curl, heat transmission, YI and haze values after heat treatment. In accordance with the present invention, thermoset polyurethane films having the highest processing temperatures and Tg described above are particularly advantageous for electronic components and display applications. Other advantages can be achieved by processing the film in a continuous process.

In view of the advantageous features and effects of the thermosetting polyurethane film of the present invention, another object of the present invention is the use of the film of the present invention as a backlight panel or display panel, preferably a flat panel display or a touch panel display. Or flexible electronic devices.

Example

The invention will be described in detail below with reference to the examples, but the invention is not limited thereto. measuring:

Glass transition temperature (Tg)

The glass transition temperature (Tg) of the synthetic polyurethane was measured according to ASTM D3418 using a differential scanning card meter (DSC) under nitrogen charging and at a heating rate of 10 ° C/min. The temperature range is from 30 ° C to 300 ° C. The sample was cooled from 300 ° C to 30 ° C at a cooling rate of 10 ° C / min. The conversion temperature from the second heating was recorded as the glass transition temperature of the sample.

Mechanical properties

Measuring machinery with Instron Universal Testing Machine 5569 nature. The fixture used is a pneumatic side-moving clamp with a rubber surface. The test was carried out under ambient conditions (RT: 25 ° C, RH 56%). The load is 100 Newtons (N) and the rate is set to 1.00 mm/min.

Optical properties

Total and transmission haze were measured using a Hunter Lab Ultrascan PRO spectrometer.

Pencil hardness

The pencil hardness was measured using an Elcometer 3086 Scratch Boy according to ASTM D3363, with a weight of 750 grams.

Maximum processing temperature

The sample size was chosen to be 150 x 150 square millimeters. The properties of the unheat treated film samples were measured first. The sample orientation is noted as machine direction (MD) and cross direction (TD). The film sample was then heat treated at 150 ° C for 2 hours. The highest processing temperature is defined as the temperature at which the above criteria can be met.

Refractive index

The refractive index of the film was measured using a Metricon 2010/M稜鏡 coupler. The source wavelength setpoint of the equipment was varied to determine the refractive indices at three different wavelengths, namely 402, 594 and 784 nanometers (nm).

Example 1:

In a PP vessel, 11.58 grams of Desmodur NZ1 isocyanate (Bayer Material Science), 6.42 grams of pentaerythritol tetrakis-mercaptopropionate (taken from THIOCURE® PETMP from Bruno Bock Chemische Fabrik GmbH & Co.) and 12 grams of MEK solvent are mixed together. Homogenize the mixture at 2000 rpm (rpm) using a Thinky Mixer (ARE 310) for 5 minutes. Thereafter, the defoaming step was carried out at 2,200 rpm for 2 minutes. The solid content was 60% and the NCO-SH ratio was 1.05 to achieve optimum film formation.

After mixing, the solution was cast onto a polyimide film using a bar coater to a thickness of 150 micrometers (μm). The cast film was then thermally cured at 80 ° C for 15 minutes and at 180 ° C for 45 minutes. The resulting film has excellent optomechanical properties. The maximum processing temperature is 150 °C.

Example 2 (control group):

In a PP vessel, 11.23 grams of Desmodur NZ1 isocyanate (Bayer Material Science), 6.77 grams of trimethylolpropane tris(3-mercaptopropionate) (taken from THOOCURE® TMPMP by Bruno Bock Chemische Fabrik GmbH & Co.) ) mixed with 12 grams of MEK solvent. The mixture was homogenized at 2000 rpm for 5 minutes using a Thinky Mixer (ARE 310), followed by a defoaming step at 2200 rpm for 2 minutes. The solid content was 60% and the NCO-SH ratio was 1.05.

After mixing, the solution was cast onto a polyimide film using a bar coater to a thickness of 150 μm. The cast film was then thermally cured at 80 ° C for 15 minutes and at 180 ° C for 45 minutes. This resin is not film-forming but is in the form of a sheet.

Example 3:

The enlarging process is performed by a winding type test coating line and a blade coater. In a 2 liter metal container, 386.12 grams of Desmodur NZ1 and 213.88 grams of PETMP were dissolved in 150 grams of BA and homogenized using an overhead stirrer (300 rpm) for 20 minutes. The solid content was 80% and the NCO-SH ratio was 1.05. The current viscosity after mixing was measured to be 100 centipoise (cP). The components are only mixed for 1 hour before actual use to avoid improper solidification caused by high solid content. The resulting film is optically transparent and easily peels off from the substrate (PI). The film was annealed at 180 ° C for 1 hour before all tests. The results show excellent results Mechanical, optical and surface properties and good chemical resistance. The results are summarized in Table 1 below.

Claims (14)

A method of making a polyurethane film comprising a cast polyurethane composition comprising at least one isocyanate and at least one thiol selected from the group consisting of tetrathiols and/or polythiols. The method of claim 1, wherein the at least one ester of a thiol-based polyol. The method of claim 1 or 2, wherein the at least one thiol is an ester of a tetraol, pentaol or hexaol. The method of at least one of the preceding claims, wherein the at least one thiol is an ester of neopentyl alcohol or butyltetraol. The method of at least one of the preceding claims, wherein the at least one thiol pentaerythritol tetrakis-mercaptopropionate. The method according to at least one of the preceding claims, wherein the at least one isocyanate is selected from the group consisting of tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2-methylpentamethylene diisocyanate, 2, 2 ,4-trimethylhexamethylene diisocyanate, dodecamethylene diisocyanate, 1,4-diisocyanate cyclohexane, 3-isocyanatomethyl-3,3,5-trimethyl Cyclohexyl isocyanate, 4,4'-diisocyanate dicyclohexylmethane, 4,4'-diisocyanate-3,3'-dimethyldicyclohexylmethane, 4,4'-diisocyanate a group consisting of -2,2-dicyclohexylpropane and a mixture thereof, preferably 1,6-hexamethylene diisocyanate and 3-isocyanatomethyl-3,3,5-trimethyl ring a mixture of hexyl isocyanates. The method of claim 6, wherein the at least one isocyanate trimer, urethane, biuret, urea or uretdione. The method of at least one of the preceding claims, wherein the NCO:SH ratio is from 10:1 to 1:10, preferably from 5:1 to 1:5, more preferably from 2:1 to 1:2. It is 1.01:1 to 1.2:1. The method of at least one of the preceding claims, further comprising a solvent, and optionally an antifoaming agent, a heat stabilizer and/or a wetting agent. The method of at least one of the preceding claims, wherein the pouring step is a solvent casting step. The method of at least one of the preceding claims, wherein the casting step comprises continuously casting on a substrate, preferably a polymer substrate. A polyurethane film obtainable by the method of at least one of claims 1 to 11. The polyurethane film of claim 12, wherein the maximum processing temperature is at least 140 ° C, and the glass transition temperature Tg is at least 80 ° C according to ASTM D3418. A use of the film of claim 12 or 13 for use as a backlight panel or display panel, preferably a flat panel display, a touch panel display or a flexible electronic device.