JP2006182904A - Polyurethane resin coating agent - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the performances of a polyurethane resin coating agent without using any special polyurethane resin so as to sufficiently improve adhesion to the surface of a silicone rubber molding such as the keypad of e.g., a portable phone and so as to balancedly improve softness to touch with fingers, abrasion resistance, weathering resistance, toughness, etc. <P>SOLUTION: The polyurethane resin coating agent comprises (A) a polymer polyol containing the following components (A1) and (A2), (B) an organic diisocyanate, and optionally (C) a chain extender, wherein the component (A1) is a polycarbonate polyol having a number-average molecular weight of 500 to 5,000, and the component (B) is an acrylic polyol having a number-average molecular weight of 5,000 to 30,000 and having 1 or 2 hydroxy groups in the molecule. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a polyurethane resin coating agent having good adhesion to silicone rubber and the like. Specifically, polycarbonate polyol and a specific acrylic polyol are used as a polyol component, and adhesion (adhesion) to a molding surface, abrasion resistance, and flexibility. The present invention relates to a polyurethane resin composition that has excellent properties and is useful as a surface coating agent for keypads of mobile phones and the like.

The coating agent made of polyurethane resin composition is excellent in other properties such as abrasion resistance, chemical resistance, weather resistance, adhesion and antifouling property, utilizing the excellent properties of urethane bonds, tough and economical. Is widely used as a coating material.
Recently, due to its excellent performance, it has been attracting attention and used as a coating agent for the molding surface of silicone rubber (or silicone resin) in keypads such as mobile phones and remote controllers of electronic devices, and it has wear resistance, weather resistance and flexibility. However, since silicone rubber has very low surface adhesion as a natural property of the resin, even polyurethane resin coating agents have insufficient adhesion. Is high.

  Whether the keypad part of the mobile phone is painted for design or printed with numbers and characters for communication input on the top surface (key top) of the push button as a conductive switch in the keypad formed of silicone rubber In addition, a member in which a plastic sheet on which numbers and letters are printed is integrated on the surface of a silicone rubber keypad is mainly used (see Patent Documents 1 and 2). Even if it is surface-treated with various resin coating agents in order to avoid printing abrasion, peeling, moisture and oil contamination from fingertips, and elution of silicone oligomers, the adhesion between silicone rubber and resin coating Is very low, and in the case of a plastic sheet with numbers and letters printed on the back side, numbers and letters are printed. No contamination from wear and peeling and fingertips, but for the intervention of a plastic sheet, it has become inferior in flexibility in the missing touch sensitive as keypad push button member.

It is very important to solve these problems even if the demand for mobile phones is increasing not only in Japan but also globally. A coating of polyurethane resin that can form a relatively strong and tough film is mainly used as a material to be coated on the surface of keypads that are molded with silicone rubber and printed with numbers and letters. Reference 3).
Silicone rubber has a very low surface adhesion as a natural property of the resin, so even a polyurethane resin coating agent has insufficient adhesion. Many proposals have been made to improve adhesion (adhesion or adhesion).

  Typical examples thereof include a urethane polymer having an aliphatic unsaturated hydrocarbon group in the side chain, a coating agent containing an organohydrogenpolysiloxane and a hydrosilylation catalyst (see Patent Document 4), both having a siloxane bond. Using a linear polymer having a hydroxyl group or an amino group at the terminal, an overcoat material for silicone rubber containing urethane resin as a main component (see Patent Document 5), an aliphatic compound obtained by reacting an aliphatic unsaturated group-containing polysiloxane A polyurethane resin having an unsaturated group, a polyurethane resin coating agent for silicone rubber containing an organohydrogenpolysiloxane and a hydrosilylation catalyst (see Patent Document 6), and the like are disclosed. Adhesion is improved, and polyurethane-based resin provides wear resistance and oil penetration resistance Surface protective layer such as fine flexibility is improved is formed on the silicone rubber key pad surface.

As another improvement method for improving the adhesion between the silicone rubber molding surface and the polyurethane resin coating agent, a method of specially treating the silicone rubber molding surface is also employed, such as polishing treatment, corona treatment or plasma treatment. Although generally used, the effect of improving adhesion is not sustained, and a three-dimensional surface such as an uneven surface of a keypad cannot be sufficiently treated.
For this reason, a method of applying a primer containing a silane coupling agent to the plasma modified surface (see Patent Document 7), a method of applying an electron beam to the surface of the silicone rubber (see Patent Document 8), etc. are presented. Yes.

Japanese Patent Laid-Open No. 11-167838 (abstract, claim 1 of the claim, paragraph 0012) JP-A-9-212272 (summary) JP 7-296676 A (Abstract, paragraph 0014) JP 2001-26648 A (summary) Japanese Patent Laid-Open No. 2001-26748 (Abstract, Claim 7) Japanese Patent Laid-Open No. 2002-206071 (Abstract, Claim 6) Japanese Patent No. 2883880 (claims 1 and 2, paragraph 0014) JP 2002-363318 A (Abstract, paragraphs 0001 and 0016)

As described above in paragraphs 0002 to 0006, keypads such as mobile phones are remarkably demanded, the frequency of acupressure input is extremely high, and the use outdoors is complicated. Keys that have a polyurethane coating on the surface of silicone rubber due to extremely high demands for excellent input sensitivity (input reliability), flexible fingertip feel, good wear resistance, and weather resistance. Pads are heavily used, and many improvement proposals have been made to improve the adhesion between silicone rubber and polyurethane coating agents.
However, in an improved method for improving the adhesion as a silicone rubber molding surface by modifying or modifying the polyurethane resin to improve the performance as a coating agent (the above Patent Documents 4 to 6), the adhesion of the coating agent ( (Adhesion) is not necessarily improved sufficiently, it is necessary to synthesize a special polyurethane resin, and there is a balance between flexibility (softness) to the touch, weather resistance, and toughness. It cannot be said that it is well enhanced. In addition, the method of applying special treatments such as corona treatment or plasma treatment to the silicone rubber molding surface (the previous Patent Documents 7 to 8) generally lacks the effect of improving adhesion, and the tertiary such as the uneven surface of the keypad. The original surface cannot be treated sufficiently.

  In view of the current state of the prior art in keypads such as mobile phones, the present invention improves the performance of polyurethane resin coating agents without requiring a special polyurethane resin, and adheres to a silicone rubber molding surface. It is a problem to be solved by the present invention to sufficiently improve the properties (adhesiveness) and to improve the flexibility to the touch, weather resistance, toughness and the like in a balanced manner.

  In order to solve the above problems, the inventors of the present application use an easily available polyurethane resin in a polyurethane resin coating agent for coating a silicone rubber molding surface, and adhere to the silicone rubber molding surface. In addition, it is necessary to find a method for improving the flexibility, weather resistance or toughness of finger touch in a well-balanced manner, and to obtain polyols and diisocyanates as raw materials in polyurethane resins, chain extenders, coupling agents, and polymerization. Various considerations, various experimental studies, and tests of prototypes were carried out regarding the catalyst, the special treatment method of the silicone rubber surface and primers.

In the process, it is considered that the polyol component plays an important role (function) in solving the above-mentioned problems, and the polycarbonate polyol is used for imparting hydrolysis resistance, water resistance and flexibility in the polyurethane resin coating agent. Acrylic polyols were selected for use and to improve weatherability, solvent resistance and quick-drying to improve adhesion.
However, when acrylic polyol is used, the coating film lacks flexibility and does not have flexibility and becomes hard and less stretched, making it easier to crack and wrinkle. Recognizing that the number of hydroxyl groups in one molecule of acrylic polyol (acrylic polymer) is involved, the number of hydroxyl groups in one molecule so as not to impair the flexibility (flexibility) of the film by gelation or reticulation When the acrylic polyol is combined with a polycarbonate polyol in a specific amount, the compatibility with other raw material components is good, and the flexibility, flexibility, and stretchability of the film are sufficient. At the same time, it is known that this coating agent has extremely good adhesion (adhesion) and abrasion resistance to the silicone rubber molding surface. I was able to.

  As a result of the above, the above problems can be solved basically by applying a novel but easy-to-obtain acrylic polyol and combining it with a polycarbonate polyol. By using a ring agent and specifying the mass ratio of both polyols, the type of chain extender, etc., the inventors have found that the effect of the action is further increased, thereby creating the present invention.

Specifically, an acrylic polyol containing 1 to 2 hydroxyl groups in one molecule as an acrylic polyol that is unique but easily available is used in combination with a polycarbonate polyol as a polyol component, and the number average thereof. By specifying molecular weights of 5,000 to 30,000 and 500 to 5,000, respectively, the adhesion to silicone rubber in polyurethane resin is significantly improved. In addition, by specifying the number of hydroxyl groups in acrylic polyol, etc. In addition, the softness to the touch, weather resistance or toughness of the keypad can be improved in a well-balanced manner.
Such an improvement in performance from two aspects of a keypad or the like is one of the features of the present invention, and can be said to be a disclosure of a marked improvement technique that makes a significant advance over the prior art.
In addition, the incorporation of the silane coupling agent into the polymer, the use as a primer, or the combination of corona treatment or other special treatment on the silicone molding surface can improve the adhesion, and further into the polymer of the silane coupling agent. Incorporation of can also add a primer function and eliminate the primer treatment step.

More specifically, the mass ratio of polycarbonate polyol to acrylic polyol is preferably 90/10 to 50/50, and chain extenders, silane coupling agents, reaction terminators, etc. are used as usual. A silicone rubber molding surface in a cellular phone keypad is optimal, but it is also suitably used for coating a surface of a remote controller in an electronic device such as a television or an audio, and further covering a roll material such as an OA electronic device.
If pigments and dyes are blended in the coating agent, it is possible to improve the design properties in combination with surface pattern printing such as a keypad, and to make a beautiful product.

  By the way, even if contrasted with each of the prior documents described in paragraphs 0003 to 0006, a polyurethane-based resin in which a siloxane bond is incorporated in the molecule, an aliphatic double bond is contained in the urethane molecule, and polysiloxanes are used in combination. Compared to each prior art using a polyurethane-based resin, the polyurethane resin of the present invention can be easily obtained by a simple production method, and by adopting the resin, the remarkable effects described in paragraph 0011 are obtained. In addition, the combination of the silane coupling agent or the combined use as a primer or the combination with a special surface treatment can further enhance the adhesive action and effect of each of the examples and comparative examples described later. It can be said that it is clear also by comparison.

  In the above, the features of the present invention and the basic configuration requirements, the background and background of the creation of the present invention, and the comparison with the prior art, etc. have been generally described. Then, the present invention is composed of the following group of inventions, and the invention of [1] is a basic invention, and the inventions below that embody the basic invention or form an embodiment. The entire invention group of [1] to [13] is collectively referred to as “the present invention”.

[1] A polyurethane resin coating agent in which (A) the polymer polyol contains the components (A1) and (A2), and (B) an organic diisocyanate and optionally (C) a chain extender.
(A1) Polycarbonate polyol having a number average molecular weight of 500 to 5,000 (A2) Acrylic polyol [2] (D) having a number average molecular weight of 5,000 to 30,000 and containing 1 to 2 hydroxyl groups in one molecule The polyurethane resin coating agent according to [1], wherein a silane coupling agent is an optional component.
[3] The mass ratio (A1) / (A2) of (A1) polycarbonate polyol and (A2) acrylic polyol in (A) the polymer polyol is 90/10 to 50/50, and (C) the chain extender is A short-chain glycol, a short-chain diamine or an alkanolamine having a number average molecular weight of less than 500, wherein (D) the silane coupling agent has a reactive group of an epoxy group, an amino group or a mercapto group, [1 ] Or the polyurethane resin coating agent in [2].
[4] The polyurethane resin coating agent according to any one of [1] to [3], wherein a diamine is reacted with an isocyanate group- terminated prepolymer to form a urea bond and / or alkanolamine is used for terminating the reaction. .
[5] The polyurethane resin coating agent according to any one of [1] to [4], which is a two-component type comprising a combination of a polyurethane resin and an isocyanate curing agent.
[6] A coating method using the polyurethane resin coating agent according to any one of [1] to [5], wherein the molding surface of a silicone resin or silicone rubber is coated as a surface coating agent having good adhesion .
[7] The coating method according to [6], wherein a silane coupling agent is added at the time of blending or coating the coating agent.
[8] The coating method according to [6] or [7], wherein the molding surface subjected to corona treatment, itro treatment or plasma treatment is coated.
[9] The coating method according to any one of [6] to [8], wherein the molding surface is subjected to a primer treatment.
[10] The coating method according to any one of [6] to [9], wherein the molded product is a keypad.
[11] A product obtained by coating the surface of the silicone resin or silicone rubber with the polyurethane resin coating agent according to any one of [1] to [5].
[12] A keypad in which the polyurethane resin coating agent according to any one of [1] to [5] is coated on a silicone resin or silicone rubber surface.
[13] The product or keypad according to [11] or [12], which is coated with a polyurethane resin coating agent to which a pigment or dye is added and has excellent design properties.

In the present invention, in a polyurethane resin that is easily available due to a simple component, the adhesion to the silicone rubber molding surface in a keypad and the like is remarkably improved, and at the same time, by specifying the number of hydroxyl groups in the acrylic polyol, etc. The flexibility, weather resistance, toughness, hydrolysis resistance, durability and the like of the touch in a pad and the like can be improved in a well-balanced manner, and the performance of the keypad etc. can be improved from two sides.
Adhesion is further improved by combining the incorporation of a silane coupling agent into the polymer, the use as a primer, or a corona treatment or other special treatment on the silicone molding surface.

  Although the present invention has been described in accordance with the basic configuration of the present invention as means for solving the problems, the embodiments of the invention of the present invention group described above will be specifically described in detail below. To do.

1. Polyurethane resin (1) Polymer polyol component (A component)
i) Combination of two components
The polyol component (polymer polyol) is formed by polyaddition with diisocyanate to form a polyurethane bond. As the polyol component, two components of polycarbonate polyol and acrylic polyol are used to form the special effects of the present invention. Is used as an essential component.
Polycarbonate polyol is used to provide hydrolysis resistance, water resistance, and flexibility in polyurethane resin coating agents, providing weather resistance, solvent resistance, and quick drying (which increases the speed of the coating process) and improves adhesion. Acrylic polyol is used to improve.

In addition, when ordinary acrylic polyol is used, the glass transition point becomes high, the coating film lacks flexibility and does not have flexibility, it becomes hard and less stretched, and the film tends to crack and wrinkle. In addition to the combined use of polycarbonate polyol, the number of hydroxyl groups in one molecule of acrylic polyol (acrylic polymer) is specified to 1 to 2 and such acrylic polyol is combined with polycarbonate polyol in a specific amount. Thus, the improvement in performance becomes remarkable, and this configuration forms one of the features of the present invention.
Due to its structure, compatibility with other raw material components is improved, gelation due to hydroxyl groups is avoided, and flexibility, flexibility, elongation, etc. are fully expressed in the coating film, and in addition, silicone rubber molding The adhesion to the surface and the wear resistance are also particularly good.

ii) Polycarbonate polyol (A1 component)
Polycarbonate polyol is a polyol having a hydroxyl group at the molecular end and an alkylene group bonded in a straight chain via a carbonate bond, obtained by reaction of ethylene carbonate, dimethyl carbonate, diethyl carbonate, diphenyl carbonate, etc., with an alkylene diol. It is done. Examples of the alkylene diol include 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, and 1,9-nonanediol. Etc. are preferably used, and these are used alone or as a copolymer of two or more.

  The number average molecular weight of the polycarbonate polyol is preferably 500 to 5,000, more preferably 500 to 3,000 because it is easy to handle. If it is less than 500, the coating film becomes too hard, and if it exceeds 5,000, it is difficult to produce, and even if it is intentionally produced, it is not economical.

iii) Acrylic polyol (A2 component)
The acrylic polyol is obtained by copolymerization of an acrylic monomer having a hydroxyl group such as hydroxyethyl acrylate and another unsaturated double bond monomer such as methyl (meth) acrylate and styrene.
The acrylic polyol is preferably diluted with a solvent from the viewpoint of ease of handling. The hydroxyl group content of the acrylic polyol is preferably about 3.5 to 11.2 mgKOH / g in terms of solid content.

  For the acrylic polyol, the number of hydroxyl groups in one molecule is specified to be 1-2 for the reason described in paragraph 0021. Two in one molecule are preferable, and if more than two hydroxyl groups are present, it is undesirable because it causes gelation (networking of polymer molecules) and thickening, and the flexibility and flexibility of the coating film are reduced. I have to. In addition, if less than one or no hydroxyl group is present, the compatibility with the polycarbonate polyol will deteriorate, it will not function as a polyol and will not react with the diisocyanate, resulting in a simple mixture (blend), resulting in separation of components and variations in physical properties. Cannot be used.

The number average molecular weight of the acrylic polyol is preferably 5,000 to 30,000, and if it is less than 5,000, the acrylic amount increases and becomes too hard. The compatibility of is not good.
These acrylic polyols are suitably used singly or in combination of two or more.

iv) Amount ratio of the two components The mixture ratio of the two components of the polycarbonate polyol and the acrylic polyol is used as 90/10 to 50/50 (90 to 50:10 to 50 parts by mass) in mass ratio.
Outside this range, the functionality of the polycarbonate polyol for imparting hydrolysis resistance, water resistance and flexibility in the polyurethane resin coating agent, and acrylic polyol for improving the adhesion by providing weather resistance and solvent resistance. This is not preferable because the function of is insufficient.
More specifically, when the amount ratio of the polycarbonate polyol exceeds 90 parts by mass, the hydrolysis resistance and blocking properties are lowered, and the flexibility is improved, but the drying time is slowed, and floating dust adheres during coating drying. There are also concerns. When the amount ratio of the acrylic polyol exceeds 50 parts by mass, the adhesion, weather resistance, drying property, blocking property and the like are partially improved, but the glass transition point becomes too high and the flexibility becomes poor, and the coating is cracked. A crease occurs and it cannot be used. Although the upper limit of these components also determines the lower limit of the ratio of both components, if both components fall below the lower limit of their respective ratios, the performance improvement effect of each component becomes insufficient.

(2) Diisocyanate component (component B)
As the diisocyanate component used in the present invention, an organic diisocyanate is used, and an ordinary one is used and is not particularly defined.
In order to avoid yellowing of the coating film due to ultraviolet rays, aliphatic or alicyclic diisocyanates are preferred over aromatic diisocyanates.
Examples of the aliphatic diisocyanate include tetramethylene diisocyanate, hexamethylene diisocyanate, and 2-methyl-1,5-pentane diisocyanate. Examples of the alicyclic diisocyanate include 1-methylcyclohexane-2,4-diisocyanate, isophorone diisocyanate (abbreviation IPDI), dicyclohexylmethane-4,4′-diisocyanate, and the like. These diisocyanates are used individually by 1 type or in mixture of 2 or more types.
From the viewpoint of improving the weather resistance of the coating film, hexamethylene diisocyanate, dicyclohexylmethane-4,4′-diisocyanate (hydrogenated MDI), 1,3-bis (isocyanate methyl) cyclohexane, isophorone diisocyanate, 2,2,4- Trimethylhexamethylene diisocyanate and the like are preferable.

(3) Other components i) Chain extender (component C)
In the present invention, a chain extender in a usual polyaddition reaction is preferably used as necessary.
As the chain extender in urethane polymerization, a normal low molecular compound having two or more active hydrogen groups is used, and a short chain glycol, a short chain diamine or an alkanolamine having a number average molecular weight of less than 500 is used.
Specific examples include ethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, neopentyl glycol, diethanolamine, triethanolamine and the like. Examples of the diamine include isophorone diamine and ethylene diamine. When the linear alkylene group becomes longer like hexamethylene, it can contribute to improvement in flexibility.

ii) Silane coupling agent (component D)
A silane coupling agent is used for improving adhesion between a polyurethane resin and a coating surface such as silicone rubber.
Use modes include a mode in which an amino group and the like are incorporated into a polymer chain by mixing with a polyurethane raw material component, a mode to be added later when preparing a coating solution of a coating agent, and a direct or organic solvent diluent on a coated surface The mode of application at can be arbitrarily taken.
As the silane coupling agent, a normal silane coupling agent having a reactive group such as an epoxy group, an amino group, or a mercapto group is used.
Specific examples include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-glycidoxypropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane. Etc. are exemplified.

iii) Curing catalyst and curing agent Resinization catalyst (urethanization catalyst) as a curing catalyst (polymerization catalyst) for urethane reaction is used as necessary, and dibutyltin dilaurate or naphthenic acid is used to adjust pot life and curing conditions. A normal curing catalyst such as a metal catalyst such as zinc or an amine catalyst such as triethylenediamine or N-methylmorpholine is used, and the reaction rate can be increased and the reaction temperature can be lowered.
The addition amount of the curing catalyst is, relative to the isocyanate-terminated urethane prepolymer, 0.005 to 0.10% by mass in solid content ratio. If it is less than 0.005% by mass, the desired resinification promotion cannot be achieved, and if it exceeds 0.10% by mass, the storage stability is hindered.
As a curing agent for curing the polyurethane resin, a trimer or adduct having 3 or more NCO groups in one molecule, which is composed of hexamethylene diisocyanate or isophorone diisocyanate, is used as necessary. In the present invention, it is preferable to add 0.5 to 5 parts of a trimer type curing agent composed of hexamethylene diisocyanate (solid content: 100%, NCO content: 21%) with respect to 100 parts of the main agent.

iv) Others In the reaction of only the main component polymer polyol and organic diisocyanate, a rigid skeleton is not formed in the polymer. Therefore, if heat resistance is insufficient, a diamine may be reacted with an isocyanate terminal to introduce a urea bond. Good.
Moreover, alkanolamine can also be used for a reaction terminator using the difference in the reactivity with respect to diisocyanate.

2. Polyurethane resin coating agent (1) Coating agent i) Components of coating agent The coating agent of the present invention is prepared from the polyurethane resin described in detail in paragraphs 0020 to 0032, and comprises (A) a polymer polyol and (B) an organic diisocyanate. It consists of a main component and is composed of (C) a chain extender, (D) a silane coupling agent, (E) a curing agent, and the like as other components.

ii) Aspect of Coating Agent The coating agent of the present invention is a material that can be said to be a polyurethane resin coating composition, and is used without a solvent, or may be diluted with an organic solvent for viscosity adjustment, or may be aqueous. .
The coating agent is a normal one-pack type or two-pack type, and in the two-pack type, it is not a composition in which all the components are mixed in advance, but a combined material such as a urethane polymer and a two-component curing agent, An embodiment in which two components are mixed when used as a coating agent is also included.
Further, the polyurethane resin may be cured at the time of coating, or a mode in which a pre-cured polyurethane resin is coated and a coat film is formed by removing the solvent by drying may be used.
Coating is used herein as a broad term for film formation, including all of the usual applications, coatings or coats.

iii) Additives As various additives, flame retardants, plasticizers, antioxidants, ultraviolet absorbers, dyes, pigments, fillers, internal mold release agents, reinforcing materials, matting agents, which are commonly used in general Conductivity imparting agents, charge control agents, antistatic agents, lubricants, and other processing aids can be used.

iv) Manufacturing method of coating agent Specifically, a coating agent is extended from a polymer polyol and an organic diisocyanate with a glycol or a diamine as necessary to synthesize polyurethane as a main agent of the coating agent. In addition, the curing agent described in paragraph 0031 is added before or at the time of use as a coating agent as necessary. Further, optional components such as a silane coupling agent, a solvent and a diluent, and paint addition It is manufactured as a one-component or two-component polyurethane resin coating composition by blending an agent, particularly a pigment.
When coating is performed by a spray method, the molecular weight of the main agent cannot be increased, and therefore the heat resistance and mechanical properties tend to be insufficient only with the main agent. In order to improve them, it is preferable to use a curing agent.

(2) Coating treatment i) Coating method The method for coating (coating or coating) the coating agent of the present invention is not particularly limited, and various commonly used methods can be applied. The printing method is simple and suitable. These two methods are suitable for coating the silicone rubber molding surface of the keypad.
Drying after coating is also carried out as appropriate, and since it is quick drying, drying at 50 ° C. to 200 ° C. for about 1 minute to 10 minutes is sufficient.

ii) Utilization of coating The coating treatment of the present invention can be used for surface coating of various materials such as metals, plastics or rubber members without any particular limitation, but is preferably used for silicone rubber (and silicone resin) members, for example, , Keypads (also referred to as keyboards and key panels) for mobile phones and remote controls for electronic devices, touch panels for electronic devices or plugs for personal computer components, and surface coatings for roll members of OA devices (formation of surface protective layers, etc.) ) Can be applied effectively.

As the silicone rubber base material, conventionally used millable silicone rubber by peroxide vulcanization, injection molded silicone rubber by hydroxylation crosslinking, and the like are preferably used.
In silicone rubber, hydroxyl groups in components and unreacted residual vinyl groups undergo hydroxylation reaction during heating and drying, and hydroxyl groups also react with isocyanate groups in the coating agent, making the coating agent and the silicone rubber molding surface stronger. Adhere to (attach).

iii) Thickness of coating film In the present invention, the thickness of the coating film by the coating agent is arbitrary, but in the keypad coating, it is about 5 to 100 μm, preferably 10 to 50 μm.
In the covering of roll members such as OA equipment, the thickness is about 1 to 100 μm, preferably 5 to 40 μm.

iv) Primer treatment If the surface to be coated is previously primed with a silane coupling agent or the like prior to coating, the adhesion of the coating film is further enhanced.
In the coating agent, if a primer agent such as a silane coupling agent is previously incorporated into the polymer molecule or blended by mixing, the primer coating treatment step can be omitted.

v) Special surface treatment In the present invention, surface special treatment is basically not required, but physical special auxiliary treatment such as polishing treatment, corona treatment, itro treatment or plasma treatment is applied to the surface to be coated. It is also possible to enhance the adhesion of the coating agent by applying in advance prior to coating. It is more effective when performed in combination with primer coating.
Corona treatment and plasma treatment are physical treatments commonly used for improving adhesion, and plasma such as corona flame or nitrogen gas is irradiated. The itro process is a technique of coating the surface with ultra-thin silicon oxide of nanometer order by combustion chemical vapor deposition (CCVD).

  In the following description, the present invention will be illustrated in more detail, the configuration of the present invention will be clarified, and the rationality and significance of each requirement of the configuration of the invention will be described in detail by comparing the comparative examples by the description of the examples. To demonstrate.

(1) Production Example of Polyurethane Resin Coating Agent [Production Example-1]
As a production apparatus, a reactor equipped with a stirrer with a torque meter, a thermometer, a nitrogen gas introduction pipe and a reflux condenser was used, and a mantle heater capable of adjusting the temperature from the outside was used.
In a 2-liter separable flask made of tempered glass of 2 liters, 430 parts of polycarbonate diol (number average molecular weight: 2,000) consisting of dehydrated 1,6-hexanediol, 6.6 parts of 1,4-butanediol, MMA acrylic polyol (AP-1: acrylic polyol obtained by polymerization reaction of methacryl acrylate and hydroxyethyl acrylate, number average molecular weight 20,000, hydroxyl value 5.6 mg KOH / g, average number of hydroxyl groups per molecule calculated from both values 2.0 ) Was added with 108 parts of toluene and 120 parts of toluene, and heated to 50 ° C. with uniform stirring, and then 64 parts of hydrogenated MDI (dicyclohexylmethane-4,4′-diisocyanate) and IPDI ( 36 parts of isophorone diisocyanate) was charged in the funnel at the same time.
Thereafter, 0.06 part of dibutyltin dilaurate was added, heated to 80 ° C. and reacted for 4 hours, 33 parts of toluene, 4.8 parts of aminosilane coupling agent (γ-aminopropyltriethoxysilane), and 200 parts of methyl ethyl ketone. Was added to obtain an isocyanate-containing urethane prepolymer (NCO content 0.76%).
140 parts of methyl ethyl ketone was added and diluted, and an amine solution prepared with 8.8 parts of IPDA (isophoronediamine) and 200 parts of methyl ethyl ketone was dropped into the prepolymer solution under stirring, and the increase in torque of the stirrer was confirmed. 6.3 parts of ethanolamine was added, and the reaction was continued at a reaction temperature of 50 ° C. until the NCO group disappeared.
The obtained resin solution (A) had a resin solid content of 40.1% and a viscosity of 1,400 mPa · s (25 ° C.).

[Production Examples-2 to 5 and Comparative Production Examples-1 to 4]
Polyurethane resin liquids B to I were obtained using the same reaction apparatus and reaction conditions as in Production Example-1. The reaction conditions and the reaction results are shown in Table-1.
The symbols in the table are as follows. PCD: polycarbonate diol BD: 1,4-butanediol AP1 and 2: acrylic polyol (AP1: described in paragraph 0044) AP2: acrylic polyol obtained by polymerization of methyl methacrylate and hydroxyethyl acrylate Number average molecular weight 20,000 Hydroxyl value 14.0 mg KOH / g 40% toluene solution Calculated from the number average molecular weight and hydroxyl value, the OH group numbers are 2.0 and 5.0, respectively.) Hydrogenated MDI: Dicyclohexylmethane-4,4′-diisocyanate IPDI: Isophorone diisocyanate DBTDL: Dibutyltin dilaurate Coupling agent: γ-aminopropylethoxysilane IPDA: Isophoronediamine MEA: Monoethanolamine PBA: Polybutylene adipate Viscosity: Measured at 25 ° C

(2) Examples and Comparative Examples in Coating Processing [Examples 1 to 5 and Comparative Examples 1 to 4]
A coating agent was prepared using the polyurethane resin liquids A to E and F to I produced in Production Examples-1 to 5 and Comparative Production Examples 1 to 4, and coated on a silicone rubber molding surface. The following physical properties were measured as -5 and Comparative Examples 1-4, and the results are shown in Table-2 and Table-3.

(3) Measurement of physical properties The measurement methods and evaluation methods of each physical property are as follows.

[Adhesiveness]
To 100 parts of the synthesized resin, 0 part or 2 parts of a curing agent (HDI trimer solid content 100% NCO content 21%) is added, and an appropriate amount of solvent (methyl ethyl ketone or toluene) is added to a silicone sheet (Shin-Etsu Silicone). A sheet of general industrial BA grade manufactured by Itro treatment was spray-coated, pre-dried and heat cured at 120 ° C. for 3 minutes, and then allowed to stand at 25 ° C. for 3 days.
A grid pattern (100 pieces per 1 cm ² ) was prepared with a cross-cut guide, adhered with cello tape, the tape was peeled off rapidly, the remaining number of grids was counted, and the following criteria were evaluated.
A: 100/100 pieces remain and no peeling occurs.
○: 80/100 to 99/100 pieces remain.
Δ: 50/100 to 79/100 pieces remain.
X: Remaining number of 49/100 or less.
XX: 0/100 remaining, and the entire amount peels off.
Impossible: Measurement is impossible due to gelation, etc. (same below)

[Flexibility]
In the state where the coating agent was applied to the silicone sheet, the state of wrinkles that formed creases was observed and evaluated according to the following criteria.
(Double-circle): A crease | fold follows a sheet | seat and it is hard to produce a wrinkle.
○: A slight wrinkle occurs, but the wrinkle disappears as soon as the crease is returned.
Δ: Slightly large wrinkles are produced, but the wrinkles disappear immediately after the crease is returned.
X: Large wrinkles are likely to occur.
XX: There is no flexibility at all and cracks occur on the entire surface.

[Abrasion resistance]
The surface on which the coating agent is applied to the silicone sheet so that the thickness after drying is about 30 μm is rubbed repeatedly with the eraser (trade name MONO, made by dragonfly pencil) until the surface is broken. The number of times was counted and evaluated according to the following criteria.
A: No tearing occurs even after rubbing 200 times or more.
○: Breaking is observed after 100 to 200 rubbing.
(Triangle | delta): The tear is seen by 50-100 times of rubbing.
X: The tear is seen by rubbing 50 or less.
Xx: A crack is seen from the beginning.

[Weatherability]
The film was irradiated for 60 hours by weathering, the state of the coating film of the coating agent was observed, and evaluated according to the following criteria.
○: No cracks or breaks occur.
Δ: Slight cracking is observed.
X: Cracks and breaks occur.

[Quick drying]
On the release paper, a coating agent was applied so that the thickness after drying was about 30 μm, cured at 120 ° C. for 90 seconds, taken out to room temperature, then attached with absorbent cotton and observed for the attached condition of absorbent cotton, Evaluation based on the criteria.
○: Absorbent cotton does not adhere at all within 15 seconds after taking out.
Δ: Absorbent cotton does not adhere in 30 to 90 seconds after removal.
X: Absorbent cotton adheres also after 90 seconds after taking out.

[Physical properties of free film]
On the release paper, a coating agent was applied so as to have a thickness of about 150 μm after drying, a film was prepared and placed at room temperature for 3 days, and a test piece was prepared using a JIS No. 4 dumbbell. It was measured at 25 ° C. with a Tensilon tensile tester at a crosshead speed of 200 mm, and 100% modulus (MPa), breaking strength (MPa) and breaking elongation (%) were measured.

  In addition, in order to clarify the relationship of each comparative example, Table-4 is shown. (○: Use-: Not use)

[Consideration of results of Examples and Comparative Examples]
By contrasting each of the above Examples and Comparative Examples, in the present invention, it is novel, but using a polyurethane resin that is easily available for simple components, a silicone rubber molding surface in a keypad or the like The adhesiveness (adhesiveness) of the ink is markedly improved, and at the same time, by specifying the number of hydroxyl groups in the acrylic polyol, the softness to the touch, wear resistance, weather resistance, quick drying, and toughness of the keypad etc. It is understood that the stretchability of the coating and the like are also improved in a well-balanced manner, and the performance from two sides in the keypad and the like is sufficiently improved.
It has also been shown that adhesion is further improved by combining the incorporation of a silane coupling agent into the polymer, use as a primer, or corona treatment of the silicone molding surface or other special treatments.
Specifically, in Table 3, the results for each example were generally uniform, with sufficiently high adhesion and other performance, demonstrating the significance and superiority of the novel configuration of the present invention.
On the other hand, in Comparative Example-1, since no acrylic polyol is used, the adhesiveness is very poor and the wear resistance and quick-drying property are also poor. In Comparative Example-2, since the number of hydroxyl groups of the acrylic polyol exceeds 2, it cannot be practically used due to gelation during the production of the polyurethane resin. Since Comparative Example-3 does not use a polycarbonate polyol and uses a polyester polyol, it is inferior in weather resistance and quick-drying property and has low mechanical strength (toughness). In Comparative Example-4, since only acrylic polyol is used as the polyol, the quick-drying property is too high and each performance cannot be measured and cannot be used practically.
From the above data results and discussion, it can be said that the rationality and significance of the constituent elements of the present invention are demonstrated, and it is clear that the present invention has a remarkable superiority as compared with the prior art.

Claims (13)

(A) A polyurethane resin coating agent in which the polymer polyol contains the components (A1) and (A2), and (B) an organic diisocyanate and optionally (C) a chain extender.
(A1) Polycarbonate polyol having a number average molecular weight of 500 to 5,000 (A2) Acrylic polyol having a number average molecular weight of 5,000 to 30,000 and containing 1 to 2 hydroxyl groups in one molecule (D) The polyurethane resin coating agent according to claim 1, wherein a silane coupling agent is an optional component. (A) In the polymer polyol, the mass ratio (A1) / (A2) of (A1) polycarbonate polyol and (A2) acrylic polyol is 90/10 to 50/50, and (C) the chain extender is the number average molecular weight. The short-chain glycol or short-chain diamine or alkanolamine of less than 500, wherein (D) the silane coupling agent has a reactive group of an epoxy group, an amino group or a mercapto group. Item 3. A polyurethane resin coating agent according to Item 2. The polyurethane resin coating agent according to any one of claims 1 to 3, wherein a diamine is reacted with an isocyanate group-terminated prepolymer to form a urea bond and / or alkanolamine is used for terminating the reaction. . The polyurethane resin coating agent according to any one of claims 1 to 4, wherein the polyurethane resin coating agent is a two-component type comprising a combination of a polyurethane resin and an isocyanate curing agent. The coating method using the polyurethane resin coating agent according to any one of claims 1 to 5, wherein the molding surface of the silicone resin or silicone rubber is coated as a surface coating agent having good adhesion. . The coating method according to claim 6, wherein a silane coupling agent is added at the time of blending or coating the coating agent. The coating method according to claim 6 or 7, wherein a coating surface subjected to corona treatment, ittro treatment or plasma treatment is coated. The coating method according to any one of claims 6 to 8, wherein the molding surface is subjected to a primer treatment. The coating method according to claim 6, wherein the molded product is a keypad. A product obtained by coating the surface of a silicone resin or silicone rubber with the polyurethane resin coating agent according to any one of claims 1 to 5. A keypad wherein the surface of the silicone resin or silicone rubber is coated with the polyurethane resin coating agent according to claim 1. The product or keypad according to claim 11 or 12, wherein the product or keypad is coated with a polyurethane resin coating agent to which a pigment or a dye is added and has excellent design.