JPS605260A - Formation of scratch resistant film - Google Patents

Abstract

PURPOSE:To form a high hardness scratch resistance film within a short time, by coating the surface of a substrate with a paint containing an urethane acrylate type oligomer and comprising a reactive diluent and a specific solvent while applying heat treatment to the formed coating layer under a thermostatic condition. CONSTITUTION:A paint consisting of 100pts.wt. of an urethane acrylate type oligomer and 15-60pts.wt. of polyfunctional acrylate such as 1, 4-cyclohexane diol acrylate being a reactive diluent is diluted to about 40-15% by a solvent such as a cellosolve type, an alcholic type, an aromatic type or an acetate type solvent. An objected to be coated is preheated to 140-200 deg.C and the paint is applied to the preheated object to be held at the above mentioned temp. for a definite time in air. The paint is cured within a short time of 4-5 min and a high hardness scratch resistant film is obtained.

Description

[Detailed description of the invention] The present invention relates to a method of forming an abrasion-resistant coating film.

More specifically, ultraviolet curable paints were originally developed to compensate for the shortcomings of thermosetting paints. By applying the heat curing method to paints that are coated, the drawbacks of conventional coating film formation methods using various paints are overcome, and it is possible to form highly hard coatings on arbitrary shaped surfaces and surfaces in a short time. It relates to a simple method that enables the formation of

Traditionally, paints have been classified into three types depending on their curing method: room temperature drying type (oil-based, alkyd resin-based paints, etc.), heat-drying type (melamine-based, aminoalkyd-based paints, vinyl-based paints, etc.), and ultraviolet curing type (vinyl-based paints, However, room temperature drying type and heat drying type paints are generally solvent-based paints, meaning that cross-linking or polymerization reactions occur between resins by volatilizing the solvent after painting. A coating film is formed. Among these, when addition polymerization type paints are used in the presence of air, preventive measures are taken (e.g., wax method, non-wax method, etc.) to eliminate the curing inhibiting effect caused by oxygen.
is required. In this case, the coating film is generally cured at a temperature of 100° C. or lower (mainly room temperature to 50° C.), which makes it difficult to obtain a highly hard coating film.

Further, as for the treatment for the curing inhibiting effect of oxygen, there is a method of gas replacement, but this requires separate equipment and a special gas replacement operation, which prolongs the overall operation time.

In addition, with conventional thermosetting paints, generally the higher the temperature during the heating operation, the greater the surface hardness of the coating film obtained. For example, for melamine paints, baking conditions such as 160°C for 20 minutes are applied. , it is possible to obtain a coating film with relatively high hardness.

However, this type of paint contains eight agents, and when it is directly heat-treated under the above-mentioned high temperature conditions, it has the disadvantage that the eight agents contained therein form bubbles on the coating surface. Therefore, when heat treating this type of paint under high temperature conditions as described above, preliminary drying under low temperature conditions is required. C1
Pre-drying for 10 minutes or the like is required.

In addition, in UV-curable paints, when exposed to light from a light source such as a mercury lamp or xenon lamp, a radical polymerization reaction occurs in combination with the catalytic action of the photosensitizer contained in the paint, and the paint film forms within a short period of several seconds. Curing is complete. The processing operation in this case is particularly room-temperature curing, so it can be applied to heat-sensitive surfaces such as plastics, and it also has the advantage of being able to obtain coatings with high hardness comparable to silicone coatings. has. However, the above-mentioned ultraviolet irradiation method using this type of paint requires expensive light irradiation equipment separately, and since it is impossible to paint in the shadow and fj areas, the objects to be painted are limited. It is particularly difficult to coat complex shaped structures. Furthermore, the photosensitizers they contain are generally harmful, and their handling is dangerous and poses an operational obstacle.

In particular, the general formula (where A represents a group such as -CH, -CH, -, -
Indicates groups such as CH, -1-CH, -CH, -CH, -, and the like. In addition, in paints whose main component is a urethane acrylate oligomer represented by n = "l~20), and a reactive diluent is a polyfunctional acrylate such as 1,4 cyclohexanediol acrylate, it is especially important to use a solvent. (hereinafter referred to as the paint), which further contains a photosensitizer, which concentrates the high energy of the irradiated light in an extremely short period of time, such as a few seconds, as described above. Therefore, if the paint is irradiated with light immediately after painting, the solvent contained therein will rapidly volatilize, causing bubbles to form within the paint film.Therefore, when applying the light irradiation curing method to the paint, Pre-dried in advance (e.g. 60-70'C15
minutes) is required.

The present invention eliminates the various drawbacks of the above-mentioned conventional methods,
The aim is to create a scratch-resistant coating film with the aim of forming a highly hard coating film on surfaces of various shapes and configurations in a short period of time using existing equipment and using safe and easy-to-operate means. The formation method has the following structural characteristics.

That is, the present paint is composed of a urethane acrylate oligomer as a main component, a polyfunctional acrylate as a reactive diluent, and a suitable solvent, the present paint is appropriately applied onto the surface of the material to be coated, and the coated material is The method is characterized in that heat treatment is performed for a certain period of time under constant temperature conditions such that the substrate temperature of the coated material is 140°C to 200°C.

As described above, in the method for forming a scratch-resistant coating film according to the present invention, first, the coating material used is only compatible with the light irradiation curing method, as described above. In addition, the above-mentioned paint that is designed to do so is also applied. However, since the method according to the present invention does not include a light irradiation step, as described above, no photosensitizer is added to the applied paint. Therefore, it is possible to carry out the method with a simpler equipment configuration (2. The process operation is relatively easy, and the coating film itself is harmless, and the product can be handled easily.) or is particularly safe to use.

Next, in the method of the present invention, the mixing ratio of the urethane acrylate oligomer as the main component and the polyfunctional acrylate as the reactive diluent in the paint is determined based on the viscosity of the paint required at the time of painting and after curing. It is determined according to the physical properties of the coating film, especially its required hardness. in particular,
Usually, a mixing ratio of 50MTj (polyfunctional acrylate) to 100 parts by weight of the urethane acrylate oligomer is adopted, but based on the above-mentioned reasons, the polyfunctional acrylate can be used in a range of 15 to 60 parts by weight. .

Furthermore, in order to obtain appropriate solubility, the present paint is diluted with a common solvent to about 40% to 15% before use for painting. As a solvent, cellosolve type (methyl cellosolve, ethyl cellosolve, butyl cellosolve) can be used as a high boiling point solvent, alcohol type (methanol, ethanol, butanol, etc.), aromatic type (Hensen, toluene, etc.), acetic acid ester etc. F, [methyl l'kk acid, ethyl acetate, butyl acetate, etc.), and ketones can be used similarly. However, petroleum hydrocarbons cannot be used alone as a solvent.

Next, the paint can be applied to metallic or non-metallic substrates formed into various shapes such as dish-shaped, bowl-shaped, etc. applied. In the present invention, since a heat curing method is applied in a constant temperature atmosphere when curing the coating film, unlike the case of the light irradiation curing method, it can be applied to coated substrates of arbitrary shapes and sizes. can do.

Furthermore, in terms of the coating thickness of the paint in this case, since the main component of the paint is an olicomer dissolved in a polyfunctional acrylate and a solvent, it is compared to the conventional general solvent-based paint described above. Although there are limitations due to the fact that G1 paints have a low susceptibility, and cracks and scratches are likely to occur if the coating thickness becomes too large, as is well-known with G1 paints in general, they are different from ordinary solvent-based paints. There is no difference, and it is possible to form a hard coating film with a thickness of 10 to 40 μm.

Next, as for the heating conditions during the heat treatment in the method of the present invention, the base material itself of the above-mentioned coating material is heated to 140°C to 200°C.
The condition is that the product must be heated for a certain period of time in a constant temperature atmosphere maintained at a constant temperature. At this time, the heating time is determined by the heating temperature and the size and weight of the object. If the heating temperature exceeds 200°C, cracks may occur depending on the type of base material of the object. Regarding the iron plate-shaped base shrine, 2-0
No cracks occur even when heated at 0°C. ), and the heating time is short, making heating management difficult. Furthermore, if the heating temperature is below 140°C, the applied paint will flow down from the surface of the material being coated due to its low activity as mentioned above.
It becomes extremely difficult to form a coating film of uniform thickness.

Next, in the method according to the present invention described above, the processing time is significantly shortened compared to the case where the heat curing method is applied to the conventional thermosetting paint. ,
This is thought to be caused by extremely active free radicals generated in the molecules of the urethane acrylate oligomer, which is the main component of the paint.

In this way, the paint in question is a so-called anaerobic paint that radically polymerizes through a reaction with very active free radicals, so it is generally thought that its curing is suppressed in the presence of air. In the method of the invention, the curing speed of the coating film is extremely rapid, and in the reaction system between the free radicals and oxygen in the air that causes curing inhibition, the supply of oxygen is delayed and the rate of curing inhibition is reduced. The new binding molecules generated in the reaction system of the above free radicals and oxygen are
Since it is reactivated by the strong energy during the heat treatment and comes to contribute to the curing polymerization reaction again, the heat treatment can be carried out in the presence of air without being affected by oxygen.

In addition, in the case of mixing a coloring agent into the paint, the coloring agent may absorb a large amount of energy and suppress the curing of the coating film in the light irradiation curing method described above, but in the method of the present invention, a heat curing method is not used. Since it is adapted, its limitations are small.

Furthermore, in the method of the present invention, during the heat treatment, energy is not concentrated on the coated material within an extremely short period of several seconds, unlike in the light irradiation curing method.
Since energy is gradually applied within several minutes in a gas phase where a constant temperature condition is maintained, the energy received by the cured coating film is relatively small and uniform in unit time, and the energy received by the coating film is relatively small and uniform in unit time. There is no formation of air bubbles in the solvent, as is the case with the facilitation method, and therefore steps such as pre-drying are not required.

Next, to specifically explain the hardness of the cured coating film obtained by the two-part method according to the present invention from the aspect of scratch resistance, the scratch resistance of the cured coating film obtained by the above-mentioned conventional method was compared. The results are shown in the table below.

(Table) In the above table, A - and -E are respectively coated with an acrylic-melamine paint on a base material formed into a plate shape of aluminum alloy, and the markings are displayed on the surface of the coated material. These are the results for coating films (40μ thick) obtained under each condition during heat treatment, where A is the coating film obtained by the method according to the present invention, and B is the coating film obtained by adding a photosensitizer to the paint. This shows a coating film obtained by a light irradiation curing method using a paint (in A and H, the applied paint was urethane acrylate oligomer 100 parts, polyfunctional acrylate 5 parts).
). In addition, C and 'C' are coating films obtained by high temperature heating drying method using acrylic-melamine paint, D and σ are coating films obtained by high temperature heating drying method using epoxy paint, and E is coating film obtained by high temperature heating drying method using epoxy paint. The coating films obtained using a silicone-based paint by a high-temperature heating drying method are shown. In addition, B was suitably pre-dried before the light irradiation process, and C-E was suitably pre-dried before the high-temperature heating process.

In addition, the test method for scratch resistance shown in the table above was based on the steel wool abrasion method, which is not affected by the hardness of the base coating. Measurement using this steel wool abrasion method is
#000 steel wool is reciprocated under a constant load over the coating film to be tested, and the number of times when scratches begin to occur is measured. In addition, the steel wool load in the table above is based on the unit area (
cd) shows the load value per hit, and the number of times shows the number of times of rubbing when the scratches start to form.

From the results shown in Table 2, it can be seen that coating film A produced by the method according to the present invention
The product maintains scratch resistance without scratches even after being rubbed more than 100 times with a steel wool load of 5 oo (g//c, y), and this level of scratch resistance is higher than that of conventional products. It can be assured that the hardness of the coating is comparable to that obtained using silicone-based paint.

In addition, as another expression confirmed regarding the hardness of the coating film obtained by the method according to the present invention, the coating film formed directly on the iron plate material surface exhibited a pencil hardness (1 to 9 load) of 8H.

As shown above, the present invention uses existing equipment with a simple structure, is safer and easier to operate, and can be applied to surfaces of arbitrary shapes and sizes with high hardness and scratch resistance within a short time. It provides a method capable of forming a coating film, and therefore,
The implementation of the method is energy-saving, and the resulting product is non-hazardous, making the range of use extremely wide, such as application to clear coatings on various tableware.

Example 1 First, an acrylic-melamine paint was applied as a base onto the surface of an aluminum alloy base material (310 g) cast into a dish shape (diameter 22 cm), and baked at 175°C for 15 minutes.
A coating film with a thickness of 5 to 20 μm was formed.

Next, the chemical formula is obtained by chemical synthesis using inphorone diisocyanate, ethylene glycol, and acrylic acid as raw materials.

111 Note that n = '1 to 13, 20 parts by weight of a urethane acrylate oligomer as the main component, and 10 parts by weight of a mixture of pentaerythritol tetraacrylate and dipentaerythritol hexane acrylate as a polyfunctional acrylate as a reactive diluent. , 6 parts by weight of ethyl cellosolve as a solvent,
24 parts by weight of methyl isobutyl ketone and 69 parts by weight of toluene.
A paint consisting of 9 parts by weight and 0.1 suspended part of a leveling agent was prepared, and the paint was applied onto the primed surface of the dish by dipping, and then immediately dried in a hot air dryer maintained at 180'C. and heated for 12 minutes.

The plate-shaped object obtained in this way has a topcoat film thickness of 2Q~
25μ, there are no adverse effects such as cracks, and the measured value by the steel wool abrasion method shows that the steel wool load s o o
(g/,,) was 100 times or more.

Example 2 First, an acrylic-melamine paint was applied as an undercoat to the surface of an aluminum alloy base material (180 g) cast into a pot shape (maximum diameter 8 Crn), and baked at 1750C for 15 minutes to form a 20-25μ thick A coating film was formed.

Next, the paint made of the urethane acrylate oligomer etc. shown in Example 1 was applied by spraying it onto the undercoated surface of the pot-shaped object using a spray gun, and then immediately placed in a hot air dryer maintained at 180°C. and heated for 8 minutes.

The pot-shaped object obtained in this way has a topcoat film thickness of 20 to
It is formed uniformly over the entire surface with a thickness of 25μ, and there are no adverse effects such as cracks, and the measured value by the steel wool abrasion method is 10 at a steel wool load of 500 (g/C, ff).
It was 0 or more times.

Claims (2)

[Claims] (1) A urethane acrylate oligomer as a main component, a polyfunctional acrylate as a reactive diluent,
Further, a paint consisting of a suitable solvent, the paint is appropriately applied onto the surface of the material to be coated, and the coated material is heat-treated for a certain period of time under constant temperature conditions such that the base material temperature of the coated material is 14,000 to 200°C. A method for forming an abrasion-resistant coating film characterized by applying. (2) The method for forming a scratch-resistant coating film according to claim 1, wherein the heat treatment is performed in the presence of air.