JP7415386B2 - Paint alternative film - Google Patents

Description

The present invention relates to a paint substitute film that coats parts such as outer panels of vehicles such as automobiles with a film instead of painting them, and achieves both design and rust prevention properties.

Conventionally, spray painting has been commonly used to improve the design of exterior parts of vehicles (for example, resin molded products such as fenders, bumpers, bonnets, and wheel caps). However, in recent years, the painting process including spray painting requires large equipment and space due to repeated painting and drying, which reduces productivity, so efforts have been made to streamline the painting process. A method of improving the appearance of a product by laminating a decorative film (hereinafter referred to as a paint substitute film) to the exterior parts has been studied.

A paint substitute film 1 according to this type of conventional technology is constructed by sequentially laminating a clear layer 19, a colored layer 12, and an adhesive layer 14, as shown in FIG. 4, for example. reference).

Here, the clear layer 19 is formed using a highly transparent resin material such as polyurethane, acrylic resin, polyester resin, silicone resin, PVDF (polyvinyldene fluoride), or a mixture thereof, and protects the colored layer 12, It has functions such as polishing. Further, the colored layer 12 is formed by blending a metallic pigment into a resin material substantially similar to that of the clear layer 19, thereby giving the colored layer 12 a metallic appearance similar to that of spray painting. Furthermore, the adhesive layer 14 is for adhering the paint substitute film 1 to the surface of an exterior part of an automobile or the like.

When adhering this paint substitute film 1 to the exterior parts, etc., the paint substitute film 1 is heated in advance by irradiation with an infrared lamp, etc., and then this paint substitute film 1 is applied to the exterior parts by in-mold molding, vacuum forming, etc. It is molded to match the surface shape and is bonded to the surface of the exterior component using the adhesive layer 14.

However, these conventional techniques require adhesives for objects with complex shapes, such as exterior parts of automobiles, which may result in poor adhesion depending on the adhered material. It is virtually impossible to select an adhesive that exhibits such adhesive strength. As a solution to this problem, as shown in Patent Document 3, a painting alternative film having a thermoplastic resin film, a colored layer, and a semi-hardened hard coat layer in this order is used as a method for manufacturing metal members used as exterior parts of vehicles. Using a laminate consisting of a protective film and a steel plate bonded to the surface of the hard coat layer, the paint alternative film and the heated steel plate are thermocompressed and press-molded, and the semi-hardened hard coat layer is hardened. A manufacturing method is provided. However, in the case of the exterior parts described in Patent Document 3, etc., in which a paint substitute film is bonded to a metal member, if a crack occurs in the paint substitute film itself due to sharp mechanical stimulation, the metal member will be exposed to cracks. There was a problem in that rust occurred on the surface of the steel, and the rust spread to the surrounding areas.

Japanese Unexamined Patent Publication No. 123469/1983 Japanese Patent Application Publication No. 9-183136 International Publication No. 2019/078369 pamphlet

The purpose of the present invention is to prevent rust from forming on metal components even if a paint substitute film cracks due to the application of sharp mechanical stimulation, and furthermore to prevent rust from spreading to the surrounding areas. An object of the present invention is to provide a paint substitute film that has excellent rust prevention properties.

As a result of intensive research aimed at solving the above problems, the present inventors have developed a painting alternative film having a thermoplastic resin film, a colored layer, and a hard coat layer in this order, in which at least one layer of the thermoplastic resin film has a glass transition temperature. Surprisingly, by using a heat-resistant resin layer that is resistant to temperatures above 115°C, even if the paint substitute film itself cracks, it is difficult for the metal parts to rust from that point, and the rust spreads to the surrounding areas. It has been found that it is possible to achieve a high degree of rust prevention, which is difficult to achieve.

That is, the present invention is achieved by the following requirements.
1. A painting alternative film comprising a thermoplastic resin film, a colored layer, and a hard coat layer in this order, characterized in that at least one layer of the thermoplastic resin film is a heat-resistant resin layer having a glass transition temperature of 115°C or higher. Painting alternative film.
2. 1. The paint alternative film as described in 1 above, wherein the resin used for the heat-resistant resin layer is polyethylene naphthalate.
3. 3. The paint alternative film as described in 1 or 2 above, wherein the resin used for the thermoplastic resin film is polyethylene naphthalate.
4. The coating alternative according to any one of 1 to 3 above, wherein the thermoplastic resin film has an adhesive layer made of an adhesive resin having a glass transition temperature of less than 120° C. on the surface of the heat-resistant resin layer on the side not in contact with the colored layer. film.

The paint alternative film of the present invention has at least one layer of a thermoplastic resin film as a heat-resistant resin layer with a glass transition temperature of 115°C or higher, and after being laminated to metal, sharp mechanical stimulation can be applied to the paint alternative film. Even if a crack occurs in the metal member itself, it is difficult for the metal member to rust from that point, and it also has a high level of rust prevention that prevents rust from spreading to the surrounding areas.

An example of an enlarged cross-sectional view of the paint substitute film of the present invention Enlarged sectional view of another paint substitute film of the present invention Enlarged sectional view of another paint substitute film of the present invention Partially enlarged cross-sectional view of a paint substitute film used in the conventional manufacturing method

Regarding the paint substitute film of the present invention, the components constituting each component and the adjustment method will be specifically explained below.

<Thermoplastic resin film>
The thermoplastic resin film in the paint alternative film of the present invention must have at least one heat-resistant resin layer with a glass transition temperature of 115°C or higher, and as long as this condition is met, it may be a single-layer film or a multi-layer film. good.
The glass transition temperature of the heat-resistant resin layer is 115°C or higher, which suppresses the occurrence and spread of rust even if the paint substitute film cracks due to sharp mechanical stimulation and the base metal is exposed to corrosive substances. and exhibits a high degree of rust prevention.

The lower limit of the glass transition temperature (abbreviated as Tg) of the resin composition used for the heat-resistant resin layer is 115°C or higher, preferably 118°C or higher, and more preferably 120°C or higher. On the other hand, the upper limit of Tg is preferably 155°C or less, more preferably 140°C or less, and even more preferably 130°C or less.
The mechanism is not clear, but when Tg exceeds the lower limit, molecules in the film in the heat-resistant resin layer have difficulty moving, cracks occur in the paint substitute film itself, and the base metal is exposed to highly corrosive acids for a long time. This is presumed to be due to the fact that even when exposed, corrosive acidic substances are difficult to penetrate through the film, making it difficult for metal parts to spread rust. On the other hand, when Tg is below the upper limit, the moldability of the heat-resistant resin layer becomes good, which is preferable.

Tg is determined by heating an unstretched film of the above resin composition from room temperature at a heating rate of 20°C/min to a temperature of 35°C above the melting point of the unstretched film, keeping it melted at that temperature for 3 minutes, and then taking it out and immediately putting it on ice. The temperature was determined by transferring the temperature to a glass plate, rapidly cooling it, and raising the temperature again at a temperature increase rate of 20° C./min. The reading position for the glass transition temperature is the straight line extending the baseline on the low temperature side to the high temperature side and the point where the gradient of the step curve is maximum in the step-like change part of the glass transition on the differential scanning calorimetry chart. The temperature at the intersection with the tangent line drawn from

The resin component of the heat-resistant resin layer is not particularly limited as long as it satisfies the glass transition point requirements described above, but preferred resins include polyolefin resin, polyamide resin, acrylic resin, polycarbonate resin, polyarylene sulfide resin, and polyester resin. can be mentioned. Among these, polyester resins are preferred because they allow uniform film formation with reduced thickness unevenness, and among polyester resins, polyethylene naphthalate is preferred from the standpoint of rust prevention. Polyethylene naphthalate may be a homopolyester or a copolyester. The copolymerization component can be preferably used as either an acid component or a diol component. Examples of acid components include aromatic dicarboxylic acids such as isophthalic acid, phthalic acid, terephthalic acid, diphenyl ether dicarboxylic acid, etc., as well as adipic acid, azelaic acid, sebacic acid, sulfuric acid, etc., in addition to the main acid components such as 2,6-naphthalene dicarboxylic acid. Acid, aliphatic dicarboxylic acids such as succinic acid, and oxycarboxylic acids such as p-oxybenzoic acid and p-oxyethoxybenzoic acid are preferred, and diol components include propylene glycol, trimethylene glycol, and 1,6-hexane. Aliphatic diols such as diol and alicyclic diols such as 1,4-hexamethylene dimethanol can be preferably used. These can be used alone or in combination of two or more. Among these, terephthalic acid is more preferred as the acid component. The heat-resistant resin layer used in the paint substitute film of the present invention preferably contains at least 50% by weight of a resin selected from the resin group listed above, based on the mass of the film.

Among polyethylene naphthalates, polyethylene-2,6-naphthalate resins are preferred from the viewpoint of rust prevention, and the details of the manufacturing method for this resin will be described later.

The intrinsic viscosity of the resin composition used for the heat-resistant resin layer is preferably 0.45 to 0.70, more preferably 0.50 to 0.60 when it is made of polyethylene naphthalate. It is preferable that the intrinsic viscosity is equal to or higher than the lower limit because the mechanical strength of the film is excellent. Further, below the upper limit, it is preferable because moldability is excellent.

The thermoplastic resin film is preferably a single-layer film from the viewpoint of ease of film formation, and particularly a single-layer film of polyethylene naphthalate film is more preferable from the viewpoint of rust prevention. A single layer film of polyethylene naphthalate film is more preferable for improving film strength and rust prevention.

On the other hand, a thermoplastic resin film is a multilayer film consisting of a heat-resistant resin layer and a layer with a glass transition temperature lower than that of the heat-resistant resin layer (hereinafter referred to as a low Tg resin layer) in order to make it easier to bond to a metal substrate. A multilayer film of polyethylene naphthalate and polyethylene terephthalate is particularly preferable because of interlayer adhesion, and a multilayer film of biaxially oriented polyethylene naphthalate and biaxially oriented polyethylene terephthalate is particularly preferable. It is more preferred for improving film strength and interlayer adhesion. The multilayer film is preferably produced by forming a two-layer or three-layer film using a coextruder. Here, the surface to which the metal base material is bonded is preferably a low Tg resin layer having a glass transition temperature lower than that of the heat-resistant resin layer. Even if the surface to be bonded to the metal substrate is a low-Tg resin layer, the paint substitute film will crack due to sharp mechanical stimulation, and rust may occur when the base metal is exposed to corrosive substances. Although the mechanism by which corrosion is suppressed and high rust prevention properties are achieved is not clear, it is presumed that the heat-resistant resin, especially polyethylene naphthalate, suppresses the horizontal diffusion of corrosive substances at exposed locations. Ru.

The thickness of the thermoplastic resin film is preferably 10 to 250 μm. The thickness of the thermoplastic resin film is preferably thicker than the above lower limit in order to prevent the film from being instantaneously heated to the side opposite to the metal due to the heating temperature of the steel plate when laminated with a metal base material. On the other hand, the thickness of the thermoplastic resin film is preferably below the upper limit in order to prevent deterioration of productivity during film formation and excessive stress required during molding. The lower limit of the thickness of the thermoplastic resin film is preferably 12 μm, more preferably 20 μm, particularly preferably 25 μm, and the upper limit is 188 μm, more preferably 125 μm, particularly preferably 100 μm.

Further, the thickness of the heat-resistant resin layer is preferably 5 to 250 μm for rust prevention. The minimum thickness of the heat-resistant resin layer is preferably 5 μm, more preferably 10 μm, and even more preferably 20 μm, and the upper limit of the thickness of the heat-resistant resin layer is preferably 188 μm, more preferably 175 μm, and still more preferably 100 μm.

Furthermore, the thermoplastic resin film in the paint alternative film of the present invention is formed by using an adhesive resin with a glass transition temperature of less than 120°C on the surface of the heat-resistant resin layer on the side that does not contact the colored layer for the purpose of surface modification. An adhesive layer can also be provided.

(Production method of polyethylene-2,6-naphthalate resin)
The method for producing the polyethylene-2,6-naphthalate resin used for the heat-resistant resin layer is, for example, synthesizing a polyester precursor by subjecting an aromatic dicarboxylic acid or its ester-forming derivative to an esterification reaction or transesterification reaction with an alkylene glycol. The first reaction consists of a first reaction in which the precursor is subjected to a polycondensation reaction, and a method known per se can be adopted.

The polyethylene-2,6-naphthalate used as a specific raw material for the polyethylene-2,6-naphthalate resin used in the heat-resistant resin layer is one whose repeating unit is composed of ethylene-2,6-naphthalate. It can be produced by esterifying and polymerizing naphthalene-2,6-dicarboxylic acid or a derivative thereof, and ethylene glycol under appropriate reaction conditions in the presence of a catalyst.

Regarding the preferable conditions for the first reaction, it may be carried out under normal pressure, but it is preferable to carry out it under an increased pressure of 0.05 MPa to 0.5 MPa because the reaction rate can be more easily increased. Further, the temperature of the first reaction is preferably carried out in the range of 210°C to 270°C. By setting the reaction pressure within the above range, it is possible to facilitate the progress of the reaction while suppressing the generation of by-products typified by dialkylene glycol. At this time, it is preferable to use the alkylene glycol component in 1.1 to 6 times the amount of the acid component present in the reaction system performing the first reaction, from the viewpoint of reaction rate and maintaining the physical properties of the resin. More preferably 2 to 5 times the mole, still more preferably 3 to 5 times the mole.

In order to increase the reaction rate of the first reaction, it is preferable to use a catalyst known per se, for example, a metal compound having a metal component such as Li, Na, K, Mg, Ca, Mn, Co, or Ti. Among these, when the reaction is carried out under pressure, Mn and Ti compounds are preferred from the viewpoint of the ease with which the reaction proceeds. In particular, Ti compounds are preferred because they can further be used as polycondensation reaction catalysts and cause less catalyst residue to be deposited. The titanium compound used in the present invention is preferably an organic titanium compound that is soluble in polyester from the viewpoint of suppressing the generation of insoluble coarse foreign matter due to precipitation of catalyst residues. Particularly preferred titanium compounds include titanium tetraisopropoxide, titanium tetrapropoxide, titanium tetrabutoxide, titanium tetraethoxide, titanium tetraphenoxide, titanium trimellitate, and the like.

Further, the amount of the catalyst added is preferably in the range of 10 to 150 mmol%, more preferably in the range of 20 to 100 mmol%, in terms of metal element, based on the number of moles of the total acid component present during the first reaction. In particular, a range of 30 to 70 mmol % is more preferable because it can accelerate the reaction rate, suppress the formation of coarse insoluble foreign substances caused by the catalyst, and maintain a high degree of heat resistance of the resulting copolymerized aromatic polyester. In addition, when adding the titanium compound, it is preferable to add the titanium compound so that it is present from the start of the esterification reaction of the first reaction, and as described above, it is preferably used subsequently as a polycondensation reaction catalyst. Of course, it may be added in two or more portions for the purpose of controlling the polycondensation reaction rate.

Next, a second reaction in which the precursor obtained in the first reaction undergoes a polycondensation reaction will be described.
In order to impart a high degree of thermal stability to the resin in the heat-resistant resin layer, it is preferable to add a thermal stabilizer consisting of a phosphorus compound to the reaction system before the start of the polycondensation reaction in the second reaction. Specific phosphorus compounds are not particularly limited as long as they contain a phosphorus element, and examples include phosphoric acid, phosphorous acid, trimethyl phosphate, tributyl phosphate, triphenyl phosphate, and phosphorus. Preferred examples include acid monomethyl ester, phosphoric acid dimethyl ester, phenylphosphonic acid, phenylphosphonic acid dimethyl ester, phenylphosphonic acid diethyl ester, ammonium phosphate, triethylphosphonoacetate, methyldiethylphosphonoacetate, and the like. Two or more types of compounds may be used in combination. The phosphorus compound is preferably added after the first reaction is substantially completed and at the beginning of the second reaction, which is the polycondensation reaction, and the addition may be carried out at once or twice or more. It may be divided into two parts.

When producing the polyester resin for the heat-resistant resin layer, the temperature of the polycondensation reaction is preferably carried out in the range of 270° C. to 300° C., and the pressure during the polycondensation reaction is preferably carried out under reduced pressure of 50 Pa or less. If the pressure during the polycondensation reaction is higher than the upper limit, the time required for the polycondensation reaction becomes longer and it becomes difficult to obtain a copolymerized aromatic polyester with a high degree of polymerization. As the polycondensation catalyst, metal compounds such as Ti, Al, Sb, and Ge, which are known per se, can be suitably used. Among them, it is preferable to continue using the titanium compound added during the esterification reaction or the transesterification reaction. This is preferable because generation of insoluble coarse foreign matter due to residue can be suppressed.

<Colored layer>
The colored layer in the paint substitute film of the present invention preferably contains a binder resin and a pigment or dye. If a binder resin is not used, cracks will easily occur in the colored layer due to the elongation during molding, resulting in poor appearance. Furthermore, by using pigments or dyes, a beautiful and excellent appearance can be formed. Pigments or dyes used include carbon black, iron black, titanium white, antimony white, yellow lead, titanium yellow, Bengara, cadmium red, ultramarine blue, cobalt blue, quinacridone red, isoindolinone yellow, and phthalocyanine. Preferably, it is one selected from the group consisting of blue, aluminum, brass, titanium dioxide, and pearlescent pigments. It is a preferable embodiment to use other pigments and additives for toning, as long as they do not impair the present invention. The method of forming the colored layer is not particularly limited, but a method of laminating by coating is simple and preferred. The adhesion between the colored layer and the thermoplastic resin film can be adjusted as appropriate by the type of thermoplastic resin film and the binder resin used for the colored layer. In this case, it is preferable to perform surface treatment on the thermoplastic resin film by coating to provide a surface modification layer that assists in adhesion. Naturally, there is no problem as long as the thermoplastic resin film itself can ensure adhesive strength.

As mentioned above, the surface modified layer in the paint substitute film of the present invention preferably has a thickness of not more than 1 μm. The thicker the surface modified layer, the worse it is in productivity and durability. The surface modification layer may be applied by in-line coating during the film formation of the thermoplastic resin film, or by winding the thermoplastic resin film into a roll after forming the film and then rolling it out again. Off-line coating may also be performed.

The surface modified layer in the paint substitute film of the present invention uses a material that can ensure adhesive strength between the colored layer and the thermoplastic resin film, and the binder resin is selected from polyester resin, acrylic resin, and urethane resin. It is preferable to use at least one resin selected from the group consisting of: In order to adjust the adhesive strength, it is suitable to copolymerize each resin or blend different resins to improve the adhesive strength.

In addition, in order to create a beautiful design, it is good to have a multi-layered colored layer. For example, a colored layer containing a glitter material pigment in a binder resin is provided as a glitter material layer on top of a colored layer made of a pigment. Therefore, it is preferable to have a two-layer colored layer, and in consideration of reflection characteristics from the viewing side, a colored reflective layer made of aluminum pigment, a colored pigment layer, and a clear coating are provided on the side of the colored layer closest to the thermoplastic resin film. It is also preferable that the film has a three-layer colored layer, that is, a bright material pigment layer. The purpose of the present invention is not negated in any way by using the colored layer as a single layer or as a multilayer in order to impart the necessary design properties.

<Hard coat layer>
The resin used for the hard coat layer in the paint substitute film of the present invention is preferably a thermosetting resin. In particular, acrylic resin is preferably used because of its weather resistance, scratch resistance, and transparency.

The hard coat resin in the present invention is preferably laminated on the above-mentioned colored layer by coating, and the method may be any known coating method.

The thickness of the hard coat layer is preferably 5 to 50 μm after drying. Since the thickness of the hard coat layer is at least the above lower limit, it uses less resin material and is highly economical, but it also protects the inner colored layer and thermoplastic resin film, as well as protection against scratches and chemicals after it is made into a component. Performance can be maintained at a high level. On the other hand, when the thickness is below the upper limit, although it is excellent in terms of gloss development and protective performance as a hard coat film, it is not economical because more resin is used than necessary. The lower limit of the thickness of the hard coat layer is preferably 10 μm, more preferably 15 μm, and the upper limit is 40 μm, more preferably 35 μm.

Furthermore, the hard coat layer in the paint substitute film of the present invention may be composed of a single layer or a multilayer. For example, when coating the same resin twice in multiple layers, it is possible to adjust the degree of curing by changing the drying conditions, making it easier to ensure adhesion with the protective film described below. Transfer from the protective film can be suppressed. Furthermore, a glossy surface can be achieved by forming multiple layers within the above-mentioned range.

The paint substitute film in the present invention has a thermoplastic resin film, a colored layer, and a hard coat layer in this order, and if necessary, has other functional layers such as a surface modification layer, an antifouling layer, and a glitter material layer. You can leave it there. Similarly, it is also possible to form multiple layers of thermoplastic resin and hard coat layers, if necessary.

[Thermocompression bonding]
Steel plates are usually wound up into rolls, and paint substitute films can also be made into rolls, so if they are used, lamination with rolls is possible. For example, the film may be bonded to the steel plate by heating the steel plate and thermocompression bonding the thermoplastic resin film side of the supplied paint substitute film. At this time, in order to complete the melting and cooling solidification within the thermoplastic resin film, it is preferable to keep the laminating roll when laminating the paint substitute film at a low temperature to the extent that the paint substitute film is not melted. In other words, by heating the steel plate side and cooling the hard coat layer side through the paint substitute film, it is possible to complete melting and cooling solidification within the thermoplastic resin film, and interfacial mixing within the molten resin. This makes it possible to have strong adhesive strength.

Furthermore, in order to further strengthen the adhesive strength, it is also a preferred embodiment to provide a surface modification layer on the steel plate side or the thermoplastic resin film side.

The steel plate used for thermocompression bonding may be any steel plate used for the exterior of a vehicle. Generally, a steel material with good formability and a thickness of about 0.3 to 0.6 mm is used, so it is preferable to use such a grade. Further, it is preferable that the steel used for the exterior of the vehicle be subjected to zinc alloy plating as a rust-preventive treatment.

[Press molding]
A laminated steel plate in which the steel plate and the laminate are integrated by the above-described thermocompression bonding is press-molded. As for press molding, cold pressing is preferable as described above. When performing cold press forming on the above-mentioned laminated steel sheets, whether it is stretch forming where the ends of the steel sheet are held under high pressure or forming where the edges of the steel sheet are held under low pressure and the steel sheet is sucked into the forming process, the above-mentioned process is performed. By heat-sealing a thermoplastic resin film, metal members can be covered.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited thereto in any way.
(1) Glass transition temperature (Tg) of resin composition
The unstretched film is heated from room temperature to a temperature 35° C. higher than the melting point of the unstretched film at a heating rate of 20° C./min, and after being melted and held at this temperature for 3 minutes, it is taken out and immediately transferred to ice for quenching. Then, the temperature was again determined by increasing the temperature at a rate of 20° C./min. The Tg reading position is drawn from the straight line extending the baseline on the low temperature side to the high temperature side and the point where the slope of the step curve is maximum in the step-like change part of the glass transition on the differential scanning calorimetry chart. The temperature at the intersection with the tangent line.

[Example 1]
In order to create a paint substitute film, we first created a thermoplastic resin film. The thermoplastic resin film used was a polyethylene-2,6-naphthalate resin consisting of 2,6-naphthalene dicarboxylic acid as a dicarboxylic acid component and ethylene glycol as a glycol component. After drying the polyethylene-2,6-naphthalate resin at 180° C. for 5 hours, it was supplied to an extruder and melt-extruded from a die into a sheet. After extruding into a sheet, it was vitrified with a cooling roll, longitudinally stretched at 130°C, and laterally stretched at 130°C, and a thermoplastic resin film with an area magnification of 11 times was wound into a roll.

The obtained thermoplastic resin film was unwound, and first a colored layer was applied using a comma coater. For the colored layer, a solvent paint containing an acrylic urethane resin as a binder component, 20% titanium particles as a pigment, and 35% nonvolatile components was used. The coating was applied to a thickness of 20 μm, dried in a drying oven at 90° C., and then wound up.

The raw fabric coated with the colored layer is fed out again, and then, in order to form a hard coat layer, the hard coat paint (HC-1) described below is coated with 30% HC-1 in non-volatile components in a thickness of 15 μm using a comma coater. (thickness after curing), dry thoroughly in a drying oven at 90°C, and before winding up, laminate using a biaxially stretched film made of polyethylene terephthalate resin as a protective film. Then, the film was wound up into a roll to obtain a paint substitute film.

When the obtained paint substitute film was used for the rust prevention evaluations A and B described later, it was found to have excellent performance as shown in Table 1.

<Hard coat paint (HC-1)>
150 parts of methyl isobutyl ketone (MIBK) was charged into a four-necked flask equipped with a cooling tube, a stirring device, a thermometer, and a nitrogen introduction tube, and the temperature was raised while stirring under a nitrogen atmosphere. When the temperature inside the flask reaches 74°C, maintain this temperature as the synthesis temperature and add 3 parts of methyl methacrylate, 82.54 parts of n-butyl methacrylate, 12.85 parts of 4-hydroxybutyl acrylate, and 0 parts of methacrylic acid. A monomer solution containing 0.61 parts of Fancryl FA-711MM (manufactured by Hitachi Chemical Co., Ltd., pentamethylpiperidinyl methacrylate), and 0.1 part of azobisisobutyronitrile was added dropwise over 2 hours. . The reaction was continued by adding 0.02 part of azobisisobutyronitrile every hour from 1 hour after the monomer dropwise addition was completed until the unreacted monomer in the solution became 1% or less. When the unreacted monomer content became 1% or less, the reaction was terminated by cooling to obtain an acrylic copolymer solution with a solid content of about 40%. To this acrylic copolymer solution, 59.9 parts by mass (solid mass) of Duranate "P301-75E" (manufactured by Asahi Kasei Chemicals, polyisocyanate of hexamethylene diisocyanate, hereinafter referred to as curing agent 1) was added as a polyisocyanate compound. In addition, methyl isobutyl ketone (MIBK) was added so that the solid content was 30% and stirred to obtain a hard coat paint (HC-1).

[Example 2]
The thermoplastic resin film of the paint substitute film described in Example 1 was prepared by using a copolymerized polyethylene terephthalate resin consisting of polyethylene-2,6-naphthalate resin, terephthalic acid and isophthalic acid as the dicarboxylic acid component, and ethylene glycol as the glycol component. A paint substitute film was obtained in the same manner as in Example 1, except that a two-layer laminated film was obtained. Here, the two-layer laminated film is made by drying the polyethylene-2,6-naphthalate resin at 180°C for 5 hours and the copolymerized polyethylene terephthalate resin at 160°C for 4 hours, then supplying them to separate extruders and using a feed block. The mixture was laminated into two layers, and melt-extruded from a die into a sheet.

When the obtained paint substitute film was used for the rust prevention evaluations A and B described later, it was found to have excellent performance as shown in Table 1.

[Comparative example 1]
A paint substitute film was obtained in the same manner as in Example 1, except that the thermoplastic resin film of the paint substitute film described in Example 1 was changed to a polyethylene terephthalate resin consisting of terephthalic acid as a dicarboxylic acid component and ethylene glycol as a glycol component. Ta. Here, the polyethylene terephthalate resin was dried at 160° C. for 4 hours, then supplied to an extruder, and melt-extruded from a die into a sheet shape. After extruding into a sheet, it was vitrified with a cooling roll, longitudinally stretched at 90°C, and laterally stretched at 100°C, and a thermoplastic resin film with an area magnification of 11 times was wound into a roll.

When the obtained paint substitute film was used for the rust prevention evaluations A and B described later, as shown in Table 1, the rust prevention was deteriorated.

[Comparative example 2]
A paint substitute film was obtained in the same manner as in Example 1, except that the thermoplastic film of the paint substitute film described in Example 1 was changed to syndiotactic polystyrene (SPS).

When the obtained paint substitute film was used for the rust prevention evaluations A and B described later, as shown in Table 1, the rust prevention was deteriorated.

[Rust prevention evaluation A]
The paint substitute films obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were laminated on a plated steel plate JAC270F45/45 to create a laminated steel plate. Specifically, the paint substitute film was unwound, the steel plate was heated to 290° C., the laminating roll was brought to room temperature, and the film was laminated by thermocompression bonding at a pressure of 0.3 MPa. The laminated steel sheet was rapidly cooled with cooling water to obtain a laminated steel sheet.

Two intersecting diagonal lines (scratch marks) were drawn on the resulting paint substitute film on the laminated steel plate using the cutting edge of a cutter knife so as to reach the base of the steel plate. A mist of 5 w/v % neutral sodium chloride solution (saline solution) was sprayed onto the laminated steel plate, and the laminated steel plate was held at 35°C in the same atmosphere for 96 hours, and visually evaluated using the following criteria.
○: Out of all 10 items, the steel plate is rusted only at the scratch mark, but there is no clear expansion. △: Out of all 10 items, there is a clear expansion of the rust on the steel plate at the scratch mark area. ×: Out of all 10 pieces, rust occurred in the scratch mark area and other areas as well, and the film peeled off.

[Rust prevention evaluation B]
Two intersecting diagonal lines (scratch marks) were drawn on the paint substitute film for a laminated steel plate obtained using the same method as in rust prevention evaluation A using the cutting edge of a cutter knife to reach the base of the steel plate. Then, the laminated steel plate was placed in a retort pot, filled with 3% acetic acid + 2% saline solution, and subjected to retort treatment with pressurized steam at 125° C. for 90 minutes. The laminated steel plate was taken out and its condition was visually checked.
○: Out of all 10 items, the steel plate is rusted only at the scratch mark, but there is no clear expansion. △: Out of all 10 items, there is a clear expansion of the rust on the steel plate at the scratch mark area. ×: Out of all 10 pieces, rust occurred in the scratch mark area and other areas as well, and the film peeled off.

The paint substitute film of the present invention maintains its decorative appearance even if cracks occur in the film due to sharp mechanical stimulation after it is bonded to a steel plate and formed. Even if the paint substitute film itself cracks due to mechanical stimulation, it is difficult for metal parts to rust from there, and it also has advanced rust prevention properties that prevent rust from spreading to the surrounding areas. It can be suitably used for applications such as automobile exterior parts.

1 Paint alternative film 11 Thermoplastic resin film 11A Heat-resistant resin layer 11B Low TG resin layer 11C Adhesive layer 12 Colored layer 13 Hard coat layer 14 Clear layer

Claims (3)

A paint substitute film comprising a thermoplastic resin film, a colored layer, and an unfinished thermoset hard coat layer in this order,
At least one layer of the thermoplastic resin film is a heat-resistant resin layer having a glass transition temperature of 115° C. or higher,
The resin used for the heat-resistant resin layer is polyethylene naphthalate,
Paint alternative film. The paint substitute film according to claim 1, wherein the resin used for the thermoplastic resin film is polyethylene naphthalate. 3. The paint substitute film according to claim 1, wherein the thermoplastic resin film has an adhesive layer formed of an adhesive resin having a glass transition temperature of less than 120° C. on the surface of the heat-resistant resin layer on the side not in contact with the colored layer.

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