JP4025025B2 - Method for forming protective film of automotive plastic parts - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an automotive plastic part having a protective film having scratch resistance and UV-cutting properties formed on its surface.
[0002]
[Prior art]
Conventional automobile parts and the like are currently widely used thermoplastic materials that are easy to recycle from the viewpoint of weight reduction and protection of the global environment. For example, a polycarbonate resin (hereinafter referred to as a PC resin) is mainly used as a lens material for an automobile headlamp because of its light weight and high impact strength. By the way, when such a PC resin is used as it is for an automobile exterior part as it is, the material itself has a low surface hardness and is easily scratched, and is deteriorated by ultraviolet rays and heat emitted from the sun, causing discoloration, deformation, and strength reduction. There is a weak point that it is easy to wake up.
[0003]
In order to make up for these weak points, conventionally, an acrylic paint is mainly sprayed on the surface of the PC resin to form a protective film (hard coat film) having scratch resistance and ultraviolet cut characteristics.
[0004]
[Problems to be solved by the invention]
However, plastic parts used in automobiles have a wide variety of complicated three-dimensional shapes, and in the surface coating process in which paint is sprayed on such parts, a protective film with a uniform thickness is used. In addition to being difficult to form, the coating efficiency on the plastic surface is low, and many organic solvents are wasted into the atmosphere, and the paint may adhere to unwanted surfaces.
[0005]
For this reason, it is possible to contribute to the protection of the global environment without wasting organic solvents etc. in the air to plastic parts of various and complicated three-dimensional shapes, while providing scratch resistance, UV cut characteristics, etc. It is required to form a good quality protective film with a uniform film thickness.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 uses a plasma chemical vapor deposition apparatus in which at least a part of a cathode provided in a reaction chamber has a shape that matches a surface shape of an automotive plastic part, The plastic part is attached to the cathode, and oxygen gas and diethyl zinc gas mixed with helium carrier gas by introducing helium carrier gas into the diethyl zinc liquid are introduced into the reaction chamber, and between the reaction chamber and the cathode. A high frequency power is supplied and plasma chemical vapor deposition is performed at 50 to 80 ° C. to form a protective film mainly composed of zinc oxide on the surface of the plastic part. After that, oxygen gas and helium are formed in the reaction chamber. Organosilicon gas mixed with helium carrier gas by blowing carrier gas into organosilicon liquid Together with the introduction, carried out by supplying a high frequency power plasma chemical vapor deposition between the reaction chamber and the cathode, to form a protective film composed mainly of silicon dioxide on the surface of the protective film composed mainly of the oxide of zinc.
[0008]
In the present invention, since the protective film is formed by plasma CVD in the reaction chamber, the protective film is formed on the surface of the plastic part without deteriorating the plastic and without wastefully releasing the organic solvent into the atmosphere. it can. Also, around the cathode, the speed of electrons is very fast compared to the speed of ions, so only electrons flow into the cathode quickly, and the cathode is negatively charged, resulting in a slightly negative self-bias potential. At the same time, an ion sheath is formed in which ions are concentrated around the cathode. When a plastic part is placed in the ion sheath, the ions in the ion sheath are sucked uniformly and slowly toward the cathode, and the plastic part. The surface is deposited with a substantially uniform thickness, and a high-quality protective film having a substantially uniform film thickness can be formed on the surface of a complicated three-dimensional plastic part.
[0009]
Furthermore, diethylzinc gas, by bubbling helium carrier gas in diethyl zinc solution, it is so arranged is introduced into the reaction chamber is mixed with helium carrier gas, even at low diethylzinc gas vapor pressure at room temperature, By mixing the helium carrier gas, it can be sufficiently introduced into the reaction chamber.
[0010]
Furthermore, after forming a protective film composed mainly of zinc oxide on the surface of plastic parts, oxygen gas and organic silicon gas are introduced into the reaction chamber, and high-frequency power is supplied between the reaction chamber and the cathode to perform plasma chemical vapor deposition. the go, because to form a protective film composed mainly of silicon dioxide on the surface of the protective film composed mainly of the oxide of zinc, the surface of the plastic part, protection mainly a good zinc oxide having ultraviolet shielding properties Since the film and the protective film mainly composed of hard and scratch-resistant silicon dioxide are formed continuously using the same plasma chemical vapor deposition system, the plastic parts have further improved UV protection and scratch resistance. The protective film can be formed efficiently.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The present invention uses a cathode deposition method by plasma chemical vapor deposition (hereinafter referred to as “plasma CVD”) to impart scratch resistance, ultraviolet resistance, etc. to a plastic material such as a PC resin. Is formed on the surface of plastic parts for automobiles. As a material for the protective film, oxygen gas and diethyl zinc (H ₅ C ₂ —Zn—C ₂ H ₅ , hereinafter referred to as DEZ) are used.
[0012]
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.
[0013]
A plasma CVD apparatus used in the present invention is shown in FIG. The plasma CVD equipment includes a reaction chamber 1 which is in the high vacuum is connected to the vacuum exhaust pipe 5 connected to a vacuum pump. The reaction chamber 1 has a cathode 2 disposed at the top. The cathode 2 has at least a part of the surface shape matched with the surface shape of the plastic part, and the plastic part can be attached to the cathode 2. For example, as shown in the cross-sectional view of FIG. 2, when the plastic part is a lens 10 of an automotive headlamp, a part of the surface of the cathode 2 is formed along the lens 10 surface, Both surfaces can be combined in a state where the surfaces having the same shape are in contact with each other. A portion of the cathode 2 where no plastic parts are attached is covered with a shield member 8 grounded in the reaction chamber 1 to prevent deposition of a protective film component, and an insulating film 9 is interposed between the shield member 8 and the cathode 2. Is sandwiched.
[0014]
High-frequency power (13.56 MHz, hereinafter referred to as RF output) is supplied between the cathode 2 and the reaction chamber 1 from a high-frequency power supply device 6. Here, a bias capacitor 7 is disposed between the cathode 2 and the high frequency power supply device 6. The reaction chamber 1 is provided with a heater 22 for adjusting the temperature in the reaction chamber 1.
[0015]
High-purity oxygen ( O ₂ ) gas and DEZ gas can be introduced into the reaction chamber 1 as a raw material for the protective film. As a raw material for the protective film, any material may be used as long as it includes a component capable of imparting a predetermined hardness and ultraviolet ray-cutting properties. In this example, DEZ and oxygen gas that easily generate ZnO were used. ZnO has a band gap of 3.1-3.3 eV and is excellent in ultraviolet cut characteristics, so that it is possible to obtain a protective film that is particularly effective in preventing deterioration due to ultraviolet rays.
[0016]
After the flow rate of the oxygen gas is controlled by the flow rate controller 12, the oxygen gas is introduced into the reaction chamber 1 through the oxygen introduction pipe 3, and reacts with the gas molecules of DEZ to generate ZnO by the action of oxygen radicals. In plasma CVD using oxygen gas, DEZ reacts with oxygen radicals, and the Zn—C bond and CH bond of DEZ are broken to produce precursors such as ZnOx and Zn (OH) x. As the precursor is deposited on the surface of the plastic part (lens 10), it is considered that the protective film 12 containing ZnO as a main component is formed as shown in FIG.
[0017]
Since DEZ is liquid at normal temperature and has a low vapor pressure, it is mixed with helium carrier gas (hereinafter referred to as He gas) and carried into the reaction chamber 1. First, the DEZ container 15 containing DEZ is bathed in the water tank 16, and the water temperature in the water tank 16 is adjusted to 40 ° C. by the temperature controller 20 to increase the vapor pressure of DEZ. Here, the He gas whose flow rate is controlled by the flow rate controller 12 is blown into the DEZ liquid by the helium introduction pipe 18, and the DEZ liquid is bubbled (bubbled) to obtain a mixed gas of DEZ and He. The mixed gas is introduced into the reaction chamber 1 through the raw material introduction pipe 4 after the pressure is controlled through the pressure control valve 13 and the pressure controller 14. Thus, even DEZ having a low vapor pressure at room temperature can be sufficiently introduced into the reaction chamber by mixing with He gas.
[0018]
In order to form a protective film mainly composed of ZnO on the surface of a plastic part using this plasma CVD apparatus, first, a plastic part such as a lens 10 is attached to the cathode 2, and then the air in the reaction chamber 1 is evacuated. After evacuating with a vacuum pump to make the reaction chamber 1 into a high vacuum, oxygen gas, a mixed gas of He gas and DEZ gas are introduced into the reaction chamber 1, and RF output is supplied between the cathode 2 and the reaction chamber 1. To do. Then, glow discharge is generated between the cathode 2 and the reaction chamber 1, the gas in the reaction chamber 1 is turned into plasma, and oxygen radicals react with the source gas DEZ to form a Zn—C bond and a C—H bond of DEZ. Are cut to produce precursors such as ZnOx and Zn (OH) x. Gradually, these precursors are deposited on the surface of the plastic part, so that a protective film 12 mainly composed of ZnO is formed on the surface of the plastic part.
[0019]
Thus, since the protective film 12 is formed in the reaction chamber 1 by plasma CVD, the protective film 12 can be formed at a low temperature without wastefully releasing an organic solvent or the like into the atmosphere. However, there is no deformation or deterioration due to heat when the protective film 12 is formed.
[0020]
By the way, since the velocity of electrons around the cathode 2 is very high compared to the velocity of ions, only electrons flow into the cathode 2 quickly, the cathode is negatively charged, and the self-bias is slightly negative. On the other hand, an ion sheath (ion sheath) in which ions that cannot reach the cathode are concentrated is formed uniformly around the cathode 2 while being at a potential. When the cathode 2 becomes a negative bias potential, a bias capacitor 7 disposed between the cathode 2 and the high frequency power supply device 6 holds the negative bias potential of the cathode 2. In the ion sheath, the ions dissociated and ionized further from DEZ are present in a high density, and these ions are uniformly and slowly attracted toward the cathode 2 by the slight negative bias potential of the cathode 2, It is considered that the protective film 12 is formed by depositing on the surface of the plastic part with a substantially uniform thickness.
[0021]
Using the plasma chemical CVD apparatus as shown in FIG. The area of the cathode was 216 cm ² , a test piece was attached to the cathode surface, and DEZ gas was introduced into the reaction chamber from a raw material introduction tube 8 cm below the test piece.
[0022]
First, in order to examine the film characteristics in detail, a test piece made of a single crystal silicon Si (Miller index 100) substrate having a high resistance of 100 Ωcm or more is attached on the cathode, and a protective film is deposited on the test piece. Various experiments were conducted. The suitable conditions for depositing the ZnO protective film were He flow rate of 5 cc / min, oxygen flow rate of 10 cc / min, DEZ flow rate of 0.5 cc / min, reaction chamber pressure of 0.1 Toor, and RF output of 100 W. It was.
[0023]
First, the test piece temperature was set to room temperature, and a protective film having a film thickness of 0.2 to 0.3 microns was formed on a single crystal silicon substrate (measured with a surface roughness meter DEKTAK3030 manufactured by Japan Vacuum Technology). The ultraviolet absorption spectrum characteristics of were measured. As shown in FIG. 3, this spectral characteristic shows that the absorption due to the Zn—O bond is remarkably observed at a wave number of 450 cm ⁻¹ in this protective film. Although absorption by —OH is also observed at a wave number of 3300 cm ⁻¹ , it is considered that water adhering to the test piece and the reaction chamber reacted without desorbing and was taken into the protective film. Therefore, this absorption could be removed by raising the specimen temperature to 120 ° C.
[0024]
Next, XPS spectral characteristics of the protective film are shown in FIGS. Since a single spectrum due to 2p ³ electrons of Zn is observed at a position where the binding energy is 1021 eV, it can be seen that a protective film including a component close to the chemical structure of ZnO is formed. In addition, there is a C 1s peak at 285 eV, and an O 1s peak at 531 ev. In addition to the C—C bond and C—H bond, functional groups such as C—O bond and COO— are also present in the protective film. It is understood that it is included.
[0025]
FIG. 6 shows the relationship between the test piece temperature and the deposition rate of the protective film in plasma CVD. It can be seen that the deposition rate of the protective film decreases as the temperature increases. This seems to be because the higher the temperature, the more the desorption reaction on the surface of the test piece is promoted.
[0026]
FIG. 7 shows the composition change of the deposited film depending on the test piece temperature in plasma CVD. Although the composition ratio of Zn and O was not significantly changed even when the temperature of the test piece was changed, C was hardly contained when the temperature was 75 ° C. or higher, and the quality of the protective film was improved. This is presumably because the elimination reaction of C in the protective film was promoted as the temperature increased.
[0027]
FIG. 8 shows the relationship between the crystallinity of the protective film obtained from X-ray Bragg reflection and the test piece temperature during plasma CVD. Although the crystallinity of the protective film hardly occurs at room temperature, some crystallinity of ZnO (Miller index 100) was confirmed as the temperature increased.
[0028]
FIG. 9 shows changes in the deposition rate of the protective film due to RF output. When the RF output is in the range of 30 to 100 W, the deposition rate of the protective film greatly increases as the output increases. However, when the RF output is further increased, the deposition rate of the protective film decreases. This is because, up to 100 W of RF power, oxygen radicals in the plasma increase and the reaction with DEZ is promoted to increase the deposition rate of the protective film, whereas when the RF power exceeds 100 W, the test is performed. Since charged particles and ions colliding with the pieces increase, it is considered that the deposition rate decreases due to the etching phenomenon that these scrape off the protective film.
[0029]
Next, FIG. 10 shows a spectral transmittance curve of a protective film mainly composed of 0.3 μm thick ZnO deposited on the surface of the quartz glass substrate. FIG. 10 also shows changes in the spectral transmittance curve depending on the specimen temperature in plasma CVD. The transmittance of the protective film was determined by subtracting the absorption curve of quartz glass from the transmittance curve of the protective film and the entire quartz glass. As can be seen from FIG. 10, the protective film transmits almost all visible light, but starts to cut when the wavelength becomes less than about 400 nm, cuts the UV better as the wavelength is shorter, and almost cuts when the wavelength is less than 300 nm. Yes. And the ultraviolet-ray cut performance is improving, so that the test piece temperature rises. As can be seen from FIG. 8, this is probably because the crystallinity of ZnO increases as the test piece temperature rises. From this experiment, it was found that a protective film mainly composed of ZnO can be sufficiently expected as a protective film that cuts off ultraviolet rays.
[0030]
Then, a protective film mainly composed of ZnO was formed by plasma CVD on a test piece of PC resin most frequently used for a lens for an automobile lamp, and the peel strength of the protective film was tested. The result of this experiment is shown in FIG. FIG. 11 shows changes in the peel strength of the protective film due to the test piece temperature in plasma CVD. The peel strength tends to decrease as the temperature increases. This seems to be because, as described above, the higher the temperature, the more ZnO has crystallinity and the closer to the inorganic material, the weaker the bonding with the organic PC resin. From this experiment, it was also found that there is no practical problem with the peel strength of the protective film in the range from room temperature to 120 ° C where the plastic can withstand.
[0031]
Moreover, the test piece which formed the protective film which has a ZnO as a main component on the surface of the same PC resin and the test piece only of colorless and transparent PC resin were made, and the light resistance test was done. An electron micrograph of the surface of the test piece without the protective film before the light resistance test is shown in FIG. 12, and an electron micrograph of the surface of the test piece on which the protective film before the light resistance test is formed is shown in FIG. In the light resistance test, the irradiation light of a xenon arc lamp (output 3.5 kW) is appropriately cut into ultraviolet rays by using an ultraviolet cut filter to make it close to sunlight, the irradiation rate is 100 W / m ² , the black panel temperature is 89 ±. A test piece placed in an environment of 3 ° C. and humidity of 50 ± 10% was continuously irradiated for 1000 hours. FIG. 14 shows an electron micrograph of the surface of the test piece without the protective film after the light resistance test, and FIG. 15 shows an electron micrograph of the surface of the test piece with the protective film formed on the PC resin surface. From this, unevenness was clearly recognized on the surface of the test piece without the protective film, whereas no unevenness was found on the surface of the test piece on which the protective film was formed. Therefore, it can be seen that the protective film containing ZnO as a main component completely prevents UV degradation. When such an ultraviolet deterioration prevention property is improved, design properties and impact resistance can be improved.
[0032]
Similarly, FIG. 16 shows changes in visible light transmittance with time in light resistance experiments. In the test piece in which the protective film mainly composed of ZnO is formed, the visible light transmittance hardly changes over time, but in the test piece without the protective film, the visible light transmittance greatly decreases with time. Yes.
[0033]
Similarly, FIG. 17 shows the change in the Haze value (cloudiness value) over time in the light resistance test. It can be seen that the test piece in which the protective film mainly composed of ZnO is formed has a smaller increase in the Haze value than the test piece without the protective film, and the photodegradation due to ultraviolet rays is suppressed.
[0034]
Similarly, the change in yellowness over time in the light resistance test is shown in FIG. A test piece in which a protective film mainly composed of ZnO is formed has less increase in yellowness than a test piece without a protective film.
[0035]
From the above experimental results, it can be seen that the protective film containing ZnO as a main component obtained by the cathode deposition method by plasma CVD has scratch resistance and ultraviolet cut characteristics according to this example. In addition, it has been found that plasma CVD can be performed in a range from room temperature to 135 ° C., a temperature that plastics can withstand. However, when comprehensively judged from the deposition rate of the protective film, composition, peel strength, UV cut, etc., 50 It has also been found that about −80 ° C. is desirable.
[0036]
Furthermore, in this embodiment , after forming a protective film mainly composed of ZnO on the surface of the plastic part, a protective film made of silicon dioxide (hereinafter referred to as SiO ₂ ) is formed on the protective film mainly composed of ZnO. formation to. Since SiO ₂ is hard, the scratch resistance can be further improved. In order to form a protective film mainly composed of SiO ₂ , after forming a protective film mainly composed of ZnO, in the same reaction chamber, a gas containing Si instead of DEZ gas, for example, organic silicon, together with oxygen gas Etc. (monosilane (SiH ₄ ), hexamethyldisilane (Si ₂ (CH ₃ ) ₆ ), etc.) may be introduced to perform plasma CVD. The source gas is mixed with He gas and introduced into the reaction chamber by bubbling He gas into the source liquid in the same manner as DEZ described above.
[0037]
Further, the protective film described above may be formed not only on the outer lens surface of the headlamp for automobiles, but also on the inner lens surface. It can also be formed on the surface of automotive plastic parts that are easily received. The protective film can be formed not only on PC but also on a transparent thermoplastic resin such as PMMA (polymethyl methacrylate) and AS (acrylonitrile / styrene resin).
[0040]
【The invention's effect】
In the invention according to claim 1 , since the protective film mainly composed of ZnO is formed by plasma CVD at 50 to 80 ° C., the film thickness is almost uniform even on the surface of a complicated three-dimensional plastic part. Thus, a good quality protective film can be easily formed at a low temperature, and a protective film that imparts scratch resistance and ultraviolet resistance can be formed on the surface of the plastic part without deforming or deteriorating the plastic part.
[0041]
Also, DEZ or organic silicon gas having a low vapor pressure at room temperature can be sufficiently introduced into the reaction chamber by mixing with helium carrier gas, so that a protective film can be formed efficiently.
[0042]
Furthermore, since the protective film mainly composed of hard and scratch-resistant SiO ₂ is mainly formed on the protective film mainly composed of ZnO, which has good ultraviolet cut-off property, with the same plasma CVD apparatus, It is possible to efficiently form a protective film for a plastic part with further improved scratch resistance. Furthermore, since organic solvents and the like are not wasted into the atmosphere, it can contribute to the protection of the global environment.
[Brief description of the drawings]
FIG. 1 shows a plasma CVD apparatus according to the present invention.
FIG. 2 is a cross-sectional view taken along line AA in FIG.
FIG. 3 is a diagram showing an ultraviolet absorption spectrum characteristic of a protective film containing ZnO as a main component.
FIG. 4 is a graph showing XPS spectral characteristics of the protective film.
FIG. 5 is a graph showing XPS spectral characteristics of the protective film.
FIG. 6 is a diagram showing the relationship between the test piece temperature and the deposition rate of the protective film in plasma CVD.
FIG. 7 is a diagram showing a change in the composition of the protective film depending on the test piece temperature in plasma CVD.
FIG. 8 is a diagram showing a change in crystallinity of a protective film depending on a test piece temperature in plasma CVD.
FIG. 9 is a diagram showing a change in the deposition rate of the protective film due to RF output in plasma CVD.
FIG. 10 is a diagram showing a spectral transmittance curve of the protective film.
FIG. 11 is a diagram showing a change in the peel strength of the protective film due to the test piece temperature in plasma CVD.
FIG. 12 is an electron micrograph of the surface of a test piece without a protective film before a light resistance test.
FIG. 13 is an electron micrograph of the surface of a test piece on which a protective film before a light resistance test is formed.
FIG. 14 is an electron micrograph of the surface of a test piece without a protective film after a light resistance test.
FIG. 15 is an electron micrograph of the surface of a test piece on which a protective film after a light resistance test is formed.
FIG. 16 is a diagram showing changes in visible light transmittance over time in a light resistance experiment.
FIG. 17 is a diagram showing a change in Haze value over time in a light resistance test.
FIG. 18 is a diagram showing a change in yellowness over time in a light resistance test.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Reaction chamber 2 Cathode 3 Oxygen introduction pipe 4 Raw material introduction pipe 5 Vacuum exhaust pipe 6 High frequency power supply device 10 Head lamp lens (plastic part)

Claims (1)

Using a plasma chemical vapor deposition apparatus in which at least a part of the cathode provided in the reaction chamber has a shape that matches the surface shape of the automotive plastic part, the plastic part is attached to the cathode,
  Into the reaction chamber was introduced diethyl zinc gas mixed with helium carrier gas by blowing oxygen gas and helium carrier gas into diethyl zinc liquid, and high frequency power was supplied between the reaction chamber and the cathode, Plasma chemical vapor deposition is performed at 80 ° C. to form a protective film mainly composed of zinc oxide on the surface of the plastic part.
  An oxygen gas and an organic silicon gas mixed with a helium carrier gas are introduced into the reaction chamber by blowing an oxygen gas and a helium carrier gas into the organic silicon liquid, and high-frequency power is supplied between the reaction chamber and the cathode for plasma chemistry. Vapor deposition,
  A method for forming a protective film for plastic parts for automobiles, comprising forming a protective film mainly composed of silicon dioxide on a surface of the protective film mainly composed of zinc oxide.

Images