JPH0453025A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To hold always a specified amt. of a lubricant on the front surface of the magnetic recording medium by adopting the structure in which the impregnation concn. of the lubricant in a part of the inside magnetic recording medium is higher than the impregnation concn. of the lubricant nearest the front surface of the magnetic recording medium. CONSTITUTION:The magnetic recording medium 1 is constituted by providing a magnetic film 3, a substrate 1, and a surface lubricant 4 on the film 3 or a lower layer film 2 between the film 3 and the substrate 1. The pores continuous from the front surface down to the deep part are formed in this medium. The density of the pores into which the lubricant can impregnate is so set that the the parts having the pore density higher than the pore density nearest the front surface of the magnetic recording medium exist in the deep part of the recording medium. The lubricant of the amt. sufficient to fill the pores is impregnated into the pores. The lubricant molecules impregnated into the pores of the film 3, the film 2, etc., are moved from the side of the higher concn. to the lower concn. by the concn. gradient of the lubricant molecules in the film according to the diffusion mechanism in proportion to this concn. gradient. Therefore, the parts having the higher lubricant impregnation concn. than the lubricant impregnation concn. nearest the front surface exist in the inside of the magnetic recording medium and the lubricant on the front surface is captured in the internal lubricant by this concn. gradient, by which the amt. is maintained always constant. The high mechanical reliability is obtd. in this way and the generation of head crash, etc., is prevented.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a magnetic recording medium, and is particularly suitable for use in magnetic disk drives, etc., and has excellent wear resistance. This invention relates to magnetic recording media with high mechanical reliability.

[Conventional technology]

Magnetic recording media such as magnetic disks used as external storage devices generally have a magnetic layer formed on a variety of substrates, but the surface is rubbed at high speed by a magnetic head etc. during recording and reproduction. There is. Conventionally, in order to prevent performance deterioration due to this friction, methods have been used to apply lubricant to the disk surface. Furthermore, as a lubricant, fluorinated carbon oxide such as perfluoropolyether as disclosed in U.S. Pat. No. 3,778,308 is known as a preferred lubricant for magnetic recording media. It is an important issue to use them appropriately as agents. By the way, when the above-mentioned lubricant is applied to a magnetic recording medium such as a magnetic disk, the durability of the magnetic recording medium improves as the amount of lubricant increases. But 7 On the other hand. If too much lubricant is applied to the surface of the magnetic recording medium, 1. For example, in the case of a magnetic disk device, the adsorption force between the head and the disk surface increases when one rotation is stopped; 2. When the device starts to drive, the disk or head may be damaged, or the device may become unable to operate immediately. ]: As mentioned in J.2, the adsorption force between the head and the disk is greatly influenced by the lubricant present on the disk surface. A method of appropriately controlling the amount of lubricant on the surface of the magnetic layer by impregnating it has been proposed (Japanese Patent Laid-Open No. 104202/1983).
. In addition, a method has been proposed in which this method can be applied to high-density media with thin magnetic layers, in which the underlying film is impregnated with a lubricant and the lubricant is sequentially supplied to the surface through the magnetic film. (Japanese Unexamined Patent Publication No. 193325/1983). [Problem to be Solved by the Invention] The above-mentioned prior art still has problems with mechanical reliability, since consideration has not yet been given to keeping a constant amount of lubricant on the surface of the magnetic recording medium. In other words, the lubricant on the surface of the magnetic recording medium is lost due to friction caused by the head, etc., but this surface lubricant is then replenished by the lubricant impregnated in the magnetic film and underlying film seeping out onto the surface. be done. But 17. The number of surface lubricant pockets gradually decreases as the amount of impregnated lubricant decreases, making it impossible to maintain the same amount of lubricant on the medium surface each time the medium is placed on the surface, increasing the frequency of head crashes. An object of the present invention is to propose a magnetic recording medium that can always maintain a constant lubricant on the surface even if scattering loss of the lubricant on the surface of the magnetic recording medium occurs. [Means for Solving the Problems] In order to achieve each of the above objects, a structure is adopted in which the impregnation concentration of lubricant in at least a portion of the inside of the magnetic recording medium is higher than the impregnation concentration of lubricant at the most recent value on the surface of the magnetic recording medium. Ta. The lubricant impregnation profile of the magnetic recording medium is schematically shown in FIG. In general, a magnetic recording medium is composed of a magnetic film and a substrate, and if necessary, a protective film is provided on the magnetic film and an underlayer film is provided between the magnetic film and the substrate. In a medium having a structure in which the magnetic recording medium is impregnated with a lubricant, pores are formed that extend from the surface of the magnetic recording medium to the deep part of the recording medium, and the lubricant is impregnated into the pores. The amount of lubricant impregnated is naturally restricted by the pore density, and a disk impregnated with lubricant corresponding to the pore density is realized. Therefore, a magnetic recording medium is constructed such that the density of pores that can be impregnated with lubricant is higher in the deep part of the recording medium than in the vicinity of the surface of the magnetic recording medium. If enough lubricant is impregnated into the hole to fill it, 2
The magnetic disk of the present invention is realized. However, it is sufficient that the lubricant is sufficiently impregnated to create a concentration gradient, and it is not necessary to completely fill the entire pore. If we rephrase it using the symbols shown in Figure 1, it will be as follows. When the lubricant concentration in the recording medium is represented by C(x, t), what is the saturated impregnation concentration of the lubricant Cs (x)? lI! l corresponds to the impregnable pore density of the lubricant. The structure of the magnetic recording medium of the present invention has a lubricant saturation concentration C of the most recent value on the surface of the magnetic recording medium.
5(L-), it can be written as follows. Cs, a region x such that (x)>Cs (L-)
1<x<X2. Although the above structure can be achieved even with a magnetic recording medium with a single layer of magnetic film,2For example, in the case of a magnetic recording medium with a lower layer film impregnated with lubricant under the magnetic film, specifically, as follows. Achieved with a unique structure. A magnetic recording medium is manufactured so that the impregnation concentration of the lubricant impregnated into the stone layer film is higher than the most recent lubricant impregnation concentration on the surface of the magnetic recording medium. Of course, a magnetic recording medium may be used in which the lubricant saturation concentration of the lower layer film is higher than the lubricant saturation concentration of the nearest value on the surface of the magnetic layer over the entire region of the lower layer film. The conditions at that time can be expressed by the following formula. Cs (x) >Cs (L-) O<x<L, where ILi is the thickness of the lower layer film, and all the above concentrations are expressed as volume percentages in the film. [Operation] Due to the concentration gradient of the lubricant molecules, the lubricant molecules impregnated into the pores of the magnetic film, lower layer film, etc., diffuse through the film in proportion to the concentration gradient, from higher concentration to lower concentration. Move according to. Based on FIGS. 2 and 3, the lubricant movement mechanism in the film and on the surface will be formulated for the case with the lower film. The diffusion equation for the lubricant in the magnetic film and the underlying film can be written as follows. a x, a t i) x a t where Cm and Cu are the lubricant concentrations in the magnetic film and the lower layer film, respectively, and DIIl and Du are the diffusion constants of the lubricant. Furthermore, on the condition that the lubricant does not flow into the substrate at the interface between the lower film and the substrate, the following equation holds true. X From the condition that the flow of lubricant between the magnetic film and the underlying film is conserved. ax ax holds true. By the way, on the magnetic film surface, the lubricant flux 1') Ill
(acm/ax,) is the sum of the amount of lubricant seeping out from inside the magnetic film and the amount of lubricant seeping into the inside from the surface. Since the amount of lubricant that seeps out is proportional to the lubricant concentration of the magnetic film near the two surfaces, it becomes KoCm, where Ko is the proportionality constant. In addition, since the amount of lubricant penetrating is proportional to the amount of lubricant present on the surface, this proportionality constant is defined as Ki9 surface surface lubricant amount I
As "s. K j, T" can be written as s. Therefore, the following equation holds true as a boundary condition for the four surfaces. For example, if the lubricant on surface 6 is removed due to friction caused by the head, and then the lubricant on surface 4 gradually recovers, 9
Recovery according to equation (5). In this case, after a long period of time, an equilibrium state is reached and the flow of lubricant to or from the 4 surfaces stops, so the following equation holds true. X Therefore, the amount of surface lubricant in the equilibrium state is rs (
oo) = (Ko/Ki) Cm (L, oo)
(7) and is proportional to the lubricant concentration in the magnetic film near the 4 surface. As can be seen from this result, if the lubricant concentration near the surface of the magnetic film can be kept constant, the amount of lubricant on the surface of the magnetic recording medium can always be kept constant. The changes over time in the surface lubricant will be schematically compared for four cases with different lubricant concentration distributions shown in FIGS. 4, 5, 6, and 7. In a magnetic recording medium with a lubricant impregnation profile in which the concentration of the impregnated lubricant decreases toward the inside as shown in Figure 4, as the lubricant from one surface is removed, the lubricant reaches an equilibrium state. The concentration gradually decreases both inside and on the surface. In contrast, in a magnetic recording medium as shown in FIG. 5, which has a lubricant impregnation profile in which the concentration of the impregnated lubricant increases toward the inside. The lubricant concentration decreases internally but remains constant at the surface. That is, the lubricant concentration near the surface of the magnetic recording medium gradually decreases from the beginning in FIG. 4, but in FIG. 5, there is almost no change in the surface lubricant at the beginning. Therefore 4
As estimated from equation (7), the lubricant removed by friction caused by the head etc. can be recovered and maintained at a constant level over a long period of time and many times in the case shown in FIG. Also, although Figures 4 and 5 are for the case of a sloped lubricant impregnation profile, the same applies when comparing the structures of stepped lubricant impregnation profiles as shown in Figures 6 and 7. In addition, the two-surface lubricant retaining effect is higher in the case shown in FIG. Note that the wear resistance of the magnetic film is related to the porosity of the surface of the magnetic film, and when the porosity is large, the wear resistance deteriorates and there is a limit value. In this sense. In FIGS. 4 and 5, and FIGS. 6 and 7, the saturation concentration near the surface is kept constant for comparison. As shown in FIGS. 5 and 7, the magnetic recording medium of the present invention has a portion inside the magnetic recording medium where the lubricant impregnation concentration is higher than the lubricant impregnation concentration near the surface of the magnetic recording medium. Due to its concentration gradient, the lubricant on the surface of the magnetic recording medium is supplemented by the lubricant inside, and the amount remains almost unchanged, resulting in a $1. 3 [Examples] Examples of the present invention will be given below and explained in more detail. Example] The paint for forming the magnetic layer (magnetic paint) consisted of 600'ff1ji parts of magnetic powder (CO coated γ-Fe20.), reinforcing agent (α-Fe20.
Add appropriate solvent to 2.0 parts by weight of Al, ○, ) and 380 parts by weight of an epoxy/phenolic binder (mixture of epoxy resin, phenol resin, polyvinyl butyral), and knead with a kneader and a ball mill. ↑) In addition, in order to make the magnetic film porous, a thermally decomposable additive (butene oxy[- and Copolymer of propylene oxide) was added to prepare the paint. The paint for forming the lower M film is 1 liter of magnetic powder (Go10.) 5ξ・0
The heavy foot part was adjusted by appropriately adding 450 parts by weight of a binder based on alcoholic acid and alcohol. In addition. Pyrolyzable additive (copolymer of butene oxide and propylene oxide) to binder at 1.7'-30v, r t
, % and adjust the paint, and the 80 magnetic disc is as shown in ■-1. I created it using the same paint and following the steps in the notes. First, the paint for the lower layer film was applied to the Full Miniram alloy substrate [2 and dried for 7 days. This lower M film was cured at 180°C for 2 hours (primary curing) [1]
．． Add 1 part to the specified surface roughness/film * (1.5 μm)] - Kawa, Mata. Next, the underlayer film was coated with a magnetic paint; l'l+' L and allowed to dry. After polishing, the magnetic and film surfaces are polished and subjected to heavy-duty 2. Predetermined magnetic i*co. :3 l1n
1) ・Gete. Furthermore, a magnetic disk was prepared by applying a lubricant (perfluoropolyether: R Fomblin, manufactured by Senntefu Co., Ltd.) to the surface of the magnetic disk at a constant ratio of 1:1. Lubricant concentration distribution? q
SIMS (Sec, ondary IonMa
s s spec: t r o s co .
p y ) and infrared analysis, the 8th
In Figure (a) 4, the a'a agent coating shown in Figure 4 was obtained; The concentration was approximately 8.3% by volume. In addition, the amount of lubricant deposited per unit area of the magnetic disk was 583 mg/m''. Comparative Example 1 Addition of thermally decomposable additive (copolymer of butene oxide and propylene oxide) to paint for forming the underlayer film A magnetic disk was prepared in the same manner as in Example 1, except that the amount of the binder was 10% by weight and a 6.3 μm lower layer film was formed. The lubricant distribution shown in Figure 8(b) was obtained by evaluating the concentration and adhesion amount of lubricant.The average lubricant concentration in the lower layer film was approximately 4.
6% by volume, average lubricant concentration in the magnetic film is approximately 8°1% by volume
, the amount of adhesion per unit area of the disk is 597 m g
/'m''. Comparative Example 2 A lower layer film with a thickness of about 1.4 μm was formed without adding any thermally decomposable additives to the paint for forming the lower N film. A magnetic disk was prepared in the same manner as in Example].The concentration and adhesion amount of the lubricant were evaluated in the same manner as in Example, and the lubricant 4) cloth shown in FIG. 8(c) was obtained. The average lubricant concentration in the six lower layers was approximately 1.1% by volume,
The average lubricant concentration in the magnetic film is approximately 7.3% by volume, and the amount of lubricant per unit area of the disk is 71%. , m, g/m
It was 2. By the way, the amount of lubricant present on the surface of the magnetic disk is
ESCA (Electron 5pee-tros
eopy for ChemjcalAna
], y s i s )1, and the lubricant on the surface of the magnetic disk is sputtered using Ar+ ions etc. under 1 condition 1. :Thus, the lubricant on the two surfaces can be removed without sputtering the magnetic film. Figure 9 shows the dependence of surface lubricant on the number of sputterings.
In other words, it shows the recovery characteristics of the surface lubricant. These are the results of an ESCA analysis of the lubricant on the surface of the magnetic disks prepared in Example 1 and Comparative Examples 1 and 2 6 to 7 minutes after sputtering. The value shown on the vertical axis indicates the ratio of the peak intensity attributable to the lubricant of the C(Is) peak of ESCA to the peak intensity attributable to the pineapple. Indicates that there are many. As can be seen from the figure, the magnetic disk of Example 8 has a high lubricant recovery ability, and has a high lubricant recovery ability of 2. 6) It can be seen that it recovers to an almost constant value. On the other hand, it can be seen that in the magnetic disks of Comparative Examples 1 and 2, when the lubricant on the two surfaces is removed by sputtering and spread, the amount of surface lubricant to be recovered rapidly decreases. The reason for this is thought to be that the total amount of lubricant impregnated in the magnetic disk of Comparative Example 2 was smaller than that of Example 14. However, although the magnetic disk of Comparative Example is impregnated with almost the same amount of lubricant as Example 1, the surface lubricant has a small recovery ability against repeated spatter. This is because the concentration gradient of the amount of lubricant impregnated, which is a feature of the present invention, does not exist in the comparative example. Incidentally, regarding the recovery characteristics of the surface lubricant of the magnetic disk of Example 1, the results of a simulation are shown in FIGS. 10 and 31. The diffusion mechanism of the lubricant shown in formulas (]) to (7) 7sym, 1γ22. Assume that the lubricant diffuses [11. Experimental 1: "The obtained diffusion constants Dm, u (However, it was assumed that the values are the same for the magnetic film and the T-layer film.) and l (o, and -i were used for simulation. , however, the initial concentration of lubricant is
It is approximated as having a purified form as shown in Figure 10. As shown in Figure 11, even once all the lubricant on the two surfaces is removed, the surface lubricant is almost fully recovered after about 1 minute. Further, the lubricant of the magnetic film is replenished by the lubricant of the F layer film as shown in FIG. 10, and the lubricant concentration near the surface 9 is restored to its original state. This phenomenon is V-'! This continues until the lubricant concentration in the film reaches the lubricant concentration near the surface of the magnetic film. This simulation result does not perfectly match the experimental results because the initial lubricant concentration, diffusion constant, and lubricant diffusion model are approximations, but it does well represent the characteristics of the structure in Example]. I'm here. Below, as shown in experiments and simulations,
In a magnetic recording medium provided with an F-layer film in which a lubricant is impregnated under the magnetic film, the impregnation concentration of the lubricant impregnated into the T-layer film is the most recent level of lubrication on the surface of the magnetic recording medium. In a magnetic recording medium where there is a portion where the lubricant concentration is higher than the lubricant impregnation concentration, even if the lubricant on two surfaces is removed, the lubricant in an amount close to the original amount is repeatedly recovered. Furthermore, as can be seen from one or more Examples and Comparative Examples, the above structure provides the same effect even when the magnetic disk has only a magnetic film without an underlying film, and even when the above structure is provided inside the magnetic film. It is obvious that it will be done. That is, a magnetic recording medium having a structure in which at least a portion of the inside of the magnetic recording medium has a higher lubricant impregnation concentration than the most recent lubricant impregnation concentration on the magnetic recording medium surface of the magnetic film,
It is clear from the principle that this example exhibits excellent lubricant recovery characteristics similar to the above examples. [Effects of the Invention] According to the present invention, even if the lubricant on the surface of the magnetic recording medium is removed due to friction or the like, as described above in Section 4. The lubricant on the surface recovers to a state close to its original state3. Therefore, the lubricant film on the surface of the magnetic recording medium is maintained for a long time without any change over time4, resulting in high mechanical reliability and prevention of head crashes. Such problems will not occur. It goes without saying that the structure of the present invention can be expected to have similar effects not only on coated magnetic disks but also on magnetic recording media such as sputtered or plated disks.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the lubricant impregnation profile of the magnetic recording medium of the present invention, FIG. 2 is a schematic diagram of the cross-sectional structure of the magnetic recording medium of the present invention, and FIG. 3 is a diagram showing the lubrication profile of the magnetic recording medium of the present invention. FIG. 3 is a diagram showing a coordinate system used to formulate the agent diffusion phenomenon. 4, 5, 6, and 7 show the lubricant impregnated into the magnetic recording medium and the lubricant concentration near the surface when the lubricant on the surface of the magnetic recording medium is successively removed. Figure 8 is a model diagram showing how the magnetic recording medium changes over time.
! Figure 9 shows the results of SIMS analysis of lubricant impregnation profile. Figure 9 shows the results of ESCA analysis of the recovery after the lubricant on the surface of the magnetic recording medium is removed by sputtering. . FIG. 11 is a diagram showing the results of a computer simulation of how the lubricant concentration changes in the magnetic film and the underlying film after the surface lubricant of the magnetic recording medium of the present invention is removed. FIG. 6 is a diagram showing the results of a computer simulation of how the surface lubricant recovers after the surface lubricant is removed. 1.Substrate, 2.. Lower layer film, 3.. Magnetic film, 4..
Surface Jundai? Mouth surface Junpo control XI

Claims (1)

[Claims] 1. The concentration of lubricant impregnated in at least a portion of the inside of the magnetic recording medium is higher than the concentration of lubricant impregnated in the vicinity of the surface of the magnetic recording medium, and this concentration gradient lubricates the surface of the magnetic recording medium. A magnetic recording medium characterized by being supplied with an agent. 2. In a magnetic recording medium provided with a lower layer film impregnated with a lubricant under the magnetic film, the lubricant impregnation concentration in the lower layer film is higher than the lubricant impregnation concentration in the vicinity of the surface of the magnetic recording medium. A magnetic recording medium characterized in that the lubricant is supplied to the surface of the magnetic recording medium by the concentration gradient.