JPS61107535A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To form a magnetic recording medium with which a high output and high S/N are obtd. and which has excellent heat resistance, durability, still image stability, etc. by incorporating an urethane resin having a yield point and specific compd. into a magnetic layer. CONSTITUTION:The urethane resin having the yield point and the compd. expressed by the formula 1 are incorporated into the magnetic layer. Since the urethane resin having the yield point is used, the elongation is extremely small even if the stress is exerted to the medium to the yield point and therefore adequate hardness is provided to the urethane resin. Said resin exhibits the property to elongate with the stress without destruction after the yield point and is also provided with adequate resilience and binding power as a binder resin. No substituents are incorporated into the phenyl group existing in the molecule of the compd. expressed by the formula 1 and therefore the durability (more particularly still durability), heat resistance, etc. of the magnetic layer are improved while dispersibility by the phenyl group itself is satisfactorily maintained. The high output and high S/N are thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks.

BACKGROUND OF THE INVENTION Generally, magnetic recording media such as magnetic tapes are manufactured by applying a magnetic paint made of magnetic powder, binder resin, etc. onto a support and drying it.

In such magnetic recording media, urethane resin is generally used as a binder resin for magnetic layers and the like. Conventionally known urethane resins are synthesized from polymeric diols, diisocyanates, chain extenders, and crosslinking agents (used as necessary).

Examples of polymeric diols include polyester diols obtained from adipic acid, butanediol, etc., polyether diols, and polycarbonate diols, and diphenylmethane diisocyanate and the like can be used as diisocyanates.

The chain extender may be ethylene glycol, butanediol, etc., and the crosslinking agent may be polyols, polyamines, etc.

However, although such general urethane resin has excellent flexibility, it lacks hardness, so the mechanical strength of the magnetic recording medium is poor in sliding contact with guide pins, magnetic heads, etc. Moreover, there are problems in terms of runnability and powder shedding. For example, when a polyester type urethane resin, polyvinylidene chloride, or vinyl chloride-vinyl acetate copolymer is used, there are problems particularly in heat resistance and still image stability.

On the other hand, in magnetic recording media, it has been known for a long time to add lecithin (which contains natural phosphoric acid ester as a main component and contains several kinds of higher fatty acids) to a magnetic paint as a dispersant.

However, when lecithin is added, satisfactory results cannot be obtained using a medium that uses finely divided magnetic powder, and there is also the disadvantage that the calender roll is easily soiled during calendering.

With the development of recent magnetic recording media, when urethane resin or lecithin, which is merely soft, is contained in the magnetic layer, the durability1 during running of the medium,
Still image stability, dispersibility of finely divided magnetic powder, etc. are insufficient.

Further, phosphate ester surfactants used in magnetic recording media are disclosed in, for example, Japanese Patent Publication No. 47-26882. Among phosphoric esters, those well known in the field of magnetic recording media include phosphoric esters of compounds in which ethylene oxide is added to aliphatic alcohols or alkylphenols, which are used as dispersants. This is often expressed by the following equation (1).

λ (wherein, The magnetic recording medium used is, for example, the
-21087, JP-A-53-15803, JP-A-53-15803
7-44970″o′!′@report1ciie@1-n+“
6.; The present inventor conducted various studies on these known phosphoric acid esters and found that they had the following problems. That is, in recent years, as the demand for high-strength recording has increased and magnetic powder has become finer, the above (1) has been used in conventional magnetic recording media.
It has been found that the output and S/N ratio cannot be sufficiently improved using the phosphoric acid ester of the formula. That is, especially VB2-? Adding conventional phosphoric acid ester to the magnetic layer is insufficient for video systems such as Beta system, higher-density octavo video, high-definition video, electronic stealth recording, high-density sheet recording, etc. Only magnetic recording and reproduction characteristics can be obtained.

C. OBJECTS OF THE INVENTION An object of the present invention is to provide a magnetic recording medium that can obtain high output and high S/N ratio, and has excellent heat resistance, durability, still image stability, etc.

2. Structure of the invention and its effects, that is, the magnetic recording medium according to the present invention is a magnetic recording medium in which a magnetic layer contains a urethane resin having a yield point and a compound represented by the following general formula.

(However, A is a hydroxyl group, a group coated with 10M (M is an alkali metal), or a group represented by (]XO→CH, CH, O-, n is 1
Get the real number of S30. ) According to the present invention, a urethane resin is used which has a yield point YP as shown in the curve a in FIG. , until the yield point YP, the elongation is very small even when stress is applied, which gives the urethane resin appropriate hardness, and after the yield point YP it shows the property of elongating with stress without breaking, It also has appropriate flexibility and binding strength as a binder resin. As a result, the mechanical strength of the magnetic recording medium improves, preventing damage such as wear during sliding contact.
Powder falling off, etc. is greatly reduced, and running performance is also significantly improved. In particular, magnetic tapes for VTRs do not have edges bent, and the control tracks near the edges can be retained to effectively perform their functions. The above yield point YP is important for the performance of urethane resin, and is 50 to 600'Kg/cI? , preferably 10(1
-560kll/at? It is desirable that the yield point exists in a stress range of (approximately 290 kg/CI? in the example shown in FIG. 1). If the range in which the yield point exists is set to a stress of 50 kg/- or more, the resin will be prevented from becoming too soft, and 600 to 97
cm" or less can prevent the resin from becoming hard and brittle. Also, the urethane resin having this yield point has good dispersibility and improves the durability of the magnetic layer.

In order to exhibit the above-mentioned excellent performance, the urethane resin having a yield point preferably has a cyclic hydrocarbon residue in the molecule. The cyclic hydrocarbon residue is preferably a saturated cyclic hydrocarbon residue, including a divalent or monovalent cyclopentyl group, a cyclohexyl group, etc., or a derivative thereof (for example, a substituted alkyl group such as a methyl group). , a halogen substituted product such as a chlorine atom).
These saturated cyclic hydrocarbon residues are desirable from the viewpoint of imparting appropriate hardness to the urethane resin and availability of raw materials. Further, the bonding position t of this cyclic hydrocarbon residue is preferably placed in the main chain of the urethane resin molecule, but it may be bonded to its side chain. Ninth, by changing the amount of the constituent components having cyclic hydrocarbon residues in the urethane resin, it is possible to obtain a urethane resin with an arbitrary glass transition point (Tg).
0'C5100'C1 is preferably θ°C to 90°C.

Setting Tg to -30'C or higher prevents a decrease in film strength due to softening of the resin (Tg<-30°C),
Further, if the temperature is 100° C. or lower, the film can be prevented from becoming unduly hard and brittle.

Additionally, in the process of arriving at the present invention, the inventor obtained the following new grants. Conventional phosphoric acid esters, especially aromatic phosphoric acid esters of formula (1) mentioned above, are used exclusively as dispersants to improve the dispersibility of magnetic powder, and the phenyl group in the molecule contains an alkyl group. The group is introduced by substitution to form an alkylphenyl group. Therefore, there has been a strong preconception that the phenyl group has poor dispersibility unless it has a substituent such as an alkyl group. However, upon investigation by the present inventor, the above-mentioned dispersibility is determined only by the physical properties of the phosphate ester itself, and when it is actually added to the magnetic layer, In terms of compatibility with various components, no consideration has been given to the behavior of phosphate ester molecules in magnetic paints.
In this regard, the conventional phosphoric acid esters described above have poor compatibility with other components in the magnetic layer because the substituted alkyl group of the alkylphenyl group present in the molecule causes steric hindrance and performs fc5 or a certain movement. It is thought that this results in a decrease in the durability of the magnetic layer.

In contrast, the compound of the present invention having the above general formula (hereinafter referred to as the "compound of the present invention") does not have any substituents introduced into the phenyl group present in the molecule, so the above-mentioned phenomenon does not occur. It is possible to improve the durability (especially still durability), heat resistance, etc. of the magnetic layer while sufficiently maintaining its own dispersibility, and to obtain high output and a high S/R. In this case, the phenyl group in the molecule has lipophilicity and rigidity (r
igid) and exhibits hydrophobicity, while the ethylene glycol residue (4CH,C)1tO-)-) in the molecule exhibits hydrophilicity, so by adjusting the ratio of these two differences, an appropriate HL B can be obtained. (Hydrophiformes c-
Lipophilic Balance (hydrophilic-lipophilic balance) can be obtained.

In the compound of the present invention, in the above general formula, n=1 to ÷CH,CHI in order to maintain the dispersibility of the magnetic powder in the magnetic layer.
When it is O+, it becomes a diester, but for convenience, a medium with preferable characteristics can be obtained by using this diester and a monoester having an AJj hydroxyl group in combination.

Of course, the monoester and the diester may be used alone. Also, as the person in the general formula above,
ONa.

-OK, etc. may be applied, but in this case, it is preferable to add the magnetic powder to the paint after pretreatment with the compound of the present invention.

M9. In the compound of the present invention, by selecting n in the above general formula, the HLB of the compound can be adjusted to 8-5-1.
It is desirable to set it to 4. In other words, if the HLB is small (8), the lipophilicity will be strong, and if it is larger than 14, the hydrophilicity will be strong, and in either case, it is unfavorable as a dispersant for magnetic paints etc. in terms of poor dispersion and stability over time. Sometimes.

The amount of the compound of the present invention to be added to the magnetic skin falls within an appropriate range, preferably from 1 to 10 parts by weight, more preferably from 2 to 7 parts by weight, per 100 parts by weight of the magnetic powder. By adding 17 parts or more, the dispersibility, durability, etc. are sufficient and the surface properties of the layer are improved, and by adding 10 parts by weight or less, the viscosity of the paint is sufficient and the film thickness can be controlled. It becomes easier to do.

Specific examples of the compounds of the present invention are as follows, but are not limited thereto.

Exemplary Compounds ■) Uta Niskel Exemplary Compounds ■ OH Acid Ester Exemplary Compounds ■ Exemplary Compounds ■ Exemplary Compounds ■ Exemplary Compounds ■ Exemplary Compounds ■ Exemplary Compounds ■ In addition, the above-mentioned urethane resin used in the present invention is synthesized by a reaction between a polyol and a polyisocyanate. It is possible. At this time, the following methods (1) to (4) can be employed to introduce the above-mentioned cyclic hydrocarbon residue.

(1) A method in which a polyhydric alcohol having a cyclic hydrocarbon residue in advance is used as a raw material for a polyol (for example, a polymeric diol).

(2) A method in which a dicarboxylic acid having a cyclic hydrocarbon residue in advance is used as an organic dibasic acid (dicarboxylic acid) serving as a raw material for the polyol.

(3) A method in which the polyhydric alcohol and dicarboxylic acid of (1) and (2) above are used as raw materials for polyol.

(4) A method of using a polyhydric alcohol having a cyclic hydrocarbon residue in advance as a chain extender, in combination with any of the above (1) to (3), or alone.

For example, as a synthesis method for obtaining the above urethane resin, 1,
4-di-hydroxymethylcyclohexa(CHz)+
A method of methylene-bis-phenylisocyanation of a polyester polyol obtained from C00H) is exemplified. In this case, the chain extender may be the above-mentioned 1,4-dihydroxymethylcyclohexane or other diols (eg butane-1,4-diol).

As the polyhydric alcohol which may have a cyclic hydrocarbon residue in advance, those having a cyclohexyl group in the molecular chain of the ethylene glycol structure can be used, as described above, but there are also propylene glycol, hydroxyl groups, etc. Glycols such as lengelicol and diethylene glycol, polyhydric alcohols such as trimethylolpropane, hexanetriol, chrycerin, trimethylolethane, and pentaerythritol, or these glycols, or those having cyclic hydrocarbon residues in their structure can be used. Also,
Examples of dibasic acids that can be used include phthalic acid, sulfuric acid, maleic acid, etc., and those having cyclic hydrocarbon residues in their molecules! It will be done. In place of the above polyol, S-caprolactam, α-methyl-1
- caprolactam, S-methyl-8-caprolactam,
Lactone polyester polyols synthesized from lactams such as γ-butyrolactam; or polyether polyols synthesized from ethylene oxide, butylene oxide, etc. may also be used.

These polyols are reacted with incyanate compounds such as tolylene diisocyanate, hexamethylene diisocyanate, methylene diisocyanate, and metaxylylene diisocyanate, thereby synthesizing urethanized polyester polyurethanes and polyether polyurethanes.

These urethane resins according to the present invention usually mainly include:
Produced by the reaction of polyisocyanate and polyol,
It may be in the form of a urethane resin or prepolymer containing free isocyanate groups and/or hydroxyl groups, or it may be in the form of a urethane elastomer that does not contain these reactive end groups.

Further, usable chain extenders may be the polyhydric alcohols exemplified above (which may or may not have a cyclic hydrocarbon residue in the molecule).

In addition, a binder resin containing a phenoxy resin and/or a vinyl chloride copolymer as well as the above-mentioned urethane resin improves the dispersibility of the magnetic powder when applied to the magnetic layer, and increases its mechanical strength. increase However, if only the phenoxy resin and/or the vinyl chloride copolymer is used, the layer becomes hard, but this can be prevented by containing polyurethane, and the adhesion to the support or base layer is improved.

The phenoxy resin that can be used is a polymer obtained by polymerizing bisphenol A and epichlorohydrin, and is expressed by the following general formula.

(However, n=82-13) For example, t is PKHC manufactured by Union Carbide.

There are PKHHSPKHT, etc.

Further, as the above-mentioned vinyl chloride copolymers that can be used, there are those represented by the general formula: In this case, you can smell it! The molar ratio derived from and m is 95-50 mol% for the former unit and 5-50 mol% for the latter unit.

Further, X represents a monomer residue copolymerizable with vinyl chloride, and represents at least one substance selected from the group consisting of vinyl acetate, vinyl alcohol, maleic anhydride, and the like.
The degree of polymerization expressed as (j+m) is preferably 100
-600, and if the degree of polymerization is less than 100, the magnetic layer etc. tend to become sticky, and if it exceeds 600, the dispersibility becomes poor. The above vinyl chloride copolymer may be partially hydrolyzed. As a vinyl chloride copolymer,
Preferably a vinyl chloride-vinyl acetate copolymer (
Hereinafter, it will be referred to as "vinyl chloride-vinyl acetate copolymer."

). Examples of vinyl chloride-vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride copolymers, and vinyl chloride-vinyl acetate copolymers. Among these, partially hydrolyzed copolymers are preferred.
Specific examples of the above-mentioned vinyl chloride-vinyl acetate copolymers include rVAGHJ and rVY manufactured by Union Carbide.
HHJ, ``VMcHJ, Sekisui Chemical's ``S-LEC A''
Jr S-LEC A-5", "S-LEC C", "S-LEC M", "Denkabinyl 100O" manufactured by Denki Kagaku Kogyo Co., Ltd.
GJ, ``Denkabinir 1000 WJ etc. can be used.

In addition to the above, cellulose resins can also be used as binder resins, including cellulose ether,
Cellulose inorganic acid esters, cellulose organic acid esters, etc. can be used. As the cellulose ether, methylcellulose, nityl*rose, etc. can be used.
As the cellulose inorganic acid ester, nitrocellulose, cellulose sulfate, cellulose phosphate, etc. can be used.
Further, as the cellulose organic acid ester, acetyl cellulose, propionyl cellulose, phthyryl cellulose, etc. can be used. Among these cellulose resins, nitrocellulose 2>I is preferred 1. stomach.

In addition, regarding the entire binder composition, the ratio of the above-mentioned urethane resin to other resins (total amount of phenoxy resin, vinyl chloride copolymer, etc.) is 90/1 by weight.
0S40/60'''C is desirable, 85/15
It has been confirmed that S45155 is even more desirable.
Outside this range, if the amount of urethane resin is large, dispersion tends to be poor, and if the amount of other resins is too large, the surface properties tend to be poor, and especially if it exceeds 60% by weight, the physical properties of the coating film become unfavorable overall. It disappears. In the case of vinyl chloride-vinyl acetate, it can be mixed with the urethane resin with a considerable degree of freedom, and preferably the urethane resin is 15 to 75% by weight.

As the binder resin constituting the magnetic recording medium of the present invention, in addition to those mentioned above, thermoplastic resins, thermosetting resins, reactive resins, and electron beam curable resins may be used.

The thermoplastic resin has a softening temperature of 150°C or less and an average molecular weight of 10,000 to 200,000. The degree of polymerization is about 2
For example, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, acrylic ester-styrene copolymer, etc. are used.

The thermosetting resin or reactive resin has a molecular weight of 200,000 or less in the state of a coating liquid, and after coating and drying, the molecular weight becomes infinite due to reactions such as condensation and addition. Moreover, among these resins, those which do not soften or melt before the resin is thermally decomposed are preferable. Specifically, for example, phenol resin, epoxy resin, urea resin, melamine resin, alkyd resin, etc. are used.

Examples of electron beam irradiation-curable resins include unsaturated prepolymers,
Examples include maleic anhydride type, urethane acrylic type, and polyester acrylic type.

In the magnetic recording medium of the present invention, carbon black may be further added to the layer containing the urethane resin. It is desirable that this carbon black has electrical conductivity, but carbon black with light-shielding properties may also be added. Examples of such conductive carbon black include Conductex manufactured by Columbia Carbon Co., Ltd.
) 975 (specific surface area zsom”7g, particle size 24m
μ), Conductex 900 (specific surface area 125m”7)
g, particle size 27 mμ), Palcan (Cab) manufactured by Cabot
ot Vulcan)X C-72 (specific surface area 254
! T! 2/g, particle size 30 mii), Raven 1
040.420, #44 manufactured by Mitsubishi Kasei Corporation, etc. As a light-shielding carbon black, for example, Laben 2000 manufactured by Columbia Carbon Co., Ltd. (specific surface area 190 m") is used.
/ g, particle size 18 rnμ), 2100.1170.1
000, #100, #75, #401# manufactured by Mitsubishi Kasei Corporation
35, #30, etc. can be used. It is desirable for carbon black to have an oil absorption of 90 ml (DBP) or more of 7100 g or more because it tends to form a striated structure and exhibits higher conductivity.

The magnetic recording medium of the present invention has, for example, as shown in FIG.
A magnetic layer 2 is provided on a support 1.

Further, a BC layer 3 is provided on the opposite side of the magnetic layer 2. Although this BC layer may be provided, it is not necessary to provide it. The magnetic powder used in the magnetic layer 2, especially the ferromagnetic powder, is r-pe, o, , C.

Containing r-Fe, o, , Fe1O,, Co-containing Fe, 0
Iron oxide magnetic powder such as 4: Fe%Ni, Co, pe −
4Ji-Co alloy, Fe-Mn-Zn alloy, Fe-Ni
-Zn alloy, Fe -Co-Ni-Cr alloy, Fe -
Co-Ni-P alloy, Co-Ni alloy, etc.)'e, N
Examples include various ferromagnetic powders such as metal magnetic powders containing i, Co, etc. as main components.

Among these, Co-containing iron oxide and metal magnetic powder are preferable. In addition, the BET value of magnetic powder is 25 d/g or more,
Furthermore, in the case of 30 m/g or more, the effect of adding the compound of the present invention is remarkable.

The magnetic layer 2 also contains a lubricant (e.g. silicone oil,
graphite, molybdenum disulfide, tungsten disulfide, fatty acid esters consisting of a monobasic fatty acid with 12 to 20 carbon atoms (e.g. stearic acid) and a monohydric alcohol with 13 to 26 carbon atoms, etc.), abrasives ( For example, fused alumina), antistatic agents (for example, graphite), etc. may be added.

The non-magnetic powder contained in the BC layer 3 includes carbon black, silicon oxide, titanium oxide, aluminum oxide, chromium oxide, silicon carbide, calcium carbide, zinc oxide,
Those made of α-Fe, sulfuric talc, kaolin, calcium sulfate, boron nitride, zinc fluoride, molybdenum dioxide, calcium carbonate, etc., preferably carbon black (especially conductive carbon black) and/or titanium oxide. Can be mentioned.

Further, as the non-magnetic powder, organic powder such as benzoguanamine resin, melamine resin, phthalocyanine pigment, etc. may be added.

Furthermore, the magnetic recording medium in FIG. 2 has a magnetic layer 2 and a support.
6. , ; An undercoat layer (not shown) may be provided between the special holiday 1 and the undercoat layer (not shown), or no undercoat layer may be provided (the same applies hereinafter). Further, the support may be subjected to corona discharge treatment. Further, the BC layer 3 may also contain the urethane resin according to the present invention.

The material of the support 1 may be plastics such as polyethylene terephthalate, polypropylene, etc.
Metals such as Zn, glass, BN, St carbide, porcelain,
Ceramics such as pottery are used.

In addition, when coating and forming the above-mentioned magnetic layer, etc., it is desirable to add a predetermined amount of polyfunctional incyanate as a crosslinking agent to the coating material. Examples of such crosslinking agents include, in addition to the polyfunctional polyisocyanates mentioned above, triphenylmethane triisocyanate, tris-(p-incyanate phenyl)thiophosphite, polymethylene polyphenylisocyanate, and methylene diisocyanate, Tolylene diisocyanate type is preferable.

FIG. 3 shows another magnetic recording medium.
A 00 layer 4 is provided on the magnetic layer 2 of the illustrated medium.

This 00 layer 4 is provided to protect the magnetic layer 2 from damage, etc., and for this purpose, it needs to have sufficient slipperiness. Therefore, as the binder resin for the 00 layer 4, the urethane resin used for the magnetic layer 2 described above is used (preferably in combination with a phenoxy resin and/or a vinyl chloride copolymer). 00 layer 4 interface roughness is female color S/N
Ra≦0.01 μm, Rma) (≦0
．． It is better to set it to 13/jm. In this case, the surface roughness of the support l is Ra≦0.01 μm, Rmax≦0.
It is desirable to use a smooth support 1 with a thickness of 13 μm.

FIG. 4 shows a magnetic recording medium configured as a magnetic disk, with magnetic layers 2.00 similar to those described above on both sides of the support 1.
Layers 4 are provided, and the 00 layer 4 may contain a binder resin containing the above-mentioned urethane resin as a main component.

E, Example Hereinafter, the present invention will be explained with reference to specific examples.

The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention.

After dispersing the ingredients shown in Table 1, apply 1μ of this magnetic paint.
After filtration with an M filter, 5 parts of polyfunctional incyanate was added, coated on a support to a thickness of 5 μm, supercalendered, and 1 part was slit into 2-inch widths and placed on a videotape (for each example and comparative example). (corresponding to the number). However, the numbers after the second column of Table 1 represent parts by weight, and "actual" after the second column represents examples, and "ratio" represents comparative examples.

(Margins below, continued on next page) Polyurethane synthesized from bis(1,4〒4-droxymethyl)-cyclohexane, tripolyurethane synthesized from tophthanediol, and has a molecular weight of approximately 150,000.

Mixtures of H monoester and diester The following measurements were carried out on the videotapes prepared by each of the above methods.

Chroma S/N: Color video noise meter [shiba 5ok
Measured by u925D/IJ.

Lumi S/N: Same as above.

RF output at 4MHz using a VTR deck for measuring RF output.
The specific output was measured and showed a value that was lower than the initial output after 100 reproductions.

(Units: tiB) Still image lifespan: The time it takes for a still image to degrade by 2 dB, expressed in minutes. The larger the value, the higher the durability and wear resistance of the magnetic recording medium.

The performance of each example videotape is shown in Table 2 below.

Table-2 However, 5! For -1, actual -2, ratio -3, and ratio -4, the chroma S/N and luma a/NRF output were determined using the value of ratio -1 as OdB.

Real-3 is chroma S/N with the value of ratio-2 as OdB,
Lumi S/NRF output was determined.

The above results show that the tape performance is significantly improved by adding the compound of the present invention and the urethane resin to the magnetic layer according to the present invention.

[Brief explanation of the drawing]

The drawings show examples of the present invention, in which Fig. 1 is a curve diagram showing the relationship between the stress elongation rate of urethane resin, and Figs. FIG. In addition, in the symbols used in the drawings, 2...
...Magnetic layer 3...Back coat layer (BC layer) 4...
. . . Overcoe) m (OCm).

Claims (1)

[Claims] 1. A magnetic recording medium in which a magnetic layer contains a urethane resin having a yield point and a compound represented by the following general formula. General formula: ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (However, A is a hydroxyl group or a group represented by -OM (M is an alkali metal), or ▲There are mathematical formulas, chemical formulas, tables, etc.▼
The group represented by n is a real number of 1 to 30. }