JPH027222A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To lower the coefft. of friction to a guide part and to improve traveling stability by adopting a polyurethane resin contg. an arom. ring as the essential component of the binder of a back coating layer. CONSTITUTION:The arom. ring-contg. component is used for at least either of a polyisocyanate component and polyol component or at least a part of both at the time of synthesizing the polyurethane resin from the above-mentioned two components in order to obtain the polyurethane resin contg. the arom. ring. A coating compd. for back coating consisting of the binder essentially consisting of the above-mentioned resin, nonmagnetic powder, an additive such as lubricating agent to be compounded as desired, and an org. solvent is prepd. This coating compd. is coated on the rear surface side of a nonmagnetic base after or before a magnetic layer is formed on the front surface side. The coefft. of friction is reduced in this way and the traveling stability is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magnetic recording medium such as a magnetic tape, which has a magnetic layer on the front side of a non-magnetic support and a back coat layer on the back side.

[Conventional technology]

In general, magnetic recording media such as magnetic tape have a magnetic layer containing magnetic powder and a binder formed on the surface of a non-magnetic support such as a polyester film, but with the recent increase in the density of magnetic recording, There is a tendency to increase the residual magnetic flux density, improve the output, and reduce noise by reducing the particle size of the magnetic powder used and improving the surface smoothness of the magnetic layer.

However, there is a problem in that the running stability of the magnetic layer deteriorates as the surface smoothness of the magnetic layer increases.
As a means to cope with this problem and to prevent dust from adhering to the non-magnetic support due to charging, it has been common practice to provide a back coat layer on the back side of the non-magnetic support opposite to the magnetic layer.

This backcoat layer is usually Al2O:l, Cr2
o, ,T10! , α Fe20:I , BaSO4
, Ca CO3, B a CO3% M g CO3,
Non-magnetic inorganic compound powder such as SiC and fine particulate carbon black with an average particle diameter of about 0.01 to 0.03 μm are combined with cellulose resin, vinyl chloride-vinyl acetate copolymer, and polyurethane resin. It is made by binding polymer components such as , phenol-based resins, amino-based resins, or the like with a crosslinking agent as a binder. , anti-static properties are achieved through the conductivity of carbon black. In addition, a liquid or semi-solid lubricant such as fatty acids such as stearic acid and myristic acid or esters thereof may be blended into the back coat layer in order to reduce the coefficient of friction (documents unknown). .

[Problems that the invention attempts to solve]

However, in recent years, in order to prevent the irregularities on the surface of the backcoat layer from being transferred to the magnetic layer during winding and causing noise, the surface of the backcoat layer has also tended to be smoothed. A problem has arisen in that the coefficient of friction of the surface of the back coat layer with respect to the guide portion of the recording/reproducing device increases, and sufficient running stability is not achieved.

Also, when adding a lubricant to the back coat layer, if the amount is too large, the surface of the layer will become sticky and adhere to the guide section of recording/playback equipment, causing stains. There are limitations, and it has not been possible to sufficiently reduce the coefficient of friction against the guide portion.

Furthermore, the guide pins in the guide section of recording and reproducing equipment that the back coat layer comes into sliding contact with are made of metal such as stainless steel, and plastic guide pins made of polyacetal. Although it is desirable to have a low coefficient of friction for plastic guide pins, so far, no back coat layer has been realized that can meet this demand, especially a back coat layer that exhibits a sufficiently low coefficient of friction for plastic guide pins.

This invention was made in view of the above-mentioned circumstances, and is a magnetic recording medium that has an extremely low coefficient of friction of the back coat layer against the guide portion of a recording/reproducing device, especially against a plastic guide pin, and has excellent running stability. is intended to provide.

[Means to solve the problem]

As a result of intensive studies to achieve the above object, the inventors found that when a specific polyurethane resin was used as a binder for the backcoat layer, the coefficient of friction of the backcoat layer against plastic guide pins was significantly lower. The coefficient of friction is reduced, and the difference between the coefficient of friction and that of a metal guide pin is small, and the friction coefficient is excellent even when using recording and reproducing equipment equipped with guide pins made of each of the above materials, as well as the same equipment equipped with guide pins made of both materials. It was discovered that the magnetic recording medium can exhibit running stability, and the present invention was completed.

That is, the present invention provides a magnetic recording medium in which a back coat layer formed by binding non-magnetic fine powder with a binder is formed on the back side of a non-magnetic support having a magnetic layer on the front side. The present invention relates to a magnetic recording medium characterized in that the binder is mainly composed of a polyurethane resin containing an aromatic ring.

In addition, in the present invention, in the above magnetic recording medium, the aromatic ring content of the polyurethane resin containing aromatic rings is 0.05.
A preferred embodiment is a composition in a range of 6.0 mmol/g to 6.0 mmol/g.

[Structure and operation of the invention]

The polyurethane resin used as the binder for the back coat layer in this invention has a high glass transition temperature because it contains an aromatic ring as described above, and the surface of the back coat layer containing this resin causes friction due to sliding contact with the guide section of the recording/reproducing device. It is characterized by not becoming sticky even when heated, and the coating film has good scratch resistance.

Therefore, in the magnetic recording medium of the present invention, the coefficient of friction of the back coat layer is lower than that of the conventional material, especially with respect to the plastic guide pin, which has a higher frictional resistance than the metal guide pin and is also prone to high friction due to adhesion. In comparison, the coefficient of friction is significantly reduced and approaches that of a metal guide pin, and as a result, good running stability can be obtained regardless of the material of the guide section of the recording/reproducing device used.

The aromatic ring content of the above polyurethane resin is 0°05~
About 6.0 mmol/g, particularly preferably 2.5 to 5.0 mmol/g.
A value of about 5 mmol/g is good; if it is too low, the glass transition temperature will be low and stickiness will occur; if it is too high, the solubility in the solvent will decrease, making it difficult to prepare a back coat paint. At the same time, the dispersibility of the nonmagnetic fine powder also deteriorates.

Moreover, the number average molecular weight of this polyurethane resin is 10.
000 to 60,000. If it is too small, the mechanical properties such as strength and elasticity, abrasion resistance, and heat and humidity resistance of the back coat layer will be insufficient. On the other hand, if it is too large, the above-mentioned dispersibility problem will occur. As this occurs, it becomes difficult to make it into paint.

To obtain a polyurethane resin containing such an aromatic ring,
When synthesizing a polyurethane resin from a polyisocyanate component and a polyol component, an aromatic ring-containing component may be used for at least a portion of one or both of the above components. In addition, in order to use a polyurethane resin that imparts high elastic modulus and mechanical strength to the back coat layer, at least a part of the polyol component is a high-quality polyester polyol, polyether polyol, polyurethane polyol, polycaprolactone polyol, polycarbonate polyol, etc. It is desirable to use molecular weight polyols.

Among the above polyisocyanate components, those containing an aromatic ring are preferably aromatic diisocyanates having an aromatic ring such as a benzene ring or a naphthalene ring, such as ω・ω′-diisocyanate and 1,3-dimethylpenzole. , ω・ω′-diisocyanate 1,4-diethylpenzole, ω・ω゛-diisocyanate 15-
Dimethylnaphthalene, ω・ω′-diisocyanate n
-Propylbiphenyl, 1,3-phenylene diisocyanate, 1-methylbenzo-2,4-diisocyanate, 1,3-dimethylbenzo-2,6-diisocyanate, naphthalene-1,4-diisocyanate, 1
・5-naphthylene diisocyanate, 1,1'-dinaphthyl-2,2'-diisocyanate, biphenyl-2.
4-perdiisocyanate, 3,3'-dimethylbiphenyl-4,4'-diisocyanate, diphenylmethane-
4,4'-diisocyanate, 2,2'-dimethyldiphenylmethane-4,4'-diisocyanate, 3,3'
-dimethoxydiphenylmethane-4,4'-diisocyanate, 4,4'-dimethoxydiphenylmethane-4,
Examples include 4'-diisocyanate.

On the other hand, as isocyanate components that do not contain aromatic rings, aliphatic and alicyclic diisocyanate compounds such as methylene diisocyanate, ethane diisocyanate, butane-ω・ω'-diisocyanate, hexane-
Examples include ω·ω′-diisocyanate, 2,2-dimethylpentane-ω·ω′-diisocyanate, 2↓2,4-trimethylpentane-ω·ω″-diisocyanate, decandiω·ω′-diisocyanate, and the like.

Further, as the aromatic ring-containing component of the polyol component, an aromatic ring-containing polyhydric alcohol such as hydroquinone-bis(β-hydroxyethyl) ether may be used as a low molecular weight polyol, or an aromatic ring-containing polyhydric alcohol such as hydroquinone-bis(β-hydroxyethyl) ether may be used as a high molecular weight polyol. You may use the thing containing.

Aromatic ring-containing high molecular weight polyols are synthesized from raw materials such as polysalt Ml and polyhydric alcohol for polyester polyol, polyhydric alcohol for polyether polyol,
A polyurethane polyol can be easily obtained by using a compound containing an aromatic ring as at least a part of the polyisocyanate and the polyhydric alcohol. Examples of aromatic ring-containing polybasic acids include isophthalic acid, terephthalic acid, sodium 5-sulfoisophthalate, and ethylene glycol adducts of sodium 5-sulfoisophthalate.
Examples of the aromatic ring-containing polyhydric alcohol and polyisocyanate include those mentioned above.

On the other hand, polyhydric alcohols that do not contain aromatic rings as raw materials for the synthesis of low-molecular-weight polyols and high-molecular-weight polyols include hexanediol, neopentyl glycol,
Examples include 4-butanediol, 1,3-butanediol, diethylene glycol, and the like. Among high molecular weight polyols, examples of polybasic acids containing no aromatic ring in the raw materials for synthesizing polyester polyols include adipic acid, azelaic acid, and sepathic acid.

Suitable commercially available polyurethane resins containing aromatic rings include Toyobo's UR8200 (aromatic ring content: 4.5 mmol/g) and UR8300 (aromatic ring content: 3.4 mmol/g). and so on.

In this invention, the above-mentioned polyurethane resin containing an aromatic ring may be used alone as a binder for the back coat layer, or together with this polyurethane resin, a cellulose resin such as nitrocellulose, a hydroxyl group or a carboxyl group may be used as a subcomponent. Various thermal binders conventionally known as back coat layer binders include vinyl chloride-vinyl acetate copolymers containing or not containing functional groups, polyurethane resins containing no aromatic rings, phenolic resins, amino resins, etc. One or more types of resins, such as plastic or thermosetting resins, or radiation-sensitive resins having unsaturated double bonds that are crosslinked and cured by radiation such as electron beams, may be used in combination. Furthermore, a crosslinking agent component such as an isocyanate compound that reacts with the functional group of the functional group-containing resin to crosslink and cure the resin may be added.

The non-magnetic fine powder blended into the back coat layer includes non-magnetic inorganic compound powder that imparts an appropriate surface roughness to the layer surface and has a reinforcing effect, as well as conductive powder such as carbon black that plays a role in preventing static electricity. be. As the above-mentioned inorganic compound powder, any of various non-magnetic powders conventionally blended in the back coat layer of magnetic recording media can be used, and specific examples thereof include A 120s and Crz0.
3, Tie□, a-]”ex○1, BaSO4, CaC
0, BaCO5, MgC0, SiC, etc., and two or more of these may be used in combination. Moreover, the average particle diameter of these powders is 0. It is preferable that O1 to 0.8 μm. The average particle diameter of the carbon black of the conductive powder is 0.
The thickness is preferably about 0.012 to 0.35 μm.

The amount of these non-magnetic fine powders added to the back coat layer is usually 40 to 400 parts by weight per 100 parts by weight of the binder.
It is preferable to use about parts by weight.

Furthermore, a lubricant and other additives may be added to the back coat layer as necessary. As the lubricant, any lubricant that has been conventionally used in back coat layers of magnetic recording media can be used.

Particularly suitable examples include monobasic fatty acids having about 12 to 18 carbon atoms, fatty acid esters made of these fatty acids and m alcohols having about 3 to 12 carbon atoms, dimethylpolysiloxane, methylphenylsiloxane, and the like.

Formation of the back coat layer in the magnetic recording medium of the present invention may be carried out according to a conventional method, and includes a binder mainly composed of the above-mentioned aromatic ring-containing polyurethane resin, a non-magnetic fine powder, and a lubricant, if desired. A back coat paint consisting of an additive and an organic solvent such as Bye. In addition,
The thickness of this back coat layer is preferably about 0.5 to 2 μm.

Examples of the organic solvent that can be used include ketone solvents such as methyl ethyl ketone and cyclohexanone, ester solvents such as ethyl acetate, alcohol solvents such as isopropyl alcohol, and aromatic hydrocarbon solvents such as toluene. The above may be used in combination.

Further, as the non-magnetic support, in addition to those made of synthetic resin materials such as polyethylene terephthalate and polyamide, those made of non-magnetic metal materials can also be used.

The magnetic layer of the magnetic recording medium of this invention is not particularly limited,
In addition to a coated magnetic layer containing magnetic powder and a binder, it also includes a magnetic layer made of a ferromagnetic metal thin film. The above magnetic powder includes r-FezOs, FesO4, Co-containing r-F
e20. , acicular oxide magnetic powder such as CrO2, Ba,
Plate-shaped ferrite magnetic powder such as Sr, Pb ferrite, F
e, Ni.

Examples include metal magnetic powders such as Co or alloys thereof.

- In addition, the above-mentioned binders include cellulose resins, vinyl chloride-vinyl acetate copolymers, polyurethane resins containing or not containing aromatic rings, phenolic resins, amino resins, and cross-linking with radiation such as electron beams. A radiation-sensitive resin having an unsaturated double bond that hardens is used alone or in combination.
A mixture of two or more types can be used, and a crosslinking agent component such as an isocyanate compound may be added to these.

In addition to the magnetic powder and the binder, various additives such as an abrasive, a filler, an antistatic agent, and a lubricant may be added to the above-mentioned coated magnetic layer as necessary.

〔Effect of the invention〕

Since the magnetic recording medium of the present invention uses a specific polyurethane resin as a binder for the back coat layer, the coefficient of friction of the back coat layer against the plastic guide bin is significantly reduced compared to conventional magnetic recording media. It has the excellent feature of exhibiting good running stability regardless of whether the guide bin of the recording/reproducing device used is made of metal or plastic.

In addition, the above polyurethane resin has an aromatic ring content of 0.
．． By using one having a content of 05 to 6.0 mmol/g, the effect of improving running stability based on the reduction of the friction coefficient described above can be more reliably exhibited.

〔Example〕

Hereinafter, this invention will be specifically explained based on examples.

In addition, in the following, parts mean parts by weight.

Example I Co-containing r FezO5Tli powder 100 parts cyclohexanone myristate Toluene 2 parts 120 parts 120 parts The above composition was thoroughly cross-dispersed using a sand grinder mill, and then a polyisocyanate compound (trade name: Coronet, manufactured by Nippon Polyurethane Co., Ltd.) L) 3 parts to prepare a magnetic paint, and apply this paint to one side of a 14 μm thick polyethylene terephthalate film to a dry thickness of 4.0 μm.
A magnetic layer was formed by coating the magnetic layer in an amount of m, drying, and calendering.

Next, the following composition; cyclohexanone 524 parts toluene
After thoroughly cross-dispersing 524 parts using a sand grinder mill, 17 parts of a polyisocyanate compound (Coronate L described above) was added to prepare a back coat paint. Then, this paint was applied to the surface of the polyethylene terephthalate film opposite to the magnetic layer on which the magnetic layer was formed, so that the dry thickness was 1.0 μm, and dried to form a back coat layer. Video tapes were made by cutting into inch width pieces.

Example 2 Except for changing the amount of polyurethane resin containing aromatic rings used in the back coat paint composition to 50 parts and adding 45 parts of nitrocellulose (Seltsuba 1''; mentioned above).
A videotape was produced in the same manner as in Example 1.

Example 3 A videotape was produced in the same manner as in Example 2, except that the same amount of UR-8300 (described above) was used as the aromatic ring-containing polyurethane resin of the back coat paint.

Comparative Example 1 Example except that the same amount of polyurethane resin that does not contain aromatic rings (trade name: Bandex T-5250, manufactured by Dainippon Ink Co., Ltd.) was used in place of the polyurethane resin that contains aromatic rings in the back coat paint. A videotape was produced in the same manner as in 1.

Comparative Example 2 A videotape was produced in the same manner as in Example 2, except that the same amount of polyurethane resin containing no aromatic rings (same as Comparative Example 1) was used in place of the polyurethane resin containing aromatic rings in the back coat paint. did.

The video tapes of Examples 1 to 3 and Comparative Examples 1.2 were tested for running stability based on the friction coefficient and jitter of the back coat layer by the following methods. The results are shown in the table below.

Friction coefficient〉 SUS with a diameter of 4 cranes finished with a surface roughness of 0.28
A cylinder made of 304 and a cylinder made of polyacecool with a diameter of 4 m and finished with a surface roughness of 0.58 were each supported horizontally.
Hang the videotape at a 90 degree angle with the back coat layer side as the contact surface, and place 30g on one end of the tape.
The stress (T) was determined when the other end was pulled horizontally at a speed of 14 m/sec without applying a load, and this stress (T) was applied to the following formula to determine the coefficient of friction (μ). .

π 30 The friction coefficient μ [M] for the 5O3304 cylinder against the metal guide pin, and the friction coefficient μ (P) for the polyacetal cylinder against the plastic guide pin.

<Sick> Record a white signal on the sample tape using a VTR,
The deviation of the horizontal synchronization signal when this was played back was measured as jitter using a jitter meter.

From the results in the table above, it can be seen that the video tapes of the present invention (Examples 1 to 3) using a polyurethane resin containing an aromatic ring as the binder of the back coat layer are different from those of the conventional structure using a polyurethane resin containing no aromatic ring as the binder. Compared to the videotape (Comparative Example 1.2), the coefficient of friction of the back coat layer against plastic guide pins is significantly reduced, and the coefficient of friction against metal guide pins is also the same or lower. It can be seen that it exhibits low friction and excellent running stability even in recording and reproducing equipment that has guide pins, and is highly effective in reducing jitter.

Claims (2)

[Claims] (1) In a magnetic recording medium in which a back coat layer formed by binding non-magnetic fine powder with a binder is formed on the back side of a non-magnetic support having a magnetic layer on the front side, the binder of the back coat layer is A magnetic recording medium characterized in that the main component is a polyurethane resin containing an aromatic ring. (2) Claim (1) wherein the aromatic ring content of the polyurethane resin containing aromatic rings is in the range of 0.05 to 6.0 mmol/g.
) The magnetic recording medium described in .