JPS618723A - Coating magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain the titled coating magnetic recording medium having a high- elasticity modulus and high-mechanical strength layer by providing a coating layer contg. plural resinous materials having plural functional groups and which can be cross-linked with one another on a supporting body, and forming a reticular structure having more then a specified number of cross-linking points per unit weight of the resinous component. CONSTITUTION:Plural resinous materials having plural functional groups and which can be crossed-linked with one another, e.g., an active OH group-contg. compd. having >=100OH value K of polyol and polyisocyanate having >=10% NCO content L, are allowed to react to obtain a binder wherein the number of corss-linked points may be regulated to 6.0X10<20> per 1g of resin. Magnetic powder is dispersed into the binder, and a magnetic layer is formed on a supporting body by using the mixture. A three-dimensional coating magnetic recording medium having >=600kg/mm.<2> elasticity modulus is thus obtained. Or said reticular structure is incorporated into the topcoat layer provided on the magnetic layer, the backcoat layer of the supporting body, etc. in addition to the magnetic layer. Consequently, the magnetic recording medium having excellent resistance to buckling is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Analysis] The present invention relates to a coated magnetic recording medium having a layer having so-called high mechanical strength, which has excellent elasticity and is less likely to buckle.

[Background technology]

In general, coating-type magnetic recording media are made by forming a magnetic layer using a magnetic paint made by dispersing magnetic powder, additive components as needed, and a binder component in an organic solvent, and blending the binder component as necessary. An undercoat layer is formed using a paint containing a conductive powder material dispersed in an organic solvent, and a back coat or top coat layer is formed using a paint containing a binder component and solid and liquid additive components dispersed in an organic solvent.
Each layer is formed by coating it directly or through another layer on a flexible support such as a polyester film, and drying the whole, and each layer contains a synthetic resin or a binder component. The resin raw material is used. ``Conventionally, it has been proposed to use two types of resin raw materials, polyol and polyisocyanate, as such binder components in the magnetic layer, and to crosslink them with each other to form a strong layer. (Japanese Unexamined Patent Publication No. 56-68928, etc.) Such proposals mainly involve replacing the polyol with a polymer in order to make the two components compatible, in order to uniformly harden the coating film of the magnetic layer of a videotape, which requires mechanical strength. In order to improve wear resistance, the OH value of the polyol is regulated to a specific value, and the glass turning point (T
g).

Although the magnetic layer obtained by this proposal is certainly excellent in terms of wear resistance, it is still not sufficient in terms of its elastic modulus. In the coated magnetic recording medium of
During recording and reproduction, there has been a problem in that the tape buckles due to the force that hits the tape edge due to the travel path restriction such as a tape guide. This problem has traditionally been considered, in part, to be a phenomenon that occurs when the elastic modulus of the tape is low.

There is a view that the elastic modulus of such tapes is mainly controlled by the elastic modulus of the support such as polyester film, but in recent years, with the trend toward higher density recording and space saving of tape cartridges, coated magnetic recording media have become increasingly popular. As attempts have been made to reduce the overall thickness of the U-boop as much as possible, the thickness of the support itself has become extremely thin, and the high elasticity of the support is no longer sufficient to increase the elastic modulus of the entire U-boop and prevent the above-mentioned buckling. It has become difficult to hope to prevent the phenomenon.

Under such circumstances, the present inventors discovered that in order to improve the elastic modulus of coated magnetic recording media such as tapes and prevent the buckling phenomenon, it is necessary to layer the magnetic layer, undercoat layer, top coat layer, and back coat layer. From the viewpoint that the binder should play a role of reinforcing the support, we have come to expect that the binder as the resin component of each layer can be cross-linked and cured at a high density.

[Purpose of the invention]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a coated magnetic recording medium having a coated layer such as a magnetic layer that has a high modulus of elasticity and maintains strength enough to be made thinner.

[Summary of the invention]

In line with the above objective, the present inventors conducted various studies in an attempt to obtain a material with a high elastic modulus. It became clear that it is necessary for the so-called crosslinking points of the three-dimensional network structure to be uniformly contained in a large number of spaces, and as a result of further consideration, ■ In order to ensure that a large number of crosslinking points exist in the reactant. In order to achieve this, it is necessary to carry out the crosslinking reaction using resin raw materials with a high proportion of functional groups. In order to have uniform strength, it is necessary that the plurality of resin components be uniformly mixed so that almost the same number of different functional groups are uniformly present adjacent to each other in every part of the mixed composition. (1) In order to meet the requirements in (1) above, it is sufficient to carry out a crosslinking reaction with a resin raw material having a large number of functional groups in the unit weight range, and (2) In order to meet the requirements in (2) above It has been found that it is sufficient to use two resin raw materials with low molecular weights.

In this case, such a composition includes, for example, a magnetic powder for imparting recording properties in the case of a magnetic layer, and various powders for imparting conductivity or abrasion resistance in a backcoat layer or an undercoat layer. In many cases, materials are mixed in, and in this case, considering the dispersibility of such pigment components, it is best to use a combination of polyol and polyisocyanate in terms of dispersibility. When the system is used in reverse, the conditions of
Determined by the content.

In other words, the OH number defines the total number of OH groups that 14 polyols have, and the hydroxylation value required to neutralize the acetic acid bound to the acetylated product obtained from 1 g of polyol. It means the q number of potassium.

On the other hand, the NCO content means the amount of NC'O groups in one molecule of the incyanate compound (%). Therefore,
When these two are combined, a polyisocyanate with a high NCO content and a polyol with a high OH group may be used together.

Of course, in addition to the above two combinations, it is also possible to use epoxy resin instead of polyol, polyamine or polyamide instead of isocyanate, and the two major curing types of resin raw materials with excellent reactivity, respectively. Nor.

In addition, when mixing an inorganic pigment such as a magnetic powder into the reaction composition, in order to maintain good dispersibility of the mixed composition within the system, Fiber 44 resin having an active OH group, or vinyl chloride containing vinyl alcohol,
A vinyl acetate copolymer or the like may be used in combination, and if the polyol is darkened, the OH values thereof may be added to calculate the OH value of the polyol.

However, in order to construct a three-dimensional structure as a prerequisite for crosslinking and curing both polyols and polyisocyanates, it is necessary to combine the structural units with bondable parts in at least two places and those with bondable parts in three places. In view of the geometrical consideration that the number of functional groups must be the same, it goes without saying that one molecule must have at least an average number of more than two functional groups.

Under this premise, several types of OH group-containing compounds such as polyols and several types of polyisocyanate compounds can be used simultaneously, and if necessary, resins that do not contribute to the crosslinking and curing reaction can be used together. It is also possible to intervene.

In such a case, the number N of crosslinking points per unit weight of the resin binder produced in the reaction of polyol and polyisocyanate can be estimated by the following formula, assuming that there are no unreacted crosslinkable functional groups. OH value (Ml') of the active OH group-containing compound as the i-th component; Xi is the blending amount of the active OH-group-containing compound as the i-th component; lj is the NCO content (Ml') of the polyisocyanate compound as the j-th component; d) The amount zk of the polyisocyanate compound as the yl'ij component is the amount of resin that does not contribute to crosslinking and curing as the second component.

On the other hand, although it has generally been desired that the elastic modulus of the magnetic layer in a thin video tape be on the order of 600 to 800 kq/mm, a magnetic layer with such high elasticity has not yet been obtained.

The present inventors have tried to solve this problem by blending polyols with different OH values and molecular weights and polyisocyanates with different NCO contents and molecular weights, mainly in combinations of polyols and polyisocyanates. As a result, in the above calculation formula, the number of crosslinking points per unit weight N
It has been found that those calculated as 1020 or more OX have a high elastic modulus of 600 kg or more.

Therefore, the OH value and blending amount of the polyol component and the N content of the polyisocyanate component to satisfy such a high elastic modulus are determined.
The CO content and blending amount can be appropriately determined by back calculating the above calculation formula (1).

Polyols that can be used in this invention include acrylic polyols, polyester polyols, polyether polyols, etc.;
As mentioned above, polyisocyanate compounds are incyanates and their adducts having at least two isonoanate groups in the molecule. It reacts and cures with the above polyol to form a three-dimensional polyurethane.

Specific examples of such polyisocyanates include 1-
The m' OH value % of methylbenzo-2.4.6-dolyyl and polyisocyanate, the NCO content and the blending ratio of both can be set according to your own preferences.
More preferably, the OOH value of the polyol is 100 or more, the NCO content of the polyisocyanate is 10% or more, and the blending ratio of polyol to polyisocyanate is 1 equivalent of isocyanate group and 0.8 to 1.2 equivalent of OH group. It is preferable that as much as possible, excess unreacted parts remain after the reaction so that the reaction approaches a complete ideal reaction. The weight ratio of polyol/polyisocyanate will be approximately 3/1 to 1/70. This means that the difference between the first and second terms in parentheses in the molecule of formula (1) above is extremely large. It means less.

Another practical way to achieve a 51-like reaction state without such surplus functional groups is to adjust the g of the polyol and incyanate to an appropriate level so that the polyol and incyanate are uniformly compatible, as described above. In order to achieve this, it is necessary to align each molecular weight value under certain conditions.

According to experiments conducted by the present inventors, the preferred molecular weight range of the polyol is 700 or less, more preferably 550 or less.

On the other hand, the molecular weight of the polyisocyanate is preferably 700 or less.

The improvement in elastic modulus due to the crosslinking reaction as described above is clearly observed in a so-called clear state system containing only polyol and polyisocyanate.

However, on the other hand, each layer constituting a so-called coated magnetic recording medium is rather rare to be in such a clear state, and it is customary to contain some amount of pigment, depending on the content of the pigment. The elastic modulus may also change. A typical layer that requires the inclusion of pigment is a magnetic layer.

Except for special uses, the magnetic layer generally contains 75 to 85 pigment powders based on the entire system, regardless of the type of pigment powder, such as metallic iron powder or iron oxide powder, due to the recording/reproducing characteristics required. .

When the pigment is contained in a proportion close to the upper limit, even if the pigment proportion is slightly increased or decreased, the elastic modulus will change! However, when the weight percentage of the pigment in the entire system becomes less than about 70%, such as in the so-called top coat layer, back coat layer, and undercoat layer, the elastic modulus decreases as the proportion of pigment mixed in decreases. However, this appears to be a roughly linear relationship.

This has traditionally been said to be the reinforcing effect of pigments in the case of turrets. In other words, the elastic modulus of the pigment is 70
Although it is possible to increase the amount to a certain extent by just mixing it into the system up to about 70% by weight, the reinforcing effect of the pigment becomes saturated above that level, so in reality, magnetic material content of 70% or more is required. In the layer, it can no longer be expected that the magnetic index will be further improved by the pigment reinforcing effect, and the method of the present invention based on mutual crosslinking reaction of resin raw materials is particularly important.

The reinforcing effect of the pigment can be achieved when the binder component and the pigment are well-mixed. In particular, since it is not recognized that the elastic modulus changes drastically due to differences in the resin components, it can be said that the approximate elastic modulus in a system with a high pigment concentration can be predicted from the tendency of the elastic modulus in the so-called clear state. .

In the present invention, in addition to the above-mentioned two components, other resin components unrelated to the crosslinking reaction may be used in combination as the binder component, if necessary. As such other binder components, those having good compatibility with the above two components are selected, and specifically, for example, vinyl chloride-vinyl acetate copolymers, polyester resins, etc. can be used.

When such other binder components are used, the weight ratio of the above two components, for example, the total amount of polyol and polyisocyanate compound/other binder components is 179 to 9/1.
It is preferable that the number of crosslinking points is 6×10 2 G or more within the range of 3/7 to 7/3, preferably 3/7 to 7/3.

In this invention, a paint is prepared by dissolving and dispersing the binder component and magnetic powder in an appropriate organic solvent so that the total solid content concentration is usually 30 to 50% by weight, and this is applied to a polyester film, etc. It is applied onto the substrate and cured. As a result, a layer with high surface smoothness and high elastic modulus is formed, in which the pigment optionally mixed into the three-dimensionally structured binder component is fixed in a uniformly dispersed state.

Note that the magnetic powder in the magnetic layer is γ-F.・0・
s Fe・0・ and magnetic iron oxide in the 6n form,・
Oxide type magnetic powder such as Co-containing iron oxide and CrO2, as well as Fe, Co, Fe-Ni alloy, Fe-Co
Metal magnetic powder such as alloy, Fe-Co-Ni alloy, Ni-Co-P alloy, etc. can be used. Further, if necessary, various commonly used additives such as dispersants, lubricants, abrasives, antistatic agents, etc. may be added. In addition, as pigments in the top coat layer, back coat layer, etc., pigments such as lubricating powders such as graphite, conductive powders such as carbon blank, abrasive powders such as chromium oxide, aluminum, calcium carbonate, silicon oxide, etc. are used as appropriate. Similarly to the magnetic layer, various other additives may be added.

The present invention will be explained in detail with reference to Examples below.

Example 1 Metallic iron magnetic powder 100 parts by weight (BET
Specific surface area: 5576 Needle ratio: 1/6) Polyester polyol 5 (Azo→Kani-1-Ace manufactured by Mudenka Co., Ltd.) Y T-400 Polyisocyanate 10 (Dismodule manufactured by Bayer) Methyl isobutyl ketone 70 Cyclohexane 70〃Toluene
70 After mixing and dispersing each of the above components except for the polyisocyanate compound in a ball mill for 488 hours, the above polyisocyanate compound was added thereto and further 1
A magnetic paint was prepared by time mixing and dispersion.

This magnetic paint has a thickness of 10μ and an elastic modulus of 7QQ kg/mm.
It was coated on a polyester base film of 3 µm to a dry thickness of 3 μm, oriented in a DC magnetic field of 3 KOe (Oersted), dried by heating, cured, and calendered. One copy of this was slit into a 2-inch width to make a videotape.

Example 2 Polyester polyol of Example 1 (Azo 4 manufactured by Mudenka Co., Ltd.)
Kanyu Ace Y-cho-400, OH value 550゜Molecular weight 4
00), 10 parts of polyester polyol (Dezumifen 1100, manufactured by Nippon Polyester Co., Ltd., OH value 210, molecular weight 1000) was used, and the polyisocyanate was replaced with Dismodur L manufactured by Bayer (NCO content: 1). - A videotape was made using R (NCO content: 3).

Comparative Example 1 Polyester polyol of Example 1 (Azo manufactured by Mudenka Co., Ltd.)
Power New Ace YT-400, OH value 550.

Polyester polyol (manufactured by Kadenka Co., Ltd. Y-52-11, OH value 1102, molecular weight 1000)
), and the amount of polyisocyanate used was 5 parts.
A videotape was produced in exactly the same manner as in Example 1, except that the video tape was changed to

Comparative Example 2 The polyester polyol of Example 1 (Adekika New Ace YT-400 manufactured by Mudenka Co., Ltd., OH value 550).

Instead of polyurethane polyol (molecular weight 400), polyester polyol Y'l-101 manufactured by Asahi Denka Co., Ltd., OH value 165 was used as described in JP-A-56-68925.

Synthesized by reaction of molecular weight 1000) and tolylene diincyanate (OH value 51.2, molecular weight 30000)
except that 12 parts of polyisocyanate and 3 parts of polyisocyanate were used.
A videotape was produced in exactly the same manner as in Example 1.

The results are shown in the table below. Incidentally, the elastic modulus flexitropism was measured according to the following description.

[Buckling resistance]

6. Roll up a 12.5 width videotape cut into 20 lengths into a cylindrical shape with the magnetic layer on the outside.

3 By measuring the load when the cylindrical tape buckles by applying a load while using an annular groove with nrφ, depth 10mm, and sill width 0.01lIff, we can determine the strength against the force that the tape receives from the edge direction during running. This was used as a guideline.

[Elastic modulus of magnetic layer]

Measure the elastic modulus of the entire tape at 0.5 inch elongation and the elastic modulus of only the polyester base film under the conditions of a sample length of 10α and a tensile speed of 5 mm/min. From the constant values on both sides, calculate the elastic modulus of only the magnetic layer according to the following formula. Find the ratio (phantom/I shoulder').

(dM+ dB) ET - dn Elastic modulus of En magnetic layer - □ (2) d.

dM: Thickness of magnetic layer (CM) dB: Thickness of polyester base film (CIR) E
T: Elastic modulus of the entire tape (#/strength) EB: Elastic modulus of polyester base film (kg/strength) [Elastic modulus of clear film] A sample with a width of 10 + 1 and a length of 10 parts M was pulled at a speed of 20111
The elastic modulus at 2% elongation was measured under the conditions of 111/min.

As is clear from the above table, the magnetic recording medium of the present invention has a large number of crosslinking points per gram of binder, and therefore has a high elastic modulus and excellent buckling resistance. Hereinafter, in order to further clarify the above points, a clear film was prepared and its elastic modulus was measured.

Example 3 Completely the same as Example 1 except that instead of the metal iron magnetic powder used in Example 1, Kinsai Tetsu 4 magnetic powder with a BET specific surface area of 40ッ9 and an acicular ratio of 1/10 was used. A videotape was made.

Example 4 In place of the metal iron magnetic powder used in Example 1, C〇-containing γ-F with a BET specific surface area of 40〃〆/g and an acicular ratio of 1/10 was added.
A videotape was produced in the same manner as in Example 1, except that e203 was used, methyl isobutyl ketone was changed from 70 parts to 55 parts, cyclohexanone was changed from 70 parts to 55 parts, and toluene was changed from 70 parts to 55 parts. . Ml'&i
Zl” child, zu.

Example 5 Vinyl chloride-vinyl acetate copolymer 10 (U, C
, VYHH manufactured by Company C) Polyester polyol 4 (Azokani, -Ace YT-400 manufactured by Asahi Denka) Polyisocyanate 11 (Tesmodur L manufactured by Bayer) MEK 30 Toluene 30 A resin solution with the above composition was prepared and a Teflon sheet was attached. A film was formed on a glass plate having a dry thickness of about 0.5 mm. 4 at 40℃
After drying for 8 hours, a sample with a width of 1α and a length of 10α was prepared for elastic modulus measurement.

Comparative Example 3 Polyester polyol of Example 5 (Adeka New Ace Y'r-400 manufactured by Mudenka Co., Ltd., OH value 550, molecular weight 4
Example 3 except that 10 parts of polyester polyol (Adekanee Ace Y 52-11 manufactured by Asahi Denka Co., Ltd., OH value 110, molecular weight 1ooo) was used instead of 00), and the polyisocyanate was changed from 11 parts to 5 parts. A sample for elastic modulus measurement was prepared in exactly the same manner.
+; : *.

As is clear from the above table, even in the case of clear films, those according to the present invention have a large elastic modulus.

Claims (10)

[Claims] (1) In a coated magnetic recording medium having a flexible support and one or more coated layers provided on the support, at least one of the coated layers has a plurality of coated layers having mutually crosslinkable functional groups. It has a three-dimensional network chain structure produced by a crosslinking reaction of resin raw materials, and the number of crosslinking points due to the reaction is 6.5% per gram of resin component after reaction.
A coated magnetic recording medium characterized in that there are 0x10^2^0 or more. (2) The plurality of resin raw materials having mutually crosslinkable functional groups contain an active OH group-containing compound and a polyisocyanate, and the OH value K of the active OH group-containing compound, the blending amount X of the OH group-containing compound, and the polyisocyanate NCO content L of isocyanate
(%) and the blending amount Y of polyisocyanate, the coating layer is formed by blending the polyisocyanate so as to satisfy the following relationship: Medium. min[1.07×10^1^9ΣKX, 1.43×1
0^2^0ΣLY]/[ΣX+ΣY+Z]≧6.0×1
0^2^0 (However, Z indicates the amount of resin that may be included in the coating layer and does not contribute to the crosslinking curing reaction. Also, min[
A, B] indicates the smaller of A and B. ) (3) The coating type magnetic recording medium according to claim (2), wherein the resin raw material is composed of at least two types, polyol and polyisocyanate. (4) The coated magnetic recording medium according to claim (3), wherein the polyol has an OH number of 100 or more, and the polyisocyanate has an NCO content of 10% or more. (5) The molecular weight of the polyol is 300-1000, and the molecular weight of the polyisocyanate is 250-8.
00. The coated magnetic recording medium according to claim (3). (6) A magnetic layer is provided by applying a magnetic paint containing a magnetic powder group and a plurality of resin raw materials having mutually crosslinking functional groups directly or through another layer onto a flexible support. In the coated magnetic recording medium, the magnetic layer has a structure in which the magnetic powder group, which accounts for 75 to 85% by weight of the whole, is bound by three-dimensional network chains produced by a crosslinking reaction of resin raw materials, and A coating type magnetic recording medium characterized by exhibiting an elastic modulus of 600 kg/mm^2 or more. (7) The BET specific surface area of the above magnetic powder is 40 m^2/g
A coated magnetic recording medium according to claim (6), which is characterized by the above. (8) The coated magnetic recording medium according to claim (6), wherein the resin raw material contains at least two types: polyol and polyisocyanate. (9) The coated magnetic recording medium according to claim (6), wherein the polyol has an OH number of 100 or more, and the polyisocyanate has an NCO content of 10% or more. (10) The polyol has a molecular weight of 300-1000, and the polyisocyanate has a molecular weight of 250-1000.
Claim No. (6) characterized in that: 800
Coating type magnetic recording medium as described in .