JPS60136914A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To obtain a magnetic recording medium having a back coat layer without falling off of nonmagnetic powder even after repetitive running and excellent wear-resistance by allowing the back coat layer to contain a specific resin mixture as a binder. CONSTITUTION:The back coat layer contains the mixture where one resin selected from a group of a vinyl chloride copolymer, a phenoxy resin and an expoxy resin is added to a mixture of a thermoplastic polyurethane resin, a saturated polyester resin and a polyisocyanate. Thus, the running stability and the bonding performance with a support due to the decrease in the wear resistance and friction coefficient of the back coat layer are improved and also the adhering force between layers when a magnetic tape is wound is decreased. Thus, the S/N, output fluctuation and dropout or the like are improved in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to magnetic recording media, and particularly to improvements in the back coat layer of a magnetic tape having a magnetic layer on the surface of the support and a bank coat layer on the back surface thereof.

BACKGROUND OF THE INVENTION Magnetic recording media such as magnetic tapes, magnetic sheets, and magnetic disks are widely used in the audio, video, and computer fields. Of these, for example, regarding magnetic tapes that have a magnetic layer as a support and are used in the video field, for example, when a magnetic tape is stored in a cassette, the cassette is inserted into the video deck when recording or playing back images. The tape is guided by guide poles and guide rollers and is slid and scanned by a magnetic head. Images are recorded on magnetic tape in this way, but when playing back the images,
It is required not to degrade image characteristics such as various S/Ns such as chroma S/N, skew, and jitter, and also to prevent output fluctuations and dropouts in which part of the image is dropped. In particular, regarding the sensitivity, in order to improve the output particularly in the high frequency range, the surface of the magnetic layer is finished to be smooth so that the sliding condition of the magnetic tape against the magnetic head does not change. However, when this magnetic tape is run on a video tape, the front and back sides of the magnetic tape are rubbed by the guide poles and guide rolls, so even if the magnetic layer on the front side has good sliding properties against the guide poles and guide rolls, it is still magnetic. If the rubbing properties of the back side of the tape are not good, excessive tension is applied to the running magnetic tape, which causes the magnetic layer to rub excessively against the magnetic head, causing the magnetic Not only is the layer damaged and the magnetic powder in the magnetic layer peeled off, but the tension at which the magnetic tape is wound fluctuates in strength, causing fluctuations in its spinal pressure and causing uneven running of the tape when it is reused. When these things occur, the image characteristics as described above deteriorate. Therefore, a back coat layer is provided on the back side of the magnetic tape.

As described above, this back coat layer is a resin layer containing an inorganic powder as a binder so as to improve the slipperiness against guide poles and guide rolls. This is done by roughening the surface of the back coat layer to reduce the contact area with guide poles, etc., reducing the coefficient of friction and improving slipperiness. This prevents powder from falling off and maintains wear resistance.

In particular, recent video equipment, such as VH3 video movies and β movies, has become smaller and more dense, making it easier to carry. Since it has become possible to manipulate video in various situations where magnetic tape is being taken out, it is hoped that magnetic tape will also be compatible with these conditions. In other words, the miniaturization and higher density of video equipment has made the path of the magnetic tape more complicated, increasing the chances of the tape coming into contact with guide poles and guide rolls, increasing the frequency of friction, and increasing the risk of high-speed outdoor use. Since they are often placed under humid and high temperature conditions, they are required to be resistant to these conditions, and are required to have even better running performance and improved abrasion resistance and durability to prevent powder falling off.

By the way, depending on the type of resin used as a binder, the properties of the bank coat layer, i.e., the abrasion resistance, which means that the inorganic powder does not peel off even after repeated use, the slipperiness when rubbed against the guide pole, and the properties of the back coat layer They differ in adhesion to the support, etc., and improvements have been made to achieve this.

For example, JP-A-57-50327 discloses that binder resins include cellulose resin, thermoplastic polyurethane resin,
One made of a saturated polyester resin and a polyisocyanate is shown. Also, JP-A-56-98719
The publication discloses a binder consisting of a cellulose resin, a thermoplastic polyurethane resin, and a polyisocyanate,
JP-A-58-37840 discloses a binder comprising a fatty acid or fatty acid ester, a cellulose resin, a thermoplastic polyurethane resin, and a polyisocyanate;
-208635 publication describes vinyl chloride-vinyl acetate,
Binder consisting of polyurethane resin and isocyanate, JP-A-57-208636. JP-A-50-92102 discloses a binder consisting of nitrocellulose, vinyl chloride-vinyl acetate resin, polyurethane resin, and an isocyanate compound, and JP-A-50-92102 discloses a binder consisting of a high molecular weight polyester resin containing terephthalic acid and a polyisocyanate. JP-A-50-147309 discloses a binder comprising a polyester type epoxy resin having a hydroxyl group, a cellulose resin, and an isocyanate compound.

However, systems using vinyl chloride-vinyl acetate generally have poor abrasion resistance, adversely affecting running durability and increasing the coefficient of friction, and tend to cause creases in the magnetic tape. Furthermore, a binder system consisting of polyurethane resin alone tends to cause interlayer adhesion when the magnetic layer and back coat layer come into contact with each other when the magnetic tape is wound. Furthermore, a binder system consisting of a polyester resin alone has good abrasion resistance and adhesion to a support, but has the drawback of poor dispersibility with inorganic powder. Conventionally used vinyl chloride-vinyl acetate resin and polyurethane resin systems have drawbacks such as poor wear resistance and an increase in the coefficient of friction after repeated running. In addition, cellulose resin, polyurethane resin systems, cellulose resins, and polyester resin systems have considerably improved properties such as abrasion resistance and friction coefficient, but have weak adhesion to the support and have some problems with durability. Moreover, it has a high coefficient of friction and cannot be said to have sufficient performance as a high-performance video tape. Therefore, improvement has been desired.

OBJECTS OF THE INVENTION A first object of the present invention is to provide a magnetic recording medium having a bank coat layer that is excellent in wear resistance and does not shed non-magnetic powder even after repeated running.

A second object of the present invention is to provide a magnetic recording medium having a bank coat layer that has a small coefficient of friction, excellent running stability, and does not cause winding disturbances after fast forwarding or rewinding.

A third object of the present invention is to provide a magnetic recording medium having a bank coat layer that does not cause interlayer adhesion when the magnetic layer and back coat layer come into contact with each other.

A fourth object of the present invention is to provide a magnetic recording medium having a bank coat layer that has good adhesion to a support and does not peel off even after repeated running.

A fifth object of the present invention is to provide an excellent magnetic recording medium that has excellent image characteristics such as S/N and is free from output fluctuations and dropouts by being provided with a bank coat layer having the above-mentioned properties. be.

Structure of the Invention The above object of the present invention is achieved by adding the below-mentioned resin to a mixture of a thermoplastic polyurethane resin, a saturated polyester resin, and a polyisocyanate as a binder resin for the back coat layer.

To this end, the present invention provides a magnetic recording medium having a magnetic layer on one side of a support and a bank coat layer on the other side of the support, in which the bank coat layer is made of thermoplastic polyurethane resin or saturated polyester as a binder. It is characterized in that it contains a resin mixture in which at least one resin selected from the group of vinyl chloride copolymer resin, phenoxy resin, and epoxy resin is added to a mixture of resin and polyisocyanate.

Next, the present invention will be explained in detail.

Almost all commercially available thermoplastic polyurethane resins can be used in the present invention.

For example, Nistan 5701 (manufactured by Goodlinch Co., Ltd.), Niraporan N-3022 (manufactured by Nippon Polyurethane Co., Ltd.), MA
U-PS-815 (manufactured by Mitsui Nisso Urethane Co., Ltd.), Soflanate j'1S-23 (manufactured by Toyo Tire & Rubber Industries, Ltd.), and Acretan (manufactured by Fujikura Kasei Co., Ltd.). Among these, Soflanate MS-23 , Ahe〇-2070, N-302
2, Nistan 5701 is preferred. The weight average molecular weight of the urethane resin is preferably 1,000 to 230,000, particularly preferably 100,000 to 180,000 for hard type, and 30,000 to 90,000 for soft type, and hard type and soft type are used in combination. is preferable.

Examples of saturated polyester resins include those obtained by condensation polymerization with various dibasic acids and various dihydric alcohols, those obtained by depolymerizing polyethylene terephthalate, and those obtained by newly introducing a diol component and polymerizing the same. The saturated polyester resin known as the product name is Toyobo@
Byron #200, #300, #500, etc. manufactured by Manufacturer.

Examples of the polyisocyanate include 2,4-tolylene diisocyanate, 6-hexamethylene diisocyanate, and triisocyanate (for example, Nippon Polyurethane Industry ■).
``Coronateshi'' (manufactured by Manufacturer) can be used.

As the vinyl chloride copolymer resin used in the present invention, there is one represented by the general formula: in this case,! The molar ratio derived from
~50 mol%. In addition, X represents a monomer residue copolymerized with vinyl chloride, including vinyl acetate, vinyl alcohol, maleic anhydride, maleic anhydride, maleic acid, maleic ester, vinylidene chloride, acrylonitrile, acrylic acid, acrylic Represents at least one member selected from the group consisting of acid ester, methacrylic acid, methacrylic ester, vinyl propionate, glycidyl methacrylate, and glycidyl acrylate.

The degree of polymerization expressed as 1+m is preferably 100 to 60
If the degree of polymerization is less than 100, the magnetic layer tends to become sticky, and if it exceeds 600, the dispersibility becomes poor. The above vinyl chloride copolymer may be partially hydrolyzed. Preferred vinyl chloride resins include vinyl chloride-vinyl acetate copolymers (salt-vinyl acetate copolymers). Examples of salt-vinyl acetate copolymers include vinyl chloride-vinyl acetate-vinyl alcohol, vinyl chloride-vinyl acetate-maleic anhydride, vinyl chloride-vinyl acetate-vinyl alcohol-maleic anhydride, and vinyl chloride-vinyl acetate. Examples include copolymers of -vinyl alcohol-maleic anhydride-maleic acid, and among vinyl chloride-vinyl acetate copolymers, partially hydrolyzed copolymers are preferred.

Specific examples of the above-mentioned vinyl chloride-vinyl acetate copolymers include r VAGHJ, r
VYHHJ, rVMCHJ, "Suresoku ^", "Slec A-5", "Suresoku C", manufactured by Water Chemistry ■
``S-LEC MJ'', ``Denkabinir 100OG J'' manufactured by Denki Kagaku Kogyo ■, ``R-Denkabinir 100OW J'', etc. can be used.

Examples of the epoxy resin used in the present invention include Araldite 6084 (average molecular weight 1740-2050,
Bisphenol A type, manufactured by Ciba Geigy), Araldite 6099 (average molecular weight 4800-8000, bisphenol A type, manufactured by Ciba Geigy), ECN-127
3 (average molecular weight 1080, novolac type, manufactured by Ciba Geigy), Epicote 834 (average molecular weight 1470, bisphenol A type, Shell Chemical M), Epicote 1004
(Average molecular weight 1600, bisphenol A type, manufactured by Shell Chemical) Epicote 1007 (Average molecular weight 2900.
Bisphenol A type, manufactured by Shell Chemical), KPV-6 (
(Urethane modified, manufactured by Asahi Denka) 1. BP-4080 (hydrogenated bisphenol A type, manufactured by Asahi Denka) is mentioned. Among epoxy resins, examples of those classified as phenoxy resins include 5TX-04 (hydrogenated type) and 5TX-05 manufactured by Tobu Kasei, PKHH and PKHCSPKHA manufactured by Union Carbide, and PKHH and PKHCSPKHA manufactured by Dainippon Ink and Chemicals. Ebichron 1030.4030, H-330, I
+-340, ■-350, H-343, etc. are mentioned.

The mixing ratio of the vinyl chloride copolymer resin, phenoxy resin and epoxy resin to the polyurethane/polyester mixed resin in the present invention is as shown in the following table.

Among those shown in the above table, polyurethane 40 is preferably
It is preferable to use 10 to 50% each of vinyl chloride copolymer resin, phenoxy resin, and epoxy resin to 10 to 50% of polyester. As the content ratio of each component increases, the properties of each resin alone will become more apparent; if there is a large amount of polyurethane, the adhesiveness will increase, and if there is a large amount of polyester (the non-magnetic powder (described later)).
Filler) has poor dispersibility and high stickiness. When the mixing ratio of vinyl chloride copolymer resin, phenoxy resin, and epoxy resin increases, problems arise in wear resistance and the like.

In the above example, vinyl chloride copolymer resin, phenoxy resin, and epoxy resin were added individually to a mixture of polyurethane and polyester, but any two of these
A combination or all of the resins may be added.

The polyisocyanate used in the present invention is used in an amount of 5 to 40% by weight based on the total binder amount, preferably 15 to 30% by weight.

If the amount of polyisocyanate used is too small, the curing reaction of the resin in the binder layer will not proceed sufficiently, resulting in poor abrasion resistance of the back coat layer of the magnetic tape. On the other hand, if the amount used is too large, the curing reaction progresses too much, causing adverse effects such as curling of the magnetic tape and residual isocyanate increasing the coefficient of friction. For this reason, it is preferable to use the isocyanate within the above range.

In the present invention, non-magnetic powder is used in the back coat layer in order to improve the sliding of the magnetic tape with respect to guide poles, etc. in a video deck. Examples of this non-magnetic powder include carbon blank. For example, Conductesox (Con) manufactured by Columbia Carbon Company.
ductex) 975 (specific surface area 270 rd/
g, particle size 46 nl), Conductex 950 (specific surface area 245 rtr/g, particle size 46 m, u), Cabot Vulcan, XC
Knee 72 (specific surface area 257 ffr/g, particle size 1B
m, c+), etc.

Non-magnetic powders other than the above carbon black include silicon oxide, titanium oxide, aluminum oxide, chromium oxide, calcium carbonate, zinc oxide, α-Fe203, talc, kaolin, silicon carbide, calcium sulfate, silicon nitride, zinc fluoride, Examples include molybdenum disulfide, among which,
One type or a combination of several types can be used, and these may also be used in combination with the above carbon black.

As the non-magnetic powder, not only inorganic powder but also organic powder can be used. As the organic powder, anything that becomes a solid powder at room temperature can be used, regardless of whether it is a low molecule or a polymer. Examples include henzoguanamine/formaldehyde condensate (trade name: Meiko Poster, manufactured by Nippon Shokubai Kagaku Kogyo Co., Ltd.), phthalocyanine blue, phthalocyanine green, and phthalocyanine red (manufactured by Dainichiseika A1 Co., Ltd.).

In addition to the binder resin described above, the back coat layer in the present invention includes a lubricant commonly used in magnetic recording media,
An antistatic agent and a dispersant may be used in combination.

Effects of the Invention As described above, the present invention provides a thermoplastic polyurethane resin,
Since the back coat layer contains a mixed resin of polyisocyanate and saturated polyester resin with at least one of vinyl chloride copolymer resin, phenoxy resin, and epoxy resin as a binder, the resistance of the back coat layer is improved. By reducing the abrasion resistance and coefficient of friction, running stability and adhesion to the support can be improved, and, for example, glabellar tackiness when magnetic tape is wound can be reduced. With these features, it is possible to improve S/N, output fluctuation, dropout, etc., and satisfy the demand for video equipment that is trending toward smaller size and higher density.

EXAMPLES Next, the present invention will be described in detail with reference to Examples, but the present invention is not limited thereto.

Example 1 A magnetic layer was previously formed on a polyethylene terephthalate support as follows.

Alumina 6 was added to a solution of 130 g of iron-based metal magnetic powder dissolved in 250 g of cyclohexanone and 4 g of phenoxy resin.
This mixture was then dispersed in a sand mill for 4 hours.

Next, 10 g of polyurethane, 1 butyl stearate) 0.
05g, myristic acid 0.1g, cyclohexanone L
A solution of 100 g of Og and tetrahydrofuran dissolved in a mixed solvent was mixed with the above dispersion, and further mixed with a sand mill for 1
Time distribution was performed. 3 g of Coronate L as a hardening agent was added to this dispersion and mixed with stirring to prepare a paint. This coating material was applied onto a base film of polyethylene terephthalate under an orienting magnetic field, further dried, and the dried material was calendered.

Next, the composition of Example 1 shown in Table 1 was milled in a ball mill for 5 minutes.
A coating solution was prepared by kneading for hours. This coating solution was applied to the back surface of the above tape using a reverse roll coater, and then dried to form a back coat layer with a dry film thickness of 0.7 μm, which was slit into 1/2 width to form the magnetic tape of Example 1. It was created.

Examples 2-3 Examples 2-3 were prepared in the same manner as in Example 1, except that instead of using the composition of Example 1 in Table 1, the compositions of Example 2.3 were used, respectively. created a magnetic tape.

Comparative Example 1 In Example 1, the composition of Comparative Example 1 was used instead of the composition of Example 1 in Table 1, and this was milled in a ball mill for 50 minutes.
A magnetic tape of Comparative Example 1 was prepared in the same manner as in Example 1 except that the coating solution was prepared by kneading for a time.

Comparative Examples 2 to 6 Comparative Examples 2 to 6 were prepared in the same manner as in Comparative Example 1, except that the compositions of Comparative Examples 2 to 6 were used instead of the composition of Comparative Example 1 in Table 1. ~6 magnetic tapes were created.

In Table 1, the numbers for the compositions indicate parts by weight; the polyurethane is N-3022 (manufactured by Nippon Polyurethane Co., Ltd.), the polyester is Vylon 200 (manufactured by Toyobo ■), and the vinyl chloride copolymer is VAGH (UCC Co., Ltd., USA). phenoxy resin is PKHH (manufactured by 100 companies in the United States), epoxy resin is Epico-1-1004 (manufactured by Shell Chemical Co., Ltd.), polyisocyanate is Coronat (manufactured by Nippon Polyurethane Co., Ltd.), and calcium carbonate is Homocal D (manufactured by Shiraishi Kogyo Co., Ltd.). Made in Japan, particle size 0.3
μm).

Table 1 The above Examples 1 to 3 and Comparative Examples 1 to 6 were tested for each item shown in Table 2, and the results are shown in the corresponding columns of Table 2.

Here, the state of wear was determined by passing each of the above magnetic tapes through a video deck (NV6200, manufactured by Matsushita Electric Co., Ltd.) 100 times, and observing the degree of abrasion of the bank coat layer using an optical microscope. If there was powder falling off, scratches would be visible on the surface of the back coat layer, so it was evaluated based on whether this was more or less.

Tape damage was evaluated by visually observing the surface of the bank coat layer of the magnetic tape that had been passed through the video deck 100 times, and evaluating the degree of damage as more or less scratched. When abnormal tension is applied to the magnetic tape, large scratches occur on the back coat layer.

For cinching, visually check the condition of the tape after fast-forwarding and rewinding with the above-mentioned video deck.If the winding is neatly wound, it is good, if the sides of the tape are not in one plane and are disordered. It was evaluated as poor.

Adhesion was tested by winding a 1/2 inch wide magnetic tape with a pressure of 1 kg in the same way as in the cinch test above, leaving it at 45°C and 80% relative humidity for 4 hours, then leaving it at room temperature for another 24 hours, then unwinding it. Those with resistance when pulled apart were evaluated as "yes," and those with no resistance were evaluated as "no."

The coefficient of dynamic friction was measured using a rotating drum type surface property measuring device manufactured by Shinto Kagaku Co., Ltd. with a rod having a diameter of 4 m at a load of 40 g and a rotation speed of 157.6 rpm.

The surface roughness was measured using a surface roughness meter (manufactured by Toyo Seimitsu Co., Ltd.).

Adhesion to the support was determined by attaching cellophane tape to the back coat layer, peeling it off, and observing the state after peeling off.

From the results in Table 2, it can be seen that Examples 1 to 3 had good test results, whereas Comparative Examples used polyurethane alone or a vinyl chloride copolymer resin, epoxy resin, or phenoxy resin. Even if each is added separately, it has poor abrasion, scintching, coefficient of dynamic friction, and poor adhesion to the support.
On the other hand, using polyester alone improves the adhesion to the support, but it is not good in other respects (it can be seen that the mixed system of polyurethane and polyester is quite good except for the slight adhesion.And these shortcomings can be improved. Therefore, it is found that it is necessary to mix other resins other than these into the mixture of polyurethane and polyester.

December 26, 1982 Patent applicant: Konishiroku Photo Industry Co., Ltd. Agent: Patent Attorney Tadashi Sano

Claims (1)

[Claims] (11) In a magnetic recording medium having a magnetic layer on one side of a support and a back coat layer on the other side of the support, the bank coat layer is made of a thermoplastic polyurethane resin, a saturated polyester resin and a polyester resin as a binder. A magnetic recording medium comprising a resin mixture obtained by adding at least one resin selected from the group of vinyl chloride copolymer resins, phenoxy resins, and epoxy resins to a mixture of isocyanates.