JPH0234793B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a recording paper for inkjet recording, and in particular has excellent ink absorbency, the ability to suppress the spread of ink dots, the ability to maintain a high recording density of recorded matter, and a certain degree of water resistance. purpose. Inkjet recording has attracted attention in recent years due to its low noise, easy colorization, high-speed recording, and the ability to use plain paper, and has been applied to various types of facsimile printers. It is expanding. It is generally accepted that plain paper can be used as the recording paper used in the inkjet recording method, but this does not mean that all the common papers widely used in the world can be used.
In order to obtain better recorded materials, the paper itself must meet several conditions. The following conditions can be listed as such: (1) It has excellent ink absorption properties, and ink dots on the paper surface can be quickly absorbed into the paper. (2) Being able to suppress the spread of ink dots on the paper surface. Condition (1) is the most basic condition that an inkjet recording paper must have, but this condition is particularly important when a color image is to be drawn by the inkjet method. In order to draw a color screen, it is necessary to create multiple colors by combining yellow, cyan, and magenta inks, so the amount of ink per unit area increases because different colored inks adhere to the same place on the paper surface. It is from. Condition (2) is a necessary condition for obtaining a vivid recorded matter, and by preventing the ink dots from spreading, it is possible to increase the reflection density of the recorded matter. Generally, the easiest way to increase the reflection density of recorded materials is to increase the concentration of dye contained in the ink, but such methods have limitations due to head clogging, etc., and are not practical. I can't. These conditions (1) and (2) are basic conditions, but
In addition, (3) the ink should not penetrate too deeply in the depth direction, (4) the paper should have excellent whiteness, and (5) the paper should have a certain degree of water resistance. Conditions such as: Condition (3) was derived from the fact that the reflection density of a recorded material is determined mostly by the surface of the paper, so if the penetration in the depth direction is too large, the reflection density cannot be increased. Regarding recording paper for inkjet having the above-mentioned conditions, JP-A-52-74340, JP-A-52-53012, JP-A-53-49113,
There are Japanese Patent Application Laid-open Nos. 55-5830 and 11829-1987. Furthermore, a patent application filed in 1983 by the same applicant
No. 115236 describes an inkjet recording paper containing polyvinylpyrrolidone or a polyvinylpyrrolidone/vinyl acetate copolymer as a surface sizing agent for inkjet recording or a binder for coating. Polyvinylpyrrolidone (abbreviated as PVP), polyvinylpyrrolidone/vinyl acetate copolymer (PVP/VAc) used in this invention
) is an excellent sizing agent or binder for inkjet recording paper.It has high water absorption that cannot be achieved with general binders or polymeric materials, and when combined with an appropriate white filler, It has been found that conditions (1) to (4) of the conditions that the inkjet recording paper should satisfy are fully satisfied. However, these PVP, PVP/VAc
Recording paper using this method has the disadvantage of being significantly inferior in terms of condition (5), that is, the water resistance of the paper. In other words, since PVP and PVP/VAc have excellent ink water absorption, the paper itself inevitably has poor water resistance. For example, on the base paper
20g of PVP/calcium carbonate at a ratio of 1/2/
The coating layer of recording paper prepared by coating ² m2 peels off in about 5 seconds after being immersed in water and dissolves in the water. Of course, we use water-soluble polymer binders such as oxidized starch, PVA, CMC, and hydroxyethyl cellulose.
The situation is somewhat improved by using PVP or PVP/VAc in combination, but in either case the coating layer dissolves in water in about 10 to 15 seconds. Moreover, by increasing the amount of these binders, the ink absorbency decreases. The present invention improves these drawbacks of PVP, PVP/VAc binders or sizing agents, and improves the water resistance of paper without deteriorating ink absorption and recording properties (reflection density, etc.). This is the purpose. And the following polymer materials
It has been found that the above object can be achieved by using it together with PVP and PVP/VAc binder. They are generally polymers of the aqueous emulsion type, such as polyvinyl acetate, ethylene-vinyl acetate copolymers (ethylene content up to 30%), acrylic esters, aqueous silica, and the like. In addition to these materials, alcohol-soluble polymers such as polyvinyl butyral, polyacrylamide, polyamide epichlorohydrin, and silica can also be used. All of these resins are characterized by forming a film with relatively good water resistance after drying. The present invention will be explained in more detail below with reference to actual data. Recording by inkjet was performed using an on-demand type head with a nozzle diameter of 40 μm, and three colors of ink, cyan, yellow, and magenta, were ejected from each of the three inkjet heads. Combinations of these inks produced red, green, blue, and sepia colors. The amount of ink ejected was varied in seven steps by controlling the applied voltage and recorded at 6 lines/mm. The discharge amount per unit area at each stage in the case of a single color is as follows. 1st
Stage, 2.6×10 ^-4 cc/cm ² , second stage, 4.7×10 ^-4
cc/cm ² , 3rd stage, 6.4×10 ^-4 cc/cm ² , 4th stage,
7.0×10 ^-4 cc/cm ² , 5th stage, 7.9×10 ^-4 cc/cm ² ,
6th stage, 8.7×10 ^-4 cc/cm ² , 7th stage, 9.4×
10 ^-4 cc/cm ² . The discharge amount is doubled for red, green, and blue, and tripled for sepia. Therefore, sepia color is the most severe recording condition. In addition to these records, we also made a record of 2 lines/mm. Also, the water resistance rating of paper is 1×2
A cm ² piece of paper was placed vertically in water, and the time required for the coated surface to completely peel off from the base paper was measured. Evaluation of recorded materials involves measuring the reflection density of each color in the seventh step, and determining at what stage of sepia color bleeding or bleeding occurs in order to determine the degree of ink bleeding or bleeding (this indicates the absorbency of the paper). Determine whether. Measurement of how many seconds it takes for the sepia color in the 7th stage to become apparently dry after recording, measurement of the area ratio of the recorded material in the first stage when recording at 2 lines/mm (this is The test was conducted on four items: the degree of spread of ink dots (indicating the degree of so-called blur). Here, PVP has an average molecular weight of 360,000 (abbreviated as K-90), and one with an average molecular weight of 160,000 (K-90).
60), one with an average molecular weight of 40,000 (abbreviated as K-30), and one with an average molecular weight of 10,000 (abbreviated as K-10). No difference was observed, and both had equally good effects. Therefore, the K-30 will be shown as a representative example of the PVP described below. Also, as PVP/VAc, PVP and
VAc ratio is 70/30, 60/40, 50/50, 30/70
In both cases, almost no difference in recording characteristics was observed. Therefore
In the following description, the characteristics of PVP/VAc having a composition ratio of 50/50 will be shown. White pigments or fillers used at the same time include clay, talc, calcium carbonate, calcium sulfate, calcium silicate, zinc oxide, kaolin, aluminum silicate, magnesium silicate, acid clay, activated clay, magnesium oxide, carbonate. There are magnesium, aluminum oxide, etc., and these can be widely used. Example 1 This example shows the results of examining a binder resin in which 10 parts of various polymers were added to 90 parts of PVP. Calcium carbonate (particle size 0.1 to 0.2 μm) in an amount three times that of the binder resin was added to a 10% aqueous or alcoholic solution of the various binder resins as described above, and a slurry was prepared by stirring with a fan. This slurry was applied onto a commercially available coated paper using a wire bar and then pressed using a roll to obtain a surface coated paper. The thickness of the coating layer is 5 to 20 μm, and 0.3 to 2.0 g of coating agent is coated on the A4 paper. The recording paper thus produced was recorded and evaluated according to the method described above. The results are shown in Table 1. The reflection density results are for the magenta stage 7, but the other six colors show essentially the same trend.

【table】

[Table] * indicates methanol solvent In these results, when PVP or PVP/VAc is used alone, the water resistance is 5 seconds or less than 5 seconds, and when PVP or PVP/VAc is used with other water-soluble polymers ( It can be seen that even in a system in which 10% of oxidized starch, PVA, and hydroxyethyl cellulose were added, water resistance hardly improved after about 5 seconds. On the other hand, a binder resin containing 10% of polyvinyl acetate, ethylene/vinyl acetate copolymer, acrylic ester, water-based silica, etc., which forms a highly water-resistant film after drying with water-based emulsion-type polymers, is water-resistant. is 25
It can be seen that the water resistance is significantly improved. At this time, in terms of the recording characteristics of the recorded material, the stage where bleeding occurs is the 7th stage, and the drying time is 13 to 19 seconds.
There is a slight deterioration in recording characteristics compared to when PVP and PVP/VAc are used alone. However, such slight deterioration in properties is practically negligible, and the effect of improving water resistance is much greater. Similar results were obtained when coating was performed using methanol solvent.
That is, it can also be obtained by using polymers such as polyvinyl butyral, polyacrylamide, polyamide/epichlorohydrin, and silica. Other binders include vinyl acetate/acrylic copolymer resin, styrene resin, styrene/acrylic copolymer, vinyl acetate/acrylic copolymer, methacrylate ester, polyamide resin, melamine resin, melamine/urea resin, etc. Can be used. Example 2 This example shows the influence of the amount of polyvinyl acetate added in a binder resin consisting of PVP and polyvinyl acetate. Talc (Manchurian talc) was used as the white pigment. Coating is 10% binder resin
The test was carried out using an aqueous solution containing twice the amount of talc as the binder resin. The method for preparing the coated paper, the thickness of the coating layer, the recording and evaluation methods were all the same as in Example 1. The results are shown in Table 2.

[Table] As is clear from the results, as the amount of polyvinyl acetate added increases, the water resistance improves. However, reflection density, blur characteristics,
On the contrary, properties such as drying time deteriorate as the amount of polyvinyl acetate added increases. For example, drying time
In the system of PVP/polyvinyl acetate = 40/60
This is 49 seconds, which is longer than the time it takes to remove an image from the machine after it is written, and is not suitable for practical use. Considering these conditions, the maximum amount of polyvinyl acetate that can be added is 50% of the binder amount.
%, that is, it is necessary not to exceed the amount of PVP. On the other hand, in a system where polyvinyl acetate was 2% of the binder amount, almost no effect was observed.
It can be seen that it is necessary to add more than %. In this way, the range of addition amounts of various additives was determined. The results are shown in Table 3. This range is influenced to some extent by the type and amount of white filler and the thickness of the coating layer, but does not vary greatly.

【table】

[Table] Example 3 This example shows the characteristics of an inkjet recording paper manufactured by the size press method. A 10% solution of various binders (PVP to additive ratio of 90/10) and calcium carbonate mixed at a ratio of 1:2 was used as a paint and applied to commercially available recycled paper using the size press method. Surface coated paper with a coating weight of 4.0 g/cm ² was obtained. Table 4 shows the recording properties of the coated paper obtained. As is clear from the results in Table 4, the characteristics of the recording paper manufactured by the size press method are essentially the same as those of the recording paper coated with wire bars (Table 1) and are good. . Regarding water resistance, the size press method is slightly better. Therefore, the size press method can be used in the same way as the surface coating method.

【table】

[Table] As described above, the present invention provides an inkjet recording paper characterized in that polyvinylpyrrolidone or polyvinylpyrrolidone-vinyl acetate copolymer is used as a binder for surface coating or a surface sizing agent. , an aqueous emulsion, or an inkjet recording paper characterized by adding a resin that is soluble in alcohol and forms a film with relatively good water resistance after drying, and by adding such additives, The water resistance of paper can be improved without impairing the high ink absorption and high density characteristics of recorded matter, which are originally obtained by using polyvinylpyrrolidone or polyvinylpyrrolidone/vinyl acetate copolymer.

Claims (1)

[Claims] 1 As a binder agent or surface sizing agent for surface coating, in addition to polyvinylpyrrolidone or polyvinylpyrrolidone/vinyl acetate copolymer, polyvinyl acetate, ethylene/vinyl acetate copolymer, acrylic ester, aqueous silica, polyvinyl butyral, polyacrylamide, An inkjet recording paper characterized by containing any one of polyamide, epichlorohydrin, and silica.