JPH01250494A - Coating composition for printing paper used in offset rotary printing - Google Patents

Abstract

PURPOSE:To obtain the subject composition, containing a pigment containing a specific amount or more of delaminated clay and a binder and excellent in surface strength and blister resistance. CONSTITUTION:The objective composition containing delaminated clay in an amount of >=30wt.%, preferably >=50wt.% based on the total pigment and a binder (e.g., synthetic rubber latices). Furthermore, kaolin clay, calcined clay, hydrated halloysite, heavy calcium carbonate, titanium white, aluminum hydroxide, barium sulfate, etc., are cited as other pigment.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a coating composition for rotary offset printing paper. More specifically, the present invention relates to a coating composition for rotary offset printing paper that makes it possible to produce coated paper for rotary offset printing with excellent surface strength and blister resistance by using a specific pigment.

(Prior Art) Pigment-coated paper has been used in large quantities as printing paper in recent years because it provides excellent printing effects.

In response to the increase in the number of printed materials, printing speeds have been increased, and in recent years, offset rotary printing has increased significantly. In rotary offset printing, heat-set ink is used, so it undergoes high-temperature drying immediately after printing.

When drying at high temperatures, the water in the coated paper evaporates rapidly, causing rapid expansion within the paper layer, which may cause blisters that destroy the paper layer. Since the occurrence of blisters significantly reduces printing quality, blisters are less likely to occur in rotary offset printing. That is, it is necessary to use coated paper with good blister resistance. Methods for obtaining coated paper with good blister resistance include increasing the strength of the paper layer of the base paper to give it sufficient strength to prevent it from being destroyed by water vapor pressure, and increasing the water vapor permeability of the coating layer to prevent blistering. There is a method of preventing high water vapor pressure from occurring within the paper layer by allowing the water vapor to easily escape from the paper layer.

Attempts to improve blister resistance by using specific coating compositions have been widely made, but basically the aim is to provide the latter mechanism described above.

As a method for imparting blister resistance to a coating composition, there have been many proposals for using a specific binder component in the coating composition, particularly the synthetic polymer latex used as the main binder. However, in all methods of imparting blister resistance using synthetic polymer latex, the surface strength of the coated paper decreases, causing problems such as piling and blanket staining during high-speed printing, and improvements are awaited.

(Problems to be Solved by the Invention) Therefore, an object of the present invention is to provide a coated paper for offset rotary printing that has excellent blister resistance and surface strength sufficient to withstand high-speed printing in offset rotary printing. The object of the present invention is to provide a composition. The present inventors have arrived at the present invention as a result of intensive research into the relationship between pigments and blister resistance, in view of the fact that pigments have not been studied from the viewpoint of blister resistance.

(Means for Solving the Problems) An object of the present invention is to contain delaminate clay in an amount of 30% by weight or more based on the total amount of pigment in a paper coating composition containing a pigment and a binder. This is achieved by using a characterized rotary offset printing paper coating composition.

Paper coating compositions generally consist of pigments, binders, and additives.

Pigments used include inorganic pigments such as clays, calcium carbonate, aluminum hydroxide, titanium oxide, barium sulfate, talc, and satin white; organic pigments known as plastic pigments; and organic pigments with adhesive properties called binder pigments. .

A feature of the present invention is that the total pigment used contains 30% by weight or more of delaminate clay.

Delaminate clay is a type of kaolin clay, which is a type of clay, and is specially treated.

Kaolin clay is generally hexagonal plate-shaped kaolinite (theoretical composition 5io246.54% by weight, A/20359
．． Kaolin from Georgia, USA, which is most commonly used as a paper coating pigment, contains 85 to 95 mt of kaolinite.
Contains %. Kaolinite is produced in the form of stacked hexagonal plate-shaped crystals. This laminated kaolin is separated into plate shapes by shearing force and is called delaminate clay. Further, the process of separating the laminated material into plate shapes is called delamination. Delaminated clay, which is an essential requirement of the present invention, refers to plate-shaped kaolin obtained by delaminating kaolin whose main component is kaolinite.

The present inventors focused their research on the surface memory properties of delaminate clay and found that, surprisingly, pigment-coated paper for rotary offset printing to which a coating composition containing delaminate clay was applied was extremely effective. It was discovered that it has excellent blister resistance and surface strength, and the present invention was completed.

As mentioned above, delaminate clay is not a spherical particle, so it is difficult to specify its particle size, and it is generally considered to be a spherical particle by the sedimentation method, and the equivalent particle size (Eq.
uivalent spherical diamete
It is generally expressed as r ). Delaminated clay can have a desired equivalent particle size depending on the particle size of the clay before delamination treatment and the degree of treatment. The equivalent particle size is expressed as the content ratio of the equivalent particle size portion of less than 2 μns. In general delaminate clay, the content ratio of particles of 2 μm or less is 70 to 85% by weight, and in fine delaminate clay, the content ratio of particles of 2 μm or less is 90 to 98% by weight. Moreover, the coarse delaminate clay has a breath of 2 μm or less of 40 to 65 inches. Layer ratio (aspect ratio) indicating the degree of plate-likeness
o) is thicker as there are fewer particles of 2 μm or less.

The delaminate clay used in the present invention preferably has a large plate-like shape, and coarse-grained delaminate clay gives the best results.

In the present invention, delaminate clay is present at 50% by weight in the total pigment.
It is essential to contain the above amount. If it is less than 30% by weight, good blister resistance cannot be obtained. Preferably it is 50% by weight or more.

Layer ratio of delaminate clay (Fillνcl ratI
The larger J is, the greater the effect is, and the effect is produced even with a small content r4.

In the present invention, three delaminate clays are added to the total pigment.
It is essential to contain at least 0 weight mold, and any pigment can be used as the remaining pigment. The remaining pigments include clays such as kaolin clay, calcined clay, and hydrated halloysite, calcium carbonates such as ground calcium carbonate, ultrafine ground calcium carbonate, and precipitated carbonate, titanium white, aluminum hydroxide, and sulfuric acid. Various inorganic pigments such as barium, satin white, Merck, zinc oxide, etc., and organic pigments such as plastic pigments and binder pigments can be optionally used.

The binder (which is the main component along with the pigment in the coating composition)
Any binder can also be used. Binders include synthetic rubber latex, synthetic polymer resins, synthetic water-soluble polymers, and natural polymers such as powder, casein, and soy protein. It is well known that conventionally, synthetic rubber latexes used as binders in coating compositions for rotary offset printing paper have a relatively low gel content for the purpose of imparting blister resistance. In the present invention, by using delaminate clay, blister resistance can be imparted.
It is no longer necessary to require blister resistance from the synthetic rubber latex used as a binder.

In terms of heat theory, this does not preclude the use of synthetic rubber latexes with good blister resistance as binders.

Various auxiliary materials such as dispersants, pH adjusters, viscosity modifiers, water retention agents, antifoaming agents, lubricants, dyes, fluorescent dyes, coloring pigments, waterproofing agents, and preservatives are necessary as components of coating compositions. It can be used as desired.

Known methods can also be used for applying the coating composition to the base paper for coating in the present invention. Namely - blade coater, f-if coater, used for manufacturing coated paper for boat fishing;
Any of a roll coater, a bar coater, etc. may be used. However, the amount of the coating composition applied to the base paper can be arbitrarily selected.

(Example) The present invention will be described in more detail with reference to Examples below. In addition, parts and parts in Examples and Comparative Examples are based on weight unless otherwise specified.

Examples 1-7, Comparative Examples 1-5 Coating compositions were prepared according to the procedures in Table 1.

A coated paper was obtained by applying the coating composition shown in Table 1 to a base paper to be coated, drying, and supercalendering.

The surface strength (dry and wet) and blister resistance tests of the obtained coated paper were conducted. The results are shown in Table 2.

The test method is as follows.

(Method for measuring gel content of latex) The thickness of the sample latex when dried is 0.21! Pour onto a glass plate with a frame to 20°C.

The dried film was prepared by leaving it for 48 hours at a constant temperature and humidity of 65 SRH. Next, this film is finely divided into about 21111 square pieces, about 0.5 gr of which are precisely weighed, placed in a 100 mesh stainless steel wire gauze that has been accurately weighed in advance, and immersed in benzene 10 OrrLt at room temperature for 24 hours. Thereafter, the wire mesh was taken out and dried in a vacuum dryer for 24 hours, and then accurately weighed to measure the weight of the undissolved components.

(Method for evaluating physical properties of coated paper). Printing was carried out using a Dry Vic Strength RI tester (manufactured by Mei No Seisakusho), and the occurrence of blisters was visually determined. Evaluation was made using a 5-point system, with 5 points being given for cases in which no shock occurred, and 1 point being given for cases in which a noticeable shock occurred.

Using an O Wet Pit 2 strength RI tester (manufactured by Mei Seisakusho), printing was carried out after adding dampening water, and the occurrence of blisters was visually determined. Evaluation points were made using a 5-point system similar to the Dry Vic strength.

Blister-resistant double-sided coated paper was kept in a constant temperature and humidity chamber of 20" Q and 65 SRH for a day and night, and then heated to a predetermined temperature and immersed in a silicone oil bath to determine the degree of blistering. The lowest temperature at which blistering occurred is indicated.The product with a higher minimum temperature at which blistering occurs is superior in blister resistance.

Table 2 shows that the composition of the present invention provides excellent blister resistance and surface strength, whereas the coating composition does not contain delaminate clay or has a content of less than 3ON. In the examples, it can be seen that if the blister resistance is insufficient or if the blister resistance is sufficient, the surface strength is poor.

Claims (1)

[Claims] A paper coating composition for rotary offset printing, characterized in that the paper coating composition contains a delaminate clay in an amount of 30% by weight or more based on the total pigment.