JPS5827502B2 - image forming particles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to imaging particles that are particularly useful in electrostatic imaging using fine particles.

Conventionally, as representative image forming methods using fine particles, an electronic distortion method using photoconductive particles as the particles, a Sugarman method, and the like have been proposed.

However, in both methods, charged particles and uncharged particles are selectively distinguished by mechanical or electrical means depending on the charged state of photoconductive particles dispersed on a conductive support. This method was used to obtain particle images.

That is, it is an image forming method that converts a light image into a particle image by utilizing the photoconductive function of the particles themselves, and in the electronic distortion method, a material containing zinc oxide as the main component is used as the photoconductive particle. In addition, it is actually difficult for the photoconductive particles to be arranged on the conductive support in a single layer and as densely as possible, and also for the particles to be in ohmic contact with the conductive support. are in a difficult situation.

Therefore, since the charges of the exposed particles remained, only images with a large amount of fog were obtained.

In addition, in the Sugarman method, due to insufficient contact between the photoconductive pigment particles and the injection electrode, even if exposed to light, sufficient electrons are not injected within the breakdown voltage of air, resulting in images with poor contrast. There was a drawback that I couldn't get it.

Furthermore, it is technically difficult to make the electrostatic properties of individual particles uniform, which further reduces the contrast.

Furthermore, when obtaining a color image using the above-mentioned particles, the colors cannot be superimposed sufficiently due to poor transparency.

Therefore, the obtained image had poor color reproducibility and poor clarity.

The present invention provides novel imaging particles that overcome these conventional drawbacks.

That is, an object of the present invention is to provide image forming particles for obtaining clear images with less fog.

Another object of the present invention is to provide color image-forming particles that are suitable for a method of obtaining a color image with good color reproducibility by one-time exposure and one-time development, and are easy to manufacture.

The present invention relates to light-transmitting particles used for electrostatic image formation in which a photoconductive support is imagewise exposed through particles thereon, the particles being characterized in that they are hollow. .

The basic structure and principle of the method for forming images using the image-forming particles of the present invention is that when particles uniformly distributed on a photoconductive support are irradiated with a light image, the light passes through the particles. reaches the photoconductive support, dissipating the pre-charged charge on the photoconductive support and weakening the electrostatic attraction between the photoconductive support and the particles.

Next, a particle image is obtained by selectively distinguishing between particles that are exerting electrostatic attraction with the support and particles that are not, using mechanical or electrical means.

Therefore, since the particles of the present invention are essentially light-transmissive, when irradiated with light, they do not have the disadvantage of residual charge as in conventional photoconductive particles, and can provide images with less fog. can.

Further, when the conventional particles and the particles of the present invention are irradiated with light, the state in which light passes through the particles is compared as follows.

1 to 4 show the conventional example.

Figures 1 and 2 show the case where the refractive index of particle 1 is 2.0 or less, and parallel light rays irradiated onto the surface of particle 10 are refracted, enter particle 1, and pass through particle 1. The emitted light is in a focused state on the photoconductive support 2.

Moreover, FIG. 3 shows the case where the refractive index of the particle 1 is approximately 2.0, and the irradiated light is focused almost on the circumference of the particle, and is condensed to one point on the photoconductive support 2. be done.

As shown in FIG. 4, when the refractive index of the particles 1 is 2.0 or more, the focal point is inside the particles and the light is condensed on the photoconductive support 2.

Since the refractive index of a typical light-transmitting substance applied to this type of particle is about 1-12 to 2.0, the irradiated light is focused on the photoconductive support. .

Therefore, a portion of the projected area of the particle is irradiated with light, and the remaining portion is not irradiated with light and becomes a shadow.

That is, with respect to the projected area of the particle, only a portion of the charge near the center can be eliminated, which causes fogging or images with poor contrast.

FIG. 5 shows the state in which light passes through the particles of the present invention. The light irradiated onto the surface of the particle 3 is refracted when it enters the particle 3, and further reaches the hollow part 4 inside the particle. The light is refracted to the same angle as that incident on the particle and then passes through the wall 5 of the particle onto the photoconductive support 20 in an extension of the incident light.

Therefore, the area of the shadow part is extremely small compared to the projected area of the particles, eliminating the inconvenience of charge remaining on the photoconductive support even when irradiated with light, providing images with good contrast and little fogging. can do.

In this case, the effect is noticeable when the diameter of the hollow part of the particle is less than % of the particle diameter.

Further, in the case of a material containing a sublimable image forming member, an image can be arbitrarily and easily obtained on a support or a transfer paper by heating.

In addition, the particles according to the present invention can be easily provided with a color separation function using a general-purpose dye, and when a sublimable dye is used as a sublimable image forming member, the sublimable dye can mix colors in a molecular state, so color reproduction is possible. It is characterized by the ability to obtain color images with excellent quality.

Furthermore, it is preferable that the image forming particles have electrical conductivity.

In other words, if the particles are conductive enough to easily receive electrostatic induction without becoming charged due to friction between particles or other objects, there will be no electrostatic attraction between the particles, and the particles will be Because they are electrically independent and the particles do not stick to each other electrostatically, and the particles stick by electrostatic induction of charges imparted to the photoconductive support, the particles do not stick on top of each other. It can be arranged uniformly, layer-wise, and densely on the photoconductive support.

Therefore, a clear image with less fog can be provided.

Furthermore, when the particles are electrically conductive, the charge on the photoconductive support can be easily attenuated, resulting in a clearer image.

Specific materials used in the present invention are shown below.

The image forming member includes a sublimable electron-accepting substance that develops a color by reacting with a sublimable dye and a colorless dye.
It can be classified as a sublimable colorless dye that is normally colorless and develops color upon reaction with an electron-accepting substance.

Colored sublimable dyes include Malachite Green, Tsukushin, Frimodianin B
Triphenylmethane-based basic dyes such as 3B), Miketon Fast Flu IJ Ant Blue B (manufactured by Mitsui Toatsu Chemical Co., Ltd.), Kayalon Fast Flu B R (Nippon Kayaku Co., Ltd.)
Disperse dyes such as Diacel), Nscarletz) B (manufactured by Mitsubishi Chemical Corporation), Sumikalon Yellow 6G (manufactured by Sumitomo Chemical Corporation), Miketon Polyester Scarlet 3R (manufactured by Mitsui Toatsu Chemical Corporation), and Oil Yellow There are oil-soluble dyes such as #140 (manufactured by Sansui Kagakusei ■) and Oil Brown BB (manufactured by Orient Chemical Industry ■).

In addition, as colorless sublimable dyes, Michler's ketone, bis(4-dimethylaminophenyl)methoxyethane, N
-bis(4-dimethylphenyl)methyl-N-ethylaniline, N-bis(4-dimethylphenyl)methyl-(
4-β-hydroxyethyl)aniline, 2-(4'-hydroxy)styryl-3,3-dimethyl-3H-indole, 2(2',4'-methoxyanilinovinylene)-
3,3-dimethyl-3H-indole, 2,7-di(dimethylamino)-7enazine, 2-amino7-dimethylphenazine, 3-dialkylaminobenzofluorane,
2~(omega-substituted vinylene)3-3-2-substituted-3H-
Indole, 4,4' dimethylamino diphenylethylene, 1,4,5,8-tetraaminoanthraquinone, carboxy, amino, alkyl, alkoxy or nitro-substituted triphenyl derivatives, ■-methylamino 4-
Examples include ethanol anthraquinone.

Electron-accepting substances that develop color by reacting with these sublimable colorless dyes include oxalic acid, tartaric acid, trichloroacetic acid, citric acid, malic acid, fumaric acid, citraconic acid, speric acid, maleic acid, hehenic acid, and nano-acid. There are fatty acids and acids with a cyclic structure such as ascorbic acid, phenylacetic acid, salicylic acid, gallic acid, and picric acid.

In addition to these organic acids, inorganic acids such as acid clay, phenolic substances such as bisphenol A, and acidic polymers such as polyparaphenylphenol can be used.

It is also possible to reverse the combination of sublimable colorless dye and electron-accepting substance.

That is, a sublimable electron-accepting substance can be used as the sublimable image forming member, and a colorless dye that develops a color by reacting with the sublimable electron-accepting substance can be used.

Specifically, examples of the sublimable electron-accepting substance include 5-bromsalicylic acid, 5-chlorosalicylic acid, and acetylsalicylic acid.

In addition, as colorless dyes, crystal violet lactone, benzoyl leucomethylene flurhodamine B
lactams, etc.

In addition to the above-mentioned combinations, combinations of couplers and coloring dyes, diazo compounds and phenolic substances, iodine and starch, etc. used in silver salt photography can also be used as image forming members.

When obtaining a color image, it is necessary to impart a color separation function to the image forming particles.

That is, at least one selected from the three additive primary colors.
A color separation function can be provided by a coloring material that transmits color.

The coloring material is used in combination with the above-mentioned image forming member that develops at least one color selected from the three subtractive primary colors.

As such coloring materials, ordinary coloring dyes such as direct dyes, acid dyes, basic dyes, mordant dyes, metal complex dyes, vat dyes, sulfur dyes, naphthol dyes, oil-soluble dyes, and reactive dyes can be used. can.

Pigments with excellent transparency can also be used.

To give a specific example, red light transmitting dyes include C,
I, Andred 6, C01, Acid Red 14, C0
■、Andred 18、C0■、Acid Red 27、C
6■, Acid Red 42, C1I-Acid Red 82,
C0 ■, Acid Red 133, C,1, Acid Red 2
11. There are C,1, Basic Red 14, C,1, Basic Red 27, C01, Basic Red 34, etc.

Green transmitting dyes include C61, And Green 9, C
1■, And Green 27, C01, Acid Green 4
0, C, 1, acid green 43, C0■, basic green 1, C4■, basic green 4, etc.

As the blue transmitting dye, C4I, Acid Blue 23,
C0■, Acid Blue 40, C, I, Acid Blue 62
, C11, Acid Blue 113, C, I, Acid Blue 183, C,1, Direct Blue 86, C,1, Basic Blue, C0 ■, Basic Blue 22, C,
1, Basic Blue 65 etc.

It is also possible to use a mixture of two or more types of dyes.

For example, mixing C,1, Acid Violet 49 and C,1, Acid Blue 1 gives blue transparency, mixing C,1, Acid Red 94 and C,1, Acid Yellow 19 gives red transparency, and further, C,1, , Acid Blue 1 and C,I.

By mixing Acid Yellow 19, it becomes green transparent.

A color image can be obtained by mixing these coloring materials with three types of image forming particles each containing a sublimable dye that develops at least one color selected from the three primary colors of the corresponding subtractive color method.

When this type of sublimable dye is used, an image can be easily and arbitrarily obtained on a support or an image receiving medium by heating, and the dye is capable of superimposing colors in the molecular state. As a result, a color image with good color reproducibility can be obtained.

Note that it is desirable that sublimable image forming members such as sublimable dyes and sublimable electron-accepting substances be sublimed at a temperature of 80 to 220°C under normal pressure. It is desirable that the dyes sublime at approximately the same temperature.

A binder can be used as necessary to granulate and coat the above materials.

As the binder, natural and synthetic resins with excellent transparency can be used.

For example, styrene resin, acrylic ester resin, methacrylic ester resin, polyester resin, petroleum resin, nitrocellulose, acetylcellulose, epoxy resin,
Examples include melamine resin, urea resin, starch, polyvinyl alcohol, gelatin, rosin, etc., and light-transmitting materials are preferable.

In addition to the above, inorganic substances such as glass and silica gel can also be used as the light-transmitting substance.

Next, the structure of the image forming particles will be explained based on the drawings.

Figures 5 to 8 show imaging particles. Particles 3 shown in FIG. 5 have a single-cell hollow structure, and are obtained by dispersing a sublimable image forming member in a light-transmitting binder in particle or molecular dispersion.

Particles 6 shown in FIG. 6 are obtained by changing the single-cell structure to a multi-cell structure, and the effect is almost the same as that of the single-cell structure.

Particles 7 in FIG. 7 have a structure in which a light-transmitting particle 8 having a multicellular structure is used as a core, and the surface thereof is covered with a layer 9 containing a sublimable image forming member.

Further, the particles 3 shown in FIG. 5 can be similarly formed by using single-cell structure particles of a light-transmitting substance as cores, and covering the surface thereof with a layer containing a sublimable image forming member.

Particles 10 in FIG. 8 are formed by forming single cells with multicellular walls in which a sublimable image forming member is dispersed in particles or molecules in a light-transmitting binder.

The shape of the particles of the present invention is preferably spherical, and the particle size is suitably 1 to 50 microns.

Further, the diameter of the hollow portion of the particle is preferably at least % -L of the particle diameter.

Conventional granulation methods can be applied to manufacture the particles of the present invention.

For example, physical methods include transfer granulation, melt granulation, spray drying, fluidized coating, agitation granulation, and surface coating, while chemical methods include interfacial polymerization and submerged curing coating. , a phase separation method from an aqueous solution system, a phase separation method from an organic solution, an in-liquid drying method, a melt dispersion cooling method, a capsule encapsulation exchange method, a powder bed method, etc.

If necessary, it is also possible to use several types of solvents or blowing agents.

Further, distillation methods, plating methods, etc. can also be applied.

Next, the principle of a method for forming an image using the image forming particles of the present invention will be explained based on the drawings.

First, as shown in FIG. 9, a photoconductive support 13 comprising a conductive substrate 11 and a photoconductive substance 12 containing an electron-accepting substance is negatively charged in a dark place using, for example, a corona charger 14. .

At this time, if the photoconductive substance is a P-type semiconductor, it is natural that it will be positively charged.

Next, as shown in FIG.
The particles 16 are electrostatically deposited on the support 14-+r- by scattering on the surface.

At this time, it is desirable that the particles 16 are arranged in substantially one layer.

Next, as shown in FIG. 11, image exposure is performed through the transparent original 17, and the charge in the portion that has passed through the particles 16 is optically attenuated.

Next, as shown in FIG. 12, the photoconductive support 13 obtained in FIG. 11 is vibrated using, for example, an electromagnetic vibrator 18 to remove the particles 16' whose electrostatic attraction has been weakened or removed. In the body 13, a particle image is obtained in which only the particle i (lr') on which the electrostatic attraction is acting remains.

Next, as shown in FIG. 13, the particle image obtained by development is heated by a pressure roller 19 heated to, for example, 100 to 250°C to sublimate the sublimable image forming member in the particles 16, and at the same time When the particles are broken into fine powder, they react with the electron-accepting substance in the photoconductive material 12 to develop color, and as the particles are broken, the colored area is expanded and a dense colored image is obtained.

Next, as shown in FIG. 14, when the broken fine powder of the particles 1g' is removed with a cleaning brush 20, a colored image 21 is obtained on the support 13.

Another image forming method is shown in FIG.

The particles 16'/ After electrostatically transferring the image to the image receiving medium 22, the image quality is as shown in FIG.
The particles on the image-receiving medium 22 are broken into fine powder by the pressure roller 19 heated to 0.degree. The image-receiving medium 2 is then colored by reacting with the acid clay of the particles, and then, as shown in FIG.
A colored image 21 is obtained on 2.

In this case, the photoconductive support 13 does not necessarily need to contain an electron-accepting substance, and a colored photoconductive substance can also be used, and furthermore, it can be used repeatedly.

If a color image is to be obtained, the image forming particles must be at least 3
You need to prepare different types.

That is, particles R that transmit red light and develop cyan color.
1. Particles G transmit green light and develop magenta color, and particles B transmit blue light and develop yellow color.

As shown in FIG. 18, the charge on the support 13 is transmitted through each of the R, G, and B particles of the particles 24 corresponding to the color original 23 consisting of red, green (G), and blue (B). Sensitive to light and attenuated.

12, a particle image as shown in FIG. 19 is obtained. In the same manner as in FIG. 15, the support 13 having the particle image and paper, plastic sheet, etc. The particles 2 are placed in close contact with or in close proximity to the image receiving medium 22 coated with white clay, and are charged by the corona charger 14.
4 is electrostatically transferred onto the image receiving medium 22, as shown in FIG. At the same time, the sublimable image forming member contained in the particles is sublimated to react with the acid clay on the image receiving medium 22 to develop color, and then the 21st
As shown in the figure, when the broken fine powder 25 of the particles 24 is removed by the cleaning brush 20, the part corresponding to red (8) on the color original 23, for example, appears on the image receiving medium 22. Due to the yellow sublimation image forming member in the B particles, magenta and yellow colors are mixed and red can be reproduced.

Green (q) and blue (B) are also reproduced in the same way.Hereinafter,
An example of image formation using the particles of the present invention will be described in detail.

Example] In a 10% by weight aqueous solution of polyvinyl alcohol 2001,
5 tons of malachite green and 20 g of methanol were dissolved and granulated by spray drying, and the resulting Neko 10P was subjected to ECR
-34 (manufactured by Dow Chemical Company) 10% aqueous solution 101
The particles were dispersed in water, spray-dried again, and classified to prepare image-forming particles of 20 to 25 microns.

The particles were in the form of single-cell hollow spheres as shown in Figure 5, and had a specific resistance of 8 x 107 g-.

Next, as a photoconductive support, a 30% by weight toluene solution of styrene-butadiene copolymer was added to
A photoconductive support was prepared by applying a solution of ZEX #4000) 150f (manufactured by Sakai Chemical Industry Co., Ltd.) and acid clay 62 and thoroughly dispersing and mixing the mixture using a ball mill onto aluminum vapor-deposited paper to a film thickness of 10 to 30 microns.

First, the photoconductive support is negatively charged in a dark place using a corona charger to which a voltage of -6 to -7 KV is applied, and then the above-mentioned image forming particles are sprinkled on the surface of the support, and electrostatic attraction is applied to the photoconductive support. After shaking off excess particles that are not affected by
A structure in which particles were arranged in almost a single layer on the surface of the support was obtained.

Next, after image exposure was performed for 5 seconds through a black and white transparent original using an incandescent light bulb as a light source, the support was vibrated.
The particles in the area exposed to light were shaken off, and a positive particle image was obtained on the support relative to the original.

Next, the support body was heated to 180°C and then
After passing the sample under a pressure of 0 kg/crrL, the fine particles remaining on the support were brushed off with a bristle brush, and a green colored image was obtained on the support.

Example 2 The following composition was added to 100P of a 10% by weight aqueous solution of polyvinyl alcohol, and heated at 80°C for 20 minutes while stirring at high speed.
Particles containing the sublimable imaging member were obtained by reacting for a minute.

Methyl methacrylate monomer 201α-α′ Azobisisobutyronitrile 0.6P5-Fromosalicylic acid 2r Ammonium carbonate
0.51 The obtained shakotsuko had a hollow spherical shape with many bubbles as shown in FIG.

The particles were classified to prepare image forming particles having a particle size of 20 to 25 microns.

Next, as a photoconductive support, a 20% by weight solution of Nisder acrylate resin in l. Zinc oxide (
Zazex #4000) 101' manufactured by Sakai Chemical Industry ■ and 4 g of crystal violet lactone, a colorless dye that develops color by reacting with an electron-accepting substance, were mixed thoroughly in a ball mill, and the solution was coated on aluminum vapor-deposited paper with a film thickness of 10 mm. ~30
When a micron coating was prepared and an image was formed in the same manner as in Example 1, a clear blue image was obtained.

Example 3 A sublimable colorless dye 2-(4,'-hydroxy)styryl-3.3- which reacts with an electron-accepting substance to develop a magenta color is added to a 5% by weight aqueous solution of polyvinyl alcohol 3001.
A solution containing 2.51 ml of dimethyl-3H-indole,
Image-forming particles were prepared by coating glass microballoons (manufactured by Toyo Honda) 501 with a particle size of about 30 microns by a fluid coating method.

Next, a particle image was obtained in the same manner as in Example 1 using dye-sensitized and panchromated zinc oxide photosensitive paper obtained by a conventional manufacturing method as a support, and then a 3% by weight solution of tartaric acid in acetone was applied to E-quality paper. in close contact with an image-receiving medium coated with
℃ under a pressure of 10 kg/cm and peeled off, the fine powder of particles remaining on the image receiving medium H was removed with a bristle brush, resulting in a clear magenta color on the image receiving medium. A color image was obtained.

Example 4 Sumitex Resin M-3 (Sumitomo Chemical Co., Ltd. (Melamine resin made by Kiki) θ-) 40% by weight aqueous solution 200? From Rose Bengal 7.1;' and Sumi, Norr Levelingui -
NR (manufactured by Sumitomo Chemical ■)] -2,6? , and 25 g of Metatsuru were added and thoroughly mixed to obtain Solution A.

In addition, 40% by weight aqueous solution 2 of Sumitex Resin M-3
00P, Patent Pure Blue vX (3.6P manufactured by Sumitomo Nii Koku Kagaku Ohgyo (Kiyomi)), Suminol Leveling Yellow NR19,1,P, and 25 g of methanol were added and thoroughly mixed to obtain liquid B.

Furthermore, Acid Violet 6B23. :l'
Then, Patin [Pure Flu VX1.6.8S' and 25 g of methanol were added and thoroughly mixed to obtain liquid C.

When the above liquids A, B, and C were each spray-dried and granulated, particles having a single cell hollow structure and colored red, green, and blue were obtained, respectively, as shown in FIG.

Next, 50P of each of the obtained particles were taken, and for the red particles, 4,4'-dimethylaminodiphenyl, a sublimable colorless dye that develops a cyan color by reacting with an electron tube-soluble substance, was added to a 10% by weight toluene solution of styrene resin (501). Ethylene2. O
It was added together with r and thoroughly stirred to obtain Solution D.

The green particles are a sublimable colorless dye 2-(4,'hydroxy)styryl-3,3-dimethyl 3H that develops magenta color by reacting with an electron-accepting substance in 50 y' of a 10 wt% toluene solution of styrene resin. - It was added together with indole 1-81 and thoroughly stirred to obtain liquid E.

Furthermore, the blue particles were added to a 10% by weight toluene solution of styrene resin (5 M') together with a sublimable colorless dye, Michler's ketone 4.3Z, which develops a yellow color by reacting with an electron-accepting substance, and the mixture was sufficiently stirred to obtain a liquid F.

The above glue, E, and F solutions were spray-dried to obtain image-forming particles whose surfaces were coated with a layer containing a sublimable colorless dye.

The image forming particles are classified into 3 particles each having a size of 20 to 25μ.
01 were taken and thoroughly mixed to obtain color image forming particles.

Next, a dye-sensitized and panchromated zinc oxide photosensitive paper obtained by a conventional manufacturing method was used as a photoconductive support, and -
The color image forming particles mixed with the above three types were shaken off on the surface of the support described in ^↑J after being negatively charged with a corona charger applying a voltage of 6 to -7 KV. 39 Next, a light source with a color temperature of 55,000 was exposed through a color original.
After exposing the particles to light using an incandescent light bulb and developing them using the apparatus described in FIG. pressure 10k
g/Cm between heated pressure rollers, and after peeling, the broken fine powder of particles remaining on the image receiving medium was removed with a bristle brush. Moreover, clear color images were obtained.

As explained above, the image forming particles of the present invention are particularly suitable for 1
It is ideal for obtaining color images with good color reproducibility through multiple exposures and single development.

In other words, because the particles have good transparency, there is little fogging.
In addition, since the particles are hollow, when light is irradiated, there is very little shadow compared to the projected area of the particles, so there is very little charge remaining on the photoconductive support, and there is no fog. This allows an image with good contrast to be obtained.

In addition, when the image forming member contains a sublimable image forming member, an image can be arbitrarily and easily obtained on a support or an image receiving medium by heating.

In addition, these particles can be easily provided with a color separation function using a general-purpose dye, and are easy to manufacture.Furthermore, when forming a color image, a sublimable dye is used as a sublimable image forming member. As a result of superposition of colors in the molecular state of the sublimable dye, a color image with good color reproducibility is obtained.

Further, since the particles of the present invention are easily broken down into fine powder by heating and pressurizing at the same time, color images with even better color reproducibility can be obtained.

[Brief explanation of the drawing]

1 to 4 are diagrams showing the state of light passing through conventional particles, FIG. 5 is a diagram showing a configuration example of the image forming particle of the present invention and the state of light passing through it, and FIGS. Figure 8 is a diagram showing another example of the structure of the image forming particles of the present invention, Figures 9 to 14 are diagrams showing the principle of an image forming method using the particles of the present invention, and Figures 15 to 17 are diagrams showing the principle of an image forming method using the particles of the present invention. FIGS. 18 to 21 are diagrams showing the principle of another image forming method using the particles of the present invention. FIGS. 18 to 21 are diagrams showing the principle of a color image forming method using the particles of the present invention. 3...Particle, 4...Hollow part.

Claims (1)

[Claims] 1. Image-forming particles used in electrostatic image formation in which a photoconductive support is imagewise exposed to light through particles thereon, which are characterized by being optically transparent and hollow.