JP3365266B2 - Base paper for transfer paper - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a base paper for transfer paper used for painting pottery and the like.

[0002]

2. Description of the Related Art Conventionally, in order to paint on an inorganic material such as pottery, glass, or enamel, a paint transfer paper is used, which is immersed in water for slide transfer. As such a painting transfer paper, as shown in FIG. 1, a pigment-containing pigment coating is provided on a no-size base paper (base paper: 1) in order to fill the irregularities and to obtain a more stable picture. An undercoat layer (3) provided with a working layer (2), on which unevenness is adjusted (maintenance of smoothness) and hydrophilic starch (which hardly elutes in water) for holding absorbed water, and On the undercoat layer, a topcoat layer (4) containing a yellow dextrin, a re-wetting paste (which is easily dissolved in water) such as methylcellulose (MC), a printing layer (5) comprising screen printing or offset printing, It is common to have a structure in which an overcoat layer (6) made of an acrylic resin is provided. A back coat layer (7) is provided on the back surface of the base paper to prevent curling.

As a specific method of using the transfer paper having the above-mentioned structure, first, water is applied to the transfer paper to dissolve the topcoat layer containing rewetting glue, and the transfer paper is used as a target. It is applied to the surface, and the printed layer portion is slid with fingers to move it to a predetermined position on the object to be fixed, and then baked at 800 to 1000 ° C. for painting. In this case, the action of the undercoat layer containing a hydrophilic starch located below the topcoat layer is extremely important. That is, the water that has passed through the base paper and the pigment coating layer is sufficiently retained by the hydrophilic starch that is a component of the undercoat layer, and the moisture absorbed by the starch causes rewetting paste such as dextrin in the topcoat layer. After elution promptly, the printing layer (pattern) provided on the top coat layer acts so that it can be smoothly moved and separated by fingers than the smooth hydrophilic starch (undercoat layer) that retains water. It is a thing. In short, the function of the undercoat layer (hydrophilic starch) is that the surface layer is smooth and has excellent water absorbency, elutes the re-wetting paste such as dextrin existing on it, and retains sufficient water content. Thus, the printing layer provided on the top coat layer has a function of smoothly and promptly separating it from the undercoat layer.

Regarding printing for painting on transfer paper, in order to attach importance to the reproducibility of the pattern after printing, a large amount of printing ink containing acrylic resin as a main component is used, and printing by a screen printing method is generally used. Is being done. In this printing, it is extremely important that the printing ink is uniformly transferred onto the topcoat layer containing the rewetting paste. Regarding the actual use of the transfer paper for painting, as described above, the transfer paper is immersed in water to elute the topcoat layer into water, and then the fingers are used to print from the undercoat layer (interface) to the printing layer. The object is achieved by sticking the object on a transfer target object such as pottery. Therefore, the water absorption of the transfer paper is an extremely important quality characteristic. By the way, such transfer paper was manufactured.
Looking at the process, the backcoat layer and surface
Surface has a pigment coating layer, an undercoat layer, and a topcoat layer
Sequentially formed, then on topcoat layer (rewetting glue layer)
Screen printed on the printed layer
The transfer coat is completed with the overcoat layer.
It At this time , when a component other than the re-wetting glue layer, for example, a component (which cannot be specified) contained in the undercoat layer elutes and reaches the topcoat layer portion, in the next step ,
Perform printing over a multi-layer by printing ink solvent system to the top coat layer, further, it is intended that the overcoat layer according to an acrylic resin is provided thereon, is said to that time Ha <br/> magnetic phenomena However, a so-called defective portion of a pattern is generated, and when a pattern is printed on an object, a defective portion is often generated, resulting in a decrease in commercial value.

[0005]

According to the present invention, the layer constitution is the same as that of the conventional one, and in particular, the printing layer (pattern) is used.
By improving the base paper for transfer paper before the provision of the sheet, a repellency phenomenon is effectively eliminated, and a base paper for transfer paper that can be finished as a transfer paper capable of printing a beautiful pattern with excellent reproducibility is provided. It is a thing. That is, the present invention uses a non-size base paper or a base paper of a small size (base paper) as a base paper which is the base of the base paper for the transfer paper as in the conventional case, and the pigment and the adhesive are applied to one surface of the base paper. To form a support by providing a pigment coating layer containing as a main component, an undercoat layer containing hydrophilic starch as a main component on the pigment coating layer, and dextrin or methylcellulose (MC) on the undercoat layer. A base paper for transfer paper, which is formed by applying a water-soluble liquid containing a rewetting paste, etc., and drying it to form a topcoat layer, and further providing a backcoat layer on the back surface of the support for the purpose of preventing curling,
Especially in the undercoat layer whose main component is hydrophilic starch,
It is a base paper for transfer paper, which contains a copolymer latex and a waterproofing agent.

[0006]

SUMMARY OF THE INVENTION The present invention comprises an undercoat layer containing starch and a rewetting paste on a support comprising a base paper and a pigment coating layer containing a pigment and an adhesive as main components. A base paper for transfer paper comprising a top coat layer and a back coat layer provided on the back surface of a support, wherein the undercoat layer contains a copolymer latex and a waterproofing agent. is there. Furthermore, in a more preferred embodiment, the copolymer latex and the water-proofing agent are starch 1 which are the main components of the undercoat layer.
0.05 to 10 parts by weight,
And 0.1 to 1.0 parts by weight of the raw material for transfer paper.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the base paper for transfer paper according to the present invention has a base paper, a pigment coating layer containing a pigment and an adhesive as main components, and a hydrophilic starch on one surface thereof. An undercoat layer containing a main component and a topcoat layer containing a water-soluble rewetting paste such as dextrin as a main component are sequentially provided, and a backcoat layer for curling is provided on the back surface of the base paper. It is taken. By incorporating a copolymer latex and a water-proofing agent in the undercoat layer, the cissing phenomenon often seen in the past when used as a transfer paper is eliminated, and a beautiful printed pattern with excellent reproducibility can be obtained. The present invention has been completed and the present invention has been completed.

The undercoat layer is made of a hydrophilic starch, and its action and function are such that it has a sufficient water-absorbing ability and does not dissolve itself by water absorption, while maintaining its shape. , The upper layer of topcoat layer (rewetting glue / for example, dextrin) is dissolved by the absorbed water, and the printing layer formed on the topcoat layer is made smoother than that on the undercoat layer through the eluted rewetting glue. It functions as a medium for sliding and moving it onto the transfer target. Therefore, the undercoat layer is
It is important to have sufficient water absorption capacity and water retention capacity and to be able to maintain a smooth state.

On the other hand, regarding the constitution of the base paper for transfer paper, the support before the formation of the undercoat layer is formed of the base paper and the pigment coating layer containing the pigment and the adhesive as the main components on the base paper. It is a thing. In this case, the pigment coating layer is used as it is or in a state where supercalendering is performed. As a result, the unevenness inherent in the base paper is eliminated or reduced, and an undercoat layer is usually added thereon in an amount of 0.5 to 2.5 g / m ² (as solid content).
A smooth layer can be obtained by coating. Furthermore, by applying a topcoat layer of rewetting glue on the undercoat layer in an amount of ² to 4 g / m ² , a clear pattern without cissing can be obtained when the final product, transfer paper, is finished. It is a thing. In this way, since the base paper for transfer paper has a multi-layered structure, the load in the manufacturing process,
Considering paper peculiarity, reproducibility of the final transferred pattern, economy, etc., in forming each layer (especially undercoat layer and topcoat layer), the initial purpose can be achieved with the smallest possible coating amount. Should be considered.

An object of the present invention is to eliminate the cissing phenomenon (partial defect of the pattern) often found in the conventional transfer paper, and to maintain the sharpness of the pattern after printing on the object. It is to provide a base paper for transfer paper. The present inventors have made extensive studies as to why the cissing phenomenon occurs. As a result, they found that the cissing phenomenon was based on the substance contained in the pigment coating layer of the base paper for transfer paper. That is, the inventors of the present invention tried some experiments in the process of preparing the base paper for transfer paper, and obtained the following findings. First, in the process of preparing a base paper for transfer paper, a base paper (no-size base paper) is coated with a coating composition containing a pigment and an adhesive as main components, and dried to form a pigment coating layer. , Wipe the surface of this pigment coating layer with gauze soaked in water several times,
After cleaning the surface of the pigment coating layer, provide a top coat layer made of dextrin on it, print on the top coat layer as usual, and finish the surface with xylene, naphtha, butyl cellosolve, 3-methoxybutanol. An acrylic resin dissolved in a solvent having a high boiling point (180 to 220 ° C.) such as the above was applied and dried to form an overcoat layer. Using the transfer paper thus obtained, a pattern was transferred to an object and printed by a conventional prescription, that is, a water transfer method, but no cissing phenomenon was observed. Also,
In the preparation of the base paper for transfer paper, a large amount of hydrophilic starch was directly applied to the base paper without forming a pigment coating layer and dried, and then a top coat layer made of dextrin was provided on the base paper, and so on. A transfer paper was prepared, and the design was transferred to the object and printed, but in this case also, the cissing phenomenon was not observed.

From the above facts, the present inventors have not confirmed what the substance is, but a certain aqueous (water-soluble) substance contained in the pigment coating layer forms the base paper for transfer paper. In the process, it passes through the undercoat layer to reach the topcoat layer, and in the next step, the process of printing on the topcoat layer and forming the overcoat layer, the substance influences and induces the cissing phenomenon. It was concluded that they are doing this, and repeated studies and research were conducted as a countermeasure. As a result, they have found that the cissing phenomenon is eliminated by incorporating a specific amount of the copolymer latex and the water-proofing agent in the undercoat layer made of hydrophilic starch, and have completed the present invention. That is, the present invention relates to a support comprising a base paper and a pigment coating layer containing a pigment and an adhesive as main components, an undercoat layer containing starch, a topcoat layer containing rewetting paste, and a support. In a base paper for transfer paper having a back coat layer provided on the back side, a copolymer latex and a water-proofing agent are contained in the undercoat layer, and particularly, these copolymer latex and A more preferable base paper for transfer paper is obtained when the amount of the water-proofing agent is 0.05 to 10 parts by weight and 0.1 to 1.0 parts by weight, respectively, relative to the solid content relative to 100 parts by weight of starch in the undercoat layer. It is what is done.

Here, it should be noted that although the undercoat layer is conventionally required to be composed of a material (starch) having strong hydrophilicity and water retention, it has a water repellency opposite to hydrophilicity. It has been found that the cissing phenomenon is extremely effectively eliminated or reduced by using a strong copolymer latex. The reason why the cissing phenomenon is eliminated by using a part of the copolymer latex together is not always clear, but it is presumed as follows. That is, in the process of preparing a base paper for transfer paper, first, a pigment coating layer is provided on the base paper, then a hydrophilic starch aqueous solution is applied on the base coating layer, dried to form a starch layer, and then a starch layer is further formed thereon. A wet paste solution (dextrin) is applied and dried to finish. Upon coating at this time, the water-based substance (which elutes or moves due to water) contained in the pigment coating layer, which causes cissing, is trapped in the copolymer latex contained in the undercoat layer. As a result of being collected, further movement is suppressed, and it is considered that there is no influence at the time of the next step of printing and forming the overcoat layer.

In the present invention, in order to maintain the original function of the undercoat layer, it is necessary to maintain a hydrophilic and water-retaining state as a whole as described above. Therefore, the blending amount of the copolymer latex to be contained in the undercoat layer is not particularly specified, but it is preferably 100 parts by weight of the hydrophilic starch which is the main component of the undercoat layer in terms of solid content. 0.
05 to 10 parts by weight, more preferably 0.1 to 5 parts by weight,
It is more preferably 0.2 to 3 parts by weight. By the way,
If it is less than 0.05 parts by weight, the effect of eliminating the cissing phenomenon is poor, while if it exceeds 10 parts by weight, the hydrophilicity of the entire undercoat layer is lowered, and the original action and function may not be fulfilled. There is

Examples of the copolymer latex to be incorporated in the undercoat layer include styrene-butadiene copolymer latex and carboxylic acid modified products thereof.
One or more of a styrene-acrylic copolymer latex and an ethylene-vinyl acetate copolymer latex are preferably used.

As the hydrophilic starch which is the main component of the undercoat layer, for example, modified tapioca starch (trade name:
Yuri, Yuri II / Matsuya Chemical Co., Ltd., potato starch (Matsuya Chemical Co., Ltd.), corn starch (Oji corn starch) and the like are exemplified, and one or more of these are appropriately used.

[0016] Next, the function of the water-proofing agent incorporated in the undercoat layer may induce unnecessary stains during printing or printing, and may further reduce water retention. It is to promote the water resistance (water insolubility) of starch and the like. In this case, the amount of the water-proofing agent added is adjusted in the range of 0.1 to 1.0 parts by weight based on 100 parts by weight of starch based on the solid content. Incidentally, if the amount is less than 0.1 parts by weight, the water resistance becomes insufficient and a part of the starch and the copolymer latex becomes water-soluble, which may cause stains such as printed patterns. On the other hand, if the amount exceeds 1.0 part by weight, yellowing of the paper or a change in the viscosity of the paste solution or a decrease in slime due to an excessive amount of the water-proofing agent may occur during the coating operation.

[0017] Note that as the waterproofing agent, for example glyoxal, glycerol diglycidyl ether, polyamide - having an epoxy group or an epi chloro <br/> hydrin group-containing compound such as an epoxy resin, an aldehyde group, such as dialdehyde starch Compound, urea-formaldehyde resin, melamine-formaldehyde resin, polyamide polyurea-
Examples thereof include a methylol group such as formaldehyde resin or a lower alkylated product thereof.

An outline of each constituent element and the manufacturing method of the base paper for transfer paper of the present invention will be described below.
First, the base paper to be the base is appropriately beaten various publicly known pulp fibers known in the paper manufacturing industry, and after adding a necessary internal additive to prepare a paper stock, a Fourdrinier paper machine, a round net paper machine or Non-sized paper or low-sized paper, which is made by Yankee machine or the like, is preferably used. Next, as the pigment constituting the pigment coating layer, for example, one or more kinds selected from organic pigments such as calcium carbonate, aluminum hydroxide, titanium oxide, satin white, talc, and plastic pigment are appropriately used. Examples of the adhesive include copolymer latexes such as styrene-butadiene copolymer latex and carboxylic acid modified products thereof, styrene-acrylic copolymer latex, ethylene-vinyl acetate copolymer latex, and oxidized starch. , Phosphate esterified starch,
Starch such as etherified starch, proteins such as polyvinyl alcohol, casein, soybean protein and the like can be exemplified, and one or more of them can be appropriately used.

The amount of the adhesive compounded is adjusted within the range of 1 to 30 parts by weight based on 100 parts by weight of the pigment and the solid content. The composition for a pigment coating layer (paint) having such a constitution is a publicly known coating device such as an air knife coater, a blade coater, a roll coater, a gravure coater, a bar coater, a rod blade coater, or a curtain coater. It is appropriately used and coated on the base paper so as to have a dry weight of about 5 to ²⁰ g / m ² (one side) and dried.

As described above, the undercoat layer is made of hydrophilic starch (however, after being applied as an undercoat layer and dried, it retains water absorption but is made water resistant so that it is hardly eluted in water. Is the main component,
In addition, a polymer latex and a waterproofing agent are added. In addition, antiseptics, viscosity modifiers, etc. may be added as necessary. An aqueous coating composition (coating liquid) having such a composition is formed on the above pigment coating layer,
An undercoat layer is formed by applying a dry weight of 0.5 to 2.5 g / m ² (one side) using the same coating device as that used for forming the pigment coating layer, and drying. To be done.

Then, an aqueous composition consisting of a water-soluble component having a low ash content such as yellow dextrin and methyl cellulose is dried on the undercoat layer using the same coating apparatus as used for forming the pigment coating layer. 2.0-4 by weight.
The top coat layer is formed by coating and drying so that the amount becomes 0 g / m ² .

A back coat layer such as stearic acid, sulfosuccinic acid or sulfonic acid is used on the back surface of the base paper for transfer paper of the present invention (back surface of the base paper) for the purpose of preventing curling, blocking, slipping and the like. The salt compound or the like is coated and dried so that the coating amount after drying is 0.1 to 5.0 g / m ² .

[0023]

EXAMPLES The present invention will be specifically described with reference to the following examples. In the examples, parts and% are unless otherwise specified.
Parts by weight and% by weight shall be shown respectively. In addition,
The obtained base paper for transfer paper was evaluated as follows to determine its quality.

[Water absorption speed] 23
Floating in water at ℃, the time for water to penetrate and penetrate the surface was measured. ◎: Less than 10 seconds (good) ○: 10 to less than 30 seconds △: 30 to less than 60 seconds

[Repelling Phenomenon] Multicolor printing of 8 colors is performed on the topcoat layer of the base paper for transfer paper using a screen printing machine, and then an overcoat layer of acrylic resin is further provided on the uppermost printing layer. Thus, a painting transfer paper was obtained.
At this time, the repelling phenomenon after forming the printing ink and the overcoat layer was visually observed and evaluated. ○: Repelling does not occur at all △: There is no problem, but there is no problem ×: Repelling occurs on the entire surface, and there is no commercial value

[Slurry state] 2 on the back side of the base paper for transfer paper
Float in water at 3 ° C., and after 2 minutes have passed, the back surface is made to face the glass plate. Then, when a finger is pressed against the surface (top coat layer) of the base paper for transfer paper and the finger is moved so as to draw a circle with a certain sensation, the finger can move smoothly and draw a circle. The number of times was measured. ○: 10 times or more △: 5 to less than 10 times ×: less than 5 times

[Contaminated State in Water / Water Solubility] The base paper for transfer paper was immersed in water at 23 ° C. for 1 hour, and the turbid state in water was visually observed and evaluated. ○: Transparent to slightly turbid △: The turbid state can be confirmed. ×: The turbidity can be clearly seen

[Printing quality after pattern printing] A transfer paper finished in the same manner as in the cissing evaluation was floated in water at 23 ° C. for 2 minutes, and then faced on the glass plate so that the back surface was in contact with the glass plate. Place, then press your finger on the printing surface side (on the overcoat layer) and slide it lightly to separate the printed pattern from the topcoat layer, press on the pottery, immobilize it, and then bake it in an electric furnace (800 ° C) After that, the printed pattern was visually observed and evaluated. ◯: There is no defect and the reproducibility of the printed pattern is excellent. Δ: There is a stain or a defective part on the printed pattern.

Example 1 Lily II (etherified starch / Matsuya Chemical) 6% aqueous solution,
Carboxy modified styrene-butadiene copolymer latex as a copolymer latex (trade name: T-2580 /
Japan Synthetic Rubber (JSR) 48% emulsion, 10% aqueous glyoxal solution as a water-proofing agent, in terms of solid content, based on 100 parts of the etherified starch, respectively.
1 part and 1 part were added and mixed to prepare a paste solution for the undercoat layer. Then, the glue solution Stockigt sizing degree 1 second, and Oken type smoothness is provided a pigment coating layer on the basis weight 165 g / m ² fine paper on the base paper is 72 seconds
Then , a roll coater was used on the coating layer so that the coating amount after drying was 2 g / m ² to form an undercoat layer. In addition, 3 on this undercoat layer
The coating amount after drying the 0% aqueous dextrin solution is 5 g / m.
^After coating and drying to form a topcoat layer of 2, a 15% starch aqueous solution was applied to the back surface of the base paper using a gravure roll coater so that the coating amount after drying was 2 g / m ^2. After coating and drying, a base paper for transfer paper was obtained.

Example 2 In Example 1, in the preparation of the paste solution for the undercoat layer, the amount of the copolymer latex and glyoxal added to the aqueous solution of etherified starch was 100 parts of etherified starch based on the solid content. A base paper for transfer paper was obtained in the same manner as in Example 1 except that the contents were changed to 1 part and 0.1 part, respectively.

Example 3 In Example 1, in the preparation of the paste solution for the undercoat layer, the amount of the copolymer latex and glyoxal added to the aqueous solution of etherified starch was 100 parts of etherified starch based on the solid content. A base paper for transfer paper was obtained in the same manner as in Example 1 except that the contents were changed to 10 parts and 0.1 parts, respectively.

Example 4 In Example 1, in the preparation of the paste solution for the undercoat layer, the amount of the copolymer latex added to the aqueous etherified starch solution was 100 parts by weight of etherified starch based on the solid content.
A base paper for transfer paper was obtained in the same manner as in Example 1 except that the amount was changed to 10.

Example 5 In Example 1, a 6% aqueous solution of potato starch (Matsuya Chemical Co., Ltd.) was used in place of the 6% aqueous solution of Yuri II in the preparation of the undercoat layer paste solution, and Carboxy-modified styrene-butadiene copolymer latex (trade name: T-2580) and glyoxal 10% aqueous liquid are added in an amount of 1 part and 0.1 part, respectively, relative to 100 parts of the potato starch, based on the solid content. A base paper for transfer paper was obtained in the same manner as in Example 1 except that the paste solution was prepared by adding and mixing so that

Example 6 In Example 2, a vinyl acetate copolymer latex (commercial product) was used instead of the carboxy-modified styrene-butadiene copolymer latex (commercial name: T-2580) in the preparation of the paste solution for the undercoat layer. A base paper for transfer paper was obtained in the same manner as in Example 2, except that the same amount of (Name: Movinyl 630 / Hoechst Synthetic Co., Ltd.) was added.

Example 7 In Example 2, in the preparation of the paste solution for the undercoat layer, glycerol polyglycidyl ether (trade name: Denacol PC-1000 / was used instead of glyoxal.
A base paper for transfer paper was obtained in the same manner as in Example 2 except that the same amount of the Nagase chemical product was replaced.

Example 8 In Example 2, in the preparation of the paste solution for the undercoat layer, a polyamide epichlorohydrin resin (trade name: Wetmaster 500A /, instead of glyoxal, was used.
A base paper for transfer paper was obtained in the same manner as in Example 2 except that the same amount of the Nagase chemical product was replaced.

Comparative Example 1 In Example 1, the carboxy-modified styrene-butadiene copolymer latex (trade name: T-2580) and glyoxal 10% aqueous solution were not added in the preparation of the paste solution for the undercoat layer. A base paper for transfer paper was obtained in the same manner as in Example 1 except that the paste solution was used.

Comparative Example 2 A transfer sheet was prepared in the same manner as in Example 1 except that a paste solution containing no 10% aqueous glyoxal solution was used in the preparation of the paste solution for the undercoat layer. I got the base paper.

COMPARATIVE EXAMPLE 3 In Example 2, except that a carboxy-modified styrene-butadiene copolymer latex was not added when preparing the undercoat layer paste solution,
A base paper for transfer paper was obtained in the same manner as in Example 2.

The base papers for transfer paper in the examples and comparative examples obtained as described above were evaluated based on the above-described evaluation method, and the obtained results are summarized in Table 1.

[0041]

[Table 1]

[0042]

As is clear from the results shown in Table 1, when the transfer paper base paper obtained in the present invention is used to make a transfer paper, cissing phenomenon does not occur, and printed patterns after printing are also obtained. It was excellent in reproducibility.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a base paper for transfer paper (and transfer paper) according to the present invention.

[Explanation of symbols]

(1): Base paper (2): Pigment coating layer (3): Undercoat layer (4): Top coat layer (5): Printed layer (6): Overcoat layer (7): Back coat layer

Claims (4)

(57) [Claims] 1. An undercoat layer containing starch, a topcoat layer containing rewetting paste, and a support on a support comprising a base paper and a pigment coating layer containing a pigment and an adhesive as main components. A base paper for transfer paper having a back coat layer on its back surface, wherein the undercoat layer contains a copolymer latex and a water-proofing agent. 2. The contents of the copolymer latex and the water-proofing agent are 0.05 to 10 parts by weight and 0.1 to 1.0 parts by weight, respectively, relative to 100 parts by weight of starch based on the solid content. The base paper for transfer paper according to claim 1. 3. A copolymer latex comprising a styrene-butadiene copolymer latex and a carboxylic acid modified product thereof,
Styrene-acrylic copolymer latex, ethylene-
The base paper for transfer paper according to claim 1 or 2, which is a copolymer latex selected from at least one vinyl acetate copolymer latex. 4. A water-proofing agent is glyoxal, glycerol diglycidyl ether, polyamide - epoxy or epi chlorohydrin group-containing compound such as an epoxy resin, a compound having an aldehyde group such as dialdehyde starch, urea -
Selected from methylol groups such as formaldehyde resin, melamine-formaldehyde resin, polyamide polyurea-formaldehyde resin or lower alkylated products thereof,
The base paper for transfer paper according to any one of claims 1 to 3, which is at least one waterproofing agent.