JPH11172599A - Flame-retardant sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide flame-retardant sheets that have excellent flame retardancy as well as smoothness and whiteness. SOLUTION: A slurry that mainly contains calcium carbonate whiskers and 5-30 pts.wt., per 100 pts.wt. of the calcium carbonate whiskers, of pulp is subjected to paper making. In order to increase the sheet strength, reinforcing fibers as glass fibers or synthetic fibers may be added and a binder as an ionic polyacrylamide or the like may be added. Since this sheet contains a high content of' calcium carbonate whiskers resistant to the temperature of >=600 deg.C, excellent flame retardancy can be attained. In addition, fine, fibrous calcium carbonate whiskers constructs fine-grained homogeneous texture structure and gives excellent surface smoothness and whiteness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flame-retardant sheet used as a surface covering material such as a wall covering material, decorative board or various building materials, a core material such as a honeycomb or a substrate for a total heat exchanger. More specifically, a flame-retardant sheet (flame-retardant paper) which is produced in the form of paper or cardboard by a papermaking method, that is, a papermaking method, has excellent flame retardancy, and also has excellent surface smoothness and whiteness. ).

[0002]

2. Description of the Related Art In recent years, there has been a great deal of interest in "functional paper" which is a papermaking sheet in which special functions and characteristics different from general pulp paper are highly pursued, and its development and research are being actively conducted. . Flame-retardant sheets, which have a wide range of applications in fields where fire resistance or fire resistance is required, such as building materials, are also one type, and various materials have been developed as alternative materials for asbestos paper (asbestos paper). It has also been proposed.

The most typical example of the flame-retardant sheet is one that has already been widely put into practical use.
Aluminum hydroxide-rich paper manufactured by papermaking a slurry containing pulp and a large amount of aluminum hydroxide powder as main materials [Japanese Patent Publication Nos. 59-5720 and 2-299.
8, etc.]. In addition, a product using hydrated calcium borate (peridotite powder) in place of the aluminum hydroxide [Japanese Unexamined Patent Publication No.
-4679], those using magnesium hydroxide [Japanese Patent Publication No. 4-50437, etc.], those using calcium silicate (Wollastonite) [JP-A-58-98495,
And the like using a combination of aluminum hydroxide and a hydrous magnesium silicate mineral such as sepiolite [JP-A-6-49795].

[0004] Apart from these, the present applicant has developed a non-combustible or flame-retardant sheet using sepiolite, which is a fibrous hydrated magnesium silicate mineral, as a main material, and proposed it in an earlier application [ JP-A-2-219558,
etc].

Furthermore, the present applicant has also developed and proposed a flame-retardant sheet using a ground material in the form of plate-like particles of brucite, which is a magnesium hydroxide mineral, as a main material [Japanese Patent Laid-Open No. 7-1995]. 279090].

[0006] Japanese Patent Publication No. 4-53994 discloses that a whisker sheet is produced by forming a whisker of silicon nitride or silicon carbide together with a fibrous material having a specific freeness, for example, pulp (NBKP). It has been disclosed. However, this sheet is mainly intended to be used as a reinforcing material for a composite material.

[0007]

As described above, most of flame-retardant sheets as functional papers which do not spread even when ignited use mineral materials as a main material. Various types have conventionally been developed.
And, these flame-retardant sheets exhibit high flame retardancy due to the high content of inorganic material, and unlike ordinary flame-retardant paper in which pulp paper is impregnated with a flame retardant, it is harmful even when heated and burned. It has effects such as no generation of gas and the like.

In particular, among these, the flame-retardant sheet containing sepiolite as a main material has high strength even with a relatively small amount of pulp material because its fibrous form, sepiolite, has excellent consolidation properties. A paper-made sheet can be obtained, that is, a sheet having a high inorganic content and excellent flame retardancy can be obtained.Moreover, due to the sinterability of sepiolite, the sheet does not collapse even if the pulp is burned out in the event of a flame. It has the feature that it can maintain its original shape well and can prevent the transmission of smoke.

Further, in the flame-retardant sheet using brucite composed of plate-like particles as a main material, the brucite, which is a magnesium hydroxide mineral, has a dehydration endothermic effect due to thermal decomposition similarly to aluminum hydroxide. Due to its self-extinguishing properties, it exhibits excellent fire resistance, and because it is in the form of plate-like particles, it has better sheet surface smoothness than aluminum hydroxide powder, which has an irregular spherical shape. There are features such as being obtained.

[0010] However, these sepiolites, brucites, etc. are all natural products, and it is difficult to always ensure good quality thereof, and their resources themselves are limited. Therefore, as for the inorganic material used as the main material of the flame-retardant sheet, there has been a demand for the search and development of a new material that can replace the inorganic material.

In the search for such a new material, the present inventors have developed calcium carbonate, which has been developed for use as a plastic reinforcing material (filler) or a heat insulating filler, and has recently been industrially put to practical use. Focusing on CaCO ₃ whiskers (whiskers), as a result of repeated tests and investigations, the use of this as the main material of the flame-retardant sheet has not only excellent flame retardancy, but also particularly excellent surface smoothness And whiteness were obtained and confirmed.

Accordingly, an object of the present invention is to provide a flame-retardant sheet having excellent flame retardancy, surface smoothness and whiteness.

[0013]

That is, a flame-retardant sheet according to the present invention is obtained by using the above-mentioned calcium carbonate whisker together with a small amount of pulp as a main material and sheeting it by a papermaking method. The slurry is obtained by making a slurry containing 5 to 30 parts by weight of pulp as a main material with respect to 100 parts by weight of the calcium carbonate whisker.

Here, calcium carbonate whiskers are obtained by controlling the reaction conditions in a gas-liquid reaction for carbonating calcium hydroxide Ca (OH) ₂ and growing crystals only in a certain direction. In contrast to spindle calcium carbonate (calcite type) or acicular calcium carbonate (argonite type), it is fibrous and generally has a diameter of 15 to 15 μm for a short diameter (thickness) of 0.3 to 1.5 μm.
It has a major axis (length) of 40 μm. Therefore, this calcium carbonate whisker, which has good binding properties with each other or pulp and has good papermaking properties, is used in the present invention at a sufficiently high ratio as a main material, and pulp having combustibility is used at a relatively small ratio. Can be

Therefore, according to the flame-retardant sheet of the present invention, a high proportion of calcium carbonate whiskers having a heat resistance of at least 600 ° C. is contained, so that excellent flame retardancy can be obtained. In addition, since calcium carbonate whiskers are in the form of fine short fibers, a fine and uniform tissue structure is formed by papermaking, thereby obtaining excellent surface smoothness and whiteness (opacity). be able to.

The flame-retardant sheet of the present invention can be formed so as to further include reinforcing fibers such as glass fibers. That is, a reinforcing fiber is further added to the above slurry, and the reinforcing fiber can be formed into a slurry. Thereby, a stronger flame-retardant sheet can be obtained.

[0017]

As described above, the flame retardant sheet of the present invention uses calcium carbonate whiskers and a small amount of pulp as main materials, or further uses reinforcing fibers and disperses them in water. A slurry is formed and then formed into a paper. And it is basically the same as a conventional flame-retardant sheet except that calcium carbonate whiskers are used as a main material.

Here, any calcium carbonate whiskers can be used, but those having a relatively large aspect ratio are more preferable. Specifically, those having a minor axis (thickness, average) of about 0.3 to 1.5 μm and a major axis (length, average) of about 15 to 40 μm can be used. However, it is more preferable that the short diameter is 0.5 to 1.0 μm and the long diameter is 20 to 30 μm.
And the aspect ratio is preferably about 20 to 30. And, as described below, this calcium carbonate whisker is used in the maximum ratio as a main material.

Pulp, which is a natural cellulose fiber, is used as a binding fiber of calcium carbonate whiskers. Pulp-like synthetic fibers such as fibrillated aramid fibers can also be used in the meaning of the binding fibers, but in the present invention, softwood pulp widely used as a raw material for papermaking,
Typical pulp such as hardwood pulp or linter pulp is preferably used. However, in the flame-retardant sheet of the present invention, which is characterized by whiteness on the surface, etc., it is preferable that the pulp used is of good quality. And, specifically,
Softwood bleached kraft pulp (NBKP), hardwood bleached kraft pulp (LBKP) and the like can be mentioned.

The pulp is preferably used as little as possible in order to obtain excellent flame retardancy. The pulp should not exceed 30 parts by weight based on 100 parts by weight of calcium carbonate whiskers.
Used in a proportion of 30 parts by weight. In particular, if the amount exceeds 30 parts by weight, it becomes difficult to secure excellent flame retardancy, and more preferably, the amount is 20 parts by weight or less. The use ratio of this pulp is equivalent to 5 to 23% of the total amount with the calcium carbonate whisker. In other words, the calcium carbonate whisker is used at a ratio of 95 to 77% of the total amount with the pulp. Is done. Such a ratio is common to the flame-retardant sheet, but is far from that of a filler such as heavy calcium carbonate in general paper which is at most 50 to 60% by pulp. is there.

In the present invention, reinforcing fibers can be further used to increase the strength of the sheet. And as this reinforcing fiber, glass fiber, carbon fiber,
Ceramic fibers such as silica-alumina fibers, or inorganic fibers such as rock wool fibers, rayon, polyester fibers, polyvinyl alcohol fibers, acrylic fibers, synthetic fibers such as nylon fibers, and the like. They can be used alone or in an appropriate combination. In addition, the fiber length is generally preferably about 3 to 15 mm.

This reinforcing fiber can be used in a total amount of generally 5 to 35 parts by weight based on 100 parts by weight of calcium carbonate whisker. However, inorganic fibers having relatively high rigidity are preferably used in a small proportion in order to maintain excellent smoothness of the sheet surface by the calcium carbonate whiskers, and specifically, a use proportion of 15 parts by weight or less is preferred. . In addition, as for synthetic fibers having organic properties and combustibility, it is preferable to use the synthetic fibers in the smallest possible proportion, as in the case of pulp.In this case, depending on the proportion of pulp used, , 30 parts by weight or less is preferred. Therefore, in order to obtain higher sheet strength, it is preferable to use inorganic fibers such as glass fibers in combination with an appropriate synthetic fiber, and in this case, the inorganic fibers are preferably used in combination with inorganic fibers having the desired surface properties. While being used in large quantities, the organic fibers can be used in a maximum amount depending on the proportion of pulp used.

A part of the calcium carbonate whisker is
Other inorganic materials can be used as long as the properties are not impaired. Examples of such inorganic materials include colloidal silica, which is effective in increasing sheet strength and improving whiteness, further increasing surface smoothness, and having a swelling mica or synthetic smectite effect of enhancing softness. And aluminum hydroxide, hydrous calcium borate, sepiolite, brucite and the like used in conventional flame-retardant sheets. However, the proportion of these inorganic materials used is preferably kept within 10% by weight thereof so as not to impair the excellent properties of the calcium carbonate whiskers.

Further, in the flame-retardant sheet of the present invention containing calcium carbonate whiskers, which are fine fibers, in order to secure sufficient sheet strength (paper strength), a binder made of a high-molecular organic compound (paper strength enhancement) is used. It is desirable to use them together. And as such a binder,
Starch, polyvinyl alcohol, polyethylene oxide, carboxymethylcellulose, polyacrylamide, and urea-formaldehyde resin that is a thermosetting resin, melamine-formaldehyde resin, epoxidized polyamide resin, methylolated polyacrylamide, and the like. , Especially polyacrylamide,
Preferably, an ionic, ie, anionic, cationic, or amphoteric modified product (copolymer) that enhances fixability and also has a function as a retention agent or a flocculant.
Used as As the binder, an acrylic or polyester-based synthetic resin emulsion can be used, but in general, the above-mentioned water-soluble binder can be more preferably used.

This binder is based on 100 parts by weight of calcium carbonate whisker.
Practically, it can be used at a ratio of 1.5 parts by weight or more. However, in order to ensure excellent flame retardancy, it is naturally preferable that the amount of addition is as small as possible, and it is generally preferable to use it in a proportion of 5.0 parts by weight or less. Also, with such relatively small usage,
Practically sufficient sheet strength can be secured.

Then, using these calcium carbonate whiskers and pulp, furthermore, reinforcing fibers and binders,
The flame-retardant sheet of the present invention is manufactured by a usual general papermaking method. That is, the raw materials are uniformly dispersed in water, and the aggregated flocs are formed, and a slurry preparation step of preparing a raw material slurry for papermaking, and the prepared slurry is filtered through a paper net. It is manufactured by a paper making process of forming a wet sheet by a paper machine, followed by a drying process of squeezing and dewatering the wet sheet, followed by drying. In addition, as the paper machine, any type such as a short net type, long net type, circular net type, or combination type can be used, and a net making machine of about 60 to 80 mesh is generally used. be able to. In addition, in the slurry preparation step, an inorganic coagulant such as a sulfuric acid band, or a polymer coagulant is appropriately added separately from the binder in order to form a good coagulated floc of the main material component. Can be. And
This sheet is generally 0.15 depending on the specific application and the like.
It can be manufactured as a material having a thickness of about 1.0 mm or a weight of about 80 to 200 g.

The flame-retardant sheet of the present invention is thus produced by papermaking, has a composition substantially corresponding to the solid composition of the slurry, and contains a high proportion of calcium carbonate whiskers. Therefore, it has excellent flame retardancy, is also excellent in surface smoothness and whiteness, and has good appearance and printability or notation. Therefore, this flame-retardant sheet can be used widely in the field where fire resistance or fire resistance is required, but it can be suitably used particularly as a base paper for a wall material or a surface material of a building material. In addition, the flame-retardant sheet can be further subjected to a water-repellent treatment with a silicone resin or the like, or a non-combustible treatment by impregnation with an inorganic composition, thereby further expanding the use of the sheet. it can.

[0028]

EXAMPLES Example 1 Using the following materials, the flame-retardant sheet of the example of the present invention was experimentally produced by a TAPPI hand-making apparatus. (Raw material blend) 100 parts by weight of calcium carbonate whisker 15 parts by weight of pulp 1.5 parts by weight of anionic polyacrylamide 1.0 part by weight of epoxidized polyamide resin Here, the minor diameter of calcium carbonate whisker is about 0.1 part.
"Wiscal" (Maruo Calcium Co., Ltd.) having a diameter of 7 μm and a major axis of about 25 μm was used. As the pulp, softwood bleached kraft pulp (NBKP) was used.

Based on the above composition, pulp beaten in advance is defibrated by a mixer to form a slurry,
Calcium carbonate whiskers were added to this and dispersed well. To this, the diluted anionic acrylamide was added and sufficiently stirred, and then the epoxidized polyamide resin was added and further stirred. As a result, a slurry in which the material components were flocked was formed.

[0030] This slurry was polished to a 90-mesh paper net (20
× 25 cm) using a hand-making device, and then
The obtained wet sheet is dried under pressure at 100 ° C. by a heating press machine, and has a thickness (average of 10 sheets, the same applies hereinafter) of 0.316 m
m, a flame-retardant sheet having a basis weight of 168.4 g / m ² was obtained. In addition, the yield was about 82%.

This flame retardant sheet was excellent in smoothness and whiteness. Also, its tensile strength (JIS
P 8113) was 1.26 kgf [break length 0.50 km]. Further, when a flame of a gas lighter was applied to this sheet to perform a combustion test, the portion where the flame was applied burned during that time and was carbonized to black brown, but the surrounding area did not burn,
It was only slightly discolored. The carbonized portion did not collapse. That is, excellent flame retardancy could be confirmed.

Example 2 A flame-retardant sheet of another example of the present invention was produced in the same manner as in Example 1 except that reinforcing fibers were further added. (Ingredients) Calcium carbonate whisker 100 parts by weight Pulp 15 parts by weight Glass fiber 5 parts by weight Acrylic fiber 10 parts by weight Anionic polyacrylamide 1.6 parts by weight Epoxidized polyamide resin 1.1 parts by weight The glass fiber has a diameter of 9 μm. The acrylic fiber is a papermaking fiber made of an acrylonitrile copolymer and has a length of 1.5 d and a fiber length of 5 mm.

With the above composition, glass fibers and acrylic fibers are defibrated with a mixer together with pulp that has been beaten in advance to form a slurry thereof, and then anionic polyacrylamide and epoxidized polyamide resin are sequentially used as a binder. This was added to prepare a flocked raw material slurry. Then, in the same manner as in Example 1, the slurry was hand-made and hand-pressed to produce a flame-retardant sheet.

The obtained flame retardant sheet has a thickness of 0.384.
mm, basis weight 191.7 g / m ² , and its tensile strength is 4.26 kgf [tear length 1.48 km], tear strength (JI
SP 8117) was 259 gf. The yield is about 85
%Met.

Further, a flame retardancy test of this sheet was performed. As in Example 1, excellent flame retardancy was confirmed. In particular, the shape retention of the sheet after combustion (carbonization) was more excellent than that of the sheet of Example 1 due to the inclusion of glass fibers.

[0036]

As described above, the flame-retardant sheet according to claim 1 is a slurry containing calcium carbonate whiskers and 5 to 30 parts by weight of pulp based on 100 parts by weight of the calcium carbonate whiskers. Is made by papermaking.

Therefore, according to this flame retardant sheet,
As a non-combustible inorganic main material, calcium carbonate whiskers, which are in a fibrous form and have excellent binding properties with each other and pulp (entanglement), are used, so that pulp as a binding fiber is contained in a minimum amount. Therefore, calcium carbonate whiskers having a heat resistance of 600 ° C. or more can be contained in a high ratio. Therefore, excellent flame retardancy can be obtained. In addition, since calcium carbonate whiskers are in the form of fine fibers, they can form a fine-grained and homogeneous sheet structure, thereby providing excellent smoothness and whiteness, and excellent sheet surface and printability. Can be obtained. That is, according to the flame retardant sheet, excellent surface smoothness and whiteness can be obtained together with excellent flame retardancy.

The flame-retardant sheet according to claim 2 is
The above-mentioned slurry further contains a reinforcing fiber. Therefore, according to the flame-retardant sheet, since the reinforcing fibers are further contained, higher sheet strength can be secured.

Claims (2)

[Claims] 1. A flame-retardant sheet obtained by forming a slurry containing calcium carbonate whiskers and 5 to 30 parts by weight of pulp based on 100 parts by weight of the calcium carbonate whiskers as a main material. 2. The flame-retardant sheet according to claim 1, wherein the slurry further comprises reinforcing fibers.