JP4339915B2 - Low density process paper - Google Patents

Description

  The present invention relates to a process paper used in a process for producing a laminated board or the like used as a substrate for printed wiring boards, and in particular, has excellent cushioning properties and low dust generation properties, and can be recycled to raw paper raw materials. It relates to density process paper.

  Conventionally, as a laminate base paper used for a laminate for a printed wiring board, for example, as shown in Patent Document 1, it is impregnated with a thermosetting resin such as an epoxy resin or a phenol resin, and this is heated and dried. Dust-free paper or the like produced by making a semi-cured resin, further laminating a plurality of these, and hot pressing with a metal foil is used.

  The hot pressing is a method in which an object to be hot pressed, that is, an object to be pressed, is sandwiched between press plates of stainless steel plates called hot plates or mirror plates, and is formed by applying a certain pressure and heat. At this time, in order to obtain an accurate molded product, a high-pressure and high heat applied to the press object by interposing a flat molding heat press cushion material between the press object and the press plate It is common practice to make it even over the entire surface.

  Conventionally, as a cushioning material for molding hot press (process slip paper) used in this hot-press molding, glass fiber fabrics such as glass fiber cloth and glass nonwoven fabric, and cellulose systems such as kraft paper and linter paper Inorganic fiber-based sheet-like or belt-like materials such as fiber-based paper and asbestos cloth are used. Among these, kraft paper is often used from the viewpoint of cost and the like.

  However, such conventional process slips are mainly for the purpose of protecting the surface of the metal foil and the metal surface of the hot-press molding machine in hot-press molding, so that the peelability from the metal surface is poor and the rigidity is also low. Unfortunately, there was a problem that the slip sheet removal operation could not be performed smoothly. Furthermore, there was a problem that the cushioning property was poor and the laminated board for the printed wiring board was damaged.

  Therefore, as a paperboard having cushioning properties, for example, a bulky paperboard shown in Patent Document 2, a low-density paper shown in Patent Document 3, and the like have been proposed and put into practical use. Such bulky paperboard contains a bulking agent in the raw pulp to obtain a uniform air layer on both sides of the thermal conductivity, mechanical pulp with soft properties, softwood pulp freeness Means such as increasing the press line pressure and the calender line pressure in the paper making process are used. However, either means weakens or reduces the entanglement between the pulp fibers, and as a result, although it has excellent cushioning properties, it causes a decrease in inter-fiber strength. The problem of doing was not able to be solved.

  In addition, with the recent thinning and miniaturization of electrical products, the mounting density of electrical components such as ICs, capacitors, resistors, etc. has increased, and the conductor patterns of printed wiring have been made thinner. Therefore, when a large dimensional change or deformation such as warping, twisting, or scratching occurs in the laminated plate during hot pressing, troubles may occur in the process and the product may not be put to practical use. For this reason, not only the electrical performance of laminates but also the demands for preventing deformation such as warpage, torsion, and scratches in the machining process of laminates is increasing.

  However, the above-described bulky paperboard described in, for example, the cited documents 2 and 3 may change in dimensions when used as a process slip sheet in a laminated board processing step, and is used for electrical equipment with a higher component mounting density. It is not suitable as a process slip sheet in a hot-pressure molding machine for printed wiring boards or printed wiring boards for electronic devices such as computers that require high precision. Such process slips also have problems from the viewpoint of effective use of resources and environmental considerations.

Japanese Patent Laid-Open No. 2003-21614 JP 2001-73299 A JP-A-11-200222

  The present invention has been made in view of the above-described circumstances, and the object of the present invention is to use a hot-press molding machine in a process for processing a laminated board for printed wiring, in which the laminated board undergoes a large dimensional change and warpage. The object is to provide low-density process paper that prevents deformation such as twisting and scratching, has cushioning properties, generates little dust, and can be recycled even after use.

The above object of the present invention is a low-density process paper having at least a surface layer, a back layer, and an intermediate layer composed of one or more layers disposed between the surface layer and the back layer. Heat-expandable particles having an average particle diameter of 5 to 15 μm in at least one layer and starting to expand by heating at 75 to 130 ° C. are obtained by previously mixing (aggregating) the heat-expandable particles and the cationic polymer resin. and aggregates of the heat expandable particles, relative to the pulp solid content of the intermediate layer, blended 1-8 wt% in terms of solid content, and, as a fixing agent for the thermally expandable particles, polyacrylamide or polyethyleneimine 0.1 to 0.8% by mass of a polymer based on pulp solid content is used to form a foam layer, and the raw material constituting the surface layer and the back layer is NBKP and / or LBKP, and , The surface layer, before Freeness of pulp used for the backing layer and the intermediate layer is 500～600Cc, density 0.45~0.55g / cm ^3, compressed paper thickness residual ratio was 55 to 61%, the surface layer and Low density process characterized in that thermal conductivity difference of said back layer is 0.001 W / mk or less, and dust generation amount of 10 μm or more by tear test according to SEMI G67-0996 is 500 pieces / cm ² or less This is accomplished by providing paper.

  The low-density process paper according to the present invention has at least a surface layer, a back layer, and an intermediate layer composed of one or more layers disposed between the front layer and the back layer, and at least one of the intermediate layers. The foamed layer is formed by blending thermally foamable particles, and the raw material constituting the surface layer and back layer is kraft pulp made of NBKP and / or LBKP. Since it can be used as a low-density process paper with a small amount, it can be used as a process slip sheet (cushion material) used at the time of hot-pressure molding in the process of manufacturing a laminated board used as a printed wiring board.

  Hereinafter, the low-density process paper according to the present invention will be described in detail by taking, as an example, a case where the low-density process paper is composed of three paper layers of a surface layer, one intermediate layer, and a back layer. The low-density process paper according to the present invention is not limited to the following embodiments, and it is needless to say that the configuration can be changed as appropriate without departing from the scope of the claims.

  The low-density process paper according to the present invention (hereinafter referred to as “the present low-density process paper”) is composed of a three-layer paper layer of a surface layer, at least one intermediate layer, and a back layer, and is a raw material pulp of the intermediate layer A heat-expandable particle is mix | blended in it.

  The low-density process paper can be made into a multi-layer paper as described above, so that only the intermediate layer can contain heat-expandable particles. That is, a low density process paper can be comprised, without containing a thermally foamable particle in a surface layer and a back layer. This makes it possible to form a more stable foam of thermally foamable particles by accelerating the expansion of the thermally foamable particles of the intermediate layer by the amount of heat of the wet paper of the front and back layers not containing the thermally foamable particles in the papermaking process. be able to. In addition, in the dryer after forming the foam of thermally foamable particles and in the process after the dryer outlet, the thermally foamable particles are not exposed on the paper surface (does not appear on the paper surface), and thus bonded to the foamed particles and fibers. Objects do not adhere to the surface of the dryer, tools, rolls, etc. In the case of single-layer paper, the heat-expandable particles are naturally exposed on the paper surface and adhere to the dryer, tools, and rolls, resulting in reduced operability and increased dust generation in the product after papermaking. Therefore, it cannot be used as a cushion material in the processing process of precision equipment such as a laminated board for printed wiring boards.

Moreover, in the raw material pulp of the intermediate layer of the present low-density process paper, thermally foamable particles are contained, the intermediate layer is a cushion layer, the density is 0.45 to 0.55 g / cm ³ , and the thermal conductivity of the front and back sides Reduced the difference. In the low-density process paper, the intermediate layer may be composed of two or more layers. In this case, the entire layer of the intermediate layer may contain thermally foamable particles to form a cushion layer. That is, if at least one intermediate layer contains thermally foamable particles to form a cushion layer, the object of the present invention can be achieved, and the cushioning property is excellent, the thermal conductivity has a small difference in front and back, and the dust generation Since it can be a low-density process paper with a small amount, it can be suitably used as a process slip sheet (cushion material) used at the time of hot-pressure molding in the process of manufacturing a laminated board used as a printed wiring board. And can be recycled after use.

If the density of the low-density process paper is less than 0.45 g / cm ³ , the distance between the fibers becomes large, so that the bond between fibers becomes weak, the amount of dust generation is large, and the low initial dust property is poor. On the other hand, if the density exceeds 0.55 g / cm ³ , the cushioning property is lost, the substrate-like foreign matters and irregularities cannot be absorbed, and there is a problem that the printed wiring board laminate is damaged.

  Moreover, 1-8 mass% in conversion of solid content is added with respect to the pulp solid content of the intermediate | middle layer added, Preferably heat-expandable particle is added 2-5 mass%. Thereby, the residual thickness ratio of the compressed paper can be 55 to 61%, and the balance between the thermal conductivity and the low dusting effect of the low-density process paper becomes more excellent. The compressed paper thickness remaining rate is a measurement of the paper thickness of the low-density process paper before press compression and the paper thickness immediately after press compression, and the paper thickness immediately after press compression is the thickness of the low-density process paper before press compression. It is the ratio of the remaining paper to the original paper thickness (paper thickness before compression) divided by the paper thickness.

  The content of heat-expandable particles per layer of the intermediate layer (when the intermediate layer is composed of two or more layers, one layer of each layer to which the heat-expandable particles are added) is 1% by mass. If it is less than this, even if the thermally foamable particles are in a foamed state, the distance between the thermally foamable particles is increased, and the expansion effect of the thermally foamable particles is not exhibited, so that sufficient inter-fiber voids cannot be obtained. It becomes difficult to impart a predetermined density to the paper. On the other hand, if the content of heat-expandable particles per layer exceeds 8% by mass, it is difficult to adjust the amount of heat for uniformly foaming the heat-expandable particles, resulting in poor foaming, and the appearance of the paper is deteriorated. At the same time, the manufacturing cost is increased.

  The heat-expandable particles that can be used in the low-density process paper are those in which a low-boiling solvent is enclosed in a fine particle outer shell made of a thermoplastic synthetic resin mainly composed of an acrylic copolymer. The thermally foamable particles preferably have an average particle diameter of 5 to 15 μm and start to expand upon heating at 75 to 130 ° C. Thereby, the balance of the cushioning property of this low density process paper, thermal conductivity, and the effect of low dust generation becomes more excellent.

  Examples of the thermoplastic synthetic resin constituting the outer shell include copolymers such as vinylidene chloride, acrylonitrile, acrylic acid ester, and methacrylic acid ester.

  Examples of the low boiling point solvent enclosed in the outer shell include isobutane, pentane, petroleum ether, hexane, low boiling point halogenated hydrocarbon, and methylsilane.

  Examples of such thermally expandable particles include “Matsumoto Microsphere F-20 Series”, “F-30 Series”, “F-36 Series”, and “F-46” manufactured by Matsumoto Yushi Seiyaku Co., Ltd. Series "," Expancel WU "and" Same DU "sold by Nippon Philite Co., Ltd. can be used, but the heat-expandable particles used in this low-density paper are not limited to these. Absent.

  However, in the present invention, since the temperature of the paper drying step is generally about 100 to 130 ° C., the low temperature expansion type in which the foaming start temperature of the thermally expandable particles is 75 to 130 ° C. is preferable.

  The thermally foamable particles are heated above the softening point of the thermoplastic synthetic resin constituting the outer shell, and at the same time, the low boiling point solvent such as isobutane encapsulated is vaporized to increase the vapor pressure, and the outer shell expands. During expansion, the internal pressure and the tension / external pressure of the shell are balanced to maintain the expanded state. Thermally foamable resins are generally expanded to this state and used as lightening agents, bulking agents, cushioning agents, heat insulating agents, and the like. If additional heat is applied to this expanded thermo-expandable resin, and gas is permeated and diffused from the expanded and thin shell, the tension and external pressure of the shell become larger than the internal pressure. As a result, the foamed resin shrinks.

  The heat-expandable particles used in the low-density process paper are foamed by a dryer in the drying process. For the above reasons, it is preferable to use low-temperature expansion type heat-expandable particles having a foaming start temperature of 75 to 130 ° C. It is. That is, when the foaming start temperature is less than 75 ° C., when the foaming is performed by the dryer in the drying process, the once expanded particles are contracted again as described above, and the thermal conductivity is uniform. It becomes difficult to apply an air layer to the intermediate layer.

  Further, as the thermally foamable particles added to the raw material pulp of the intermediate layer, an aggregate obtained by mixing (aggregating) the thermally foamable particles with a cationic polymer resin in advance is used. Hereinafter, mixing (aggregation) of the thermally foamable particles and the cationic polymer resin in the present invention will be described.

  In order to obtain an aggregate of thermally foamable particles by mixing (aggregating) the thermally foamable particles and the cationic polymer resin, the concentration of the slurry formed by the thermally foamable particles, the cationic polymer resin, and water Is 5 to 30%, preferably 10 to 20%. That is, if the concentration of the slurry in which the heat-expandable particles and the cationic polymer resin are mixed (aggregated) is less than 5%, the viscosity of the slurry is low, the aggregate of the heat-expandable particles cannot be formed, and the yield decreases. To do. On the other hand, if the concentration of the slurry in which the heat-expandable particles and the cationic polymer resin are mixed (aggregated) exceeds 30%, the viscosity of the slurry becomes too high and the dispersion state is deteriorated, and it is blended in a granular form. When the density process paper is manufactured, it is detected as a foreign object.

  Note that it is preferable to use a fixing agent because the thermally foamable particles do not self-fix. As this fixing agent, polyacrylamide type paper strength agent, polyamide epichlorohydrin type paper strength agent, polyethyleneimine type paper strength agent, starches such as starch, oxidized starch, carboxymethylated starch, plant gum, polyvinyl alcohol, Various known materials such as carboxymethyl cellulose can be used. Of these, polyacrylamide-based or polyethyleneimine-based polymer chemicals are particularly preferable. Specifically, for example, a cationic fixing agent such as Haktron KC-100 (manufactured by Hakuto Co., Ltd.) or an anionic ceramic fix ST (manufactured by Meisei Chemical Co., Ltd.) and a cationic Phyrex M (Meisei Chemical Industry Co., Ltd.) And a combination thereof are preferably used.

  Further, the content of the fixing agent is 0.1 to 0.8% by mass, preferably 0.2 to 0.5% by mass in terms of solid content with respect to the pulp solid content. When an anionic fixing agent and a cationic fixing agent are used in combination, the total amount is set to the above content. When the content of the fixing agent is less than 0.1% by mass, there is no sufficient fixing effect. When the content exceeds 0.8% by mass, the aggregating effect is increased, and the pulp becomes flock, and the formation is Unfortunately, the fixing effect of the heat-expandable particles reaches a peak, and the cost effect cannot be exhibited.

  This low-density process paper contains cushions, thermal conductivity, low dust generation by containing aggregates in which heat-expandable particles are mixed (aggregated) with a cationic polymer resin in the raw pulp of the intermediate layer in advance. However, the surface strength and interlayer strength are reduced. For this reason, kraft pulp made of NBKP and / or LBKP is used as a raw material pulp constituting the surface layer and the back layer, and cationic PAM is internally added.

  The raw pulp constituting the surface layer and the back layer of the low-density processed paper includes hardwood bleached kraft pulp (LBKP), softwood bleached kraft pulp (NBKP), hardwood unbleached kraft pulp (LUKP), and softwood unbleached kraft pulp (NUKP) ), Main raw materials containing wood fibers such as hardwood sulfite pulp, coniferous sulfite pulp, etc., chemically treated pulp, non-wood fibers such as kenaf, hemp, straw, etc. which are fiber raw materials other than wood Pulp, which has been mechanically pulped from treated pulp and chips, chemi-ground pulp, which has been mechanically pulped with chemicals added to wood or chips, and digesters until chips are softened, then refiner, etc. Semi-chemical pulps pulped with However, since the low-density process paper is mainly used as a cushioning material in a process for processing a laminated board for printed wiring, it is required that there is no dust generation / foreign matter from the paper. Therefore, non-wood pulp has weak pulp strength and high dusting properties, unbleached pulp has more foreign matter and knots than bleached pulp, and mechanical pulp has a higher proportion of fine fibers, which is attributed to these fine fibers. LBKP or NBKP kraft pulp is used because it generates a lot of dust. Furthermore, in the method of use in this technical field, in LBKP and NBKP, LBKP generates less dust than NBKP, but in terms of balance with other qualities such as inter-fiber strength, cutting suitability and rigidity, In particular, it is preferable to use NBKP at 20 to 40% by mass of the raw material pulp used for the front and back layers.

  In addition, as a raw material pulp used for the intermediate | middle layer of this low-density process paper, even if it is a raw material pulp which mix | blended 100% of used paper, it can be used, without affecting the expansion | swelling of a heat-expandable particle. However, since the low-density process paper is mainly used as a cushioning material in the processing process of a laminated board for printed wiring as described above, the pulp containing 100% used paper has a lot of fine fibers. As the amount of dust generation increases, the drainage rate deteriorates, the production speed decreases, the foam formation defect of the thermally foamed particles occurs, and the appearance of the paper surface deteriorates. Therefore, it is preferable to use raw material pulp having a waste paper pulp content of less than 40%. Furthermore, in the method of use in the present technical field, LBKP and NBKP have a smaller amount of dust generation than LBKP, but in terms of balance with other qualities such as inter-fiber strength, cutting suitability and rigidity. It is preferable that 20-40 mass% of the raw material pulp used for the intermediate layer is NBKP.

  The freeness of the raw pulp used for the surface layer and the back layer is preferably 500 to 600 cc. When the freeness exceeds 600 cc, voids between the fibers increase and the bonding strength between the fibers decreases, so that the surface strength decreases. For this reason, paper dust is easily generated due to friction, surface peeling problems occur, and the amount of dust generation in low-density process paper increases significantly, so this low-density coated paper is used for printed wiring. It becomes difficult to use it for the processing steps of the substrate. Furthermore, since the surface of the low density coated paper is uneven and the paper thickness is uniform, there is a problem that pressure and heat during press molding are not uniformly applied to the paper surface. On the other hand, if the freeness is less than 500 cc, the bonding strength between the fibers increases, but the gaps between the fibers decrease too much, and the fibers become dense. It must be increased and the paper density will increase. As a result, the process paper is inferior in cushioning properties, and there is a problem in thermal conductivity during press molding.

  Moreover, it is preferable that the drainage degree of the raw material pulp used for an intermediate | middle layer shall be 500-600cc. When the freeness exceeds 600 cc, the gap between fibers increases and the bonding force between fibers decreases, so the amount of dust generated from low-density process paper increases significantly and a uniform air layer is formed by thermally foamable particles. This also causes a problem in thermal conductivity. On the other hand, if the freeness is less than 500 cc, the bonding strength between the fibers increases, but the gap between the fibers decreases too much and the fibers become dense. Must be increased, which increases the density of the paper. As a result, it becomes a low-density process paper having inferior cushioning properties, which causes a problem in thermal conductivity during press molding.

  Further, in the present low density process paper, a specific cationic polyacrylamide (cationic PAM) is contained in the surface layer and the back layer. In addition, since this low density process paper is a multilayer papermaking as mentioned above, cationic PAM can be contained only in a surface layer and a back layer.

  Thus, this low-density process paper contains thermally foamable particles in the raw material pulp of the intermediate layer, uses kraft pulp made of NBKP and / or LBKP as the raw material pulp constituting the surface layer and the back layer, and is also cationic. By containing the modified PAM, troubles due to peeling of the surface layer do not occur, and it is possible to satisfy the conflicting quality of being excellent in cushioning properties, thermal conductivity, and low dust generation.

  The raw pulp of each of the surface layer, the intermediate layer, and the back layer described above is subjected to a known paper making process, for example, a wire part, a press part, a dryer part, a size press, a calendar part, and the like to form the present low density process paper.

  The paper making method of the present low density process paper is not particularly limited, and any of acidic paper making method, neutral paper making method and alkaline paper making method may be used. However, the general papermaking method uses a sulfuric acid band in an acidic papermaking process to improve the yield of chemicals. However, when the pH of the paper in this papermaking method is measured, it becomes about 4 and the sulfate ion Under the influence, deterioration of the low density process paper is accelerated. For this reason, in order to fix the heat-foamable particles to the intermediate layer, which is the cushion layer, with a fixing agent and to effectively exhibit the cushion function, the paper is manufactured by neutral papermaking so that the hot water extraction pH is 5-9. It is preferable.

  Also, since the paper machine is not particularly limited, for example, various known paper machines such as a long net paper machine, a twin wire paper machine, a circular net paper machine, and a short net combination machine can be used. it can.

  Moreover, since the ratio of the applied amount of the cushion layer to the basis weight of the low-density process paper is 60 to 80% by mass, the balance of the effects of cushioning properties, thermal conductivity, and low dust generation properties should be more excellent. Can do.

The present low-density process paper configured as described above can reduce the difference in thermal conductivity between the front and back surfaces. That is, the difference in thermal conductivity between the front and back surfaces can be 0.001 W / mk or less. Further, according to SEMI G67-0996, the low density process paper can have a dust generation amount of 10 μm or more by a tear test of 500 pieces / cm ² or less, and further 200 pieces / cm ² or less. Therefore, this low-density process paper can be suitably used as a process slip sheet (cushion material) used at the time of hot-pressure molding in the process of manufacturing a laminated board used as a printed wiring board.

  As described above, the case where the paper layer is composed of the three layers of the surface layer, the intermediate layer, and the back layer has been described for the low density process paper. Also, a low-density process paper composed of four paper layers or a low-density process paper composed of three intermediate layers and five paper layers may be used. In the low-density process paper having a plurality of intermediate layers, all the intermediate layers may be cushion layers, and the intermediate layers may be formed as cushion layers according to the purpose of use or the like.

  In order to confirm the effect of the low-density process paper according to the present invention, the following various samples were prepared, and a test for evaluating the quality of each sample was performed. In addition, in a present Example, the numerical value which shows a mixing | blending, a density | concentration, etc. is a numerical value of the solid content or the mass reference | standard of an active ingredient. Moreover, since the pulp, chemical | medical agent, etc. which are shown in a present Example are only examples, it cannot be overemphasized that this invention is not restrict | limited by these Examples, and can be selected suitably.

  For comparison with 15 types of low-density process papers (referred to as “Example 1” to “Example 15”) according to the present invention and these Examples 1 to 15, Density-processed paper (referred to as “Comparative Example 1” to “Comparative Example 6”) was prepared with the configuration shown in Table 1. Moreover, two types of commercially available kraft paper and dust-free paper (referred to as “Comparative Example 7” and “Comparative Example 8”) were evaluated as reference examples.

(Example 1)
Using the following raw materials, a low-density process paper having a 6-layer structure consisting of a surface layer, a back layer, and an intermediate layer (4 layers) located between both layers was obtained according to the following production method.
<Raw material>
・ Surface and back layers Cationic polyacrylamide to 25% by weight of softwood bleached kraft pulp (NBKP), 75% by weight of hardwood bleached kraft pulp (LBKP), and adjusted to 570cc Canadian Standard Freeness (CSF) (Trade name “Harifix UM570” manufactured by Harima Kasei Co., Ltd.) was blended in an amount of 0.25 mass% in terms of solid content to obtain a raw material pulp slurry for the surface layer and the back layer.
・ Intermediate layer Thermally expandable particles with a mean particle size of 8-14 μm and a foaming start temperature of 75-100 ° C. (commodity) mixed with 25% by mass of NBKP and 75% by mass of LBKP and adjusted to 540 cc CSF The name “Matsumoto Microsphere F-46” manufactured by Matsumoto Yushi Seiyaku Co., Ltd.) is 4.0% by mass with pulp and 0.4% by mass of heat-expandable particle fixing agent (“Haktron KC100” manufactured by Hakuto Co., Ltd.). A pulp slurry was obtained.
Using these raw material pulp slurries, the surface layer, the 4 layers of the intermediate layer, and the back layer of the paper layer were made with a circular 6-layer paper machine, and the surface layer weight was 75 g / m ² . A 6-layer low density process paper (Example 1) having a weight of 350 g / m ² , a back layer of 75 g / m ² , and a basis weight of the entire low density process paper of 500 g / m ² is obtained. It was.

(Examples 2-3)
A low-density process paper obtained in the same manner as in Example 1 except that the addition ratio of the heat-expandable particles contained in the raw material pulp slurry of the intermediate layer and the addition ratio of the fixing agent are changed as shown in Table 1.

(Example 4)
Low density process paper obtained in the same manner as in Example 1 except that the type of thermally expandable particles contained in the raw material pulp slurry of the intermediate layer, that is, the product number, was changed as shown in Table 1.

(Example 5)
Low density process paper obtained in the same manner as in Example 1 except that the composition of raw material pulp and the freeness (CSF) in the raw pulp slurry of the surface layer and the back layer were changed as shown in Table 1.

(Examples 6 to 8)
A low-density process paper obtained in the same manner as in Example 1 except that the composition of the raw pulp in the intermediate pulp slurry and the freeness (CSF) were changed as shown in Table 1.

(Examples 9 to 10)
Low density process paper obtained in the same manner as in Example 1 except that the addition rate of the cationic PAM in the raw pulp slurry of the surface layer and the back layer was changed as shown in Table 1.

(Comparative Example 1)
Low-density process paper obtained in the same manner as in Example 1 except that the addition ratio of the heat-expandable particles in the raw material raw material slurry is changed as shown in Table 1.

(Comparative Example 2)
Table 1 shows that except that the raw pulp slurry of the surface layer and the back layer is not used, only the raw pulp slurry of the intermediate layer is used, and the weight (basis weight) is a single layer low density process paper of 430 g / m ^2. Thus, a low-density process paper obtained in the same manner as in Example 1.

(Comparative Example 4)
Low density process paper obtained in the same manner as in Example 1 except that the type of thermally foamable particles in the raw material pulp slurry of the intermediate layer, that is, the product number, average particle diameter, and foaming start temperature were changed as shown in Table 1. .

(Comparative Example 5)
In the same manner as in Example 1 except that the type of thermally expandable particles in the raw material pulp slurry of the intermediate layer, that is, the product number, average particle diameter, foaming start temperature, and addition rate of the fixing agent were changed as shown in Table 1. The obtained low density process paper.

(Comparative Example 6)
Low density process paper obtained in the same manner as in Example 1 except that the composition of the raw pulp in the raw pulp slurry of the intermediate layer and the freeness (CSF) were changed as shown in Table 1.

(Comparative Example 7)
It is a kraft paper in which the composition of the raw pulp in the raw pulp slurry of the surface layer and the back layer, the freeness (CSF), and the weight are as shown in Table 1 (“commercially available kraft paper”).

(Comparative Example 8)
It is a dust-free paper in which the blending of the raw pulp in the raw-layer pulp slurry of the surface layer and the back layer, the freeness (CSF), and the application amount are as shown in Table 1 (“commercially available dust-free paper”).

“Amount (g / m ² )” in Table 1 refers to the delamination of each sample and the basis weight of each layer in accordance with “Paper and paperboard—basis weight measurement method” described in JIS-P8142. It is a measured value. The delamination was performed according to the following procedure. First, each sample obtained from each sample is immersed in water at room temperature for about 1 hour. Each sample immersed in water is wound around a round bar of about 10 mmΦ starting from a corner, and then the round bar is rolled to squeeze each sample. This operation is repeated starting from all four corners of each sample, and the ironing force is applied to the sample from each direction. As a result, a part of the layers of each sample is peeled off, and this is used to separate the layers into a surface layer, an intermediate layer, and a back layer. After delamination, each layer of each sample was sufficiently dried with a hot air dryer or the like and used for the test.

  The results of quality evaluation for all of these Examples and Comparative Examples are as shown in Table 2.

In addition, “basis weight (g / m ² )” in Table 2 is the basis weight of all layers of each sample, that is, the entire low density process paper, and is described in “Paper and paperboard—basis weight measuring method” described in JIS-P8142. It is a value measured according to.

  The “paper thickness (μm)” is a value measured in accordance with “Paper and paperboard—Test method for thickness and density” described in JIS-P8118.

“Density (g / cm ³ )” refers to the basis weight measured in accordance with “paper and paperboard—basis weight measurement method” described in JIS-P8142, and “paper and paperboard—thickness” described in JIS-P8118. It is a value calculated from the thickness measured according to the “Test method for thickness and density”.

  “Air permeability (second)” is a value measured according to the paper and paperboard-air permeability test method (Gurley test method) described in JIS-P8117.

  “Surface strength (A)” is a value measured according to the paper and paperboard-surface strength test method described in the wax pick test method of JIS-P8129, and is the highest value that does not cause peeling of the paper surface. The wax number (A) was measured and 5 or more was determined to be acceptable.

“Compressed paper thickness remaining rate (%)” is the ratio of the paper thickness immediately after pressing for 30 minutes under the conditions of 120 ° C. and 60 kg / cm ² in a hot press to the initial paper thickness (paper thickness before pressing). Is a value calculated by the following equation. The hot press used was a thermal compression tester (TP500G type, manufactured by Eto Seisakusho).
(Formula) Compressed paper thickness remaining rate (%) = paper thickness immediately after pressing / initial paper thickness × 100 (%)
“Thermal conductivity difference (W / mk)” means “Measurement method of thermal resistance and thermal conductivity of thermal insulation material-Part 2: Heat flow meter method” described in the thermal conductivity test method of JIS-A1412-2. Measure the thermal conductivity of the front and back of the paper (the front and back of each sample) using the Eihiro Seiki thermal conductivity measuring device (HC-072) in accordance with It is the value which calculated the difference of.

“Dust generation amount (pieces / cm ² )” refers to the amount of tear dusting paper powder, and was measured as follows according to “Measurement of particles generated from sheet material” of SEMI G67-0996.
(Dust generation measurement by tear test)
(1) Each sample is cut into a flow direction of 50 mm and a width direction of 200 mm with a press cutter to produce a sample.
(2) Prepare one sample and tear it into 5 equal parts in the vertical direction in the glove box.
(3) Measure 0.1 m ² of air in the glove box with a particle counter, measure the number of paper dust of 10 μm or more (number / m ³ ) generated by tearing, and measure the value per cm ² of the cross-sectional area of the sample The numerical value divided by was calculated, and the number thereof was defined as the amount of dust generation.

  “Evaluation of seizure” is a visual evaluation of seizure of each sample (low density process paper) on a stainless steel plate. In addition, this evaluation is evaluated by a score of 5 stages, and the larger the score, the more “represents that there is no seizure and the low-density process paper is easily peeled from the stainless steel plate”, and 3 points or more are regarded as passing points. did.

The “texture” is an evaluation of the paper texture. That is, the number of flocs and foaming unevenness due to the bundling of fibers found in a 210 × 297 mm size base paper is measured, 5 is 5 or less, 6 to 10 is Δ, 11 or more is X, and Δ is passed. It was.

From Table 2, the low-density process paper according to the present invention, that is, the low-density process paper according to Examples 1 to 15, has a cushioning property and a small amount of dust generation while the laminated board does not undergo a large dimensional change. I understand that.

Claims (1)

A low-density process paper having at least a surface layer, a back layer, and an intermediate layer composed of one or more layers disposed between the surface layer and the back layer,
At least one of the intermediate layers has an average particle diameter of 5 to 15 μm, and heat-expandable particles that start to expand by heating at 75 to 130 ° C. are previously mixed (aggregated) with heat-expandable particles and a cationic polymer resin. ) To obtain an agglomerate of heat-expandable particles, blended in an amount of 1 to 8% by mass in terms of solid content with respect to the pulp solid content of the intermediate layer, and polyacrylamide as a fixing agent for the heat-expandable particles Or 0.1 to 0.8% by mass of a polymer or polyethyleneimine polymer in terms of pulp solid content to form a foam layer,
The raw material constituting the surface layer and the back layer is kraft pulp made of NBKP and / or LBKP,
Moreover, the freeness of the raw material pulp used for the said surface layer, the said back layer, and the said intermediate | middle layer is 500-600cc,
Density is 0.45-0.55 g / cm ³ , compressed paper thickness remaining rate is 55-61%, thermal conductivity difference between the surface layer and the back layer is 0.001 W / mk or less, according to SEMI G67-0996 A low-density process paper characterized by having a dust generation amount of 10 μm or more by a tear test of 500 pieces / cm ² or less.