JPS60119262A - Production of raised product - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an example of a method for manufacturing napped products, particularly fur-like high f-force products.

There have been numerous attempts and proposals to obtain artificial fur, but they are still unsatisfactory. The purpose of Zero Hatsu 91 is to provide fur-like products with a high degree of quality.

Natural 0/% fur consists of a large number of thin, short fluffs that are curled, and a relatively small number of long, thick, prickly hairs that are uncurled or have a weak single curl. Historically, the tips of the stinging hairs have been tapered.

Even in advanced artificial products, 2IL #f construction of fluff/prickly hair and thinning of the tips of 11 hairs are required. To make the fluff shorter than medium wool, treat the fluff made of hollyester fiber with a water solution containing strong chirukari, such as Na, Oli, or KOH, and cut it to an appropriate length (4). Excellent method
[There is. Similarly, treating the tips of stinging hair with alkali is an excellent method. One problem with Jin's method is that one hair is damaged by cutting the fluff. If a polymer having strong resistance to alkali is used as the pricking bristles, it is impossible or inefficient to thin the tip with alkali because it requires a lot of time and effort.

Kihatsu! The present invention provides a method for minimizing damage to stinging hairs caused by Ih', Mi hair (7JktTIC) and efficiently thinning the tips of stinging hairs in a short period of time.

The present invention consists of kPi5 a J:), which is made of easily soluble Borien, which has a high decomposition rate with aqueous alkali solution, fluff of F, and a sheath with an average thickness A of 0.5 to 10 μm, which is made of soluble polyester, which has a low decomposition rate with aqueous alkaline solution. A cut-pile raised product having a core made of easily soluble polyester and a weight fiber having a fineness of more than 5d made of a composite fiber is deformed using an alkaline aqueous solution at a point at least 5 feet away from the base fabric, I & thins the tip of the stinging hair
It is characterized by f'J h.

In the present invention, fluff refers to fluff having an Fi viscosity of 5d or more, and refers to fluff having a 1FIJ hair melting fineness of more than 5d.

The fluff fineness is preferably 0.5 to 5 d, most preferably 1 to 2 d. The cross section of the fluff may be circular or non-circular, but the
Flat products as shown in Figure ~%13ZK, especially those with an oblateness ratio (major axis/minor axis ratio) of 1.5 to 5, have high flexibility, hair handling properties, heat retention properties, bulkiness, and νJ run speed.・Ra is preferable. Further, it is preferable that the sticky hair is crimped, and in particular, a weak one with a crimping rate of 30% or less is preferable, and a crimping/stretching rate of 1 to 20% is most preferable. The curling/elongation ratio is made into a bundle of about t-50d of fluff, measured at 20° C. and 65% RH, and one sheet is taken out according to equation (2)K.

-11 Curling/expansion rate = -X 100 (%) Sample length at 1° similar Lo: rdrm 2 my/a (
cm ) t: Sample length 2 minutes after applying a load of 50 kg/d (
圀) The method of crimping is arbitrary, such as the false twisting method, the pressing method, and the composite spinning method. If the crimping is too strong, it may become intertwined and cause brushing.
and poor hair handling.

On the other hand, the fineness of the stinging hair is preferably 6 to 60 d, and 10 to 30 d.
d is also good for carp. The cross section of the φ bristles may be circular or non-circular, but those having 1 to 4 wing-like projections (hereinafter referred to as F-wings) as shown in FIGS. 4 to 1B8Z are particularly preferred. Wings are the outer parts of the largest inscribed circle (Gl), and there are one wing in FIG. 5, two wings in FIGS. 4 and 6, three wings in FIG. 7, and four wings in the eighth factor.

It is preferable that the stem gradually tapers toward the tip.

If there is a constriction in the middle, it will cause branching when the tip is tapered, spoiling the aesthetic appearance. The flatness of the cross section of the stinging bristles is preferably 1.5 to 5 in terms of flexibility, covering power, light translation, etc. Conventionally, such zero-flat medium fluff had a problem in that the damage when cutting the fluff was particularly large compared to circular cross-sections, but with the present invention, even those with a sufficiently large flatness can be used with less damage, which is an advantage. fully demonstrate.

FIG. 1 is an example of an explanatory view of the M cross-section of the raised nap of the product obtained by the present invention 1, and particularly shows the thickness of the center point on an enlarged scale. In the figure, (1) is the sheath of the stinging hair made of poorly soluble polyester, and 12Lt is the core. (4) is fluff and (
5) It is a base cloth. The base fabric may be a knitted fabric, a woven fabric, a non-woven fabric, etc., and the flocking method may be a pie rho Jlli method, an electrostatic flocking method, a tufting method, etc., but the pile knitting method provides the most advanced method. In FIG. 1, the fluff (41#) is distanced from the base fabric (5) by 9J#+ in terms of Dl.

The tips of the stinging hairs, which consist of a sheath (1) and a core (2), are long ^)
It is narrowed in a tapered shape across K. The middle part of the stinging hair is uniform in thickness (y) over the length (al), but it has been damaged by the fluff cutting process, and the radius has become smaller by tit.The root part of the stinging hair has been damaged. The length Fi is the same as the length of the fluff (Dl, the length of the transition between the middle part and the root part of the seta, C) is usually less than 2 fins, but especially 3 / + 5 m K. It may even extend.

The purpose of the present invention is to minimize the damage to the stinging hairs, that is, the reduction in the radius of the middle part, and to thin the tips beautifully and efficiently.

FIG. 2 is an enlarged cross-sectional view of raised hair showing an example of a particularly preferred method of the present invention. In the figure, hair III is a sheath (1
), T>(In addition to 21, it has an inner core (6).
) is made of a polymer with high resistance to alkali, and although it is exposed during the tip thinning process, it is not damaged much and the tips of the erect hairs are shaped. Generally, the thinning of the tip of polyester nap with alkali is not necessarily done uniformly, resulting in unevenness and other unevenness, making it difficult to make the tip uniform. However, the method shown in Figure 2 can achieve beautiful uniformity. Excellent, finely erected hair can be easily obtained by bathing. Figures 5 to 8 show tR#+, a three-layer composite fiber suitable for pricking hair with an inner core (3).
This is an example of a surface (the inner core can also be omitted).

The polymer for the stinging hair sheath (1) is a poorly soluble polyester, and the polymer for the fluff is a easily soluble polyester. to show difference. The decomposition rate of polyester was determined by using a knitted fabric of round wh face yarn with a single yarn fineness of about 10 d, which had been subjected to spinning and stretching and heat treatment as necessary (according to the actual manufacturing process), in a 15% NaOH aqueous solution at 100°C. In the weight loss curve (horizontal axis: time, vertical axis: weight loss rate), it is determined from the slope of the curve at the time of 50% weight loss of easily soluble polyester ~ For example, easily soluble polyester A/weight loss rate is 69 b/
If the rate of weight loss of the poorly soluble polyester is 1%/min, the decomposition rate ratio (R1 is 6).

Examples of poorly soluble polyesters include homopolymers of fibrous polyesters such as polyethylene terephthalate (hereinafter referred to as PIT) and polyethylene terephthalate (hereinafter referred to as PBT), and small amounts (for example, 5% or less, particularly 6% or less) of fibrous polyesters. ) polyester with a low degree of modification mixed with or copolymerized with the third sulfur content, among which PBT
and PBT with a low degree of modification are preferred.

Ti, pg'r, modified PET as easily soluble polyester
% modified PBT etc. can be opened. For example, HpaT'tli
1. When used as a soluble polyester, %PIT can be made into an easily soluble polyester (the decomposition rate ratio of the two,
p! i! T/PBTj″ about 3 to 7 terol].

In the case of polymers of the same type, those with a high degree of modification are suitable for easily soluble polyesters as well as poorly soluble polyesters. For example, in the case of a copolymer of PET and polyethylene glycol,
When using 5% PF and G components as the poorly soluble polyester, 7 to 7% PIG components are used as the easily soluble polyester.
It is often preferable to use 15%. However, excessively modified polyester/I/Fi generally deteriorates in color fastness, so X4! : It is preferable to trap it to the minimum necessary O. It is preferable that the thickness of the stinging hair sheath (1) is uniform, for example, 50% of the sheath is in the range of + to 2 times the average thickness.
Above all, 759b or higher is particularly suitable. The average thickness of the sheath must be 0.5 to 10 μm, particularly preferably 1 to 5 μm. An extremely thin sheath is difficult to manufacture and lacks a protective effect on the core, while a too thick sheath reduces the efficiency of tip attenuation and causes the attenuation to occur in steps, impairing the beauty and uniformity of the tip. From this point of view, it is preferable to use a highly poorly soluble polymer to make the sheath as thin as possible.

The average thickness of the sheath is preferably around the thickness t (reference thickness) at which the sheath is completely decomposed and removed under the fluff cutting treatment conditions, that is, in the range of 0.3t to 6t.
Particularly preferred is 0.5t to 2t, most preferred is 0.7t to 1.5t. The radius of the maximum inscribed circle of fluff (
It is approximated by dividing Xl. That is, 8/R in t, and the preferable range of the average thickness of the sheath (Zl is expressed by the formula (11
It is indicated by.

The bristle core (2) is made of easily soluble polyester ρ. The easily soluble polyester for the sheath (1) may be one that has a high rate of decomposition by alkali, and may be the same or different from that for fluff.

The inner core (6) of the bristles is made of a polymer whose resistance to alkaline aqueous solutions is considerably lower than that of the core (2). This highly alkali-resistant polymer may be the same as or different from the poorly soluble polyester for the sheath (1).

In the case that they are the same, there is an advantage that they are easy to manufacture because the stinging hair #'i is composed of two types of raw material polymers. For example, the polymer for the inner core (6) has an alkali decomposition rate ratio of 0.5 or less, particularly preferably 0.6 or less, and 0.2 or less is the worst. Polymers for the inner core (6) that are resistant to aqueous alkaline solutions or those that have a bend of 1 minute are also useful.

Also for fluff (21 easily soluble polyester and sheath)
1) Decomposition rate ratio of poorly soluble polyester (r+H-t
Although it is necessary that it be larger than l, a range of 1.5 to 50 is preferred, 2 to 20 is particularly preferred, and 6 to 10 is most preferred. Increase the decomposition rate ratio fR1 (for example, 100
It is possible to do the above, for example, by increasing the degree of modification of the easily soluble polyester, but in terms of deterioration of various properties of the highly modified polyester, uniformity of processing, and ease of control, A range is preferred.

Modification of polyester by copolymerization is facilitated by using polyester polymerization raw materials such as glycol, dicarboxylic acid, hydroxycarboxylic acid, cyclic dichthone, and derivatives thereof as the sixth component during polymerization of the ester. Examples of glycol/silicone include ethylene glycol, fluoroethylene glycol, butylene glycol, hexanediol, diethylene glycol, triethylene glycol, polyethylene glycol, polyfluoroethylene glycol/l', and dicarboxylic acids include acyhinic acid. , cepatic acid, azelaic acid, terephthalic acid, isophthalic acid, sulfoisophthalic acid (or its alkali gold yi4
salts), naphthalene dicarboxylic acid, hydroxymethybenzoic acid, and cabrolactone. Copolymerized polyester (!-) can be obtained by adding one or more of these polymerization raw materials as a third component during polyester polymerization, for example, 1 to 30%, especially 3 to 15%. The higher the number, the higher the degree of denaturation.

The edibility of non-polyesters can be easily determined by mixing with the polyesters during or after the polymerization. For example, polyethylene glycol, which can be used for mixing.

Polyflo 0 hing glycol, polybutylene glycol,
Boriakylene ethers such as polyethylene glycol/l//l/tuborobylene glycol copolymers, co-compounds and derivatives thereof, polyethylene adipate, polyethylene sepacate, polybutylene adipate, polybutylene sepacate, Examples include aliphatic polyesters such as polycaprodictone, and their co-combinants and derivatives.

The X fluff and 111 fluff may be approximately 11 m long, but may be of multiple types. That is, the fluff and/or the prickly hair may be a mixture of multiple types of fibers having different polymer types, cross sections, finenesses, etc. In that case, cut off all the fluff! The thickness of the sheath of the stinging hair and the polymer (decomposition rate ratio) can be selected by applying the formula (II). 9) If the other part is not cut, you can choose the sheath polymer and 〃 based on the fluff to be cut. In addition to applying the above-mentioned method to all of the piloerection, the present invention also applies a part of the prickly hair or fluff (for example, λ, 1
096 or more, especially 50% or more). Of course, it is preferable that the present invention is applied to most (50% or more) of prickly hair and fluff, and most preferably ξ is applied to all of the raised hair.

The inner core (3) of the stinging hair is exposed to form the tip when the tip is tapered. If the thickness is too large, the tip will be rough and hard, and if it is too thin, it will easily become intertwined, so the average diameter (
In the case of a non-circular shape, the diameter of a circle with the same area) is 5 to 30μ.
m is preferred, and 7 to 20 μm is most preferred. Inner core (3
) Suitable polymers include polybutylene terephthalate, polyethylene terephthalate, and those with a low degree of modification, polyamides, polyolefins,
Other fiber-forming polymers that have high resistance to alkaline aqueous solutions are available. Poriputylene terephtha v to 11#
Polyethylene terephthalate, polyamides such as nylon 6, nylon 66, nylon 610, and nylon 612, and polypropylene are preferred.

ψ J and punch the hair & put it on the synthetic fiber, sheath (1), core (
21. The composite ratio ([ti + face ratio) of the inner core (3) is related to the thinning of the tip, and the ratio of the inner core (3) is the same as that of the sheath (1) in order to obtain a smooth and tapered tip. Composite ratio t less than 50 cities, especially 6
5% or less is preferred, and 5-25% is most preferred. The composite ratio of the inner core (6) is preferably 65% or more F1, particularly 25% or more, and most preferably 1 to 15%.

VJN of fluff and the tip of one fluff are made using an aqueous solution of strong alkali, such as RaCIH%KOH. It may contain a sticky agent etc. The concentration of alkali and the reaction temperature are also arbitrary, but usually 5 to 30, Ik
l:IIJ ~20%, 81~130°C, especially 90~1
20°C is often used. The method of cutting the fluff and thinning the fluff is arbitrary, but this
The method disclosed in No. 86, in which the fluff is raised using centrifugal force and the treatment liquid is melted, is suitable.

The length of each part of the bristles and the length of the fluff are also arbitrary depending on the purpose. Thinning of heavy hair shown in Figure gA1 and the second cause 1) 1
The length of 11AI is preferably 11 m or more, particularly preferably 2 to 15 fins. The length of the tip of the stinging hair and the exposed part of the inner core is 1'
i 1-tl ta or more is preferable, and about 2 to 10 fins is particularly preferable. Of course, for special design purposes, a tip of 10 or more may be useful.The length of the middle part of the hair +8
1 is often used from 3 to 505 m, and in many cases from 5 to 50 m.
Cod is suitable. The length Dl of the root of the stinging hair is often the same as the length of the fluff, or 3 to 50 mm is often used, and 5 to 30 mm is most commonly used. The transition part tel between the root part and the middle part of the stinging hair is about 1 to 5 fi in most cases. If the transition is very gradual and the boundaries are unknown, the transition part-to-intermediate fls (81) is assumed.

making, fluff 9) cutting, thinning of the tip of the hair, tipping, scouring, bleaching,
Dyeing and bleaching of the nape, greasy treatment of the nape (imparting properties such as antistatic, hydrophilic, water repellent, bending, antifouling, and gloss), surface treatment, heat treatment, shaping processing, glassing, YLL cotton, and base fabric. Many other processes are used, including the finished product, applying paulownia fat to the base fabric (backing, etc.), raising the back side, laminating, and others. The selection, combination, and arrangement order of these steps are arbitrary depending on the purpose, but
In many cases, it is advantageous to perform one capillary reduction after cutting the fluff.

The fluff is treated with 9J11r, so the bristles are even! ! This is because the thinning of the tip becomes more uniform. However, it is also possible to use fluff 9JII9+ after thinning.

In the following examples, parts, percentages, etc. indicate weight ratios unless otherwise specified.

Example 1 PET with a molecular weight of 18,000 and 0 T101 particles as a pigment
．． A polymer containing 6% is designated as polymer P1. Molecular weight 180
00 PET containing no pigment is referred to as polymer P. PBT with a molecular weight of 20,000 and containing no pigment is called Polymer P*,! :do. The alkali decomposition rate ratio is about 5 for polymer P (/P!) and about 4 for polymer Ps/h.

Polymer P was melt-spun from a dumbbell-shaped spinning hole at 295°C, wound at a speed of 1500m/+, stretched 5.7 times at 90°C, and subjected to tensile heat treatment at 150°C to produce 160d/80
f's Oni Okiito Ytt-obtained. Yta had a peanut-shaped cross section as shown in FIG. 10, and its oblateness (major axis/minor axis ratio) was 2.2. Yl was crimped by the pressing method (at 190°C), and the yarn was suppressed by being brought into contact with a heater at 180°C under mild tension to give a weak crimping. shall be. Y, was treated in water at 100° C. for 15 minutes under no tension and air-dried, and the resulting yarn had a curling/stretching rate of 9.3%.

Polymer P is a component of the sheath (1) and inner Th (51),
Polymer P is melt composited as a core +21 vi, minutes,
Yarn Yl is 150d/6f obtained by spinning and drawing in the same manner as y.
Let Y be the extended oki thread. y, Fi2 as shown in Figure 6
It is a flattened thread with two wings, the flatness ratio is 3.7, the average thickness of the sheath (1) is about 21 m, the composite ratio of the sheath (body*) is 28%, and the average diameter of the inner core (5) is about 15 μm. It is 8%. The composite ratio of core (2) is 64%. Since the maximum inscribed radius of yarn Y1 for fine hair is approximately 5 μm, Ml\, 9J #
Thickness of sheath t#'i5μm which is just decomposed and removed by t
It is estimated that 15=1 μm, but for safety reasons, the thickness of the sheath was set to −12 μm.

One thread Y for fluff and one thread Y for embroidery were mixed with an air jet nozzle and then heated at 120 times/m to be used as a hale thread and cut pie/I/II#L. The product cp1 was obtained. The ground yarn (warp and weft) of CPl is polyester (1,
5d) spun yarn 40 count twin yarn is used, the pile length is 67
Crocodile, flocking density 70/-1 W type 0 cpl is processed by force swimming as disclosed by one person in Special Application No. 56-15486. That is, CPL is attached to a rotating inner cylinder with a diameter of 1 m and 60 Rotate at a speed of Orpm (centrifugal force of about 20Of). Rotate an outer cylinder with a diameter of 1.1 m on the same axis at the same speed, and pour two liquids into it.
Inject NaOH aqueous solution (98°C). The surface of the alkaline aqueous solution may be the base fabric 1511! Fill the container to the 1st position and treat for 60 minutes, then drain and wash with water. In this treatment, the length of fluff #i was approximately 15 fins, but the weight loss of the fluff (estimated from the cross-sectional photograph) was approximately 1596.

Next 1c: Pour 18% NaOH aqueous solution (98°C) into the barrel and treat for 25 minutes at a position 27 m below the base cloth to completely dissolve the sheath, then gradually drain the liquid and lower the liquid level in 45 minutes. 3
3. Let the cod reach the position and process at that position for 60 minutes.
Drained and washed with water. With this treatment, the inner core of the stinging hair is completely removed.
The tip of the cod with a length of approximately 4, the tapered tapered part of the long wire FJ 6 m, the non-thinned part S (middle part) with a length of 12 cm, and the root part of the length #''!115. A busy song with the shape shown in Figure 2.

Next, dye the fluff light brown with a brown fractional dye (using a carrier), and similarly dye the fluff over 11 wool (more than 20 colors from the base fabric).
The fabric was dyed black, taken out of the centrifuge, coated with a polyurethane resin solution from the back side of the base fabric, and dried. After drying, 1.2% of a water-repellent bending agent made of fluorine-based fat was applied to the raised fabric and heat treated. After glassing, the fluff was slightly tilted and heat set (180°C for 5 minutes) to obtain artificial fur AF1. The AF1 nap had excellent gloss, flexibility, stiffness, covering power, uniformity of the tip, etc., and was always at a high level of 11.

Next, for comparison, artificial fur hF2'kfl was made in the same manner as Y, using a similar flat yarn made only of PET for Y and Y. However, the tip of the stinging hair is thinned when the alkaline liquid level is 35m in the 60 minute direction, and from 55m to 27m++ in the 60 minute direction.
It was moved steadily in 0 minutes. For AF1, damage to stinging hair (intermediate non-thinning area) due to rib traps was approximately 63% at age %9J.

AlF2 is also of excellent quality, but due to damage to one hair, the piloerection, gloss, bulk, covering power, etc. are poor, and the tips are uneven, bent and intertwined, and the overall appearance and feel are poor. It was far inferior to AFL in terms of heat insulation and other properties.

Next, in place of the above Y, five types of composite cotton Y yarns having different sheath thicknesses were used to obtain five types of artificial fur AF'3 to AF7 in the same manner as AF1. However, the thinning of stinging hair is 11
The 9kff- was largely adjusted depending on the thickness of the hair sheath. The results are shown in Table 1.

As seen in Section 1g, hairs with poorly soluble sheaths are less susceptible to damage from fluff cutting. The thickness of the sheath is 1μm
If it exceeds 0.3 pm to 5 pm, the sheath will be cut off at the top of the first hair even after cutting the fluff, and the opening will be longer when the tip is thinned, 0.3 pm to 5 pm.
A range of pm (0.5t to 3t) is preferred.

Example 2 A modified PET with a molecular weight of 19,000 ('1'10. content 0.6%) obtained by copolymerizing 6% polyethylene glycol with a molecular weight of 600 is designated as polymer P4. A yarn obtained by spinning, grinding, and crimping the polymer P4 in the same manner as the yarn Y of Example 1 is referred to as Y. Same as polymer P, except T10. The core is y-type PET that does not contain PET, the sheath is the polymer p of Example 1 (pgT), and the polymer P of Example 1 is
(PBT) is the inner core, and the composite ratio is set to 5.t#1t.
A flat composite yarn whose lr plane has five Xs as shown in Figure 7,
T3 of Example 1 was spun and drawn in an xM manner to obtain 5 yuzu yarn for one hair. The decomposition rate ratio of polymer P for Nt1 hairs and polymer P for stinging hair sheaths is approximately 5=, and the base BP of the sheaths
! ! ! The average length of each yarn sheath was approximately 2 μm. Average inner core diameter 1k
The yarn with O15, 12, 17, and 22pm is called Oodai yarn Y1.
, V@ , Y, -+os YHs Yl! Thread Y, 1k
Artificial fur AF8-12 was obtained in a large scale in the same manner as in Example 1 using Wd hair and threads Y, 2, and 2 as prickly hair.

The damage to 11 hairs caused by cutting 91 fluffs of each artificial fur is approximately 299
b (the injury rate when there is no sheath is d69%).

Shinki 2 comparing the appearance of each artificial fur, especially the beauty of the tip
It was as shown in the table.

Table 2

[Brief explanation of the drawing]

Figures 1 to 2 are schematic diagrams of the piloerection obtained by the present invention, and Figures 5 to 13 are horizontal curve diagrams of fibers suitable for the present invention. 11!I Co., Ltd. Figure 2

Claims (1)

[Scope of Claims] (1) Iron & 5a or less fluff made of easily soluble polyester that has a high decomposition rate with aqueous alkaline solution, and a slightly soluble polyester that has a low decomposition rate with alkaline aqueous solution and has an average thickness of 0.5 to 10 μm. A cut-pile raised product having a sheath of 100% and a core of easily soluble polyester, and bristle with a fineness of more than 5d made of a composite fiber, is treated with an alkaline aqueous solution at a point of at least 6 mm away from the base fabric to make it fluffy. 9
A method for producing a napped product, characterized by performing J-cutting and thinning treatment at the tip of the pricked hair (f: I). (2) The method according to claim 1, wherein the decomposition rate of the easily soluble polyester with alkaline water is 1.5 times or more that of the dissolvable polyester. (3) The exfoliation of stinging hairs is caused by the uniform thickness of the polyester sheath (zl).
However, the ratio of the decomposition rate of the easily soluble polyester of fluff in an alkaline aqueous solution to the decomposition rate of the dissolvable polyester forming the sheath of the stinging hair in an alkaline aqueous solution (R1 and the diameter of the largest inscribed circle of the fluff ( The method according to claim 1, which has the relationship between xl and formula (1).
1 #1 Water range The method described in item 1. t51 Il1 A method according to claim 1 in which the oblateness of the cross section of the hair is 1.5 to 5 8° (6) The cross section of the stinging hair has 1 to 4 steam-like projections The method according to claim 4s1. (C) The method according to claim 1, wherein the 11 bristles are made of a polymer having high resistance to alkaline aqueous solutions in the innermost part of the core and have an inner core with an average diameter of 5 to 30 μm.